Fine-scale structure in the -185 kilometers per second absorption by HCO(+) in the Galactic center

NASA Technical Reports Server (NTRS)

Marr, Jonathan M.; Rudolph, Alexander L.; Pauls, Thomas A.; Wright, Melvyn C. H.; Backer, Donald C.

1992-01-01

We present a high-resolution study of the HCO(+) (J = 1-0) absorption by the 'high-velocity gas' at velocities between -170 and -200 km/s in Sgr A West. The absorption against the continuum radiation from the ionized gas features in Sgr A West (in particular the 'bar') is stronger than it is against Sgr A which is separated from the ionized gas by a few arcseconds. The positions of peak HCO(+) opacity coincide with the positions of Ne II emission at these velocities. These observations suggest that, even though emission is detected from gas at these high velocities over several arcminutes, some of the absorbing molecular gas may be mixed in with the ionized gas close to Sgr A. Simple calculations show that sufficient shielding can exist in the ionized features to allow molecules to survive very close to the ionizing source.

Proper Motion of the Compact, Nonthermal Radio Source in the Galactic Center, Sagittarius A*

NASA Astrophysics Data System (ADS)

Backer, D. C.; Sramek, R. A.

1999-10-01

Proper motions and radial velocities of luminous infrared stars in the Galactic center have provided strong evidence for a dark mass of 2.5×106 Msolar in the central 0.05 pc of the Galaxy. The leading hypothesis for this mass is a black hole. High angular resolution measurements at radio wavelengths find a compact radio source, Sagittarius (Sgr) A*, that is either the faint glow from a small amount of material accreting onto the hole with low radiative efficiency or a miniature active galactic nucleus (AGN) core-jet system. This paper provides a full report on the first program that has measured the apparent proper motion of Sgr A* with respect to background extragalactic reference frame. Our current result isμl,*=[-6.18+/-0.19] mas yr-1 μb,*=[-0.65+/-0.17] mas yr-1 . The observations were obtained with the NRAO Very Large Array at 4.9 GHz over 16 yr. The proper motion of Sgr A* provides an estimate of its mass based on equipartition of kinetic energy between the hole and the surrounding stars. The measured motion is largest in galactic longitude. This component of the motion is consistent with the secular parallax that results from the rotation of the solar system about the center, which is a global measure of the difference between Oort's constants (A-B), with no additional peculiar motion of Sgr A*. The current uncertainty in Oort's galactic rotation constants limits the use of this component of the proper motion for a mass inference. In latitude, we find a small, and weakly significant, peculiar motion of Sgr A*, -19+/-7 km s-1 after correction for the motion of the solar system with respect to the local standard of rest. We consider sources of peculiar motion of Sgr A* ranging from unstable radio wave propagation through intervening turbulent plasma to the effects of asymmetric masses in the center. These fail to account for a significant peculiar motion. One can appeal to an m=1 dynamical instability that numerical simulations have revealed. However, the measurement of a latitude peculiar proper motion of comparable magnitude and error but with opposite sign in the companion paper by Reid leads us to conclude at the present time that our errors may be underestimated and that the actual peculiar motion might therefore be closer to zero. Improvement of these measurements with further observations and resolving the differences between independent experiments will provide the accuracies of a few km s-1 in both coordinates that will provide both a black hole mass estimate and a definitive determination of Oort's galactic rotation constants on a global Galactic scale.

Radial Distribution of X-Ray Point Sources Near the Galactic Center

NASA Astrophysics Data System (ADS)

Hong, Jae Sub; van den Berg, Maureen; Grindlay, Jonathan E.; Laycock, Silas

2009-11-01

We present the log N-log S and spatial distributions of X-ray point sources in seven Galactic bulge (GB) fields within 4° from the Galactic center (GC). We compare the properties of 1159 X-ray point sources discovered in our deep (100 ks) Chandra observations of three low extinction Window fields near the GC with the X-ray sources in the other GB fields centered around Sgr B2, Sgr C, the Arches Cluster, and Sgr A* using Chandra archival data. To reduce the systematic errors induced by the uncertain X-ray spectra of the sources coupled with field-and-distance-dependent extinction, we classify the X-ray sources using quantile analysis and estimate their fluxes accordingly. The result indicates that the GB X-ray population is highly concentrated at the center, more heavily than the stellar distribution models. It extends out to more than 1fdg4 from the GC, and the projected density follows an empirical radial relation inversely proportional to the offset from the GC. We also compare the total X-ray and infrared surface brightness using the Chandra and Spitzer observations of the regions. The radial distribution of the total infrared surface brightness from the 3.6 band μm images appears to resemble the radial distribution of the X-ray point sources better than that predicted by the stellar distribution models. Assuming a simple power-law model for the X-ray spectra, the closer to the GC the intrinsically harder the X-ray spectra appear, but adding an iron emission line at 6.7 keV in the model allows the spectra of the GB X-ray sources to be largely consistent across the region. This implies that the majority of these GB X-ray sources can be of the same or similar type. Their X-ray luminosity and spectral properties support the idea that the most likely candidate is magnetic cataclysmic variables (CVs), primarily intermediate polars (IPs). Their observed number density is also consistent with the majority being IPs, provided the relative CV to star density in the GB is not smaller than the value in the local solar neighborhood.

XTE J1908+094

NASA Technical Reports Server (NTRS)

Woods, P. M.; Kouveliotou, C.; Finger, M. H.; Gogus, E.; Swank, J.; Markwardt, C.; Strohmayer, T.; Six, N. Frank (Technical Monitor)

2002-01-01

Goddard Space Flight Center reports the serendipitous discovery of a new x-ray transient, XTE J1908+094, in RXTE (Rossi X-ray Timing Explorer) PCA (Proportional Counter Array) observations of the soft-gamma-ray repeater SGR 1900+14, triggered following the burst activity on Feb. 17-18 (GCN 1253). These observations failed to detect the 5.2-s SGR pulsations, pointing towards a possible new source as the origin of the high x-ray flux. An RXTE PCA scan of the region around SGR 1900+14 on Feb. 21 was consistent with emission only from known sources (and no new sources). However, the scans required SGR 1900+14 to be 20 times brighter than its quiescent flux level (GCN 1256). A Director's Discretionary Time Chandra observation on Mar. 11 showed that the SGR was quiescent and did not reveal any new source within the Chandra ACIS (Advanced CCD (charge coupled device) Imaging Spectrometer) field-of-view. A subsequent RXTE PCA scan on Mar. 17, taken in combination with the first scan, required that a new source be included in the fit. The best-fit position is R.A. 19h 08m 50s, Decl. = +9 22 deg .5 (equinox J2000.0; estimated 2 deg systematic error radius), or approximately 24 deg away from the SGR source. The source spectrum (2-30 kev) can be best fit with a power-law function including photoelectric absorption (column density N_h = 2.3 x 10(exp 22), photon index = 1.55). Iron line emission is present, but may be due to the Galactic ridge. Between Feb. 19 and Mar. 17, the source flux (2-10 keV) has risen from 26 to 64 mCrab. The power spectrum is flat between 1 mHz and 0.1 Hz, falling approximately as 1/f**0.5 up to 1 Hz. At 1 Hz is seen a broad quasiperiodic oscillation peak and a break to a 1/f**2 power law, which continues to 4 Hz. The fractional rms (root mean square) amplitude from 1 mHz to 4 Hz is 43 percent. No coherent pulsations are seen between 0.001 and 1024 Hz. The authors conclude that XTE J1908+094 is a new blackhole candidate.

Identification of the Infrared Counterpart of SGR 1935+2154 with the Hubble Space Telescope

NASA Astrophysics Data System (ADS)

Levan, Andrew; Kouveliotou, Chryssa; Fruchter, Andrew

2018-02-01

We present deep Hubble Space Telescope observations of a new magnetar source, the soft gamma-repeater SGR 1935+2154, discovered by Swift. We obtained three epochs of observations: while the source was active in 2015 March, during a quiescent period in 2015 August, and during a further active phase in 2016 May. Close to the center of the X-ray error region identified by Chandra, we find a faint (F140W(AB) = 25.3) source, which fades by a factor of ∼2 over the course of 5 months between the first two epochs of observations, before rebrightening during the second active period. If this source is indeed the counterpart to SGR 1935+2154, then it is among the faintest yet located for a magnetar. Our observations are spaced over 1.3 years and enable us to place limits on the source velocity of μ = (60 ± 40) km s‑1 kpc‑1 observations on timescales of a decade can hence probe proper motion limits smaller than the velocities observed for the majority of pulsars. The comparison of the optical/IR and X-ray light curves of the source suggests that emission in the two regimes is associated but not directly correlated, offering support for a magnetospheric versus a fallback disk origin.

Exploring Molecular Complexity with Alma (EMoCA): High-Angular Observations of SAGITTARIUS~B2(N) at 3~mm

NASA Astrophysics Data System (ADS)

Müller, Holger S. P.; Belloche, Arnaud; Menten, Karl M.; Garrod, Robin T.

2015-06-01

Sagittarius (Sgr for short) B2 is the most massive and luminous star-forming region in our Galaxy, located close to the Galactic Center. We have carried out a molecular line survey with the IRAM~30~m telescope toward its two major sites of star-formation, Sgr~B2(M) and (N). Toward the latter source, which is particularly rich in Complex Organic Molecules (COMs), we detected three molecules for the first time in space, aminoacetonitrile, ethyl formate, and n}-propyl cyanide. We have recently obtained ALMA data of Sgr~B2(N) between ˜84 and ˜111~GHz within Cycle~0 and one additional setup up to 114.4~GHz within Cycle~1. At angular resolutions of 1.8'' and 1.4'', respectively, the two main hot cores, the prolific Sgr~B2(N-LMH) (or Sgr~B2(N)-SMA1) and the likely less evolved Sgr~B2(N)-SMA2 are well separated, and line confusion is reduced greatly for the latter. As a consequence, we have been able to identify the first branched alkyl molecule in space, iso-propyl cyanide, toward Sgr~B2(N)-SMA2. Our ongoing analyses include investigations of cyanides and isocyanides, alkanols and thioalkanols, and deuterated molecules among others. We will present some of our results. A. Belloche et al., A&A 559 (2013) Art. No. A47. A. Belloche et al., Science 345 (2014) 1584.

DISENTANGLING CONFUSED STARS AT THE GALACTIC CENTER WITH LONG-BASELINE INFRARED INTERFEROMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stone, Jordan M.; Eisner, J. A.; Monnier, J. D.

2012-08-01

We present simulations of Keck Interferometer ASTRA and VLTI GRAVITY observations of mock star fields in orbit within {approx}50 mas of Sgr A*. Dual-field phase referencing techniques, as implemented on ASTRA and planned for GRAVITY, will provide the sensitivity to observe Sgr A* with long-baseline infrared interferometers. Our results show an improvement in the confusion noise limit over current astrometric surveys, opening a window to study stellar sources in the region. Since the Keck Interferometer has only a single baseline, the improvement in the confusion limit depends on source position angles. The GRAVITY instrument will yield a more compact andmore » symmetric point-spread function, providing an improvement in confusion noise which will not depend as strongly on position angle. Our Keck results show the ability to characterize the star field as containing zero, few, or many bright stellar sources. We are also able to detect and track a source down to m{sub K} {approx} 18 through the least confused regions of our field of view at a precision of {approx}200 {mu}as along the baseline direction. This level of precision improves with source brightness. Our GRAVITY results show the potential to detect and track multiple sources in the field. GRAVITY will perform {approx}10 {mu}as astrometry on an m{sub K} = 16.3 source and {approx}200 {mu}as astrometry on an m{sub K} = 18.8 source in 6 hr of monitoring a crowded field. Monitoring the orbits of several stars will provide the ability to distinguish between multiple post-Newtonian orbital effects, including those due to an extended mass distribution around Sgr A* and to low-order general relativistic effects. ASTRA and GRAVITY both have the potential to detect and monitor sources very close to Sgr A*. Early characterizations of the field by ASTRA, including the possibility of a precise source detection, could provide valuable information for future GRAVITY implementation and observation.« less

Eclipsing Stellar Binaries in the Galactic Center

NASA Astrophysics Data System (ADS)

Li, Gongjie; Ginsburg, Idan; Naoz, Smadar; Loeb, Abraham

2017-12-01

Compact stellar binaries are expected to survive in the dense environment of the Galactic center. The stable binaries may undergo Kozai–Lidov oscillations due to perturbations from the central supermassive black hole (Sgr A*), yet the general relativistic precession can suppress the Kozai–Lidov oscillations and keep the stellar binaries from merging. However, it is challenging to resolve the binary sources and distinguish them from single stars. The close separations of the stable binaries allow higher eclipse probabilities. Here, we consider the massive star SO-2 as an example and calculate the probability of detecting eclipses, assuming it is a binary. We find that the eclipse probability is ∼30%–50%, reaching higher values when the stellar binary is more eccentric or highly inclined relative to its orbit around Sgr A*.

Background Information: Magnetars, Soft Gamma-Ray Repeaters and the Most Powerful Magnetic Fields in the Universe

NASA Astrophysics Data System (ADS)

1998-08-01

Near the end of its life, a star more massive than our Sun finds itself no longer able to support its own weight from the crush of gravity and so it collapses, producing an expanding shock wave that sweeps through the surrounding gas, creating what is called a supernova remnant. All that remains of the original star is a dense, compact object known as a neutron star. Magnetars are the latest addition to the "zoo" of neutron stars and they are truly exotic beasts with magnetic fields hundreds of millions of times stronger than have ever been seen on Earth. The story which led to the prediction of magnetars and then to their discovery is given elsewhere. Here we will focus on the other part of the story, the supernova remnants born at the same time as magnetars and the diffuse emission produced by the energetic outpourings of the magnetars. All four of the soft gamma-ray repeaters that we currently know are located in or near a supernova remnant. It was this discovery that led astronomers to determine that soft gamma-ray repeaters were in our Galaxy and the nearby galaxy known as the Large Magellanic Cloud. Through the study of these supernova remnants, astronomers were able to infer that soft gamma-ray repeaters were solitary young neutron stars speeding away from their birthplace at 3 million miles per hour. Theories predict that the same process which can produce the fantastic bursts of hard X-ray emission that give soft gamma-ray repeaters their name, can also accelerate particles (electrons, protons, etc) to speeds approaching the speed of light. As the saying goes, "where there's smoke there's fire" and this case is no exception. Most of the energy released by the burst event is carried away by these high energy particles and not the gamma-ray burst itself. As the particles spiral in the surrounding magnetic field, they too emit radiation, creating extended nebulae called "plerions". Provided there is some way to confine the outflow, these plerions act as "wind bags" containing the accumulated history of this bursting activity. The study of these plerionic supernova remnants (detailed below) gives us a new and different perspective on the magnetar phenomena. SGR 0526-66: The Famous March 5 1979 Burst SGR 0526-66 lays claim to having produced the brightest gamma-ray burst ever observed: the famous March 5 1979 burst. Owing to the large number of satellites which saw this burst (10 in total) an accurate position could be determined. This put SGR 0526-66 on the edge of the supernova remnant N49 in the Large Magellanic Cloud 180,000 light years from our Sun. This should have been sufficient to convince everyone that the burst and the supernova remnant were associated. However, in 1979 astronomers were working under the misconception that all gamma-ray bursts came from a local (500 light years) population of neutron stars. This new piece of the puzzle didn't fit. Real progress in this area had to wait until the mid-1980's when soft gamma-ray repeaters were recognized as a distinct class of high energy transient and then in the early 1990's when SGR 1806-20 was tied to its supernova remnant (see below). The significance of two other important clues also went unnoticed in the early 1980's. The first was the large offset in the location of SGR 0526-66 from the center of the supernova remnant (i.e. its birthplace) and the second was a compact X-ray source at this same location. These observations, combined with the known age of the supernova remnant (5000 years), require that the magnetar be moving at a high speed and depositing energy into its surroundings as it goes. SGR 1806-20: A Magnetar Powers a Nebula While SGR 1806-20 was the most prolific burster in the 1980's, its true location wasn't known until it was detected by the Japanese X-ray ASCA satellite in 1993, verifying an earlier claim that it was associated with the supernova remnant G10.0-0.3. SGR 1806-20 lies at the center of this egg-shaped supernova remnant whose radio emission peaks toward the center and falls away at its outer edge. On both large scales and small scales G10.0-0.3 fits the conventional definition of a plerion. Prior to the discovery of the pulsed X-ray emission from this magnetar, this nebula was the best evidence that an unusual neutron star was powering its emission. Closer in to SGR 1806-20 the radio images made at the Very Large Array show evidence of large scale outflow of particles that has persisted for a long time. This out-flowing particle wind is especially evident in the abrupt changes seen from a jet-like feature centered on SGR 1806-20, where the "jet" was seen to rotate on the sky by 50 degrees in 1.4 years. The properties of this source are best understood if it is the result of a sudden injection of electrons accelerated nearly at the speed of light and produced as part of the high energy bursts from magnetars. Comparison of the energy contained in these particles versus the total energy released by the flashes of high energy light, shows that the particles are a significant (if not dominant) part of the total energy in these bursts. Moreover, because the lifetime of the particles is so long, studying the plerions is much like looking at the rings of a tree: the burst history of the magnetar is revealed through the study of the plerion. Figure Caption: Two views toward SGR 1806-20. These radio images, taken with the Very Large Array, were made 1.4 years apart on 1994 March (left) and 1995 August (right). A jet-like feature is seen to rotate on the sky during this time. This behavior is thought to result from the sudden injection of high energy particles from the magnetar. SGR 1900+14: New Evidence of Particle Injection by a Magnetar Until recently you could have been excused for thinking that SGR 1900+14 was the least interesting of the four SGRs. It was somewhat inactive as a gamma-ray source, bursting a few times in 1979 and again in 1993. An approximate position for SGR 1900+14 has been determined via triangulation of burst arrival times from the satellites in the Interplanetary Network (IPN). In the next figure we superimpose this long needle-like region on a radio image of the sky taken in this direction. There is an X-ray source interior to this which is thought to be the quiescent X-ray emission from SGR 1900+14. The X-ray source, which goes by the name of RX J190717+0919.3, lies just outside the galactic supernova remnant G42.8+0.6. This is a fairly ordinary-looking supernova remnant located some 15,000 light years from the Sun, and is less than 10,000 years old. It is likely (but still unproven) that SGR 1900+14 and G42.8+0.6 were born in the same explosive event but SGR 1900+14 caught up with and punched through the expanding supernova shock. In late May and late August of this year SGR 1900+14 awoke from its slumber and began bursting like never before. Numerous bright bursts occurred during these two active periods. On August 27 an intense burst occurred that was reminiscent of the famous March 5 1979 burst from SGR 0526-66, causing the detectors of several satellites to saturate. Click here to see the light curve of the August 27 burst as detected by the Ulysses satellite. Shortly after the August 27 burst we observed the region around the quiescent X-ray emission from SGR 1900+14 using the Very Large Array in Socorro, New Mexico. While prior observations of this region have shown only empty sky, our observations in early September 1998 detected a new radio source coincident (within the position uncertainties) with the X-ray source. As an added bonus the discovery of this nebula gives us a position for SGR 1900+14 with sufficient accuracy to search for an optical counterpart. Perhaps even more interestingly than the detection of the radio source was the fact that it was short-lived, fading below detection in only one week. At the top of this page we show a movie of this fast fading source. In a forthcoming scientific paper we argue that we have detected a radio nebula shining in the light of particles accelerated to nearly the speed of light by the same event that gave rise to the bright gamma-ray bursts. Figure Caption: Two views toward SGR 1900+14. These radio images, taken with the Very Large Array, were made on 1998 June 25 (left) and September 3 (right). The position of the quiescent X-ray source RX J190717+0919.3, thought to indicate the approximate location of SGR 1900+14, is indicated by the circle. The radio source turned on shortly after the bright gamma-ray burst of August 27th and then rapidly faded from view a week later. SGR 1627-41: The Newest SGR SGR 1627-41 is the newest member of the SGR family. See the NASA press release announcing this exciting discovery. While its position is not well-determined yet, there is only one known supernova remnant in the region: G337.0-0.1. It is a compact supernova remnant 35,000 light years from the Sun which lies in the CTB 33 complex (see below), a young region with plenty of active star formation going on.

7 Millimeter VLBA Observations of Sagittarius A*

NASA Astrophysics Data System (ADS)

Bower, Geoffrey C.; Backer, Donald C.

1998-04-01

We present 7 mm Very Long Baseline Array observations of the compact nonthermal radio source in the Galactic center, Sagittarius A*. These observations confirm the hypothesis that the image of Sgr A* is a resolved elliptical Gaussian caused by the scattering of an intervening thermal plasma. The measured major axis of Sgr A* is 0.76+/-0.04 mas, consistent with the predicted scattering size of 0.67+/-0.03. We find an axial ratio of 0.73+/-0.10 and a position angle of 77.0d +/- 7.4d. These results are fully consistent with VLBI observations at longer wavelengths and at 3 mm. We find no evidence for any additional compact structure to a limit of 35 mJy. The underlying radio source must be smaller than 4.1 AU for a Galactocentric distance of 8.5 kpc. This result is consistent with the conclusion that the radio emission from Sgr A* results from synchrotron or cyclo-synchrotron radiation of gas in the vicinity of a black hole with a mass near 106 Msolar.

NuSTAR Hard X-Ray Survey of the Galactic Center Region I: Hard X-Ray Morphology and Spectroscopy of the Diffuse Emission

NASA Astrophysics Data System (ADS)

Mori, Kaya; Hailey, Charles J.; Krivonos, Roman; Hong, Jaesub; Ponti, Gabriele; Bauer, Franz; Perez, Kerstin; Nynka, Melania; Zhang, Shuo; Tomsick, John A.; Alexander, David M.; Baganoff, Frederick K.; Barret, Didier; Barrière, Nicolas; Boggs, Steven E.; Canipe, Alicia M.; Christensen, Finn E.; Craig, William W.; Forster, Karl; Giommi, Paolo; Grefenstette, Brian W.; Grindlay, Jonathan E.; Harrison, Fiona A.; Hornstrup, Allan; Kitaguchi, Takao; Koglin, Jason E.; Luu, Vy; Madsen, Kristen K.; Mao, Peter H.; Miyasaka, Hiromasa; Perri, Matteo; Pivovaroff, Michael J.; Puccetti, Simonetta; Rana, Vikram; Stern, Daniel; Westergaard, Niels J.; Zhang, William W.; Zoglauer, Andreas

2015-12-01

We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456-2901 into non-thermal X-ray filaments, molecular clouds, point sources, and a previously unknown central component of hard X-ray emission (CHXE). NuSTAR detects four non-thermal X-ray filaments, extending the detection of their power-law spectra with Γ ˜ 1.3-2.3 up to ˜50 keV. A morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission spatially correlated with the 6.4 keV Fe Kα fluorescence line emission associated with two Sgr A molecular clouds: MC1 and the Bridge. Broadband X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density (˜1023 cm-2), primary X-ray spectra (power-laws with Γ ˜ 2) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to LX ≳ 1038 erg s-1. Above ˜20 keV, hard X-ray emission in the central 10 pc region around Sgr A* consists of the candidate PWN G359.95-0.04 and the CHXE, possibly resulting from an unresolved population of massive CVs with white dwarf masses MWD ˜ 0.9 M⊙. Spectral energy distribution analysis suggests that G359.95-0.04 is likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS J1745-290, strongly favoring a leptonic origin of the GC TeV emission.

VizieR Online Data Catalog: Sgr B2(N) and Sgr B2(M) IRAM 30m line survey (Belloche+, 2013)

NASA Astrophysics Data System (ADS)

Belloche, A.; Mueller, H. S. P.; Menten, K. M.; Schilke, P.; Comito, C.

2013-08-01

The list of line identifications corresponding to the blue labels in Figs. 2 to 7 where the labels are often too crowded to be easily readable are available in ASCII format. The lists are split into six files, three for Sgr B2(N) and three for Sgr B2(M). For each source, there is one file per atmospheric window (3, 2, and 1mm). Each file is ordered by increasing frequency. The observed and synthetic spectra of Sgr B2(N) and Sgr B2(M) between 80 and 116GHz are available both in ASCII and FITS formats. The synthetic spectra were resampled to the same frequency channels as the observed spectra. The blanking value is -1000K for the ASCII files. There is one ASCII file per source. There are two FITS files per source, one for the observed spectrum and one for the synthetic spectrum. The intensities are in main-beam temperature scale in K. The blanking value is 42.75234K for the observed spectrum of SgrB2(N) and 53.96533K for the observed spectrum of SgrB2(M). (9 data files).

The Distance to M54 using Infrared Photometry of RR Lyrae Variable Stars and the Implications of its Relation to the Sagittarius Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Gupta, Arvind F.; Beaton, Rachael L.; Majewski, Steven R.; SMHASH Team

2018-01-01

CDM cosmological models predict that dark matter halo density profiles will have central cusps. Yet for many dwarf spheroidal galaxies (dSphs), this expectation is in contrast with observations of cored, rather than cusped, halos. This 'cusp-core problem' is apparent in the Sagittarius Dwarf Galaxy (Sgr), one of the largest satellites of the Milky Way. The globular cluster M54, one of several clusters associated with Sgr, coincides in on-sky position with the center of the main body of Sgr. While several studies find that M54 lies within the center of Sgr, other findings show that M54 is offset from the center by several kiloparsecs along our line of sight. The latter requires Sgr to have a cored dark matter distribution. In the presence of a cuspy halo, the orbit of M54 would have decayed via dynamical friction and the cluster would have fallen to the center of Sgr. A clear determination of the relation of the two bodies may help us better understand the distribution of dark matter in Sgr and other dSphs. Here we present a measurement of the distance modulus to M54 using a set of RR Lyrae variable stars in near-infrared Magellan data mid-infrared Spitzer data. The magnitudes of individual stars are measured using multi-epoch PSF photometry and light curve fitting. From precise RR Lyrae period-luminosity relations at these wavelengths, we then find the mean M54 distance modulus to be 17.126 ± 0.023 (ran) ± 0.080 (sys). Our result is consistent with a distance measurement to Sgr derived via nearly identical methods and thus also consistent with the expectation of a central cusp in the dark matter density profile of Sgr.

NuSTAR Observations of Two New Black Hole X-ray Binary Candidates within 1 pc of Sgr A*

NASA Astrophysics Data System (ADS)

Hord, Benjamin; Hailey, Charles; Mori, Kaya; Mandel, Shifra

2018-01-01

Remarkably, two new X-ray transients were discovered in outburst within ~1 pc of the Galactic Center by the Swift X-ray Telescope in the first half of 2016. A few weeks after each outburst began, NuSTAR ToO observations were triggered for both of the objects. These sources have no known counterparts at other energies. Both objects exhibit relativistically broadened Fe lines in their spectra and possible quasi-periodic oscillations (QPO) in their power spectra, which are features seen in many black hole X-ray binaries. Combined with the fact that there have been no previously observed large outbursts at these positions over the decade of the Swift X-ray Telescope galactic center monitoring campaign, these sources make for prime black hole binary candidates (BHC) rather than neutron star low-mass X-ray binaries (NS-LMXB), which have a known short (<~5 year) recurrence time. We will present 3-79 keV NuSTAR spectra and timing analysis of these sources that supports a black hole binary interpretation over a neutron star scenario. These new BHC, combined with at least one other previously discovered BHC near the Galactic Center, hint at a potentially substantive black hole population in the vicinity of the supermassive black hole at Sgr A*.

Chandra Finds Evidence for Swarm of Black Holes Near the Galactic Center

NASA Astrophysics Data System (ADS)

2005-01-01

A swarm of 10,000 or more black holes may be orbiting the Milky Way's supermassive black hole, according to new results from NASA's Chandra X-ray Observatory. This would represent the highest concentration of black holes anywhere in the Galaxy. These relatively small, stellar-mass black holes, along with neutron stars, appear to have migrated into the Galactic Center over the course of several billion years. Such a dense stellar graveyard has been predicted for years, and this represents the best evidence to date of its existence. The Chandra data may also help astronomers better understand how the supermassive black hole at the center of the Milky Way grows. The discovery was made as part of Chandra's ongoing program of monitoring the region around Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way. It was announced today by Michael Muno of the University of California, Los Angeles (UCLA) at a meeting of the American Astronomical Society in San Diego, CA. Animation: Sequence Showing Evidence of Black Hole Swarm in Context Animation: Sequence Showing Evidence of Black Hole Swarm in Context Among the thousands of X-ray sources detected within 70 light years of Sgr A*, Muno and his colleagues searched for those most likely to be active black holes and neutron stars by selecting only the brightest sources that also exhibited large variations in their X-ray output. These characteristics identify black holes and neutron stars that are in binary star systems and are pulling matter from nearby companion stars. Of the seven sources that met these criteria, four are within three light years of Sgr A*. "Although the region around Sgr A* is crowded with stars, we expected that there was only a 20 percent chance that we would find even one X-ray binary within a three-light-year radius," said Muno. "The observed high concentration of these sources implies that a huge number of black holes and neutron stars have gathered in the center of the Galaxy." Mark Morris, also of UCLA and a coauthor on the present work, had predicted a decade ago that a process called dynamical friction would cause stellar black holes to sink toward the center of the Galaxy. Black holes are formed as remnants of the explosions of massive stars and have masses of about 10 suns. As black holes orbit the center of the Galaxy at a distance of several light years, they pull on surrounding stars, which pull back on the black holes. Combined Chandra X-ray Image of Galactic Center X-ray Binaries Combined Chandra X-ray Image of Galactic Center X-ray Binaries The net effect is that black holes spiral inward, and the low-mass stars move out. From the estimated number of stars and black holes in the Galactic Center region, dynamical friction is expected to produce a dense swarm of 20,000 black holes within three light years of Sgr A*. A similar effect is at work for neutron stars, but to a lesser extent because they have a lower mass. Once black holes are concentrated near Sgr A*, they will have numerous close encounters with normal stars there, some of which are in binary star systems. The intense gravity of a black hole can induce an ordinary star to "change partners" and pair up with the black hole while ejecting its companion. This process and a similar one for neutron stars are expected to produce several hundreds of black hole and neutron star binary systems. "If only one percent of these binary systems are X-ray active each year, they can account for the sources we see," said Eric Pfahl of the University of Virginia in Charlottesville and a coauthor of a paper describing these results that has been submitted to the Astrophysical Journal Letters. "Although the evidence is mostly circumstantial, it makes a strong case for the existence of a large population of neutron stars and stellar-mass black holes within three light-years of the center of our Galaxy." Galactic Center X-ray Binaries in Context Galactic Center X-ray Binaries in Context The black holes and neutron stars in the cluster are expected to gradually be swallowed by the supermassive black hole, Sgr A*, at a rate of about one every million years. At this rate, about 10,000 black holes and neutron stars would have been captured in a few billion years, adding about 3 percent to the mass of the central supermassive black hole, which is currently estimated to contain the mass of 3.7 million suns. In the meantime, the acceleration of low-mass stars by black holes will eject low-mass stars from the central region. This expulsion will reduce the likelihood that normal stars will be captured by the central supermassive black hole. This may explain why the central regions of some galaxies, including the Milky Way, are fairly quiet even though they contain a supermassive black hole. The region analyzed in this research near Sgr A* has been observed 16 times between 1999 and 2004 using Chandra's Advanced CCD Imaging Spectrometer (ACIS) instrument. Other members of the research team include Frederick K. Baganoff (Massachusetts Institute of Technology), Niel Brandt (Penn State), Andrea Ghez and Jessica Lu (UCLA). NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate, Washington. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

ALMA Observations of the Galactic Center: SiO Outflows and High Mass Star Formation Near Sgr A

NASA Technical Reports Server (NTRS)

Yusef-Zadeh, F.; Royster, M.; Wardle, M.; Arendt, R.; Bushouse, H.; Gillessen, S.; Lis, D.; Pound, M. W.; Roberts, D. A.; Whitney, B.;

The Milky Way's Supermassive Black Hole: How Good a Case Is It?

NASA Astrophysics Data System (ADS)

Eckart, Andreas; Hüttemann, Andreas; Kiefer, Claus; Britzen, Silke; Zajaček, Michal; Lämmerzahl, Claus; Stöckler, Manfred; Valencia-S, Monica; Karas, Vladimir; García-Marín, Macarena

2017-05-01

The compact and, with {˜ }4.3± 0.3× 10^6 M_{\\odot }, very massive object located at the center of the Milky Way is currently the very best candidate for a supermassive black hole (SMBH) in our immediate vicinity. The strongest evidence for this is provided by measurements of stellar orbits, variable X-ray emission, and strongly variable polarized near-infrared emission from the location of the radio source Sagittarius A* (SgrA*) in the middle of the central stellar cluster. Simultaneous near-infrared and X-ray observations of SgrA* have revealed insights into the emission mechanisms responsible for the powerful near-infrared and X-ray flares from within a few tens to one hundred Schwarzschild radii of such a putative SMBH. If SgrA* is indeed a SMBH it will, in projection onto the sky, have the largest event horizon and will certainly be the first and most important target for very long baseline interferometry observations currently being prepared by the event horizon telescope (EHT). These observations in combination with the infrared interferometry experiment GRAVITY at the very large telescope interferometer and other experiments across the electromagnetic spectrum might yield proof for the presence of a black hole at the center of the Milky Way. The large body of evidence continues to discriminate the identification of SgrA* as a SMBH from alternative possibilities. It is, however, unclear when the ever mounting evidence for SgrA* being associated with a SMBH will suffice as a convincing proof. Additional compelling evidence may come from future gravitational wave observatories. This manuscript reviews the observational facts, theoretical grounds and conceptual aspects for the case of SgrA* being a black hole. We treat theory and observations in the framework of the philosophical discussions about "(anti)realism and underdetermination", as this line of arguments allows us to describe the situation in observational astrophysics with respect to supermassive black holes. Questions concerning the existence of supermassive black holes and in particular SgrA* are discussed using causation as an indispensable element. We show that the results of our investigation are convincingly mapped out by this combination of concepts.

High-Resolution, Wide-Field Imaging of the Galactic Center Region at 330 MHz

DTIC Science & Technology

2004-10-01

associated with the massive black hole in the center of our galaxy, Sgr A *, is slightly circularly polarized at higher frequencies (Bower et al. 1999...axy’s central massive black hole , was detected utilizing a subset of these data. This is the first detection of this source at comparable frequencies...first detection of Sagittarius A * in this frequency range. Key words: Galaxy: center — radio continuum: general — techniques: interferometric 1

Infrared photometry of the black hole candidate Sagittarius A*

NASA Technical Reports Server (NTRS)

Close, Laird M.; Mccarthy, Donald W. JR.; Melia, Fulvio

1995-01-01

An infrared source has been imaged within 0.2 +/- 0.3 arcseconds of the unique Galactic center radio source Sgr A* High angular resolution (averaged value of the Full Width at Half Maximum (FWHM) approximately 0.55 arcseconds) was achieved by rapid (approximately 50 Hz) real-time images motion compensation. The source's near-infrared magnitudes (K = 12.1 +/- 0.3, H = 13.7 +/- 0.3, and J = 16.6 +/- 0.4) are consistent with a hot object reddened by the local extinction A(sub v) approximately 27). At the 3 sigma level of confidence, a time series of 80 images limits the source variability to less than 50% on timescales from 3 to 30 minutes. The photometry is consistent with the emission from a simple accretion disk model for a approximately 1 x 10(exp 6) solar mass black hole. However, the fluxes are also consistent with a hot luminous (L approximately 10(exp 3.5) to 10(exp 4-6) solar luminosity) central cluster star positionally coincident with Sgr A*.

High-Energy X-Ray Detection of G359.89-0.08 (SGR A-E): Magnetic Flux Tube Emission Powered by Cosmic Rays?

NASA Technical Reports Server (NTRS)

Zhang, Shuo; Hailey, Charles J.; Baganoff, Frederick K.; Bauer, Franz E.; Boggs, Steven E.; Craig, William W.; Christensen, Finn E.; Gotthelf, Eric V.; Harrison, Fiona A.; Mori, Kaya;

Local Circumnuclear Magnetar Solution to Extragalactic Fast Radio Bursts

NASA Astrophysics Data System (ADS)

Pen, Ue-Li; Connor, Liam

2015-07-01

We synthesize the known information about fast radio bursts (FRBs) and radio magnetars, and describe an allowed origin near nuclei of external, but non-cosmological, galaxies. This places them at z\\ll 1, within a few hundred megaparsecs. In this scenario, the high dispersion measure (DM) is dominated by the environment of the FRB, modeled on the known properties of the Milky Way center, whose innermost 100 pc provides 1000 pc cm-3. A radio loud magnetar is known to exist in our galactic center, within ˜2 arcsec of Sgr A*. Based on the polarization, DM, and scattering properties of this known magnetar, we extrapolate its properties to those of Crab-like giant pulses and SGR flares and point out their consistency with observed FRBs. We conclude that galactic center magnetars could be the source of FRBs. This scenario is readily testable with very long baseline interferometry measurements as well as with flux count statistics from large surveys such as CHIME or UTMOST.

Magnetar Observations with Fermi/GBM

NASA Technical Reports Server (NTRS)

Kouveliotou, Chryssa

2009-01-01

NASA's Fermi Observatory was launched June 11, 2009; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. In the first year of operations we recorded emission from four magnetar sources; of these, only one was an old magnetar: SGR 1806+20. The other three detections were: SGR J0501+4516, newly discovered with Swift and extensively monitored with both Swift and GBM, SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP) and a very recently discovered new source, SGR 0418+5729. I report below on the current status of the analyses efforts of the GBM data.

Bipolar Molecular Outflows within 1pc of Sgr A*:Evidence for Low-mass Star Formation Activity

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, Farhad; Wardle, Mark; Kunneriath, Devaky; Royster, Marc; Wootten, Al; Roberts, Douglas

2018-01-01

The 4 million solar mass black hole, Sgr A*, is expected to suppress star formation because the measured density of the cloud is insufficient for self-gravity to overcome tidal disruption by the black hole's gravitational field. Nevertheless, objects resembling dust-enshrouded young stars and photo-evaporative flows from their disks have been identified within 2pc of Sgr A*. Clear identification of the nature of these objects has been hampered by the Galactic center's distance, 30 magnitudes of foreground extinction, and stellar crowding. Here, we report the discovery of 11 bipolar molecular outflows using ALMA within a projected distance of one pc from Sgr A*. These unambiguous signatures of young protostars manifest as approaching and receding lobes of dense gas swept up by the jets created during the formation and early evolution of low-mass stars. The mean dynamical age of the outflow sources and the rate of star formation are estimated to be ~6500 years and ~5x10^{-4} solar mass per year, respectively. These measurements suggest that star formation could take place in the immediate vicinity of supermassive black holes in the nuclei of external galaxies.

Sgr A* as Source of the Positrons Observed in the Galactic Center Region

NASA Astrophysics Data System (ADS)

Jean, Pierre; Guessoum, Nidhal; Ferrière, Katia

2017-01-01

We explore the possibility that a substantial fraction of the positrons observed to annihilate in the central region of our Galaxy come from the supermassive black hole Sgr A* that lies at the center. This idea was proposed by several authors, but the propagation of the emitted positrons into the bulge and beyond remained a serious problem for models of the origin of GC positrons. We assume models of positron production with different energies. The propagation of positrons from their production site is followed in detail with Monte-Carlo simulations, taking into account the physical conditions of the propagation regions as well as various physical interactions. Using the known physics of positron annihilation in astrophysical environments, we calculate the properties of the annihilation emission (time evolution and spatial distribution) for the different models under consideration. We present the results of these simulations and the conclusions/constraints that can be inferred from them.

Magnetar Observations in the Swift-Fermi/GBM Era

NASA Technical Reports Server (NTRS)

Kouveliotou, Chryssa

2010-01-01

NASA's Fermi Observatory was launched June 11, 2008; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. Since then, and against all odds, GBM recorded over 600 bursts from 4 SGRs. Of these four sources, only one was an old magnetar: SGR J1806+20. SGR J0501+4516, was discovered with Swift and extensively monitored with GBM. A source originally classified as AXP 1E1547.0-5408 exhibited SGR-like bursting behavior and we reclassified it as SGR J1550-5418. Finally, GBM discovered SGR J0418+5729 on 2009 June. Finally, on March 2010, a third new magnetar was discovered with Swift, SGR J1833-0832. I report below on the current status of the field and on several results combining multi-satellite and ground-based data

NuSTAR HARD X-RAY SURVEY OF THE GALACTIC CENTER REGION. I. HARD X-RAY MORPHOLOGY AND SPECTROSCOPY OF THE DIFFUSE EMISSION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mori, Kaya; Hailey, Charles J.; Perez, Kerstin

2015-12-01

We present the first sub-arcminute images of the Galactic Center above 10 keV, obtained with NuSTAR. NuSTAR resolves the hard X-ray source IGR J17456–2901 into non-thermal X-ray filaments, molecular clouds, point sources, and a previously unknown central component of hard X-ray emission (CHXE). NuSTAR detects four non-thermal X-ray filaments, extending the detection of their power-law spectra with Γ ∼ 1.3–2.3 up to ∼50 keV. A morphological and spectral study of the filaments suggests that their origin may be heterogeneous, where previous studies suggested a common origin in young pulsar wind nebulae (PWNe). NuSTAR detects non-thermal X-ray continuum emission spatially correlated with the 6.4more » keV Fe Kα fluorescence line emission associated with two Sgr A molecular clouds: MC1 and the Bridge. Broadband X-ray spectral analysis with a Monte-Carlo based X-ray reflection model self-consistently determined their intrinsic column density (∼10{sup 23} cm{sup −2}), primary X-ray spectra (power-laws with Γ ∼ 2) and set a lower limit of the X-ray luminosity of Sgr A* flare illuminating the Sgr A clouds to L{sub X} ≳ 10{sup 38} erg s{sup −1}. Above ∼20 keV, hard X-ray emission in the central 10 pc region around Sgr A* consists of the candidate PWN G359.95–0.04 and the CHXE, possibly resulting from an unresolved population of massive CVs with white dwarf masses M{sub WD} ∼ 0.9 M{sub ⊙}. Spectral energy distribution analysis suggests that G359.95–0.04 is likely the hard X-ray counterpart of the ultra-high gamma-ray source HESS J1745–290, strongly favoring a leptonic origin of the GC TeV emission.« less

Study of diffuse H II regions potentially forming part of the gas streams around Sgr A*

NASA Astrophysics Data System (ADS)

Armijos-Abendaño, J.; López, E.; Martín-Pintado, J.; Báez-Rubio, A.; Aravena, M.; Requena-Torres, M. A.; Martín, S.; Llerena, M.; Aldás, F.; Logan, C.; Rodríguez-Franco, A.

2018-05-01

We present a study of diffuse extended ionized gas towards three clouds located in the Galactic Centre (GC). One line of sight (LOS) is towards the 20 km s-1 cloud (LOS-0.11) in the Sgr A region, another LOS is towards the 50 km s-1 cloud (LOS-0.02), also in Sgr A, while the third is towards the Sgr B2 cloud (LOS+0.693). The emission from the ionized gas is detected from Hnα and Hmβ radio recombination lines (RRLs). Henα and Hemβ RRL emission is detected with the same n and m as those from the hydrogen RRLs only towards LOS+0.693. RRLs probe gas with positive and negative velocities towards the two Sgr A sources. The Hmβ to Hnα ratios reveal that the ionized gas is emitted under local thermodynamic equilibrium conditions in these regions. We find a He to H mass fraction of 0.29±0.01 consistent with the typical GC value, supporting the idea that massive stars have increased the He abundance compared to its primordial value. Physical properties are derived for the studied sources. We propose that the negative velocity component of both Sgr A sources is part of gas streams considered previously to model the GC cloud kinematics. Associated massive stars with what are presumably the closest H II regions to LOS-0.11 (positive velocity gas), LOS-0.02, and LOS+0.693 could be the main sources of ultraviolet photons ionizing the gas. The negative velocity components of both Sgr A sources might be ionized by the same massive stars, but only if they are in the same gas stream.

The 3 Ms Chandra campaign on Sgr A*: a census of X-ray flaring activity from the Galactic center

NASA Astrophysics Data System (ADS)

Neilsen, J.; Nowak, M. A.; Gammie, C.; Dexter, J.; Markoff, S.; Haggard, D.; Nayakshin, S.; Wang, Q. D.; Grosso, N.; Porquet, D.; Tomsick, J. A.; Degenaar, N.; Fragile, P. C.; Houck, J. C.; Wijnands, R.; Miller, J. M.; Baganoff, F. K.

2014-05-01

Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief flares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of the closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including the brightest flare ever seen from Sgr A*. Focusing on the statistics of the flares and the quiescent emission, we discuss the physical implications of X-ray variability in the Galactic center.

The 3 megasecond Chandra campaign on Sgr A*: a census of x-ray flaring activity from the galactic center

NASA Astrophysics Data System (ADS)

Neilsen, Joey

Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief flares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic Center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of our closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including the brightest flare ever seen from Sgr A*. Focusing on the statistics of the flares, the quiescent emission, and the relationship between the X-ray and the infrared, we discuss the physical implications of X-ray variability in the Galactic Center.

The 3 Megasecond Chandra Campaign on Sgr A*: A Census of X-ray Flaring Activity from the Galactic Center

NASA Astrophysics Data System (ADS)

Neilsen, Joseph; Nowak, Michael; Gammie, Charles F.; Dexter, Jason; Markoff, Sera; Haggard, Daryl; Nayakshin, Sergei; Wang, Q. Daniel; Grosso, N.; Porquet, D.; Tomsick, John; Degenaar, Nathalie; Fragile, P. Christopher; Houck, John C.; Wijnands, Rudy; Miller, Jon M.; Baganoff, Frederick K.

2014-08-01

Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief ares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic Center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of our closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including one of the brightest flares ever seen from Sgr A*. Focusing on the statistics of the flares, the quiescent emission, and the relationship between the X-ray and the infrared, we discuss the physical implications of X-ray variability in the Galactic Center.

Evolution of Supernova Remnants Near the Galactic Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yalinewich, A.; Piran, T.; Sari, R.

Supernovae near the Galactic center (GC) evolve differently from regular Galactic supernovae. This is mainly due to the environment into which the supernova remnants (SNRs) propagate. SNRs near the GC propagate into a wind swept environment with a velocity directed away from the GC, and a graded density profile. This causes these SNRs to be non-spherical, and to evolve faster than their Galactic counterparts. We develop an analytic theory for the evolution of explosions within a stellar wind, and verify it using a hydrodynamic code. We show that such explosions can evolve in one of three possible morphologies. Using thesemore » results we discuss the association between the two SNRs (SGR East and SGR A’s bipolar radio/X-ray lobes) and the two neutron stars (the Cannonball and SGR J1745-2900) near the GC. We show that, given the morphologies of the SNR and positions of the neutron stars, the only possible association is between SGR A’s bipolar radio/X-ray lobes and SGR J1745-2900. If a compact object was created in the explosion of SGR East, it remains undetected, and the SNR of the supernova that created the Cannonball has already disappeared.« less

Time Domain Filtering of Resolved Images of Sgr A{sup ∗}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shiokawa, Hotaka; Doeleman, Sheperd S.; Gammie, Charles F.

The goal of the Event Horizon Telescope (EHT) is to provide spatially resolved images of Sgr A*, the source associated with the Galactic Center black hole. Because Sgr A* varies on timescales that are short compared to an EHT observing campaign, it is interesting to ask whether variability contains information about the structure and dynamics of the accretion flow. In this paper, we introduce “time-domain filtering,” a technique to filter time fluctuating images with specific temporal frequency ranges and to demonstrate the power and usage of the technique by applying it to mock millimeter wavelength images of Sgr A*. Themore » mock image data is generated from the General Relativistic Magnetohydrodynamic (GRMHD) simulation and the general relativistic ray-tracing method. We show that the variability on each line of sight is tightly correlated with a typical radius of emission. This is because disk emissivity fluctuates on a timescale of the order of the local orbital period. Time-domain filtered images therefore reflect the model dependent emission radius distribution, which is not accessible in time-averaged images. We show that, in principle, filtered data have the power to distinguish between models with different black-hole spins, different disk viewing angles, and different disk orientations in the sky.« less

Time Domain Filtering of Resolved Images of Sgr A∗

NASA Astrophysics Data System (ADS)

Shiokawa, Hotaka; Gammie, Charles F.; Doeleman, Sheperd S.

2017-09-01

The goal of the Event Horizon Telescope (EHT) is to provide spatially resolved images of Sgr A*, the source associated with the Galactic Center black hole. Because Sgr A* varies on timescales that are short compared to an EHT observing campaign, it is interesting to ask whether variability contains information about the structure and dynamics of the accretion flow. In this paper, we introduce “time-domain filtering,” a technique to filter time fluctuating images with specific temporal frequency ranges and to demonstrate the power and usage of the technique by applying it to mock millimeter wavelength images of Sgr A*. The mock image data is generated from the General Relativistic Magnetohydrodynamic (GRMHD) simulation and the general relativistic ray-tracing method. We show that the variability on each line of sight is tightly correlated with a typical radius of emission. This is because disk emissivity fluctuates on a timescale of the order of the local orbital period. Time-domain filtered images therefore reflect the model dependent emission radius distribution, which is not accessible in time-averaged images. We show that, in principle, filtered data have the power to distinguish between models with different black-hole spins, different disk viewing angles, and different disk orientations in the sky.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fish, Vincent L.; Doeleman, Sheperd S.; Lu, Ru-Sen

The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve the 1.3 mm emission from this source on angular scales comparable to that of the general relativistic shadow. Previous EHT observations have used visibility amplitudes to infer the morphology of the millimeter-wavelength emission. Potentially much richer source information is contained in the phases. We report on 1.3 mm phase information on Sgr A* obtained with the EHT on a total of 13 observing nights over four years. Closure phases, which are the sum of visibility phases along a closedmore » triangle of interferometer baselines, are used because they are robust against phase corruptions introduced by instrumentation and the rapidly variable atmosphere. The median closure phase on a triangle including telescopes in California, Hawaii, and Arizona is nonzero. This result conclusively demonstrates that the millimeter emission is asymmetric on scales of a few Schwarzschild radii and can be used to break 180° rotational ambiguities inherent from amplitude data alone. The stability of the sign of the closure phase over most observing nights indicates persistent asymmetry in the image of Sgr A* that is not obscured by refraction due to interstellar electrons along the line of sight.« less

Fragments of the past activity of Sgr A* inferred from X-ray echoes in Sgr C

NASA Astrophysics Data System (ADS)

Chuard, D.; Terrier, R.; Goldwurm, A.; Soldi, S.; Clavel, M.; Morris, M.; Ponti, G.; Walls, M.; Chernyakova, M.

2017-10-01

Giant molecular clouds populating the central molecular zone have a high enough column density to reflect X-rays coming from strong compact sources in their neighbourhood, including possible powerful outbursts from the Galactic supermassive black hole Sgr A*. We study this reflected emission in observations of the molecular complex Sgr C made with the X-ray observatories XMM-Newton and Chandra between 2000 and 2014. We show that this complex exhibits clear variability in both space and time, which strongly favours the reflection scenario, the most likely illuminating source being Sgr A*. By comparing data to Monte-Carlo simulated reflection spectra, we are able to put the best constraints to date on the line-of-sight positions of the main bright clumps of the molecular complex. Ultimately, extending this approach by the inclusion of other molecular complexes allows us to partially reconstruct the past lightcurve of the Galactic supermassive black hole.

An XMM-Newton Study of 9SGR and the Lagoon Nebula

NASA Technical Reports Server (NTRS)

Rauw, G.; Blomme, R.; Waldron, W. L.; Naze, Y.; Harries, T. J.; Chapman, J. M.; Corcoran, M. F.; Detal, A.; Gosset, E.

2001-01-01

We report preliminary results of an XMM-Newton observation of the 04 V star 9 Sgr (= HD 164794). 9 Sgr is one of a few single OB stars that display a non-thermal radio emission attributed to synchrotron emission by relativistic electrons. Inverse Compton scattering of photospheric UV photons by these relativistic electrons is a priori expected to generate a non-thermal power-law tail in the X-ray spectrum. Our EPIC and RGS spectra of 9 Sgr suggest a more complex situation than expected from this 'simple' theoretical picture. Furthermore, soft-band EPIC images of the region around 9 Sgr reveal a number of point sources inside the Lagoon Nebula (M8). Most of these sources have optical counterparts inside the very young open cluster NGC 6530 and several X-ray sources are associated with low and intermediate mass pre-main sequence stars. Finally, we also detect (probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the HG region.

Revealing the Galactic Center in the Far-Infrared with SOFIA/FORCAST

NASA Astrophysics Data System (ADS)

Lau, Ryan M.; Herter, Terry; Morris, Mark; Li, Zhiyuan; Becklin, Eric; Adams, Joseph; Hankins, Matthew

2015-08-01

We present a summary of far-infrared imaging observations of the inner 40 pc of the Galactic center addressing the dense, dusty torus around Sgr A*, massive star formation, and dust production around massive stars and in the Sgr A East supernova remnant. Observations of warm dust emission were performed using the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). The Circumnuclear Ring (CNR) surrounding and heated by central cluster in the vicinity of Sgr A* shows no internal active star formation but does exhibit significant density “clumps,” a surprising result because tidal shearing should act quickly to smear out structure. G-0.02-0.07, a complex consisting of three compact HII regions and one ultracompact HII region, is site of the most recent confirmed star formation within ~10 pc of the Galactic center. Our observations reveal the dust morphologies and SEDs of the regions to constrain the composition and gas-to-dust mass ratios of the emitting dust and identify heating sources candidates from archival near-IR images. FORCAST observations Luminous Blue Variables (LBVs) located in and near the Quintuplet Cluster reveal the asymmetric, compressed shell of hot dust surrounding the Pistol Star and provide the first detection of the thermal emission from the symmetric, hot dust envelope surrounding G0.120-0.048. These two LBV’s have nebulae with similar quantities of dust (~0.02 M⊙) but exhibit contrasting appearances due to the external influence of their different environments. Finally, the far-infrared observations indicate the presence of ~0.02 M⊙ of warm (~100 K) dust in the hot interior of the ~10,000 yr-old SgrA East supernova remnant indicating the dust has survived the passage of the reverse shock. The results suggest that supernovae may indeed be the dominant dust production mechanism in the dense environment of early Universe galaxies.

Rapid Optical Follow-up Observations of SGR Events with ROTSE-I

NASA Astrophysics Data System (ADS)

Akerlof, C.; Balsano, R.; Barthelmy, S.; Bloch, J.; Butterworth, P.; Casperson, D.; Cline, T.; Fletcher, S.; Gisler, G.; Hills, J.; Kehoe, R.; Lee, B.; Marshall, S.; McKay, T.; Pawl, A.; Priedhorsky, W.; Seldomridge, N.; Szymanski, J.; Wren, J.

2000-10-01

In order to observe nearly simultaneous emission from gamma-ray bursts (GRBs), the Robotic Optical Transient Search Experiment (ROTSE) receives triggers via the GRB Coordinates Network (GCN). Since beginning operations in 1998 March, ROTSE has also taken useful data for 10 SGR events: eight from SGR 1900+14 and two from SGR 1806-20. We have searched for new or variable sources in the error regions of these SGRs, and no optical counterparts were observed. Limits are in the range mROTSE~12.5-15.5 during the period 20 s to 1 hr after the observed SGR events.

The Parallax of the Red Hypergiant VX Sgr with Accurate Tropospheric Delay Calibration

NASA Astrophysics Data System (ADS)

Xu, Shuangjing; Zhang, Bo; Reid, Mark J.; Menten, Karl M.; Zheng, Xingwu; Wang, Guangli

2018-05-01

We report astrometric results of VLBI phase-referencing observations of 22 GHz H2O masers emission toward the red hypergiant VX Sgr, one of most massive and luminous red hypergiant stars in our Galaxy, using the Very Long Baseline Array. A background source, J1820‑2528, projected 4.°4 from the target VX Sgr, was used as the phase reference. For the low decl. of these sources, such a large separation normally would seriously degrade the relative astrometry. We use a two-step method of tropospheric delay calibration, which combines the VLBI geodetic-block (or Global Positioning System) calibration with an image-optimization calibration, to obtain a trigonometric parallax of 0.64 ± 0.04 mas, corresponding to a distance of {1.56}-0.10+0.11 kpc. The measured proper motion of VX Sgr is 0.36 ± 0.76 and ‑2.92 ± 0.78 mas yr‑1 in the eastward and northward directions. The parallax and proper motion confirms that VX Sgr belong to the Sgr OB1 association. Rescaling bolometric luminosities in the literature to our parallax distance, we find that the luminosity of VX Sgr is (1.95 ± 0.62) × 105 L ⊙, where the uncertainty is dominated by differing photometry measurements.

A Nonthermal Radio Filament Connected to the Galactic Black Hole?

NASA Astrophysics Data System (ADS)

Morris, Mark R.; Zhao, Jun-Hui; Goss, W. M.

2017-12-01

Using the Very Large Array, we have investigated a nonthermal radio filament (NTF) recently found very near the Galactic black hole and its radio counterpart, Sgr A*. While this NTF—the Sgr A West Filament (SgrAWF)—shares many characteristics with the population of NTFs occupying the central few hundred parsecs of the Galaxy, the SgrAWF has the distinction of having an orientation and sky location that suggest an intimate physical connection to Sgr A*. We present 3.3 and 5.5 cm images constructed using an innovative methodology that yields a very high dynamic range, providing an unprecedentedly clear picture of the SgrAWF. While the physical association of the SgrAWF with Sgr A* is not unambiguous, the images decidedly evoke this interesting possibility. Assuming that the SgrAWF bears a physical relationship to Sgr A*, we examine the potential implications. One is that Sgr A* is a source of relativistic particles constrained to diffuse along ordered local field lines. The relativistic particles could also be fed into the local field by a collimated outflow from Sgr A*, perhaps driven by the Poynting flux accompanying the black hole spin in the presence of a magnetic field threading the event horizon. Second, we consider the possibility that the SgrAWF is the manifestation of a low-mass-density cosmic string that has become anchored to the black hole. The simplest form of these hypotheses would predict that the filament be bi-directional, whereas the SgrAWF is only seen on one side of Sgr A*, perhaps because of the dynamics of the local medium.

Star Formation at the Galactic Center

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh ultraviolet radiation streaming from hot stars orbiting close to Sgr A*. The gas of the proplyds is heated and stripped away by this radiation, forming bow shocks around the disks. Both the proplyds themselves and the bow shocks surrounding them are visible in Yusef-Zadeh’s observations. Potential for Planet Formation: Unlike the young massive stars that have previously been identified in the galactic center, the proplyd candidates in this study are associated with low-mass stars. This has led to speculation that it may in fact be easier for low-mass stars to form in the hostile surroundings of the black hole than it is for them to form elsewhere in the Milky Way. In addition, the rate at which material is lost from such proplyds is expected to be low, so there is a chance for the disk to eventually form planets. With that comes the tantalizing possibility that as telescope resolution and data-analysis techniques improve, we may even be able to watch planet formation occur near Sgr A*. Citation: F. Yusef-Zadeh et al. 2015, ApJ, 801, L26, doi:10.088/2041-8205/801/2/L26 Bonus: Check out the authors' video abstract below, which shows the locations of the proplyd candidates relative to Sgr A* and provides more information about how the observations were made and analyzed.

X-ray and gamma-ray emission of Sagittarius A* as a wind-accreting black hole

NASA Technical Reports Server (NTRS)

Mastichiadis, A.; Ozernoy, L. M.

1994-01-01

If, as many believe, Sgr A* is a massive black hole at the Galactic center, one should expect it to be a source of X-ray and gamma-ray activity, behaving basically as a scaled-down active galactic nucleus. An unavoidable source of accretion is the wind from IRS 16, a nearby group of hot, massive stars. Since the density and velocity of the accreting matter are known from observations, the accretion rate is basically a function of the putative black hole mass, M(sub h), only; this value represents a reliable lower limit to a real rate, given the other possible sources of accreting matter. Based on this and on the theories about shock acceleration in active galactic nuclei, we have estimated the expected production of relativistic particles and their hard radiation. These values turn out to be a function of M(sub h) as well. Comparing our results with available X-ray and gamma-ray observations which show Sgr A* to have a relatively low activity level, we conclude tentatively that the putative black hole in the Galactic center cannot have a mass greater than approximately 6 x 10(exp 3) solar mass. This conclusion is consistent with the upper limits to the black hole mass found by different methods earlier, although much more work is needed to make calculations of shock acceleration around black holes more reliable.

44 GHZ CLASS I METHANOL (CH{sub 3}OH) MASER SURVEY IN THE GALACTIC CENTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

McEwen, Bridget C.; Pihlström, Ylva M.; Sjouwerman, Loránt O.

2016-12-01

We report on a large 44 GHz (7{sub 0}–6{sub 1} A {sup +}) methanol (CH{sub 3}OH) maser survey of the Galactic Center. The Karl G. Jansky Very Large Array was used to search for CH{sub 3}OH maser emission covering a large fraction of the region around Sgr A. In 25 pointings, over 300 CH{sub 3}OH maser sources (>10 σ ) were detected. The majority of the maser sources have a single peak emission spectrum with line of sight velocities that range from about −13 to 72 km s{sup −1}. Most maser sources were found to have velocities around 35−55 kmmore » s{sup −1}, closely following velocities of neighboring interacting molecular clouds (MCs). The full width at half-maximum of each individual spectral feature is very narrow (∼0.85 km s{sup −1} on average). In the north, where Sgr A East is known to be interacting with the 50 km s{sup −1} MC, more than 100 44 GHz CH{sub 3}OH masers were detected. In addition, three other distinct concentrations of masers were found, which appear to be located closer to the interior of the interacting MCs. It is possible that a subset of masers is associated with star formation, although conclusive evidence is lacking.« less

Rossi X-Ray Timing Explorer All-Sky Monitor Localization of SGR 1627-41

NASA Astrophysics Data System (ADS)

Smith, Donald A.; Bradt, Hale V.; Levine, Alan M.

1999-07-01

The fourth unambiguously identified soft gamma repeater (SGR), SGR 1627-41, was discovered with the BATSE instrument on 1998 June 15. Interplanetary Network (IPN) measurements and BATSE data constrained the location of this new SGR to a 6° segment of a narrow (19") annulus. We present two bursts from this source observed by the All-Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer. We use the ASM data to further constrain the source location to a 5' long segment of the BATSE/IPN error box. The ASM/IPN error box lies within 0.3 arcmin of the supernova remnant G337.0-0.1. The probability that a supernova remnant would fall so close to the error box purely by chance is ~5%.

RXTE All-Sky Monitor Localization of SGR 1627-41

NASA Astrophysics Data System (ADS)

Smith, D. A.; Bradt, H. V.; Levine, A. M.

1999-09-01

The fourth unambiguously identified Soft Gamma Repeater (SGR), SGR 1627--41, was discovered with the BATSE instrument on 1998 June 15 (Kouveliotou et al. 1998). Interplanetary Network (IPN) measurements and BATSE data constrained the location of this new SGR to a 6(deg) segment of a narrow (19('') ) annulus (Hurley et al. 1999; Woods et al. 1998). We report on two bursts from this source observed by the All-Sky Monitor (ASM) on RXTE. We use the ASM data to further constrain the source location to a 5(') long segment of the BATSE/IPN error box. The ASM/IPN error box lies within 0.3(') of the supernova remnant (SNR) G337.0--0.1. The probability that a SNR would fall so close to the error box purely by chance is ~ 5%.

Sgr A* and general relativity

NASA Astrophysics Data System (ADS)

Johannsen, Tim

2016-06-01

General relativity has been widely tested in weak gravitational fields but still stands largely untested in the strong-field regime. According to the no-hair theorem, black holes in general relativity depend only on their masses and spins and are described by the Kerr metric. Mass and spin are the first two multipole moments of the Kerr spacetime and completely determine all higher-order moments. The no-hair theorem and, hence, general relativity can be tested by measuring potential deviations from the Kerr metric affecting such higher-order moments. Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, is a prime target for precision tests of general relativity with several experiments across the electromagnetic spectrum. First, near-infrared (NIR) monitoring of stars orbiting around Sgr A* with current and new instruments is expected to resolve their orbital precessions. Second, timing observations of radio pulsars near the Galactic center may detect characteristic residuals induced by the spin and quadrupole moment of Sgr A*. Third, the event horizon telescope, a global network of mm and sub-mm telescopes, aims to study Sgr A* on horizon scales and to image the silhouette of its shadow cast against the surrounding accretion flow using very-long baseline interferometric (VLBI) techniques. Both NIR and VLBI observations may also detect quasiperiodic variability of the emission from the accretion flow of Sgr A*. In this review, I discuss our current understanding of the spacetime of Sgr A* and the prospects of NIR, timing, and VLBI observations to test its Kerr nature in the near future.

Swift/XRT detects a new accretion outburst of the Galactic center neutron star transient GRS 1741-2853

NASA Astrophysics Data System (ADS)

Degenaar, N.; Wijnands, R.; Reynolds, M. T.; Miller, J. M.; Kennea, J. A.

2017-10-01

Daily Swift/XRT monitoring observations of the Galactic center (Degenaar et al. 2015) have picked up renewed activity of the transient neutron star low-mass X-ray binary and thermonuclear X-ray burster GRS 1741-2853, which is located 10 arcmin NW of Sgr A*. During a 1 ks PC-mode observation performed on 2017 October 11 the source is detected at a net count rate of 0.015 counts/s and it has been steadily brightening since, indicating the onset of a new accretion outburst.

Infrared studies of galactic center x-ray sources

NASA Astrophysics Data System (ADS)

DeWitt, Curtis

In this dissertation I use a variety of approaches to discover the nature of a subset of the nearly 10,000 X-ray point sources in the 2° x 0.8° region around the Galactic Center. I produced a JHK s source catalog of the 170 x170 region around Sgr A* an area containing 4339 of these X-ray sources, with the ISPI camera on the CTIO 4-m telescope. I cross-correlated the Chandra and ISPI catalogs to find potential near-infrared (NIR) counterparts to the X-ray sources. The extreme NIR source crowding in the field means that it is not possible to establish the authenticity of the matches with astrometry and photometry alone. I found 2137 IR/X-ray astrometrically matched sources; statistically I calculated that my catalog contains 289+/-13 true matches to soft X-ray sources and 154 +/- 39 matches to hard X-ray sources. However, the fraction of matches to hard sources that are spurious is 90%, compared to 40% for soft source matches, making the hard source NIR matches particularly challenging for spectroscopic follow-up. I statistically investigated the parameter space of matched sources and identified a set of 98 NIR matches to hard X-ray sources with reddenings consistent with the GC distance which have a 45% probability of being true counterparts. I created two additional photometric catalogs of the GC region to investigate the variability of X-ray counterparts over a time baseline of several years. I found 48 variable NIR sources matched to X-ray sources, with 2 spectroscopically confirmed to be true counterparts (1 in previous literature and one in this study). I took spectra of 46 of my best candidates for counterparts to X-ray sources toward the GC, and spectroscopically confirmed 4 sources as the authentic physical counterpart on the basis of emission lines in the H and K band spectra. These sources include a Be high mass X-ray binary located 16 pc in projection away from Sgr A*; a hard X-ray symbiotic binary located 22 pc in projection from Sgr A*; an O-type supergiant at an distance of 3.7 kpc; and an O star at the Galactic Center distance. I also identified 3 foreground X-ray source counterparts within a distance of 1 kpc which do not show obvious emission features in their spectra. However, on the basis of the low surface density of unreddened sources along the line-of-sight to the Galactic Center and our previous statistical analysis (DeWitt et al., 2010), these can be securely identified as the true counterparts to their coincident X-ray point sources. Lastly, I used the results of my matching simulations to infer the presence of 7+/-2 true counterparts within a set of late type giants that I observed without detectable emission features. I conclude from this work that the probable excess in red giant X-ray counterparts without emission lines needs to be confirmed both with larger samples of spectroscopically surveyed counterparts and more advanced statistical simulations of the match authenticity. Also, the nature of the compact object in two of my counterpart discoveries, the Be HMXB and the symbiotic binary, can be strongly constrained with X-ray spectral fitting. Lastly, I conclude that spectroscopic surveys for new X-ray source counterparts in the GC may be able to increase their efficiency by specifically targeting photometric variables and very close astrometric matches of IR/X-ray sources.

An accreting black hole model for Sagittarius A

NASA Technical Reports Server (NTRS)

Melia, Fulvio

1992-01-01

Several observations, notably of broad He I, Br-alpha, and Br-gamma emission lines from the vicinity of IRS 16, indicate the presence of a strong circumnuclear wind near the dynamical center of the Galaxy. Sgr A, a hypothesized supermassive object situated about 0.06 pc to the west of IRS 16, should be accreting from this wind if it is not itself a source of gaseous outflow, for which there is currently no observational evidence. Here, the spectrum and flux of radiation resulting from this process are calculated, and it is shown that they are consistent with the data over at least 12 decades of frequency. Together with the kinematic studies of the stellar and gas distributions in this region, the model argues strongly in favor of Sgr A being a black hole with mass over a million solar masses.

High-resolution VLBA imaging of the radio source Sgr A* at the Galactic Centre

NASA Technical Reports Server (NTRS)

Lo, K. Y.; Backer, D. C.; Kellermann, K. I.; Reid, M.; Zhao, J. H.; Goss, W. M.; Moran, J. M.

1993-01-01

Images of Sgr* A with milliarcsecond resolution obtained by using five telescopes of the partially completed Very Long Baseline Array (VLBA) in conjunction with a few additional telescopes are presented. The image of Sgr A* at a wavelength of 3.6 cm confirms almost exactly the elliptical Gaussian model that has been proposed on the basis of previous data. The source size at 1.34 cm wavelength is 2.4 +/- 0.2 mas, similar to previous results. At both wavelengths, the radio source is smooth, without detectable fine structure. These observations support the suggestion that the radio emission from Sgr A* is strongly scattered by electron-density fluctuations along the line of sight. On the assumption that the emission is due to a black hole accreting stellar winds from massive stars in the central 0.5 pc, the observations are consistent with a black hole mass of less than about 2 million solar masses.

Magnetars: Challenging the Extremes of Nature

NASA Technical Reports Server (NTRS)

Kouveliotou, Chryssa

2011-01-01

Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They are discovered and emit predominantly in the X- and gamma-rays. Very few sources (roughly 15) have been found since their discovery in 1987. NASA s Fermi Observatory was launched June 11, 2009; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. Since then, we recorded emission from four magnetar sources; of these, only one was an old magnetar: SGR 1806+20. The other three detections were two brand new sources, SGR J0501+4516, discovered with Swift and extensively monitored with both Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN), and SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP 1E1547.0-5408). In my talk I will give a short history of the discovery of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the properties of these sources and the current status of our knowledge of the magnetar population and birth rate.

TEV GAMMA-RAY OBSERVATIONS OF THE GALACTIC CENTER RIDGE BY VERITAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archer, A.; Buckley, J. H.; Bugaev, V.

2016-04-20

The Galactic Center ridge has been observed extensively in the past by both GeV and TeV gamma-ray instruments revealing a wealth of structure, including a diffuse component and the point sources G0.9+0.1 (a composite supernova remnant) and Sgr A* (believed to be associated with the supermassive black hole located at the center of our Galaxy). Previous very high energy (VHE) gamma-ray observations with the H.E.S.S. experiment have also detected an extended TeV gamma-ray component along the Galactic plane in the >300 GeV gamma-ray regime. Here we report on observations of the Galactic Center ridge from 2010 to 2014 by themore » VERITAS telescope array in the >2 TeV energy range. From these observations we (1) provide improved measurements of the differential energy spectrum for Sgr A* in the >2 TeV gamma-ray regime, (2) provide a detection in the >2 TeV gamma-ray emission from the composite SNR G0.9+0.1 and an improved determination of its multi-TeV gamma-ray energy spectrum, and (3) report on the detection of VER J1746-289, a localized enhancement of >2 TeV gamma-ray emission along the Galactic plane.« less

AUSTRALIA TELESCOPE COMPACT ARRAY RADIO CONTINUUM 1384 AND 2368 MHz OBSERVATIONS OF SAGITTARIUS B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, David I.; Protheroe, Raymond J.; Crocker, Roland M.

2011-03-15

We present images of the Sagittarius (Sgr) B giant molecular cloud at 1384 and 2368 MHz obtained using new, multi-configuration Australia Telescope Compact Array observations. We have combined these observations with archival single-dish observations yielding images at resolutions of 47'' x 14'' and 27'' x 8'' at 1384 and 2368 MHz, respectively. These observations were motivated by our theoretical work indicating the possibility that synchrotron emission from secondary electrons and positrons created in hadronic cosmic ray (CR) collisions with the ambient matter of the Sgr B2 cloud could provide a detectable (and possibly linearly polarized) non-thermal radio signal. We findmore » that the only detectable non-thermal emission from the Sgr B region is from a strong source to the south of Sgr B2, which we label Sgr B2 Southern Complex (SC). We find Sgr B2(SC) integrated flux densities of 1.2 {+-} 0.2 Jy at 1384 MHz and 0.7 {+-} 0.1 Jy at 2368 MHz for a source of FWHM size at 1384 MHz of {approx}54''. Despite its non-thermal nature, the synchrotron emission from this source is unlikely to be dominated due to secondary electrons and positrons. Failing to find clear evidence of non-thermal emission due to secondary electrons and positrons, we use polarization data to place 5{sigma} upper limits on the level of polarized intensity from the Sgr B2 cloud of 3.5 and 3 mJybeam{sup -1} at 1384 and 2368 MHz, respectively. We also use the angular distribution of the total intensity of archival 330 MHz Very Large Array and the total intensity and polarized emission of our new 1384 and 2368 MHz data to constrain the diffusion coefficient for transport of the parent hadronic CRs into the dense core of Sgr B2 to be no larger than about 1% of that in the Galactic disk. Finally, we have also used the data to perform a spectral and morphological study of the features of the Sgr B cloud and compare and contrast these to previous studies.« less

Chandra X-Ray Spectroscopic Imaging of Sagittarius A* and the Central Parsec of the Galaxy

NASA Astrophysics Data System (ADS)

Baganoff, F. K.; Maeda, Y.; Morris, M.; Bautz, M. W.; Brandt, W. N.; Cui, W.; Doty, J. P.; Feigelson, E. D.; Garmire, G. P.; Pravdo, S. H.; Ricker, G. R.; Townsley, L. K.

2003-07-01

We report the results of the first-epoch observation with the ACIS-I instrument on the Chandra X-Ray Observatory of Sagittarius A* (Sgr A*), the compact radio source associated with the supermassive black hole (SMBH) at the dynamical center of the Milky Way. This observation produced the first X-ray (0.5-7 keV) spectroscopic image with arcsecond resolution of the central 17'×17' (40pc×40pc) of the Galaxy. We report the discovery of an X-ray source, CXOGC J174540.0-290027, coincident with Sgr A* within 0.27"+/-0.18". The probability of a false match is estimated to be <~0.5%. The spectrum is well fitted either by an absorbed power law with photon index Γ~2.7 or by an absorbed optically thin thermal plasma with kT~1.9 keV and column density NH~1×1023 cm-2. The observed flux in the 2-10 keV band is ~1.3×10-13 ergs cm-2 s-1, and the absorption-corrected luminosity is ~2.4×1033 ergs s-1. The X-ray emission at the position of Sgr A* is extended, with an intrinsic size of ~1.4" (FWHM), consistent with the Bondi accretion radius for a 2.6×106 Msolar black hole. A compact component within the source flared by up to a factor of 3 over a period of ~1 hr at the start of the observation. The search for Kα line emission from iron was inconclusive, yielding an upper limit on the equivalent width of 2.2 keV. Several potential stellar origins for the X-ray emission at Sgr A* are considered, but we conclude that the various properties of the source favor accretion onto the SMBH as the origin for the bulk of the emission. These data are inconsistent with ``standard'' advection-dominated accretion flow (ADAF) models or Bondi models, unless the accretion rate from stellar winds is much lower than anticipated. The central parsec of the Galaxy contains an ~1.3 keV plasma with electron density ne~26η-1/2fcm-3, where ηf is the filling factor. This plasma should supply ~10-6 Msolar yr-1 of material to the accretion flow at the Bondi radius, whereas measurements of linear polarization at 150 GHz and above limit the accretion rate near the event horizon to <~10-8 Msolar yr-1, assuming an equipartition magnetic field. Taken together, the X-ray and radio results imply that outflows or convection are playing a role in ADAF models and subequipartition magnetic fields in Bondi models, or else the X-ray emission must be generated predominantly via the synchrotron self-Compton (SSC) process. The measured extent of the source and the detection of short timescale variability are evidence that the emission from Sgr A* contains both thermal and nonthermal emission components at comparable levels. We also discuss the complex structure of the X-ray emission from the Sgr A radio complex and along the Galactic plane. Morphological evidence is presented that Sgr A* and the H II region Sgr A West lie within the hot plasma in the central cavity of Sgr A East, which we interpret as a supernova remnant that may have passed through the position of the SMBH, leading to a period of increased activity that ended within the past ~300 yr. Similarly, we have discovered bright clumps of X-ray emission located on opposite sides of the Galactic plane, along a line passing through the central parsec of the Galaxy. The arrangement of these lobes suggests that Sgr A* may have experienced an earlier period of increased activity lasting several thousand years during which it expelled hot gas in a bipolar outflow oriented roughly perpendicular to the Galactic plane. Additionally, we present an analysis of stellar emission within the central parsec of the Galaxy.

PROPER MOTIONS AND ORIGINS OF SGR 1806-20 AND SGR 1900+14

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tendulkar, Shriharsh P.; Kulkarni, Shrinivas R.; Cameron, P. Brian, E-mail: spt@astro.caltech.edu

2012-12-10

We present results from high-resolution infrared observations of magnetars SGR 1806-20 and SGR 1900+14 over 5 years using laser-supported adaptive optics at the 10 m Keck Observatory. Our measurements of the proper motions of these magnetars provide robust links between magnetars and their progenitors and provide age estimates for magnetars. At the measured distances of their putative associations, we measure the linear transverse velocity of SGR 1806-20 to be 350 {+-} 100 km s{sup -1} and of SGR 1900+14 to be 130 {+-} 30 km s{sup -1}. The transverse velocity vectors for both magnetars point away from the clusters ofmore » massive stars, solidifying their proposed associations. Assuming that the magnetars were born in the clusters, we can estimate the braking index to be {approx}1.8 for SGR 1806-20 and {approx}1.2 for SGR 1900+14. This is significantly lower than the canonical value of n = 3 predicted by the magnetic dipole spin-down suggesting an alternative source of dissipation such as twisted magnetospheres or particle winds.« less

Signatures of Young Star Formation Activity within Two Parsecs of Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, F.; Wardle, M.; Sewilo, M.; Roberts, D. A.; Smith, I.; Arendt, R.; Cotton, W.; Lacy, J.; Martin, S.; Pound, M. W.; Rickert, M.; Royster, M.

2015-07-01

We present radio and infrared observations indicating ongoing star formation activity inside the ˜2-5 pc circumnuclear ring at the Galactic center. Collectively these measurements suggest a continued disk-based mode of ongoing star formation has taken place near Sgr A* over the last few million years. First, Very Large Array observations with spatial resolution 2.″17 × 0.″81 reveal 13 water masers, several of which have multiple velocity components. The presence of interstellar water masers suggests gas densities that are sufficient for self-gravity to overcome the tidal shear of the 4× {10}6 {M}⊙ black hole. Second, spectral energy distribution modeling of stellar sources indicates massive young stellar object (YSO) candidates interior to the molecular ring, supporting in situ star formation near Sgr A* and appear to show a distribution similar to that of the counter-rotating disks of ˜100 OB stars orbiting Sgr A*. Some YSO candidates (e.g., IRS 5) have bow shock structures, suggesting that they have gaseous disks that are phototoevaporated and photoionized by the strong radiation field. Third, we detect clumps of SiO (2-1) and (5-4) line emission in the ring based on Combined Array for Research in Millimeter-wave Astronomy and Sub-Millimeter Array observations. The FWHM and luminosity of the SiO emission is consistent with shocked protostellar outflows. Fourth, two linear ionized features with an extent of ˜0.8 pc show blue and redshifted velocities between +50 and -40 km s-1, suggesting protostellar jet driven outflows with mass-loss rates of ˜ 5× {10}-5 {M}⊙ yr-1. Finally, we present the imprint of radio dark clouds at 44 GHz, representing a reservoir of molecular gas that feeds star formation activity close to Sgr A*.

Unraveling the Cooling Trend of the Soft Gamma Repeater, SGR162-41

NASA Technical Reports Server (NTRS)

Kouveliotou, C.; Eichler, D.; Woods, P. M.; Lybarsky, Y.; Patel, S. K.; Gogus, E.; vanderKlis, M.; Tennant, A.; Wachter, S.

2003-01-01

SGR 1627-41 was discovered in 1998 after a single active episode which lasted approx. 6 weeks. We report here our monitoring results of the decay trend of the persistent X-ray luminosity of the source during the last 5 years. We find an initial temporal power law decay with index 0.47, reaching a piateau which is followed by a sharp (factor of ten) flux decline approx. 800 days after the source activation. The source spectrum is best described during the entire period by a single power law with high absorption (N(sub H) = 9.0(7) x 10(exp 22)/sq cm); the spectral index, however, varies dramatically between 2.2-3.8 spanning the entire range for all known SGR sources. We discuss the cooling behavior of the neutron star assuming a deep crustal heating initiated by the burst activity of the source during 1998.

A NEW PERSPECTIVE OF THE RADIO BRIGHT ZONE AT THE GALACTIC CENTER: FEEDBACK FROM NUCLEAR ACTIVITIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Jun-Hui; Morris, Mark R.; Goss, W. M., E-mail: jzhao@cfa.harvard.edu

2016-02-01

New observations of Sgr A have been carried out with the Jansky VLA in the B and C arrays using the broadband (2 GHz) continuum mode at 5.5 GHz. The field of view covers the central 13′ (30 pc) region of the radio-bright zone at the Galactic center. Using the multi-scale and multi-frequency-synthesis (MS-MFS) algorithms in CASA, we have imaged Sgr A with a resolution of 1″, achieving an rms noise of 8 μJy beam{sup −1}, and a dynamic range of 100,000:1. Both previously known and newly identified radio features in this region are revealed, including numerous filamentary sources. The radiomore » continuum image is compared with Chandra X-ray images, with a CN emission-line image obtained with the Submillimeter Array and with detailed Paschen-α images obtained with Hubble Space Telescope/NICMOS. We discuss several prominent features in the radio image. The “Sgr A west Wings” extend 2′ (5 pc) from the NW and SE tips of the Sgr A west H ii region (the “Mini-spiral”) to positions located 2.9 and 2.4 arcmin to the northwest and southeast of Sgr A*, respectively. The NW wing, along with several other prominent features, including the previously identified “NW Streamers,” form an elongated radio lobe (NW lobe), oriented nearly perpendicular to the Galactic plane. This radio lobe, with a size of 6.′3 × 3.′2 (14.4 pc × 7.3 pc), has a known X-ray counterpart. In the outer region of the NW lobe, a row of three thermally emitting rings is observed. A field containing numerous amorphous radio blobs extends for a distance of ∼2 arcmin beyond the tip of the SE wing; these newly recognized features coincide with the SE X-ray lobe. Most of the amorphous radio blobs in the NW and SE lobes have Paschen-α counterparts. We propose that they have been produced by shock interaction of ambient gas concentrations with a collimated nuclear wind or an outflow that originated from within the circumnuclear disk (CND). We also discuss the possibility that the ionized wind or outflow has been launched by radiation force produced by the central star cluster. Finally, we remark on the detailed structure of a prominent radio emission feature located within the shell of the Sgr A east supernova remnant. Because this feature—the “Sigma Front”—correlates well in shape and orientation with the nearby edge of the CND, we propose that it is a reflected shock wave resulting from the impact of the Sgr A east blast wave on the CND.« less

A New Perspective of the Radio Bright Zone at The Galactic Center: Feedback from Nuclear Activities

NASA Astrophysics Data System (ADS)

Zhao, Jun-Hui; Morris, Mark R.; Goss, W. M.

2016-02-01

New observations of Sgr A have been carried out with the Jansky VLA in the B and C arrays using the broadband (2 GHz) continuum mode at 5.5 GHz. The field of view covers the central 13‧ (30 pc) region of the radio-bright zone at the Galactic center. Using the multi-scale and multi-frequency-synthesis (MS-MFS) algorithms in CASA, we have imaged Sgr A with a resolution of 1″, achieving an rms noise of 8 μJy beam-1, and a dynamic range of 100,000:1. Both previously known and newly identified radio features in this region are revealed, including numerous filamentary sources. The radio continuum image is compared with Chandra X-ray images, with a CN emission-line image obtained with the Submillimeter Array and with detailed Paschen-α images obtained with Hubble Space Telescope/NICMOS. We discuss several prominent features in the radio image. The “Sgr A west Wings” extend 2‧ (5 pc) from the NW and SE tips of the Sgr A west H II region (the “Mini-spiral”) to positions located 2.9 and 2.4 arcmin to the northwest and southeast of Sgr A*, respectively. The NW wing, along with several other prominent features, including the previously identified “NW Streamers,” form an elongated radio lobe (NW lobe), oriented nearly perpendicular to the Galactic plane. This radio lobe, with a size of 6.‧3 × 3.‧2 (14.4 pc × 7.3 pc), has a known X-ray counterpart. In the outer region of the NW lobe, a row of three thermally emitting rings is observed. A field containing numerous amorphous radio blobs extends for a distance of ˜2 arcmin beyond the tip of the SE wing; these newly recognized features coincide with the SE X-ray lobe. Most of the amorphous radio blobs in the NW and SE lobes have Paschen-α counterparts. We propose that they have been produced by shock interaction of ambient gas concentrations with a collimated nuclear wind or an outflow that originated from within the circumnuclear disk (CND). We also discuss the possibility that the ionized wind or outflow has been launched by radiation force produced by the central star cluster. Finally, we remark on the detailed structure of a prominent radio emission feature located within the shell of the Sgr A east supernova remnant. Because this feature—the “Sigma Front”—correlates well in shape and orientation with the nearby edge of the CND, we propose that it is a reflected shock wave resulting from the impact of the Sgr A east blast wave on the CND.

High-frequency VLBI Imaging of Sgr A* and VX Sgr

NASA Astrophysics Data System (ADS)

Lu, R.-S.; Krichbaum, T. P.; Zensus, A. J.

VLBI observations at millimeter wavelengths provide unprecedented high angular resolution and allow to image regions, which are self-absorbed at longer wavelengths. Here we present new results from a multi-frequency VLBA monitoring of SgrA* at 22, 43, and 86 GHz performed on 10 consecutive days in May 2007. We discuss the source structure of Sgr A* through the analysis of the closure phase and closure amplitude, of which the latter improves the calibration accuracy and shows indications of a non-Gaussian brightness distribution at the highest frequency. We also present preliminary maps of the maser emission lines (v=1, J=1-0, and J=2-1) in the circumstellar SiO maser of VX Sgr. This will put new constraints on the kinematics and the pumping mechanisms of SiO masers.

Search for soft gamma repeaters in the SMM/HXRBS data

NASA Technical Reports Server (NTRS)

Kouveliotou, C.; Norris, J. P.; Wood, K. S.; Cline, T. L.; Dennis, B. R.; Desal, U. D.; Orwig, L. E.

1992-01-01

The triggered fast memory of the hard X-ray burst spectrometer (HXRBS) on board the SMM is used to describe the results of a search for short transients resembling soft gamma repeater (SGR) bursts. Memory data for a total of about 4000 burst triggers, out of which only a very few could be considered as valid SGR candidate events, are analyzed. The search methodology is outlined, the HXRBS exposure and sensitivity to SGR bursts are calculated, and the criteria which constrain the number of candidate events are described. An upper limit is given for the SGR source number density. This limit, combined with results from other relevant observations and the assumption of a neutron star origin, are applied to obtain a constraint on SGR-active lifetimes.

X-Ray Emitting Supermassive Nuclei of the Local Group

NASA Astrophysics Data System (ADS)

Melia, Fulvio; Liu, Siming

2001-09-01

In this talk, we will focus on a theoretical interpretation of what we have learned with recent Chandra observations of the supermassive black hole at the Galactic center (Sgr A*) and in the nucleus of M31 (M31*). The recent detection of Sgr A* in the X-ray band, together with the radio polarization measurements conducted over the past few years, offer the best constraints yet for understanding the nature of the emitting gas within several Schwarzschild radii (rS) of this object. It now appears that the sub-mm radiation from this source may be associated with thermal synchrotron emission from an inner Keplerian region within the circularization radius of the accreting plasma. In this talk, we discuss the implied high-energy emission of Sgr A* associated with the orbiting, hot, magnetized gas. For the accretion rate inferred from the fits to the sub-mm data, the dominant contribution to Sgr A*'s X-ray flux is due to self-Comptonization of the radio photons, rather than from bremsstrahlung. The latter is a two-body process, which would produce significant X-ray emission only at much higher accretion rates. This picture leads to the testable prediction that the physical conditions within the inner ~5rS are variable on a time scale of order a year. In particular, the accretion rate dot M appears to have changed by about 15% between the sub-mm measurements in 1996 and 1999. Given that the radio and self-Comptonized fluxes are strongly correlated, upcoming multi-wavelength observations of Sgr A* may provide the direct evidence required to test this picture. M31* has many features in common with Sgr A*, yet they differ in several significant and important ways. Though M31* is probably ten times heavier, its radio luminosity at 3.6 cm is only one third that of Sgr A*. At the same time, M31* is apparently thousands of times more luminous in X-rays than its Galactic Center counterpart. Thus, a comparative study of these objects can be valuable in helping us to understand the underlying physical basis for their activity. We will discuss how the accretion model developed for Sgr A* comprises two branches of solutions, distinguished by the relative importance of cooling compared to compressional heating at the radius RC where the ambient gas is captured by the black hole. For typical conditions in the ISM, the initial temperature (T[RC]~106-107 K) sits on the unstable branch of the cooling function. Depending on the actual value of T(RC) and the accretion rate, the plasma settles either onto a hot branch (attaining a temperature as high as 1010 K or so at small radii) or a cold branch, in which T drops to ~104 K. Sgr A* is presumably a `hot' black hole. We show here that the VLA, UV and Chandra observations of M31* reveal it to be a member of the `cold' black hole family. We discuss several predicted features in the spectrum of M31* that may be testable by future multi-wavelength observations, including the presence of a prominent UV spike (from hydrogen line emission) that would be absent on the hot branch.

Radio Observations of Sgr B2

NASA Astrophysics Data System (ADS)

Mao, Xin-Jie; Su, Jiang-Tao

2001-10-01

The 13CO (J=1-0) map of the molecular cloud Sgr B2 reveals that the mass center of the molecular cloud nucleus does not coincide with that of compact HII regions which are likely to be the outcome of a shock on the cloud. We find evidence of cloud contraction probably resulting from cloud-cloud collision at subsonic speed.

Massive Star Formation of the SGR a East H (sub II) Regions Near the Galactic Center

NASA Technical Reports Server (NTRS)

Yusef-Zadeh, F.; Lacy, J. H.; Wardle, M.; Whitney, B.; Bushouse, H.; Roberts, D. A.; Arendt, R. G.

2010-01-01

A group of four compact H II regions associated with the well-known 50 km/s molecular cloud is the closest site of on-going star formation to the dynamical center of the Galaxy, at a projected distance of approximately 6 pc. We present a study of ionized gas based on the [Ne II] (12.8 micron) line, as well as multi-frequency radio continuum, Hubble Space Telescope Pa alpha, and Spitzer Infrared Array Camera observations of the most compact member of the H II group, Sgr A East H II D. The radio continuum image at 6 cm shows that this source breaks up into two equally bright ionized features, D1 and D2. The spectral energy distribution of the D source is consistent with it being due to a 25 =/- 3 solar mass star with a luminosity of 8 +/- 3 x 10(exp 4) Solar luminosity . The inferred mass, effective temperature of the UV source, and the ionization rate are compatible with a young O9-B0 star. The ionized features D1 and D2 are considered to be ionized by UV radiation collimated by an accretion disk. We consider that the central massive star photoevaporates its circumstellar disk on a timescale of 3x (exp 4) years giving a mass flux approximately 3 x 10(exp -5) Solar Mass / year and producing the ionized material in D1 and D2 expanding in an inhomogeneous medium. The ionized gas kinematics, as traced by the [Ne II] emission, is difficult to interpret, but it could be explained by the interaction of a bipolar jet with surrounding gas along with what appears to be a conical wall of lower velocity gas. The other H II regions, Sgr A East A-C, have morphologies and kinematics that more closely resemble cometary flows seen in other compact H II regions, where gas moves along a paraboloidal surface formed by the interaction of a stellar wind with a molecular cloud.

Exploring the Minispiral at the Milky Way's Center

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-06-01

An image of the continuum emission from the galactic center minispiral, previously taken by ALMA at 100 GHz. This image labels the structures of the minispiral: a bar and multiple arcing arms, andthe black hole Sgr A* near the center. [Tsuboi et al. 2017]The region around Sgr A*, the 4-million-solar-mass black hole at the heart of our galaxy, is a complex and dynamic place. New Atacama Large Millimeter/submillimeter Array (ALMA) observations of the Milky Ways center now reveal more about this harsh, inhospitable environment.A New ViewOne of the prominent structures at the heart of the Milky Way is a bundle of ionized gas streams located surrounding Sgr A* within the close distance of 6.5 light-years. These streams take the form of a bar and a series of arms that make it look much like a tiny spiral galaxy earning it the name of the galactic center minispiral.Where did this gas come from? Whats happening to it now? And what can it tell us about the environment about Sgr A*? A team of scientists led by Masato Tsuboi (Japan Aerospace Exploration Agency) has now obtained new ALMA images of the minispiral that are helping us to answer these questions.Electron temperature in K (numbers in yellow) and density in cm-3 (numbers in red) from the new ALMA observations of the ionized gas streamers. [Tsuboi et al. 2017]Clues from GasTsuboi and collaborators imaged the gas within the galactic center minispiral and its surroundings as part of the first ALMA observation cycle. This powerful telescopes images allowed the team to observe the streamers of ionized gas within the arms of the minispiral and determine their velocities. The authors were then able to use these measurements to identify which gas components are related and the speeds and directions of motion for the different components.Besides tracking the dynamics of the ionized gas in the minispiral, the team also confirmed that the electron temperatures and densities in the streamers increase with proximity to Sgr A*. We would expect these increases to cause the arms to expand laterally closer to the black hole but thats not whats observed. Instead, the arms remain closely confined.This discrepancy tells us something about the environment around the minispiral: there must be surrounding, ambient ionized gas thats pushing on the streamers, providing the external pressure to keep them confined.An Explanation for ProplydsThe ALMA observations of ionized gas (top panel) line up nicely with the JVLA detections of candidate proplyds near Sgr A* (bottom panel, with the ionized gas emission from the top panel shown as contours). [Tsuboi et al. 2017]Lastly, Tsuboi and collaborators compare their ALMA observations of the ionized gas in the minispiral with previous observations of the galactic center made with the Jansky Very Large Array. The JVLA observations revealed the presence of compact half-shell-like structures that may be proplyds protostars being photoevaporated by the hot radiation coming from the central star cluster around Sgr A*.These candidate proplyds have posed an astronomical puzzle: between Sgr A*s strong tidal forces and the radiation being emitted from the central star cluster, conditions are extremely inhospitable to star formation. So how did these proplyds get there?Tsuboi and collaborators observations may shed some light on this. Lining up the new ALMA images with the old JVLA ones, its clear that the proplyds are all concentrated along the ionized gas streamer of the northeastern arm in the minispiral. This suggests that the protostars may have formed further away from Sgr A*, and they were brought to their present-day location as the streamer fell inwards toward the black hole.CitationMasato Tsuboi et al 2017 ApJ 842 94. doi:10.3847/1538-4357/aa74e3

Winds from the S-Star Cluster Reduce the Accretion Rate onto Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, Farhad; Wardle, M.; Roberts, D. A; Haggard, Daryl; Lacy, John H.; Royster, Marc; Cotton, William D.

2014-06-01

High-resolution radio continuum images of the region within a few arcseconds of Sgr A* at wavelengths of 7 and 12 mm show three new radio structures. One is a 2-3'' hollow teardrop-shaped structure centered on Sgr A*. Highly blue-shifted [NeII] and [FeIII] line emission is detected along the boundary of this teardrop-shaped bubble, ~2.2'' south of Sgr A*. The second structure is a faint, incomplete ring surrounding Sgr A* with typical surface brightness at 7 mm of ~0.1 mJy per ~0.04'' x 0.08'' beam. This partial ring coincides with the outer boundary of the S-star cluster which consists of ~30 B dwarfs orbiting within 1'' of Sgr A*. Lastly, on a scale of ~20'' to the N of Sgr A*, a balloon-shaped structure is detected.We interpret that the new morphological and kinematic structures result from the dynamical effects of a combined cluster wind. This wind is created at a rate ~3 x 10^{-5} solar mass per year by the merging of individual stellar winds from the B stars in the S-star cluster. What is significant about this interpretation is that the expanding wind excludes the shocked winds from O and WR stars in the central parsec of the Galaxy. Meanwhile Sgr A* accretes material from within the S cluster at a rate less than or equal 3 x 10^{-7} solar mass per year, thus explaining the low luminosity of Sgr A* without the ejection of a large fraction of the accreted material.

The Chandra Source Catalog 2.0: the Galactic center region

NASA Astrophysics Data System (ADS)

Civano, Francesca Maria; Allen, Christopher E.; Anderson, Craig S.; Budynkiewicz, Jamie A.; Burke, Douglas; Chen, Judy C.; D'Abrusco, Raffaele; Doe, Stephen M.; Evans, Ian N.; Evans, Janet D.; Fabbiano, Giuseppina; Gibbs, Danny G., II; Glotfelty, Kenny J.; Graessle, Dale E.; Grier, John D.; Hain, Roger; Hall, Diane M.; Harbo, Peter N.; Houck, John C.; Lauer, Jennifer L.; Laurino, Omar; Lee, Nicholas P.; Martínez-Galarza, Juan Rafael; McCollough, Michael L.; McDowell, Jonathan C.; Miller, Joseph; McLaughlin, Warren; Morgan, Douglas L.; Mossman, Amy E.; Nguyen, Dan T.; Nichols, Joy S.; Nowak, Michael A.; Paxson, Charles; Plummer, David A.; Primini, Francis Anthony; Rots, Arnold H.; Siemiginowska, Aneta; Sundheim, Beth A.; Tibbetts, Michael; Van Stone, David W.; Zografou, Panagoula

2018-01-01

The second release of the Chandra Source Catalog (CSC 2.0) comprises all the 10,382 ACIS and HRC-I imaging observations taken by Chandra and released publicly through the end of 2014. Among these, 534 single observations surrounding the Galactic center are included, covering a total area of ~19deg2 and a total exposure time of ~9 Ms.The single 534 observations were merged into 379 stacks (overlapping observations with aim-points within 60") to increase the flux limit for source detection purposes.Thanks to the combination of the point source detection algorithm with the maximum likelihood technique used to asses the source significance, ~21,000 detections are listed in the CSC 2.0 for this field only, 80% of which are unique sources. The central region of this field around the SgrA* location has the deepest exposure of 2.2 Ms and the highest source density with ~5000 sources. In this poster, we present details about this region including source distribution and density, coverage, exposure.This work has been supported by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the ChandraX-ray Center.

Interstellar Scattering Towards the Galactic Center as Probed by OH/IR Stars

NASA Technical Reports Server (NTRS)

Vanlangevelde, Huib Jan; Frail, Dale A.; Cordes, James M.; Diamond, Philip J.

1992-01-01

Angular broadening measurements are reported of 20 OH/IR stars near the galactic center. This class of sources is known to have bright, intrinsically compact (less than or equal to 20 mas) maser components within their circumstellar shells. VLBA antennas and the VLA were used to perform a MKII spectral line VLBI experiment. The rapid drop in correlated flux with increasing baseline, especially for sources closest to the galactic center, is attributed to interstellar scattering. Angular diameters were measured for 13 of our sources. Lower limits were obtained for the remaining seven. With the data, together with additional data taken from the literature, the distribution was determined of interstellar scattering toward the galactic center. A region was found of pronounced scattering nearly centered on SgrA*. Two interpretations are considered for the enhanced scattering. One hypothesis is that the scattering is due to a clump of enhanced turbulence, such as those that lie along lines of sight to other known objects, that has no physical relationship to the galactic center. The other model considers the location of the enhanced scattering to arise in the galactic center itself. The physical implications of the models yield information on the nature of interstellar scattering.

RADIO SYNCHROTRON EMISSION FROM A BOW SHOCK AROUND THE GAS CLOUD G2 HEADING TOWARD THE GALACTIC CENTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narayan, Ramesh; Sironi, Lorenzo; Oezel, Feryal

2012-10-01

A dense ionized cloud of gas has been recently discovered to be moving directly toward the supermassive black hole, Sgr A*, at the Galactic center. In 2013 June, at the pericenter of its highly eccentric orbit, the cloud will be approximately 3100 Schwarzschild radii from the black hole and will move supersonically through the ambient hot gas with a velocity of v{sub p} Almost-Equal-To 5400 km s{sup -1}. A bow shock is likely to form in front of the cloud and could accelerate electrons to relativistic energies. We estimate via particle-in-cell simulations the energy distribution of the accelerated electrons andmore » show that the non-thermal synchrotron emission from these electrons might exceed the quiescent radio emission from Sgr A* by a factor of several. The enhanced radio emission should be detectable at GHz and higher frequencies around the time of pericentric passage and in the following months. The bow shock emission is expected to be displaced from the quiescent radio emission of Sgr A* by {approx}33 mas. Interferometric observations could resolve potential changes in the radio image of Sgr A* at wavelengths {approx}< 6 cm.« less

Kinematics of the SgrB2(N-LMH) Molecular Core

NASA Technical Reports Server (NTRS)

Hollis, J. M.; Pedelty, J. A.; Boboltz, D. A.; Liu, S.-Y.; Snyder, L. E.; Palmer, Patrick; Lovas, F. J.; Jewell, P. R.

2003-01-01

Ethyl cyanide (CH3CH2CN) emission and absorption have been imaged with the Very Large Array (VLA) toward SgrB2(N-LMH) by means of the 5(sub 15)-4(sub 14) rotational transition at 43.5 GHz (lambda approx. 7 mm). The 1.5" x 1.4" VLA beam shows two principal sources of ethyl cyanide emission: an unresolved source approx. 5" north of the LMH that is kinematically consistent with simple expansion, contraction, or small-scale turbulence, and the resolved LMH core source itself that shows kinematics indicating an edge-on rotating disk that extends 23" (approx. 0.1 pc) in the approximate east-west direction. A search for the 7(sub 07)-6(sub 06) rotational transition of the amino acid glycine (NH2CH2COOH) at 43.7 GHz toward SgrB2(N-LMH) gave negative results.

The Role of Magnetic Field Dissipation in the Black Hole Candidate Sagittarius A*

NASA Astrophysics Data System (ADS)

Coker, Robert F.; Melia, Fulvio

2000-05-01

The compact, nonthermal radio source Sgr A* at the Galactic center appears to be coincident with a ~2.6×106 Msolar pointlike object. Its energy source may be the release of gravitational energy as gas from the interstellar medium descends into its deep potential well. However, simple attempts at calculating the radiative spectrum and flux based on this picture have come tantalizingly close to the observations, yet have had difficulty in accounting for the unusually low efficiency in this source. Regardless of whether the radiating particles in the accretion flow are thermal or nonthermal, there now appear to be two principal reasons for this low conversion rate of dissipated energy into radiation: (1) the plasma separates into two temperatures, with the protons attaining a significantly higher temperature than that of the radiating electrons; and (2) the magnetic field B is subequipartition, which reduces the magnetic bremsstrahlung emissivity, and therefore the overall power of Sgr A*. In this paper, we investigate the latter with a considerable improvement over what has been attempted before. In particular, rather than calculating B based on some presumed model (e.g., equipartition with the thermal energy of the gas), we instead infer its distribution with radius empirically with the requirement that the resulting spectrum matches the observations. Our assumed Ansatz for B(r) is motivated in part by earlier calculations of the expected magnetic dissipation rate due to reconnection in a compressed flow. We find reasonable agreement with the observed spectrum of Sgr A* as long as its distribution consists of three primary components: an outer equipartition field, a roughly constant field at intermediate radii (~103 Schwarzschild radii), and an inner dynamo (more or less within the last stable orbit for a nonrotating black hole), which increases B to about 100 G. The latter component accounts very well for the observed submillimiter hump in this source.

Infrared imaging spectroscopy of the Galactic center - Distribution and motions of the ionized gas

NASA Technical Reports Server (NTRS)

Herbst, T. M.; Beckwith, S. V. W.; Forrest, W. J.; Pipher, J. L.

1993-01-01

High spatial spectral resolution IR images of the Galactic center in the Br-gamma recombination line of hydrogen were taken. A coherent filament of gas extending from north of IRS 1, curving around IRS 16/Sgr A complex, and continuing to the southwest, is seen. Nine stellar sources have associated Br-gamma emission. The total Br-gamma line flux in the filament is approximately 3 x 10 exp -15 W/sq m. The distribution and kinematics of the northern arm suggest orbital motion; the observations are accordingly fit with elliptical orbits in the field of a central point of mass.

The Impact of a New Speckle Holography Analysis on the Galactic Center Orbits Initiative

NASA Astrophysics Data System (ADS)

Mangian, John; Ghez, Andrea; Gautam, Abhimat; Gallego, Laly; Schödel, Rainer; Lu, Jessica; Chen, Zhuo; UCLA Galactic Center Group; W.M. Keck Observatory Staff

2018-01-01

The Galactic Center Orbit Initiative has used two decades of high angular resolution imaging data from the W. M. Keck Observatory to make astrometric measurements of stellar motion around our Galaxy's central supermassive black hole. We present an analysis of a new approach to ten years of speckle imaging data (1995 - 2005) that has been processed with a new holography analysis. This analysis has (1) improved the image quality near the edge of the combined speckle frame and (2) increased the depth of the images and therefore increased the number of sources detected throughout the entire image. By directly comparing each holography analysis, we find a 41% increase in total detected sources and a 81% increase in sources further than 3" from the central black hole (SgrA*). Further, we find a 49% increase in sources of K-band magnitude greater than the old holography limiting magnitude due to the reduction of light halos surrounding bright sources.

Novae as a Class of Transient X-ray Sources

NASA Technical Reports Server (NTRS)

Mukai, K.; Orio, M.; Valle, M. Della

2007-01-01

Motivated by the recently discovered class of faint (10(exp 34)-10(exp 35) ergs/s) X-ray transients in the Galactic Center region, we investigate the 2-10 keV properties of classical and recurrent novae. Existing data are consistent with the idea that all classical novae are transient X-ray sources with durations of months to years and peak luminosities in the 10(exp 34)-10(exp 35)ergs/s range. This makes classical novae a viable candidate class for the faint Galactic Center transients. We estimate the rate of classical novae within a 15 arcmin radius region centered on the Galactic Center (roughly the field of view of XMM-Newton observations centered on Sgr A*) to be approx.0.1 per year. Therefore, it is plausible that some of the Galactic Center transients that have been announced to date are unrecognized classical novae. The continuing monitoring of the Galactic Center region carried out by Chandra and XMM-Newton may therefore provide a new method to detect classical novae in this crowded and obscured region, an

Probing the Extreme Environment of the Galactic Center with Observations from SOFIA/FORCAST

NASA Astrophysics Data System (ADS)

Lau, Ryan M.; Herter, Terry L.; Morris, Mark; Adams, Joseph D; Becklin, Eric E.

2014-06-01

In this thesis we present a study of the inner 40 pc of the Galactic center addressing the dense, dusty torus around Sgr A*, dust production around massive stars, and massive star formation. Observations of warm dust emission from the Galactic center were performed using the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). A dense, molecular torus referred to as the Circumnuclear Disk (CND) orbits Sgr A* with an inner radius of ~1.4 pc and extending to ~7 pc. The inner edge of the CND, which we refer to as the Circumnuclear Ring (CNR), exhibits features of a classic HII region and appears consistent with the prevailing paradigm in which the dust is heated by the Central cluster of hot, young stars. We do not detect any star formation occurring in the CNR; however, we reveal the presence of density “clumps” along the inner edge of the CNR. These clumps are not dense enough to be stable against tidal shear from Sgr A* and will be sheared out before completing a full orbit 10^5 yrs). Three Luminous Blue Variables (LBVs) are located in and near the Quintuplet Cluster 40 pc in projection from Sgr A*: qF362, the Pistol star, G0.120-0.048 (LBV3). FORCAST observation reveal the asymmetric, compressed shell of hot dust surrounding the Pistol Star and provide the first detection of the thermal emission from the symmetric, hot dust envelope surrounding LBV3. However, no detection of hot dust associated with qF362 is made. We argue that the Pistol star and LBV3 are identical “twins” that exhibit contrasting nebulae due to the external influence of their different environments. G-0.02-0.07, a complex consisting of three compact HII regions and one ultracompact HII region, is located at the edge of a molecular cloud 6 pc in projection to the east of Sgr A* and contains the most recent episode of star formation in the Galactic center. We probe the dust morphology, energetics, and composition of the regions to study the star forming conditions of a molecular cloud in the strong gravitational potential of Sgr A*.

Three millimeter molecular line observations in Sagittarius B2. 1: Full synthesis mapping study of HNO, CCS, and HC(13)CCN

NASA Technical Reports Server (NTRS)

Kuan, Yi-Jehng; Snyder, Lewis E.

1994-01-01

We present the first full synthesis maps of the small molecules HNO, CCS, and HC(13)CCN in Sgr B2. We have observed the 3.8 mm continuum, the HNO J(sub K(sub -1)K(sub 1)) = 1(sub O1)-0(sub OO), the CCS J(sub N) = 7(sub 6)-6(sub 5), and the HC(13)CCN J = 9-8 transitions in the core of the Sgr B2 molecular cloud, using the Berkeley Illinois Maryland Association (BIMA) millimeter array and the NRAO 12 m telescope. We have found that HNO exists in five major gas clumps in the Sgr B2 region, which we have labeled HNO(N), HNO(NW), HNO(E), HNO(M), and HNO(S). Of particular interest is HNO(M), a major molecular gas concentration approximately 15 sec west of Sgr B2(M) in a region of young star formation. HNO is found to be closely associated with the ionized gas and might be depleted around bright H II complexes. In general, the peak intensity of the HNO emission is found to be offset from the peak of the continuum emission. We found evidence for some chemical differentiation among the three species, HNO, CCS, and HC(13)CCN, but the abundance ratios are in fair agreement with theoretical models. Two unidentified lines, U81420 and U81518, were observed, and a previously unknown compact dust source was detected. Our HNO data indicate the presence of a rotating approximately (2.2-4.4) x 10(exp 3)solar mass gas envelope surrounding Sgr B2(N), a possible bipolar gas outflow in HNO(M), and possibly a large (approximately 4.2 x 10(exp 4)solar mass) extended rotating disk associated with HNO(S). In addition, the CCS and HC(13)CCN data approximately outline the extended component of Sgr B2 and clearly show that the southern continuum source Sgr B2(S) is actually a major molecular source as well. Consequently, the kinematics of the Sgr B2 molecular cloud is quite complex, but in moving from the northwest to south, the LSR velocity generally changes from 79 to 46 km/s.

Observing the Super-Massive Black Hole of the Galactic center with Simbol-X .

NASA Astrophysics Data System (ADS)

Goldwurm, A.

The Center of our Galaxy is one of the prime objective of the Simbol-X mission. This region of several square degrees around the dynamical center of the galaxy hosts a large variety of high energy sources and violent phenomena that involve different non-thermal processes contributing to the hard X-ray emission from the region. Here we present in detail the case for the observation of Sgr A*, the super-massive black hole of the galactic nucleus, with Simbol-X, stressing on the presently open questions and on the crucial measurements that will be performed in the hard X-ray domain with this formation-flying hard X-ray focussing telescope expected to flight in the next decade.

Viewing the Shadow of the Black Hole at the Galactic Center

NASA Astrophysics Data System (ADS)

Falcke, Heino; Melia, Fulvio; Agol, Eric

2000-01-01

In recent years, evidence for the existence of an ultracompact concentration of dark mass associated with the radio source Sagittarius A* in the Galactic center has become very strong. However, unambiguous proof that this object is indeed a black hole is still lacking. A defining characteristic of a black hole is the event horizon. To a distant observer, the event horizon casts a relatively large ``shadow'' with an apparent diameter of ~10 gravitational radii that is due to the bending of light by the black hole, and this shadow is nearly independent of the black hole spin or orientation. The predicted size (~30 μas) of this shadow for Sgr A* approaches the resolution of current radio interferometers. If the black hole is maximally spinning and viewed edge-on, then the shadow will be offset by ~8 μas from the center of mass and will be slightly flattened on one side. Taking into account the scatter broadening of the image in the interstellar medium and the finite achievable telescope resolution, we show that the shadow of Sgr A* may be observable with very long baseline interferometry at submillimeter wavelengths, assuming that the accretion flow is optically thin in this region of the spectrum. Hence, there exists a realistic expectation of imaging the event horizon of a black hole within the next few years.

The Short Bursts in SGR 1806-20, 1E 1048-5937, and SGR 0501+4516

NASA Astrophysics Data System (ADS)

Qu, Zhijie; Li, Zhaosheng; Chen, Yupeng; Dai, Shi; Ji, Long; Xu, Renxin; Zhang, Shu

2015-03-01

We analyzed temporal and spectral properties, focusing on the short bursts, for three anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs), including SGR 1806-20, 1E 1048-5937 and SGR 0501+4516. Using the data from XMM-Newton, we located the short bursts by Bayesian blocks algorithm. The short bursts' duration distributions for three sources were fitted by two lognormal functions. The spectra of shorter bursts ($< 0.2~\\rm s$) and longer bursts ($\\geq 0.2~\\rm s$) can be well fitted in two blackbody components model or optically thin thermal bremsstrahlung model for SGR 0501+4516. We also found that there is a positive correlation between the burst luminosity and the persistent luminosity with a power law index $\\gamma = 1.23 \\pm 0.18 $. The energy ratio of this persistent emission to the time averaged short bursts is in the range of $10 - 10^3$, being comparable to the case in Type I X-ray burst.

High-Energy Radiation from a Model of Quasars, Active Galactic Nuclei, and the Galactic Center with Magnetic Monopoles

NASA Astrophysics Data System (ADS)

Peng, Qiu-he; Chou, Chih-kang

2001-04-01

The fact that magnetic monopoles may catalyze nucleon decay (the Rubakov-Callan [RC] effect) as predicated by the grand unified theory of particle physics is invoked as the energy source of quasars and active galactic nuclei. Recent study of this model revealed that the radius of the supermassive object (SMO) located at the Galactic center is much larger than its Schwarzschild radius. We propose that this SMOs could be the source of high-energy gamma-ray radiation, although the emitted radiation may be mainly concentrated in the infrared. The surface temperature of the SMO at the Galactic center is taken as 121 K, inferred from the observed maximum of the flux spectrum of Sgr A* at the near infrared (1×1013 Hz); the radius of the SMO is about 8.1×1015 cm or 1.1×104RS (RS is the Schwarzschild radius). The mass of the SMO is derived from the observed total luminosity of Sgr A* (1×1037 ergs s-1) as 2.5×106 Msolar. Strong gamma-ray radiation with energy higher than 0.5 MeV may be emitted from the SMO. The flux of positrons emitted from the SMO is estimated to be 6.5×1042e+ s-1. The content parameter of magnetic monopoles ξ≡[(Nm/NB)/1.9×10- 25](<σβ>/10-27) also may be deduced from observations to be 230. Taking the cross section of the RC effect as 1×10-27 cm2, the strength of the radial magnetic field at the surface of the SMO is estimated to be 20-100 G. Our model also can predict the production of extreme ultra-high-energy cosmic rays.

Probing the Magnetic Field Structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

NASA Astrophysics Data System (ADS)

Gold, Roman; McKinney, Jonathan C.; Johnson, Michael D.; Doeleman, Sheperd S.

2017-03-01

Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source Sagittarius A* (Sgr A*). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotational instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford-Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in Sgr A*, though both disk- and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.

Radio and Millimeter Monitoring of Sgr A*: Spectrum, Variability, and Constraints on the G2 Encounter

NASA Astrophysics Data System (ADS)

Bower, Geoffrey C.; Markoff, Sera; Dexter, Jason; Gurwell, Mark A.; Moran, James M.; Brunthaler, Andreas; Falcke, Heino; Fragile, P. Chris; Maitra, Dipankar; Marrone, Dan; Peck, Alison; Rushton, Anthony; Wright, Melvyn C. H.

2015-03-01

We report new observations with the Very Large Array, Atacama Large Millimeter Array, and Submillimeter Array at frequencies from 1.0 to 355 GHz of the Galactic Center black hole, Sagittarius A*. These observations were conducted between 2012 October and 2014 November. While we see variability over the whole spectrum with an amplitude as large as a factor of 2 at millimeter wavelengths, we find no evidence for a change in the mean flux density or spectrum of Sgr A* that can be attributed to interaction with the G2 source. The absence of a bow shock at low frequencies is consistent with a cross-sectional area for G2 that is less than 2× {10}29 cm2. This result fits with several model predictions including a magnetically arrested cloud, a pressure-confined stellar wind, and a stellar photosphere of a binary merger. There is no evidence for enhanced accretion onto the black hole driving greater jet and/or accretion flow emission. Finally, we measure the millimeter wavelength spectral index of Sgr A* to be flat; combined with previous measurements, this suggests that there is no spectral break between 230 and 690 GHz. The emission region is thus likely in a transition between optically thick and thin at these frequencies and requires a mix of lepton distributions with varying temperatures consistent with stratification.

Status of GRMHD simulations and radiative models of Sgr A*

NASA Astrophysics Data System (ADS)

Mościbrodzka, Monika

2017-01-01

The Galactic center is a perfect laboratory for testing various theoretical models of accretion flows onto a supermassive black hole. Here, I review general relativistic magnetohydrodynamic simulations that were used to model emission from the central object - Sgr A*. These models predict dynamical and radiative properties of hot, magnetized, thick accretion disks with jets around a Kerr black hole. Models are compared to radio-VLBI, mm-VLBI, NIR, and X-ray observations of Sgr A*. I present the recent constrains on the free parameters of the model such as accretion rate onto the black hole, the black hole angular momentum, and orientation of the system with respect to our line of sight.

The X-Ray Variability of Sagittarius A*

NASA Astrophysics Data System (ADS)

Neilsen, Joseph; Nowak, Michael; Gammie, Charles F.; Dexter, Jason; Markoff, Sera; Haggard, Daryl; Nayakshin, Sergei; Wang, Q. Daniel; Grosso, Nicolas; Porquet, Delphine; Tomsick, John; Degenaar, Nathalie; Fragile, P. Christopher; Wijnands, Rudy; Miller, Jon M.; Baganoff, Frederick K.

2015-01-01

Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief ares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole accretion. To study the accretion processes in the Galactic Center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of our closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including one of the brightest flares ever seen from Sgr A*. Focusing on the statistics of the flares, the quiescent emission, and the relationship between the X-ray and the infrared, we discuss the physical implications of X-ray variability in the Galactic Center.

The Event Horizon Telescope: Future Polarimetric Capabilities

NASA Astrophysics Data System (ADS)

Fish, Vincent L.; Doeleman, S. S.; EHT Collaboration

2010-01-01

The Event Horizon Telescope (EHT) is a (sub)mm wavelength VLBI network that will achieve angular resolutions sufficient to resolve and image the Event Horizons of the nearest supermassive black holes. Recent millimeter observations with the initial three stations of the EHT (located in Hawaii, Arizona, and California) have constrained the size of the emitting region of Sgr A*, the Galactic Center radio/infrared/X-ray source associated with a supermassive black hole, to be no more than a few Schwarzschild radii. While EHT observations have heretofore focused on detecting Sgr A* in total intensity, theoretical models predict large polarization signatures well in excess of the few percent linear polarization detected by low resolution arrays (e.g., SMA). Here, we generalize our previous total intensity simulations of future EHT observations to include full polarimetric quantities. Ratios of polarimetric visibilities provide baseline-based observables that are robust against most calibration errors. We find that the shortest VLBI baselines track the integrated polarization fraction and position angle, as presently observed by connected-element arrays, while longer VLBI baselines are sensitive to highly-polarized substructures that are beam-diluted at lower angular resolution. Ratios of polarized visibilities may be even more sensitive to detecting periodic structural changes, as might be expected from a hot spot near the innermost stable circular orbit of the black hole, than closure quantities obtained from total intensity quantities. These results suggest that high priority should be given to upgrading telescopes in the EHT collaboration in order to allow full polarimetric observations of Sgr A* and other supermassive black hole sources. This research is made possible thanks to funding provided by the National Science Foundation.

BlackHoleCam: Fundamental physics of the galactic center

NASA Astrophysics Data System (ADS)

Goddi, C.; Falcke, H.; Kramer, M.; Rezzolla, L.; Brinkerink, C.; Bronzwaer, T.; Davelaar, J. R. J.; Deane, R.; de Laurentis, M.; Desvignes, G.; Eatough, R. P.; Eisenhauer, F.; Fraga-Encinas, R.; Fromm, C. M.; Gillessen, S.; Grenzebach, A.; Issaoun, S.; Janßen, M.; Konoplya, R.; Krichbaum, T. P.; Laing, R.; Liu, K.; Lu, R.-S.; Mizuno, Y.; Moscibrodzka, M.; Müller, C.; Olivares, H.; Pfuhl, O.; Porth, O.; Roelofs, F.; Ros, E.; Schuster, K.; Tilanus, R.; Torne, P.; van Bemmel, I.; van Langevelde, H. J.; Wex, N.; Younsi, Z.; Zhidenko, A.

Einstein’s General theory of relativity (GR) successfully describes gravity. Although GR has been accurately tested in weak gravitational fields, it remains largely untested in the general strong field cases. One of the most fundamental predictions of GR is the existence of black holes (BHs). After the recent direct detection of gravitational waves by LIGO, there is now near conclusive evidence for the existence of stellar-mass BHs. In spite of this exciting discovery, there is not yet direct evidence of the existence of BHs using astronomical observations in the electromagnetic spectrum. Are BHs observable astrophysical objects? Does GR hold in its most extreme limit or are alternatives needed? The prime target to address these fundamental questions is in the center of our own Milky Way, which hosts the closest and best-constrained supermassive BH candidate in the universe, Sagittarius A* (Sgr A*). Three different types of experiments hold the promise to test GR in a strong-field regime using observations of Sgr A* with new-generation instruments. The first experiment consists of making a standard astronomical image of the synchrotron emission from the relativistic plasma accreting onto Sgr A*. This emission forms a “shadow” around the event horizon cast against the background, whose predicted size (˜50μas) can now be resolved by upcoming very long baseline radio interferometry experiments at mm-waves such as the event horizon telescope (EHT). The second experiment aims to monitor stars orbiting Sgr A* with the next-generation near-infrared (NIR) interferometer GRAVITY at the very large telescope (VLT). The third experiment aims to detect and study a radio pulsar in tight orbit about Sgr A* using radio telescopes (including the Atacama large millimeter array or ALMA). The BlackHoleCam project exploits the synergy between these three different techniques and contributes directly to them at different levels. These efforts will eventually enable us to measure fundamental BH parameters (mass, spin, and quadrupole moment) with sufficiently high precision to provide fundamental tests of GR (e.g. testing the no-hair theorem) and probe the spacetime around a BH in any metric theory of gravity. Here, we review our current knowledge of the physical properties of Sgr A* as well as the current status of such experimental efforts towards imaging the event horizon, measuring stellar orbits, and timing pulsars around Sgr A*. We conclude that the Galactic center provides a unique fundamental-physics laboratory for experimental tests of BH accretion and theories of gravity in their most extreme limits.

ALMA and VLA observations of emission from the environment of Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, F.; Schödel, R.; Wardle, M.; Bushouse, H.; Cotton, W.; Royster, M. J.; Kunneriath, D.; Roberts, D. A.; Gallego-Cano, E.

2017-10-01

We present 44 and 226 GHz observations of the Galactic Centre within 20 arcsec of Sgr A*. Millimetre continuum emission at 226 GHz is detected from eight stars that have previously been identified at near-IR and radio wavelengths. We also detect a 5.8 mJy source at 226 GHz coincident with the magnetar SGR J1745-29 located 2.39 arcsec SE of Sgr A* and identify a new 2.5 arcsec × 1.5 arcsec halo of mm emission centred on Sgr A*. The X-ray emission from this halo has been detected previously and is interpreted in terms of a radiatively inefficient accretion flow. The mm halo surrounds an EW linear feature that appears to arise from Sgr A* and coincides with the diffuse X-ray emission and a minimum in the near-IR extinction. We argue that the millimetre emission is produced by synchrotron emission from relativistic electrons in equipartition with an ˜1.5 mG magnetic field. The origin of this is unclear but its coexistence with hot gas supports scenarios in which the gas is produced by the interaction of winds either from the fast moving S-stars, the photoevaporation of low-mass YSO discs or by a jet-driven outflow from Sgr A*. The spatial anti-correlation of the X-ray, radio and mm emission from the halo and the low near-IR extinction provides a compelling evidence of an outflow sweeping up the interstellar material, creating a dust cavity within 2 arcsec of Sgr A*. Finally, the radio and mm counterparts to eight near-IR identified stars within ˜10 arcsec of Sgr A* provide accurate astrometry to determine the positional shift between the peak emission at 44 and 226 GHz.

Reflection features in the Galactic Center and past activity of Sagittarius A*

NASA Astrophysics Data System (ADS)

Clavel, Maïca; Terrier, Regis; Goldwurm, Andrea; Morris, Mark; Jin, Chichuan; Ponti, Gabriele; Chuard, Dimitri

2016-07-01

X-ray observations carried out over the past two decades have captured an increasing number of reflection features within the molecular clouds located in the inner regions of our Galaxy. The intensity of these structures along with the correlated variations which are detected over the entire central molecular zone are strong evidence that this diffuse emission is created by the past activity of the supermassive black hole at the Galactic center, Sagittarius A*. In particular, within the last centuries, Sgr A* is likely to have experienced several short outbursts during which the black hole was at least a million times brighter than today. However, the precise description of the corresponding past catastrophic events is difficult to assess, mainly because the properties of the reflection features that they create while propagating away from Sgr A* depend on the line-of-sight distance, the geometry, and the size of the reflecting clouds, all of which are poorly known. I will review the different attempts to reconstruct Sgr A*'s past activity from the constraints obtained through the observation of the reflection features in the Galactic center, including the current Chandra monitoring.

The habitability of the Milky Way during the active phase of its central supermassive black hole.

PubMed

Balbi, Amedeo; Tombesi, Francesco

2017-11-30

During the peak of their accretion phase, supermassive black holes in galactic cores are known to emit very high levels of ionizing radiation, becoming visible over intergalactic distances as quasars or active galactic nuclei (AGN). Here, we quantify the extent to which the activity of the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*), may have affected the habitability of Earth-like planets in our Galaxy. We focus on the amount of atmospheric loss and on the possible biological damage suffered by planets exposed to X-ray and extreme ultraviolet (XUV) radiation produced during the peak of the active phase of Sgr A*. We find that terrestrial planets could lose a total atmospheric mass comparable to that of present day Earth even at large distances (~1 kiloparsec) from the galactic center. Furthermore, we find that the direct biological damage caused by Sgr A* to surface life on planets not properly screened by an atmosphere was probably significant during the AGN phase, possibly hindering the development of complex life within a few kiloparsecs from the galactic center.

Periastron shifts of stellar orbits near the Galactic Center

NASA Astrophysics Data System (ADS)

Rubilar, G. F.; Eckart, A.

2001-07-01

The presence of a 2.9+/-0.4 million solar mass object in the central stellar cluster of the Milky Way has recently been demonstrated via measurements of the stellar proper motions and radial velocities. This mass is located at the position of the compact radio source Sagittarius A* (Sgr A*) at a distance of Ro=8.0 kpc and is most likely present in the form of a massive black hole (BH). Some of the stars have a projected distance to Sgr A* of <=0.005 pc and have proper motion velocities of up to 1400 km s-1. Recent measurements indicate that their orbits show significant curvatures indicating that the stars indeed orbit the central compact object. Detailed measurements of the stellar orbits close to Sgr A* will allow us to precisely determine the distribution of this mass. With an increased point source sensitivity due to the combination of large telescope apertures, adaptive optics, and - in the very near future - NIR interferometry it is likely that stars with orbital time scales of the order of one year will be detected. Theses sources, however, will most likely not be on simple Keplerian orbits. The effects of measurable prograde relativistic and retrograde Newtonian periastron shifts will result in rosetta shaped orbits. A substantial Newtonian periastron rotation can already be expected if only a few percent of the central mass are extended. We discuss the conditions under which an extended mass can (over-) compensate the relativistic periastron shift. We also demonstrate that measuring a single periastron shift is not sufficient to determine the distribution of an extended mass component. A periastron shift will allow us to determine the inclination of the stellar orbits and to derive inclination corrected shift values. These have to be acquired for three stars on orbits with different energy or angular momentum in order to unambiguously solve for the compactness, extent and shape of any extended mass contribution.

GREEN BANK TELESCOPE OBSERVATIONS OF THE NH{sub 3} (3, 3) AND (6, 6) TRANSITIONS TOWARD SAGITTARIUS A MOLECULAR CLOUDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minh, Young Chol; Liu, Hauyu Baobab; Ho, Paul T. P.

2013-08-10

Ammonia (3, 3) and (6, 6) transitions have been observed using the Green Bank Telescope toward the Sgr A region. The gas is mainly concentrated in 50 km s{sup -1} and 20 km s{sup -1} clouds located in a plane inclined to the galactic plane. These 'main' clouds appear to be virialized and influenced by the expansion of the supernova remnant Sgr A East. The observed emission shows very complicated features in the morphology and velocity structure. Gaussian multi-component fittings of the observed spectra revealed that various 'streaming' gas components exist all over the observed region. These components include thosemore » previously known as 'streamers' and 'ridges', but most of these components appear not to be directly connected to the major gas condensations (the 50 km s{sup -1} and 20 km s{sup -1} clouds). They are apparently located out of the galactic plane, and they may have a different origin than the major gas condensations. Some of the streaming components are expected to be sources that feed the circumnuclear disk of our Galactic center directly and episodically. They may also evolve differently than major gas condensations under the influence of the activities of the Galactic center.« less

Single Pulse Searches for Pulsars in the Galactic Center

NASA Astrophysics Data System (ADS)

Cushey, Daniel Joseph; Majid, Walid A.; Prince, Thomas Allen

2017-01-01

The discovery of the magnetar J1745-2900 within 3'' of Sgr A* by Mori et al. (2013) has renewed strong interest in Galactic Center (GC) pulsars and motivated expanded searches for their pulses due to their extensive applications to gravitational and plasma physics. There are currently 5 known pulsars within 15' of the Sgr A*; however, gamma ray excesses from the GC suggest a source population of 102-103 millisecond pulsars within the same region. Although this discrepancy is readily explained by the hyper-strong scattering environment of the GC which obscures pulses, the discovery of J1745-2900 challenges this attribution and further observations and analysis are needed to reconcile the observed GC pulsar population with theory. We present a pipeline developed to search for these "missing" GC pulsars using a single pulse search algorithm. Observations of the GC using the Deep Space Network 70m antenna were taken in the high frequency regime in order to minimize scattering, and search parameters were calibrated using pulses from RRAT J1819-1458. Any detected pulses that are distinct from those of J1745-2900 warrant extensive follow-up observations and analysis, and confirmed new members of the elusive GC pulsar population would be incredibly valuable as probes of the GC's magnetic and potential fields.

Action at the Horizon: Chandra/EHT Observations of Sgr A*

NASA Astrophysics Data System (ADS)

Neilsen, Joseph

2017-09-01

In April 2017, the Event Horizon Telescope will observe Sgr A* with imaging quality sufficient to resolve the shadow of the black hole, while providing a close-up view of accretion at the horizon. As Sgr A* is a well-known source of X-ray flares, coordinated Chandra/EHT observations offer an incredible opportunity: a chance to observe structures (e.g., hotspots) near the event horizon while tracking their high-energy variability. In anticipation of a follow-up campaign in 2018, we are requesting 4x33 ks Chandra observations of Sgr A* to be coordinated with EHT. This campaign will double our chances of simultaneous flares. We will search for flares and hotspots, provide priors for EHT image reconstruction, and track any activity associated with the closest approach of the massive star S0-2.

SGR J1550-5418 Bursts Detected with the Fermi Gamma-Ray Burst Monitor during Its Most Prolific Activity

NASA Technical Reports Server (NTRS)

vanderHorst, A. J.; Kouveliotou, C.; Gorgone, N. M.; Kaneko, Y.; Baring, M. G.; Guiriec, S.; Gogus, E,; Granot, J.; Watts, A. L.; Lin, L.;

Discovery of Fast X-ray Oscillations During the 1998 Giant Flare from SGR 1900+14

NASA Technical Reports Server (NTRS)

Strohmayer, T.; Watts, A.

2005-01-01

We report the discovery of complex high frequency variability during the August 27, 1998 giant flare from SGR 1900+14 using the Rossi X-ray Timing Explorer (RXTE). We detect an approx. equals 84 Hz oscillation (QPO) during a 1 s interval beginning approximately 1 min after the initial hard spike. The amplitude is energy dependent, reaching a maximum of 26% (rms) for photons above 30 keV, and is not detected below 11 keV, with a 90% confidence upper limit of 14% (rms). Remarkably, additional QPOs are detected in the average power spectrum of data segments centered on the rotational phase at which the 84 Hz signal was detected. Two signals, at 53.5 and 155.1 Hz, are strongly detected, while a third feature at 28 Hz is found with lower significance. These QPOs are not detected at other rotational phases. The phenomenology seen in the SGR 1900+14 flare is similar to that of QPOs recently reported by Israel et al. (2005) from the December 27, 2004 flare from SGR 1806-20, suggesting they may have a common origin, perhaps torsional vibrations of the neutron star crust. Indeed, an association of the four frequencies (in increasing order) found in SGR 1900+14 with l = 2, 4, 7, and 13 toroidal modes appears plausible. We discuss our findings in the context of this model and show that if the stars have similar masses then the magnetic field in SGR 1806-20 must be about twice as large as in SGR 1900+14, broadly consistent with estimates from pulse timing.

X-ray flaring from Sagittarius A*: exploring the Milky Way black hole through its brightest flares

NASA Astrophysics Data System (ADS)

Nynka, Melania; Haggard, Daryl

2017-08-01

Sagittarius A* is the supermassive black hole at the center of our own Milky Way galaxy. Ambitious monitoring campaigns have yielded rich multiwavelength, time-resolved data, which have the power to probe the physical processes that underlie Sgr A*'s quiescent and flare emission. In 2013 and 2014 the Chandra X-ray Observatory captured two extremely luminous flares from Sgr A*, the two brightest ever detected in X-ray. I will describe the spectral and temporal properties of these flares, how they compare to previous analysis, and the possible physical processes driving the Sgr A* variability. I will also discuss the power spectral densities of the flares which may contain information about the black hole's ISCO and spin.

Astronomers Surprised to Find Elongated Radio-Emitting Region At Center of Milky Way

NASA Astrophysics Data System (ADS)

1998-12-01

For the first time, astronomers have determined the intrinsic size and shape of the highly charged region of radio emission surrounding what most scientists believe to be a supermassive black hole at the center of our own Milky Way Galaxy. The new evidence may force theorists to revise their ideas about how material behaves in the vicinity of black holes. Using the National Science Foundation's Very Long Baseline Array (VLBA) of radio telescopes, an international team of astronomers from the United States and Taiwan studied the area generally thought to mark the Galactic center. This object, known as Sgr A*, and commonly called "Sagittarius A-star," is some 26,000 light years from Earth in the constellation of Sagittarius. Instead of finding something symmetrical, as expected, the researchers observed an odd, cigar-shaped area of radio emission. "If placed in our Solar System at the Sun's location, it would extend beyond Mars," says K. Y. Lo of the Academia Sinica Institute of Astronomy and Astrophysics in Taipei and leader of the research team. "But it would be only a quarter of that distance wide." The VLBA data support the current hypothesis that the central object has a mass about 2.5 million times that of the Sun. The researchers think Sgr A* may be an extremely energetic inner region of ionized gas accreting onto a supermassive black hole. "However, none of the competing models for a black hole can completely explain both the small size and asymmetrical shape of Sgr A* we have observed," says Jun-Hui Zhao, a member of the team from the Harvard-Smithsonian Center for Astrophysics. "The models would have to be changed to include some other mechanism such as a jet or wind to help explain the VLBA data." The nature of Sgr A* has been a long-standing puzzle in astronomy since its discovery in 1974 by Bruce Balick and Bob Brown. Since then, there have been many theories about the structure and emission mechanism of Sgr A*, but, in the past few years, astronomers have found increasing evidence that it is a supermassive black hole. The team of astronomers used the VLBA to determine the structure of Sgr A* at five radio wavelengths (6.0, 3.6, 2.0, 1.35 cm, and 7 mm). At long radio wavelengths the radiation from Sgr A* is seriously blurred due to the scattering by the interstellar electrons between the Galactic center and the Earth. But, as one moves to shorter wavelengths, the scatter -- or distortion -- decreases exponentially, thereby creating increasingly clearer images. Indeed, at the shortest wavelength of 7 mm, the scattering effects are finally small enough to reveal the true size and shape of Sgr A*. For an object of 2.5 million solar masses, its Schwarzschild radius -- or outer edge of the "gravity well" from which not even light itself can escape from the black hole's pull -- would be only about 7.5 million kilometers. That distance translates into only a twentieth of the mean distance between the Earth and the Sun -- an extraordinarily small area. The astronomers are particularly intrigued that the radio-emitting area immediately surrounding the event horizon has an elongated shape. The VLBA, a series of 10 individual telescopes located at sites across North America, can create, in effect, an enormous single telescope with an aperture thousands of kilometers wide, thus providing the resolution necessary to probe the relatively small region at the core of our galaxy. "We needed to be able to resolve very fine detail in order to determine Sgr A*'s size and shape," said Paul Ho of the Harvard-Smithsonian Center for Astrophysics. "The only way we were able to find these exciting results was through the excellent data we received from the VLBA." The VLBA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Making Sense of Black Holes: Modeling the Galactic Center and Other Low-power AGN

NASA Astrophysics Data System (ADS)

Falcke, Heino; Moscibrodzka, Monika

2018-06-01

The Galactic center host a well-known flat-spectrum radio source, Sgr A*, that is akin to the radio nuclei of quasars and radio galaxies. It is the main target of the Event Horizon Telescope to image the shadow of the black hole. There is, however, still considerable discussion on where the near-horizon emission originates from. Does it come from an accretion flow or is it produced in a relativistic jet-like outflow? Using advanced three-dimensional general relativistic magnetohydrodynamics simulations coupled to general relativistic ray tracing simulations, we now model the dynamics and emission of the plasma around starving black holes in great detail out to several thousand Schwarzschild radii. Jets appear almost naturally in theses simulations. A crucial parameter is the heating of radiating electrons and we argue that electron-proton coupling is low in the accretion flow and high in the magnetized region of the jets, making the jet an important ingredient for the overall appearance of the source. This comprehensive model is able to predict the radio size and appearance, the spectral energy distribution from radio to X-rays, the variability, and the time lags of Sgr A* surprisingly well. Interestingly, the same model can be easily generalized to other low-power AGN like M87, suggesting that GRMHD models for AGN are finally becoming predictive. With upcoming submm-VLBI experiment on the ground and in space, we will be able to further test these models in great detail and see black holes in action.

SGR 1822-1606: Constant Spin Period

NASA Astrophysics Data System (ADS)

Serim, M.; Baykal, A.; Inam, S. C.

2011-08-01

We have analyzed light curve of the new source SGR 1822-1606 (Cummings et al. GCN 12159) using the real time data of RXTE observations. We have extracted light curve for 11 pointings with a time span of about 20 days and employed pulse timing analysis using the harmonic representation of pulses. Using the cross correlation of harmonic representation of pulses, we have obtained pulse arrival times.

Fermi/GBM Results of Magnetars

NASA Technical Reports Server (NTRS)

Kouveliotou, chryssa

2011-01-01

Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11,2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501 +4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR Jl550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP IEI547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields.

The Extreme Case of Magnetars

NASA Technical Reports Server (NTRS)

Kouveliotou, Chryssa

2011-01-01

Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11, 2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501+4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP 1E1547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields.

Extended VHE γ-ray emission towards SGR1806-20 and stellar cluster C1 1806-20

NASA Astrophysics Data System (ADS)

Rowell, Gavin; de Naurois, Mathieu; Ataï, Arache Djannati; Gallant, Yves; H.E.S.S. Collaboration

2012-12-01

We report the discovery, with the H.E.S.S. telescopes, of steady and extended VHE γ-ray emission towards the magnetar candidate SGR 1806-20 and parent stellar cluster C1 1806-20. Preliminary analysis suggests the VHE γ-ray flux of this source, designated HESS J1808-204 is a few×10-13 ph cm-2 s-1 TeV-1 at 1 TeV with a power-law photon spectral index Γ = 2.4+/-0.2. The instrinsic extension and orientation matches that of the synchrotron radio nebula G10.0-0.3 which may be powered by the luminous blue variable star LBV 1806-20, a prominent member of the C1 1806-20 cluster. From the energetics of the combined VHE, X-ray, and nearby Fermi-LAT GeV emission, magnetar magnetic energy may be a dominant source of energy over spin-down power, should SGR 1806-20 power the source. Alternatively, C1 1806-20 and/or LBV 1806-20 by itself, via stellar winds, could supply sufficient energy.

Sagittarius A* as an origin of the Galactic PeV cosmic rays?

NASA Astrophysics Data System (ADS)

Fujita, Yutaka; Murase, Kohta; Kimura, Shigeo S.

2017-04-01

Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ("Pevatron"). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 107 yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujita, Yutaka; Murase, Kohta; Kimura, Shigeo S., E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: murase@psu.edu, E-mail: szk323@psu.edu

Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ('Pevatron'). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 10{sup 7} yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galacticmore » halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.« less

Probing the Magnetic Field Structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gold, Roman; McKinney, Jonathan C.; Johnson, Michael D.

Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source Sagittarius A* (Sgr A*). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotationalmore » instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford–Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in Sgr A*, though both disk- and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.« less

Exploring molecular complexity with ALMA (EMoCA): Simulations of branched carbon-chain chemistry in Sgr B2(N)

NASA Astrophysics Data System (ADS)

Garrod, R. T.; Belloche, A.; Müller, H. S. P.; Menten, K. M.

2017-05-01

Context. Using millimeter wavelength data from the Atacama Large Millimeter/submillimeter Array (ALMA), the EMoCA spectral line survey recently revealed the presence of both the straight-chain (normal) and branched (iso) forms of propyl cyanide (C3H7CN) toward the Galactic Center star-forming source Sgr B2(N2). This was the first interstellar detection of a branched aliphatic molecule. Aims: Through computational methods, we seek to explain the observed I:n ratio for propyl cyanide, and to predict the abundances of the four different forms of the homologous nitrile, butyl cyanide (C4H9CN). We also investigate whether other molecules will show a similar degree of branching, by modeling the chemistry of alkanes up to pentane (C5H12). Methods: We use the coupled three-phase chemical kinetics model, MAGICKAL, to simulate the chemistry of the hot-core source Sgr B2(N2), using an updated chemical network that includes grain-surface/ice-mantle formation routes for branched nitriles and alkanes. The network explicitly considers radical species with an unpaired electron on either the primary or secondary carbon in a chain. We also include mechanisms for the addition of the cyanide radical, CN, to hydrocarbons with multiple bonds between carbon atoms, using activation energy barriers from the literature. We use the EMoCA survey data to search for the straight-chain form of butyl cyanide toward Sgr B2(N2). Results: The observed I:n ratio for propyl cyanide is reproduced by the models, with intermediate to fast warm-up timescales providing the most accurate result. Butyl cyanide is predicted to show similar abundances to propyl cyanide, and to exhibit strong branching, with the sec form clearly dominant over all others. Normal and iso-butyl cyanide are expected to have similar abundances to each other, while the tert form is significantly less abundant. The addition of CN to acetylene and ethene is found to be important to the production of vinyl, ethyl, propyl, and butyl cyanide. The alkanes also show significant branching. We report a non-detection of n-C4H9CN toward Sgr B2(N2), with an abundance at least 1.7 times lower than that of n-C3H7CN. This value is within the range predicted by the chemical models. Conclusions: The models indicate that the degree of branching rises with increasing molecular size. The efficiency of CN addition to unsaturated hydrocarbons boosts the abundances of nitriles in the model, and enhances the ratio of straight-to-branched molecule production. Other types of molecule may be less abundant, but show an even greater degree of branching. The predicted abundance of, in particular, s-C4H9CN, which at its peak is comparable to that of propyl cyanide, makes it a good candidate for future detection toward Sgr B2(N2).

Modelling the thermal X-ray emission around the Galactic centre from colliding Wolf-Rayet winds

NASA Astrophysics Data System (ADS)

Russell, Christopher M. P.; Wang, Q. Daniel; Cuadra, Jorge

2017-11-01

We compute the thermal X-ray emission from hydrodynamic simulations of the 30 Wolf-Rayet (WR) stars orbiting within a parsec of Sgr A*, with the aim of interpreting the Chandra X-ray observations of this region. The model well reproduces the spectral shape of the observations, indicating that the shocked WR winds are the dominant source of this thermal emission. The model X-ray flux is tied to the strength of the Sgr A* outflow, which clears out hot gas from the vicinity of Sgr A*. A moderate outflow best fits the present-day observations, even though this supermassive black hole (SMBH) outflow ended ~100 yr ago.

Comparative Analysis between Simultaneous Resection and Staged Resection for Synchronous Colorectal Liver Metastases - A Single Center Experience on 300 Consecutive Patients.

PubMed

Alexandrescu, Sorin; Diaconescu, Andrei; Ionel, Zenaida; Zlate, Cristian; Grigorie, Răzvan; Hrehoreţ, Doina; Braşoveanu, Vladislav; Dima, Simona; Botea, Florin; Ionescu, Mihnea; Tomescu, Dana; Droc, Gabriela; Fota, Ruxandra; Croitoru, Adina; Gramaticu, Iulia; Buica, Florina; Iacob, Razvan; Gheorghe, Cristian; Herlea, Vlad; Grasu, Mugur; Dumitru, Radu; Boroş, Mirela; Popescu, Irinel

2017-01-01

Introduction: In synchronous colorectal liver metastases (SCLMs), simultaneous resection (SR) of the primary tumor and liver metastases has not gained wide acceptance. Most authors prefer staged resections (SgR), especially in patients presenting rectal cancer or requiring major hepatectomy. Methods: Morbidity, mortality, survival rates and length of hospital stay were compared between the two groups of patients (SR vs. SgR). A subgroup analysis was performed for patients with similar characteristics (e.g. rectal tumor, major hepatectomy, bilobar metastases, metastatic lymph nodes, preoperative chemotherapy). Results: Between 1995 and 2016, SR was performed in 234 patients, while 66 patients underwent SgR. Comparative morbidity (41% vs. 31.8%, respectively, p = 0.1997), mortality (3.8% vs. 3%, respectively, p = 1) and overall survival rates (85.8%, 51.3% and 30% vs. 87%, 49.6% and 22.5%, at 1-, 3- and 5-years, respectively, p = 0.386) were similar between the SR and SgR group. Mean hospital stay was significantly shorter in patients undergoing SR than SgR (15.11 ‚+- 8.60 vs. 19.42 ‚+- 7.36 days, respectively, p 0.0001). The characteristics of SR and SgR groups were similar, except the following parameters: rectal tumor (34.1% vs. 19.7%, respectively, p = 0.0245), metastatic lymph nodes (68.1% vs. 86.3%, respectively, p = 0.0383), bilobar liver metastases (22.6% vs. 37.8%, respectively, p = 0.0169), major hepatectomies (13.2% vs. 30.3%, respectively, p= 0.0025) and neo-adjuvant chemotherapy (13.2% vs. 77.2%, respectively, p 0.0001). A comparative analysis of morbidity, mortality and survival rates between SR and SgR was performed for subgroups of patients presenting these parameters. In each of these subgroups, SR was associated with similar morbidity, mortality and survival rates compared with SgR (p value 0.05). In patients with SCLMs, SR provides similar short-term and long-term outcomes as SgR, with a shorter hospital stay. Therefore, in most patients with SCLMs, SR might be considered the treatment of choice. Celsius.

Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre.

PubMed

Doeleman, Sheperd S; Weintroub, Jonathan; Rogers, Alan E E; Plambeck, Richard; Freund, Robert; Tilanus, Remo P J; Friberg, Per; Ziurys, Lucy M; Moran, James M; Corey, Brian; Young, Ken H; Smythe, Daniel L; Titus, Michael; Marrone, Daniel P; Cappallo, Roger J; Bock, Douglas C-J; Bower, Geoffrey C; Chamberlin, Richard; Davis, Gary R; Krichbaum, Thomas P; Lamb, James; Maness, Holly; Niell, Arthur E; Roy, Alan; Strittmatter, Peter; Werthimer, Daniel; Whitney, Alan R; Woody, David

2008-09-04

The cores of most galaxies are thought to harbour supermassive black holes, which power galactic nuclei by converting the gravitational energy of accreting matter into radiation. Sagittarius A* (Sgr A*), the compact source of radio, infrared and X-ray emission at the centre of the Milky Way, is the closest example of this phenomenon, with an estimated black hole mass that is 4,000,000 times that of the Sun. A long-standing astronomical goal is to resolve structures in the innermost accretion flow surrounding Sgr A*, where strong gravitational fields will distort the appearance of radiation emitted near the black hole. Radio observations at wavelengths of 3.5 mm and 7 mm have detected intrinsic structure in Sgr A*, but the spatial resolution of observations at these wavelengths is limited by interstellar scattering. Here we report observations at a wavelength of 1.3 mm that set a size of 37(+16)(-10) microarcseconds on the intrinsic diameter of Sgr A*. This is less than the expected apparent size of the event horizon of the presumed black hole, suggesting that the bulk of Sgr A* emission may not be centred on the black hole, but arises in the surrounding accretion flow.

Milky Way Monster Stars in Cosmic Reality Show

NASA Astrophysics Data System (ADS)

2003-01-01

The longest X-ray look yet at the supermassive black hole at the Milky Way's center has given astronomers unprecedented access to its life and times. The new data from NASA's Chandra X-ray Observatory revealed that our galaxy's central black hole is a frequent bad actor, prone to numerous outbursts and occasional large explosions. The observations of the black hole, a.k.a. Sagittarius A* or Sgr A*, occurred over a two-week period for a total exposure time of 164 hours. During this time Sgr A* flared up in X-ray intensity half a dozen or more times. Astronomers also found evidence that suggests it had an even more boisterous past. These discoveries will help to unlock the secrets of how Sgr A* grows and how it interacts with its environment "We are getting a look at the everyday life of a supermassive black hole like never before," said Frederick K. Baganoff of the Massachusetts Institute of Technology in Cambridge, who presented these new results on behalf of an international team at a press conference today at the American Astronomical Society meeting in Seattle. "We see it flaring on an almost daily basis." Sagittarius A* More images of Sagittarius A* The cause of the flares is not understood, but the rapidity with which they rise and fall indicates that they are occurring near the event horizon, or point of no return, around the black hole. Even when it flares, the intensity of the X-ray emission from the vicinity of the black hole is relatively weak, which suggests that Sgr A*, weighing in at 3 million times the mass of the Sun, is a starved black hole. "Although it appears to snack often, this black hole is definitely on a severe diet," says Baganoff. "This could be because explosive events in the past blew away much of the gas from the neighborhood of the black hole." Indeed, evidence for such events - which astronomers are viewing 26,000 years later due to the time it takes light to travel to Earth from the center of the Galaxy - can be found in the image. A faint streak of X-rays about 1 light-year long has been discovered 1.5 light years from Sgr A*. The streak points at Sgr A*, suggesting that it may be a jet of particles expelled at nearly the speed of light from just outside the event horizon of the black hole. The intensity and size of this jet indicate that the flaring activity has been occurring for many years. Labeled image of Sagittarius A* Jet Labeled image of Sagittarius A* Jet On a much larger scale, huge lobes of 20-million-degree-Centigrade gas extending over dozens of light years on either side of the black hole have also been discovered. "These lobes show that enormous explosions have occurred several times over the last ten thousand years," said Mark Morris of UCLA, lead author of a second paper on Sgr A*, who also participated in the press conference. Sangwook Park, of Penn State University in University Park, and Michael Muno, of MIT, were lead authors of two other papers presented at the meeting. These papers focused on the extraordinarily rich region around the central black hole, where they detected more than 2,000 X-ray sources. Other members of the team include Mark Bautz and George Ricker of MIT, Niel Brandt, Patrick Broos, George Chartas, Eric Feigelson, Gordon Garmire, and Leisa Townsley of Penn State, Yoshitomo Maeda of the Institute of Space and Astronautical Science in Japan, and Christian Howard of UCLA. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program, and TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass., for the Office of Space Science at NASA Headquarters, Washington. Images and additional information about this result are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

A RAPIDLY EVOLVING REGION IN THE GALACTIC CENTER: WHY S-STARS THERMALIZE AND MORE MASSIVE STARS ARE MISSING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Xian; Amaro-Seoane, Pau, E-mail: Xian.Chen@aei.mpg.de, E-mail: Pau.Amaro-Seoane@aei.mpg.de

2014-05-10

The existence of ''S-stars'' within a distance of 1'' from Sgr A* contradicts our understanding of star formation, due to Sgr A* 's forbiddingly violent environment. A suggested possibility is that they form far away and were brought in by some fast dynamical process, since they are young. Nonetheless, all conjectured mechanisms either fail to reproduce their eccentricities—without violating their young age—or cannot explain the problem of {sup i}nverse mass segregation{sup :} the fact that lighter stars (the S-stars) are closer to Sgr A* and more massive ones, Wolf-Rayet (WR) and O-stars, are farther out. In this Letter we proposemore » that the mechanism responsible for both the distribution of the eccentricities and the paucity of massive stars is the Kozai-Lidov-like resonance induced by a sub-parsec disk recently discovered in the Galactic center. Considering that the disk probably extended to a smaller radius in the past, we show that in as short as (a few) 10{sup 6} yr, the stars populating the innermost 1'' region would redistribute in angular-momentum space and recover the observed ''super-thermal'' distribution. Meanwhile, WR and O-stars in the same region intermittently attain ample eccentricities that will lead to their tidal disruptions by the central massive black hole. Our results provide new evidences that Sgr A* was powered several millions years ago by an accretion disk as well as by tidal stellar disruptions.« less

The Sleeping Monster: NuSTAR Observations of SGR 1806-20, 11 Years After the Giant Flare

NASA Astrophysics Data System (ADS)

Younes, George; Baring, Matthew G.; Kouveliotou, Chryssa; Harding, Alice; Donovan, Sophia; Göğüş, Ersin; Kaspi, Victoria; Granot, Jonathan

2017-12-01

We report the analysis of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of SGR 1806-20 spread over a year from 2015 April to 2016 April, more than 11 years following its giant flare (GF) of 2004. The source spin frequency during the NuSTAR observations follows a linear trend with a frequency derivative \\dot{ν }=(-1.25+/- 0.03)× {10}-12 Hz s-1, implying a surface dipole equatorial magnetic field B≈ 7.7× {10}14 G. Thus, SGR 1806-20 has finally returned to its historical minimum torque level measured between 1993 and 1998. The source showed strong timing noise for at least 12 years starting in 2000, with \\dot{ν } increasing one order of magnitude between 2005 and 2011, following its 2004 major bursting episode and GF. SGR 1806-20 has not shown strong transient activity since 2009, and we do not find short bursts in the NuSTAR data. The pulse profile is complex with a pulsed fraction of ˜ 8 % with no indication of energy dependence. The NuSTAR spectra are well fit with an absorbed blackbody, {kT}=0.62+/- 0.06 {keV}, plus a power law, {{Γ }}=1.33+/- 0.03. We find no evidence for variability among the five observations, indicating that SGR 1806-20 has reached a persistent and potentially its quiescent X-ray flux level after its 2004 major bursting episode. Extrapolating the NuSTAR model to lower energies, we find that the 0.5-10 keV flux decay follows an exponential form with a characteristic timescale τ =543+/- 75 days. Interestingly, the NuSTAR flux in this energy range is a factor of ˜2 weaker than the long-term average measured between 1993 and 2003, a behavior also exhibited in SGR 1900+14. We discuss our findings in the context of the magnetar model.

Testing SgrA{sup *} with the spectrum of its accretion structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Nan; Li, Zilong; Bambi, Cosimo

2015-09-01

SgrA{sup *} is the supermassive black hole candidate at the center of the Galaxy and an ideal laboratory to test general relativity. Following previous work by other authors, we use the Polish doughnut model to describe an optically thin and constant angular momentum ion torus in hydrodynamical equilibrium and model the accretion structure around SgrA{sup *}. The radiation mechanisms are bremsstrahlung, synchrotron emission, and inverse Compton scattering. We compute the spectrum as seen by a distant observer in Kerr and non-Kerr spacetimes and we study how an accurate measurement can constrain possible deviations form the Kerr solution. As in themore » case of emission from a thin accretion disk, we find a substantial degeneracy between the determination of the spin and of possible deviations from the Kerr geometry, even when the parameters of the ion torus are fixed. This means that this technique cannot independently test the nature of SgrA{sup *} even in the presence of good data and with the systematics under control. However, it might do it in combination with other measurements (black hole shadow, radio pulsar, etc.)« less

Detection of amino acetonitrile in Sgr B2(N)

NASA Astrophysics Data System (ADS)

Belloche, A.; Menten, K. M.; Comito, C.; Müller, H. S. P.; Schilke, P.; Ott, J.; Thorwirth, S.; Hieret, C.

2008-04-01

Context: Amino acids are building blocks of proteins and therefore key ingredients for the origin of life. The simplest amino acid, glycine (NH2CH2COOH), has long been searched for in the interstellar medium but has not been unambiguously detected so far. At the same time, more and more complex molecules have been newly found toward the prolific Galactic center source Sagittarius B2. Aims: Since the search for glycine has turned out to be extremely difficult, we aimed at detecting a chemically related species (possibly a direct precursor), amino acetonitrile (NH2CH2CN). Methods: With the IRAM 30 m telescope we carried out a complete line survey of the hot core regions Sgr B2(N) and (M) in the 3 mm range, plus partial surveys at 2 and 1.3 mm. We analyzed our 30 m line survey in the LTE approximation and modeled the emission of all known molecules simultaneously. We identified spectral features at the frequencies predicted for amino acetonitrile lines having intensities compatible with a unique rotation temperature. We also used the Very Large Array to look for cold, extended emission from amino acetonitrile. Results: We detected amino acetonitrile in Sgr B2(N) in our 30 m telescope line survey and conducted confirmatory observations of selected lines with the IRAM Plateau de Bure and the Australia Telescope Compact Array interferometers. The emission arises from a known hot core, the Large Molecule Heimat, and is compact with a source diameter of 2 arcsec (0.08 pc). We derived a column density of 2.8 × 1016 cm-2, a temperature of 100 K, and a linewidth of 7 km s-1. Based on the simultaneously observed continuum emission, we calculated a density of 1.7 × 108 cm-3, a mass of 2340 M_⊙, and an amino acetonitrile fractional abundance of 2.2 × 10-9. The high abundance and temperature may indicate that amino acetonitrile is formed by grain surface chemistry. We did not detect any hot, compact amino acetonitrile emission toward Sgr B2(M) or any cold, extended emission toward Sgr B2, with column-density upper limits of 6 × 1015 and 3 × 1012-14 cm-2, respectively. Conclusions: Based on our amino acetonitrile detection toward Sgr B2(N) and a comparison to the pair methylcyanide/acetic acid both detected in this source, we suggest that the column density of both glycine conformers in Sgr B2(N) is well below the best upper limits published recently by other authors, and probably below the confusion limit in the 1-3 mm range. Based on observations carried out with the IRAM Plateau de Bure Interferometer, the IRAM 30 m telescope, the Australia Telescope Compact Array, and the NRAO Very Large Array. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). The Australia Telescope Compact Array is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Table [see full textsee full text] and Fig. [see full textsee full text] are only available in electronic form at http://www.aanda.org The calibrated and deconvolved data cubes and images (line and continuum) obtained with the PdBI, the ATCA, and the VLA are available in FITS format at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/482/179

Hustle and Bustle at Center of Milky Way

NASA Image and Video Library

2013-05-07

This artist concept illustrates the frenzied activity at the core of our Milky Way galaxy. The galactic center hosts a supermassive black hole in the region known as Sagittarius A*, or Sgr A*, with a mass of about four million times that of our sun.

Large Torque Variations in Two Soft Gamma Repeaters

NASA Technical Reports Server (NTRS)

Woods, Peter M.; Kouveliotou, Chryssa; Gogus, Ersin; Finger, Mark H.; Swank, Jean; Markwardt, Craig B.; Hurley, Kevin; vanderKlis, Michiel; Six, N. Frank (Technical Monitor)

2001-01-01

We have monitored the pulse frequencies of the two soft gamma repeaters SGR 1806-20 and SGR 1900+14 through the beginning of year 2001 using primarily Rossi X-ray Timing Explorer Proportional Counter Array observations. In both sources, we observe large changes in the spin-down torque up to a factor of approximately 4, which persist for several months. Using long baseline phase-connected timing solutions as well as the overall frequency histories, we construct torque noise power spectra for each SGR. The power spectrum of each source is very red (power-law slope approximately -3.5). These power spectra are consistent in normalization with some accreting systems, yet much steeper in slope than any known accreting source. To the best of our knowledge, torque noise power spectra with a comparably steep frequency dependence have only been seen in young, glitching radio pulsars (e.g. Vela). The observed changes in spin-down rate do not correlate with burst activity, therefore, the physical mechanisms behind each phenomenon are also likely unrelated. Within the context of the magnetar model, seismic activity cannot account for both the bursts and the long-term torque changes unless the seismically active regions are decoupled from one another.

Detection of interstellar sodium hydroxide in self-absorption toward the galactic center

NASA Technical Reports Server (NTRS)

Hollis, J. M.; Rhodes, P. J.

1982-01-01

A weak self-absorbed emission line, which is identified as the J = 4-3 transition of sodium hydroxide, has been detected in the direction of Sgr B2(OH). The correspondingly weak Sgr B2(QH) emission line U75406, previously reported as an unidentified spectral feature by other investigators, is consistent with the J = 3-2 transition of sodium hydroxide. This detection may represent the first evidence of a grain reaction formation mechanism for simple metal hydroxides. The detection of H62 Delta toward Orion A is also reported.

Unraveling the Cooling Trend of the Soft Gamma Repeater SGR 1627-41

NASA Technical Reports Server (NTRS)

Kouveliotou, C.; Eichler, D.; Woods, P. M.; Lyubarsky, Y.; Patel, S. K.; Gogus, E.; vanderKlis, M.; Tennant, A.; Wachter, S.; Hurley, K.

2003-01-01

SGR 1627-41 was discovered in 1998 after a single active episode that lasted approximately 6 weeks. We report here our monitoring results of the decay trend of the persistent X-ray luminosity of the source during the last 5 years. We find an initial temporal power-law decay with index 0.47, reaching a plateau that is followed by a sharp (factor of 10) flux decline approximately 800 days after the source activation. The source spectrum is best described during the entire period by a single power law with high absorption [N(sub H) = 9.0(7) x 10(exp 22) per square centimeter]; the spectral index, however, varies dramatically between 2.2 and 3.8 spanning the entire range for all known soft gamma repeater sources. We discuss the cooling behavior of the neutron star assuming a deep crustal heating initiated by the burst activity of the source during 1998.

The SSS classical nova V5116 Sgr

NASA Astrophysics Data System (ADS)

Sala, G.; Ness, J.; Greiner, J.; Hernanz, M.

2017-10-01

XMM-Newton observed the nova V5116 Sgr during its supersoft phase (SSS). V5116 Sgr showed a decrease of the flux by a factor around 8 during 2/3 of the orbital period. The broad band EPIC spectra remain unchanged during the different flux phases, suggesting an occultation of the central source in a high inclination system. While the global SED does not change significantly, the RGS spectrum is changing between the high and the low flux phases. The non-occultation phase shows a typical white dwarf atmosphere spectrum, dominated by absorption lines. During the low flux periods an extra component of emission lines is superimposed to the soft X-ray continuum. This supports the picture of V5116 Sgr as the clearest example of a system switching between the SSa class of SSS novae, with spectra dominated by absorption lines, and the SSe class, showing an emission lines component. In addition, the simultaneous OM images allow us to find a phase solution for the X-ray light-curve. A thick rim of the accretion disk as the one developed for the SSSs CAL 87, RX J0019.8, and RX J0513.9 could provide a plausible model both for the optical and the X-ray light curve of V5116 Sgr.

Probing Galactic Center Cosmic-Rays in the X-ray Regime

NASA Astrophysics Data System (ADS)

Zhang, Shuo; Baganoff, Frederick K.; Bulbul, Esra; Miller, Eric D.; Bautz, Mark W.

2017-08-01

The central few hundred parsecs of the Galaxy harbors 5-10% of the molecular gas mass of the entire Milky Way. This central molecular zone exhibits 6.4 keV Fe Kα line and continuum X-ray emission with time-variability. The time-variable X-ray emission from the gas clouds is best explained by light echoes of past X-ray outbursts from the central supermassive black hole Sgr A*. However,MeV-GeV cosmic-ray particles may also contribute to a constant X-ray emission component from the clouds, through collisional ionization and bremsstrahlung. Sgr B2 is the densest and most massive cloud in the central molecular zone. It is the only known gas cloud whose X-ray emission has kept fading over the past decade and will soon reach a constant X-ray level in 2017/2018, and thus serves as the best probe for MeV-GeV particles in the central 100 pc of the Galaxy. At the same time, the Fe Kα emission has also been discovered from molecular structures beyond the central molecular zone, extening to ~1 kpc from the Galactic center. The X-ray reflection scenario meets challenges this far from the Galactic center, while the MeV-GeV cosmic-ray electrons serve as a more natural explanation. Our studies on Sgr B2 and the large-scale moleuclar structures will for the first time constrain the MeV-GeV particles in the Galactic center, and point to their origin: whether they rise from particle acceleration or dark matter annihilation.

Sgr A* Emission Parametrizations from GRMHD Simulations

NASA Astrophysics Data System (ADS)

Anantua, Richard; Ressler, Sean; Quataert, Eliot

2018-06-01

Galactic Center emission near the vicinity of the central black hole, Sagittarius (Sgr) A*, is modeled using parametrizations involving the electron temperature, which is found from general relativistic magnetohydrodynamic (GRMHD) simulations to be highest in the disk-outflow corona. Jet-motivated prescriptions generalizing equipartition of particle and magnetic energies, e.g., by scaling relativistic electron energy density to powers of the magnetic field strength, are also introduced. GRMHD jet (or outflow)/accretion disk/black hole (JAB) simulation postprocessing codes IBOTHROS and GRMONTY are employed in the calculation of images and spectra. Various parametric models reproduce spectral and morphological features, such as the sub-mm spectral bump in electron temperature models and asymmetric photon rings in equipartition-based models. The Event Horizon Telescope (EHT) will provide unprecedentedly high-resolution 230+ GHz observations of the "shadow" around Sgr A*'s supermassive black hole, which the synthetic models presented here will reverse-engineer. Both electron temperature and equipartition-based models can be constructed to be compatible with EHT size constraints for the emitting region of Sgr A*. This program sets the groundwork for devising a unified emission parametrization flexible enough to model disk, corona and outflow/jet regions with a small set of parameters including electron heating fraction and plasma beta.

Detection of Intrinsic Source Structure at ∼3 Schwarzschild Radii with Millimeter-VLBI Observations of SAGITTARIUS A*

NASA Astrophysics Data System (ADS)

Lu, Ru-Sen; Krichbaum, Thomas P.; Roy, Alan L.; Fish, Vincent L.; Doeleman, Sheperd S.; Johnson, Michael D.; Akiyama, Kazunori; Psaltis, Dimitrios; Alef, Walter; Asada, Keiichi; Beaudoin, Christopher; Bertarini, Alessandra; Blackburn, Lindy; Blundell, Ray; Bower, Geoffrey C.; Brinkerink, Christiaan; Broderick, Avery E.; Cappallo, Roger; Crew, Geoffrey B.; Dexter, Jason; Dexter, Matt; Falcke, Heino; Freund, Robert; Friberg, Per; Greer, Christopher H.; Gurwell, Mark A.; Ho, Paul T. P.; Honma, Mareki; Inoue, Makoto; Kim, Junhan; Lamb, James; Lindqvist, Michael; Macmahon, David; Marrone, Daniel P.; Martí-Vidal, Ivan; Menten, Karl M.; Moran, James M.; Nagar, Neil M.; Plambeck, Richard L.; Primiani, Rurik A.; Rogers, Alan E. E.; Ros, Eduardo; Rottmann, Helge; SooHoo, Jason; Spilker, Justin; Stone, Jordan; Strittmatter, Peter; Tilanus, Remo P. J.; Titus, Michael; Vertatschitsch, Laura; Wagner, Jan; Weintroub, Jonathan; Wright, Melvyn; Young, Ken H.; Zensus, J. Anton; Ziurys, Lucy M.

2018-05-01

We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in the Galactic center, Sgr A*, at 1.3 mm (230 GHz). The observations were performed in 2013 March using six VLBI stations in Hawaii, California, Arizona, and Chile. Compared to earlier observations, the addition of the APEX telescope in Chile almost doubles the longest baseline length in the array, provides additional uv coverage in the N–S direction, and leads to a spatial resolution of ∼30 μas (∼3 Schwarzschild radii) for Sgr A*. The source is detected even at the longest baselines with visibility amplitudes of ∼4%–13% of the total flux density. We argue that such flux densities cannot result from interstellar refractive scattering alone, but indicate the presence of compact intrinsic source structure on scales of ∼3 Schwarzschild radii. The measured nonzero closure phases rule out point-symmetric emission. We discuss our results in the context of simple geometric models that capture the basic characteristics and brightness distributions of disk- and jet-dominated models and show that both can reproduce the observed data. Common to these models are the brightness asymmetry, the orientation, and characteristic sizes, which are comparable to the expected size of the black hole shadow. Future 1.3 mm VLBI observations with an expanded array and better sensitivity will allow more detailed imaging of the horizon-scale structure and bear the potential for a deep insight into the physical processes at the black hole boundary.

SGR 1822-1606 (Swift J1822.3-1606): X-ray spectrum and refined spin period from Swift XRT analysis

NASA Astrophysics Data System (ADS)

Esposito, P.; Rea, N.; Israel, G. L.

2011-07-01

We have analysed 1.6 ks s of Photon Counting (PC) XRT data of the new SGR/magnetar candidate Swift J1822.3-1606 (Cummings et al. GCN #12159), including the first 0.6 ks on which Pagani et al. reported in GCN #12163. We found that the source spectrum is well described by a power-law plus blackbody model, modified for the interstellar absorption (reduced chi-squared = 1.04 for 97 degrees of freedom).

Polarization and long-term variability of Sgr A* X-ray echo

NASA Astrophysics Data System (ADS)

Churazov, E.; Khabibullin, I.; Ponti, G.; Sunyaev, R.

2017-06-01

We use a model of the molecular gas distribution within ˜100 pc from the centre of the Milky Way (Kruijssen, Dale & Longmore) to simulate time evolution and polarization properties of the reflected X-ray emission, associated with the past outbursts from Sgr A*. While this model is too simple to describe the complexity of the true gas distribution, it illustrates the importance and power of long-term observations of the reflected emission. We show that the variable part of X-ray emission observed by Chandra and XMM-Newton from prominent molecular clouds is well described by a pure reflection model, providing strong support of the reflection scenario. While the identification of Sgr A* as a primary source for this reflected emission is already a very appealing hypothesis, a decisive test of this model can be provided by future X-ray polarimetric observations, which will allow placing constraints on the location of the primary source. In addition, X-ray polarimeters (like, e.g. XIPE) have sufficient sensitivity to constrain the line-of-sight positions of molecular complexes, removing major uncertainty in the model.

Monitoring magnetar outbursts .

NASA Astrophysics Data System (ADS)

Israel, G. L.

We report on recent results concerning the timing properties of two transient sources, namely SGR 0418+5729 and Swift J1822.3-1606, for which dedicated monitoring programs have been carried out in the latest years. The timing analysis allowed us to obtain the first measurement of the first period derivative of SGR 0418+5729, dot {P}=4(1)×1015ss-1, significant at a ˜3.5sigma confidence level. This leads to a surface dipolar magnetic field of Bdip˜6×1012 Gauss, confirming SGR 0418+5729 as the lowest magnetic field magnetar. The X-ray timing analysis of Swift J1822.3-1606 showed that a second period derivative is needed in order to fit well the pulsation phases. The period derivative of dot {P}=1.1(4)×10-13s s-1leads to an estimate of the dipolar surface magnetic field of Bdip=3×1013 G. This measurement makes Swift J1822.3-1606, the second magnetar with a dipolar magnetic field lower than the electron critical field (after SGR 0418+5729; \\citealt{rea10}).

Large Torque Variations in Two Soft Gamma Repeaters

NASA Technical Reports Server (NTRS)

Woods, Peter M.; Kouveliotou, Chryssa; Gogus, Ersin; Finger, Mark H.; Swank, Jean; Markwardt, Craig B.; Hurley, Kevin; vanderKlis, Michiel

2002-01-01

We have monitored the pulse frequencies of the two soft gamma repeaters SGR 1806-20 and SGR 1900+14 through the beginning of year 2001 using primarily Rossi X-Ray Timing Explorer Proportional Counter Array observations. In both sources, we observe large changes in the spin-down torque up to a factor of approximately 4, which persist for several months. Using long-baseline phase-connected timing solutions as well as the overall frequency histories, we construct torque noise power spectra for each SGR (Soft Gamma Repeater). The power spectrum of each source is very red (power-law slope is approximately -3.5). The torque noise power levels are consistent with some accreting systems on timescales of approximately 1 yr, yet the full power spectrum is much steeper in frequency than any known accreting source. To the best of our knowledge, torque noise power spectra with a comparably steep frequency dependence have been seen only in young, glitching radio pulsars (e.g., Vela). The observed changes in spin-down rate do not correlate with burst activity; therefore, the physical mechanisms behind each phenomenon are also likely unrelated. Within the context of the magnetar model, seismic activity can not account for both the bursts and the long-term torque changes unless the seismically active regions are decoupled from one another.

Extended VHE γ-ray emission towards SGR1806-20, LBV 1806-20, and stellar cluster Cl* 1806-20

NASA Astrophysics Data System (ADS)

H.E.S.S. Collaboration; Abdalla, H.; Abramowski, A.; Aharonian, F.; Ait Benkhali, F.; Akhperjanian, A. G.; Angüner, E. O.; Arrieta, M.; Aubert, P.; Backes, M.; Balzer, A.; Barnard, M.; Becherini, Y.; Becker Tjus, J.; Berge, D.; Bernhard, S.; Bernlöhr, K.; Birsin, E.; Blackwell, R.; Böttcher, M.; Boisson, C.; Bolmont, J.; Bordas, P.; Bregeon, J.; Brun, F.; Brun, P.; Bryan, M.; Bulik, T.; Capasso, M.; Carr, J.; Casanova, S.; Chakraborty, N.; Chalme-Calvet, R.; Chaves, R. C. G.; Chen, A.; Chevalier, J.; Chrétien, M.; Colafrancesco, S.; Cologna, G.; Condon, B.; Conrad, J.; Couturier, C.; Cui, Y.; Davids, I. D.; Degrange, B.; Deil, C.; deWilt, P.; Djannati-Ataï, A.; Domainko, W.; Donath, A.; Drury, L. O.'C.; Dubus, G.; Dutson, K.; Dyks, J.; Dyrda, M.; Edwards, T.; Egberts, K.; Eger, P.; Ernenwein, J.-P.; Eschbach, S.; Farnier, C.; Fegan, S.; Fernandes, M. V.; Fiasson, A.; Fontaine, G.; Förster, A.; Funk, S.; Füßling, M.; Gabici, S.; Gajdus, M.; Gallant, Y. A.; Garrigoux, T.; Giavitto, G.; Giebels, B.; Glicenstein, J. F.; Gottschall, D.; Goyal, A.; Grondin, M.-H.; Grudzińska, M.; Hadasch, D.; Hahn, J.; Hawkes, J.; Heinzelmann, G.; Henri, G.; Hermann, G.; Hervet, O.; Hillert, A.; Hinton, J. A.; Hofmann, W.; Hoischen, C.; Holler, M.; Horns, D.; Ivascenko, A.; Jacholkowska, A.; Jamrozy, M.; Janiak, M.; Jankowsky, D.; Jankowsky, F.; Jingo, M.; Jogler, T.; Jouvin, L.; Jung-Richardt, I.; Kastendieck, M. A.; Katarzyński, K.; Katz, U.; Kerszberg, D.; Khélifi, B.; Kieffer, M.; King, J.; Klepser, S.; Klochkov, D.; Kluźniak, W.; Kolitzus, D.; Komin, Nu.; Kosack, K.; Krakau, S.; Kraus, M.; Krayzel, F.; Krüger, P. P.; Laffon, H.; Lamanna, G.; Lau, J.; Lees, J.-P.; Lefaucheur, J.; Lefranc, V.; Lemière, A.; Lemoine-Goumard, M.; Lenain, J.-P.; Leser, E.; Lohse, T.; Lorentz, M.; Liu, R.; Lypova, I.; Marandon, V.; Marcowith, A.; Mariaud, C.; Marx, R.; Maurin, G.; Maxted, N.; Mayer, M.; Meintjes, P. J.; Menzler, U.; Meyer, M.; Mitchell, A. M. W.; Moderski, R.; Mohamed, M.; Morå, K.; Moulin, E.; Murach, T.; de Naurois, M.; Niederwanger, F.; Niemiec, J.; Oakes, L.; Odaka, H.; Öttl, S.; Ohm, S.; Ostrowski, M.; Oya, I.; Padovani, M.; Panter, M.; Parsons, R. D.; Paz Arribas, M.; Pekeur, N. W.; Pelletier, G.; Petrucci, P.-O.; Peyaud, B.; Pita, S.; Poon, H.; Prokhorov, D.; Prokoph, H.; Pühlhofer, G.; Punch, M.; Quirrenbach, A.; Raab, S.; Reimer, A.; Reimer, O.; Renaud, M.; de Reyes, R.; Rieger, F.; Romoli, C.; Rosier-Lees, S.; Rowell, G.; Rudak, B.; Rulten, C. B.; Sahakian, V.; Salek, D.; Sanchez, D. A.; Santangelo, A.; Sasaki, M.; Schlickeiser, R.; Schüssler, F.; Schulz, A.; Schwanke, U.; Schwemmer, S.; Seyffert, A. S.; Shafi, N.; Shilon, I.; Simoni, R.; Sol, H.; Spanier, F.; Spengler, G.; Spies, F.; Stawarz, Ł.; Steenkamp, R.; Stegmann, C.; Stinzing, F.; Stycz, K.; Sushch, I.; Tavernet, J.-P.; Tavernier, T.; Taylor, A. M.; Terrier, R.; Tluczykont, M.; Trichard, C.; Tuffs, R.; van der Walt, J.; van Eldik, C.; van Soelen, B.; Vasileiadis, G.; Veh, J.; Venter, C.; Viana, A.; Vincent, P.; Vink, J.; Voisin, F.; Völk, H. J.; Vuillaume, T.; Wadiasingh, Z.; Wagner, S. J.; Wagner, P.; Wagner, R. M.; White, R.; Wierzcholska, A.; Willmann, P.; Wörnlein, A.; Wouters, D.; Yang, R.; Zabalza, V.; Zaborov, D.; Zacharias, M.; Zdziarski, A. A.; Zech, A.; Zefi, F.; Ziegler, A.; Żywucka, N.

2018-04-01

Using the High Energy Spectroscopic System (H.E.S.S.) telescopes we have discovered a steady and extended very high-energy (VHE) γ-ray source towards the luminous blue variable candidate LBV 1806-20, massive stellar cluster Cl* 1806-20, and magnetar SGR 1806-20. The new VHE source, HESS J1808-204, was detected at a statistical significance of >6σ (post-trial) with a photon flux normalisation (2.9 ± 0.4stat ± 0.5sys) × 10-13 ph cm-2 s-1 TeV-1 at 1 TeV and a power-law photon index of 2.3 ± 0.2stat ± 0.3sys. The luminosity of this source (0.2 to 10 TeV; scaled to distance d = 8.7 kpc) is LVHE 1.6 × 1034(d/8.7 kpc)2 erg s-1. The VHE γ-ray emission is extended and is well fit by a single Gaussian with statistical standard deviation of 0.095° ± 0.015°. This extension is similar to that of the synchrotron radio nebula G10.0-0.3, which is thought to be powered by LBV 1806-20. The VHE γ-ray luminosity could be provided by the stellar wind luminosity of LBV 1806-20 by itself and/or the massive star members of Cl* 1806-20. Alternatively, magnetic dissipation (e.g. via reconnection) from SGR 1806-20 can potentially account for the VHE luminosity. The origin and hadronic and/or leptonic nature of the accelerated particles responsible for HESS J1808-204 is not yet clear. If associated with SGR 1806-20, the potentially young age of the magnetar (650 yr) can be used to infer the transport limits of these particles to match the VHE source size. This discovery provides new interest in the potential for high-energy particle acceleration from magnetars, massive stars, and/or stellar clusters.

Six Years of Monitoring of the Sgr B2 Molecular Cloud with INTEGRAL

NASA Astrophysics Data System (ADS)

Terrier, R.; Bélanger, G.; Ponti, G.; Trap, G.; Goldwurm, A.; Decourchelle, A.

2009-05-01

Several molecular clouds around the Galactic Centre (GC) emit strong neutral iron fluorescence line at 6.4 keV, as well as hard X-ray emission up to 100 keV. The origin of this emission has long been a matter of controversy: irradiation by low energy cosmic ray electrons or X-rays emitted by a nearby flaring source in the central region. A recent evidence for time variability in the iron line intensity that has been detected in the Sgr B2 cloud favors the reflexion scenario. We present here the data obtained after 6 years of INTEGRAL monitoring of the GC. In particular, we show a lightcurve of Sgr B2 that reveals a decrease in the hard X-ray flux over the last years and discuss its implications. We finally discuss perspectives with Simbol-X.

High temperature attenuates the gravitropism of inflorescence stems by inducing SHOOT GRAVITROPISM 5 alternative splicing in Arabidopsis.

PubMed

Kim, Joo-Young; Ryu, Jae Yong; Baek, Kon; Park, Chung-Mo

2016-01-01

In higher plants, gravitropism proceeds through three sequential steps in the responding organs: perception of gravity signals, signal transduction and asymmetric cell elongation. Light and temperature also influence the gravitropic orientation of plant organs. A series of Arabidopsis shoot gravitropism (sgr) mutants has been shown to exhibit disturbed shoot gravitropism. SGR5 is functionally distinct from other SGR members in that it mediates the early events of gravitropic responses in inflorescence stems. Here, we demonstrated that SGR5 alternative splicing produces two protein variants (SGR5α and SGR5β) in modulating the gravitropic response of inflorescence stems at high temperatures. SGR5β inhibits SGR5α function by forming non-DNA-binding heterodimers. Transgenic plants overexpressing SGR5β (35S:SGR5β) exhibit reduced gravitropic growth of inflorescence stems, as observed in the SGR5-deficient sgr5-5 mutant. Interestingly, SGR5 alternative splicing is accelerated at high temperatures, resulting in the high-level accumulation of SGR5β transcripts. When plants were exposed to high temperatures, whereas gravitropic curvature was reduced in Col-0 inflorescence stems, it was uninfluenced in the inflorescence stems of 35S:SGR5β transgenic plants and sgr5-5 mutant. We propose that the thermoresponsive alternative splicing of SGR5 provides an adaptation strategy by which plants protect the shoots from hot air under high temperature stress in natural habitats. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Glimpses of the past activity of Sgr A★ inferred from X-ray echoes in Sgr C

NASA Astrophysics Data System (ADS)

Chuard, D.; Terrier, R.; Goldwurm, A.; Clavel, M.; Soldi, S.; Morris, M. R.; Ponti, G.; Walls, M.; Chernyakova, M.

2018-02-01

Context. For a decade now, evidence has accumulated that giant molecular clouds located within the central molecular zone of our Galaxy reflect X-rays coming from past outbursts of the Galactic supermassive black hole. However, the number of illuminating events as well as their ages and durations are still unresolved questions. Aims: We aim to reconstruct parts of the history of the supermassive black hole Sgr A★ by studying this reflection phenomenon in the molecular complex Sgr C and by determining the line-of-sight positions of its main bright substructures. Methods: Using observations made with the X-ray observatories XMM-Newton and Chandra and between 2000 and 2014, we investigated the variability of the reflected emission, which consists of a Fe Kα line at 6.4 keV and a Compton continuum. We carried out an imaging and a spectral analysis. We also used a Monte Carlo model of the reflected spectra to constrain the line-of-sight positions of the brightest clumps, and hence to assign an approximate date to the associated illuminating events. Results: We show that the Fe Kα emission from Sgr C exhibits significant variability in both space and time, which confirms its reflection origin. The most likely illuminating source is Sgr A★. On the one hand, we report two distinct variability timescales, as one clump undergoes a sudden rise and fall in about 2005, while two others vary smoothly throughout the whole 2000-2014 period. On the other hand, by fitting the Monte Carlo model to the data, we are able to place tight constraints on the 3D positions of the clumps. These two independent approaches provide a consistent picture of the past activity of Sgr A★, since the two slowly varying clumps are located on the same wavefront, while the third (rapidly varying) clump corresponds to a different wavefront, that is, to a different illuminating event. Conclusions: This work shows that Sgr A★ experienced at least two powerful outbursts in the past 300 yrs, and for the first time, we provide an estimation of their age. Extending this approach to other molecular complexes, such as Sgr A, will allow this two-event scenario to be tested further.

Flux Relaxation after Two Outbursts of the Magnetar SGR 1627–41 and Possible Hard X-Ray Emission

NASA Astrophysics Data System (ADS)

An, Hongjun; Cumming, Andrew; Kaspi, Victoria M.

2018-05-01

We report on the long-term flux relaxation of the magnetar SGR 1627‑41 after its 2008 outburst, and evidence for hard X-ray excess measured with NuSTAR. We use new observations made with Chandra and XMM-Newton, and an archival NuSTAR observation, which add flux measurements at ∼2000 days into quiescence after the 2008 outburst. We find that the source flux has further declined since the last measurement made in 2011, ∼1000 days after the outburst in 2008. This trend is similar to the relaxation after the source’s 1998 outburst. We use crustal cooling models to reproduce the flux relaxation; if the whole surface of the star is heated in the outbursts, the modeling suggests that the 2008 outburst of SGR 1627‑41 deposited energy into the inner crust and that the core temperature of SGR 1627‑41 is low (T c ≲ 108 K), as previously suggested. On the other hand, if only a small fraction of the surface is heated or the temperature in the crust reached the melting temperature, relaxation at early times requires another emission mechanism. Finally, we report on evidence for hard X-ray emission in SGR 1627‑41 that follows the observational correlation suggested by Kaspi & Boydstun in magnetars.

The Properties and Fate of the Galactic Center G2 Cloud

NASA Astrophysics Data System (ADS)

Shcherbakov, Roman V.

2014-03-01

The object G2 was recently discovered descending into the gravitational potential of the supermassive black hole (BH) Sgr A*. We test the photoionized cloud scenario, determine the cloud properties, and estimate the emission during the pericenter passage. The incident radiation is computed starting from the individual stars at the locations of G2. The radiative transfer calculations are conducted with CLOUDY code and 2011 broadband and line luminosities are fitted. The spherically symmetric, tidally distorted, and magnetically arrested cloud shapes are tested with both the interstellar medium dust and 10 nm graphite dust. The best-fitting magnetically arrested model has the initial density n init = 1.8 × 105 cm-3, initial radius R init = 2.2 × 1015 cm = 17 mas, mass m cloud = 4 M Earth, and dust relative abundance A = 0.072. It provides a good fit to 2011 data, is consistent with the luminosities in 2004 and 2008, and reaches an agreement with the observed size. We revise down the predicted radio and X-ray bow shock luminosities to be below the quiescent level of Sgr A*, which readily leads to non-detection in agreement to observations. The magnetic energy dissipation in the cloud at the pericenter coupled with more powerful irradiation may lead to an infrared source with an apparent magnitude m_{L^{\\prime }}\\approx 13.0. No shock into the cloud and no X-rays are expected from cloud squeezing by the ambient gas pressure. Larger than previously estimated cloud mass m cloud = (4-20) M Earth may produce a higher accretion rate and a brighter state of Sgr A* as the debris descend onto the BH.

Broadband Spectral Investigations of SGR J1550-5418 Bursts

NASA Technical Reports Server (NTRS)

Lin, Lin; Goegues, Ersin; Baring, Matthew G.; Granot, Jonathan; Kouveliotou, Chryssa; Kaneko, Yuki; van der Horst, Alexander; Gruber, David; von Kienlin, Andreas; Younes, George;

A determination of the mass of Sagittarius A* from its radio spectral and source size measurements

NASA Technical Reports Server (NTRS)

Melia, Fulvio; Jokipii, J. R.; Narayanan, Ajay

1992-01-01

There is growing evidence that Sgr A* may be a million solar mass black hole accreting from the Galactic center wind. A consideration of the spectral and source size characteristics associated with this process can offer at least two distinct means of inferring the mass M, complementing the more traditional dynamical arguments. We show that M is unmistakably correlated with both the radio spectral index and the critical wavelength below which the intrinsic source size dominates over the angular broadening due to scattering in the interstellar medium. Current observations can already rule out a mass much in excess of 2 x 10 exp 6 solar masses and suggest a likely value close to 1 x 10 exp 6 solar masses, in agreement with an earlier study matching the radio and high-energy spectral components. We anticipate that such a mass may be confirmed with the next generation of source-size observations using milliarcsecond angular resolution at 0.5 - 1 cm wavelengths.

The Second Galactic Center Black Hole? A Possible Detection of Ionized Gas Orbiting around an IMBH Embedded in the Galactic Center IRS13E Complex

NASA Astrophysics Data System (ADS)

Tsuboi, Masato; Kitamura, Yoshimi; Tsutsumi, Takahiro; Uehara, Kenta; Miyoshi, Makoto; Miyawaki, Ryosuke; Miyazaki, Atsushi

2017-11-01

The Galactic Center is the nuclear region of the nearest spiral galaxy, the Milky Way, and contains the supermassive black hole with M˜ 4× {10}6 {M}⊙ , Sagittarius A* (Sgr A*). One of the basic questions about the Galactic Center is whether or not Sgr A* is the only “massive” black hole in the region. The IRS13E complex is a very intriguing infrared (IR) object that contains a large dark mass comparable to the mass of an intermediate mass black hole (IMBH) from the proper motions of the main member stars. However, the existence of the IMBH remains controversial. There are some objections to accepting the existence of the IMBH. In this study, we detected ionized gas with a very large velocity width ({{Δ }}{v}{FWZI}˜ 650 km s-1) and a very compact size (r˜ 400 au) in the complex using the Atacama Large Millimeter/submillimeter Array (ALMA). We also found an extended component connecting with the compact ionized gas. The properties suggest that this is an ionized gas flow on the Keplerian orbit with high eccentricity. The enclosed mass is estimated to be {10}4 {M}⊙ by the analysis of the orbit. The mass does not conflict with the upper limit mass of the IMBH around Sgr A*, which is derived by the long-term astrometry with the Very Long Baseline Array (VLBA). In addition, the object probably has an X-ray counterpart. Consequently, a very fascinating possibility is that the detected ionized gas is rotating around an IMBH embedded in the IRS13E complex.

Identification of 4U 1849-31 with V1223 Sagittarii and discovery of optical pulsations

NASA Technical Reports Server (NTRS)

Steiner, J. E.; Schwartz, D. A.; Jablonski, F. J.; Busko, I. C.; Watson, M. G.; Pye, J. P.; Mchardy, I. M.

1981-01-01

The X-ray source 4U 1849-31 is identified with the 13 mag star V1223 Sgr, on the basis of a precise HEAO 1 modulation collimator X-ray position uniquely selected by the Ariel-5 sky survey location. It is shown by optical spectroscopy and photometry that V1223 Sgr is a cataclysmic variable, displaying a photometric period of 13.2 min that is interpreted as being due to the rotation of a degenerate dwarf. The similarity of this system to H2252-035 is noted.

High-Energy X-rays from J174545.5-285829, the Cannonball: a Candidate Pulsar Wind Nebula Associated with Sgr a East

NASA Technical Reports Server (NTRS)

Nynka, Melania; Hailey, Charles J.; Mori, Kaya; Baganoff, Frederick K.; Bauer, Franz E.; Boggs, Steven E.; Craig, William W.; Christensen, Finn E.; Gotthelf, Eric V.; Harrison, Fiona A.;

The Outburst Decay of the Low Magnetic Field Magnetar SGR 0418+5729

NASA Astrophysics Data System (ADS)

Rea, N.; Israel, G. L.; Pons, J. A.; Turolla, R.; Viganò, D.; Zane, S.; Esposito, P.; Perna, R.; Papitto, A.; Terreran, G.; Tiengo, A.; Salvetti, D.; Girart, J. M.; Palau, Aina; Possenti, A.; Burgay, M.; Göğüş, E.; Caliandro, G. A.; Kouveliotou, C.; Götz, D.; Mignani, R. P.; Ratti, E.; Stella, L.

2013-06-01

We report on the long-term X-ray monitoring of the outburst decay of the low magnetic field magnetar SGR 0418+5729 using all the available X-ray data obtained with RXTE, Swift, Chandra, and XMM-Newton observations from the discovery of the source in 2009 June up to 2012 August. The timing analysis allowed us to obtain the first measurement of the period derivative of SGR 0418+5729: \\dot{P}=4(1)\\times 10^{-15} s s-1, significant at a ~3.5σ confidence level. This leads to a surface dipolar magnetic field of B dip ~= 6 × 1012 G. This measurement confirms SGR 0418+5729 as the lowest magnetic field magnetar. Following the flux and spectral evolution from the beginning of the outburst up to ~1200 days, we observe a gradual cooling of the tiny hot spot responsible for the X-ray emission, from a temperature of ~0.9 to 0.3 keV. Simultaneously, the X-ray flux decreased by about three orders of magnitude: from about 1.4 × 10-11 to 1.2 × 10-14 erg s-1 cm-2. Deep radio, millimeter, optical, and gamma-ray observations did not detect the source counterpart, implying stringent limits on its multi-band emission, as well as constraints on the presence of a fossil disk. By modeling the magneto-thermal secular evolution of SGR 0418+5729, we infer a realistic age of ~550 kyr, and a dipolar magnetic field at birth of ~1014 G. The outburst characteristics suggest the presence of a thin twisted bundle with a small heated spot at its base. The bundle untwisted in the first few months following the outburst, while the hot spot decreases in temperature and size. We estimate the outburst rate of low magnetic field magnetars to be about one per year per galaxy, and we briefly discuss the consequences of such a result in several other astrophysical contexts.

A formal method for identifying distinct states of variability in time-varying sources: SGR A* as an example

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meyer, L.; Witzel, G.; Ghez, A. M.

2014-08-10

Continuously time variable sources are often characterized by their power spectral density and flux distribution. These quantities can undergo dramatic changes over time if the underlying physical processes change. However, some changes can be subtle and not distinguishable using standard statistical approaches. Here, we report a methodology that aims to identify distinct but similar states of time variability. We apply this method to the Galactic supermassive black hole, where 2.2 μm flux is observed from a source associated with Sgr A* and where two distinct states have recently been suggested. Our approach is taken from mathematical finance and works withmore » conditional flux density distributions that depend on the previous flux value. The discrete, unobserved (hidden) state variable is modeled as a stochastic process and the transition probabilities are inferred from the flux density time series. Using the most comprehensive data set to date, in which all Keck and a majority of the publicly available Very Large Telescope data have been merged, we show that Sgr A* is sufficiently described by a single intrinsic state. However, the observed flux densities exhibit two states: noise dominated and source dominated. Our methodology reported here will prove extremely useful to assess the effects of the putative gas cloud G2 that is on its way toward the black hole and might create a new state of variability.« less

Chandra X-Ray Observatory Image of Sagittarius A

NASA Technical Reports Server (NTRS)

2003-01-01

A 2 week observation through the optic eye of the Chandra X-Ray Observatory revealed this sturning explosion occurring in the super massive black hole at the Milky Way's center, known as Sagittarius A or Sgr A*. Huge lobes of 20-million degree Centigrade gas ( red loops in image) flank both sides of the black hole and extend over dozens of light years indicating that enormous explosions occurred several times over the last 10 thousand years. Weighing in at 3-million times the mass of the sun, the Sgr A* is a starved black hole, possibly because explosive events in the past have cleared much of the gas around it.

History of Chandra X-Ray Observatory

NASA Image and Video Library

2003-01-06

A 2 week observation through the optic eye of the Chandra X-Ray Observatory revealed this sturning explosion occurring in the super massive black hole at the Milky Way's center, known as Sagittarius A or Sgr A*. Huge lobes of 20-million degree Centigrade gas ( red loops in image) flank both sides of the black hole and extend over dozens of light years indicating that enormous explosions occurred several times over the last 10 thousand years. Weighing in at 3-million times the mass of the sun, the Sgr A* is a starved black hole, possibly because explosive events in the past have cleared much of the gas around it.

A General Relativistic Null Hypothesis Test with Event Horizon Telescope Observations of the Black Hole Shadow in Sgr A*

NASA Astrophysics Data System (ADS)

Psaltis, Dimitrios; Özel, Feryal; Chan, Chi-Kwan; Marrone, Daniel P.

2015-12-01

The half opening angle of a Kerr black hole shadow is always equal to (5 ± 0.2)GM/Dc2, where M is the mass of the black hole and D is its distance from the Earth. Therefore, measuring the size of a shadow and verifying whether it is within this 4% range constitutes a null hypothesis test of general relativity. We show that the black hole in the center of the Milky Way, Sgr A*, is the optimal target for performing this test with upcoming observations using the Event Horizon Telescope (EHT). We use the results of optical/IR monitoring of stellar orbits to show that the mass-to-distance ratio for Sgr A* is already known to an accuracy of ∼4%. We investigate our prior knowledge of the properties of the scattering screen between Sgr A* and the Earth, the effects of which will need to be corrected for in order for the black hole shadow to appear sharp against the background emission. Finally, we explore an edge detection scheme for interferometric data and a pattern matching algorithm based on the Hough/Radon transform and demonstrate that the shadow of the black hole at 1.3 mm can be localized, in principle, to within ∼9%. All these results suggest that our prior knowledge of the properties of the black hole, of scattering broadening, and of the accretion flow can only limit this general relativistic null hypothesis test with EHT observations of Sgr A* to ≲10%.

Transient Events in Archival Very Large Array Observations of the Galactic Center

NASA Astrophysics Data System (ADS)

Chiti, Anirudh; Chatterjee, Shami; Wharton, Robert; Cordes, James; Lazio, T. Joseph W.; Kaplan, David L.; Bower, Geoffrey C.; Croft, Steve

2016-12-01

The Galactic center has some of the highest stellar densities in the Galaxy and a range of interstellar scattering properties, which may aid in the detection of new radio-selected transient events. Here, we describe a search for radio transients in the Galactic center, using over 200 hr of archival data from the Very Large Array at 5 and 8.4 GHz. Every observation of Sgr A* from 1985 to 2005 has been searched using an automated processing and detection pipeline sensitive to transients with timescales between 30 s and 5 minutes with a typical detection threshold of ˜100 mJy. Eight possible candidates pass tests to filter false-positives from radio-frequency interference, calibration errors, and imaging artifacts. Two events are identified as promising candidates based on the smoothness of their light curves. Despite the high quality of their light curves, these detections remain suspect due to evidence of incomplete subtraction of the complex structure in the Galactic center, and apparent contingency of one detection on reduction routines. Events of this intensity (˜100 mJy) and duration (˜100 s) are not obviously associated with known astrophysical sources, and no counterparts are found in data at other wavelengths. We consider potential sources, including Galactic center pulsars, dwarf stars, sources like GCRT J1745-3009, and bursts from X-ray binaries. None can fully explain the observed transients, suggesting either a new astrophysical source or a subtle imaging artifact. More sensitive multiwavelength studies are necessary to characterize these events, which, if real, occur with a rate of {14}-12+32 {{hr}}-1 {\\deg }-2 in the Galactic center.

Pulsar and CV Observations

NASA Astrophysics Data System (ADS)

Malina, R. F.

PSR_0656+14: Measurement of surface thermal emission from neutron stars (NS) is essential to theories regarding the condensed matter state equation, the thermal evolution of NS, and of NS atmospheres. We propose to conduct 50 Ang band FUV photometric observations of PSR B0656+14, an X-ray, SXR and EUV bright isolated NS with an optical counterpart. FUV photometry will provide critical characterization of the NS's surface thermal radiation. Higher energy observations may be effected by poorly established effects including magnetized atmospheres, chemical compositions, temperature gradients and gravitational effects. Optical observations may be subject to non-thermal effects. V3885 Sgr: V3885 Sgr is one of the brightest nonmagnetic cataclysmic variables. We propose to observe V3885 Sgr for 5 to 6 contiguous FUSE orbits, achieving a S/N of about 12 at full resolution even at the troughs of the source's O VI absorption lines in each spectrum (assuming 2000 sec visibility per orbit). The primary purpose of the observations is to use the source as a bright continuum against which to study local interstellar absorption lines. Although observed on Malina's Co-I Program, the data will be analyzed in collaboration with members of the O VI Project.

Forming Stars Near Our Supermassive Black Hole

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-01-01

Is it possible to form stars in the immediate vicinity of the hostile supermassive black hole at the center of our galaxy? New evidence suggests that nature has found a way.Infrared view of the central 300 light-years of our galaxy. [Hubble: NASA/ESA/Q.D. Wang; Spitzer: NASA/JPL/S. Stolovy]Too Hostile for Stellar Birth?Around Sgr A*, the supermassive black hole lurking at the Milky Ways center, lies a population of 200 massive, young, bright stars. Their very tight orbits around the black hole pose a mystery: did these intrepid stars somehow manage to form in situ, or did they instead migrate to their current locations from further out?For a star to be born out of a molecular cloud, the self-gravity of the cloud clump must be stronger than the other forces its subject to. Close to a supermassive black hole, the brutal tidal forces of the black hole dominate over all else. For this reason, it was thought that stars couldnt form in the hostile environment near a supermassive black hole until clues came along suggesting otherwise.Science as an Iterative ProcessVery Large Array observations of candidate photoevaporative protoplanetary disks discovered in 2015. [Yusef-Zadeh et al. 2015]Longtime AAS Nova readers might recall that one of our very first highlights on the site, back in August of 2015, was of a study led by Farhad Yusef-Zadeh of Northwestern University. In this study, the authors presented observations of candidate proplyds photoevaporative protoplanetary disks suggestive of star formation within a few light-years of the galactic center.While these observations seemed to indicate that stars might, even now, be actively forming near Sgr A*, they werent conclusive evidence. Follow-up observations of these and other signs of possible star formation were hindered by the challenges of observing the distant and crowded galactic center.Two and a half years later, Yusef-Zadeh and collaborators are back now aided by high-resolution and high-sensitivity observations of the galactic center made with the Atacama Large Millimeter-Submillimeter Array (ALMA). And this time, they consider what they found to be conclusive.ALMA observations of BP1, one of 11 bipolar outflows signatures of star formation discovered within the central few light-years of our galaxy. BP1 is shown in context at left and zoomed in at right; click for a closer look.[Yusef-Zadeh et al. 2017]Unambiguous SignaturesThe authors deep ALMA observations of the galactic center revealed the presence of 11 bipolar outflows within a few light-years of Sgr A*. These outflows appear as approaching and receding lobes of dense gas that were likely swept up by the jets created as stars were formed within the last 10,000 years. Yusef-Zadeh and collaborators argue that the bipolar outflows are unambiguous signatures of young protostars.Based on these sources, the authors calculate an approximate rate of star formation of 5 x 10-4 solar masses per year in this region. This is large enough that such low-mass star formation over the past few billion years could be a significant contributor to the stellar mass budget in the galactic center.Locations and orientations of the 11 bipolar outflows found. [Yusef-Zadeh et al. 2017]The question of how these stars were able to form so near the black hole remains open. Yusef-Zadeh and collaborators suggest the possibility of events that compress the host cloud, creating star-forming condensations with enough self-gravity to resist tidal disruption by Sgr A*s strong gravitational forces.To verify this picture, the next step is to build a detailed census of low-mass star formation at the galactic center. Were looking forward to seeing how this field has progressed by the next time we report on it!CitationF. Yusef-Zadeh et al 2017 ApJL 850 L30. doi:10.3847/2041-8213/aa96a2

Exploring molecular complexity with ALMA (EMoCA): Deuterated complex organic molecules in Sagittarius B2(N2)

NASA Astrophysics Data System (ADS)

Belloche, A.; Müller, H. S. P.; Garrod, R. T.; Menten, K. M.

2016-03-01

Context. Deuteration is a powerful tracer of the history of the cold prestellar phase in star-forming regions. Apart from methanol, little is known about deuterium fractionation of complex organic molecules in the interstellar medium, especially in regions forming high-mass stars. Aims: Our goal is to detect deuterated complex organic molecules toward the high mass star-forming region Sagittarius B2 (Sgr B2) and derive the level of deuteration for these molecules. Methods: We use a complete 3-mm spectral line survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA) to search for deuterated complex organic molecules toward the hot molecular core Sgr B2(N2). We constructed population diagrams and integrated intensity maps to fit rotational temperatures and emission sizes for each molecule. Column densities are derived by modeling the full spectrum under the assumption of local thermodynamic equilibrium. We compare the results to predictions of two astrochemical models that treat the deuteration process. Results: We report the detection of CH2DCN toward Sgr B2(N2) with a deuteration level of 0.4%, and tentative detections of CH2DOH, CH2DCH2CN, the chiral molecule CH3CHDCN, and DC3N with levels in the range 0.05%-0.12%. A stringent deuteration upper limit is obtained for CH3OD (<0.07%). Upper limits in the range 0.5-1.8% are derived for the three deuterated isotopologues of vinyl cyanide, the four deuterated species of ethanol, and CH2DOCHO. Ethyl cyanide is less deuterated than methyl cyanide by at least a factor five. The [CH2DOH]/[CH3OD] abundance ratio is higher than 1.8. It may still be consistent with the value obtained in Orion KL. Except for methyl cyanide, the measured deuteration levels lie at least a factor four below the predictions of current astrochemical models. The deuteration levels in Sgr B2(N2) are also lower than in Orion KL by a factor of a few up to a factor ten. Conclusions: The discrepancy between the deuteration levels of Sgr B2(N2) and the predictions of chemical models, and the difference between Sgr B2(N2) and Orion KL may both be due to the higher kinetic temperatures that characterize the Galactic center region compared to nearby clouds. Alternatively, they may result from a lower overall abundance of deuterium itself in the Galactic center region by up to a factor ten.

Evidence for the interaction of the IRS 16 wind with the ionized and molecular gas at the Galactic center

NASA Technical Reports Server (NTRS)

Yusef-Zadeh, Farhad; Wardle, Mark

1993-01-01

We present a number of high-resolution radio images showing evidence for the dynamical interaction of the outflow arising from the IRS 16 complex with the ionized gas associated with the Northern Arm of Sgr A West, and with the northwestern segment of the circumnuclear molecular disk which engulfs the inner few parsecs of the Galactic center. We suggest that the wind disturbs the dynamics of the Northern Arm within 0.1 pc of the center, is responsible for the waviness of the arm at larger distances, and is collimated by Sgr A West and the circumnuclear disk. The waviness is discussed in terms of the Rayleigh-Taylor instability induced by the ram pressure of the wind incident on the surface of the Northern Arm. Another consequence of this interaction is the strong mid-IR polarization of the Northern Arm in the vicinity of the IRS 16 complex which is explained as a result of the ram pressure of the wind compressing the gas and the magnetic field.

The discovery, monitoring and environment of SGR J1935+2154

NASA Astrophysics Data System (ADS)

Israel, G. L.; Esposito, P.; Rea, N.; Coti Zelati, F.; Tiengo, A.; Campana, S.; Mereghetti, S.; Rodriguez Castillo, G. A.; Götz, D.; Burgay, M.; Possenti, A.; Zane, S.; Turolla, R.; Perna, R.; Cannizzaro, G.; Pons, J.

2016-04-01

We report on the discovery of a new member of the magnetar class, SGR J1935+2154, and on its timing and spectral properties measured by an extensive observational campaign carried out between 2014 July and 2015 March with Chandra and XMM-Newton (11 pointings). We discovered the spin period of SGR J1935+2154 through the detection of coherent pulsations at a period of about 3.24 s. The magnetar is slowing down at a rate of dot{P} = 1.43(1)× 10^{-11} s s-1 and with a decreasing trend due to a negative ddot{P} of -3.5(7) × 10-19 s s-2. This implies a surface dipolar magnetic field strength of ˜2.2 × 1014 G, a characteristic age of about 3.6 kyr and a spin-down luminosity Lsd ˜1.7 × 1034 erg s-1. The source spectrum is well modelled by a blackbody with temperature of about 500 eV plus a power-law component with photon index of about 2. The source showed a moderate long-term variability, with a flux decay of about 25 per cent during the first four months since its discovery, and a re-brightening of the same amount during the second four months. The X-ray data were also used to study the source environment. In particular, we discovered a diffuse emission extending on spatial scales from about 1 arcsec up to at least 1 arcmin around SGR J1935+2154 both in Chandra and XMM-Newton data. This component is constant in flux (at least within uncertainties) and its spectrum is well modelled by a power-law spectrum steeper than that of the pulsar. Though a scattering halo origin seems to be more probable we cannot exclude that part, or all, of the diffuse emission is due to a pulsar wind nebula.

A C2H2-type zinc finger protein, SGR5, is involved in early events of gravitropism in Arabidopsis inflorescence stems.

PubMed

Morita, Miyo T; Sakaguchi, Keitaro; Kiyose, Shin-Ichiro; Taira, Kensuke; Kato, Takehide; Nakamura, Moritaka; Tasaka, Masao

2006-08-01

Plants can sense the direction of gravity and change the growth orientation of their organs. To elucidate the molecular mechanisms of gravity perception and the signal transduction of gravitropism, we have characterized a number of shoot gravitropism (sgr) mutants of Arabidopsis. The sgr5-1 mutant shows reduced gravitropism in the inflorescence stem but its root and hypocotyl have normal gravitropism. SGR5 encodes a zinc finger protein with a coiled-coil motif. The SGR5-GFP fusion protein is localized in the nucleus of Arabidopsis protoplasts, suggesting that SGR5 may act as a transcription factor. Analysis of GUS expression under the control of the SGR5 promoter revealed that SGR5 is mainly expressed in the endodermis, the gravity-sensing tissue in inflorescence stems. Furthermore, the observation that endodermis-specific expression of SGR5 using the SCR promoter in the sgr5-1 mutant restores shoot gravitropism indicates that it could function in the gravity-sensing endodermal cell layer. In contrast to other sgr mutants reported previously, almost all amyloplasts in the endodermal cells of the sgr5-1 mutant sedimented in the direction of gravity. Taken together, our results suggest that SGR5 may be involved in an early event in shoot gravitropism such as gravity perception and/or a signaling process subsequent to amyloplast sedimentation as a putative transcription factor in gravity-perceptive cells.

Merging parallel tempering with sequential geostatistical resampling for improved posterior exploration of high-dimensional subsurface categorical fields

NASA Astrophysics Data System (ADS)

Laloy, Eric; Linde, Niklas; Jacques, Diederik; Mariethoz, Grégoire

2016-04-01

The sequential geostatistical resampling (SGR) algorithm is a Markov chain Monte Carlo (MCMC) scheme for sampling from possibly non-Gaussian, complex spatially-distributed prior models such as geologic facies or categorical fields. In this work, we highlight the limits of standard SGR for posterior inference of high-dimensional categorical fields with realistically complex likelihood landscapes and benchmark a parallel tempering implementation (PT-SGR). Our proposed PT-SGR approach is demonstrated using synthetic (error corrupted) data from steady-state flow and transport experiments in categorical 7575- and 10,000-dimensional 2D conductivity fields. In both case studies, every SGR trial gets trapped in a local optima while PT-SGR maintains an higher diversity in the sampled model states. The advantage of PT-SGR is most apparent in an inverse transport problem where the posterior distribution is made bimodal by construction. PT-SGR then converges towards the appropriate data misfit much faster than SGR and partly recovers the two modes. In contrast, for the same computational resources SGR does not fit the data to the appropriate error level and hardly produces a locally optimal solution that looks visually similar to one of the two reference modes. Although PT-SGR clearly surpasses SGR in performance, our results also indicate that using a small number (16-24) of temperatures (and thus parallel cores) may not permit complete sampling of the posterior distribution by PT-SGR within a reasonable computational time (less than 1-2 weeks).

A GENERAL RELATIVISTIC NULL HYPOTHESIS TEST WITH EVENT HORIZON TELESCOPE OBSERVATIONS OF THE BLACK HOLE SHADOW IN Sgr A*

DOE Office of Scientific and Technical Information (OSTI.GOV)

Psaltis, Dimitrios; Özel, Feryal; Chan, Chi-Kwan

2015-12-01

The half opening angle of a Kerr black hole shadow is always equal to (5 ± 0.2)GM/Dc{sup 2}, where M is the mass of the black hole and D is its distance from the Earth. Therefore, measuring the size of a shadow and verifying whether it is within this 4% range constitutes a null hypothesis test of general relativity. We show that the black hole in the center of the Milky Way, Sgr A*, is the optimal target for performing this test with upcoming observations using the Event Horizon Telescope (EHT). We use the results of optical/IR monitoring of stellar orbits to showmore » that the mass-to-distance ratio for Sgr A* is already known to an accuracy of ∼4%. We investigate our prior knowledge of the properties of the scattering screen between Sgr A* and the Earth, the effects of which will need to be corrected for in order for the black hole shadow to appear sharp against the background emission. Finally, we explore an edge detection scheme for interferometric data and a pattern matching algorithm based on the Hough/Radon transform and demonstrate that the shadow of the black hole at 1.3 mm can be localized, in principle, to within ∼9%. All these results suggest that our prior knowledge of the properties of the black hole, of scattering broadening, and of the accretion flow can only limit this general relativistic null hypothesis test with EHT observations of Sgr A* to ≲10%.« less

Can Sgr A* flares reveal the molecular gas density PDF?

NASA Astrophysics Data System (ADS)

Churazov, E.; Khabibullin, I.; Sunyaev, R.; Ponti, G.

2017-11-01

Illumination of dense gas in the Central Molecular Zone by powerful X-ray flares from Sgr A* leads to prominent structures in the reflected emission that can be observed long after the end of the flare. By studying this emission, we learn about past activity of the supermassive black hole in our Galactic Center and, at the same time, we obtain unique information on the structure of molecular clouds that is essentially impossible to get by other means. Here we discuss how X-ray data can improve our knowledge of both sides of the problem. Existing data already provide (I) an estimate of the flare age, (II) a model-independent lower limit on the luminosity of Sgr A* during the flare and (III) an estimate of the total emitted energy during Sgr A* flare. On the molecular clouds side, the data clearly show a voids-and-walls structure of the clouds and can provide an almost unbiased probe of the mass/density distribution of the molecular gas with the hydrogen column densities lower than few 1023 cm-2. For instance, the probability distribution function of the gas density PDF(ρ) can be measured this way. Future high energy resolution X-ray missions will provide the information on the gas velocities, allowing, for example, a reconstruction of the velocity field structure functions and cross-matching the X-ray and molecular data based on positions and velocities.

Evolving Nonthermal Electron Distributions in Simulations of Sgr A*

NASA Astrophysics Data System (ADS)

Chael, Andrew; Narayan, Ramesh

2018-01-01

The accretion flow around Sagittarius A* (Sgr A*), the black hole at the Galactic Center, produces strong variability from the radio to X-rays on timescales of minutes to hours. This rapid, powerful variability is thought to be powered by energetic particle acceleration by plasma processes like magnetic reconnection and shocks. These processes can accelerate particles into non-thermal distributions which do not quickly isothermal in the low densities found around hot accretion flows. Current state-of-the-art simulations of accretion flows around black holes assume either a single-temperature gas or, at best, a two-temperature gas with thermal ions and electrons. We present results from incorporating the self-consistent evolution of a non-thermal electron population in a GRRMHD simulation of Sgr A*. The electron distribution is evolved across space, time, and Lorentz factor in parallel with background thermal ion, electron, and radiation fluids. Energy injection into the non-thermal distribution is modeled with a sub-grid prescription based on results from particle-in-cell simulations of magnetic reconnection. The energy distribution of the non-thermal electrons shows strong variability, and the spectral shape traces the complex interplay between the local viscous heating rate, magnetic field strength, and fluid velocity. Results from these simulations will be used in interpreting forthcoming data from the Event Horizon Telescope that resolves Sgr A*'s sub-mm variability in both time and space.

Discovery of ^{13}CCC in SgrB2(M)

NASA Astrophysics Data System (ADS)

Giesen, Thomas; Mookerjea, Bhaswati; Stutzki, Jürgen; Breier, Alexander A.; Buechling, Thomas; Fuchs, Guido W.

2017-06-01

Small carbon chain molecules like linear C_3 are thought to play a crucial role in the formation of larger, complex molecules, including pre-biotic species. The formation pathways of organic molecules with carbon chains as backbones is by far not well understood. Studies of isotope fractionation have proven to be a useful tool of tracing chemical reaction pathways and to elucidate formation and destruction processes of interstellar molecules. Recent velocity-resolved observations in the far-infrared have resulted in the detection of C_3 ro-vibrational transitions in the warm envelopes of star-forming hot cores W31C, W49N and DR21(OH). Multiple far-infrared transitions of C_3 have also been detected towards the Galactic center molecular clouds SgrB2(M) and Sgr B2(N). Since C^+ is involved in an important step of the formation route of the C_3 molecule, it is likely that effects of isotopic fractionation of C^+ will manifest itself in the ^{12}C_3/^{13}CCC and ^{12}C_3/C^{13}CC ratios as well. Based on high resolution THz- laboratory measurements of C_3 and its ^{13}C-isotopologues conducted at the Kassel laboratories, we used the GREAT-receiver onboard SOFIA for a first ever detection of ^{13}CCC towards SgrB2(M). In this talk we present results and possible implications of the observation.

CHANDRA OBSERVATIONS OF SGR 1627-41 NEAR QUIESCENCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

An, Hongjun; Kaspi, Victoria M.; Cumming, Andrew

2012-09-20

We report on an observation of SGR 1627-41 made with the Chandra X-Ray Observatory on 2011 June 16. Approximately three years after its outburst activity in 2008, the source's flux has been declining, as it approaches its quiescent state. For an assumed power-law spectrum, we find that the absorbed 2-10 keV flux for the source is 1.0{sup +0.3}{sub -0.2} Multiplication-Sign 10{sup -13} erg cm{sup -2} s{sup -1} with a photon index of 2.9 {+-} 0.8 (N{sub H} = 1.0 Multiplication-Sign 10{sup 23} cm{sup -2}). This flux is approximately consistent with that measured at the same time after the source's outburstmore » in 1998. With measurements spanning three years after the 2008 outburst, we analyze the long-term flux and spectral evolution of the source. The flux evolution is well described by a double exponential with decay times of 0.5 {+-} 0.1 and 59 {+-} 6 days, and a thermal cooling model fit suggests that SGR 1627-41 may have a hot core (T{sub c} {approx} 2 Multiplication-Sign 10{sup 8} K). We find no clear correlation between flux and spectral hardness as found in other magnetars. We consider the quiescent X-ray luminosities of magnetars and the subset of rotation-powered pulsars with high magnetic fields (B {approx}> 10{sup 13} G) in relation to their spin-inferred surface magnetic field strength and find a possible trend between the two quantities.« less

Chlorophyll a is a favorable substrate for Chlamydomonas Mg-dechelatase encoded by STAY-GREEN.

PubMed

Matsuda, Kaori; Shimoda, Yousuke; Tanaka, Ayumi; Ito, Hisashi

2016-12-01

Mg removal from chlorophyll by Mg-dechelatase is the first step of chlorophyll degradation. Recent studies showed that in Arabidopsis, Stay Green (SGR) encodes Mg-dechelatase. Though the Escherichia coli expression system is advantageous for investigating the properties of Mg-dechelatase, Arabidopsis Mg-dechelatase is not successfully expressed in E. coli. Chlamydomonas reinhardtii SGR (CrSGR) has a long, hydrophilic tail, suggesting that active CrSGR can be expressed in E. coli. After the incubation of chlorophyll a with CrSGR expressed in E. coli, pheophytin a accumulated, indicating that active CrSGR was expressed in E. coli. Substrate specificity of CrSGR against chlorophyll b and an intermediate molecule of the chlorophyll b degradation pathway was examined. CrSGR exhibited no activity against chlorophyll b and low activity against 7-hydroxymethyl chlorophyll a, consistent with the fact that chlorophyll b is degraded only after conversion to chlorophyll a. CrSGR exhibited low activity against divinyl chlorophyll a and chlorophyll a', and no activity against chlorophyllide a, protochlorophyll a, chlorophyll c 2 , and Zn-chlorophyll a. These observations indicate that chlorophyll a is the most favorable substrate for CrSGR. When CrSGR was expressed in Arabidopsis cells, the chlorophyll content decreased, further confirming that SGR has Mg-dechelating activity in chloroplasts. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

Actin dynamics involved in gravity perception in Arabidopsis inflorescense stem

NASA Astrophysics Data System (ADS)

Tasaka, Masao; Nakamura, Moritaka; Morita, Miyo T.

The amyloplasts sedimentation in the endodermal cells is important for gravity perception in Arabidopsis shoot. Our previous study suggests that SGR5(SHOOT GRAVITROPISM 5) and SGR9 are synergistically involved in regulation of amyloplast movement in these cells, and shows that sgr5 sgr9 double mutant completely loses gravitropic response. SGR5 encodes putative transcription factor and SGR9 encodes a ring finger containing protein, which surrounds amyloplasts. It has been reported that amyloplasts are surrounded by actin microfilaments (MFs), and that treatment with actin polymerization inhibitor enhances gravitropic organ curvature. However, not only the molecular link between amyolplasts and MFs, but also regulatory role of MFs in gravitropic response is still unclear. Here, we found that treatment with actin polymerization inhibitor restored gravitropic response of sgr5 sgr9 double mutant stems. The result suggests that abnormal amyloplasts movement in the double mutant could result from inhibition of MFs depolymerization, leading to abnormal gravitropism. We are investigating whether SGR5 and SGR9 are involved in amyloplasts movement by regulating actin remodeling in gravity perceptive cells.

Broadband Spectral Investigations of Magnetar Bursts

NASA Astrophysics Data System (ADS)

Kırmızıbayrak, Demet; Şaşmaz Muş, Sinem; Kaneko, Yuki; Göğüş, Ersin

2017-09-01

We present our broadband (2-250 keV) time-averaged spectral analysis of 388 bursts from SGR J1550-5418, SGR 1900+14, and SGR 1806-20 detected with the Rossi X-ray Timing Explorer (RXTE) here and as a database in a companion web-catalog. We find that two blackbody functions (BB+BB), the sum of two modified blackbody functions (LB+LB), the sum of a blackbody function and a power-law function (BB+PO), and a power law with a high-energy exponential cutoff (COMPT) all provide acceptable fits at similar levels. We performed numerical simulations to constrain the best fitting model for each burst spectrum and found that 67.6% of burst spectra with well-constrained parameters are better described by the Comptonized model. We also found that 64.7% of these burst spectra are better described with the LB+LB model, which is employed in the spectral analysis of a soft gamma repeater (SGR) for the first time here, than with the BB+BB and BB+PO models. We found a significant positive lower bound trend on photon index, suggesting a decreasing upper bound on hardness, with respect to total flux and fluence. We compare this result with bursts observed from SGR and AXP (anomalous X-ray pulsar) sources and suggest that the relationship is a distinctive characteristic between the two. We confirm a significant anticorrelation between burst emission area and blackbody temperature, and find that it varies between the hot and cool blackbody temperatures differently than previously discussed. We expand on the interpretation of our results in the framework of a strongly magnetized neutron star.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kırmızıbayrak, Demet; Şaşmaz Muş, Sinem; Kaneko, Yuki

We present our broadband (2–250 keV) time-averaged spectral analysis of 388 bursts from SGR J1550−5418, SGR 1900+14, and SGR 1806−20 detected with the Rossi X-ray Timing Explorer ( RXTE ) here and as a database in a companion web-catalog. We find that two blackbody functions (BB+BB), the sum of two modified blackbody functions (LB+LB), the sum of a blackbody function and a power-law function (BB+PO), and a power law with a high-energy exponential cutoff (COMPT) all provide acceptable fits at similar levels. We performed numerical simulations to constrain the best fitting model for each burst spectrum and found that 67.6%more » of burst spectra with well-constrained parameters are better described by the Comptonized model. We also found that 64.7% of these burst spectra are better described with the LB+LB model, which is employed in the spectral analysis of a soft gamma repeater (SGR) for the first time here, than with the BB+BB and BB+PO models. We found a significant positive lower bound trend on photon index, suggesting a decreasing upper bound on hardness, with respect to total flux and fluence. We compare this result with bursts observed from SGR and AXP (anomalous X-ray pulsar) sources and suggest that the relationship is a distinctive characteristic between the two. We confirm a significant anticorrelation between burst emission area and blackbody temperature, and find that it varies between the hot and cool blackbody temperatures differently than previously discussed. We expand on the interpretation of our results in the framework of a strongly magnetized neutron star.« less

Far-IR spectroscopy of the galactic center: Neutral and ionized gas in the central 10 pc of the galaxy

NASA Technical Reports Server (NTRS)

Hollenbach, D. J.; Watson, D. M.; Townes, C. H.; Dinerstein, H. L.; Hollenbach, D.; Lester, D. F.; Werner, M.; Storey, J. W. V.

1983-01-01

The 3P1 - 3P2 fine structure line emission from neutral atomic oxygen at 63 microns in the vicinity of the galactic center was mapped. The emission is extended over more than 4' (12 pc) along the galactic plane, centered on the position of Sgr A West. The line center velocities show that the O I gas is rotating around the galactic center with an axis close to that of the general galactic rotation, but there appear also to be noncircular motions. The rotational velocity at R is approximately 1 pc corresponds to a mass within the central pc of about 3 x 10(6) solar mass. Between 1 and 6 pc from the center the mass is approximately proportional to radius. The (O I) line probability arises in a predominantly neutral, atomic region immediately outside of the ionized central parsec of out galaxy. Hydrogen densities in the (O I) emitting region are 10(3) to 10(6) cm(-3) and gas temperatures are or = 100 K. The total integrated luminosity radiated in the line is about 10(5) solar luminosity, and is a substantial contribution to the cooling of the gas. Photoelectric heating or heating by ultraviolet excitation of H2 at high densities (10(5) cm(-3)) are promising mechanisms for heating of the gas, but heating due to dissipation of noncircular motions of the gas may be an alternative possibility. The 3P1 - 3P0 fine structure line of (O III) at 88 microns toward Sgr A West was also detected. The (O III) emission comes from high density ionized gas (n 10(4) cm(-3)), and there is no evidence for a medium density region (n 10(3) cm(-3)), such as the ionized halo in Sgr A West deduced from radio observations. This radio halo may be nonthermal, or may consist of many compact, dense clumps of filaments on the inner edges of neutral condensations at R or = 2 pc.

Adaptive thermal control of stem gravitropism through alternative RNA splicing in Arabidopsis

PubMed Central

Ryu, Jae Yong; Kim, Joo-Young; Park, Chung-Mo

2015-01-01

Gravitropism is an important growth movement in response to gravity in virtually all higher plants: the roots showing positive gravitropism and the shoots showing negative gravitropism. The gravitropic orientation of plant organs is also influenced by environmental factors, such as light and temperature. It is known that a zinc finger (ZF)-containing transcription factor SHOOT GRAVITROPISM 5/INDETERMINATE DOMAIN 15 (SGR5/IDD15) mediates the early events of gravitropic responses occurring in inflorescence stems. We have recently found that SGR5 gene undergoes alternative splicing to produce 2 protein variants, the full-size SGR5α transcription factor and the truncated SGR5β form lacking functional ZF motifs. The SGR5β form inhibits SGR5α function possibly by forming nonfunctional heterodimers that are excluded from DNA binding. Notably, SGR5 alternative splicing is accelerated at high temperatures, resulting in a high-level accumulation of SGR5β proteins. Accordingly, transgenic plants overexpressing SGR5β exhibit a reduction in the negative gravitropism of inflorescence stems, as observed in the SGR5-defective mutant. It is proposed that the thermos-responsive alternative splicing of SGR5 gene provides an adaptation strategy by which plants protect the shoots from aerial heat frequently occurring in natural habitats. PMID:26452406

Adaptive thermal control of stem gravitropism through alternative RNA splicing in Arabidopsis.

PubMed

Ryu, Jae Yong; Kim, Joo-Young; Park, Chung-Mo

2015-01-01

Gravitropism is an important growth movement in response to gravity in virtually all higher plants: the roots showing positive gravitropism and the shoots showing negative gravitropism. The gravitropic orientation of plant organs is also influenced by environmental factors, such as light and temperature. It is known that a zinc finger (ZF)-containing transcription factor SHOOT GRAVITROPISM 5/INDETERMINATE DOMAIN 15 (SGR5/IDD15) mediates the early events of gravitropic responses occurring in inflorescence stems. We have recently found that SGR5 gene undergoes alternative splicing to produce 2 protein variants, the full-size SGR5α transcription factor and the truncated SGR5β form lacking functional ZF motifs. The SGR5β form inhibits SGR5α function possibly by forming nonfunctional heterodimers that are excluded from DNA binding. Notably, SGR5 alternative splicing is accelerated at high temperatures, resulting in a high-level accumulation of SGR5β proteins. Accordingly, transgenic plants overexpressing SGR5β exhibit a reduction in the negative gravitropism of inflorescence stems, as observed in the SGR5-defective mutant. It is proposed that the thermos-responsive alternative splicing of SGR5 gene provides an adaptation strategy by which plants protect the shoots from aerial heat frequently occurring in natural habitats.

Assisted stellar suicide in V617 Sagittarii

NASA Astrophysics Data System (ADS)

Steiner, J. E.; Oliveira, A. S.; Cieslinski, D.; Ricci, T. V.

2006-02-01

Context: .V617 Sgr is a V Sagittae star - a group of binaries thought to be the galactic counterparts of the Compact Binary Supersoft X-ray Sources - CBSS. Aims: .To check this hypothesis, we measured the time derivative of its orbital period. Methods: .Observed timings of eclipse minima spanning over 30 000 orbital cycles are presented. Results: .We found that the orbital period evolves quite rapidly: P/dot{P} = 1.1×106 years. This is consistent with the idea that V617 Sgr is a wind driven accretion supersoft source. As the binary system evolves with a time-scale of about one million years, which is extremely short for a low mass evolved binary, it is likely that the system will soon end either by having its secondary completely evaporated or by the primary exploding as a supernova of type Ia. Conclusions: .

SGR 0418+5729, Swift J1822.3-1606, and 1E 2259+586 as massive, fast-rotating, highly magnetized white dwarfs

NASA Astrophysics Data System (ADS)

Boshkayev, K.; Izzo, L.; Rueda Hernandez, J. A.; Ruffini, R.

2013-07-01

Aims: We describe the so-called low magnetic field magnetars, SGR 0418+5729, Swift J1822.3-1606, and the AXP prototype 1E 2259+586 as massive, fast-rotating, highly magnetized white dwarfs. Methods: We give bounds for the mass, radius, moment of inertia, and magnetic field for these sources by requesting the stability of realistic, general relativistic, uniformly rotating white dwarfs. We also present the theoretical expectation of the infrared, optical, and ultraviolet emission of these objects and show their consistency with the current available observational data. Results: We improve the theoretical prediction of the lower limit of the spindown rate of SGR 0418+5729; for a white dwarf close to its maximum stable mass we obtain the very stringent interval for the spindown rate of 4.1 × 10-16 < Ṗ < 6 × 10-15, where the upper value is the known observational limit. A lower limit has been also set for Swift J1822.3-1606, whose spindown rate is not yet fully confirmed. Our model provides for the source Ṗ ≥ 2.13 × 10-15 if the star is close to its maximum stable mass. We give in addition the frequencies at which absorption features could be present in the spectrum of these sources as the result of the scattering of photons with the quantized electrons by the surface magnetic field.

Quantifying Intrinsic Variability of Sagittarius A* Using Closure Phase Measurements of the Event Horizon Telescope

NASA Astrophysics Data System (ADS)

Roelofs, Freek; Johnson, Michael D.; Shiokawa, Hotaka; Doeleman, Sheperd S.; Falcke, Heino

2017-09-01

General relativistic magnetohydrodynamic (GRMHD) simulations of accretion disks and jets associated with supermassive black holes show variability on a wide range of timescales. On timescales comparable to or longer than the gravitational timescale {t}G={GM}/{c}3, variation may be dominated by orbital dynamics of the inhomogeneous accretion flow. Turbulent evolution within the accretion disk is expected on timescales comparable to the orbital period, typically an order of magnitude larger than t G . For Sgr A*, t G is much shorter than the typical duration of a VLBI experiment, enabling us to study this variability within a single observation. Closure phases, the sum of interferometric visibility phases on a triangle of baselines, are particularly useful for studying this variability. In addition to a changing source structure, variations in observed closure phase can also be due to interstellar scattering, thermal noise, and the changing geometry of projected baselines over time due to Earth rotation. We present a metric that is able to distinguish the latter two from intrinsic or scattering variability. This metric is validated using synthetic observations of GRMHD simulations of Sgr A*. When applied to existing multi-epoch EHT data of Sgr A*, this metric shows that the data are most consistent with source models containing intrinsic variability from source dynamics, interstellar scattering, or a combination of those. The effects of black hole inclination, orientation, spin, and morphology (disk or jet) on the expected closure phase variability are also discussed.

Noise Strength Estimates of Three SGRs: Swift J1822.3-1606, SGR J1833-0832 and Swift J1834.9-0846

NASA Astrophysics Data System (ADS)

Serim, M. M.; Inam, S. Ç.; Baykal, A.

2012-12-01

We studied timing solutions of the three magnetars SWIFT J1822.3-1606, SGR J1833-0832 and Swift J1834.9-0846. We extracted the residuals of pulse arrival times with respect to the constant pulse frequency derivative. Using polynomial estimator techniques, we estimated the noise strengths of the sources. Our results showed that the noise strength and spin-down rate are strongly correlated, indicating that increase in spin-down rate leads to more torque noise on the magnetars. We are in progress of extending our analysis to the other magnetars.

Habitable Evaporated Cores and the Occurrence of Panspermia Near the Galactic Center

NASA Astrophysics Data System (ADS)

Chen, Howard; Forbes, John C.; Loeb, Abraham

2018-03-01

Black holes growing via the accretion of gas emit radiation that can photoevaporate the atmospheres of nearby planets. Here, we couple planetary structural evolution models of sub-Neptune-mass planets to the growth of the Milky Way’s central supermassive black hole, Sgr A*, and investigate how planetary evolution is influenced by quasar activity. We find that, out to ∼20 pc from Sgr A*, the XUV flux emitted during its quasar phase can remove several percent of a planet’s H/He envelope by mass; in many cases, this removal results in bare rocky cores, many of which are situated in the habitable zones of G-type stars. Near the Galactic Center, the erosion of sub-Neptune-sized planets may be one of the most prevalent channels by which terrestrial super-Earths are created. As such, the planet population demographics may be quite different close to Sgr A* than in the galactic outskirts. The high stellar densities in this region (about seven orders of magnitude greater than the solar neighborhood) imply that the distance between neighboring rocky worlds is short (500–5000 au). The proximity between potentially habitable terrestrial planets may enable the onset of widespread interstellar panspermia near the nuclei of our galaxy. More generally, we predict these phenomena to be ubiquitous for planets in nuclear star clusters and ultra-compact dwarfs. Globular clusters, on the other hand, are less affected by the central black holes.

VizieR Online Data Catalog: 4yr 1.3mm VLBI observations of SgrA* with EHT (Fish+, 2016)

NASA Astrophysics Data System (ADS)

Fish, V. L.; Johnson, M. D.; Doeleman, S. S.; Broderick, A. E.; Psaltis, D.; Lu, R.-S.; Akiyama, K.; Alef, W.; Algaba, J. C.; Asada, K.; Beaudoin, C.; Bertarini, A.; Blackburn, L.; Blundell, R.; Bower, G. C.; Brinkerink, C.; Cappallo, R.; Chael, A. A.; Chamberlin, R.; Chan, C.-K.; Crew, G. B.; Dexter, J.; Dexter, M.; Dzib, S. A.; Falcke, H.; Freund, R.; Friberg, P.; Greer, C. H.; Gurwell, M. A.; Ho, P. T. P.; Honma, M.; Inoue, M.; Johannsen, T.; Kim, J.; Krichbaum, T. P.; Lamb, J.; Leon-Tavares, J.; Loeb, A.; Loinard, L.; MacMahon, D.; Marrone, D. P.; Moran, J. M.; Moscibrodzka, M.; Ortiz-Leon, G. N.; Oyama, T.; Ozel, F.; Plambeck, R. L.; Pradel, N.; Primiani, R. A.; Rogers, A. E. E.; Rosenfeld, K.; Rottmann, H.; Roy, A. L.; Ruszczyk, C.; Smythe, D. L.; Soohoo, J.; Spilker, J.; Stone, J.; Strittmatter, P.; Tilanus, R. P. J.; Titus, M.; Vertatschitsch, L.; Wagner, J.; Wardle, J. F. C.; Weintroub, J.; Woody, D.; Wright, M.; Yamaguchi, P.; Young, A.; Young, K. H.; Zensus, J. A.; Ziurys, L. M.

2016-06-01

The Event Horizon Telescope (EHT) obtained detections of Sgr A* on closed triangles of baselines among stations in Arizona, California, and Hawaii in 2009, 2011, 2012, and 2013. In all cases, two 480MHz bands, centered at 229.089GHz and 229.601GHz (hereafter, low and high bands, respectively), were observed. One or more telescopes from each of three sites in Arizona, California, and Hawaii participated in each set of observations. The Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) on Mt. Graham, Arizona, was used in all cases. Over the years of data analyzed here, the configuration of VLBI recording at these sites evolved as described in section 2.1. (1 data file).

Recreating the chemical evolution of the Sagittarius dwarf spheroidal from its tidal debris

NASA Astrophysics Data System (ADS)

Carlin, Jeffrey L.; Sheffield, Allyson; Cunha, Katia M. L.; Smith, Verne V.

2018-06-01

We present a detailed chemical analysis of the Sagittarius (Sgr) tidal stream based on high-resolution Gemini+GRACES spectra of 42 members of the highest surface brightness portions of both the trailing and leading arms of the Sgr stream. We select Sgr tidal stream candidates using a 2MASS+WISE color-color selection, combined with LAMOST radial velocities, allowing us to efficiently select Sgr stream members with little contamination from field stars. Sgr is a recently infallen, currently disrupting dwarf spheroidal galaxy, with roughly 70% of the luminosity of the Sgr system residing in the tidal streams. With this study, we provide a link between the (known) chemical properties in the intact Sgr core and the significant portion of the Sgr system's luminosity that is estimated to currently reside in the streams. In this talk, we focus on abundances of alpha-elements, but we will also analyze neutron-capture (both r- and s-process) and iron-peak species. We compare our chemical abundances to the few existing measurements in the stream as well as the numerous results in the Sgr core.

The GBT PRIMOS Project - A Broadband Spectral Line Survey of SgrB2N from 300 MHz to 46 GHz

NASA Astrophysics Data System (ADS)

Remijan, Anthony J.; Hollis, J. M.; Jewell, P. R.; Lovas, F.; Corby, J.

2013-01-01

Broadband, very sensitive, high spectral resolution spectral line surveys in recent years have made profound impacts into the understanding of interstellar reaction processes and in the identification of new molecular material in astronomical environments. Molecular line surveys are studies of the spectra of astronomical sources over a wide and usually continuous range of frequencies in order to determine the chemical composition (i.e., "molecular inventory"), physical properties (temperature, density), and kinematics of such regions. The National Radio Astronomy Observatory's (NRAO) 100-m Robert C. Byrd Green Bank Telescope (GBT) PRebiotic Interstellar MOlecule Survey (PRIMOS) Legacy Project started in Jan 2008 and concluded in July 2011. The PRIMOS project recorded a nearly frequency-continuous astronomical spectrum from 300 MHz to 46 GHz towards the Sgr B2(N) molecular cloud, with the pointing position centered on the Large Molecule Heimat (LMH). The PRIMOS data have resulted in numerous new detections and discoveries in astrochemistry. The data have also been widely used to demonstrate advances in molecular astrophysics in a variety of venues and have been instrumental in training the next generation of astronomers and chemists. The GBT is the only telescope in the world capable of making these groundbreaking discoveries. This presentation will highlight the recent successes from the survey and how to access these publically-available observations.

NUMERICAL SIMULATIONS OF THE POSSIBLE ORIGIN OF THE TWO SUB-PARSEC SCALE AND COUNTERROTATING STELLAR DISKS AROUND SgrA*

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alig, C.; Schartmann, M.; Burkert, A.

2013-07-10

We present a high-resolution simulation of an idealized model to explain the origin of the two young, counterrotating, sub-parsec scale stellar disks around the supermassive black hole SgrA* at the center of the Milky Way. In our model, the collision of a single molecular cloud with a circumnuclear gas disk (similar to the one observed presently) leads to multiple streams of gas flowing toward the black hole and creating accretion disks with angular momentum depending on the ratio of cloud and circumnuclear disk material. The infalling gas creates two inclined, counterrotating sub-parsec scale accretion disks around the supermassive black holemore » with the first disk forming roughly 1 Myr earlier, allowing it to fragment into stars and get dispersed before the second counterrotating disk forms. Fragmentation of the second disk would lead to the two inclined, counterrotating stellar disks which are observed at the Galactic center. A similar event might be happening again right now at the Milky Way Galactic center. Our model predicts that the collision event generates spiral-like filaments of gas, feeding the Galactic center prior to disk formation with a geometry and inflow pattern that is in agreement with the structure of the so-called mini spiral that has been detected in the Galactic center.« less

Statistical Properties of SGR J1550-5418 Bursts

NASA Technical Reports Server (NTRS)

Gorgone, Nicholas M.

2010-01-01

Magnetars are slowly rotating neutron stars with extreme magnetic fields, over 10(exp 15) Gauss. Only few have been discovered in the last 30 years. These sources are dormant most of their lifetimes and become randomly active emitting multiple soft gamma-ray bursts. We present here our results on the temporal analysis of 300 bursts from Soft Gamma Repeater SGR J1550-5418 recorded with the Gamma-ray Burst Monitor (GBM) onboard the Fermi Observatory during its activation on January 22-29, 2009. We employed an un-triggered burst search in the energy range 8-100keV to collect all events from the source, besides the ones that triggered GBM. For the entire sample of bursts we determined their durations, rise and decay times. We study here the statistical properties of these characteristics and discuss how these may help us better understand the physical characteristics of the magnetar model.

77 FR 68891 - Medicare Program; Revisions to Payment Policies Under the Physician Fee Schedule, DME Face-to...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-11-16

... Area ICD International Classification of Diseases IMRT Intensity Modulated Radiation Therapy IOM... Stereotactic body radiation therapy SGR Sustainable growth rate TC Technical component TIN Tax identification... Clinical Lab Fee Schedule, which is unaffected by the misvalued code initiative. Radiation therapy centers...

NuSTAR results from the Galactic Center - diffuse emission

NASA Astrophysics Data System (ADS)

Hailey, Charles

2016-03-01

The Nuclear Spectroscopic Telescope Array (NuSTAR) was launched in June 2012. It carried the first true, hard X-ray (>~10 keV-79 keV) focusing telescopes into orbit. Its twin telescopes provide 10 times better angular resolution and 100 times better sensitivity than previously obtainable in the hard X-ray band. Consequently NuSTAR is able to resolve faint diffuse structures whose hard X-rays offer insight into some of the most energetic processes in the Galactic Center. One of the surprising discoveries that NuSTAR made in the Galactic Center is the central hard X-ray emission (CHXE). The CHXE is a diffuse emission detected from ~10 keV to beyond 50 keV in X-ray energy, and extending spatially over a region ~8 parsecs x ~4 parsecs in and out of the plane of the galaxy respectively, and centered on the supermassive black hole Sgr A*. The CHXE was speculated to be due to a large population of unresolved black hole X-ray binaries, millisecond pulsars (MSP), a class of highly magnetized white dwarf binaries called intermediate polars, or to particle outflows from Sgr A*. The presence of an unexpectedly large population of MSP in the Galactic Center would be particularly interesting, since MSP emitting at higher energies and over a much larger region have been posited to be the origin of the gamma-ray emission that is also ascribed to dark matter annihilation in the galaxy. In addition, the connection of the CHXE to the ~9000 unidentified X-ray sources in the central the the ~100 pc detected by the Chandra Observatory, to the soft X-ray emission detected by the Chandra and XMM/Newton observatories in the Galactic Center, and to the hard X-ray emission detected by both the RXTE and INTEGRAL observatories in the Galactic Ridge, is unclear. I review these results and present recent NuSTAR observations that potentially resolve the origin of the CHXE and point to a unified origin for all these X-ray emissions. Two other noteworthy classes of diffuse structures in the Galactic Center will be discussed. The first class are the giant molecular clouds, which are strong hard X-ray emitters. These hard X-rays are believed to be produced when one or more giant outbursts from the supermassive black hole Sgr A*, more than a century ago, resulted in hard X-rays being reflected from the clouds, and detected only today. I discuss how these hard X-rays are used to elucidate the past history of the supermassive black hole, and to compare and contrast these past giant outbursts with those observed from the supermassive black hole more recently. The second class are non-thermal filaments, magnetized structures with both radio and soft X-ray emission that have now been shown by NuSTAR to be hard X-ray emitters. The electrons generating the hard X-rays observed in one of these filaments are the most energetic that have been observed in the galaxy. The filaments are a heterogeneous class of hard X-ray emitters, and the various mechanisms by which they produce hard X-ray emission will be discussed. Future NuSTAR observations of the Galactic Center with NuSTAR will also be discussed.

Probing small-scale structure in galaxies with strong gravitational lensing

NASA Astrophysics Data System (ADS)

Congdon, Arthur Benjamin

We use gravitational lensing to study the small-scale distribution of matter in galaxies. First, we examine galaxies and their dark matter halos. Roughly half of all observed four-image quasar lenses have image flux ratios that differ from the values predicted by simple lens potentials. We show that smooth departures from elliptical symmetry fail to explain anomalous radio fluxes, strengthening the case for dark matter substructure. Our results have important implications for the "missing satellites'' problem. We then consider how time delays between lensed images can be used to identify lens galaxies containing small-scale structure. We derive an analytic relation for the time delay between the close pair of images in a "fold'' lens, and perform Monte Carlo simulations to investigate the utility of time delays for probing small- scale structure in realistic lens populations. We compare our numerical predictions with systems that have measured time delays and discover two anomalous lenses. Next, we consider microlensing, where stars in the lens galaxy perturb image magnifications. This is relevant at optical wavelengths, where the size of the lensed source is comparable to the Einstein radius of a typical star. Our simulations of negative-parity images show that raising the fraction of dark matter relative to stars increases image flux variability for small sources, and decreases it for large sources. This suggests that quasar accretion disks and broad-emission-line regions may respond differently to microlensing. We also consider extended sources with a range of ellipticities, which has relevance to a population of inclined accretion disks. Depending on their orientation, more elongated sources lead to more rapid variability, which may complicate the interpretation of microlensing light curves. Finally, we consider prospects for observing strong lensing by the supermassive black hole at the center of the Milky Way, Sgr A*. Assuming a black hole on the million- solar-mass scale, we predict that the probability of observing strong lensing of a background star is roughly 56%. We also consider how lensing by Sgr A* could be used to test general relativity against alternative theories, concluding that microarcsecond resolution would make this possible.

ISOTOPIC RATIOS OF {sup 18}O/{sup 17}O IN THE GALACTIC CENTRAL REGION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, J. S.; Sun, L. L.; Riquelme, D.

The {sup 18}O/{sup 17}O isotopic ratio of oxygen is a crucial measure of the secular enrichment of the interstellar medium by ejecta from high-mass versus intermediate-mass stars. So far, however, there is a lack of data, particularly from the Galactic center (GC) region. Therefore, we have mapped typical molecular clouds in this region in the J = 1–0 lines of C{sup 18}O and C{sup 17}O with the Delingha 13.7 m telescope (DLH). Complementary pointed observations toward selected positions throughout the GC region were obtained with the IRAM 30 m and Mopra 22 m telescopes. C{sup 18}O/C{sup 17}O abundance ratios reflectingmore » the {sup 18}O/{sup 17}O isotope ratios were obtained from integrated intensity ratios of C{sup 18}O and C{sup 17}O. For the first time, C{sup 18}O/C{sup 17}O abundance ratios are determined for Sgr C (V ∼ −58 km s{sup −1}), Sgr D (V ∼ 80 km s{sup −1}), and the 1.°3 complex (V ∼ 80 km s{sup −1}). Through our mapping observations, abundance ratios are also obtained for Sgr A (∼0 and ∼50 km s{sup −1} component) and Sgr B2 (∼60 km s{sup −1}), which are consistent with the results from previous single-point observations. Our frequency-corrected abundance ratios of the GC clouds range from 2.58 ± 0.07 (Sgr D, V ∼ 80 km s{sup −1}, DLH) to 3.54 ± 0.12 (Sgr A, ∼50 km s{sup −1}). In addition, strong narrow components (line width less than 5 km s{sup −1}) from the foreground clouds are detected toward Sgr D (−18 km s{sup −1}), the 1.°3 complex (−18 km s{sup −1}), and M+5.3−0.3 (22 km s{sup −1}), with a larger abundance ratio around 4.0. Our results show a clear trend of lower C{sup 18}O/C{sup 17}O abundance ratios toward the GC region relative to molecular clouds in the Galactic disk. Furthermore, even inside the GC region, ratios appear not to be uniform. The low GC values are consistent with an inside-out formation scenario for our Galaxy.« less

A QUANTITATIVE TEST OF THE NO-HAIR THEOREM WITH Sgr A* USING STARS, PULSARS, AND THE EVENT HORIZON TELESCOPE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Psaltis, Dimitrios; Wex, Norbert; Kramer, Michael

The black hole in the center of the Milky Way, Sgr A*, has the largest mass-to-distance ratio among all known black holes in the universe. This property makes Sgr A* the optimal target for testing the gravitational no-hair theorem. In the near future, major developments in instrumentation will provide the tools for high-precision studies of its spacetime via observations of relativistic effects in stellar orbits, in the timing of pulsars, and in horizon-scale images of its accretion flow. We explore here the prospect of measuring the properties of the black hole spacetime using all of these three types of observations.more » We show that the correlated uncertainties in the measurements of the black hole spin and quadrupole moment using the orbits of stars and pulsars are nearly orthogonal to those obtained from measuring the shape and size of the shadow the black hole casts on the surrounding emission. Combining these three types of observations will therefore allow us to assess and quantify systematic biases and uncertainties in each measurement and lead to a highly accurate, quantitative test of the gravitational no-hair theorem.« less

Scientists Discover Supernova May Control Activity in the Center of Our Galaxy

NASA Astrophysics Data System (ADS)

2001-02-01

10 January 2001 -- Scientists using NASA's Chandra X-ray Observatory have discovered that an apparent supernova remnant in the center of our galaxy might help regulate a nearby supermassive black hole and that such relationships between supernova remnants and black holes might be common throughout the universe. The scientists studied Sagittarius A East, previously known by its ring-shaped radio emission, located nearly 26,000 light years from Earth in the constellation Sagittarius. Sgr A East appears to surround the black hole Sagittarius A* (denoted with an asterisk because it is a point source that emits radio waves) with its center offset by about six light years from that of the black hole. Using Chandra, scientists were able to separate Sgr A East from other complex structures for the first time in X-ray wavelengths. The properties they discovered support the long-standing hypothesis that Sgr A East is a single supernova remnant that exploded about 10,000 years ago. "With Chandra, we found hot gas concentrated within the larger radio shell of Sgr A East," said Yoshitomo Maeda, an astronomy and astrophysics research associate at Penn State who presented the research team's results at the 197th national meeting of the American Astronomical Society in San Diego, California, on 10 January 2001. "The gas is highly enriched by heavy elements, with four times more calcium and iron than the Sun, and that confirms earlier suspicions that Sgr A East is most likely a remnant of a supernova explosion. While dozens of supernova remnants are known in our galaxy, the proximity of Sgr A East to the black hole in the center of our galaxy makes it important." After a supernova explosion, scientists believe two shock waves are formed, with one moving inward and one outward. The inward shock wave heated up the ejecta that was detected with X-rays by the Advanced CCD Imaging Spectrometer (ACIS) aboard Chandra. The temperature of gas in that shock wave was measured at 20 million degrees by Chandra. Scientists believe the outward shock wave moved the cooler, heavier gas that comprises the intergalactic medium--compressing and plowing that gas past the black hole as the shock wave spread and feeding the black hole in the process. They believe the result was a period of intense feeding of material into the black hole, followed by a period of black hole "starvation." "The important question to be raised here is what effect the plowed gas has on its environment," said Frederick Baganoff, a research associate at Massachusetts Institute of Technology and lead scientist for Chandra's Galactic Center project. "It is possible that the plowed gas has passed over the supermassive black hole at some time in the recent past. During the passage, a lot of gas could have been captured by the black hole." When black holes pull matter inward, they are able to accelerate those particles to almost the speed of light. The matter accreting into a black hole releases a great deal of energy, much of it in X rays that can ionize the surrounding gas and make it visible with instruments such as ACIS. Because X-ray emissions from the black hole are weak at this time, scientists believe the shock wave already has passed by the black hole. "Radio astronomers already found that the gas in a halo surrounding Sgr A East and the supermassive black hole is largely ionized," said Mark Morris, professor of astronomy and physics at the University of California at Los Angeles. "If the gas plowed by the supernova remnant was pushed past the black hole, the spectacular interaction would very possibly have occurred as recently as a few hundred years ago, and the resulting flash of energy would likely have irradiated and ionized the surrounding gas. This could explain why the ionization of the gas still survives." In a broader sense, that activity might serve as a model for other black holes and other phenomena throughout the universe because the Chandra scientists suggest supernova explosions might regulate the activity of those phenomena. Many scientists believe black holes thrive at the center of most galaxies and when those black holes accrete material, scientists can detect an active galactic nucleus with X rays. According to the Chandra scientists, individual supernova explosions might be relevant for providing material that activates the accretion activity of black holes, thereby turning the active nucleus on and off. The Chandra observations were made 21 September 1999 using ACIS, which was conceived and developed for NASA by Penn State and Massachusetts Institute of Technology under the leadership of Gordon Garmire, Evan Pugh Professor of Astronomy and Astrophysics at Penn State. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. TRW, Inc., of Redondo Beach, California, is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Massachusetts. The ACIS detector is a sophisticated version of the CCD detectors commonly used in digital cameras or video cameras. Chandra carries an X-ray telescope to focus the X-rays from objects in the sky. An X-ray telescope cannot work on the ground because X-rays are absorbed by the Earth's atmosphere. The Chandra X-ray Observatory is the third of NASA's "Great Observatories," following the Hubble Space Telescope and the Compton Gamma-Ray Observatory. Along with Maeda and Garmire, the Penn State contingent of collaborators for results of this research presented at the astronomical society meeting comprises: Niel Brandt, David Burrows, Eric Feigelson, and Leisa Townsley. Along with Baganoff and Morris, other collaborators include: Mark Bautz, John Doty, and George Ricker from Massachusetts Institute of Technology; and Steve Pravdo from the Jet Propulsion Laboratory. This research is supported by NASA contract NAS 8-38252 and, in part, by the Jet Propulsion Laboratory, under contract with NASA. Images associated with this release are available on the World Wide Web at: http://chandra.harvard.edu AND http://chandra.nasa.gov

Long-term monitoring of Sgr A* at 7 mm with VERA and KaVA

NASA Astrophysics Data System (ADS)

Akiyama, K.; Kino, M.; Sohn, B.; Lee, S.; Trippe, S.; Honma, M.

2014-05-01

We present the results of radio monitoring observations of Sgr A* at 7 mm (i.e. 43 GHz) with the VLBI Exploration of Radio Astrometry (VERA), which is a VLBI array in Japan. VERA provides angular resolution on millisecond scales, resolving structures within 100 Schwarzschild radii of Sgr A* , similar to the Very Large Baseline Array (VLBA). We performed multi-epoch observations of Sgr A* in 2005 - 2008, and started monitoring it again with VERA from 2013 January to trace the current G2 encounter event. Our preliminary results in 2013 show that Sgr A* on mas scales has been in an ordinary state as of August 2013, although some fraction of the G2 cloud already passed the pericenter of Sgr A* in April 2013. We will continue monitoring Sgr A* with VERA and the newly developed KaVA (KVN and VERA Array).

Probing the Interstellar Dust towards the Galactic Centre using X-ray Dust Scattering Halos

NASA Astrophysics Data System (ADS)

Jin, C.; Ponti, G.; Haberl, F.; Smith, R.

2017-10-01

Dust scattering creates an X-ray halo that contains abundant information about the interstellar dust along the source's line-of-sight (LOS), and is most prominent when the LOS nH is high. In this talk, I will present results from our latest study of a bright dust scattering halo around an eclipsing X-ray binary at 1.45 arcmin away from Sgr A*, namely AX J1745.6-2901. This study is based on a large set of XMM-Newton and Chandra observations, and is so-far the best dust scattering halo study of a X-ray transient in the Galactic centre (GC). I will show that the foreground dust of AX J1745.6-2901 can be decomposed into two major thick dust layers. One layer contains (66-81)% of the total LOS dust and is several kpc away from the source, and so is most likely to reside in the Galactic disc. The other layer is local to the source. I will also show that the dust scattering halo can cause the source spectrum to severely depend on the source extraction region. Such spectral bias can be corrected by our new Xspec model, which is likely to be applicable to Sgr A* and other GC sources as well.

SETI among galaxies by virtue of black holes

NASA Astrophysics Data System (ADS)

Maccone, Claudio

2012-09-01

In two recent papers (Refs. Maccone (2011, 2009) [1,2]) this author proved that the radio communications among any pair of stars within our Galaxy are feasible with modest transmitted powers if the gravitational lenses of both stars are exploited. In the present paper we extend those innovative results to the case of radio communications among nearby galaxies. We show that the radio communications among galaxies may become feasible if the supermassive black holes, usually located at the center of galaxies, are exploited as gravitational lenses. In other words, a massive black hole may be regarded as a huge focusing device for radio waves being transmitted out of that galaxy and/or being received from another galaxy. This happens because a black hole is such a highly massive and compact object that all electromagnetic waves flying by its surface are highly deflected by its gravitational field and made to focus at a comparatively short distance from the black hole itself.Next we consider the possibility of building radio bridges between our own Galaxy (the Milky Way) and other nearby galaxies. This possibility is serious because, since 1974, astronomers have come to known that a supermassive black hole called Sagittarius A* does exist at the center of our Galaxy. In 2002 its mass was estimated to be of the order of 2.6 million solar masses, and in 2008 this estimate was increased to 4.31 million solar masses. Furthermore, in 2004 a team of astronomers reported the discovery of a potential intermediate-class black hole called GCIRS 13E orbiting around SgrA* at about three light-years and having an estimated mass of 1,300 solar masses. These two big black holes could be our Galaxy's “antennae” for communications with alien civilizations harboring in other nearby galaxies.We mathematically show that the following radio bridges may be created between SgrA* and the supermassive black hole located at the center of the nearby galaxies:The SgrA*-Andromeda's (M31) P2 Black Hole radio bridge, having the distance of 2.5 million light years. The P2 Andromeda black hole is estimated to have a mass of about 40 million solar masses.The SgrA*-M32 (a dwarf elliptical galaxy satellite of Andromeda-M31) radio bridge, with a 2.65 million light year distance. The M32 black hole is estimated to have a mass of about 3 million solar masses.The SgrA*-M106 (also called NGC 4258, a spiral galaxy with anomalous arms) radio bridge, at about 24 million light years. The M106 black hole is estimated to have a mass of about 40 million solar masses.The SgrA*-Sombrero Galaxy (also called M104 or NGC 4594, an unbarred spiral galaxy) at a distance of 29.3 million light years. Its black hole is estimated to have a mass of 1 billion solar masses.The SgrA*-M87 radio bridge. M87 is the supergiant elliptical galaxy located at the center of the super-cluster of galaxies to which we belong, i.e. the Local Super Cluster, at the edge of which we are located. The distance between M87 and us is 53.5 million light years in the direction of the constellation of Virgo, which is why M87 and its surrounding clusters of galaxies are sometimes referred to as the Virgo Super Cluster. At the center of M87 is a supermassive black hole estimated to have a mass of 6.4 billion solar masses. M87 is also well known as “the jet galaxy” since a jet of energetic plasma originates at the core and extends out at least 5000 light-years.The conclusion that we draw from the mathematics describing these radio bridges across huge inter-galactic distances is surprising: they all perform better that the simple Sun-Alpha Cen A radio bridge, first studied in detail by this author in Ref. [1]. In other words, the powers necessary to keep the radio link between SgrA* and all of the above big black holes located in other nearby galaxies are smaller than the powers requested to keep the radio bridge between the Sun and Alpha Cen A. In other words still, despite inter-galactic distances are huge with respect to ordinary interstellar distances within the Milky Way, the black hole masses in the game are so much huger than the stellar masses than the intergalactic bridges perform better than the interstellar bridges. This unexpected and new result might have profound consequences on SETI done currently by Humans on Earth. In fact, more advanced civilizations might already have built such intergalactic radio-bridges. Thus our SETI searches should be tuned-up to match with this new situation, and the conclusion is that the possibility of SETI signals reaching us from other galaxies should not be ruled out.

An expanding radio nebula produced by a giant flare from the magnetar SGR 1806-20.

PubMed

Gaensler, B M; Kouveliotou, C; Gelfand, J D; Taylor, G B; Eichler, D; Wijers, R A M J; Granot, J; Ramirez-Ruiz, E; Lyubarsky, Y E; Hunstead, R W; Campbell-Wilson, D; van der Horst, A J; McLaughlin, M A; Fender, R P; Garrett, M A; Newton-McGee, K J; Palmer, D M; Gehrels, N; Woods, P M

2005-04-28

Soft gamma-ray repeaters (SGRs) are 'magnetars', a small class of slowly spinning neutron stars with extreme surface magnetic fields, B approximately 10(15) gauss (refs 1 , 2 -3). On 27 December 2004, a giant flare was detected from the magnetar SGR 1806-20 (ref. 2), only the third such event recorded. This burst of energy was detected by a variety of instruments and even caused an ionospheric disturbance in the Earth's upper atmosphere that was recorded around the globe. Here we report the detection of a fading radio afterglow produced by this outburst, with a luminosity 500 times larger than the only other detection of a similar source. From day 6 to day 19 after the flare from SGR 1806-20, a resolved, linearly polarized, radio nebula was seen, expanding at approximately a quarter of the speed of light. To create this nebula, at least 4 x 10(43) ergs of energy must have been emitted by the giant flare in the form of magnetic fields and relativistic particles.

An infrared ring around the magnetar SGR 1900+14.

PubMed

Wachter, S; Ramirez-Ruiz, E; Dwarkadas, V V; Kouveliotou, C; Granot, J; Patel, S K; Figer, D

2008-05-29

Magnetars are a special class of slowly rotating (period approximately 5-12 s) neutron stars with extremely strong magnetic fields (>10(14 )G)--at least an order of magnitude larger than those of the 'normal' radio pulsars. The potential evolutionary links and differences between these two types of object are still unknown; recent studies, however, have provided circumstantial evidence connecting magnetars with very massive progenitor stars. Here we report the discovery of an infrared elliptical ring or shell surrounding the magnetar SGR 1900+14. The appearance and energetics of the ring are difficult to interpret within the framework of the progenitor's stellar mass loss or the subsequent evolution of the supernova remnant. We suggest instead that a dust-free cavity was produced in the magnetar environment by the giant flare emitted by the source in August 1998. Considering the total energy released in the flare, the theoretical dust-destruction radius matches well with the observed dimensions of the ring. We conclude that SGR 1900+14 is unambiguously associated with a cluster of massive stars, thereby solidifying the link between magnetars and massive stars.

Assessing the Milky Way Satellites Associated with the Sagittarius Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Law, David R.; Majewski, Steven R.

2010-08-01

Numerical models of the tidal disruption of the Sagittarius (Sgr) dwarf galaxy have recently been developed that for the first time simultaneously satisfy most observational constraints on the angular position, distance, and radial velocity trends of both leading and trailing tidal streams emanating from the dwarf. We use these dynamical models in combination with extant three-dimensional position and velocity data for Galactic globular clusters and dSph galaxies to identify those Milky Way satellites that are likely to have originally formed in the gravitational potential well of the Sgr dwarf, and have been stripped from Sgr during its extended interaction with the Milky Way. We conclude that the globular clusters Arp 2, M 54, NGC 5634, Terzan 8, and Whiting 1 are almost certainly associated with the Sgr dwarf, and that Berkeley 29, NGC 5053, Pal 12, and Terzan 7 are likely to be as well (albeit at lower confidence). The initial Sgr system therefore may have contained five to nine globular clusters, corresponding to a specific frequency SN = 5-9 for an initial Sgr luminosity MV = -15.0. Our result is consistent with the 8 ± 2 genuine Sgr globular clusters expected on the basis of statistical modeling of the Galactic globular cluster distribution and the corresponding false-association rate due to chance alignments with the Sgr streams. The globular clusters identified as most likely to be associated with Sgr are consistent with previous reconstructions of the Sgr age-metallicity relation, and show no evidence for a second-parameter effect shaping their horizontal branch morphologies. We find no statistically significant evidence to suggest that any of the recently discovered population of ultrafaint dwarf galaxies are associated with the Sgr tidal streams, but are unable to rule out this possibility conclusively for all systems.

Spitzer Infrared Spectrograph Observations of the Galactic Center: Quantifying the Extreme Ultraviolet/Soft X-ray Fluxes

NASA Astrophysics Data System (ADS)

Simpson, Janet P.

2018-04-01

It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of H II regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal H II regions. This paper describes the analysis of all GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, H II region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr B1, Sgr C, and the Arches Cluster being all about the same age, around 4.5 Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova.

Dust temperature distributions in star-forming condensations

NASA Technical Reports Server (NTRS)

Xie, Taoling; Goldsmith, Paul F.; Snell, Ronald L.; Zhou, Weimin

1993-01-01

The FIR spectra of the central IR condensations in the dense cores of molecular clouds AFGL 2591. B335, L1551, Mon R2, and Sgr B2 are reanalyzed here in terms of the distribution of dust mass as a function of temperature. FIR spectra of these objects can be characterized reasonably well by a given functional form. The general shapes of the dust temperature distributions of these objects are similar and closely resemble the theoretical computations of de Muizon and Rouan (1985) for a sample of 'hot centered' clouds with active star formation. Specifically, the model yields a 'cutoff' temperature below which essentially no dust is needed to interpret the dust emission spectra, and most of the dust mass is distributed in a broad temperature range of a few tens of degrees above the cutoff temperature. Mass, luminosity, average temperature, and column density are obtained, and it is found that the physical quantities differ considerably from source to source in a meaningful way.

Chemical Abundances of Hydrostatic and Explosive Alpha-elements in Sagittarius Stream Stars

NASA Astrophysics Data System (ADS)

Carlin, Jeffrey L.; Sheffield, Allyson A.; Cunha, Katia; Smith, Verne V.

2018-05-01

We analyze chemical abundances of stars in the Sagittarius (Sgr) tidal stream using high-resolution Gemini+GRACES spectra of 42 members of the highest surface-brightness portions of both the trailing and leading arms. Targets were chosen using a 2MASS+WISE color–color selection, combined with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) radial velocities. In this Letter, we analyze [Fe/H] and α-elements produced by both hydrostatic (O, Mg) and explosive (Si, Ca, Ti) nucleosynthetic processes. The average [Fe/H] for our Sgr stream stars is lower than that for stars in the Sgr core, and stars in the trailing and leading arms show systematic differences in [Fe/H]. Both hydrostatic and explosive elements are depleted relative to Milky Way (MW) disk and halo stars, with a larger gap between the MW trend and Sgr stars for the hydrostatic elements. Chemical abundances of Sgr stream stars show similar patterns to those measured in the core of the Sgr dSph. We explore the ratio of hydrostatic to explosive α-elements [α h/ex] (which we refer to as the “HEx ratio”). Our observed HEx ratio trends for Sgr debris are deficient relative to MW stars. Via simple chemical evolution modeling, we show that these HEx ratio patterns are consistent with a Sgr IMF that lacks the most massive stars. This study provides a link between the chemical properties in the intact Sgr core and the significant portion of the Sgr system’s luminosity that is estimated to currently reside in the streams.

AND YET IT MOVES: THE DANGERS OF ARTIFICIALLY FIXING THE MILKY WAY CENTER OF MASS IN THE PRESENCE OF A MASSIVE LARGE MAGELLANIC CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gómez, Facundo A.; O’Shea, Brian W.; Besla, Gurtina

2015-04-01

Motivated by recent studies suggesting that the Large Magellanic Cloud (LMC) could be significantly more massive than previously thought, we explore whether the approximation of an inertial Galactocentric reference frame is still valid in the presence of such a massive LMC. We find that previous estimates of the LMC’s orbital period and apocentric distance derived assuming a fixed Milky Way (MW) are significantly shortened for models where the MW is allowed to move freely in response to the gravitational pull of the LMC. Holding other parameters fixed, the fraction of models favoring first infall is reduced. Due to this interaction,more » the MW center of mass within the inner 50 kpc can be significantly displaced in phase-space in a very short period of time that ranges from 0.3 to 0.5 Gyr by as much as 30 kpc and 75 km s{sup −1}. Furthermore, we show that the gravitational pull of the LMC and response of the MW are likely to significantly affect the orbit and phase space distribution of tidal debris from the Sagittarius dwarf galaxy (Sgr). Such effects are larger than previous estimates based on the torque of the LMC alone. As a result, Sgr deposits debris in regions of the sky that are not aligned with the present-day Sgr orbital plane. In addition, we find that properly accounting for the movement of the MW around its common center of mass with the LMC significantly modifies the angular distance between apocenters and tilts its orbital pole, alleviating tensions between previous models and observations. While these models are preliminary in nature, they highlight the central importance of accounting for the mutual gravitational interaction between the MW and LMC when modeling the kinematics of objects in the MW and Local Group.« less

Additional Spitzer IRS Spectroscopy of Three Intermediate Polars: The Detection of a Mid-infrared Synchrotron Flare from V1223 Sagittarii

NASA Astrophysics Data System (ADS)

Harrison, Thomas E.; Bornak, Jillian; Rupen, Michael P.; Howell, Steve B.

2010-02-01

We present new Spitzer Infrared Spectrograph (IRS) observations of three intermediate polars: V1223 Sgr, EX Hya, and V603 Aql. We detected a strong, fading flare event from V1223 Sgr. During this event, the flux declined by a factor of 13 in 30 minutes. Given the similarity in the slope of its mid-infrared spectrum during this event to that of AE Aqr, we suggest that this event was caused by transient synchrotron emission. Thus, V1223 Sgr becomes the third cataclysmic variable known to be a synchrotron source. We were unable to confirm the mid-infrared excess noted by Harrison et al. (Paper I) for EX Hya, suggesting that this object is either not a synchrotron source, or is slightly variable. Due to a very high background, V603 Aql was not detected in the long-wavelength regions accessible to the IRS. Given the recent detection of SS Cygni at radio wavelengths during outburst, we extract archival Spitzer IRS spectra for this source obtained during two successive maxima. These spectra do not show a strong excess, but without simultaneous data at shorter wavelengths, it is not possible to determine whether there is any contribution to the mid-infrared fluxes from a synchrotron jet. Includes observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

Swift J1822.3-1606: A Probable New SGR in Ground Analysis of BAT Data

NASA Astrophysics Data System (ADS)

Cummings, J. R.; Burrows, D.; Campana, S.; Kennea, J. A.; Krimm, H. A.; Palmer, D. M.; Sakamoto, T.; Zan, S.

2011-07-01

At 2011-07-14 at 12:47:47.1 UTC, Swift-BAT triggered (#457261) on a previously unknown source, Swift J1822.3-1606. This was at the same time as Fermi-GBM trigger #332340476. Only a subthreshold source was detected onboard. There were two subsequent rate increases of similar size, probably from the same source at about T+26 sec and T+308 sec, the latter also causing a rate trigger with no significant source found onboard (#457263).

Warm and Diffuse Gas and High Ionization Rate Near the Galactic Center

NASA Astrophysics Data System (ADS)

Oka, T.; Morong, C. P.; Geballe, T. R.; Indriolo, N.; McCall, B. J.; Goto, M.; Usuda, T.

2011-06-01

Using 12 newly found bright dust-embedded stars distributed from 140 pc West to 120 pc East of Sgr A*, we have observed spectra of H_3^+ and CO in the Central Molecular Zone of the Galactic center. Sightlines toward the 12 stars have been observed at the Gemini South Observatory on Cerro Pachon, Chile, and those for 2 of the stars at the Subaru Telescope on Mauna Kea Hawaii. This has extended our previous longitudinal coverage by a factor of 7. Although complete coverage of various transitions have yet to be made for some stars, almost all sightlines showed high total column densities of H_3^+ and highly populated (J, K) = (3, 3) metastable level, demonstrating the prevalence of the warm and diffuse gas previously observed from the center to 30 pc East and high ionization rate in the environment. A few sightlines did not show strong H_3^+ absorptions. It remains to be seen whether this is due to the radial and transverse location of the stars or lack of H_3^+. While the velocity profiles of H_3^+ toward stars from the center to 30 pc East are similar apart from subtle variations, the velocity profiles of the wider regions vary greatly ^a. A remarkable similarity has been noted between the velocity profile of H_3^+ toward a star nicknamed Iota and those of H_2O^+ and 13CH^+ observed toward Sgr B2 by the HIFI instrument of the Herschel Space Observatory. Although all these ions exist in diffuse environment, this is surprising since H_3^+ favors environments with high H_2 fraction f(H_2) while H_2O^+ and CH^+ favors low f(H_2). Also the peak of Sgr B2 and Iota are separated by 17 pc. Possible interpretations of this will be discussed. T. R. Geballe and T. Oka, ApJ, 709, L70 (2010). M. Goto, T. Usuda, T. R. Geballe, N. Indriolo, B. J. McCall, Th. Henning, and T. Oka, PASJ (2011) in press. P. Schilke, et al., A&A, 521, L11 (2010). E. Falgarone, private communication

SMM hard X-ray observations of the soft gamma-ray repeater 1806-20

NASA Technical Reports Server (NTRS)

Kouveliotou, C.; Norris, J. P.; Cline, T. L.; Dennis, B. R.; Desai, U. D.; Orwig, L. E.

1987-01-01

Six bursts from the soft gamma-ray repeater (SGR) 1806-20 have been recorded with the SMM Hard X-ray Burst Spectrometer during a highly active phase in 1983. Rise and decay times of less than 5 ns have been detected. Time profiles of these events indicate low-level emission prior to and after the main peaks. The results suggest that SGRs are distinguished from classical gamma-ray bursts by repetition, softer nonvarying spectra, short durations, simple temporal profiles, and a tendency for source locations to correlate with Population I objects. SGR characteristics differ from those of type I X-ray bursts, but they appear to have similarities with the type II bursts from the Rapid Burster.

Dynamical Imaging with Interferometry

NASA Astrophysics Data System (ADS)

Johnson, Michael D.; Bouman, Katherine L.; Blackburn, Lindy; Chael, Andrew A.; Rosen, Julian; Shiokawa, Hotaka; Roelofs, Freek; Akiyama, Kazunori; Fish, Vincent L.; Doeleman, Sheperd S.

2017-12-01

By linking widely separated radio dishes, the technique of very long baseline interferometry (VLBI) can greatly enhance angular resolution in radio astronomy. However, at any given moment, a VLBI array only sparsely samples the information necessary to form an image. Conventional imaging techniques partially overcome this limitation by making the assumption that the observed cosmic source structure does not evolve over the duration of an observation, which enables VLBI networks to accumulate information as Earth rotates and changes the projected array geometry. Although this assumption is appropriate for nearly all VLBI, it is almost certainly violated for submillimeter observations of the Galactic center supermassive black hole, Sagittarius A* (Sgr A*), which has a gravitational timescale of only ∼ 20 s and exhibits intrahour variability. To address this challenge, we develop several techniques to reconstruct dynamical images (“movies”) from interferometric data. Our techniques are applicable to both single-epoch and multiepoch variability studies, and they are suitable for exploring many different physical processes including flaring regions, stable images with small time-dependent perturbations, steady accretion dynamics, or kinematics of relativistic jets. Moreover, dynamical imaging can be used to estimate time-averaged images from time-variable data, eliminating many spurious image artifacts that arise when using standard imaging methods. We demonstrate the effectiveness of our techniques using synthetic observations of simulated black hole systems and 7 mm Very Long Baseline Array observations of M87, and we show that dynamical imaging is feasible for Event Horizon Telescope observations of Sgr A*.

NSV 11749, an Elder Sibling of the Born-again Stars V605 Aql and V4334 Sgr?

NASA Astrophysics Data System (ADS)

Miller Bertolami, M. M.; Rohrmann, R. D.; Granada, A.; Althaus, L. G.

2011-12-01

We argue that NSV 11749, an eruption observed in the early twentieth century, was a rare event known as "very late thermal pulse" (VLTP). To support our argument we compare the light curve of NSV 11749 with those of the two bona fide VLTP objects known to date, V4334 Sgr and V605 Aql, and with those predicted by state-of-the-art stellar evolution models. Next, we explore the INT Photometric H-Alpha Survey (IPHAS) and Two Micron All Sky Survey (2MASS) catalogs for possible counterparts of the eruption. Our analysis shows that the VLTP scenario outperforms all other proposed scenarios as an explanation of NSV 11749. We identify an IPHAS/2MASS source at the eruption location of NSV 11749. The derived colors suggest that the object is not enshrouded in a thick dust shell as V605 Aql and V4334 Sgr. Also, the absence of an apparent planetary nebula at the eruption location suggests differences with known VLTP objects which might be linked to the intensity of the eruption and the mass of the object. Further exploration of this source and scenario seems desirable. If NSV 11749 was a born-again star, it would be the third event of its kind to have been observed and will strongly help us to increase our understanding of the later stages of stellar evolution and violent reactive convective burning.

The Galactic Centre source G2 was unlikely born in any of the known massive binaries

NASA Astrophysics Data System (ADS)

Calderón, D.; Cuadra, J.; Schartmann, M.; Burkert, A.; Plewa, P.; Eisenhauer, F.; Habibi, M.

2018-05-01

The source G2 has already completed its pericentre passage around Sgr A*, the super-massive black hole in the centre of our Galaxy. Although it has been monitored for 15 years, its astrophysical nature and origin still remain unknown. In this work, we aim to test the hypothesis of G2 being the result of a stellar wind collision. To do so, we study the motion and final fate of gas clumps formed as a result of collisions of stellar winds in massive binaries. Our approach is based on a test-particle model in order to describe the trajectories of such clumps. The model takes into account the gravitational field of Sgr A*, the interaction of the clumps with the interstellar medium as well as their finite lifetimes. Our analysis allows us to reject the hypothesis based on four arguments: i) if G2 has followed a purely Keplerian orbit since its formation, it cannot have been produced in any of the known massive binaries since their motions are not consistent; ii) in general, gas clumps are evaporated through thermal conduction on very short timescale (<100 yr) before getting close enough to Sgr A*; iii) IRS 16SW, the best candidate for the origin of G2, cannot generate clumps as massive as G2; and iv) clumps ejected from IRS 16SW describe trajectories significantly different to the observed motion of G2.

A Study of Nonthermal X-Ray and Radio Emission from the O Star 9 Sgr

NASA Technical Reports Server (NTRS)

Waldron, Wayne L.; Corcoran, Michael F.; Drake, Stephen A.

1999-01-01

The observed X-ray and highly variable nonthermal radio emission from OB stars has eluded explanation for more than 18 years. The most favorable model of X-ray production in these stars (shocks) predicts both nonthermal radio and X-ray emission. The nonthermal X-ray emission should occur above 2 keV and the variability of this X-ray component should also be comparable to the observed radio variability. To test this scenario, we proposed an ASC/VLA monitoring program to observe the OB star, 9 Sgr, a well known nonthermal, variable radio source and a strong X-ray source. We requested 625 ks ASCA observations with a temporal spacing of approximately 4 days which corresponds to the time required for a density disturbance to propagate to the 6 cm radio free-free photosphere. The X-ray observations were coordinated with 5 multi-wavelength VLA observations. These observations represent the first systematic attempt to investigate the relationship between the X-ray and radio emission in OB stars.

VizieR Online Data Catalog: Chromospherically Active Binaries (Strassmeier+ 1993)

NASA Astrophysics Data System (ADS)

Strassmeier, K. G.; Hall, D. S.; Fekel, F. C.

1996-08-01

Stars always appear in order of increasing right-ascension for the epoch 2000.0. For the current version of the catalog, the literature was searched through December 31, 1991 although a few later references are included. Additionally, some entries are cited with "private communication", which make this catalog also a first-hand source. A number in parentheses behind an entry always corresponds to a reference given in the bibliography. See the 1988 publication for specific requirements and restrictions in compiling these catalogs. See the source reference for more details about this catalog. The following binary systems, which were listed in the first edition of the catalog, were not included in the present edition due to insufficient evidence for chromospheric activity: eta And 26 Aql 4 UMi nu2 Sgr tau Sgr the following stars are chromospherically active but are components in a "wide" binary and were not included. HD 25893 HD 79211 Forty three new binary systems have been included in the present edition. (12 data files).

Rapid optical follow-up observations of SGR events with ROTSE-I

NASA Astrophysics Data System (ADS)

Balsano, R.; Akerlof, C.; Barthelmy, S.; Bloch, J.; Butterworth, P.; Casperson, D.; Cline, T.; Fletcher, S.; Gisler, G.; Hills, J.; Kehoe, R.; Lee, B.; Marshall, S.; McKay, T.; Pawl, A.; Priedhorsky, W.; Seldomridge, N.; Szymanski, J.; Wren, J.

2000-09-01

The primary mission of the Robotic Optical Transient Search Experiment (ROTSE) is to search for contemporaneous optical emission from GRBs. Among the triggers ROTSE receives via the GRB Coordinates Network (GCN), there are a number from Soft-Gamma Repeater (SGR) events. Since beginning operations in March 1998, ROTSE-I has triggered on 16 observable SGR events. Ten of these events had useful data, eight events from SGR 1900+14 and two events from SGR 1806-20. The error regions for these SGRs are a small fraction of the ROTSE 16°×16° field of view and have been searched for new or variable objects. Limits on optical transient counterparts are in the range mROTSE~12.5-15.5 during the period 10 seconds to 1 hour after the observed SGR events. .

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

NASA Astrophysics Data System (ADS)

Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H.

2013-06-01

Aims: We present the atmospheric structure and the fundamental properties of the red supergiants (RSGs) AH Sco, UY Sct, and KW Sgr based on VLTI/AMBER observations. Methods: We carried out spectro-interferometric observations of AH Sco, UY Sct, and KW Sgr in the near-infrared K band (1.92-2.47 μm) with the VLTI/AMBER instrument with spatial and spectral resolutions of 3 milliarcsec and 1500, respectively, and compared the data to a new grid of hydrostatic PHOENIX model atmospheres. Results: In our visibility data, we observe molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases at the water band centered at 1.9 μm of 10% to 25% and at the CO bandheads at 2.3-2.5 μm of 20%-35% with respect to the near-continuum bandpass at around 2.20 μm. Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models. However, the model visibilities do not predict the large observed extensions of the molecular layers. Comparing the continuum visibility values to PHOENIX models, we estimate the Rosseland-mean photospheric angular diameters of AH Sco, UY Sct, and KW Sgr to be 5.81 ± 0.15 mas, 5.48 ± 0.10 mas, and 3.91 ± 0.25 mas, respectively. Together with the distance and the spectro-photometry, we calculate radii of 1411 ± 124 R⊙ for AH Sco, 1708 ± 192 R⊙ for UY Sct, and 1009 ± 142 R⊙ for KW Sgr and effective temperatures of 3682 ± 190 K for AH Sco, 3365 ± 134 K for UY Sct, and 3720 ± 183 K for KW Sgr. Conclusions: AH Sco, UY Sct, and KW Sgr exhibit extended atmospheric layers of H2O and CO. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but cannot reproduce the large extensions of the molecular layers. This indicates that the opacities of the molecular bands are included, but that the model atmospheres are too compact compared to the observations. The observed extended layers may be levitated by processes such as pulsation or convection, which are not included in the hydrostatic atmospheric models. The location of the targets in the HR-diagram is confirmed to be close to, and possibly slightly to the right of, the Hayashi limit of recent evolutionary tracks corresponding to masses between about 20 M⊙ and 40 M⊙.

The Galactic Center observed with H.E.S.S.

NASA Astrophysics Data System (ADS)

Jouvin, Lea

2017-08-01

The Galactic Center region has been a prime target region for the H.E.S.S. Imaging Atmospheric Cherenkov Telescope Array observations since da ta taking started in 2003. H.E.S.S. has revealed the presence of a very high energy gamma-ray diffuse emission in the central 200 pc, in addition to the detection of a point like source coincident with the supermassive black hole SgrA*. With more than 250 hours of H.E.S.S. data and the continuous improvement of the analysis techniques, a detailed morphology and spectral analysis of the region is now possible. We will report on the new characterisation of the spectrum of the central source down to 100 GeV energies taking advantage of the H.E.S.S. II data, obtained after the inclusion of the large 28-meter CT5 telescope in the array centre. We will present the recent discovery of a powerful cosmic PeVatron accelerator at the center of our Galaxy as well as a new characterization of the diffuse gamma-ray emission in the central 200 pc of our Galaxy through a detailed morphology study. By analysing the nature of the various components of this emission, the existence of a strong cosmic-ray gradient and thus the presence of a strong cosmic-ray accelerator at the very centre of our Galaxy was found. We will also report on the discovery of an additional point-like source HESS J1746-285 in this region possibly associated with the pulsar wind nebula candidate G0.13-0.11.

SGR2, a Phospholipase-Like Protein, and ZIG/SGR4, a SNARE, Are Involved in the Shoot Gravitropism of Arabidopsis

PubMed Central

Kato, Takehide; Morita, Miyo Terao; Fukaki, Hidehiro; Yamauchi, Yoshiro; Uehara, Michiko; Niihama, Mitsuru; Tasaka, Masao

2002-01-01

In higher plants, the shoot and the root generally show negative and positive gravitropism, respectively. To elucidate the molecular mechanisms involved in gravitropism, we have isolated many shoot gravitropism mutants in Arabidopsis. The sgr2 and zig/sgr4 mutants exhibited abnormal gravitropism in both inflorescence stems and hypocotyls. These genes probably are involved in the early step(s) of the gravitropic response. The sgr2 mutants also had misshapen seed and seedlings, whereas the stem of the zig/sgr4 mutants elongated in a zigzag fashion. The SGR2 gene encodes a novel protein that may be part of a gene family represented by bovine phosphatidic acid–preferring phospholipase A1 containing a putative transmembrane domain. This gene family has been reported only in eukaryotes. The ZIG gene was found to encode AtVTI11, a protein that is homologous with yeast VTI1 and is involved in vesicle transport. Our observations suggest that the two genes may be involved in a vacuolar membrane system that affects shoot gravitropism. PMID:11826297

GRMHD Simulations of Visibility Amplitude Variability for Event Horizon Telescope Images of Sgr A*

NASA Astrophysics Data System (ADS)

Medeiros, Lia; Chan, Chi-kwan; Özel, Feryal; Psaltis, Dimitrios; Kim, Junhan; Marrone, Daniel P.; Sa¸dowski, Aleksander

2018-04-01

The Event Horizon Telescope will generate horizon scale images of the black hole in the center of the Milky Way, Sgr A*. Image reconstruction using interferometric visibilities rests on the assumption of a stationary image. We explore the limitations of this assumption using high-cadence disk- and jet-dominated GRMHD simulations of Sgr A*. We also employ analytic models that capture the basic characteristics of the images to understand the origin of the variability in the simulated visibility amplitudes. We find that, in all simulations, the visibility amplitudes for baselines oriented parallel and perpendicular to the spin axis of the black hole follow general trends that do not depend strongly on accretion-flow properties. This suggests that fitting Event Horizon Telescope observations with simple geometric models may lead to a reasonably accurate determination of the orientation of the black hole on the plane of the sky. However, in the disk-dominated models, the locations and depths of the minima in the visibility amplitudes are highly variable and are not related simply to the size of the black hole shadow. This suggests that using time-independent models to infer additional black hole parameters, such as the shadow size or the spin magnitude, will be severely affected by the variability of the accretion flow.

High-wattage pulsed irradiation of linearly polarized near-infrared light to stellate ganglion area for burning mouth syndrome.

PubMed

Momota, Yukihiro; Kani, Koichi; Takano, Hideyuki; Matsumoto, Fumihiro; Aota, Keiko; Takegawa, Daisuke; Yamanoi, Tomoko; Kondo, Chika; Tomioka, Shigemasa; Azuma, Masayuki

2014-01-01

The purpose of this study was to apply high-wattage pulsed irradiation of linearly polarized near-infrared light to the stellate ganglion area for burning mouth syndrome (BMS) and to assess the efficacy of the stellate ganglion area irradiation (SGR) on BMS using differential time-/frequency-domain parameters (D parameters). Three patients with BMS received high-wattage pulsed SGR; the response to SGR was evaluated by visual analogue scale (VAS) representing the intensity of glossalgia and D parameters used in heart rate variability analysis. High-wattage pulsed SGR significantly decreased the mean value of VAS in all cases without any adverse event such as thermal injury. D parameters mostly correlated with clinical condition of BMS. High-wattage pulsed SGR was safe and effective for the treatment of BMS; D parameters are useful for assessing efficacy of SGR on BMS.

SH Observations In and Toward Sgr B2(N): Linking the Missing Sulfur

NASA Astrophysics Data System (ADS)

McCarthy, Michael

Where is the missing sulfur in the molecular reservoir of the interstellar medium (ISM)? In the warm gas phase ISM, the abundance of sulfur is nearly equivalent to its solar value, but in the cold, diffuse clouds which span the space between stars, sulfur is depleted by several orders of magnitude. Our inability to account for this depletion represents a significant gap in our understanding of the fundamental chemical and physical processes occurring in the primordial reservoirs of gas and dust in the ISM. Central to this chemistry is SH, a radical for which few observations presently exist, and for which SOFIA is uniquely capable of accessing in its ground rotational state. We propose observations of SH in the cold, shocked molecular shell surrounding Sgr B2(N), and, simultaneously, in diffuse and translucent clouds along the line of sight to Sgr B2(N). We will constrain the abundance of SH, and compare it to previous measurements of SO, CS, C_2S, HCS(+) , H_2CS, and H_2S in these sources which span the evolutionary timescale from diffuse clouds to dense, cold shocked regions.

An Expanding Radio Nebula Produced by a Giant Flare from the Magnetar SGR 1806-20

NASA Technical Reports Server (NTRS)

Gaensler, B. M.; Kouveliotou, C.; Gelfand, J. D.; Taylor, G. B.; Eichler, D.; Wijers, R. A. M. J.; Granot, J.; Ramirez-Ruiz, E.; Lyubarsky, Y. E.; Hunstead, R. W.

2005-01-01

Soft gamma repeaters (SGRs) are "magnetars", a small class of slowly spinning neutron stars with extreme surface magnetic fields, B approx. 10(sup 15) gauss. On 2004 December 27, a giant flare was detected from the magnetar SGR 1806-20, the third such event ever recorded. This burst of energy, which resulted in the highest flux of gamma-rays ever measured from a celestial object, was detected by a variety of instruments and even caused an ionospheric disturbance in the Earth's upper atmosphere recorded around the globe. Here we report the detection of a very bright but rapidly-fading radio source at the position of SGR 1806-20 following this outburst. From day 6 to day 19 after the flare, we see a resolved, linearly polarized, radio nebula, expanding at a velocity of approximately 0.3c. To create this nebula, at least 4 x 10(exp 43) ergs of energy must have been emitted by the giant flare in the form of magnetic fields and relativistic particles. The steep decline of the radio flux may indicate episodic particle acceleration followed by adiabatic expansion, as could occur if the ejecta have energized a thin shell surrounding a preexisting cavity.

Surviving the hole. I. Spatially resolved chemistry around Sagittarius A∗

NASA Astrophysics Data System (ADS)

Martín, S.; Martín-Pintado, J.; Montero-Castaño, M.; Ho, P. T. P.; Blundell, R.

2012-03-01

Context. The interstellar region within the few central parsecs around the super-massive black hole, Sgr A∗, at the very Galactic center is composed of a number of overlapping molecular structures that are subject to one of the most hostile physical environments in the Galaxy. Aims: Through the study of the morphology and kinematics of the emission from different molecular species as well as the variation of their line ratios we can attain a deeper understanding of the distribution and interaction between different gas structures and the energetic phenomena taking place in the surroundings of Sgr A∗ and of the physical processes responsible for the heating in this region. Methods: We performed high-resolution (4″ × 3″ ~ 0.16 × 0.11 pc) interferometric observations of CN, 13CN, H2CO, SiO, c-C3H2 and HC3N emission at 1.3 mm toward the central ~4 pc of the Galactic center region. Results: Strong differences are observed in the distribution of the different molecules. The UV resistant species CN, the only species tracing all previously identified circumnuclear disk (CND) structures, is mostly concentrated in optically thick clumps in the rotating filaments around Sgr A∗. H2CO emission traces a shell-like structure that we interpret as the expansion of Sgr A East against the 50 km s-1 and 20 km s-1 giant molecular clouds (GMCs). We derive isotopic ratios 12C/13C ~ 15-45 across most of the CND region, except for the northeast arm, where the peak of H2CO is observed and ratios <10 are found. The densest molecular material, traced by SiO and HC3N, is located in the southern CND, likely because of shocked gas infalling from the 20 km s-1 GMC streamers, and the northeast arm, as a result of the expansion of Sgr A East or a connecting point of the 50 km s-1 streamer east of the CND. The observed c-C3H2/HC3N ratio observed in the region is more than an order of magnitude lower than in Galactic PDRs. Toward the central region only CN was detected in absorption. In addition to the known narrow line-of-sight absorptions, a 90 km s-1 wide optically thick spectral feature is observed. We found evidence of an even wider (>100 km s-1) absorption feature. About 70-75% of the gas mass, concentrated in just the 27% densest molecular clumps, is associated with rotating structures and show evidence of an association with each of the arcs of ionized gas in the mini-spiral structure. Conclusions: These observations provide a combined chemical and kinematical picture of the very central region around Sgr A∗. Chemical differentiation has been proven to be a powerful tool to distinguish the many overlapping molecular components in this crowded and heavily obscured region. Figures 12-22 and Tables 3 and 4 are available in electronic form at http://www.aanda.org

Discovery of Interstellar Hydrogen Fluoride

NASA Technical Reports Server (NTRS)

Neufeld, David A.; Zmuidzinas, Jonas; Schilke, Peter; Phillips, Thomas G.

1997-01-01

We report the first detection of interstellar hydrogen fluoride. Using the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO), we have detected the 121.6973 micron J = 2-1 line of HF in absorption toward the far-infrared continuum source Sagittarius B2. The detection is statistically significant at the 13 sigma level. On the basis of our model for the excitation of HF in Sgr B2, the observed line equivalent width of 1.0 nm implies a hydrogen fluoride abundance of about 3 x 10 (exp -10) relative to H, If the elemental abundance of fluorine in Sgr B2 is the same as that in the solar system, then HF accounts for about 2% of the total number of fluorine nuclei. We expect hydrogen fluoride to be the dominant reservoir of gas-phase fluorine in Sgr B2, because it is formed rapidly in exothermic reactions of atomic fluorine with either water or molecular hydrogen; thus, the measured HF abundance suggests a substantial depletion of fluorine onto dust grains. Similar conclusions regarding depletion have previously been reached for the case of chlorine in dense interstellar clouds. We also find evidence at a lower level of statistical significance (about 5 sigma) for an emission feature at the expected position of the 4(sub 32)-4(sub 23) 121.7219 micron line of water. The emission-line equivalent width of 0.5 mm for the water feature is consistent with the water abundance of 5 x 10(exp -6) relative to H, that has been inferred previously from observations of the hot core of Sgr B2.

Discovery of Interstellar Hydrogen Fluoride

NASA Technical Reports Server (NTRS)

Neufeld, David A.; Zmuidzinas, Jonas; Schilke, Peter; Phillips, Thomas G.

1997-01-01

We report the first detection of interstellar hydrogen fluoride. Using the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO), we have detected the 121.6973 micron J = 2-1 line of HF in absorption toward the far-infrared continuum source Sagittarius B2. The detection is statistically significant at the 13 sigma level. On the basis of our model for the excitation of HF in Sgr B2, the observed line equivalent width of 1.0 nm implies a hydrogen fluoride abundance of approximately 3 x 10(exp -10) relative to H2. If the elemental abundance of fluorine in Sgr B2 is the same as that in the solar system, then HF accounts for approximately 2% of the total number of fluorine nuclei. We expect hydrogen fluoride to be the dominant reservoir of gas-phase fluorine in Sgr B2, because it is formed rapidly in exothermic reactions of atomic fluorine with either water or molecular hydrogen; thus, the measured HF abundance suggests a substantial depletion of fluorine onto dust grains. Similar conclusions regarding depletion have previously been reached for the case of chlorine in dense interstellar clouds. We also find evidence at a lower level of statistical significance (approximately 5 sigma) for an emission feature at the expected position of the 4(sub 32)-4(sub 23) 121.7219 micron line of water. The emission-line equivalent width of 0.5 nm for the water feature is consistent with the water abundance of 5 x 10(exp -6) relative to H2 that has been inferred previously from observations of the hot core of Sgr B2.

ROSAT X-Ray Observation of the Second Error Box for SGR 1900+14

NASA Technical Reports Server (NTRS)

Li, P.; Hurley, K.; Vrba, F.; Kouveliotou, C.; Meegan, C. A.; Fishman, G. J.; Kulkarni, S.; Frail, D.

1997-01-01

The positions of the two error boxes for the soft gamma repeater (SGR) 1900+14 were determined by the "network synthesis" method, which employs observations by the Ulysses gamma-ray burst and CGRO BATSE instruments. The location of the first error box has been observed at optical, infrared, and X-ray wavelengths, resulting in the discovery of a ROSAT X-ray point source and a curious double infrared source. We have recently used the ROSAT HRI to observe the second error box to complete the counterpart search. A total of six X-ray sources were identified within the field of view. None of them falls within the network synthesis error box, and a 3 sigma upper limit to any X-ray counterpart was estimated to be 6.35 x 10(exp -14) ergs/sq cm/s. The closest source is approximately 3 min. away, and has an estimated unabsorbed flux of 1.5 x 10(exp -12) ergs/sq cm/s. Unlike the first error box, there is no supernova remnant near the second error box. The closest one, G43.9+1.6, lies approximately 2.dg6 away. For these reasons, we believe that the first error box is more likely to be the correct one.

Conversion of gas into stars in the Galactic center

NASA Astrophysics Data System (ADS)

Longmore, S. N.

2014-05-01

The star formation rate in the central 500 pc of the Milky Way is lower by a factor of > 10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. I discuss which physical mechanisms could be causing this observation and put forward a self-consistent cycle of star formation in the Galactic center, in which the plausible star formation inhibitors are combined. Their ubiquity suggests that the perception of a lowered central SFR should be a common phenomenon in other galaxies with direct implications for galactic star formation and also potentially supermassive black hole growth. I then describe a scenario to explain the presence of super star clusters in the Galactic center environment, in which their formation is triggered by gas streams passing close to the minimum of the global Galactic gravitational potential at the location of the central supermassive black hole, Sgr A*. If this triggering mechanism can be verified, we can use the known time interval since closest approach to Sgr A* to study the physics of stellar mass assembly in an extreme environment as a function of absolute time. I outline the first results from detailed numerical simulations testing this scenario. Finally, I describe a study showing that in terms of the baryonic composition, kinematics, and densities, the gas in the Galactic center is indistinguishable from high-redshift clouds and galaxies. As such, the Galactic center clouds may be used as a template to understand the evolution (and possibly the life cycle) of high-redshift clouds and galaxies.

Dramatic Outburst Reveals Nearest Black Hole

NASA Astrophysics Data System (ADS)

2000-01-01

Scientists have discovered the closest black hole yet, a mere 1,600 light years from Earth. Its discovery was heralded by four of the most dramatic rapid X-ray intensity changes ever seen from one star. Astronomers from the Massachusetts Institute of Technology (MIT) and the National Science Foundation's National Radio Astronomy Observatory (NRAO) announced their findings at the American Astronomical Society's meeting in Atlanta. The black hole in the constellation Sagittarius, along with a normal star dubbed V4641 Sgr, form a violent system that briefly flooded part of our Milky Way Galaxy with X-rays and ejected subatomic particles moving at nearly the speed of light one day last September. At the peak of its X-ray output, V4641 Sgr was the brightest X-ray emitter in the sky. Astronomers call this type of system an X-ray nova because it suddenly becomes a bright source of X-rays, but this object shows characteristics never seen in an X-ray nova. "V4641 Sgr turns on and off so fast that it seems to represent a new subclass of X-ray novae," said Donald A. Smith, postdoctoral associate in MIT's Center for Space Research. Smith worked on data from this object with MIT principal research scientist Ronald Remillard and NRAO astronomer Robert Hjellming. "In X-rays, the intensity rose by a factor of more than 1,000 in seven hours, then dropped by a factor of 100 in two hours," Remillard said. The radio emission was seen as an image of an expanding "jet" of particles shooting out from the binary system. After reaching a maximum, the radio intensity dropped by a factor of nearly 40 within two days. "Radio telescopes give us a quick glimpse of something moving at a fantastically high velocity," Hjellming said. Black holes harbor enormous gravitational force that can literally rip the gas away from a nearby star. This transfer of gas is visible in many forms of radiation. Both orbiting X-ray telescopes and ground-based radio and optical telescopes saw the outburst of V4641 Sgr. The radio observations revealed the presence of a jet escaping from the system at mind-boggling speeds. Only three other galactic X-ray stellar systems have been found to eject material at such speeds. They have been dubbed "microquasars" because, on a smaller scale, they resemble quasars, which lie at the hearts of distant galaxies and also spew out high-velocity jets of particles. In galaxy-core quasars, the black holes are millions of times more massive than the Sun; in the more nearby microquasars the black holes are roughly three to twenty times more massive than the Sun. The extremely high velocity of the jets suggests that their origin lies close to the event horizon of a black hole. Microquasar activity is thought to arise when the black hole in the binary system draws material away from its companion star. The material surrounding the black hole forms a rapidly spinning disk called an accretion disk. This disk is heated by friction to millions of degrees, causing it to emit X-rays. As spiralling gas moves into the gravity well of the black hole, it moves faster and faster. Magnetic fields in the disk are believed to expel the charged subatomic particles at speeds close to that of light. As the charged particles interact with the magnetic fields, they emit radio waves. If some of the material escapes by being magnetically expelled into space, the matter may continue moving at the tremendous speed it had attained near the black hole. After their ejection, the jets of particles expand and cool, fading from astronomers' view. V4641 Sgr excites astronomers because it is close and because it acted so differently from other microquasars. In other microquasars, outbursts have dimmed more slowly over weeks or months rather than hours. "There's something fundamentally different about this one; it's more extreme than any other example," Hjellming said. "And because this system happens to be so close to us, `it is very likely that there are more objects like V4641 Sgr waiting to be discovered," said Smith. "The rapidly flaring systems in our galaxy may have been too faint and too fast for us to notice them," added Smith. What makes it so different? Astronomers aren't sure, but Remillard speculated that, "in V4641 Sgr, either the matter can flow into the black hole without forming a large accretion disk, or the black hole itself is significantly different in its mass, spin or charge." "Theory is lagging far behind the observations in terms of explaining what's going on in this system," Hjellming said. The drama of V4641 Sgr began Sept. 15, 1999, when Australian amateur astronomer Ron Stubbings noticed that the "star" was more than six times brighter than it had been the night before. He sent an e-mail message around the world. One recipient, Japanese astronomer Taichi Kato, recalled that this object had been associated with variable X-ray emission by scientists working with the Dutch-Italian BeppoSAX spacecraft. Kato forwarded the message to Smith, a member of the All-Sky Monitor (ASM) team using the Rossi X-ray Timing Explorer (RXTE) satellite. The ASM surveys the entire sky about once every two hours, and Smith found that the most recent observation of V4641 showed it as a bright X-ray emitter. Subsequent observations showed the rapid rise and fall of the object's X-ray brightness. A few hours later, it flared again. Within 24 hours, the National Science Foundation's Very Large Array (VLA) radio telescope in New Mexico was observing V4641 Sgr. "We could immediately see that it had structure -- it was big," Hjellming said. The first VLA observation showed an object three times longer than the distance from the Sun to Pluto. "What we were seeing was the jets, and we could tell they were moving so fast that they already had expanded to a considerable size," he said. The VLA observations showed that the object's jet was moving at nine-tenths the speed of light. Other radio telescopes observing the object were NRAO's Green Bank Interferometer in West Virginia; the Australia Telescope Compact Array; the Molonglo Observatory Synthesis Telescope, also in Australia; the MERLIN array in Britain; the Ratan 600-meter radio telescope in Russia; and radio telescopes at the Owens Valley Radio Observatory in California. The radio observations also provided the distance measurement for the binary system. The dramatic X-ray flare on Sept. 15 was not the only time V4641 Sgr exploded into activity. Further examination of ASM data revealed a bright flare (about one-third as intense as the brightest flare) on Sept. 14th that lasted between three minutes and three hours. In response to the ASM team's alert, Michael McCollough and Peter Woods, members of the BATSE team at Marshall Space Flight Center, scoured their data for evidence of V4641 Sgr. In addition to the flares seen by the ASM, they found a third rapid flare that peaked two hours after the brightest flare, reaching a peak intensity about half that of the brightest flare. The RXTE Proportional Counter Array (PCA), a very large X-ray telescope, was rapidly reoriented to observe V4641 Sgr about 4.5 hours after the brightest flare. A fourth event, lasting 20 minutes, was recorded by the PCA to reach an intensity of one-sixth that of the brightest flare. The PCA data reveal complex substructure, with luminosity changes by a factor of four within one second, and by a factor of 500 within minutes. No further high-energy emission from V4641 Sgr has been observed with any satellite since the end of the flare seen by the PCA. "Combining the data from all three instruments, we saw four of the most dramatic rapid X-ray intensity changes ever seen from one star," Smith said. "This behavior is new. We've never see anything like it." The proximity of the object "gives us an unusual close-up look at this phenomenon," Hjellming said. If future searches for brief X-ray flares reveal that there are more objects like V4641 Sgr, "we will have a whole new source of information that can help us decipher just how jets in X-ray binaries work," Remillard said. The VLA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The RXTE is a NASA explorer mission consisting of X-ray instruments built by teams at Goddard Space Flight Center, MIT and the University of California at San Diego.

Detection of Sagittarius A* at 330 MHz With the Very Large Array

DTIC Science & Technology

2004-01-20

our Galaxy’s central massive black hole , at 330 MHz with the Very Large Array. Implications for the spectrum and emission processes of Sgr A * are... A East, the Sgr A West H ii region, and Sgr A *, recently established as our Galaxy’s central massive black hole (e.g., Ghez et al. 2000; Eckart et al...toward Sgr A *. This could be explained by a localized clearing of the ambient gas accomplished either through the direct influence of the black hole

The effects of redshifts and focusing on the spectrum of an accretion disk in the galactic center black hole candidate Sagittarius A(sup *)

NASA Technical Reports Server (NTRS)

Hollywood, J. M.; Melia, Fulvio

1995-01-01

There are firm indications that Sgr A(sup *), a compact, nonthermal radio source at the Galactic center, may be powered by the dissipation of gravitational energy as gas trapped from an ambient wind descends down the potential well, first through a quasi-spherical inflow (extending out to approximately 3 x 10(exp 16) cm) and then through a small accretion disk at less than or approximately = 5-10 Schwarzschild radii. Earlier three-dimensional Bondi-Hoyle numerical simulations have indicated that fluctuations in the accreted specific angular momentum can lead to a variability in the disk flux on a timescale of years. With greatly improved flux measurements at K and H, and the hint of a approximately 10 minute modulation in the IR luminosity, it is crucial to model the disk emission much more precisely than has been attempted thus far. In this Letter we take into account the effects of Doppler and gravitational redshifts, the light-travel time factor, and the light bending near the black hole to determine the measurable spectrum of Sgr A(sup *) in the increasingly important 10(exp 13) Hz less than or approximately = v less than or approximately = 10(exp 16) Hz frequency range. We find that the relativistic disk spectrum is much softer than its Newtonian counterpart, with a predicted UV flux roughly an order of magnitude smaller than had previously been anticipated. In addition, we find that when the physical conditions in the disk are taken to be consistent with the properties of the quasi-spherical infall (specifically, in terms of the accretion rate and disk size), only a slowly spinning or Schwarzschild black hole appears to fit the observations. Our calculations also reveal that the disk flux is much more weakly dependent on the observer's inclination angle than had been suspected on the basis of earlier Newtonian estimates.

Very-high energy observations of the galactic center region by VERITAS in 2010-2012

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archer, A.; Beilicke, M.; Buckley, J. H.

2014-08-01

The Galactic center is an interesting region for high-energy (0.1-100 GeV) and very-high-energy (E > 100 GeV) γ-ray observations. Potential sources of GeV/TeV γ-ray emission have been suggested, e.g., the accretion of matter onto the supermassive black hole, cosmic rays from a nearby supernova remnant (e.g., Sgr A East), particle acceleration in a plerion, or the annihilation of dark matter particles. The Galactic center has been detected by EGRET and by Fermi/LAT in the MeV/GeV energy band. At TeV energies, the Galactic center was detected with moderate significance by the CANGAROO and Whipple 10 m telescopes and with high significancemore » by H.E.S.S., MAGIC, and VERITAS. We present the results from three years of VERITAS observations conducted at large zenith angles resulting in a detection of the Galactic center on the level of 18 standard deviations at energies above ∼2.5 TeV. The energy spectrum is derived and is found to be compatible with hadronic, leptonic, and hybrid emission models discussed in the literature. Future, more detailed measurements of the high-energy cutoff and better constraints on the high-energy flux variability will help to refine and/or disentangle the individual models.« less

A pacemaker with P = 2.48 h modulated the generator of flares in the X-ray light curve of Sgr A* in the year 2012

NASA Astrophysics Data System (ADS)

Leibowitz, Elia

2017-01-01

In an intensive observational campaign in the nine month duration of Chandra X-ray Visionary Project that was conducted in the year 2012, 39 large X-ray flares of Sgr A* were recorded. An analysis of the times of the observed flares reveals that the 39 flares are separated in time by intervals that are grouped around integer numbers times 0.10333 days. This time interval is thus the period of a uniform grid of equally spaced points on the time axis. The grouping of the flares around tic marks of this grid is derived from the data with at least a 3.2 σ level of statistical significance. No signal of any period can be found among 22 flares recorded by Chandra in the years 2013-2014. If the 0.10333 day period is that of a nearly circular Keplerian orbit around the blackhole at the center of the Galaxy, its radius is at 7.6 Schwarzschild radii. Large flares were more likely to be triggered when the agent responsible for their outbursts was near the peri-center phase of its slightly eccentric orbit.

SGR9, a RING type E3 ligase, modulates amyloplast dynamics important for gravity sensing.

NASA Astrophysics Data System (ADS)

Morita, Miyo T.; Nakamura, Moritaka; Tasaka, Masao

Gravitropism is triggered when the directional change of gravity is sensed in the specific cells, called statocytes. In higher plants, statocytes contain sinking heavier amyloplasts which are particular plastids accumulating starch granules. The displacement of amyloplasts within the statocytes is thought to be the initial event of gravity perception. We have demonstrated that endodermal cells are most likely to be the statocytes in Arabidop-sis shoots. Live cell imaging of the endodermal cell of stem has shown that most amyloplasts are sediment to the direction of gravity but they are not static. Several amyloplasts move dynamically in an actin filament (F-actin) dependent manner. In the presence of actin poly-merization inhibitor, all amyloplasts become static and sediment to the direction of gravity. In addition, stems treated with the inhibitor can exhibit gravitropism. These results suggest that F-actin-dependent dynamic movement of amyloplasts is not essential for gravity sensing. sgr (shoot gravitropism) 9 mutant exhibits greatly reduced shoot gravitropism. In endodermal cells of sgr9, dynamic amyloplast movement was predominantly observed and amyloplasts did not sediment to the direction of gravity. Interestingly, inhibition of actin polymerization re-stored both gravitropism and amyloplast sedimentation in sgr9. The SGR9 encodes a novel RING finger protein, which is localized to amyloplasts in endodermal cells. SGR9 showed ubiq-uitin E3 ligase activity in vitro. Together with live cell imaging of amyloplasts and F-actin, our data suggest that SGR9 modulate interaction between amyloplasts and F-actin on amylo-plasts. SGR9 positively act on amyloplasts sedimentation, probably by releasing amyloplasts from F-actin. SGR9 that is localized to amyloplast, possibly degrades unknown substrates by its E3 ligase activity, and this might promote release of amyloplasts from F-actin.

From model to crop: functional analysis of a STAY-GREEN gene in the model legume Medicago truncatula and effective use of the gene for alfalfa improvement.

PubMed

Zhou, Chuanen; Han, Lu; Pislariu, Catalina; Nakashima, Jin; Fu, Chunxiang; Jiang, Qingzhen; Quan, Li; Blancaflor, Elison B; Tang, Yuhong; Bouton, Joseph H; Udvardi, Michael; Xia, Guangmin; Wang, Zeng-Yu

2011-11-01

Medicago truncatula has been developed into a model legume. Its close relative alfalfa (Medicago sativa) is the most widely grown forage legume crop in the United States. By screening a large population of M. truncatula mutants tagged with the transposable element of tobacco (Nicotiana tabacum) cell type1 (Tnt1), we identified a mutant line (NF2089) that maintained green leaves and showed green anthers, central carpels, mature pods, and seeds during senescence. Genetic and molecular analyses revealed that the mutation was caused by Tnt1 insertion in a STAY-GREEN (MtSGR) gene. Transcript profiling analysis of the mutant showed that loss of the MtSGR function affected the expression of a large number of genes involved in different biological processes. Further analyses revealed that SGR is implicated in nodule development and senescence. MtSGR expression was detected across all nodule developmental zones and was higher in the senescence zone. The number of young nodules on the mutant roots was higher than in the wild type. Expression levels of several nodule senescence markers were reduced in the sgr mutant. Based on the MtSGR sequence, an alfalfa SGR gene (MsSGR) was cloned, and transgenic alfalfa lines were produced by RNA interference. Silencing of MsSGR led to the production of stay-green transgenic alfalfa. This beneficial trait offers the opportunity to produce premium alfalfa hay with a more greenish appearance. In addition, most of the transgenic alfalfa lines retained more than 50% of chlorophylls during senescence and had increased crude protein content. This study illustrates the effective use of knowledge gained from a model system for the genetic improvement of an important commercial crop.

From Model to Crop: Functional Analysis of a STAY-GREEN Gene in the Model Legume Medicago truncatula and Effective Use of the Gene for Alfalfa Improvement1[W][OA

PubMed Central

Zhou, Chuanen; Han, Lu; Pislariu, Catalina; Nakashima, Jin; Fu, Chunxiang; Jiang, Qingzhen; Quan, Li; Blancaflor, Elison B.; Tang, Yuhong; Bouton, Joseph H.; Udvardi, Michael; Xia, Guangmin; Wang, Zeng-Yu

2011-01-01

Medicago truncatula has been developed into a model legume. Its close relative alfalfa (Medicago sativa) is the most widely grown forage legume crop in the United States. By screening a large population of M. truncatula mutants tagged with the transposable element of tobacco (Nicotiana tabacum) cell type1 (Tnt1), we identified a mutant line (NF2089) that maintained green leaves and showed green anthers, central carpels, mature pods, and seeds during senescence. Genetic and molecular analyses revealed that the mutation was caused by Tnt1 insertion in a STAY-GREEN (MtSGR) gene. Transcript profiling analysis of the mutant showed that loss of the MtSGR function affected the expression of a large number of genes involved in different biological processes. Further analyses revealed that SGR is implicated in nodule development and senescence. MtSGR expression was detected across all nodule developmental zones and was higher in the senescence zone. The number of young nodules on the mutant roots was higher than in the wild type. Expression levels of several nodule senescence markers were reduced in the sgr mutant. Based on the MtSGR sequence, an alfalfa SGR gene (MsSGR) was cloned, and transgenic alfalfa lines were produced by RNA interference. Silencing of MsSGR led to the production of stay-green transgenic alfalfa. This beneficial trait offers the opportunity to produce premium alfalfa hay with a more greenish appearance. In addition, most of the transgenic alfalfa lines retained more than 50% of chlorophylls during senescence and had increased crude protein content. This study illustrates the effective use of knowledge gained from a model system for the genetic improvement of an important commercial crop. PMID:21957014

Mendel's green cotyledon gene encodes a positive regulator of the chlorophyll-degrading pathway

PubMed Central

Sato, Yutaka; Morita, Ryouhei; Nishimura, Minoru; Yamaguchi, Hiroyasu; Kusaba, Makoto

2007-01-01

Mutants that retain greenness of leaves during senescence are known as “stay-green” mutants. The most famous stay-green mutant is Mendel's green cotyledon pea, one of the mutants used in determining the law of genetics. Pea plants homozygous for this recessive mutation (known as i at present) retain greenness of the cotyledon during seed maturation and of leaves during senescence. We found tight linkage between the I locus and stay-green gene originally found in rice, SGR. Molecular analysis of three i alleles including one with no SGR expression confirmed that the I gene encodes SGR in pea. Functional analysis of sgr mutants in pea and rice further revealed that leaf functionality is lowered despite a high chlorophyll a (Chl a) and chlorophyll b (Chl b) content in the late stage of senescence, suggesting that SGR is primarily involved in Chl degradation. Consistent with this observation, a wide range of Chl–protein complexes, but not the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, were shown to be more stable in sgr than wild-type plants. The expression of OsCHL and NYC1, which encode the first enzymes in the degrading pathways of Chl a and Chl b, respectively, was not affected by sgr in rice. The results suggest that SGR might be involved in activation of the Chl-degrading pathway during leaf senescence through translational or posttranslational regulation of Chl-degrading enzymes. PMID:17709752

Mendel's green cotyledon gene encodes a positive regulator of the chlorophyll-degrading pathway.

PubMed

Sato, Yutaka; Morita, Ryouhei; Nishimura, Minoru; Yamaguchi, Hiroyasu; Kusaba, Makoto

2007-08-28

Mutants that retain greenness of leaves during senescence are known as "stay-green" mutants. The most famous stay-green mutant is Mendel's green cotyledon pea, one of the mutants used in determining the law of genetics. Pea plants homozygous for this recessive mutation (known as i at present) retain greenness of the cotyledon during seed maturation and of leaves during senescence. We found tight linkage between the I locus and stay-green gene originally found in rice, SGR. Molecular analysis of three i alleles including one with no SGR expression confirmed that the I gene encodes SGR in pea. Functional analysis of sgr mutants in pea and rice further revealed that leaf functionality is lowered despite a high chlorophyll a (Chl a) and chlorophyll b (Chl b) content in the late stage of senescence, suggesting that SGR is primarily involved in Chl degradation. Consistent with this observation, a wide range of Chl-protein complexes, but not the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, were shown to be more stable in sgr than wild-type plants. The expression of OsCHL and NYC1, which encode the first enzymes in the degrading pathways of Chl a and Chl b, respectively, was not affected by sgr in rice. The results suggest that SGR might be involved in activation of the Chl-degrading pathway during leaf senescence through translational or posttranslational regulation of Chl-degrading enzymes.

A SEARCH FOR l-C{sub 3}H{sup +} AND l-C{sub 3}H IN Sgr B2(N), Sgr B2(OH), AND THE DARK CLOUD TMC-1

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGuire, Brett A.; Carroll, P. Brandon; Loomis, Ryan A.

2013-09-01

Pety et al. recently reported the detection of several transitions of an unknown carrier in the Horsehead PDR and attribute them to l-C{sub 3}H{sup +}. Here, we have tested the predictive power of their fit by searching for, and identifying, the previously unobserved J = 1-0 and J = 2-1 transitions of the unknown carrier (B11244) toward Sgr B2(N) in data from the publicly available PRIMOS project. Also presented here are observations of the J = 6-5 and J = 7-6 transitions toward Sgr B2(N) and Sgr B2(OH) using the Barry E. Turner Legacy Survey and results from the Kaifumore » et al. survey of TMC-1. We calculate an excitation temperature and column density of B11244 of {approx}10 K and {approx}10{sup 13} cm{sup -2} in Sgr B2(N) and {approx}79 K with an upper limit of {<=}1.5 Multiplication-Sign 10{sup 13} cm{sup -2} in Sgr B2(OH) and find trace evidence for the cation's presence in TMC-1. Finally, we present spectra of the neutral species in both Sgr B2(N) and TMC-1, and comment on the robustness of the assignment of the detected signals to l-C{sub 3}H{sup +}.« less

Evidence for a decay of the faint flaring rate of Sgr A* from 2013 Aug., 13 months before a rise of the before a rise of the bright one

NASA Astrophysics Data System (ADS)

Mossoux, E.; Grosso, N.

2017-10-01

Thanks to the overall 1999-2015 Chandra, XMM-Newton and Swift observations of the supermassive black hole at the center of our Galaxy, Sgr A*, we tested the significance and persistence of the increase of 'bright and very bright' X-ray flaring rate (FR) argued by Ponti et al. (2015). We detected the flares observed with Swift using the binned light curves whereas those observed by XMM-Newton and Chandra were detected using the two-steps Bayesian blocks (BB) algorithm with a prior number of change-points properly calibrated. We then applied this algorithm on the flare arrival times corrected from the detection efficiency computed for each observation thanks to the observed distribution of flare fluxes and durations. We confirmed a constant overall FR and a rise of the FR for the faintest flares from 2014 Aug. 31 and identified a decay of the FR for the brightest flares from 2013 Aug. and Nov. A mass transfer from the Dusty S-cluster Object/G2 to Sgr A* is not required to produce the rise of bright FR since the energy saved by the decay of the number of faint flares during a long time period may be later released by several bright flares during a shorter time period.

X-raying the Galactic centre

NASA Astrophysics Data System (ADS)

Ponti, G.

2017-10-01

The advent of XMM-Newton and Chandra led to major advancements in our comprehension of the physics at heart of the Milky Way. I will discuss some of the most recent findings related to the present activity of Sgr A* (the supermassive black hole at the Milky Way center), the signatures of its glorious past and the traces of powerful energy releases within the central degrees of the Galaxy.

[Methods and Applications to estimate the conversion factor of Resource-Based Relative Value Scale for nurse-midwife's delivery service in the national health insurance].

PubMed

Kim, Jinhyun; Jung, Yoomi

2009-08-01

This paper analyzed alternative methods of calculating the conversion factor for nurse-midwife's delivery services in the national health insurance and estimated the optimal reimbursement level for the services. A cost accounting model and Sustainable Growth Rate (SGR) model were developed to estimate the conversion factor of Resource-Based Relative Value Scale (RBRVS) for nurse-midwife's services, depending on the scope of revenue considered in financial analysis. The data and sources from the government and the financial statements from nurse-midwife clinics were used in analysis. The cost accounting model and SGR model showed a 17.6-37.9% increase and 19.0-23.6% increase, respectively, in nurse-midwife fee for delivery services in the national health insurance. The SGR model measured an overall trend of medical expenditures rather than an individual financial status of nurse-midwife clinics, and the cost analysis properly estimated the level of reimbursement for nurse-midwife's services. Normal vaginal delivery in nurse-midwife clinics is considered cost-effective in terms of insurance financing. Upon a declining share of health expenditures on midwife clinics, designing a reimbursement strategy for midwife's services could be an opportunity as well as a challenge when it comes to efficient resource allocation.

Molecular breeding of a novel orange-brown tomato fruit with enhanced beta-carotene and chlorophyll accumulation.

PubMed

Manoharan, Ranjith Kumar; Jung, Hee-Jeong; Hwang, Indeok; Jeong, Namhee; Kho, Kang Hee; Chung, Mi-Young; Nou, Ill-Sup

2017-01-01

Tomatoes provide a significant dietary source of the carotenoids, lycopene and β-carotene. During ripening, carotenoid accumulation determines the fruit colors while chlorophyll degradation. These traits have been, and continue to be, a significant focus for plant breeding efforts. Previous work has found strong evidence for a relationship between CYC-B gene expression and the orange color of fleshy fruit. Other work has identified a point mutation in SGR that impedes chlorophyll degradation and causes brown flesh color to be retained in some tomato varieties. We crossed two inbred lines, KNY2 (orange) and KNB1 (brown) and evaluated the relationship between these genes for their effect on fruit color. Phenotypes of F2 generation plants were analyzed and a novel 'orange-brown' fruit color was identified. We confirm two SNPs, one in CYC-B and another in SGR gene sequence, associated with segregation of 'orange-brown' fruit color in F2 generation. The carotenoid and chlorophyll content of a fleshy fruit was assessed across the different phenotypes and showed a strong correlation with expression pattern of carotenoid biosynthesis genes and SGR function. The orange-brown fruit has high β-carotene and chlorophyll. Our results provide valuable information for breeders to develop tomato fruit of a novel color using molecular markers.

Chemical Simulations of Prebiotic Molecules: Interstellar Ethanimine Isomers

NASA Astrophysics Data System (ADS)

Quan, Donghui; Herbst, Eric; Corby, Joanna F.; Durr, Allison; Hassel, George

2016-06-01

The E- and Z-isomers of ethanimine (CH3CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s-1 in the foreground of continuum emission generated by H II regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

Involvement of the Vacuoles of the Endodermis in the Early Process of Shoot Gravitropism in Arabidopsis

PubMed Central

Morita, Miyo Terao; Kato, Takehide; Nagafusa, Kiyoshi; Saito, Chieko; Ueda, Takashi; Nakano, Akihiko; Tasaka, Masao

2002-01-01

The endodermal cells of the shoot are thought to be the gravity-sensing cells in Arabidopsis. The amyloplasts in the endodermis that sediment in the direction of gravity may act as statoliths. Endodermis-specific expression of SGR2 and ZIG using the SCR promoter could complement the abnormal shoot gravitropism of the sgr2 and zig mutants, respectively. The abnormalities in amyloplast sedimentation observed in both mutants recovered simultaneously. These results indicate that both genes in the endodermal cell layer are crucial for shoot gravitropism. ZIG encodes AtVTI11, which is a SNARE involved in vesicle transport to the vacuole. The fusion protein of SGR2 and green fluorescent protein localized to the vacuole and small organelles. These observations indicate that ZIG and SGR2 are involved in the formation and function of the vacuole, a notion supported by the results of subcellular analysis of the sgr2 and zig mutants with electron microscopy. These results strongly suggest that the vacuole participates in the early events of gravitropism and that SGR2 and ZIG functions are involved. PMID:11826298

A Deep Near-Infrared Survey of the N 49 Region around the Soft Gamma-Ray Repeater 0526-66

NASA Technical Reports Server (NTRS)

Klose, S.; Henden, A. A.; Geppert, U.; Greiner, J.; Guetter, H. H.; Hartmann, D. H.; Kouveliotou, C.; Luginbuhl, C. B.; Stecklurn, B.; Vrba, F. J.

2004-01-01

We report the results of a deep near-infrared survey of the vicinity of supernova remnant N49 in the Large Magellanic Cloud (LMC), which contains the soft gamma-ray repeater (SGR) 0526-66. Two of the four confirmed SGRs are potentially associated with compact stellar clusters. We thus searched for a similar association of SGR0526-66, and find the unexplored young stellar cluster SL 463 at a projected distance of approx. 30 pc from the SGR. This constitutes the third cluster-SGR link, and lends support to scenarios in which SGR progenitors originate in young, embedded clusters. If real, the cluster-SGR association constrains the age and thus the initial mass of these stars. In addition, our high-resolution images of the super- nova remnant N49 reveal an area of excess K-band flux in the southeastern part of the SNR. This feature coincides with the maximum flux area at 8.28 microns as detected by the Midcourse Space Experiment (MSX satellite), which we identify with IRAS 052594607.

SAGITTARIUS STREAM THREE-DIMENSIONAL KINEMATICS FROM SLOAN DIGITAL SKY SURVEY STRIPE 82

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koposov, Sergey E.; Belokurov, Vasily; Evans, N. Wyn

2013-04-01

Using multi-epoch observations of the Stripe 82 region from the Sloan Digital Sky Survey (SDSS), we measure precise statistical proper motions of the stars in the Sagittarius (Sgr) stellar stream. The multi-band photometry and SDSS radial velocities allow us to efficiently select Sgr members and thus enhance the proper-motion precision to {approx}0.1 mas yr{sup -1}. We measure separately the proper motion of a photometrically selected sample of the main-sequence turn-off stars, as well as spectroscopically selected Sgr giants. The data allow us to determine the proper motion separately for the two Sgr streams in the south found in Koposov etmore » al. Together with the precise velocities from SDSS, our proper motions provide exquisite constraints of the three-dimensional motions of the stars in the Sgr streams.« less

XMM-Newton observations of the Galactic Centre Region - II. The soft-thermal emission

NASA Astrophysics Data System (ADS)

Heard, V.; Warwick, R. S.

2013-09-01

We have extended our earlier study of the X-ray emission emanating from the central 100 pc × 100 pc region of our Galaxy to an investigation of several features prominent in the soft X-ray (2-4.5 keV) band. We focus on three specific structures: a putative bipolar outflow from the vicinity of Sgr A*; a high surface brightness region located roughly 12 arcmin (25 pc) to the north-east of Sgr A* and a lower surface brightness extended loop feature seen to the south of Sgr A*. We show, unequivocally, that all three structures are thermal in nature and have similar temperatures (kT ≈ 1 keV). The inferred X-ray luminosities lie in the range (2-10) × 1034 erg s-1. In the case of the bipolar feature we suggest that the hot plasma is produced by the shock heating of the winds from massive stars within the Central Cluster, possibly collimated by the Circumnuclear Disc. Alternatively the outflow may be driven by outbursts on Sgr A*, which follow tidal disruption events occurring at a rate of roughly one every 4000 yr. The north-east enhancement is centred on a candidate pulsar wind nebula which has a relatively hard non-thermal X-ray spectrum. We suggest that the coincident soft-thermal emission traces the core of a new thermal-composite supernova remnant, designated as SNR G0.13-0.12. There is no clear evidence for an associated radio shell but such a feature may be masked by the bright emission of the nearby Radio Arc and other filamentary structures. SNR G0.13-0.12 is very likely interacting with the nearby molecular cloud, G0.11-0.11, and linked to the Fermi source, 2FGL J1746.4-2851c. Finally we explore a previous suggestion that the elliptically shaped X-ray loop to the south of Sgr A*, of maximum extent ˜45 pc, represents the shell of a superbubble located in the GC region. Although plausible, the interpretation of this feature in terms a coherent physical structure awaits confirmation.

Early Terrestrial Mantle Differentiation Recorded in Paleoarchean Komatiites

NASA Astrophysics Data System (ADS)

Puchtel, I. S.; Blichert-Toft, J.; Touboul, M.; Horan, M. F.; Walker, R. J.

2016-12-01

Geochmical signatures generated in the manle as a result of radioactive decay of short- and long-lived nuclides can be used to constrain the timing of formation and the nature of now mostly vanished early terrestrial reservoirs. The 3.55 Ga komatiites from the Schapenburg Greenstone Remnant (SGR) located in the Barberton Greenstone Belt in South Africa have a unique combination of trace element abundances and isotopic compositions that place strong constraints on the origin of these reservoirs. The SGR komatiites define a Re-Os isochron with an age of 3550±87 Ma and an initial γ187Os = +3.7±0.2 (2SD). The absolute HSE abundances in the mantle source of the SGR komatiite system are estimated to be only 29±5% of those in the present-day bulk silicate Earth (BSE) estimates. The SGR komatiites show coupled depletion, relative to the modern mantle, in 142Nd and 182W (μ142Nd = -5.0±2.8, μ182W = -8.4±4.5), the decay products of the short-lived 146Sm and 182Hf nuclides, respectively, indicating derivation from a mantle domain that was enriched in incompatible elements 30 Ma after Solar System formation. Early Hadean contributors to this mantle domain could include high-pressure fractionates from a primordial magma ocean. By contrast, the long-lived Sm-Nd and Lu-Hf isotope systems (ɛ143Nd = +2.4±0.1, ɛ176Hf = +5.7±0.3) indicate that the mantle domain that the SGR komatiites were ultimately derived from underwent additional processing after the early Hadean, including melt depletion at lower pressures. The preservation of early-formed 182W and 142Nd anomalies in the mantle until at least 3.55 Ga indicates that the products of early planetary differentiation survived both later planetary accretion and convective mantle mixing during the Hadean. This study lends further support to the notion that variable late accretion, by itself, cannot account for all of the observed W isotope and absolute and relative HSE abundance variations in the Archean mantle recorded by komatiites.

MAPPING THE DYNAMICS OF COLD GAS AROUND SGR A* THROUGH 21 cm ABSORPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christian, Pierre; Loeb, Abraham, E-mail: pchristian@cfa.harvard.edu

2015-11-20

The presence of a circumnuclear stellar disk around Sgr A* and megamaser systems near other black holes indicates that dense neutral disks can be found in galactic nuclei. We show that depending on their inclination angle, optical depth, and spin temperature, these disks could be observed spectroscopically through 21 cm absorption. Related spectroscopic observations of Sgr A* can determine its HI disk parameters and the possible presence of gaps in the disk. Clumps of dense gas similar to the G2 could could also be detected in 21 cm absorption against Sgr A* radio emission.

An Arabidopsis E3 Ligase, SHOOT GRAVITROPISM9, Modulates the Interaction between Statoliths and F-Actin in Gravity Sensing[W][OA

PubMed Central

Nakamura, Moritaka; Toyota, Masatsugu; Tasaka, Masao; Morita, Miyo Terao

2011-01-01

Higher plants use the sedimentation of amyloplasts in statocytes as statolith to sense the direction of gravity during gravitropism. In Arabidopsis thaliana inflorescence stem statocyte, amyloplasts are in complex movement; some show jumping-like saltatory movement and some tend to sediment toward the gravity direction. Here, we report that a RING-type E3 ligase SHOOT GRAVITROPISM9 (SGR9) localized to amyloplasts modulates amyloplast dynamics. In the sgr9 mutant, which exhibits reduced gravitropism, amyloplasts did not sediment but exhibited increased saltatory movement. Amyloplasts sometimes formed a cluster that is abnormally entangled with actin filaments (AFs) in sgr9. By contrast, in the fiz1 mutant, an ACT8 semidominant mutant that induces fragmentation of AFs, amyloplasts, lost saltatory movement and sedimented with nearly statically. Both treatment with Latrunculin B, an inhibitor of AF polymerization, and the fiz1 mutation rescued the gravitropic defect of sgr9. In addition, fiz1 decreased saltatory movement and induced amyloplast sedimentation even in sgr9. Our results suggest that amyloplasts are in equilibrium between sedimentation and saltatory movement in wild-type endodermal cells. Furthermore, this equilibrium is the result of the interaction between amyloplasts and AFs modulated by the SGR9. SGR9 may promote detachment of amyloplasts from AFs, allowing the amyloplasts to sediment in the AFs-dependent equilibrium of amyloplast dynamics. PMID:21602290

Altered gravitropic response, amyloplast sedimentation and circumnutation in the Arabidopsis shoot gravitropism 5 mutant are associated with reduced starch levels.

PubMed

Tanimoto, Mimi; Tremblay, Reynald; Colasanti, Joseph

2008-05-01

Plants have developed sophisticated gravity sensing mechanisms to interpret environmental signals that are vital for optimum plant growth. Loss of SHOOT GRAVITROPISM 5 (SGR5) gene function has been shown to affect the gravitropic response of Arabidopsis inflorescence stems. SGR5 is a member of the INDETERMINATE DOMAIN (IDD) zinc finger protein family of putative transcription factors. As part of an ongoing functional analysis of Arabidopsis IDD genes (AtIDD) we have extended the characterisation of SGR5, and show that gravity sensing amyloplasts in the shoot endodermis of sgr5 mutants sediment more slowly than wild type, suggesting a defect in gravity perception. This is correlated with lower amyloplast starch levels, which may account for the reduced gravitropic sensitivity in sgr5. Further, we find that sgr5 mutants have a severely attenuated stem circumnutation movement typified by a reduced amplitude and an decreased periodicity. adg1-1 and sex1-1 mutants, which contain no starch or increased starch, respectively, also show alterations in the amplitude and period of circumnutation. Together these results suggest that plant growth movement may depend on starch levels and/or gravity sensing. Overall, we propose that loss of SGR5 regulatory activity affects starch accumulation in Arabidopsis shoot tissues and causes decreased sensitivity to gravity and diminished circumnutational movements.

Feasibility of partial replacement of fishmeal with proteins from different sources in diets of Korean rockfish ( Sebastes schlegeli)

NASA Astrophysics Data System (ADS)

Yan, Quangen; Zhu, Xiaoming; Yang, Yunxia; Han, Dong; Xie, Shouqi

2014-12-01

An 8-week feeding experiment was conducted in an indoor recirculation seawater system to investigate the effects of partial replacement of dietary fishmeal with proteins from five sources on the growth performance and feed utilization of Sebastes schlegeli. Six isonitrogenous and isoenergetic diets were formulated using fishmeal (FM, the control) as sole protein source, or proteins from five sources including poultry by-product meal (PBM), meat and bone meal (MBM), soybean meal (SBM), cottonseed meal (CSM) and canola meal (CNM). Fifteen percent of the crude protein provided by fish meal was replaced, respectively. The results showed that the differences in specific growth rate (SGR) and survival rate (SR) among fish fed PBM, MBM, SBM, CSM and whole FM diets were not significant. However, SGR and SR of fish fed CNM diet was significantly lower than that of other treatments. Feeding rate, feed conversion, nutrient retention showed similar patterns to that of growth. Fish fed CSM and CNM showed significantly lower apparent digestibility coefficient (ADC) of dry matter and gross energy than those fed others while fish fed CNM showed lower ADC of crude protein than those fed others ( P<0.05). These results suggested that it was feasible to substitute 15% dietary protein provided by fishmeal with PBM, MBM, SBM and CSM, respectively, but not with CNM as the replacement with CNM reduced fish growth and feed utilization.

The Story of a Boring Encounter with a Black Hole

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-07-01

Remember the excitement three years ago before the gas cloud G2s encounter with the supermassive black hole at the center of our galaxy, Sgr A*? Did you notice that not much was said about it after the fact? Thats because not much happened and a new study suggests that this isnt surprising.An Anticipated ApproachG2,an object initially thought to be a gas cloud, was expected to make its closest approach to the 4.6-million-solar-mass Sgr A* in 2014. At the pericenter of its orbit, G2 was predicted to pass as close as 36 light-hours from the black hole.Log-scale column density plots from one of the authors simulations, showing the cloud at a time relative to periapsis (t=0) of 5, 1, 0, 1, 5, and 10 yr (left to right, top to bottom). [Morsony et al. 2017]This close brush with such a massive black hole was predicted to tear G2 apart, causing much of its material to accrete onto Sgr A*. It was thought that this process would temporarily increase the accretion rate onto the black hole relative to its normal background accretion rate, causing Sgr A*s luminosity to increase for a time.Instead, Sgr A* showed a distinct lack of fireworks, with very minimal change to its brightness after G2s closest approach. This cosmic fizzle has raised questions about the nature of G2: was it really a gas cloud? What else might it have been instead? Now, a team of scientists led by Brian Morsony (University of Maryland and University of Wisconsin-Madison) have run a series of simulations of the encounter to try to address these questions.No FireworksMorsony and collaborators ran three-dimensional hydrodynamics simulations using the FLASH code. They used a range of different simulation parameters, like cloud structure, background structure, background density, grid resolution, and accretion radius, in order to better understand how these factors might have affected the accretion rate and corresponding luminosity of Sgr A*.Accretion rate vs. time for two of the simulations, one with a wind background and one with no wind background. The accretion rate in both cases displays no significant increase when G2 reaches periapsis. [Morsony et al. 2017]Based on their simulations, the authors showed that we actually shouldnt expect G2s encounter to have caused a significant change in Sgr A*s accretion rate relative to its normal rate from background accretion: with the majority of the simulation parameters used, only 321% of the material Sgr A* accreted from 05 years after periapsis is from the cloud, and only 0.0310% of the total cloud mass is accreted.Not Just a Cloud?By comparing their simulations to observations of G2 after its closest approach, Morsony and collaborators find that to fit the observations, G2 cannot be solely a gas cloud. Instead, two components are likely needed: an extended, cold, low-mass gas cloud responsible for most of the emission before G2 approached pericenter, and a very compact component such as a dusty stellar object that dominates the emission observed since pericenter.The authors argue that any future emission detected should no longer be from the cloud, but only from the compact core or dusty stellar object. Future observations should help us to confirm this model but in the meantime these simulations give us a better sense of why G2s encounter with Sgr A* was such a fizzle.CitationBrian J. Morsony et al 2017 ApJ 843 29. doi:10.3847/1538-4357/aa773d

Toxic effects of two sources of dietborne cadmium on the juvenile cobia, Rachycentron canadum L. and tissue-specific accumulation of related minerals.

PubMed

Liu, Kang; Chi, Shuyan; Liu, Hongyu; Dong, Xiaohui; Yang, Qihui; Zhang, Shuang; Tan, Beiping

2015-08-01

In the present study, juvenile cobia, Rachycentron canadum L. were fed diets contaminated by two different sources of cadmium: squid viscera meal (SVM-Cd, organic form) and cadmium chloride (CdCl2-Cd, inorganic form). The Cd concentrations in fish diet were approximate 3.0, 5.0 and 10.0mg Cd kg(-1) for both inorganic and organic forms. In the control diet (0.312mg Cd kg(-1) diet, Cd mainly come from fish meal), no cadmium was added. The experiment lasted for 16 weeks and a statistically significant inverse relationship was observed between specific growth rate (SGR) and the concentration of dietary Cd. The SGR of cobia fed a diet with SVM-Cd increased at the lowest doses and decreased with the increasing level of dietary SVM. Fish fed diet contaminated SVM-Cd had significantly higher SGR than those fed diets contaminated CdCl2-Cd among the high Cd level diets treatments. The dietary Cd levels also significantly affected the survival rate of the fish. Among the hematological characteristics and plasma constituents, glutamic-pyruvic transaminase activities and alkaline phosphatase activities in serum and liver increased and hepatic superoxide dismutase activity decreased with the increasing dietary Cd levels. The cobia fed diet contaminated by high level of CdCl2-Cd had significantly higher ALP activity than cobia fed diet contaminated by high level of SVM-Cd. The results from these studies indicate no differences in toxicity response to dietborne SVM-Cd and CdCl2-Cd at a low level of Cd. However, at a higher level, cobia was more sensitive to dietborne CdCl2-Cd than SVM-Cd. Based on quadratic regression of SGR, The Cd concentrations was 3.617mg kg(-1) in the optimal diet, Cd source was SVM (126mg Cd kg(-1) in SVM) which stimulate the growth of cobia and the added level was determined to be 26.7g kg(-1) diet in the present study. Cd accumulations in the kidney of cobia fed both types of Cd were higher than other tissues, and the order of Cd accumulation in tissues were kidney>liver>intestine>gill>muscle. Iron accumulation in liver and kidney and calcium accumulation in vertebra and scale were also significantly affected by dietary Cd levels. Copyright © 2015 Elsevier B.V. All rights reserved.

Magnetic novae

NASA Astrophysics Data System (ADS)

Zemko, Polina; Orio, Marina

2016-07-01

We present the results of optical and X-ray observations of two quiescent novae, V2491 Cyg and V4743 Sgr. Our observations suggest the intriguing possibility of localization of hydrogen burning in magnetic novae, in which accretion is streamed to the polar caps. V2491 Cyg was observed with Suzaku more than 2 years after the outburst and V4743 Sgr was observed with XMM Newton 2 and 3.5 years after maximum. In the framework of a monitoring program of novae previously observed as super soft X-ray sources we also obtained optical spectra of V4743 Sgr with the SALT telescope 11.5 years after the eruption and of V2491 Cyg with the 6m Big Azimutal Telescope 4 and 7 years post-outburst. In order to confirm the possible white dwarf spin period of V2491 Cyg measured in the Suzaku observations we obtained photometric data using the 90cm WIYN telescope at Kitt Peak and the 1.2 m telescope in Crimea. We found that V4743 Sgr is an intermediate polar (IP) and V2491 Cyg is a strong IP candidate. Both novae show modulation of their X-ray light curves and have X-ray spectra typical of IPs. The Suzaku and XMM Newton exposures revealed that the spectra of both novae have a very soft blackbody-like component with a temperature close to that of the hydrogen burning white dwarfs in their SSS phases, but with flux by at least two orders of magnitude lower, implying a possible shrinking of emitting regions in the thin atmosphere that is heated by nuclear burning underneath it. In quiescent IPs, independently of the burning, an ultrasoft X-ray flux component originates at times in the polar regions irradiated by the accretion column, but the soft component of V4743 Sgr disappeared in 2006, indicating that the origin may be different from accretion. We suggest it may have been due to an atmospheric temperature gradient on the white dwarf surface, or to continuing localized thermonuclear burning at the bottom of the envelope, before complete turn-off. The optical spectra of V2491 Cyg and V4743 Sgr showed the prominent He II 4686 A line and the Bowen blend, which indicate a hot region, with peak temperature in the ultraviolet range. This may be the same region that previously emitted supersoft X-rays, and later cooled shifting the peak of emission to the ultraviolet.

Frequency analysis of heart rate variability: a useful assessment tool of linearly polarized near-infrared irradiation to stellate ganglion area for burning mouth syndrome.

PubMed

Momota, Yukihiro; Takano, Hideyuki; Kani, Koichi; Matsumoto, Fumihiro; Motegi, Katsumi; Aota, Keiko; Yamamura, Yoshiko; Omori, Mayuko; Tomioka, Shigemasa; Azuma, Masayuki

2013-03-01

Burning mouth syndrome (BMS) is characterized by the following subjective complaints without distinct organic changes: burning sensation in mouth or chronic pain of tongue. BMS is also known as glossodynia; both terms are used equivalently in Japan. Although the real cause of BMS is still unknown, it has been pointed out that BMS is related to some autonomic abnormality, and that stellate ganglion near-infrared irradiation (SGR) corrects the autonomic abnormality. Frequency analysis of heart rate variability (HRV) is expected to be useful for assessing autonomic abnormality. This study investigated whether frequency analysis of HRV could reveal autonomic abnormality associated with BMS, and whether autonomic changes were corrected after SGR. Eight subjects received SGR; the response to SGR was assessed by frequency analysis of HRV. No significant difference of autonomic activity concerning low-frequency (LF) norm, high-frequency (HF) norm, and low-frequency/high-frequency (LF/HF) was found between SGR effective and ineffective groups. Therefore, we proposed new parameters: differential normalized low frequency (D LF norm), differential normalized high frequency (D HF norm), and differential low-frequency/high-frequency (D LF/HF), which were defined as differentials between original parameters just before and after SGR. These parameters as indexes of responsiveness of autonomic nervous system (ANS) revealed autonomic changes in BMS, and BMS seems to be related to autonomic instability rather than autonomic imbalance. Frequency analysis of HRV revealed the autonomic instability associated with BMS and enabled tracing of autonomic changes corrected with SGR. It is suggested that frequency analysis of HRV is very useful in follow up of BMS and for determination of the therapeutic efficacy of SGR. Wiley Periodicals, Inc.

Stars Form Surprisingly Close to Milky Way's Black Hole

NASA Astrophysics Data System (ADS)

2005-10-01

The supermassive black hole at the center of the Milky Way has surprisingly helped spawn a new generation of stars, according to observations from NASA's Chandra X-ray Observatory. This novel mode of star formation may solve several mysteries about the supermassive black holes that reside at the centers of nearly all galaxies. "Massive black holes are usually known for violence and destruction," said Sergei Nayakshin of the University of Leicester, United Kingdom, and coauthor of a paper on this research in an upcoming issue of the Monthly Notices of the Royal Astronomical Society. "So it's remarkable that this black hole helped create new stars, not just destroy them." Black holes have earned their fearsome reputation because any material -- including stars -- that falls within the so-called event horizon is never seen again. However, these new results indicate that the immense disks of gas known to orbit many black holes at a "safe" distance from the event horizon can help nurture the formation of new stars. Animation of Stars Forming Around Black Hole Animation of Stars Forming Around Black Hole This conclusion came from new clues that could only be revealed in X-rays. Until the latest Chandra results, astronomers have disagreed about the origin of a mysterious group of massive stars discovered by infrared astronomers to be orbiting less than a light year from the Milky Way's central black hole, a.k.a. Sagittarius A*, or Sgr A*. At such close distances to Sgr A*, the standard model for star formation predicts that gas clouds from which stars form should have been ripped apart by tidal forces from the black hole. Two models to explain this puzzle have been proposed. In the disk model, the gravity of a dense disk of gas around Sgr A* offsets the tidal forces and allows stars to form; in the migration model, the stars formed in a star cluster far away from the black hole and migrated in to form the ring of massive stars. The migration scenario predicts about a million low mass, sun-like stars in and around the ring, whereas in the disk model, the number of low mass stars could be much less. Nayakshin and his coauthor, Rashid Sunyaev of the Max Plank Institute for Physics in Garching, Germany, used Chandra observations to compare the X-ray glow from the region around Sgr A* to the X-ray emission from thousands of young stars in the Orion Nebula star cluster. They found that the Sgr A* star cluster contains only about 10,000 low mass stars, thereby ruling out the migration model. "We can now say that the stars around Sgr A* were not deposited there by some passing star cluster, rather they were born there," said Sunyaev . "There have been theories that this was possible, but this is the first real evidence. Many scientists are going to be very surprised by these results." Because the Galactic Center is shrouded in dust and gas, it has not been possible to look for the low-mass stars in optical observations. In contrast, X-ray data have allowed astronomers to penetrate the veil of gas and dust and look for these low mass stars. Scenario Dismissed by Chandra Results Scenario Dismissed by Chandra Results "In one of the most inhospitable places in our Galaxy, stars have prevailed," said Nayakshin. "It appears that star formation is much more tenacious than we previously believed." The results suggest that the "rules" of star formation change when stars form in the disk of a giant black hole. Because this environment is very different from typical star formation regions, there is a change in the proportion of stars that form. For example, there is a much higher percentage of massive stars in the disks around black holes. And, when these massive stars explode as supernovae, they will "fertilize" the region with heavy elements such as oxygen. This may explain the large amounts of such elements observed in the disks of young supermassive black holes. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass. Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Detection of sulfur in the galactic center

NASA Technical Reports Server (NTRS)

Herter, T.; Briotta, D. A., Jr.; Gull, G. E.; Shure, M. A.; Houck, J. R.

1983-01-01

A strong detection at the S III forbidden 18.71 micron line is reported for the galactic center region, Sgr A West. A line flux of 1.7 + or - 0.2 x 10 to the -17th W/sq cm is found for a 20 inch beam size measurement centered on IRS 1. A preliminary analysis indicates that the S III abundance relative to hydrogen is consistent with the cosmic abundance of sulfur, 0.000016, if a filling factor of unity within the known clumps is assumed. However, the sulfur abundance in the galactic center may be as much as a factor of 3 overabundant if a filling factor of 0.03 is adopted, a value found to hold for some galactic H II regions.

AN IMPROVED DISTANCE AND MASS ESTIMATE FOR SGR A* FROM A MULTISTAR ORBIT ANALYSIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boehle, A.; Ghez, A. M.; Meyer, L.

2016-10-10

We present new, more precise measurements of the mass and distance of our Galaxy’s central supermassive black hole, Sgr A*. These results stem from a new analysis that more than doubles the time baseline for astrometry of faint stars orbiting Sgr A*, combining 2 decades of speckle imaging and adaptive optics data. Specifically, we improve our analysis of the speckle images by using information about a star’s orbit from the deep adaptive optics data (2005–2013) to inform the search for the star in the speckle years (1995–2005). When this new analysis technique is combined with the first complete re-reduction ofmore » Keck Galactic Center speckle images using speckle holography, we are able to track the short-period star S0-38 ( K -band magnitude = 17, orbital period = 19 yr) through the speckle years. We use the kinematic measurements from speckle holography and adaptive optics to estimate the orbits of S0-38 and S0-2 and thereby improve our constraints of the mass ( M {sub bh}) and distance ( R {sub o} ) of Sgr A*: M {sub bh} = (4.02 ± 0.16 ± 0.04) × 10{sup 6} M {sub ⊙} and 7.86 ± 0.14 ± 0.04 kpc. The uncertainties in M {sub bh} and R {sub o} as determined by the combined orbital fit of S0-2 and S0-38 are improved by a factor of 2 and 2.5, respectively, compared to an orbital fit of S0-2 alone and a factor of ∼2.5 compared to previous results from stellar orbits. This analysis also limits the extended dark mass within 0.01 pc to less than 0.13 × 10{sup 6} M {sub ⊙} at 99.7% confidence, a factor of 3 lower compared to prior work.« less

SGRL can regulate chlorophyll metabolism and contributes to normal plant growth and development in Pisum sativum L.

PubMed

Bell, Andrew; Moreau, Carol; Chinoy, Catherine; Spanner, Rebecca; Dalmais, Marion; Le Signor, Christine; Bendahmane, Abdel; Klenell, Markus; Domoney, Claire

2015-12-01

Among a set of genes in pea (Pisum sativum L.) that were induced under drought-stress growth conditions, one encoded a protein with significant similarity to a regulator of chlorophyll catabolism, SGR. This gene, SGRL, is distinct from SGR in genomic location, encoded carboxy-terminal motif, and expression through plant and seed development. Divergence of the two encoded proteins is associated with a loss of similarity in intron/exon gene structure. Transient expression of SGRL in leaves of Nicotiana benthamiana promoted the degradation of chlorophyll, in a manner that was distinct from that shown by SGR. Removal of a predicted transmembrane domain from SGRL reduced its activity in transient expression assays, although variants with and without this domain reduced SGR-induced chlorophyll degradation, indicating that the effects of the two proteins are not additive. The combined data suggest that the function of SGRL during growth and development is in chlorophyll re-cycling, and its mode of action is distinct from that of SGR. Studies of pea sgrL mutants revealed that plants had significantly lower stature and yield, a likely consequence of reduced photosynthetic efficiencies in mutant compared with control plants under conditions of high light intensity.

The 12C/13C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

NASA Astrophysics Data System (ADS)

Halfen, D. T.; Woolf, N. J.; Ziurys, L. M.

2017-08-01

A study has been conducted of 12C/13C ratios in five complex molecules in the Galactic center. H2CS, CH3CCH, NH2CHO, CH2CHCN, and CH3CH2CN and their 13C-substituted species have been observed in numerous transitions at 1, 2, and 3 mm, acquired in a spectral-line survey of Sgr B2(N), conducted with the telescopes of the Arizona Radio Observatory (ARO). Between 22 and 54 individual, unblended lines for the 12C species and 2-54 for 13C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found to consistently exhibit two velocity components near V LSR ˜ 64 and 73 km s-1, with column densities ranging from N tot ˜ 3 × 1014 - 4 × 1017 cm-2 and ˜2 × 1013 - 1 × 1017 cm-2 for the 12C and 13C species, respectively. Based on 14 different isotopic combinations, ratios were obtained in the range 12C/13C = 15 ± 5 to 33 ± 13, with an average value of 24 ± 7, based on comparison of column densities. These measurements better anchor the 12C/13C ratio at the Galactic center, and suggest a slightly revised isotope gradient of 12C/13C = 5.21(0.52) D GC + 22.6(3.3). As indicated by the column densities, no preferential 13C enrichment was found on the differing carbon sites of CH3CCH, CH2CHCN, and CH3CH2CN. Because of the elevated temperatures in Sgr B2(N), 13C isotopic substitution is effectively “scrambled,” diminishing chemical fractionation effects. The resulting ratios thus reflect stellar nucleosynthesis and Galactic chemical evolution, as is likely the case for most warm clouds.

Search for gamma-ray events in the BATSE data base

NASA Technical Reports Server (NTRS)

Lewin, Walter

1994-01-01

We find large location errors and error radii in the locations of channel 1 Cygnus X-1 events. These errors and their associated uncertainties are a result of low signal-to-noise ratios (a few sigma) in the two brightest detectors for each event. The untriggered events suffer from similarly low signal-to-noise ratios, and their location errors are expected to be at least as large as those found for Cygnus X-1 with a given signal-to-noise ratio. The statistical error radii are consistent with those found for Cygnus X-1 and with the published estimates. We therefore expect approximately 20 - 30 deg location errors for the untriggered events. Hence, many of the untriggered events occurring within a few months of the triggered activity from SGR 1900 plus 14 are indeed consistent with the SGR source location, although Cygnus X-1 is also a good candidate.

Unveiling the past of the Galactic nucleus with X-ray echoes

NASA Astrophysics Data System (ADS)

Chuard, D.; Terrier, R.; Goldwurm, A.; Clavel, M.; Soldi, S.; Morris, M. R.; Ponti, G.; Walls, M.; Chernyakova, M.

2017-12-01

Giant molecular clouds populating the central molecular zone have a high enough column density to reflect X-rays coming from strong compact sources in their neighbourhood, including possible powerful outbursts from the Galactic supermassive black hole SgrA. From observations of the molecular complex Sgr C made with the X-ray observatories XMM and Chandra between 2000 and 2014, we confirm this reflection scenario, even though the region hosts several objects (including two PWN candidates) that may be responsible for intense cosmic-ray production. By comparing data to Monte Carlo simulated reflection spectra, we are able to put the best constraints to date on the line-of-sight positions of the main bright clumps of the molecular complex. Ultimately, extending this approach by the inclusion of other molecular complexes allows us to partially reconstruct the past lightcurve of the Galactic supermassive black hole.

The 2001 April Burst Activation of SGR 1900-14: Pulse Properties and Torque

NASA Technical Reports Server (NTRS)

Woods, P. M.; Kouveliotou, C.; Goegues, E.; Finger, M. H.; Feroci, M.; Mereghetti, S.; Swank, J. H.; Hurley, K.; Heise, J.; Smith D.

2003-01-01

We report on observations of SGR 1900+14 made with the Rossi X-Ray Timing Explorer (RXTE) and BeppoSAXduring the 2001 April burst activation of the source. Using these data, we measure the spin-down torque on the star and confirm earlier findings that the torque and burst activity are not directly correlated. We compare the X-ray pulse profile to the gamma-ray profile during the April 18 intermediate flare and show that (1) their shapes are similar and (1) the gamma-ray profile aligns closely in phase with the X-ray pulsations. The good phase alignment of the gamma-ray and X-ray profiles suggests that there was no rapid spin-down following this flare of the magnitude inferred for the August 27 giant flare. We discuss how these observations further constrain magnetic field reconfiguration models for the large flares of SGRs.

The Sagittarius Dwarf Galaxy Survey (SDGS) - I. Colour-magnitude diagrams, reddening and population gradients. First evidence of a very metal-poor population

NASA Astrophysics Data System (ADS)

Bellazzini, M.; Ferraro, F. R.; Buonanno, R.

1999-04-01

We present the first results of a large photometric survey devoted to the study of the star formation history of the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Three wide strips (size ~ 9 x 35 arcmin ^2) located at ~ (l deg b deg) = (6.5;-16), (6;-14), (5;-12) have been observed. Each strip is roughly east-west oriented, nearly along the major axis of the galaxy. A control field (size ~ 9 x 24 arcmin ^2), located outside the body of Sgr dSph [~ (l deg b deg) = (354;-14)] has also been observed for statistical decontamination purposes. Accurate and well-calibrated V, I photometry down to V ~ 22 has been obtained for ~ 90 000 stars towards the Sgr dSph and ~ 8000 stars in the control field. This is the largest photometric sample (covering the widest spatial extension) ever observed in the Sgr dSph up to now. The main new results presented in this paper are: (1) the possible discovery of a strong asymmetry in the distribution of stars along the major axis, since the north-western arm of the Sgr galaxy (i.e. the region nearer to the Galactic bulge) apparently shows a significant deficiency of Sgr stars and (2) the first direct detection of a very metal-poor (and presumably old) population in the Sgr stellar content. Hints at a metallicity gradient towards the densest region of the galaxy are also reported.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dierickx, Marion I. P.; Loeb, Abraham, E-mail: mdierickx@cfa.harvard.edu, E-mail: aloeb@cfa.harvard.edu

The extensive span of the Sagittarius (Sgr) stream makes it a promising tool for studying the gravitational potential of the Milky Way (MW). Characterizing its stellar kinematics can constrain halo properties and provide a benchmark for the paradigm of galaxy formation from cold dark matter. Accurate models of the disruption dynamics of the Sgr progenitor are necessary to employ this tool. Using a combination of analytic modeling and N -body simulations, we build a new model of the Sgr orbit and resulting stellar stream. In contrast to previous models, we simulate the full infall trajectory of the Sgr progenitor frommore » the time it first crossed the MW virial radius 8 Gyr ago. An exploration of the parameter space of initial phase-space conditions yields tight constraints on the angular momentum of the Sgr progenitor. Our best-fit model is the first to accurately reproduce existing data on the 3D positions and radial velocities of the debris detected 100 kpc away in the MW halo. In addition to replicating the mapped stream, the simulation also predicts the existence of several arms of the Sgr stream extending to hundreds of kiloparsecs. The two most distant stars known in the MW halo coincide with the predicted structure. Additional stars in the newly predicted arms can be found with future data from the Large Synoptic Survey Telescope. Detecting a statistical sample of stars in the most distant Sgr arms would provide an opportunity to constrain the MW potential out to unprecedented Galactocentric radii.« less

Search for quasi-periodic signals in magnetar giant flares. Bayesian inspection of SGR 1806-20 and SGR 1900+14

NASA Astrophysics Data System (ADS)

Pumpe, Daniel; Gabler, Michael; Steininger, Theo; Enßlin, Torsten A.

2018-02-01

Quasi-periodic oscillations (QPOs) discovered in the decaying tails of giant flares of magnetars are believed to be torsional oscillations of neutron stars. These QPOs have a high potential to constrain properties of high-density matter. In search for quasi-periodic signals, we study the light curves of the giant flares of SGR 1806-20 and SGR 1900+14, with a non-parametric Bayesian signal inference method called D3PO. The D3PO algorithm models the raw photon counts as a continuous flux and takes the Poissonian shot noise as well as all instrument effects into account. It reconstructs the logarithmic flux and its power spectrum from the data. Using this fully noise-aware method, we do not confirm previously reported frequency lines at ν ≳ 17 Hz because they fall into the noise-dominated regime. However, we find two new potential candidates for oscillations at 9.2 Hz (SGR 1806-20) and 7.7 Hz (SGR 1900+14). If these are real and the fundamental magneto-elastic oscillations of the magnetars, current theoretical models would favour relatively weak magnetic fields B̅ 6× 1013-3 × 1014 G (SGR 1806-20) and a relatively low shear velocity inside the crust compared to previous findings. Data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/610/A61

Star motion around rotating black hole in the Galactic Center in real time

NASA Astrophysics Data System (ADS)

Dokuchaev, Vyacheslav; Nazarova, Natalia

2017-12-01

The Event Horizon Telescope team intends by the 2020 to resolve the shadow of supermassive black hole SgrA* in the Galactic Center. It would be the first attempt for direct identification of the enigmatic black hole. In other words, it would be the first experimental verification of the General Relativity in the strong field limit. There is a chance to find a star moving on the relativistic orbit close to this black hole. We present the animated numerical model of the gravitational lensing of a star (or any other lighting probe), moving around rotating Kerr black hole in the Galactic Center and viewed by the distant observer.

Galactic center gamma-ray excess from dark matter annihilation: is there a black hole spike?

PubMed

Fields, Brian D; Shapiro, Stuart L; Shelton, Jessie

2014-10-10

If the supermassive black hole Sgr A* at the center of the Milky Way grew adiabatically from an initial seed embedded in a Navarro-Frenk-White dark matter (DM) halo, then the DM profile near the hole has steepened into a spike. We calculate the dramatic enhancement to the gamma-ray flux from the Galactic center (GC) from such a spike if the 1-3 GeV excess observed in Fermi data is due to DM annihilations. We find that for the parameter values favored in recent fits, the point-source-like flux from the spike is 35 times greater than the flux from the inner 1° of the halo, far exceeding all Fermi point source detections near the GC. We consider the dependence of the spike signal on astrophysical and particle parameters and conclude that if the GC excess is due to DM, then a canonical adiabatic spike is disfavored by the data. We discuss alternative Galactic histories that predict different spike signals, including (i) the nonadiabatic growth of the black hole, possibly associated with halo and/or black hole mergers, (ii) gravitational interaction of DM with baryons in the dense core, such as heating by stars, or (iii) DM self-interactions. We emphasize that the spike signal is sensitive to a different combination of particle parameters than the halo signal and that the inclusion of a spike component to any DM signal in future analyses would provide novel information about both the history of the GC and the particle physics of DM annihilations.

THE GALACTIC CENTER CLOUD G2-A YOUNG LOW-MASS STAR WITH A STELLAR WIND

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scoville, N.; Burkert, A.

2013-05-10

We explore the possibility that the G2 gas cloud falling in toward SgrA* is the mass-loss envelope of a young T Tauri star. As the star plunges to smaller radius at 1000-6000 km s{sup -1}, a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA*. For a stellar mass-loss rate of 4 Multiplication-Sign 10{sup -8} M{sub Sun} yr{sup -1} and wind velocity 100 km s{sup -1}, the bow shock will have an emission measure (EM = n {sup 2} vol) at a distance {approx}10{sup 16} cm, similar tomore » that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA*, while the latter will have increasing emission at lesser distances. In this model, the star and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter ({approx}3 AU for a stellar mass of 2 M{sub Sun }). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.« less

The Essential Oils of Rhaponticum carthamoides Hairy Roots and Roots of Soil-Grown Plants: Chemical Composition and Antimicrobial, Anti-Inflammatory, and Antioxidant Activities.

PubMed

Skała, Ewa; Rijo, Patrícia; Garcia, Catarina; Sitarek, Przemysław; Kalemba, Danuta; Toma, Monika; Szemraj, Janusz; Pytel, Dariusz; Wysokińska, Halina; Śliwiński, Tomasz

2016-01-01

The essential oils were isolated by hydrodistillation from the hairy roots (HR) and roots of soil-grown plants (SGR) of Rhaponticum carthamoides and were analyzed by GC-MS method. In the both essential oils 62 compounds were identified. The root essential oils showed the differences in the qualitative and quantitative composition. The sesquiterpene hydrocarbons (55-62%) dominated in both essential oils. The major compounds of HR essential oil were cyperene, 13-norcypera-1(5),11(12)-diene, and cadalene while aplotaxene, nardosina-1(10),11-diene, and dauca-4(11),8-diene dominated in SGR essential oil. Both essential oils showed antibacterial activity especially against Enterococcus faecalis (ATCC 29212) and Pseudomonas aeruginosa (ATCC 27853) (MIC value = 125  µ g/mL). HR and SGR essential oils also decreased the expression of IL-1 β , IL-6, and TNF- α and the ROS level in LPS-treatment astrocytes. This is the first report to describe the chemical composition of R. carthamoides essential oil from hairy roots, its protective effect against LPS-induced inflammation and ROS production in astrocytes, and its antimicrobial potential. The results show that R. carthamoides hairy roots may be a valuable source of the essential oil and may be an alternative to the roots of soil-grown plants.

The Essential Oils of Rhaponticum carthamoides Hairy Roots and Roots of Soil-Grown Plants: Chemical Composition and Antimicrobial, Anti-Inflammatory, and Antioxidant Activities

PubMed Central

Rijo, Patrícia; Garcia, Catarina; Kalemba, Danuta; Toma, Monika; Szemraj, Janusz; Pytel, Dariusz; Śliwiński, Tomasz

2016-01-01

The essential oils were isolated by hydrodistillation from the hairy roots (HR) and roots of soil-grown plants (SGR) of Rhaponticum carthamoides and were analyzed by GC-MS method. In the both essential oils 62 compounds were identified. The root essential oils showed the differences in the qualitative and quantitative composition. The sesquiterpene hydrocarbons (55–62%) dominated in both essential oils. The major compounds of HR essential oil were cyperene, 13-norcypera-1(5),11(12)-diene, and cadalene while aplotaxene, nardosina-1(10),11-diene, and dauca-4(11),8-diene dominated in SGR essential oil. Both essential oils showed antibacterial activity especially against Enterococcus faecalis (ATCC 29212) and Pseudomonas aeruginosa (ATCC 27853) (MIC value = 125 µg/mL). HR and SGR essential oils also decreased the expression of IL-1β, IL-6, and TNF-α and the ROS level in LPS-treatment astrocytes. This is the first report to describe the chemical composition of R. carthamoides essential oil from hairy roots, its protective effect against LPS-induced inflammation and ROS production in astrocytes, and its antimicrobial potential. The results show that R. carthamoides hairy roots may be a valuable source of the essential oil and may be an alternative to the roots of soil-grown plants. PMID:28074117

The Sagittarius Dwarf Galaxy Survey (SDGS): Constraints on the Star Formation History of the Sgr dSph

NASA Astrophysics Data System (ADS)

Bellazzini, M.; Ferraro, F. R.; Buonanno, R.

1999-01-01

We present the first results of a large photometric survey devoted to the study of the star formation history in the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Three large (size: 9 x 35 arcmin2) and widely spaced fields located nearly along the Sgr dSph major axis [(l,b) = (6.5 -16);(6-14);(5-12)] have been observed in the V and I passbands with the ESO-NTT 3.5-m telescope (La Silla - Chile). Well-calibrated photometry has been obtained for ˜90000 stars toward Sgr dSph and for ˜9000 stars in a (9 x 24 arcmin2) control field down to a limiting magnitude of V 22. At present this is the largest photometric (CCD) sample of Sgr dSph stars and the wide spacing between field provides the first opportunity of studying the stellar content of different regions of the galaxy (over a range of ˜2 Kpc across). Age and metallicity estimates are obtained for the detected stellar populations and the very first evidences are presented for (a) spatial differences in the stellar content and (b) the detection of a very metal poor population in the field of the Sgr galaxy.

The LSS 4300: A hot counterpart of Upsilon Sgr and KS Per?

NASA Technical Reports Server (NTRS)

Drilling, J. S.; Schoenberner, D.

1983-01-01

A number of observations indicate that the star LSS 4300 is a high temperature analog of the hydrogen-deficient binaries upsilon Sgr and KS Per. A preliminary model-atmosphere analysis based on high-dispersion spectra obtained at Kitt Peak and Cerro Tololo yields T(eff) = 14,400 K, log(g) = 1.4, n(H)/n(He) = 0.003, and n(N)/n(C) = 20 (the corresponding values for upsilon Sgr are T(eff) = 10,000 K, log(g) = 1, n(H)/n(He) = 0.0005, and n(N)/n(C) = 20). The optical emission-line spectrum of LSS 4300 is nearly identical to that of upsilon Sgr, including strong, broad H alpha, FeII and Ca II emission. The ultraviolet spectrum of LSS 4300 was observed with IUE, and can be attributed almost entirely to the visible star. The JHKL photometry of LSS 4300 obtained at Cerro Tololo reveals an infrared excess nearly identical to that of upsilon Sgr. It is suggested that LSS 4300, like upsilon Sgr and KS Per, is a close binary system consisting of a helium supergiant of about one solar mass, and a secondary which is overluminous for its mass due to the accretion of matter from the primary, which is undergoing its second mass exchange.

The influence of Sagittarius and the Large Magellanic Cloud on the stellar disc of the Milky Way Galaxy

NASA Astrophysics Data System (ADS)

Laporte, Chervin F. P.; Johnston, Kathryn V.; Gómez, Facundo A.; Garavito-Camargo, Nicolas; Besla, Gurtina

2018-06-01

We present N-body simulations of a Sagittarius-like dwarf spheroidal galaxy (Sgr) that follow its orbit about the Milky Way (MW) since its first crossing of the Galaxy's virial radius to the present day. As Sgr orbits around the MW, it excites vertical oscillations, corrugating and flaring the Galactic stellar disc. These responses can be understood by a two-phase picture in which the interaction is first dominated by torques from the wake excited by Sgr in the MW dark halo before transitioning to tides from Sgr's direct impact on the disc at late times. We show for the first time that a massive Sgr model simultaneously reproduces the locations and motions of arc-like over densities, such as the Monoceros Ring and the Triangulum Andromeda stellar clouds, that have been observed at the extremities of the disc, while also satisfying the solar neighbourhood constraints on the vertical structure and streaming motions of the disc. In additional simulations, we include the Large Magellanic Cloud (LMC) self consistently with Sgr. The LMC introduces coupling through constructive and destructive interference, but no new corrugations. In our models, the excitation of the current structure of the outer disk can be traced to interactions as far back as 6-7 Gyr ago (corresponding to z ≤ 1). Given the apparently quiescent accretion history of the MW over this timescale, this places Sgr as the main culprit behind the vertical oscillations of the disc and the last major accretion event for the Galaxy with the capacity to modulate its chemodynamical structure.

Detection of sulphur in the galactic center

NASA Technical Reports Server (NTRS)

Herter, T.; Briotta, D. A., Jr.; Gull, G. E.; Shure, M. A.; Houck, J. R.

1983-01-01

A strong detection at the (SIII) 18.71 micron line is reported for the Galactic Center region, Sgr A West. A line flux of 1.7 + or - 0.2x10 to the -17th power W cm(-2) is found for a 20-arc second beam-size measurement centered on IRS 1. A preliminary analysis indicates that the SIII abundance relative to hydrogen is consistent with the cosmic abundance of sulfur, 1.6x10 to the -5th power, if a filling factor of unity within the known clumps is assumed. However, the sulfur abundance in the Galactic Center may be as much as a factor of 3 overabundant if a filling factor of 0.03 is adopted, a value found to hold for some galactic HII regions.

Understanding Sgr A* with PIC Simulations of Particle Acceleration in Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Ozel, Feryal

2017-09-01

Sgr A* has been the subject of intense observational studies with Chandra. In the proposed work, we will investigate magnetic reconnection and particle acceleration in low-luminosity black hole accretion flows using a combination of GRMHD and particle-in-cell (PIC) simulations. We will use the PIC simulations to understand how particles are accelerated when magnetic energy is dissipated and quantify the resulting electron energy distributions. Incorporating the results of the microphysical studies into the global simulations of Sgr A*, we will investigate the origin of the intense X-ray flares observed with Chandra. We will also study how these processes affect the 1.3 mm image size in preparation for the upcoming simultaneous Chandra and EHT observations of Sgr A*.

Chemistry of the organic-rich hot core G327.3-0.6

NASA Technical Reports Server (NTRS)

Gibb, E.; Nummelin, A.; Irvine, W. M.; Whittet, D. C.; Bergman, P.; Ferris, J. P. (Principal Investigator)

2000-01-01

We present gas-phase abundances of species found in the organic-rich hot core G327.3-0.6. The data were taken with the Swedish-ESO Submillimetre Telescope (SEST). The 1-3 mm spectrum of this source is dominated by emission features of nitrile species and saturated organics, with abundances greater than those found in many other hot cores, including Sgr B2 and OMC-1. Population diagram analysis indicates that many species (CH3CN, C2H3CN, C2H5CN, CH3OH, etc.) have hot components that originate in a compact (2") region. Gas-phase chemical models cannot reproduce the high abundances of these molecules found in hot cores, and we suggest that they originate from processing and evaporation of icy grain mantle material. In addition, we report the first detection of vibrationally excited ethyl cyanide and the first detection of methyl mercaptan (CH3SH) outside the Galactic center.

Detection of interstellar N2O: A new molecule containing an N-O bond

NASA Astrophysics Data System (ADS)

Ziurys, L. M.; Apponi, A. J.; Hollis, J. M.; Snyder, L. E.

1994-12-01

A new interstellar molecule, N2O, known as nitrous oxide or 'laughing gas,' has been detected using the NRAO 12 m telescope. The J = 3 - 2, 4 - 3, 5 - 4, and 6 - 5 rotational transitions of this species at 75, 100, 125, and 150 GHz, respectively, were observed toward Sgr B2(M). The column density derived for N2O in this source is Ntot approx. 1015/sq. cm, which corresponds to a fractional abundance of approx. 10-9, relative to H2. This value implies abundance ratios of N2O/NO approx. 0.1 and N2O/HNO approx. 3 in the Galactic center. Such ratios are in excellent agreement with predictions of ion-molecule models of interstellar chemistry using early-time calculations and primarily neutral-neutral reactions. N2O is the third interstellar molecule detected thus far containing an N-O bond. Such bonds cannot be so rare as previously thought.

Detection of interstellar N2O: A new molecule containing an N-O bond

NASA Technical Reports Server (NTRS)

Ziurys, L. M.; Apponi, A. J.; Hollis, J. M.; Snyder, L. E.

1994-01-01

A new interstellar molecule, N2O, known as nitrous oxide or 'laughing gas,' has been detected using the NRAO 12 m telescope. The J = 3 - 2, 4 - 3, 5 - 4, and 6 - 5 rotational transitions of this species at 75, 100, 125, and 150 GHz, respectively, were observed toward Sgr B2(M). The column density derived for N2O in this source is N(sub tot) approx. 10(exp 15)/sq. cm, which corresponds to a fractional abundance of approx. 10(exp -9), relative to H2. This value implies abundance ratios of N2O/NO approx. 0.1 and N2O/HNO approx. 3 in the Galactic center. Such ratios are in excellent agreement with predictions of ion-molecule models of interstellar chemistry using early-time calculations and primarily neutral-neutral reactions. N2O is the third interstellar molecule detected thus far containing an N-O bond. Such bonds cannot be so rare as previously thought.

Studying the SGR 1806-20/Cl* 1806-20 Region Using the Fermi Large Area Telescope

NASA Astrophysics Data System (ADS)

Yeung, Paul K. H.; Kong, Albert K. H.; Tam, P. H. Thomas; Lin, Lupin C. C.; Hui, C. Y.; Hu, Chin-Ping; Cheng, K. S.

2016-08-01

The region around SGR 1806-20 and its host stellar cluster Cl* 1806-20 is a potentially important site of particle acceleration. The soft γ-ray repeater and Cl* 1806-20, which also contains several very massive stars including a luminous blue variable hypergiant LBV 1806-20, are capable of depositing a large amount of energy to the surroundings. Using the data taken with the Fermi Large Area Telescope (LAT), we identified an extended LAT source to the southwest of Cl* 1806-20. The centroid of the 1-50 GeV emission is consistent with that of HESS J1808-204 (until now unidentified). The LAT spectrum is best-fit by a broken power law with the break energy {E}{{b}}=297+/- 15 {MeV}. The index above E b is 2.60 ± 0.04 and is consistent with the flux and spectral index above 100 GeV for HESS J1808-204, suggesting an association between the two sources. Meanwhile, the interacting supernova remnant SNR G9.7-0.0 is also a potential contributor to the LAT flux. A tentative flux enhancement at the MeV band during a 45 day interval (2011 January 21-March 7) is also reported. We discuss possible origins of the extended LAT source in the context of both leptonic and hadronic scenarios.

The Sleeping Giant, NuSTAR Observations of magnetar SGR 1806-20

NASA Astrophysics Data System (ADS)

Younes, George; Baring, Matthew; Kouveliotou, Chryssa; Harding, Alice; Donavan, Sophia; Gogus, Ersin; Kaspi, Victoria; Granot, Jonathan

2018-01-01

Magnetars are a subclass of isolated neutron stars known for their extreme transient behavior, on different time-scales ranging from milliseconds to years. On the seconds time-scales, almost all magnetars have been observed to enter bursting episodes where they emit 10s to 100s of short (~0.1 s), bright (1.0e37-1.0e41 erg), hard X-ray bursts within the span of days to weeks. These episodes are usually accompanied by an alteration of the source persistent X-ray emission, during which the spectral and temporal properties of the magnetar change drastically. The source persistent X-ray flux increases, occasionally by as many as three orders of magnitude, while its timing properties vary, either in the form of a glitch or a more gradual change in the spin-down rate. Three magnetars have so far shown a Gaint Flare, an immense flare of energy (E~1.0e46 erg) lasting for few hundred seconds. I will report on the analysis of 5 NuSTAR observations of SGR 1806-20, the last magnetar to emit a giant flare (December 2004), taken between April 2015 to April 2016. I will discuss the long-term temporal and spectral behavior of the source from 1993 to 2016, i.e., prior, during, and after its major bursting bursting episode of 2004.

A snapshot of the inner dusty regions of a R CrB-type variable

NASA Astrophysics Data System (ADS)

Leão, I. C.; de Laverny, P.; Chesneau, O.; Mékarnia, D.; de Medeiros, J. R.

2007-05-01

Context: R Coronae Borealis (R CrB) variable stars are suspected to sporadically eject optically thick dust clouds causing, when one of them lies on the line-of-sight, a huge brightness decline in visible light. Direct detections with 8-m class adaptive optics of such clouds located at about 0.2-0.3 arcsec from the center (~1000 stellar radii) were recently reported for RY Sgr, the brightest R CrB of the southern hemisphere. Aims: Mid-infrared interferometric observations of RY Sgr allowed us to explore the circumstellar regions much closer to the central star (~20-40 mas) to look for the signature of any heterogeneities and to characterize them. Methods: Using the VLTI/MIDI instrument, five dispersed visibility curves in the N-band were recorded in May and June 2005 with different projected baselines oriented towards two roughly perpendicular directions. The large spatial frequencies' visibility curves exhibit a sinusoidal shape, whereas, at shorter spatial frequencies' visibility curves follow a Gaussian decrease. These observations are well interpreted with a geometrical model consisting of a central star surrounded by an extended circumstellar envelope in which one bright cloud is embedded. Results: Within this simple geometrical scheme, the inner 110 AU dusty environment of RY Sgr is dominated at the time of observations by a single dusty cloud, which at 10 μm represents ~10% of the total flux of the whole system, slightly less that the star flux. The cloud is located at about 100 stellar radii (or ~30 AU) from the center toward the East-North-East direction (or the symmetric direction with respect to center) within a circumstellar envelope whose FWHM is about 120 stellar radii. This first detection of a cloud so close to the central star supports the classical scenario of the R CrB brightness variations in the optical spectral domain and demonstrates the feasibility of a temporal monitoring of the dusty environment of this star on a monthly scale. Based on observations collected with the VLTI/MIDI instrument at Paranal Observatory, ESO (Chile) - Programme 75.D-0660. FITS files for the visibilities are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/466/L1

Approaching hell's kitchen: Molecular daredevil clouds in the vicinity of Sagittarius A* ⋆⋆

NASA Astrophysics Data System (ADS)

Moser, Lydia; Sánchez-Monge, Álvaro; Eckart, Andreas; Requena-Torres, Miguel A.; García-Marin, Macarena; Kunneriath, Devaky; Zensus, Anton; Britzen, Silke; Sabha, Nadeen; Shahzamanian, Banafsheh; Borkar, Abhijeet; Fischer, Sebastian

2017-07-01

We report serendipitous detections of line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) in bands 3, 6, and 7 in the central parsec down to within 1'' around Sgr A* at an up to now highest resolution (<0.5'') view of the Galactic center (GC) in the submillimeter (sub-mm) domain. From the 100 GHz continuum and the H39α emission we obtain a uniform electron temperature around Te 6000 K for the minispiral. The spectral index (S ∝ να) of Sagittarius A* (Sgr A*) is 0.5 at 100-250 GHz and 0.0 at 230-340 GHz. The bright sources in the center show spectral indices around -0.1 implying Bremsstrahlung emission, while dust emission is emerging in the minispiral exterior. Apart from CS, which is most widespread in the center, H13CO+, HC3N, SiO, SO, C2H, CH3OH, 13CS and N2H+ are also detected. The bulk of the clumpy emission regions is at positive velocities and in a region confined by the minispiral northern arm (NA), bar, and the sources IRS 3 and 7. Although partly spatially overlapping with the radio recombination line (RRL) emission at same negative velocities, the relation to the minispiral remains unclear. A likely explanation is an infalling clump consisting of denser cloud cores embedded in diffuse gas. This central association (CA) of clouds shows three times higher CS/X (X: any other observed molecule) ratios than the circumnuclear disk (CND) suggesting a combination of higher excitation, by a temperature gradient and/or infrared (IR) pumping, and abundance enhancement due to UV and/or X-ray emission. Hence, we conclude that this CA is closer to the center than the CND is to the center. Moreover, we find molecular line emission at velocities up to 200 km s-1. Apart from the CA, we identified two intriguing regions in the CND. One region shows emission in all molecular species and higher energy levels tested in this and previous observations and contains a methanol class I maser. The other region shows similar behavior of the line ratios such as the CA. Outside the CND, we find the traditionally quiescent gas tracer N2H+ coinciding with the largest IR dark clouds in the field. Methanol emission is found at and around previously detected methanol class I masers in the same region. We propose to make these particular regions subject to further studies in the scope of hot core, cold core, and extreme photon and/or X-ray dominated region (PDR/XDR) chemistry and consequent star formation in the central few parsecs. Based on ALMA observations under the project number 2011.0.00887.S, which were executed on 18 May 2012.Supplementary data (reduced FITS cubes and images) of the continuum and line emission listed in Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/603/A68

APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy System

NASA Astrophysics Data System (ADS)

Hasselquist, Sten; Shetrone, Matthew D.; Smith, Verne V.; Holtzman, Jon A.; McWilliam, Andrew; APOGEE Team

2018-06-01

The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze the chemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars with [Fe/H] > -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function. We then exploit the unique chemical abundance patters of the Sgr core to trace stars belonging to the Sgr tidal streams elsewhere in the Milky Way.

Study of the gamma-ray spectrum from the Galactic Center in view of multi-TeV dark matter candidates

NASA Astrophysics Data System (ADS)

Belikov, Alexander V.; Zaharijas, Gabrijela; Silk, Joseph

2012-10-01

Motivated by the complex gamma-ray spectrum of the Galactic Center source now measured over five decades in energy, we revisit the issue of the role of dark matter (DM) annihilations in this interesting region. We reassess whether the emission measured by the HESS collaboration could be a signature of dark matter annihilation, and we use the Fermi LAT spectrum to model the emission from SgrA*, using power-law spectral fits. We find that good fits are achieved by a power law with an index ˜2.5-2.6, in combination with a spectrum similar to the one observed from pulsar population and with a spectrum from a ≳10TeV DM annihilating to a mixture of bb¯ and harder τ+τ- channels and with boost factors of the order of a hundred. Alternatively, we also consider the combination of a log-parabola fit with the DM contribution. Finally, as both the spectrum of gamma rays from the Galactic Center and the spectrum of cosmic ray electrons exhibit a cutoff at TeV energies, we study the dark matter fits to both data sets. Constraining the spectral shape of the purported dark matter signal provides a robust way of comparing data. We find a marginal overlap only between the 99.999% C.L. regions in parameter space.

The SGR-ReSI and its application for GNSS reflectometry on the NASA EV-2 CYGNSS mission

NASA Astrophysics Data System (ADS)

Unwin, M.; Jales, P.; Blunt, P.; Duncan, S.; Brummitt, M.; Ruf, C.

As part of the EV-2 Cyclone Global Navigation Satellite System (CYGNSS) mission team, Surrey will be providing the Delay Doppler Mapping Instrument (DDMI) for eight Observatories designed and built by the University of Michigan and Southwest Research Institute (SwRI). Following the success of the GPS Reflectometry Experiment on the UK-DMC 1 satellite launched in 2003, Surrey has developed the SGR-ReSI as a move towards operational reflectometry and other applications. The Space GPS Receiver Remote Sensing Instrument (SGR-ReSI) is a COTS-electronics based GNSS receiver which can support up to eight programmable front-ends. It allows collection of raw sampled data but also is capable of processing the reflections into Delay Doppler Maps in real time. The first flight of the SGR-ReSI will be on the UK TechDemoSat-1 to prove the instrument and its various applications. The SGR-ReSI on CYGNSS has a different configuration to that on TechDemoSat-1 which is needed to focus on the requirements for operational cyclone sensing.

Sanguinarine interacts with chromatin, modulates epigenetic modifications, and transcription in the context of chromatin.

PubMed

Selvi B, Ruthrotha; Pradhan, Suman Kalyan; Shandilya, Jayasha; Das, Chandrima; Sailaja, Badi Sri; Shankar G, Naga; Gadad, Shrikanth S; Reddy, Ashok; Dasgupta, Dipak; Kundu, Tapas K

2009-02-27

DNA-binding anticancer agents cause alteration in chromatin structure and dynamics. We report the dynamic interaction of the DNA intercalator and potential anticancer plant alkaloid, sanguinarine (SGR), with chromatin. Association of SGR with different levels of chromatin structure was enthalpy driven with micromolar dissociation constant. Apart from DNA, it binds with comparable affinity with core histones and induces chromatin aggregation. The dual binding property of SGR leads to inhibition of core histone modifications. Although it potently inhibits H3K9 methylation by G9a in vitro, H3K4 and H3R17 methylation are more profoundly inhibited in cells. SGR inhibits histone acetylation both in vitro and in vivo. It does not affect the in vitro transcription from DNA template but significantly represses acetylation-dependent chromatin transcription. SGR-mediated repression of epigenetic marks and the alteration of chromatin geography (nucleography) also result in the modulation of global gene expression. These data, conclusively, show an anticancer DNA binding intercalator as a modulator of chromatin modifications and transcription in the chromatin context.

Unveiling the Nature of Soft Gamma Repeaters and Magnetars: Scientists Measure the Most Powerful Magnet Known

NASA Technical Reports Server (NTRS)

Swank, Jean (Technical Monitor); Parke, William

2002-01-01

This newsletter from NASA Goddard Space Flight Center (GSFC) announces measurements of the magnetic field of a magnetar. The magnetic field was approx. 10(exp 15) gauss, up to 10 times more powerful than previous estimates. The newsletter also describes how the star's magnetic field slows its rotation, and how starquakes emit protons, which are trapped in this neutron star's magnetic field, and make it a soft gamma repeater (SGR).

Symbiotic Stars in X-rays. II. Faint Sources Detected with XMM-Newton and Chandra

NASA Technical Reports Server (NTRS)

Nunez, N. E.; Luna, G. J. M.; Pillitteri, I.; Mukai, K.

2014-01-01

We report the detection from four symbiotic stars that were not known to be X-ray sources. These four object show a ß-type X-ray spectrum, that is, their spectra can be modeled with an absorbed optically thin thermal emission with temperatures of a few million degrees. Photometric series obtained with the Optical Monitor on board XMM-Newton from V2416 Sgr and NSV 25735 support the proposed scenario where the X-ray emission is produced in a shock-heated region inside the symbiotic nebulae.

ISOLATED WOLF-RAYET STARS AND O SUPERGIANTS IN THE GALACTIC CENTER REGION IDENTIFIED VIA PASCHEN-{alpha} EXCESS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mauerhan, J. C.; Stolovy, S. R.; Cotera, A.

We report the discovery of 19 hot, evolved, massive stars near the Galactic center region (GCR). These objects were selected for spectroscopy owing to their detection as strong sources of Paschen-{alpha} (P{alpha}) emission-line excess, following a narrowband imaging survey of the central 0.{sup 0}65 x 0.{sup 0}25 (l, b) around Sgr A* with the Hubble Space Telescope. Discoveries include six carbon-type (WC) and five nitrogen-type (WN) Wolf-Rayet stars, six O supergiants, and two B supergiants. Two of the O supergiants have X-ray counterparts having properties consistent with solitary O stars and colliding-wind binaries. The infrared photometry of 17 stars ismore » consistent with the Galactic center distance, but 2 of them are located in the foreground. Several WC stars exhibit a relatively large infrared excess, which is possibly thermal emission from hot dust. Most of the stars appear scattered throughout the GCR, with no relation to the three known massive young clusters; several others lie near the Arches and Quintuplet clusters and may have originated within one of these systems. The results of this work bring the total sample of Wolf-Rayet (WR) stars in the GCR to 88. All sources of strong P{alpha} excess have been identified in the area surveyed with HST, which implies that the sample of WN stars in this region is near completion, and is dominated by late (WNL) types. The current WC sample, although probably not complete, is almost exclusively dominated by late (WCL) types. The observed WR subtype distribution in the GCR is a reflection of the intrinsic rarity of early subtypes (WNE and WCE) in the inner Galaxy, an effect that is driven by metallicity.« less

Temporal and Spectral Analyses of SGRs Observed by HETE-2

NASA Astrophysics Data System (ADS)

Nakagawa, Y. E.; Yoshida, A.; Maetou, M.; Suzuki, M.; Tamagawa, T.; Sakamoto, T.; Kawai, N.; Shirasaki, Y.; Tanaka, K.; Matsuoka, M.; Fenimore, E. E.; Galassi, M.; Atteia, J.-L.; Hurley, K.; Ricker, G. R.

2006-05-01

HETE-2 localized 63 flares from SGR1806-20 and 6 flares from SGR1900+14 in the summer periods from June 18 2001 through August 7 2005. We report on the temporal and spectral analyses of short flares from those SGRs. The estimation of T90 durations in 2-30 keV and 30-100 keV revealed that there is no difference between them with a few exceptions. For these exceptional short flares, there seems softening or possibly hardening during flares, but these spectral evolution are not common. We also found a good linear correlation between the rise and decay time, and they do not depend on a peak flux. We also found that the spectra are well reproduced by a sum of two blackbody models for all short flares. The temperatures are lying around 4 keV and 11 keV which are consistent with previous studies. They are not depend on either the magnitude of flare, the event morphology or the source.

Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre.

PubMed

Genzel, R; Schödel, R; Ott, T; Eckart, A; Alexander, T; Lacombe, F; Rouan, D; Aschenbach, B

2003-10-30

Recent measurements of stellar orbits provide compelling evidence that the compact radio source Sagittarius A* (refs 4, 5) at the Galactic Centre is a 3.6-million-solar-mass black hole. Sgr A* is remarkably faint in all wavebands other than the radio region, however, which challenges current theories of matter accretion and radiation surrounding black holes. The black hole's rotation rate is not known, and therefore neither is the structure of space-time around it. Here we report high-resolution infrared observations of Sgr A* that reveal 'quiescent' emission and several flares. The infrared emission originates from within a few milliarcseconds of the black hole, and traces very energetic electrons or moderately hot gas within the innermost accretion region. Two flares exhibit a 17-minute quasi-periodic variability. If the periodicity arises from relativistic modulation of orbiting gas, the emission must come from just outside the event horizon, and the black hole must be rotating at about half of the maximum possible rate.

A Comprehensive Approach to Assess Feathermeal as an Alternative Protein Source in Aquafeed.

PubMed

Jasour, Mohammad Sedigh; Wagner, Liane; Sundekilde, Ulrik K; Larsen, Bodil K; Greco, Ines; Orlien, Vibeke; Olsen, Karsten; Rasmussen, Hanne T; Hjermitslev, Niels H; Hammershøj, Marianne; Dalsgaard, Anne J T; Dalsgaard, Trine K

2017-12-06

The effect of partially replacing fishmeal in aquafeed with feathermeal (FTH) at three levels (0%: FTH0, 8%: FTH8, 24%: FTH24) and two extrusion temperatures (100 and 130 °C) was evaluated in rainbow trout (Oncorhynchus mykiss) with respect to growth performance, metabolism response, and oxidative status of the feed proteins. Multivariate data analyses revealed that FTH24 correlated positively with high levels of oxidation products, amino acids (AA) racemization, glucogenic AAs level in liver, feed intake (FI), specific growth rate (SGR), and feed conversion ratio (FCR); and low AAs digestibility. Both FI and SGR were significantly increased when 8 and 24% feathermeal was included in the feed extruded at 100 °C, while there was a negative effect on FCR in fish fed FTH24. In conclusion, higher oxidation levels in FTH24 may give rise to metabolic alterations while lower levels of FTH may be considered as fishmeal substitute in aquafeed for rainbow trout.

The Surprising Complexity of Diffuse and Translucent Clouds Toward SGR B2: Diatomics and COMs from 4 GHz to 1.2 THz

NASA Astrophysics Data System (ADS)

McGuire, Brett A.; Corby, Joanna F.; Martin-Drumel, Marie-Aline; Schilke, P.; McCarthy, Michael C.; Remijan, Anthony

2017-06-01

Many diffuse and translucent clouds lie along the line of sight between Earth and the Galactic Center that can be probed through molecular absorption at characteristic velocities. We highlight results of a study of diffuse and translucent clouds along the line of sight to Sgr B2, including SOFIA observations of SH near 1.4 THz and GBT PRIMOS observations from 4 to 50 GHz. We find significant variation in the chemical conditions within these clouds, and the abundances do not appear to correlate with the total optical depth. Additionally, from the GBT observations, we report the first detections of multiple complex organic molecules (COMs) in diffuse and translucent clouds, including CH_3CN, HC_3N, CH_3CHO, and NH_2CHO. We compare the GBT results to complementary observations of SH, H_2S, and others at mm, sub-mm, and THz frequencies from the NRAO 12m, Herschel HIFI, and SOFIA facilities, and comment on the insights into interstellar sulfur chemistry which is currently not well constrained.

Detection of interstellar CH in the far-infrared

NASA Technical Reports Server (NTRS)

Stacey, Gordon J.; Lugten, J. B.; Genzel, R.

1987-01-01

The first astronomical detection of CH in the far-infrared has been made. A ground state of rotational transition was observed in absorption against the far-infrared continuum peak of Sgr B2. The lines are resolved at a velocity resolution of 62 km/s, have a line width of roughly 250 km/s, and a line center optical depth of about 0.29. The inferred total column density of CH in the ground state along the line of sight is roughly 1.6 x 10 to the 15th/sq cm. Comparison of the far-infrared profiles to the 3 GHz emission lines confirms that the ground-state Lambda-doublet levels are inverted and gives an accurate estimate of the excitation temperature. The excitation temperature of the 3264 MHz line varies from cloud to cloud along the line of sight, the levels being most inverted in the Sgr B2 molecular cloud. The large intensity of the 3264 MHz line in this cloud relative to other clouds along the line of sight may thus be primarily an excitation effect.

Bayesian Techniques for Comparing Time-dependent GRMHD Simulations to Variable Event Horizon Telescope Observations

NASA Astrophysics Data System (ADS)

Kim, Junhan; Marrone, Daniel P.; Chan, Chi-Kwan; Medeiros, Lia; Özel, Feryal; Psaltis, Dimitrios

2016-12-01

The Event Horizon Telescope (EHT) is a millimeter-wavelength, very-long-baseline interferometry (VLBI) experiment that is capable of observing black holes with horizon-scale resolution. Early observations have revealed variable horizon-scale emission in the Galactic Center black hole, Sagittarius A* (Sgr A*). Comparing such observations to time-dependent general relativistic magnetohydrodynamic (GRMHD) simulations requires statistical tools that explicitly consider the variability in both the data and the models. We develop here a Bayesian method to compare time-resolved simulation images to variable VLBI data, in order to infer model parameters and perform model comparisons. We use mock EHT data based on GRMHD simulations to explore the robustness of this Bayesian method and contrast it to approaches that do not consider the effects of variability. We find that time-independent models lead to offset values of the inferred parameters with artificially reduced uncertainties. Moreover, neglecting the variability in the data and the models often leads to erroneous model selections. We finally apply our method to the early EHT data on Sgr A*.

BAYESIAN TECHNIQUES FOR COMPARING TIME-DEPENDENT GRMHD SIMULATIONS TO VARIABLE EVENT HORIZON TELESCOPE OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Junhan; Marrone, Daniel P.; Chan, Chi-Kwan

2016-12-01

The Event Horizon Telescope (EHT) is a millimeter-wavelength, very-long-baseline interferometry (VLBI) experiment that is capable of observing black holes with horizon-scale resolution. Early observations have revealed variable horizon-scale emission in the Galactic Center black hole, Sagittarius A* (Sgr A*). Comparing such observations to time-dependent general relativistic magnetohydrodynamic (GRMHD) simulations requires statistical tools that explicitly consider the variability in both the data and the models. We develop here a Bayesian method to compare time-resolved simulation images to variable VLBI data, in order to infer model parameters and perform model comparisons. We use mock EHT data based on GRMHD simulations to explore themore » robustness of this Bayesian method and contrast it to approaches that do not consider the effects of variability. We find that time-independent models lead to offset values of the inferred parameters with artificially reduced uncertainties. Moreover, neglecting the variability in the data and the models often leads to erroneous model selections. We finally apply our method to the early EHT data on Sgr A*.« less

X-Ray and Radio Observations of the Magnetar SGR J1935+2154 during Its 2014, 2015, and 2016 Outbursts

NASA Astrophysics Data System (ADS)

Younes, George; Kouveliotou, Chryssa; Jaodand, Amruta; Baring, Matthew G.; van der Horst, Alexander J.; Harding, Alice K.; Hessels, Jason W. T.; Gehrels, Neil; Gill, Ramandeep; Huppenkothen, Daniela; Granot, Jonathan; Göğüş, Ersin; Lin, Lin

2017-10-01

We analyzed broadband X-ray and radio data of the magnetar SGR J1935+2154 taken in the aftermath of its 2014, 2015, and 2016 outbursts. The source soft X-ray spectrum <10 keV is well described with a blackbody+power-law (BB+PL) or 2BB model during all three outbursts. Nuclear Spectroscopic Telescope Array observations revealed a hard X-ray tail, with a PL photon index Γ = 0.9, extending up to 50 keV, with flux comparable to the one detected <10 keV. Imaging analysis of Chandra data did not reveal small-scale extended emission around the source. Following the outbursts, the total 0.5-10 keV flux from SGR J1935+2154 increased in concordance to its bursting activity, with the flux at activation onset increasing by a factor of ˜7 following its strongest 2016 June outburst. A Swift/X-Ray Telescope observation taken 1.5 days prior to the onset of this outburst showed a flux level consistent with quiescence. We show that the flux increase is due to the PL or hot BB component, which increased by a factor of 25 compared to quiescence, while the cold BB component kT = 0.47 keV remained more or less constant. The 2014 and 2015 outbursts decayed quasi-exponentially with timescales of ˜40 days, while the stronger 2016 May and June outbursts showed a quick short-term decay with timescales of about four days. Our Arecibo radio observations set the deepest limits on the radio emission from a magnetar, with a maximum flux density limit of 14 μJy for the 4.6 GHz observations and 7 μJy for the 1.4 GHz observations. We discuss these results in the framework of the current magnetar theoretical models.

Relative astrometry of compact flaring structures in Sgr A* with polarimetric very long baseline interferometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Michael D.; Doeleman, Sheperd S.; Fish, Vincent L.

2014-10-20

We demonstrate that polarimetric interferometry can be used to extract precise spatial information about compact polarized flares of Sgr A*. We show that, for a faint dynamical component, a single interferometric baseline suffices to determine both its polarization and projected displacement from the quiescent intensity centroid. A second baseline enables two-dimensional reconstruction of the displacement, and additional baselines can self-calibrate using the flare, enhancing synthesis imaging of the quiescent emission. We apply this technique to simulated 1.3 mm wavelength observations of a 'hot spot' embedded in a radiatively inefficient accretion disk around Sgr A*. Our results indicate that, even withmore » current sensitivities, polarimetric interferometry with the Event Horizon Telescope can achieve ∼5 μas relative astrometry of compact flaring structures near Sgr A* on timescales of minutes.« less

Quasi-periodic oscillations in short recurring bursts of magnetars SGR 1806–20 and SGR 1900+14 observed with RXTE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huppenkothen, D.; Heil, L. M.; Watts, A. L.

2014-11-10

Quasi-periodic oscillations (QPOs) observed in the giant flares of magnetars are of particular interest due to their potential to open up a window into the neutron star interior via neutron star asteroseismology. However, only three giant flares have been observed. We therefore make use of the much larger data set of shorter, less energetic recurrent bursts. Here, we report on a search for QPOs in a large data set of bursts from the two most burst-active magnetars, SGR 1806-20 and SGR 1900+14, observed with Rossi X-ray Timing Explorer. We find a single detection in an averaged periodogram comprising 30 burstsmore » from SGR 1806–20, with a frequency of 57 Hz and a width of 5 Hz, remarkably similar to a giant flare QPO observed from SGR 1900+14. This QPO fits naturally within the framework of global magneto-elastic torsional oscillations employed to explain giant flare QPOs. Additionally, we uncover a limit on the applicability of Fourier analysis for light curves with low background count rates and strong variability on short timescales. In this regime, standard Fourier methodology and more sophisticated Fourier analyses fail in equal parts by yielding an unacceptably large number of false-positive detections. This problem is not straightforward to solve in the Fourier domain. Instead, we show how simulations of light curves can offer a viable solution for QPO searches in these light curves.« less

Observational results of a multi-telescope campaign in search of interstellar urea [(NH{sub 2}){sub 2}CO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Remijan, Anthony J.; Snyder, Lewis E.; Kuo, Hsin-Lun

In this paper, we present the results of an observational search for gas phase urea [(NH{sub 2}){sub 2}CO] observed toward the Sgr B2(N-LMH) region. We show data covering urea transitions from ∼100 GHz to 250 GHz from five different observational facilities: the Berkeley-Illinois-Maryland-Association (BIMA) Array, the Combined Array for Research in Millimeter-wave Astronomy (CARMA), the NRAO 12 m telescope, the IRAM 30 m telescope, and the Swedish-ESO Submillimeter Telescope (SEST). The results show that the features ascribed to urea can be reproduced across the entire observed bandwidth and all facilities by best-fit column density, temperature, and source size parameters whichmore » vary by less than a factor of two between observations merely by adjusting for telescope-specific parameters. Interferometric observations show that the emission arising from these transitions is cospatial and compact, consistent with the derived source sizes and emission from a single species. Despite this evidence, the spectral complexity of both (NH{sub 2}){sub 2}CO and of Sgr B2(N) makes the definitive identification of this molecule challenging. We present observational spectra, laboratory data, and models, and discuss our results in the context of a possible molecular detection of urea.« less

An XMM-Newton Observation of the Lagoon Nebula and the Very Young Open Cluster NGC 6530

NASA Technical Reports Server (NTRS)

Rauw, G.; Naze, Y.; Gosset, E.; Stevens, I. R.; Blomme, R.; Corcoran, M. F.; Pittard, J. M.; Runacres, M. C.

2002-01-01

We report the results of an XMM-Newton observation of the Lagoon Nebula (M 8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC 6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experiences a flare-like increase of its X-ray flux making it the second brightest source in M 8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of kT approximately a few keV. Only a few of the X-ray selected PMS candidates are known to display H(alpha) emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC 6530 are weak line T Tauri stars. In addition to 9 Sgr, our EPIC field of view contains also a few early-type stars. The X-ray emission from HD 164816 is found to be typical for an O9.5III-IV star. At least one of the known Herbig Be stars in NGC 6530 (LkH(alpha) 115) exhibits a relatively strong X-ray emission, while most of the main sequence stars of spectral type B1 and later are not detected. We also detect (probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the Hourglass Region.

Detection by Sardinia Radio Telescope of radio pulses at 7 GHz from the Magnetar PSR J1745-2900 in the Galactic center region

NASA Astrophysics Data System (ADS)

Buttu, Marco; D'Amico, Nichi; Egron, Elise; Iacolina, Maria Noemi; Marongiu, Pasqualino; Migoni, Carlo; Pellizzoni, Alberto; Poppi, Sergio; Possenti, Andrea; Trois, Alessio; Vargiu, Gian Paolo

2013-05-01

During the Sardinia Radio Telescope (SRT) science verification phase, we observed PSR J1745-2900, firstly detected as an X-ray flare from Sgr A* by Swift and then identified as a 3.76 s X-ray magnetar with NuSTAR telescope (ATels #5006, #5020, #5027, #5032, #5033, #5035), at a central frequency of 7.30 GHz. We used a Beam Wave Guide focus cryogenically cooled receiver (system temperature ~25 K).

sRecovery Act: Geologic Characterization of the South Georgia Rift Basin for Source Proximal CO 2 Storage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waddell, Michael

This study focuses on evaluating the feasibility and suitability of using the Jurassic/Triassic (J/TR) sediments of the South Georgia Rift basin (SGR) for CO 2 storage in southern South Carolina and southern Georgia The SGR basin in South Carolina (SC), prior to this project, was one of the least understood rift basin along the east coast of the U.S. In the SC part of the basin there was only one well (Norris Lightsey #1) the penetrated into J/TR. Because of the scarcity of data, a scaled approach used to evaluate the feasibility of storing CO 2 in the SGR basin.more » In the SGR basin, 240 km (~149 mi) of 2-D seismic and 2.6 km2 3-D (1 mi2) seismic data was collected, process, and interpreted in SC. In southern Georgia 81.3 km (~50.5 mi) consisting of two 2-D seismic lines were acquired, process, and interpreted. Seismic analysis revealed that the SGR basin in SC has had a very complex structural history resulting the J/TR section being highly faulted. The seismic data is southern Georgia suggest SGR basin has not gone through a complex structural history as the study area in SC. The project drilled one characterization borehole (Rizer # 1) in SC. The Rizer #1 was drilled but due to geologic problems, the project team was only able to drill to 1890 meters (6200 feet) instead of the proposed final depth 2744 meters (9002 feet). The drilling goals outlined in the original scope of work were not met. The project was only able to obtain 18 meters (59 feet) of conventional core and 106 rotary sidewall cores. All the conventional core and sidewall cores were in sandstone. We were unable to core any potential igneous caprock. Petrographic analysis of the conventional core and sidewall cores determined that the average porosity of the sedimentary material was 3.4% and the average permeability was 0.065 millidarcy. Compaction and diagenetic studies of the samples determined there would not be any porosity or permeability at depth in SC. In Georgia there appears to be porosity in the J/TR section based on neutron log porosity values. The only zones in Rizer #1 that appear to be porous were fractured diabase units where saline formation water was flowing into the borehole. Two geocellular models were created for the SC and GA study area. Flow simulation modeling was performed on the SC data set. The injection simulation used the newly acquired basin data as well as the Petrel 3-D geologic model that included geologic structure. Due to the new basin findings as a result of the newly acquired data, during phase two of the modeling the diabase unit was used as reservoir and the sandstone units were used as caprock. Conclusion are: 1) the SGR basin is composed of numerous sub-basins, 2) this study only looked at portions of two sub-basins, 3) in SC, 30 million tonnes of CO 2 can be injected into the diabase units if the fracture network is continuous through the units, 4) due to the severity of the faulting there is no way of assuring the injected CO 2 will not migrate upward into the overlying Coastal Plain aquifers, 5) in Georgia there appears to porous zones in the J/TR sandstones, 6) as in SC there is faulting in the sub-basin and the seismic suggest the faulting extends upward into the Coastal Plain making that area not suitable for CO 2 sequestration, 7) the complex faulting observed at both study areas appear to be associated with transfer fault zones (Heffner 2013), if sub-basins in the Georgia portion of the SGR basin can be located that are far away from the transfer fault zones there is a strong possibility of sequestering CO 2 in these areas, and 9) the SGR basin covers area in three states and this project only studied two small areas so there is enormous potential for CO 2 sequestration in other portions the basin and further research needs to be done to find these areas.« less

Acquired resistance to an epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) in an uncommon G719S EGFR mutation.

PubMed

Osoegawa, Atsushi; Hashimoto, Takafumi; Takumi, Yohei; Abe, Miyuki; Yamada, Tomonori; Kobayashi, Ryoji; Miyawaki, Michiyo; Takeuchi, Hideya; Okamoto, Tatsuro; Sugio, Kenji

2018-03-28

Background Acquired resistance (AR) to an epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) is a common event, and several underlying mechanisms, including T790 M, MET amplification and PTEN downregulation, have been reported for the common EGFR mutations. EGFR G719X is an uncommon mutation that has been reported to show sensitivity to EGFR-TKIs. However, no established cell lines harboring the EGFR G719X have been reported in the literature. Materials and Methods G719S-GR cells were established from malignant pleural effusion of a patient whose tumor developed AR from gefitinib treatment. G719S-GR cells were then genotyped and tested for drug sensitivities. Multiplex ligation-dependent probe amplification (MLPA) was used to compare the clinical tumor samples with G719S-GR. Results G719S-GR cells were resistant to EGFR-TKIs with an LC50 of around 10 μM. A genomic analysis showed that G719S-GR cells harbor the EGFR G719S mutation as well as the amplification of EGFR locus. The homozygous deletion of CDKN2A and the loss of PTEN and TSC1 were also detected. On comparing the copy number of tumor suppressor genes using MLPA, G719S-GR cells were found to lack one copy of PTEN, which was not observed in a tumor obtained before gefitinib treatment. Loss of PTEN may result in AKT activation. The mTORC1/2 inhibitor Torin-1 was able to inhibit the downstream signaling when combined with osimertinib. Discussion The newly established G719S-GR cell line may be useful for investigating the mechanism underlying the development of AR in the G719X mutation; the loss of PTEN may be one such mechanism.

Ages and Heavy Element Abundances from Very Metal-poor Stars in the Sagittarius Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Hansen, Camilla Juul; El-Souri, Mariam; Monaco, Lorenzo; Villanova, Sandro; Bonifacio, Piercarlo; Caffau, Elisabetta; Sbordone, Luca

2018-03-01

Sagittarius (Sgr) is a massive disrupted dwarf spheroidal galaxy in the Milky Way halo that has undergone several stripping events. Previous chemical studies were restricted mainly to a few, metal-rich ([Fe/H] \\gtrapprox -1) stars that suggested a top-light initial mass function (IMF). Here we present the first high-resolution, very metal-poor ([Fe/H] =‑1 to ‑3) sample of 13 giant stars in the main body of Sgr. We derive abundances of 13 elements, namely C, Ca, Co, Fe, Sr, Ba, La, Ce, Nd, Eu, Dy, Pb, and Th, that challenge the interpretation based on previous studies. Our abundances from Sgr mimic those of the metal-poor halo, and our most metal-poor star ([Fe/H] ∼ -3) indicates a pure r-process pollution. Abundances of Sr, Pb, and Th are presented for the first time in Sgr, allowing for age determination using nuclear cosmochronology. We calculate ages of 9+/- 2.5 {Gyr}. Most of the sample stars have been enriched by a range of asymptotic giant branch (AGB) stars with masses between 1.3 and 5 M ⊙. Sgr J190651.47–320147.23 shows a large overabundance of Pb (2.05 dex) and a peculiar abundance pattern best fit by a 3 M ⊙ AGB star. Based on star-to-star scatter and observed abundance patterns, a mixture of low- and high-mass AGB stars and supernovae (15–25 M ⊙) is necessary to explain these patterns. The high level (0.29 ± 0.05 dex) of Ca indicates that massive supernovae must have existed and polluted the early ISM of Sgr before it lost its gas. This result is in contrast with a top-light IMF with no massive stars polluting Sgr. Based on data obtained UVES/VLT ID: 083.B-0774, 075.B-0127.

A mathematical analysis of the Janus combat simulation weather effects models and sensitivity analysis of sky-to-ground brightness ratio on target detection

NASA Astrophysics Data System (ADS)

Shorts, Vincient F.

1994-09-01

The Janus combat simulation offers the user a wide variety of weather effects options to employ during the execution of any simulation run, which can directly influence detection of opposing forces. Realistic weather effects are required if the simulation is to accurately reproduce 'real world' results. This thesis examines the mathematics of the Janus weather effects models. A weather effect option in Janus is the sky-to-ground brightness ratio (SGR). SGR affects an optical sensor's ability to detect targets. It is a measure of the sun angle in relation to the horizon. A review of the derivation of SGR is performed and an analysis of SGR's affect on the number of optical detections and detection ranges is performed using an unmanned aerial vehicle (UAV) search scenario. For comparison, the UAV's are equipped with a combination of optical and thermal sensors.

Repeal of the Sustainable Growth Rate: an overview for surgeons.

PubMed

Sangji, Naveen F

2014-10-01

The Medicare sustainable growth rate (SGR) formula is used to control Medicare spending on physician services. Under the current SGR formula, physicians face an almost 24% cut to the Medicare fee schedule on April 1, 2015. The US House Way & Means and Energy & Commerce Committees and the Senate Finance Committee released jointly proposed legislation to permanently repeal the SGR, and transition Medicare physician payment to a value-based payment method. This review summarizes the key components of the proposed legislation, and discusses some of the political challenges ahead. House Committees on Energy & Commerce and Ways & Means, and the Senate Committee on Finance staff write-ups. Physician Medicare reimbursement will move from a volume-based model to a value-based model over the next decade. Surgeons should remain engaged with the political process to ensure repeal of the SGR. Copyright © 2014 Elsevier Inc. All rights reserved.

Genetic analysis of the role of amyloplasts in shoot gravisensing

NASA Astrophysics Data System (ADS)

Tasaka, M.; Morita, M.

Plant can change the growth direction after sensing the gravity orientation This response calls gravitropism and the initial step is the gravisensing We have isolated many Arabidopsis mutants shoot gravitropism sgr with reduced or no gravitropic response in inflorescence stems The analysis of sgr1 and sgr7 revealed that endoderm cells in the inflorescence stems were gravisensing sites zig zigzag sgr4 and sgr3 showed no or reduced gravitropism in shoot respectively and their amyloplasts thought to be statoliths did not sedimented to the orientation of gravity in the endoderm cells ZIG encoded a SNARE AtVTI11 and SGR3 encoded other SNARE AtVAM3 These two SNAREs made a complex in the shoot endoderm cells suggesting that the vesicle transport from trans-Golgi network TGN to prevacuolar compartment PVC and or vacuole was involved in the amyloplasts localization and movement The analysis to visualize amyloplasts and vacuolar membrane in living endoderm cells supported that the vacuole function was important for the amyloplasts movement Recently we have isolated many suppressor mutants of zig One of them named zig suppressor zip 1 had a point mutation in the gene encoded other SNARE of AtVTI12 This protein is a homologous to ZIG AtVTI11 and these two proteins have partially redundant functions Although wild type At VTI 12 could not rescued zig mutated AtVTI12 protein ZIP1 could almost completely play the part of ZIG In zigzip1 amyloplasts in endoderm cells sedimented normally and the shoots showed normal gravitropic response The other

C II forbidden-line 158 micron mapping in Sagittarius A Rotation curve and mass distribution in the galactic center

NASA Technical Reports Server (NTRS)

Lugten, J. B.; Genzel, R.; Crawford, M. K.; Townes, C. H.

1986-01-01

Based on data obtained with the NASA Kuiper Airborne Observatory 91.4 cm telescope, the 158-micron fine structure line emission of C(+) is mapped near the galactic center. The strongest emission comes from a 10-pc FWHM diameter disk centered on Sgr A West whose dominant motion is rotation. Extended C(+) emission is also found from the +50 km/s galactic center molecular cloud, and a second cloud at v(LSR) of about -35 km/s. The rotation curve and mass distribution within 10 pc of the galactic center are derived, and the C(+) profiles show a drop-off of rotation velocity between 2 and 10 pc. A mass model is suggested with 2-4 million solar masses in a central point mass, and a M/L ratio of the central stellar cluster of 0.5 solar masses/solar luminosities, suggesting a large abundance of giants and relatively recent star formation in the center.

Alma Polarization Measurements Towards Sgr A* (Poster)

NASA Astrophysics Data System (ADS)

Liu, Hauyu Baobab; Wright, M. C. H.; Zhao, J.-H.

2017-10-01

We have observed linear polarization of the Sgr A* at band 3, 6, 7, 8, and 9 using ALMA. I will outline our method, and compare our measurements with the records taken since 2005 by Geoffrey Bower and Dan Marrone.

A multi-wavelength investigation of the non-thermal radio emitting O-star 9 Sgr

NASA Astrophysics Data System (ADS)

Rauw, G.; Blomme, R.; Waldron, W. L.; Corcoran, M. F.; Pittard, J. M.; Pollock, A. M. T.; Runacres, M. C.; Sana, H.; Stevens, I. R.; Van Loo, S.

2002-11-01

We report the results of a multi-wavelength investigation of the O4 V star 9 Sgr (= HD 164794). Our data include observations in the X-ray domain with XMM-Newton, in the radio domain with the VLA as well as optical spectroscopy. 9 Sgr is one of a few presumably single OB stars that display non-thermal radio emission. This phenomenon is attributed to synchrotron emission by relativistic electrons accelerated in strong hydrodynamic shocks in the stellar wind. Given the enormous supply of photospheric UV photons in the wind of 9 Sgr, inverse Compton scattering by these relativistic electrons is a priori expected to generate a non-thermal power law tail in the X-ray spectrum. Our EPIC and RGS spectra of 9 Sgr reveal a more complex situation than expected from this simple theoretical picture. While the bulk of the thermal X-ray emission from 9 Sgr arises most probably in a plasma at temperature ~ 3 x 106 K distributed throughout the wind, the nature of the hard emission in the X-ray spectrum is less clear. Assuming a non-thermal origin, our best fitting model yields a photon index of >=2.9 for the power law component which would imply a low compression ratio of <=1.79 for the shocks responsible for the electron acceleration. However, the hard emission can also be explained by a thermal plasma at a temperature >=2 x 107 K. Our VLA data indicate that the radio emission of 9 Sgr was clearly non-thermal at the time of the XMM-Newton observation. Again, we derive a low compression ratio (1.7) for the shocks that accelerate the electrons responsible for the synchrotron radio emission. Finally, our optical spectra reveal long-term radial velocity variations suggesting that 9 Sgr could be a long-period spectroscopic binary. Based on observations with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member states and the USA (NASA). Also based on observations collected at the European Southern Observatory (La Silla, Chile) and with the Very Large Array. The VLA is a facility of the National Radio Astronomy Observatory which is operated by the Associated Universities Inc. under cooperative agreement with the National Science Foundation.

Evidence for Low Black Hole Spin and Physically Motivated Accretion Models from Millimeter-VLBI Observations of Sagittarius A*

NASA Astrophysics Data System (ADS)

Broderick, Avery E.; Fish, Vincent L.; Doeleman, Sheperd S.; Loeb, Abraham

2011-07-01

Millimeter very long baseline interferometry (mm-VLBI) provides the novel capacity to probe the emission region of a handful of supermassive black holes on sub-horizon scales. For Sagittarius A* (Sgr A*), the supermassive black hole at the center of the Milky Way, this provides access to the region in the immediate vicinity of the horizon. Broderick et al. have already shown that by leveraging spectral and polarization information as well as accretion theory, it is possible to extract accretion-model parameters (including black hole spin) from mm-VLBI experiments containing only a handful of telescopes. Here we repeat this analysis with the most recent mm-VLBI data, considering a class of aligned, radiatively inefficient accretion flow (RIAF) models. We find that the combined data set rules out symmetric models for Sgr A*'s flux distribution at the 3.9σ level, strongly favoring length-to-width ratios of roughly 2.4:1. More importantly, we find that physically motivated accretion flow models provide a significantly better fit to the mm-VLBI observations than phenomenological models, at the 2.9σ level. This implies that not only is mm-VLBI presently capable of distinguishing between potential physical models for Sgr A*'s emission, but further that it is sensitive to the strong gravitational lensing associated with the propagation of photons near the black hole. Based upon this analysis we find that the most probable magnitude, viewing angle, and position angle for the black hole spin are a = 0.0+0.64 + 0.86, \\theta ={68^\\circ }^{+5^\\circ +9^\\circ }_{-20^\\circ -28^\\circ }, and \\xi ={-52^\\circ }^{+17^\\circ +33^\\circ }_{-15^\\circ -24^\\circ } east of north, where the errors quoted are the 1σ and 2σ uncertainties.

X-ray flare properties of Sgr A*

NASA Astrophysics Data System (ADS)

Wang, Daniel; Yuan, Qiang

2016-04-01

Daily X-ray flaring represents an enigmatic phenomenon of Sgr A* --- the supermassive black hole at the center of our Galaxy. We report results from a systematic X-ray study of this phenomenon, based on extensive Chandra observations obtained from 1999 to 2012, totaling about 4.5 Ms. We detect flares, using a combination of the maximum likelihood and Markov Chain Monte Carlo methods, which allow for a direct accounting for the pile-up effect in the modeling of the flare lightcurves and an optimal use of the data, as well as the measurements of flare parameters, including their uncertainties. A total of 82 flares are detected. About one third of them are relatively faint, which were not detected previously. The observation-to-observation variation of the quiescent emission has an average root-mean-square of 6%-14%, including the Poisson statistical fluctuation of faint flares below our detection limits. We find no significant long-term variation in the quiescent emission and the flare rate over the 14 years. In particular, we see no evidence of changing quiescent emission and flare rate around the pericenter passage of the S2 star around 2002. We show clear evidence of a short-term clustering for the flares on time scale of 20-70 ks. We will also report new results on the spectral and lightcurve properties of the flares, as well as their fluence-duration relation after carefully accounting for the detection incompleteness and bias. Finally, we will use these results to constrain the origin and emission mechanism of the flares, which further helps to establish Sgr A* as a unique laboratory to understand the astrophysics of prevailing low-luminosity black holes in the Universe.

GREEN BANK TELESCOPE AND SWIFT X-RAY TELESCOPE OBSERVATIONS OF THE GALACTIC CENTER RADIO MAGNETAR SGR J1745–2900

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lynch, Ryan S.; Archibald, Robert F.; Kaspi, Victoria M.

We present results from eight months of Green Bank Telescope 8.7 GHz observations and nearly 18 months of Swift X-ray telescope observations of the radio magnetar SGR J1745–2900. We tracked the radio and X-ray flux density, polarization properties, profile evolution, rotation, and single-pulse behavior. We identified two main periods of activity. The first is characterized by approximately 5.5 months of relatively stable evolution in radio flux density, rotation, and profile shape, while in the second these properties varied substantially. Specifically, a third profile component emerged and the radio flux also became more variable. The single pulse properties also changed, mostmore » notably with a larger fraction of pulses with pulse widths ∼5–20 ms in the erratic state. Bright single pulses are well described by a log-normal energy distribution at low energies, but with an excess at high energies. The 2–10 keV flux decayed steadily since the initial X-ray outburst, while the radio flux remained stable to within ∼20% during the stable state. A joint pulsar timing analysis of the radio and X-ray data shows a level of timing noise unprecedented in a radio magnetar, though during the time covered by the radio data alone the timing noise was at a level similar to that observed in other radio magnetars. While SGR J1745–2900 is similar to other radio magnetars in many regards, it differs by having experienced a period of relative stability in the radio that now appears to have ended, while the X-ray properties evolved independently.« less

The Dust Properties of Hot R Coronae Borealis Stars and a Wolf-Rayet Central Star of a Planetary Nebula: In Search of the Missing Link

NASA Technical Reports Server (NTRS)

Clayton, Geoffrey C.; De Marco, O.; Whitney, B. A.; Babler, B.; Gallagher, J. S.; Nordhaus, J.; Speck, A. K.; Wolff, M. J.; Freeman, W. R.; Camp, K. A.;

Fermi bubbles as a source of cosmic rays above 1015 eV

NASA Astrophysics Data System (ADS)

Chernyshov, D. O.; Cheng, K. S.; Dogiel, V. A.; Ko, C. M.

2014-11-01

Fermi bubbles are giant gamma-ray structures extended north and south of the Galactic center with characteristic sizes of order of 10 kpc recently discovered by Fermi Large Area Telescope. Good correlation between radio and gamma-ray emission in the region covered by Fermi bubbles implies the presence of high-energy electrons in this region. Since it is relatively difficult for relativistic electrons of this energy to travel all the way from the Galactic sources toward Fermi bubbles one can assume that they accelerated in-situ. The corresponding acceleration mechanism should also affect the distribution of the relativistic protons in the Galaxy. Since protons have much larger lifetimes the effect may even be observed near the Earth. In our model we suggest that Fermi bubbles are created by acceleration of electrons on series of shocks born due to periodic star accretions by supermassive black hole Sgr A*. We propose that hadronic CR within the 'knee' of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Reacceleration of these particles in the Fermi Bubble produces CRs beyond the knee. This model provides a natural explanation of the observed CR flux, spectral indexes, and matching of spectra at the knee.

STAY-GREEN and Chlorophyll Catabolic Enzymes Interact at Light-Harvesting Complex II for Chlorophyll Detoxification during Leaf Senescence in Arabidopsis[C][W

PubMed Central

Sakuraba, Yasuhito; Schelbert, Silvia; Park, So-Yon; Han, Su-Hyun; Lee, Byoung-Doo; Andrès, Céline Besagni; Kessler, Felix; Hörtensteiner, Stefan; Paek, Nam-Chon

2012-01-01

During leaf senescence, plants degrade chlorophyll to colorless linear tetrapyrroles that are stored in the vacuole of senescing cells. The early steps of chlorophyll breakdown occur in plastids. To date, five chlorophyll catabolic enzymes (CCEs), NONYELLOW COLORING1 (NYC1), NYC1-LIKE, pheophytinase, pheophorbide a oxygenase (PAO), and red chlorophyll catabolite reductase, have been identified; these enzymes catalyze the stepwise degradation of chlorophyll to a fluorescent intermediate, pFCC, which is then exported from the plastid. In addition, STAY-GREEN (SGR), Mendel’s green cotyledon gene encoding a chloroplast protein, is required for the initiation of chlorophyll breakdown in plastids. Senescence-induced SGR binds to light-harvesting complex II (LHCII), but its exact role remains elusive. Here, we show that all five CCEs also specifically interact with LHCII. In addition, SGR and CCEs interact directly or indirectly with each other at LHCII, and SGR is essential for recruiting CCEs in senescing chloroplasts. PAO, which had been attributed to the inner envelope, is found to localize in the thylakoid membrane. These data indicate a predominant role for the SGR-CCE-LHCII protein interaction in the breakdown of LHCII-located chlorophyll, likely to allow metabolic channeling of phototoxic chlorophyll breakdown intermediates upstream of nontoxic pFCC. PMID:22366162

Sustainable growth rate 2013: time for definitive intervention.

PubMed

Hirsch, Joshua A; Rosman, David A; Liu, Raymond W; Ding, Alexander; Manchikanti, Laxmaiah

2013-07-01

Federal healthcare spending has been a subject of intense concern as the US Congress continues to search for ways to reduce the budget deficit. The Congressional Budget Office (CBO) estimated that, even though it is growing more slowly than previously projected, federal spending on Medicare, Medicaid and the State Children's Health Insurance Program (SCHIP) will reach nearly $900 billion in 2013. In 2011 the Medicare program paid $68 billion for physicians and other health professional services, 12% of total Medicare spending. Since 2002 the sustainable growth rate (SGR) correction has called for reductions to physician reimbursements; however, Congress has typically staved off these reductions, although the situation remains precarious for physicians who accept Medicare. The fiscal cliff agreement that came into focus at the end of 2012 averted a 26.5% reduction to physician reimbursements related to the SGR correction. Nonetheless, the threat of these devastating cuts continues to loom. The Administration, Congress and others have devised many options to fix this unsustainable situation. This review explores the historical development of the SGR, touches on elements of the formula itself and outlines current proposals for fixing the SGR problem. A recent CBO estimate reduces the potential cost of a 10-year fix of SGR system to $138 billion. This has provided new hope for resolution of this long-standing issue.

Development of Predictive Models for the Growth Kinetics of Listeria monocytogenes on Fresh Pork under Different Storage Temperatures.

PubMed

Luo, Ke; Hong, Sung-Sam; Wang, Jun; Chung, Mi-Ja; Deog-Hwan, Oh

2015-05-01

This study was conducted to develop a predictive model to estimate the growth of Listeria monocytogenes on fresh pork during storage at constant temperatures (5, 10, 15, 20, 25, 30, and 35°C). The Baranyi model was fitted to growth data (log CFU per gram) to calculate the specific growth rate (SGR) and lag time (LT) with a high coefficient of determination (R(2) > 0.98). As expected, SGR increased with a decline in LT with rising temperatures in all samples. Secondary models were then developed to describe the variation of SGR and LT as a function of temperature. Subsequently, the developed models were validated with additional independent growth data collected at 7, 17, 27, and 37°C and from published reports using proportion of relative errors and proportion of standard error of prediction. The proportion of relative errors of the SGR and LT models developed herein were 0.79 and 0.18, respectively. In addition, the standard error of prediction values of the SGR and LT of L. monocytogenes ranged from 25.7 to 33.1% and from 44.92 to 58.44%, respectively. These results suggest that the model developed in this study was capable of predicting the growth of L. monocytogenes under various isothermal conditions.

Dietary protein requirement of juvenile turbot ( Scophthalmus maximus Linnaeus)

NASA Astrophysics Data System (ADS)

Liu, Xingwang; Mai, Kangsen; Liufu, Zhiguo; Ai, Qinghui

2015-04-01

The dietary protein requirement of juvenile turbot (initial average weight, 38.2 g ± 0.1 g) reared indoor in aerated aquaria was determined in this study. Five energy equal experimental diets were formulated with fish meal as protein source, which contained different concentrations of protein (47.2%, 51.0%, 54.6%, 59.3% and 63.6% of dry diet). Three groups of fish with 18 individuals in each, were cultured in 300-L tanks and fed twice a day for 8 weeks. During culture, temperature was controlled between 15.0 and 18.0°C, salinity was controlled between 28.5 and 32.0, acidity was controlled between pH7.8 and pH8.5, and ammonia nitrogen was maintained below 0.03 mg L-1 and dissolved oxygen was maintained about 7 mg L-1. Results showed that the growth of fish was significantly affected by dietary protein content ( P < 0.05). Specific growth rate ( SGR) of turbot increased when dietary protein content varied between 47.2% and 51.0% ( P < 0.05), and then kept stable when dietary protein content was higher than 51.0%. Fish which were fed the diet containing 63.6% protein showed the highest SGR while those fed the diet containing 59.3% protein showed the highest feed efficiency rate. No significant difference of feed intake and protein efficiency ratio was found among experimental diets ( P > 0.05). Broken-line regression analysis of SGR showed that the optimal dietary protein requirement of turbot was about 57.0%.

Superresolution Interferometric Imaging with Sparse Modeling Using Total Squared Variation: Application to Imaging the Black Hole Shadow

NASA Astrophysics Data System (ADS)

Kuramochi, Kazuki; Akiyama, Kazunori; Ikeda, Shiro; Tazaki, Fumie; Fish, Vincent L.; Pu, Hung-Yi; Asada, Keiichi; Honma, Mareki

2018-05-01

We propose a new imaging technique for interferometry using sparse modeling, utilizing two regularization terms: the ℓ 1-norm and a new function named total squared variation (TSV) of the brightness distribution. First, we demonstrate that our technique may achieve a superresolution of ∼30% compared with the traditional CLEAN beam size using synthetic observations of two point sources. Second, we present simulated observations of three physically motivated static models of Sgr A* with the Event Horizon Telescope (EHT) to show the performance of proposed techniques in greater detail. Remarkably, in both the image and gradient domains, the optimal beam size minimizing root-mean-squared errors is ≲10% of the traditional CLEAN beam size for ℓ 1+TSV regularization, and non-convolved reconstructed images have smaller errors than beam-convolved reconstructed images. This indicates that TSV is well matched to the expected physical properties of the astronomical images and the traditional post-processing technique of Gaussian convolution in interferometric imaging may not be required. We also propose a feature-extraction method to detect circular features from the image of a black hole shadow and use it to evaluate the performance of the image reconstruction. With this method and reconstructed images, the EHT can constrain the radius of the black hole shadow with an accuracy of ∼10%–20% in present simulations for Sgr A*, suggesting that the EHT would be able to provide useful independent measurements of the mass of the supermassive black holes in Sgr A* and also another primary target, M87.

MODELING THE GAMMA-RAY EMISSION IN THE GALACTIC CENTER WITH A FADING COSMIC-RAY ACCELERATOR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Ruo-Yu; Wang, Xiang-Yu; Prosekin, Anton

2016-12-20

Recent HESS observations of the ∼200 pc scale diffuse gamma-ray emission from the central molecular zone (CMZ) suggest the presence of a PeV cosmic-ray accelerator (PeVatron) located in the inner 10 pc region of the Galactic center. Interestingly, the gamma-ray spectrum of the point-like source (HESS J1745-290) in the Galactic center shows a cutoff at ∼10 TeV, implying a cutoff around 100 TeV in the cosmic-ray proton spectrum. Here we propose that the gamma-ray emission from the inner and the outer regions may be explained self-consistently by run-away protons from a single yet fading accelerator. In this model, gamma-rays frommore » the CMZ region are produced by protons injected in the past, while gamma-rays from the inner region are produced by protons injected more recently. We suggest that the blast wave formed in a tidal disruption event (TDE) caused by the supermassive black hole (Sgr A*) could serve as such a fading accelerator. With typical parameters of the TDE blast wave, gamma-ray spectra of both the CMZ region and HESS J1745-290 can be reproduced simultaneously. Meanwhile, we find that the cosmic-ray energy density profile in the CMZ region may also be reproduced in the fading accelerator model when appropriate combinations of the particle injection history and the diffusion coefficient of cosmic rays are adopted.« less

THE DUST PROPERTIES OF TWO HOT R CORONAE BOREALIS STARS AND A WOLF-RAYET CENTRAL STAR OF A PLANETARY NEBULA: IN SEARCH OF A POSSIBLE LINK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clayton, Geoffrey C.; Gallagher, J. S.; Freeman, W. R.

2011-08-15

We present new Spitzer/IRS spectra of two hot R Coronae Borealis (RCB) stars, one in the Galaxy, V348 Sgr, and one lying in the Large Magellanic Cloud, HV 2671. These two objects may constitute a link between the RCB stars and the late Wolf-Rayet ([WCL]) class of central stars of planetary nebulae (CSPNe), such as CPD -56{sup 0} 8032, that has little or no hydrogen in their atmospheres. HV 2671 and V348 Sgr are members of a rare subclass that has significantly higher effective temperatures than most RCB stars, but shares the traits of hydrogen deficiency and dust formation thatmore » define the cooler RCB stars. The [WC] CSPN star, CPD -56{sup 0} 8032, displays evidence of dual-dust chemistry showing both polycyclic aromatic hydrocarbons (PAHs) and crystalline silicates in its mid-IR spectrum. HV 2671 shows strong PAH emission but no sign of having crystalline silicates. The spectrum of V348 Sgr is very different from that of CPD -56{sup 0} 8032 and HV 2671. The PAH emission seen strongly in the other two stars is not present. Instead, the spectrum is dominated by a broad emission centered at about 8.2 {mu}m. This feature is not identified with either PAHs or silicates. Several other cool RCB stars, novae, and post-asymptotic giant branch stars show similar features in their IR spectra. The mid-IR spectrum of CPD -56{sup 0} 8032 shows emission features that may be associated with C{sub 60}. The other two stars do not show evidence of C{sub 60}. The different nature of the dust around these stars does not help us in establishing further links that may indicate a common origin. HV 2671 has also been detected by Herschel/PACS and SPIRE. V348 Sgr and CPD -56{sup 0} 8032 have been detected by AKARI/Far-Infrared Surveyor. These data were combined with Spitzer, IRAS, Two Micron All Sky Survey, and other photometry to produce their spectral energy distributions (SEDs) from the visible to the far-IR. Monte Carlo radiative transfer modeling was used to study the circumstellar dust around these stars. HV 2671 and CPD -56{sup 0} 8032 require both a flared inner disk with warm dust and an extended diffuse envelope with cold dust to fit their SEDs. The SED of V348 Sgr can be fit with a much smaller disk and envelope. The cold dust in the extended diffuse envelopes inferred around HV 2671 and CPD -56{sup 0} 8032 may consist of interstellar medium swept up during mass-loss episodes.« less

Quantum Electronic Solids

DTIC Science & Technology

2013-03-07

surface (yellow circles) indicate presence of strong antiferromagnetic fluctuations 0 +π −π ky kx 0 +π +2π • Simple, archetypal structure of...It seamlessly connects to graphene to make atomically thin, gateable SGr-Gr junctions. • Digital electronics is feasible; • SGr is stable at

A Comprehensive Study of Short Bursts from SGR1806-20 and SGR1900+14 Detected by HETE-2

NASA Astrophysics Data System (ADS)

Nakagawa, Yujin E.; Yoshida, Atsumasa; Hurley, Kevin; Atteia, Jean-Luc; Maetou, Miki; Tamagawa, Toru; Suzuki, Motoko; Yamazaki, Tohru; Tanaka, Kaoru; Kawai, Nobuyuki; Shirasaki, Yuji; Pelangeon, Alexandre; Matsuoka, Masaru; Vanderspek, Roland; Crew, Geoff B.; Villasenor, Joel S.; Sato, Rie; Sugita, Satoshi; Kotoku, Jun'ichi; Arimoto, Makoto; Pizzichini, Graziella; Doty, John P.; Ricker, George R.

2007-06-01

Temporal and spectral studies of short bursts (≲ a few hundred milliseconds) are presented for the soft gamma repeaters (SGRs) 1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005, HETE-2 localized 50 bursts from SGR1806-20 and 5 bursts from SGR1900+14. The cumulative number-intensity distribution of SGR1806-20 in the active year 2004 is well described by a power-law model with an index of -1.1±0.6. It is consistent with previous studies, but burst data taken in other years clearly give a steeper distribution. This may suggest that more energetic bursts could occur more frequently in periods of greater activity. From the data, the spectral evolution during bursts with a time scale of ≳ 20ms does not seem to be common in the HETE-2 sample. The spectra of all short bursts are well reproduced by a two blackbody function with temperatures of ˜ 4 and ˜ 11keV. From a timing analysis to the SGR1806-20 data, a time lag of 2.2±0.4ms is found between the 30-100keV and 2-10keV radiation bands. This may imply (1) a very rapid spectral softening and energy reinjection, (2) diffused (elongated) emission plasma along the magnetic field lines in pseudo-equilibrium with multi-temperatures, or (3) a separate (located at ≲ 700km) emission region of a softer component (say, ˜ 4keV), which could be reprocessed X-rays by higher energy (≳ 11keV) photons from an emission region near the stellar surface.

Hard Burst Emission from the Soft Gamma Repeater SGR 1900+14

NASA Technical Reports Server (NTRS)

Woods, Peter M.; Kouveliotou, Chryssa; VanParadijs, Jan; Briggs, Michael S.; Hurley, Kevin; Gogus, Ersin; Preece, Robert D.; Giblin, Timothy W.; Thompson, Christopher; Duncan, Robert C.

1999-01-01

We present evidence for burst emission from SGR 1900 + 14 with a power-law high-energy spectrum extending beyond 500 keV. Unlike previous detections of high-energy photons during bursts from soft gamma repeaters (SGRs), these emissions are not associated with extraordinarily bright flares. Not only is the emission hard, but the spectra are better fitted by D. Band's gamma-ray burst (GRB) function rather than by the traditional optically thin thermal bremsstrahlung model. We find that the spectral evolution within these hard events obeys a hardness/intensity anticorrelation. Temporally, these events are distinct from typical SGR burst emissions in that they are longer (approximately 1 s) and have relatively smooth profiles. Despite a difference in peak luminosity of approximately > 10(exp 11) between these bursts from SGR 1900 + 14 and cosmological GRBs, there are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution. We outline an interpretation of these events in the context of the magnetar model.

Silver nanoparticle-alginate composite beads for point-of-use drinking water disinfection.

PubMed

Lin, Shihong; Huang, Rixiang; Cheng, Yingwen; Liu, Jie; Lau, Boris L T; Wiesner, Mark R

2013-08-01

Silver nanoparticles (AgNPs)-alginate composite beads were synthesized using three different approaches as filler materials of packed columns for simultaneous filtration-disinfection as an alternative portable water treatment process. The prepared composite beads were packed into a column through which Escherichia coli containing water was filtered to evaluate the disinfection efficacy. Excellent disinfection performance (no detectable viable colony) was achieved with a hydraulic retention time (HRT) as short as 1 min (the shortest tested) with the SGR (Simultaneous-Gelation-Reduction) and AR (Adsorption-Reduction) beads that were prepared using in situ reduction of Ag(+). Comparatively, the SGR beads released significantly less Ag(+)/AgNPs than the AR beads did within the same HRT. From the results of this study it was identified that SGR may be the best choice among all three different synthesis approaches in that the SGR beads can achieve satisfactory bactericidal performance with a relatively low material consumption rate. Copyright © 2012 Elsevier Ltd. All rights reserved.

The black hole at the Galactic Center: observations and models in a nutshell

NASA Astrophysics Data System (ADS)

Zakharov, Alexander

2017-12-01

The Galactic Center (Sgr A*) is a peculiar place in our Galaxy (Milky Way). Our Solar system is located at a distance around 8 kpc from the Galactic Center (GC). There were a number of different including exotic ones such as boson stars, fermion balls, neutrino balls, a cluster of neutron stars. Some of these models are significantly constrained with consequent observations and now supermassive black hole with mass around 4 × 106 M ⊙ is the preferable model for GC. Moreover, one can test alternative theories of gravity with observations of bright stars near the Galactic Center and and observations of bright structures near the black hole at the Galactic Center to reconstruct shadow structure around the black hole with current and future observational VLBI facilities such as the Event Horizon Telescope. In particular, we got a graviton mass constraint which is comparable and consistent with constraints obtained recently by the LIGO-Virgo collaboration.

Impact of Pretreatment Tumor Growth Rate on Outcome of Early-Stage Lung Cancer Treated With Stereotactic Body Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Atallah, Soha; Cho, B.C. John; Allibhai, Zishan

2014-07-01

Purpose: To determine the influence of pretreatment tumor growth rate on outcomes in patients with early-stage non-small cell lung cancer (NSCLC) treated with stereotactic body radiation therapy (SBRT). Methods and Materials: A review was conducted on 160 patients with T1-T2N0M0 NSCLC treated with SBRT at single institution. The patient's demographic and clinical data, time interval (t) between diagnostic and planning computed tomography (CT), vital status, disease status, and cause of death were extracted from a prospectively kept database. Differences in gross tumor volume between diagnostic CT (GTV1) and planning CT (GTV2) were recorded, and growth rate was calculated by usemore » of specific growth rate (SGR). Kaplan-Meier curves were constructed for overall survival (OS). Differences between groups were compared with a log-rank test. Multivariate analyses were performed by use of the Cox proportional hazard model with SGR and other relevant clinical factors. Cumulative incidence was calculated for local, regional, and distant failures by use of the competing risk approach and was compared with Gray's test. Results: The median time interval between diagnostic and planning CT was 82 days. The patients were divided into 2 groups, and the median SGR was used as a cut-off. The median survival times were 38.6 and 27.7 months for the low and high SGR groups, respectively (P=.03). Eastern Cooperative Oncology Group performance status (P=.01), sex (P=.04), SGR (P=.03), and GTV2 (P=.002) were predictive for OS in multivariable Cox regression analysis and, except sex, were similarly predictive for failure-free survival (FFS). The 3-year cumulative incidences of regional failure were 19.2% and 6.0% for the high and low SGR groups, respectively (P=.047). Conclusion: High SGR was correlated with both poorer OS and FFS in patients with early-stage NSCLC treated with SBRT. If validated, this measurement may be useful in identifying patients most likely to benefit from adjuvant therapy after SBRT.« less

Chemical evolution and stellar populations in the Sagittarius dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Sbordone, L.; Bonifacio, P.; Giuffrida, G.; Marconi, G.; Monaco, L.; Zaggia, S.

2007-05-01

The closest neighbour of the Milky Way (MW), the Sagittarius dwarf Spheroidal Galaxy (Sgr dSph) is being tidally destroyed by the interaction with our Galaxy, losing its stellar content along a huge stream clearly detectable within the Halo. This makes the Sgr dSph an ideal laboratory to study at the same time the chemical evolution of dwarf galaxies and their role in building bigger structures such as the MW. Since some years we are studying the stellar populations of the Sgr main body and stream, with particular attention to their detailed chemical composition. We collected detailed abundances (up to 22 elements, O to Eu) for 27 stars in the Sgr dSph main body, 5 in the associated globular cluster Terzan 7, and 12 more in the trailing Sgr tidal arm (UVES@VLT and SARG@TNG data). We are also conducting a large FLAMES@VLT chemical and dynamical analysis aimed at obtaining metallicities, alpha-elements content and radial velocities from automated analysis of the spectra. Finally, we just completed the first large scale photometric and spectroscopic survey of the stellar populations across all the dSph main body extension with VIMOS@VLT, aimed at exploring the variations in stellar populations and at deriving radial velocity memberships for future high resolution spectroscopic analysis. The picture emerging from all these studies portraits a large and extremely complex object, with signs of a long and still unclear evolution. Metallicity varies across three orders of magnitude ([Fe/H] from -3 to 0), CMDs change surprisingly from the core to the outskirts of the galaxy, and the chemical composition of the most metal rich objects show a very characteristic signature, with underabundant alpha elements, deficient Na, underabundant Fe-peak Mn, Co, Ni, Cu and Zn, and strongly enhanced n-capture elements La and Nd. This highly peculiar "signature" can also be effectively used to recognized stripped populations lost by Sgr in favour of the MW system, as clearly showed by the globular Palomar 12, which shows the same chemical anomalies detected in Sgr dSph.

Dynamics and stellar population of the Galactic Center (French Title: Étude de la cinématique et de la population stellaire du Centre Galactique)

NASA Astrophysics Data System (ADS)

Paumard, Thibaut

2003-09-01

The central parsec of the Galaxy has been observed using BEAR spectroimagery at high spectral resolution (up to 21 km/s) and medium spatial resolution (0.5"), in Bracket gamma (2.16 microns) and He I (2.06 microns), and high resolution imaging. These data were used to study the young, massive stars of the central parsec, and the structure and dynamics of ionized gas in Sgr A West. The stellar population has been separated into two groups: the IRS 16 complex of 6 LBVs, and at least 20 Wolf-Rayets. The IRS 13E complex has been identified as a cluster of at least 6 massive stars. All this is consistent with the young stars being born in a massive cluster a few tens of parsecs from the Galactic Centre. Providing a deep insight into the morphology of Sgr A West, our data allowed us to derive a kinematic model for the Northern Arm. Our results are in agreement with the idea that the Minispiral is made of ionisation fronts of wider neutral clouds, gravitationally stretched, coming from the CND.

Weak deflection gravitational lensing for photons coupled to Weyl tensor in a Schwarzschild black hole

NASA Astrophysics Data System (ADS)

Cao, Wei-Guang; Xie, Yi

2018-03-01

Beyond the Einstein-Maxwell model, electromagnetic field might couple with gravitational field through the Weyl tensor. In order to provide one of the missing puzzles of the whole physical picture, we investigate weak deflection lensing for photons coupled to the Weyl tensor in a Schwarzschild black hole under a unified framework that is valid for its two possible polarizations. We obtain its coordinate-independent expressions for all observables of the geometric optics lensing up to the second order in the terms of ɛ which is the ratio of the angular gravitational radius to angular Einstein radius of the lens. These observables include bending angle, image position, magnification, centroid and time delay. The contributions of such a coupling on some astrophysical scenarios are also studied. We find that, in the cases of weak deflection lensing on a star orbiting the Galactic Center Sgr A*, Galactic microlensing on a star in the bulge and astrometric microlensing by a nearby object, these effects are beyond the current limits of technology. However, measuring the variation of the total flux of two weak deflection lensing images caused by the Sgr A* might be a promising way for testing such a coupling in the future.

GRB070610: A Curious Galactic Transient

NASA Technical Reports Server (NTRS)

Kasliwal, M. M.; Kulkrarni. S. R.; Cameron, P. B.; Nakar, E.; Ofek, E. O.; Rau, A.; Soderberg, A. M.; Campana, S.; Bloom, J. S.; Perley, D. A.;

GRB 070610: A Curious Galactic Transient

NASA Astrophysics Data System (ADS)

Kasliwal, M. M.; Cenko, S. B.; Kulkarni, S. R.; Cameron, P. B.; Nakar, E.; Ofek, E. O.; Rau, A.; Soderberg, A. M.; Campana, S.; Bloom, J. S.; Perley, D. A.; Pollack, L. K.; Barthelmy, S.; Cummings, J.; Gehrels, N.; Krimm, H. A.; Markwardt, C. B.; Sato, G.; Chandra, P.; Frail, D.; Fox, D. B.; Price, P. A.; Berger, E.; Grebenev, S. A.; Krivonos, R. A.; Sunyaev, R. A.

2008-05-01

GRB 070610 is a typical high-energy event with a duration of 5 s. Yet within the burst localization we detect a highly unusual X-ray and optical transient, Swift J195509.6+261406. We see high-amplitude X-ray and optical variability on very short timescales even at late times. Using near-infrared imaging assisted by a laser guide star and adaptive optics, we identified the counterpart of Swift J195509.6+261406. Late-time optical and near-infrared imaging constrain the spectral type of the counterpart to be fainter than a K-dwarf, assuming it is of Galactic origin. It is possible that GRB 070610 and Swift J195509.6+261406 are unrelated sources. However, the absence of a typical X-ray afterglow from GRB 070610 in conjunction with the spatial and temporal coincidence of the two motivate us to suggest that the sources are related. The closest (imperfect) analog to Swift J195509.6+261406 is V4641 Sgr, an unusual black hole binary. We suggest that Swift J195509.6+261406 along with V4641 Sgr define a subclass of stellar black hole binaries—the fast X-ray novae. We further suggest that fast X-ray novae are associated with bursts of gamma rays. If so, GRB 070610 defines a new class of celestial gamma-ray bursts and these bursts dominate the long-duration GRB demographics.

How Soft Gamma Repeaters Might Make Fast Radio Bursts

NASA Astrophysics Data System (ADS)

Katz, J. I.

2016-08-01

There are several phenomenological similarities between soft gamma repeaters (SGRs) and fast radio bursts (FRBs), including duty factors, timescales, and repetition. The sudden release of magnetic energy in a neutron star magnetosphere, as in popular models of SGRs, can meet the energy requirements of FRBs, but requires both the presence of magnetospheric plasma, in order for dissipation to occur in a transparent region, and a mechanism for releasing much of that energy quickly. FRB sources and SGRs are distinguished by long-lived (up to thousands of years) current-carrying coronal arches remaining from the formation of the young neutron star, and their decay ends the phase of SGR/AXP/FRB activity even though “magnetar” fields may persist. Runaway increases in resistance when the current density exceeds a threshold, releases magnetostatic energy in a sudden burst, and produces high brightness GHz emission of FRB by a coherent process. SGRs are produced when released energy thermalizes as an equlibrium pair plasma. The failures of some alternative FRB models and the non-detection of SGR 1806-20 at radio frequencies are discussed in the appendices.

La Freccia Rossa: An IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate

NASA Astrophysics Data System (ADS)

Ravi, Vikram; Vedantham, Harish; Phinney, E. Sterl

2018-05-01

The dynamics of the high-velocity compact molecular cloud CO-0.40-0.22 have been interpreted as evidence for a ˜105M⊙ black hole within 60 pc of Sgr A*. Recently, Oka et al. have identified a compact millimetre-continuum source, CO-0.40-0.22*, with this candidate black hole. Here we present a collation of radio and infrared data at this location. ATCA constraints on the radio spectrum, and the detection of a mid-infrared counterpart, are in tension with an Sgr A*-like model for CO-0.40-0.22* despite the comparable bolometric to Eddington luminosity ratios under the IMBH interpretation. A protostellar-disk scenario is, however, tenable. CO-0.40-0.22(*) is positionally coincident with an arrowhead-shaped infrared-dark cloud (which we call the Freccia Rossa). If the VLSR ≈ 70 km s-1 systemic velocity of CO-0.40-0.22 is common to the entire Freccia Rossa system, we hypothesise that it is the remnant of a high-velocity cloud that has plunged into the Milky Way from the Galactic halo.

HOW SOFT GAMMA REPEATERS MIGHT MAKE FAST RADIO BURSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katz, J. I., E-mail: katz@wuphys.wustl.edu

2016-08-01

There are several phenomenological similarities between soft gamma repeaters (SGRs) and fast radio bursts (FRBs), including duty factors, timescales, and repetition. The sudden release of magnetic energy in a neutron star magnetosphere, as in popular models of SGRs, can meet the energy requirements of FRBs, but requires both the presence of magnetospheric plasma, in order for dissipation to occur in a transparent region, and a mechanism for releasing much of that energy quickly. FRB sources and SGRs are distinguished by long-lived (up to thousands of years) current-carrying coronal arches remaining from the formation of the young neutron star, and theirmore » decay ends the phase of SGR/AXP/FRB activity even though “magnetar” fields may persist. Runaway increases in resistance when the current density exceeds a threshold, releases magnetostatic energy in a sudden burst, and produces high brightness GHz emission of FRB by a coherent process. SGRs are produced when released energy thermalizes as an equlibrium pair plasma. The failures of some alternative FRB models and the non-detection of SGR 1806-20 at radio frequencies are discussed in the appendices.« less

The 2001 April Burst Activation of SGR 1900+14: Pulse Properties and Torque

NASA Technical Reports Server (NTRS)

Woods, P. M.; Kouveliotou, C.; Goegues, E.; Finger, M. H.; Feroci, M.; Mereghetti, S.; Swank, J. H.; Hurley, K.; Heise, J.; Smith, D.;

VizieR Online Data Catalog: Disk of {upsilon} Sgr (Netolicky+, 2009)

NASA Astrophysics Data System (ADS)

Netolicky, M.; Bonneau, D.; Chesneau, O.; Harmanec, P.; Koubsky, P.; Mourard, D.; Stee, P.

2010-01-01

The aim of this paper is to determine the properties of the dusty environment of the hydrogen-deficient binary system upsilon Sgr, whose binary properties and other characteristics are poorly known. We obtained the first mid-IR interferometric observations of upsilon Sgr using the instrument MIDI of the VLTI used with different pairs of 1.8m and 8m telescopes. The calibrated visibilities, the N band spectrum, and the SED were compared with disk models computed with the MC3D code to determine the geometry and chemical composition of the envelope. ************************************************************************** * * * Sorry, but the author(s) never supplied the tabular material * * announced in the paper * * * **************************************************************************

VizieR Online Data Catalog: 22GHz observations of VX Sgr (Murakawa+, 2003)

NASA Astrophysics Data System (ADS)

Murakawa, K.; Yates, J. A.; Richards, A. M. S.; Cohen, R. J.

2012-07-01

The 22-GHz H2O maser emission from VX Sgr was observed on 1994 26 and 1999 January 16 for 5 and 7hr, respectively, in both left and right circular polarization, using 5 antennas of MERLIN. (3 data files).

Reducing acetate excretion from E. coli K-12 by over-expressing the small RNA sgrS

PubMed Central

Negrete, Alejandro; Majdalani, Nadim; Phue, Je Nie; Shiloach, Joseph

2011-01-01

When exposed to the non-metabolized glucose derivative alpha methyl glucoside, both E. coli K-12 (JM109 and MG1655) and E. coli B (BL21) respond by reducing the concentration of the mRNA of the ptsG gene which is responsible for the biosynthesis of the glucose transporter EIICBglu. This occurs through the over-expression of the non-coding small RNA SgrS, which interacts specifically with the mRNA of the ptsG gene and prevents its translation. However, when these bacteria are exposed to a glucose concentration of 40 g/L, over-expression of SgrS is observed only in E. coli B (BL21). Unlike E. coli K-12 (JM109 and MG1655), which are affected by high glucose concentration and produce higher levels of acetate, E. coli B (BL21) is not affected. Based on this information, it was assumed that over-expression of SgrS enables E. coli B (BL21) to reduce its acetate excretion by controlling the glucose transport. When SgrS was over-expressed in both E. coli K-12 strains from a multicopy plasmid, it was possible to reduce their acetate excretion levels to those seen in E. coli B. This observation opens a new approach towards controlling bacterial metabolism through the use of non-coding RNA. PMID:22107968

Reducing acetate excretion from E. coli K-12 by over-expressing the small RNA SgrS.

PubMed

Negrete, Alejandro; Majdalani, Nadim; Phue, Je-Nie; Shiloach, Joseph

2013-01-25

When exposed to the nonmetabolized glucose derivative alpha methyl glucoside (αMG), both Escherichia coli K-12 (JM109 and MG1655) and E. coli B (BL21) respond by reducing the concentration of the mRNA of the ptsG gene which is responsible for the biosynthesis of the glucose transporter EIICB(glu). This occurs through the over-expression of the noncoding small RNA SgrS, which interacts specifically with the mRNA of the ptsG gene and prevents its translation. However, when these bacteria are exposed to a glucose concentration of 40 g/L, over-expression of SgrS is observed only in E. coli B (BL21). Unlike E. coli K-12 (JM109 and MG1655), which are affected by high glucose concentration and produce higher levels of acetate, E. coli B (BL21) is not affected. Based on this information, it was assumed that over-expression of SgrS enables E. coli B (BL21) to reduce its acetate excretion by controlling the glucose transport. When SgrS was over-expressed in both E. coli K-12 strains from a multicopy plasmid, it was possible to reduce their acetate excretion levels to those seen in E. coli B. This observation opens a new approach towards controlling bacterial metabolism through the use of noncoding RNA. Published by Elsevier B.V.

RXTE Detection of the Spin Period of Swift J1822.3-1606

NASA Astrophysics Data System (ADS)

Gogus, Ersin; Kouveliotou, Chryssa; Strohmayer, Tod

2011-07-01

RXTE/PCA observed the new source, Swift J1822.3-1606 (Cummings et al. GCN Circ. 12159) on 2011 July 16, for 6.7 ks. We performed a timing analysis on the barycentered data and detected a coherent pulsation at 0.1185149(2) Hz corresponding to 8.4377585 s. Pulsations are clearly visible in the PCA light curve. The peak-to-peak pulsed amplitude in the 2-10 keV band is 0.41. This pulsed fraction is highly unlikely from an SGR source, and very reminiscent of the outburst onset of Swift J1626.6-5156 (Palmer et al.

NLTE Model Atmospheres for Super-Soft X-ray Sources

NASA Astrophysics Data System (ADS)

Rauch, Thomas; Werner, Klaus

2009-09-01

Spectral analysis by means of fully line-blanketed Non-LTE model atmospheres has arrived at a high level of sophistication. The Tübingen NLTE Model Atmosphere Package (TMAP) is used to calculate plane-parallel NLTE model atmospheres which are in radiative and hydrostatic equilibrium. Although TMAP is not especially designed for the calculation of burst spectra of novae, spectral energy distributions (SEDs) calculated from TMAP models are well suited e.g. for abundance determinations of Super Soft X-ray Sources like nova V4743 Sgr or line identifications in observations of neutron stars with low magnetic fields in low-mass X-ray binaries (LMXBs) like EXO 0748-676.

Rapid re-brightening of the red nova V4332 Sgr remnant

NASA Astrophysics Data System (ADS)

Goranskij, V. P.; Zharova, A. V.; Barsukova, E. A.; Valeev, A. F.

2018-06-01

V4332 Sgr is a luminous red nova exploded in 1994. We perform CCD BVRcIc photometry of its remnant since 2003, and medium resolution spectroscopy since 2005 using Russian 6 m telescope BTA, SAO 1 m Zeiss telescope and smaller telescopes of SAI Crimean Station.

Universal statistics of soft gamma-ray repeating (SGR) bursts

NASA Astrophysics Data System (ADS)

Kondratyev, V. N.; Korovina, Yu. V.

2018-01-01

Soft gamma repeater (SGR) bursts are considered as a release of magnetic energy stored in the baryon degrees of freedom of the magnetar crust. It is shown that this interpretation allows all observations of these bursts to be systematized and universal statistical properties to be revealed and explained.

Ionized gas at the edge of the central molecular zone

NASA Astrophysics Data System (ADS)

Langer, W. D.; Goldsmith, P. F.; Pineda, J. L.; Velusamy, T.; Requena-Torres, M. A.; Wiesemeyer, H.

2015-04-01

Context. The edge of the central molecular zone (CMZ) is the location where massive dense molecular clouds with large internal velocity dispersions transition to the surrounding more quiescent and lower CO emissivity region of the Galaxy. Little is known about the ionized gas surrounding the molecular clouds and in the transition region. Aims: We determine the properties of the ionized gas at the edge of the CMZ near Sgr E using observations of N+ and C+. Methods: We observed a small portion of the edge of the CMZ near Sgr E with spectrally resolved [C ii] 158 μm and [N ii] 205 μm fine structure lines at six positions with the GREAT instrument on SOFIA and in [C ii] using Herschel HIFI on-the-fly strip maps. We use the [N ii] spectra along with a radiative transfer model to calculate the electron density of the gas and the [C ii] maps to illuminate the morphology of the ionized gas and model the column density of CO-dark H2. Results: We detect two [C ii] and [N ii] velocity components, one along the line of sight to a CO molecular cloud at - 207 km s-1 associated with Sgr E and the other at -174 km s-1 outside the edge of another CO cloud. From the [N ii] emission we find that the average electron density is in the range of ~5 to 21 cm-3 for these features. This electron density is much higher than that of the disk's warm ionized medium, but is consistent with densities determined for bright diffuse H ii nebula. The column density of the CO-dark H2 layer in the -207 km s-1 cloud is ~1-2 × 1021 cm-2 in agreement with theoretical models. The CMZ extends further out in Galactic radius by ~7 to 14 pc in ionized gas than it does in molecular gas traced by CO. Conclusions: The edge of the CMZ likely contains dense hot ionized gas surrounding the neutral molecular material. The high fractional abundance of N+ and high electron density require an intense EUV field with a photon flux of order 106 to 107 photons cm-2 s-1, and/or efficient proton charge exchange with nitrogen, at temperatures of order 104 K, and/or a large flux of X-rays. Sgr E is a region of massive star formation as indicated by the presence of numerous compact H ii regions. The massive stars are potential sources of the EUV radiation that ionizes and heat the gas. In addition, X-ray sources and the diffuse X-ray emission in the CMZ are candidates for ionizing nitrogen.

NuSTAR Results and Future Plans for Magnetar and Rotation-Powered Pulsar Observations

NASA Technical Reports Server (NTRS)

An, H.; Kaspi, V. M.; Archibald, R.; Bachetti, M.; Bhalerao, V.; Bellm, E. C.; Beloborodov, A. M.; Boggs, S. E.; Chakrabarty, D.; Christensen, F. E.;

Rotational spectrum of 3-aminopropionitrile and searches for it in Sagittarius B2(N)

NASA Astrophysics Data System (ADS)

Richard, C.; Belloche, A.; Margulès, L.; Motiyenko, R. A.; Menten, K. M.; Garrod, R. T.; Müller, H. S. P.

2018-03-01

Aminoacetonitrile (NH2CH2CN) was detected in the interstellar medium (ISM) one decade ago in the course of a spectral survey of the hot molecular core Sagittarius (Sgr) B2(N) with the IRAM 30 m telescope. With the advent of sensitive telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA), the degree of chemical complexity in the ISM can be further explored. In the family of aminoacetonitrile, the next stage in complexity with one additional CH2 group is aminopropionitrile. This molecule has two structural isomers, a chain-like (3-aminopropionitrile, NH2CH2CH2CN) and a branched, chiral one (2-aminopropionitrile, CH3CH(NH2) CN). The latter was studied in the laboratory a few years ago and was not detected in the IRAM 30 m survey. We present the search for both isomers in the EMoCA (Exploring Molecular Complexity with ALMA) survey, a sensitive spectral survey of Sgr B2(N) performed with ALMA. The rotational spectrum of 3-aminopropionitrile has been recorded in laboratory with a submillimeter spectrometer using solid-state sources. Helped by ab initio calculations performed for the different possible conformations, we present here the analysis based on a Watson Hamiltonian for an asymmetric one-top rotor in A-reduction performed in the frequency range 150-500 GHz for two conformers. More than 6200 lines of the ground-state and lowest excited vibrational states, corresponding to more than 8200 transitions, were assigned in the experimental spectrum. Partition functions, including the vibrational contribution of these states, and predictions in the JPL-CDMS catalog format were determined in order to search for both conformers of 3-aminopropionitrile in Sgr B2(N). Neither 3-aminopropionitrile, nor 2-aminopropionitrile are detected. The derived upper limits imply that they are at least 12 and 5 times less abundant than aminoacetonitrile, respectively. A comparison to ethyl cyanide and n-propyl cyanide detected in this source suggests that an improvement by a factor three in sensitivity may be sufficient to detect 3-aminopropionitrile, which should be within the range of our on-going follow-up project with ALMA.

Surfing a Black Hole

NASA Astrophysics Data System (ADS)

2002-10-01

Star Orbiting Massive Milky Way Centre Approaches to within 17 Light-Hours [1] Summary An international team of astronomers [2], lead by researchers at the Max-Planck Institute for Extraterrestrial Physics (MPE) , has directly observed an otherwise normal star orbiting the supermassive black hole at the center of the Milky Way Galaxy. Ten years of painstaking measurements have been crowned by a series of unique images obtained by the Adaptive Optics (AO) NAOS-CONICA (NACO) instrument [3] on the 8.2-m VLT YEPUN telescope at the ESO Paranal Observatory. It turns out that earlier this year the star approached the central Black Hole to within 17 light-hours - only three times the distance between the Sun and planet Pluto - while travelling at no less than 5000 km/sec . Previous measurements of the velocities of stars near the center of the Milky Way and variable X-ray emission from this area have provided the strongest evidence so far of the existence of a central Black Hole in our home galaxy and, implicitly, that the dark mass concentrations seen in many nuclei of other galaxies probably are also supermassive black holes. However, it has not yet been possible to exclude several alternative configurations. In a break-through paper appearing in the research journal Nature on October 17th, 2002, the present team reports their exciting results, including high-resolution images that allow tracing two-thirds of the orbit of a star designated "S2" . It is currently the closest observable star to the compact radio source and massive black hole candidate "SgrA*" ("Sagittarius A") at the very center of the Milky Way. The orbital period is just over 15 years. The new measurements exclude with high confidence that the central dark mass consists of a cluster of unusual stars or elementary particles, and leave little doubt of the presence of a supermassive black hole at the centre of the galaxy in which we live . PR Photo 23a/02 : NACO image of the central region of the Milky Way . PR Photo 23b/02 : NACO image of the central region of the Milky Way (close-up) . PR Photo 23c/02 : Orbit of the star "S2" around the central Black Hole. PR Video Clip 02/02 : Motion of "S2" and other stars around the central Black Hole. Quasars and Black Holes Ever since the discovery of the quasars (quasi-stellar radio sources) in 1963, astrophysicists have searched for an explanation of the energy production in these most luminous objects in the Universe. Quasars reside at the centres of galaxies, and it is believed that the enormous energy emitted by these objects is due to matter falling onto a supermassive Black Hole, releasing gravitational energy through intense radiation before that material disappears forever into the hole (in physics terminology: "passes beyond the event horizon" [4]). To explain the prodigious energy production of quasars and other active galaxies, one needs to conjecture the presence of black holes with masses of one million to several billion times the mass of the Sun. Much evidence has been accumulating during the past years in support of the above "accreting black hole" model for quasars and other galaxies, including the detection of dark mass concentrations in their central regions. However, an unambiguous proof requires excluding all possible other, non-black hole configurations of the central mass concentration. For this, it is imperative to determine the shape of the gravitational field very close to the central object - and this is not possible for the distant quasars due to technological limitations of the currently available telescopes. The centre of the Milky Way ESO PR Photo 23a/02 ESO PR Photo 23a/02 [Preview - JPEG: 400 x 427 pix - 95k [Normal - JPEG: 800 x 853 pix - 488k] Caption : PR Photo 23a/02 is a reproduction of an image of the innermost area of the Milky Way, only a few light-years across, obtained in mid-2002 with the NACO instrument [3] at the 8.2-m VLT YEPUN telescope. It combines frames in three infrared wavebands between 1.6 and 3.5 µm. The compact objects are stars and their colours indicate their temperature (blue = "hot", red = "cool"). There is also diffuse infrared emission from interstellar dust between the stars. The two yellow arrows mark the position of the black hole candidate "SgrA*" at the very centre of the Milky Way galaxy. The scale is indicated; the 1 light-year bar subtends an angle of 8 arcsec in the sky. The centre of our Milky Way galaxy is located in the southern constallation Sagittarius (The Archer) and is "only" 26,000 light-years away [5]. On high-resolution images, it is possible to discern thousands of individual stars within the central, one light-year wide region (this corresponds to about one-quarter of the distance to "Proxima Centauri", the star nearest to the solar system). Using the motions of these stars to probe the gravitational field, observations with the 3.5-m New Technology Telescope (NTT) at the ESO La Silla Observatory (Chile) (and subsequently at the 10-m Keck telescope , Hawaii, USA) over the last decade have shown that a mass of about 3 million times that of the Sun is concentrated within a radius of only 10 light-days [5] of the compact radio and X-ray source SgrA* ("Sagittarius A") at the center of the star cluster. This means that SgrA* is the most likely counterpart of the putative black hole and, at the same time, it makes the Galactic Center the best piece of evidence for the existence of such supermassive black holes . However, those earlier investigations could not exclude several other, non-black hole configurations. "We then needed even sharper images to settle the issue of whether any configuration other than a black hole is possible and we counted on the ESO VLT telescope to provide those" , explains Reinhard Genzel , Director at the Max-Planck Institute for Extraterrestrial Physics (MPE) in Garching near Munich (Germany) and member of the present team. "The new NAOS-CONICA (NACO) instrument, built in a close collaboration between our institute, the Max-Planck Institute for Astronomy (MPIA: Heidelberg, Germany), ESO and the Paris-Meudon and Grenoble Observatories (France), was just what we needed to take this decisive step forward" . The NACO observations of the Milky Way centre ESO PR Photo 23b/02 ESO PR Photo 23b/02 [Preview - JPEG: 400 x 618 pix - 82k] [Normal - JPEG: 800 x 1236 pix - 456k] ESO PR Photo 23c/02 ESO PR Photo 23c/02 [Preview - JPEG: 486 x 400 pix - 78k] [Normal - JPEG: 971 x 800 pix - 352k] ESO PR Video Clip 02/02 [MPEG] ESO PR Video Clip 02/02 [MPEG Video; 533 k] Caption : PR Photo 23b/02 shows an infrared NACO image of a ~ 2 x 2 arcsec 2 area, centred on the position of the compact radio source "SgrA*" at the centre of the Milky Way Galaxy; it is marked by a small cross. The image was obtained in the K s -band at wavelength 2.1 µm in May 2002 and the angular resolution (image sharpness) is about 0.060 arcsec. At about the same time, the star designated "S2" came within 0.015 arcsec of the radio source. At the distance of the Milky Way Center, 1 arcsec on the sky corresponds to 46 light-days [5]; the bar is 20 light-days long (0.44 arcsec). In PR Photo 23c/02 , "SgrA*" and S2 are identified in the left panel. The right panel displays the orbit of S2 as observed between 1992 and 2002, relative to SgrA* (marked with a circle). The positions of S2 at the different epochs are indicated by crosses with the dates (expressed in fractions of the year) shown at each point. The size of the crosses indicates the measurement errors. The solid curve is the best-fitting elliptical orbit - one of the foci is at the position of SgrA* . The 2002 data points come from NACO observations done during the early commissioning, fine adjustement, and Science Verification phases for this instrument; these data were promptly made public through the ESO Archive, cf. the NACO data webpage. PR Video Clip 02/02 was produced by the Max-Planck-Society and shows the observed motions of S2 and other stars in this area. The new NACO instrument [3] was installed in late 2001 at the VLT 8.2-m YEPUN telescope. Already during the initial tests, it produced many impressive images, some of which have been the subject of earlier ESO press releases [6]. "The first observations this year with NACO gave us right away the sharpest and 'deepest' images of the Milky Way Centre ever taken, showing a large number of stars in that area in great detail" , says Andreas Eckart of the University of Cologne, another member of the international team that is headed by Rainer Schödel, Thomas Ott and Reinhard Genzel from MPE. "But we were still to be overwhelmed by the wonderful outcome of those data! " Combining their infrared images with high-resolution radio data, the team was able to determine - during a ten-year period - very accurate positions of about one thousand stars in the central area with respect to the compact radio source SgrA* , see PR Photo 23c/02 . "When we included the latest NACO data in our analysis in May 2002, we could not believe our eyes. The star S2 , which is the one currently closest to SgrA*, had just performed a rapid swing-by near the radio source. We suddenly realised that we were actually witnessing the motion of a star in orbit around the central black hole, taking it incredibly close to that mysterious object" , says a very happy Thomas Ott , who is now working in the MPE team on his PhD thesis. In orbit around the central black hole No event like this one has ever been recorded . These unique data show unambiguously that S2 is moving along an elliptical orbit with SgrA* at one focus, i.e. S2 orbits SgrA* like the Earth orbits the Sun, cf. the right panel of PR Photo 23c/02 . The superb data also allow a precise determination of the orbital parameters (shape, size, etc.). It turns out that S2 reached its closest distance to SgrA* in the spring of 2002, at which moment it was only 17 light-hours [5] away from the radio source, or just 3 times the Sun-Pluto distance. It was then moving at more than 5000 km/s, or nearly two hundred times the speed of the Earth in its orbit around the Sun. The orbital period is 15.2 years. The orbit is rather elongated - the eccentricity is 0.87 - indicating that S2 is about 10 light-days away from the central mass at the most distant orbital point [7]. "We are now able to demonstrate with certainty that SgrA* is indeed the location of the central dark mass we knew existed. Even more important, our new data have "shrunk" by a factor of several thousand the volume within which those several million solar masses are contained" , says Rainer Schödel , PhD student at MPE and also first author of the resulting paper. In fact, model calculations now indicate that the best estimate of the mass of the Black Hole at the centre of the Milky Way is 2.6 ± 0.2 million times the mass of the Sun . No other possibilities According to the detailed analysis presented in the Nature article, other previously possible configurations, such as very compact clusters of neutron stars, stellar size black holes or low mass stars, or even a ball of putative heavy neutrinos, can now be definitively excluded. The only still viable non-black hole configuration is a hypothetical star of heavy elementary particles called bosons, which would look very similar to a black hole. "However" , says Reinhard Genzel , "even if such a boson star is in principle possible, it would rapidly collapse into a supermassive black hole anyhow, so I think we have pretty much clinched the case!" Next observations "Most astrophysicists would accept that the new data provide compelling evidence that a supermassive black hole exists in the center of the Milky Way. This makes even more likely the supermassive black hole interpretation for the enormous concentration of dark mass detected at the center of many other galaxies" , says Alvio Renzini , VLT Programme Scientist at ESO. So what remains to be done? The next big quest now is to understand when and how these supermassive black holes formed and why almost every massive galaxy appears to contain one. The formation of central black holes and that of their host galaxies themselves increasingly appear to be just one problem and the same. Indeed, one of the outstanding challenges for the VLT to solve in the next few years. There is also little doubt that coming interferometric observations with instruments at the VLT Interferometer (VLTI) and the Large Binocular Telescope (LBT) will also result in another giant leap within this exciting field of research. Andreas Eckart is optimistic: "Perhaps it will even be possible with X-ray and radio observations in the next few years to directly demonstrate the existence of the event horizon." More information The information presented in this Press Release is based on a research article ("Seeing a Star Orbit around the Supermassive Black Hole at the centre of the Milky Way" by Rainer Schödel et al.) that appears in the research journal "Nature" on October 17, 2002. Notes [1]: This press release is issued in coordination between ESO and the Max-Planck-Institute for Extraterrestrial Physics (MPE) in Garching, Germany. A German version is available at http://www.mpg.de/pri02/pri0287.htm. [2]: The team consists of Rainer Schödel, Thomas Ott, Reinhard Genzel, Reiner Hofmann and Matt Lehnert (Max-Planck-Institut für extraterrestrische Physik, Garching, Germany), Andreas Eckart and Nelly Mouawad (Physikalisches Institut, Universität zu Köln, Cologne, Germany), Tal Alexander (The Weizmann Institute of Science, Rehovot, Israel), Mark J. Reid (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass., USA), Rainer Lenzen and Markus Hartung (Max-Planck-Institut für Astronomie, Heidelberg, Germany), François Lacombe, Daniel Rouan, Eric Gendron and Gérard Rousset (Observatoire de Paris - Section de Meudon, France), Anne-Marie Lagrange (Laboratoire d'Astrophysique, Observatoire de Grenoble, France), Wolfgang Brandner, Nancy Ageorges, Chris Lidman, Alan F.M. Moorwood, Jason Spyromilio and Norbert Hubin (ESO) and Karl M. Menten (Max-Planck-Institut für Radioastronomie, Bonn, Germany). [3]: The NACO facility has two major components, CONICA and NAOS . The COudé Near-Infrared CAmera (CONICA) was developed by a German Consortium, with an extensive ESO collaboration. The Consortium consists of Max-Planck-Institut für Astronomie (MPIA) (Heidelberg) and the Max-Planck-Institut für Extraterrestrische Physik (MPE) (Garching). The Nasmyth Adaptive Optics System (NAOS) was developed, with the support of INSU-CNRS, by a French Consortium in collaboration with ESO. The French consortium consists of Office National d'Etudes et de Recherches Aérospatiales (ONERA) , Laboratoire d'Astrophysique de Grenoble (LAOG) and Observatoire de Paris (DESPA and DASGAL). [4]: In Albert Einstein's Theory of General Relativity, any mass has a characteristic radius, the "event horizon", or "Schwarzschild radius" named after the German astrophysicist Karl Schwarzschild . Within this radius, even light cannot escape the pull of the gravitational force. The radius for a 2.6 ± 0.2 million solar masses black hole (as the one at the centre of the Milky Way galaxy) is about 7.7 million km (26 light-seconds). [5]: Astronomical distances are often expressed in the time it takes the light, travelling at 300,000 km/sec, to cover them. 1 light-hour = 1.08 10 9 km; 1 light-day = 2.6 10 10 km; 1 light-month = 7.8 10 11 km; 1 light-year = 9.5 10 12 km. [6]: Earlier NACO images have been published in ESO PR 25/01 , ESO PR Photos 04a-c/02 , ESO PR Photos 19a-c/02 and ESO PR Photos 21a-c/02. [7]: S2 is an otherwise "normal" star, but some 15 times more massive and 7 times larger than the Sun. Its orbit around the Black Hole is comparatively stable. Even though it moves relatively close to the Black Hole in the present orbit, S2 would have to be at least 70 times closer (about 16 light-minutes from the Black Hole) before it would risk being disrupted by tidal forces. Astronomers refer to the extreme orbital points as "perenigricon" (closest to the Black Hole) and "aponigricon" (farthest away).

SGR reform and nephrology: difficult problems, potential solutions.

PubMed

Velez, Ruben; Singer, Dale; Blaser, Robert

2012-09-01

In light of the massive uncertainty with both the federal government in general and health policy priorities specifically, it is probably constructive to focus on the things we know for sure. In Medicare Part B reimbursement, the SGR system is fundamentally flawed, and must be replaced. All of Congress has recognized this fact, and there is legislation in the House that would move the ball forward on SGR repeal and replacement. Likewise, coordinated care models like ACOs offer a logical process for achieving a triple aim: improving individual health care, improving population health, and promoting cost efficiency in health care. Hopefully, policy makers in Washington will recognize and act on these truths as well.

Investigating the Relativistic Motion of the Stars Near the Supermassive Black Hole in the Galactic Center

NASA Astrophysics Data System (ADS)

Parsa, M.; Eckart, A.; Shahzamanian, B.; Karas, V.; Zajaček, M.; Zensus, J. A.; Straubmeier, C.

2017-08-01

The S-star cluster in the Galactic center allows us to study the physics close to a supermassive black hole, including distinctive dynamical tests of general relativity. Our best estimates for the mass of and the distance to Sgr A* using the three stars with the shortest period (S2, S38, and S55/S0-102) and Newtonian models are M BH = (4.15 ± 0.13 ± 0.57) × 106 M ⊙ and R 0 = 8.19 ± 0.11 ± 0.34 kpc. Additionally, we aim at a new and practical method to investigate the relativistic orbits of stars in the gravitational field near Sgr A*. We use a first-order post-Newtonian approximation to calculate the stellar orbits with a broad range of periapse distance r p . We present a method that employs the changes in orbital elements derived from elliptical fits to different sections of the orbit. These changes are correlated with the relativistic parameter defined as ϒ ≡ r s /r p (with r s being the Schwarzschild radius) and can be used to derive ϒ from observational data. For S2 we find a value of ϒ = 0.00088 ± 0.00080, which is consistent, within the uncertainty, with the expected value of ϒ = 0.00065 derived from M BH and the orbit of S2. We argue that the derived quantity is unlikely to be dominated by perturbing influences such as noise on the derived stellar positions, field rotation, and drifts in black hole mass.

Imaging black holes: past, present and future

NASA Astrophysics Data System (ADS)

Falcke, Heino

2017-12-01

This paper briefly reviews past, current, and future efforts to image black holes. Black holes seem like mystical objects, but they are an integral part of current astrophysics and are at the center of attempts to unify quantum physics and general relativity. Yet, nobody has ever seen a black hole. What do they look like? Initially, this question seemed more of an academic nature. However, this has changed over the past two decades. Observations and theoretical considerations suggest that the supermassive black hole, Sgr A*, in the center of our Milky Way is surrounded by a compact, foggy emission region radiating at and above 230 GHz. It has been predicted that the event horizon of Sgr A* should cast its shadow onto that emission region, which could be detectable with a global VLBI array of radio telescopes. In contrast to earlier pictures of black holes, that dark feature is not supposed to be due to a hole in the accretion flow, but would represent a true negative image of the event horizon. Currently, the global Event Horizon Telescope consortium is attempting to make such an image. In the future those images could be improved by adding more telescopes to the array, in particular at high sites in Africa. Ultimately, a space array at THz frequencies, the Event Horizon Imager, could produce much more detailed images of black holes. In combination with numerical simulations and precise measurements of the orbits of stars - ideally also of pulsars - these images will allow us to study black holes with unprecedented precision.

A possible origin of the Galactic Center magnetar SGR 1745-2900

NASA Astrophysics Data System (ADS)

Cheng, Quan; Zhang, Shuang-Nan; Zheng, Xiao-Ping

2017-05-01

Since there is a large population of massive O/B stars and putative neutron stars (NSs) located in the vicinity of the Galactic Center (GC), intermediate-mass X-ray binaries (IMXBs) constituted by an NS and a B-type star probably exist there. We investigate the evolutions of accreting NSs in IMXBs (similar to M82 X-2) with a ˜ 5.2 {M}⊙ companion and orbital period ≃ 2.53 d. By adopting a mildly super-Eddington rate \\dot{M}=6× {10}-8 {M}⊙ {{yr}}-1 for the early Case B Roche-lobe overflow (RLOF) accretion, we find that only in accreting NSs with quite elastic crusts (slippage factor s = 0.05) can the toroidal magnetic fields be amplified within 1 Myr, which is assumed to be the longest duration of the RLOF. These IMXBs will evolve into NS+white dwarf (WD) binaries if they are dynamically stable. However, before the formation of NS+WD binaries, the high stellar density in the GC will probably lead to frequent encounters between the NS+evolved star binaries (in post-early Case B mass transfer phase) and NSs or exchange encounters with other stars, which may produce single NSs. These NSs will evolve into magnetars when the amplified poloidal magnetic fields diffuse out to the NS surfaces. Consequently, our results provide a possible explanation for the origin of the GC magnetar SGR 1745-2900. Moreover, the accreting NSs with s> 0.05 will evolve into millisecond pulsars (MSPs). Therefore, our model reveals that the GC magnetars and MSPs could both originate from a special kind of IMXB.

Dynamical and Radiative Modeling of Sagittarius A*

NASA Astrophysics Data System (ADS)

Shcherbakov, Roman V.

2011-09-01

Sgr A* in our Galactic Center is the closest supermassive black hole (SMBH) with the largest event horizon angular size. Most other SMBHs are likely in the same dormant low-luminosity accretion state as Sgr A*. Thus, the important physical effects in lives of BHs can be best observed and studied in our Galactic Center. One of these effects is electron heat conduction. Conduction may be the main reason why Sgr A* is so dramatically underluminous: it transfers heat outwards from the inner flow and unbinds the outer flow, quenching the accretion. In Chapter 3 I build a realistic model of accretion with conduction, which incorporates feeding by stellar winds. In a model with accretion rate < 1% of the naive Bondi estimate I achieve agreement of the X-ray surface brightness profile and Faraday rotation measure to observations. An earlier model proposed in Chapter 2 with adiabatic accretion of turbulent magnetized medium cannot be tweaked to match the observations. Its accretion rate appears too large, so turbulent magnetic field cannot stop gas from falling in. Low accretion rate leads to a peculiar radiation pattern from near the BH: cyclo-synchrotron polarized radiation is observed in radio/sub-mm. Since it comes from several Schwarzschild radii, the BH spin can be determined, when we overcome all modeling challenges. I fit the average observed radiation spectrum with a theoretical spectrum, which is computed by radiative transfer over a simulation-based model. Relevant plasma effects responsible for the observed polarization state are accurately computed for thermal plasma in Chapter 4. The prescription of how to perform the correct general relativistic polarized radiative transfer is elaborated in Chapter 5. Application of this technique to three-dimensional general relativistic magneto hydrodynamic numerical simulations is reported in Chapter 6. The main results of analysis are that the spin inclination angle is estimated to lie within a narrow range theta est = 50° -- 59°, and most probable value of BH spin is a* = 0.9. I believe the researched topics will play a central role in future modeling of typical SMBH accretion and will lead to effective ways to determine the spins of these starving eaters. Computations of plasma effects reported here will also find applications when comparing models of jets to observations.

The {sup 12}C/{sup 13}C Ratio in Sgr B2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halfen, D. T.; Ziurys, L. M.; Woolf, N. J., E-mail: halfend@email.arizona.edu

A study has been conducted of {sup 12}C/{sup 13}C ratios in five complex molecules in the Galactic center. H{sub 2}CS, CH{sub 3}CCH, NH{sub 2}CHO, CH{sub 2}CHCN, and CH{sub 3}CH{sub 2}CN and their {sup 13}C-substituted species have been observed in numerous transitions at 1, 2, and 3 mm, acquired in a spectral-line survey of Sgr B2(N), conducted with the telescopes of the Arizona Radio Observatory (ARO). Between 22 and 54 individual, unblended lines for the {sup 12}C species and 2–54 for {sup 13}C-substituted analogs were modeled in a global radiative transfer analysis. All five molecules were found to consistently exhibit twomore » velocity components near V {sub LSR} ∼ 64 and 73 km s{sup −1}, with column densities ranging from N {sub tot} ∼ 3 × 10{sup 14} − 4 × 10{sup 17} cm{sup −2} and ∼2 × 10{sup 13} − 1 × 10{sup 17} cm{sup −2} for the {sup 12}C and {sup 13}C species, respectively. Based on 14 different isotopic combinations, ratios were obtained in the range {sup 12}C/{sup 13}C = 15 ± 5 to 33 ± 13, with an average value of 24 ± 7, based on comparison of column densities. These measurements better anchor the {sup 12}C/{sup 13}C ratio at the Galactic center, and suggest a slightly revised isotope gradient of {sup 12}C/{sup 13}C = 5.21(0.52) D {sub GC} + 22.6(3.3). As indicated by the column densities, no preferential {sup 13}C enrichment was found on the differing carbon sites of CH{sub 3}CCH, CH{sub 2}CHCN, and CH{sub 3}CH{sub 2}CN. Because of the elevated temperatures in Sgr B2(N), {sup 13}C isotopic substitution is effectively “scrambled,” diminishing chemical fractionation effects. The resulting ratios thus reflect stellar nucleosynthesis and Galactic chemical evolution, as is likely the case for most warm clouds.« less

Swift J1822.3-1606: pre-outburst ROSAT limits (plus erratum)

NASA Astrophysics Data System (ADS)

Esposito, P.; Rea, N.; Israel, G. L.; Tieng, A.

2011-07-01

We report on a pre-outburst ROSAT PSPC observation of the new SGR discovered by Swift-BAT on 2011 July 14 (Cummings et al. Atel #3488). The PSPC observation was performed on 1993 September 12 for ~6.7ks. We find a source at: RA (2000) = 18 22 18.1 and Dec (2000)= -16 04 26.4, with a 5sigma detection significance. The count-rate (corrected for the PSPC PSF, sampling dead time, and vignetting) is about 0.012 counts/s.

Tempus Pro Patient Monitoring System

DTIC Science & Technology

2015-04-03

AFMSA SG5T, (AFMESA) Mr. John Ingram, AFMSA SG5T, AFMESA Mr. John Plaga , 711 HPW/HP Human Factors Engineering Mr. Paul Bailey, AMC SG/SGR Ms. Lynn...John Plaga , 711 HPW/HP Human Factors Engineering Mr. Paul Bailey, AMC SG/SGR Lt Col Cheryl Hale, AMC SG/SGK Mr. Graham Murphy, RDT Mr. Nigel

VizieR Online Data Catalog: K giant stars along Sagittarius streams (Ren+, 2017)

NASA Astrophysics Data System (ADS)

Ren, H.-B.; Shi, W.-B.; Zhang, X.; Tang, Y.-K.; Zhang, Y.; Hou, Y.-H.; Wang, Y.-F.

2017-08-01

Law & Majewski (2010ApJ...714..229L) provided a Sgr model that has 105 points with angular position, distance and radial velocity. By using the model of Law & Majewski (2010ApJ...714..229L), we selected K giant samples belonging to the leading Sgr stream. (1 data file).

Sgr A* envelope explosion and the young stars in the centre of the Milky Way

NASA Astrophysics Data System (ADS)

Nayakshin, Sergei; Zubovas, Kastytis

2018-05-01

Sgr A* is the super massive black hole residing in the centre of the Milky Way. There is plenty of observational evidence that a massive gas cloud fell into the central parsec of the Milky Way ˜6 million years ago, triggering formation of a disc of young stars and activating Sgr A* . In addition to the disc, there is an unexplained population of young stars on randomly oriented orbits. Here we hypothesize that these young stars were formed by fragmentation of a massive quasi-spherical gas shell driven out from Sgr A* potential well by an energetic outflow. To account for the properties of the observed stars, the shell must be more massive than 105 Solar masses, be launched from inside ˜0.01 pc, and the feedback outflow has to be highly super-Eddington albeit for a brief period of time, producing kinetic energy of at least 1055 erg. The young stars in the central parsec of the Galaxy may be a unique example of stars formed from atomic rather than molecular hydrogen, and forged by extreme pressure of black hole outflows.

V5588 SGR = Nova Sagittarii 2011 No. 2 = Pnv J18102135-2305306

NASA Astrophysics Data System (ADS)

Waagen, Elizabeth O.

2011-04-01

Announces the discovery of Nova Sgr 2011 No. 2 = V5588 SGR = PNV J18102135-2305306 by Koichi Nishiyama (Kurume, Japan) and Fujio Kabashima (Miyaki, Japan) on ~ 2011 March 27.832 UT at unfiltered CCD magnitude mag 11.7. Spectra obtained by A. Arai, M. Nagashima, T. Kajikawa, and C. Naka (Koyama Astronomical Observatory, Kyoto Sangyo University) on Mar. 28.725 UT suggest that the object is a classical nova reddened by interstellar matter. The object was designated PNV J18102135-2305306 when posted on the Central Bureau's Transient Objects Confirmation Page (TOCP) webpage. E. Kazarovets, on behalf of the GCVS team, reports that the name V5588 Sgr has been assigned to this nova. It was nitially announced in CBET 2679 (Daniel W. E. Green, ed.) and AAVSO Special Notice #237 (Waagen). Additional information published in IAU Circular 9203 (Green, ed.). Finder charts with sequence may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details and observations.

360-degree video and X-ray modeling of the Galactic center's inner parsec

NASA Astrophysics Data System (ADS)

Russell, Christopher Michael Post; Wang, Daniel; Cuadra, Jorge

2017-08-01

360-degree videos, which render an image over all 4pi steradian, provide a unique and immersive way to visualize astrophysical simulations. Video sharing sites such as YouTube allow these videos to be shared with the masses; they can be viewed in their 360° nature on computer screens, with smartphones, or, best of all, in virtual-reality (VR) goggles. We present the first such 360° video of an astrophysical simulation: a hydrodynamics calculation of the Wolf-Rayet stars and their ejected winds in the inner parsec of the Galactic center. Viewed from the perspective of the super-massive black hole (SMBH), the most striking aspect of the video, which renders column density, is the inspiraling and stretching of clumps of WR-wind material as they makes their way towards the SMBH. We will brielfy describe how to make 360° videos and how to publish them online in their desired 360° format. Additionally we discuss computing the thermal X-ray emission from a suite of Galactic-center hydrodynamic simulations that have various SMBH feedback mechanisms, which are compared to Chandra X-ray Visionary Program observations of the region. Over a 2-5” ring centered on Sgr A*, the spectral shape is well matched, indicating that the WR winds are the dominant source of the thermal X-ray emission. Furthermore, the X-ray flux depends on the SMBH feedback due to the feedback's ability to clear out material from the central parsec. A moderate outburst is necessary to explain the current thermal X-ray flux, even though the outburst ended ˜100 yr ago.

Discovery of a Transient Magnetar: XTE J1810-197

NASA Technical Reports Server (NTRS)

Ibrahim, Alaa I.; Markwardt, Craig B.; Swank, Jean H.; Ransom, Scott; Roberts, Mallory; Kaspi, Victoria; Woods, Peter M.; Safi-Harb, Samar; Balman, Solen; Parke, William C.

2004-01-01

We report the discovery of a new X-ray pulsar, XTE J1810-197, that was serendipitously discovered on 2003 July 15 by the Rossi X-Ray Timing Explorer (RXTE) while observing the soft gamma repeater SGR 1806-20. The pulsar has a 5.54 s spin period, a soft X-ray spectrum (with a photon index of approx. = 4). and is detectable in earlier RXTE observations back to 2003 January but not before. These show that a transient outburst began between 2002 November 17 and 2003 January 23 and that the source's persistent X-ray flux has been declining since then. The pulsar exhibits a high spin-down rate P approx.= l0(exp -11) s/s with no evidence of Doppler shifts due to a binary companion. The rapid spin-down rate and slow spin period imply a supercritical characteristic magnetic field B approx. = 3 x l0(exp 14) G and a young age tau less than or = 7600 yr. Follow-up Chandra observations provided an accurate position of the source. Within its error radius, the 1.5 m Russian-Turkish Optical Telescope found a limiting magnitude R(sub c) = 21.5. All such properties are strikingly similar to those of anomalous X-ray pulsars ad soft gamma repeaters, providing strong evidence that the source is a new magnetar. However, archival ASCA and ROSAT observations found the source nearly 2 orders of magnitude fainter. This transient behavior and the observed long-term flux variability of the source in absence of an observed SGR-like burst activity make it the first confirmed transient magnetar and suggest that other neutron stars that share the properties of XTE 51810- 197 during its inactive phase may be unidentified transient magnetars awaiting detection via a similar activity. This implies a larger population of magnetars than previously surmised and a possible evolutionary connection between magnetars and other neutron star families. Subject headings: pulsars: general -pulsars: individual (XTE 51810- 197) - stars: magnetic fields -

Trans-ethyl methyl ether, the struggle for the detection of a complex molecule in hot cores

NASA Astrophysics Data System (ADS)

Fuchs, G. W.; Fuchs, U.; Giesen, T. F.; Wyrowski, F.

Many large and complex molecules of prebiotic importance have been found as constituents of interstellar clouds but their detection remains difficult and sometimes doubtful (Snyder et al. 2005). The complex spectrum of trans-ethyl methyl ether (EME) has been investigated in the laboratory (Fuchs et al. 2003) up to 350 GHz and is now known with high frequency precision, see Figure 1. In this work we present an extensive search for EME towards G34.26, NGC6334(I), Orion KL, SgrB2(N) and W51e2 in the 1 to 3 mm wavelength region. These sources have previously been shown to have a rich chemistry of complex molecules. The IRAM 30m telescope at Pico Veleta, Spain and the SEST 15m radio telescope in La Silla, Chile have been used for the observations. We looked at 5 - 11 frequency bands where EME has strong transitions. All sources were examined using long integration times up to 220 min (on+off), elevations greater 40◦ and under good weather conditions. For our analysis of the data we used the method of rotational-temperature-diagrams but also the myXCLASS (written by Peter Schilke) extension program to the GILDAS (Grenoble Image and Line Data Analysis Software) software which enabled us to simulate spectra of several molecules including their linewidth and intensities at the same time, see Figure 2. With this program a consistency check of molecular abundances and overall composition is possible even in dense spectra with many overlapping lines. The effect of the source size on the measured intensities has been considered and cross checks with other important molecules such as methanol, ethanol and di-methyl ether have been performed. Charnley et al. (2001) assigned one line in W51 e1/e2 and one line in Orion KL at 160.1 GHz, as well as a line in SgrB2(N) at 79.6 GHz to trans-ethyl methyl ether. From their isolated measurements, the column density of EME was estimated to be in the range 1014-1015 cm-2 in Sgr B2(N) corresponding to a fractional abundance of 10-10-10-9 and in the W51 region they estimate a fractional abundance of 10-10. However, our observations cannot confirm the tentative detection of EME in Orion KL within their given column density limits. There is evidence for the existence of the trans-ethyl methyl ether towards W51e2 with a column density of N=2×1014 cm-2 based on the detection of 14 lines which coincide with EME transition frequencies. We present new upper limits of 7-8×1013 cm-2 for the column densities of EME toward Orion KL, G34.26, NGC6334(I) and estimate the column density of SgrB2(N) to be of the same order. The W51e2 observations are discussed in more detail.

ALMA Detection of Bipolar Outflows: Evidence for Low-mass Star Formation within 1 pc of Sgr A*

NASA Astrophysics Data System (ADS)

Yusef-Zadeh, F.; Wardle, M.; Kunneriath, D.; Royster, M.; Wootten, A.; Roberts, D. A.

2017-12-01

We report the discovery of 11 bipolar outflows within a projected distance of 1 pc from Sgr A* based on deep ALMA observations of 13CO, H30α, and SiO (5-4) lines with subarcsecond and ˜1.3 km s-1 resolutions. These unambiguous signatures of young protostars manifest as approaching and receding lobes of dense gas swept up by the jets created during the formation and early evolution of stars. The lobe masses and momentum transfer rates are consistent with young protostellar outflows found throughout the disk of the Galaxy. The mean dynamical age of the outflow population is estimated to be {6.5}-3.6+8.1× {10}3 years. The rate of star formation is ˜5 × 10-4 {M}⊙ yr-1 assuming a mean stellar mass of ˜0.3 {M}⊙ . This discovery provides evidence that star formation is taking place within clouds surprisingly close to Sgr A*, perhaps due to events that compress the host cloud, creating condensations with sufficient self-gravity to resist tidal disruption by Sgr A*. Low-mass star formation over the past few billion years at this level would contribute significantly to the stellar mass budget in the central few parsecs of the Galaxy. The presence of many dense clumps of molecular material within 1 pc of Sgr A* suggests that star formation could take place in the immediate vicinity of supermassive black holes in the nuclei of external galaxies.

The Sagittarius dwarf galaxy: Where did all the gas go?

NASA Astrophysics Data System (ADS)

Tepper-García, Thor; Bland-Hawthorn, Joss

2018-05-01

The remarkable 1994 discovery of the Sagittarius dwarf galaxy (Sgr) revealed that, together with the Magellanic Clouds, there are at least three major dwarf galaxies, each with a total mass of order 1010 - 1011M⊙, falling onto the Galaxy in the present epoch. Beyond a Galactic radius of 300 kpc, dwarfs tend to retain their gas. At roughly 50 kpc, the Magellanic Clouds have experienced substantial gas stripping as evidenced by the Magellanic Stream which extends from them. Since Sgr experienced star formation long after it fell into the Galaxy, it is interesting to explore just how and when this dwarf lost its gas. To date, there has been no definitive detection of an associated gas component. We revisit recent simulations of the stellar and dark matter components of Sgr but, for the first time, include gas that is initially bound to the infalling galaxy. We find that the gas stripping was 30 - 50% complete at its first disc crossing ˜2.7 Gyr ago, then entirely stripped at its last disc crossing ˜1 Gyr ago. Our timeline is consistent with the last substantial burst of star formation in Sgr which occurred about the time of the last disc crossing. We discuss the consequences of gas stripping and conclude that the vast majority of the stripped gas was fully settled onto the Galaxy by ˜300 Myr ago. It is highly unlikely that any of the high- or intermediate-velocity clouds have a direct association with the Sgr dwarf.

APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasselquist, Sten; Holtzman, Jon; Shetrone, Matthew

The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze thechemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars withmore » [Fe/H] ≳ −0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function.« less

APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Hasselquist, Sten; Shetrone, Matthew; Smith, Verne; Holtzman, Jon; McWilliam, Andrew; Fernández-Trincado, J. G.; Beers, Timothy C.; Majewski, Steven R.; Nidever, David L.; Tang, Baitian; Tissera, Patricia B.; Fernández Alvar, Emma; Allende Prieto, Carlos; Almeida, Andres; Anguiano, Borja; Battaglia, Giuseppina; Carigi, Leticia; Delgado Inglada, Gloria; Frinchaboy, Peter; García-Hernández, D. A.; Geisler, Doug; Minniti, Dante; Placco, Vinicius M.; Schultheis, Mathias; Sobeck, Jennifer; Villanova, Sandro

2017-08-01

The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze thechemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars with [Fe/H] ≳ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function.

STAYGREEN (CsSGR) is a candidate for the anthracnose (Colletotrichum orbiculare) resistance locus cla in Gy14 cucumber.

PubMed

Pan, Junsong; Tan, Junyi; Wang, Yuhui; Zheng, Xiangyang; Owens, Ken; Li, Dawei; Li, Yuhong; Weng, Yiqun

2018-04-21

Map-based cloning identified a candidate gene for resistance to the anthracnose fungal pathogen Colletotrichum orbiculare in cucumber, which reveals a novel function for the highly conserved STAYGREEN family genes for host disease resistance in plants. Colletotrichum orbiculare is a hemibiotrophic fungal pathogen that causes anthracnose disease in cucumber and other cucurbit crops. No host resistance genes against the anthracnose pathogens have been cloned in crop plants. Here, we reported fine mapping and cloning of a resistance gene to the race 1 anthracnose pathogen in cucumber inbred lines Gy14 and WI 2757. Phenotypic and QTL analysis in multiple populations revealed that a single recessive gene, cla, was underlying anthracnose resistance in both lines, but WI2757 carried an additional minor-effect QTL. Fine mapping using 150 Gy14 × 9930 recombinant inbred lines and 1043 F 2 individuals delimited the cla locus into a 32 kb region in cucumber Chromosome 5 with three predicted genes. Multiple lines of evidence suggested that the cucumber STAYGREEN (CsSGR) gene is a candidate for the anthracnose resistance locus. A single nucleotide mutation in the third exon of CsSGR resulted in the substitution of Glutamine in 9930 to Arginine in Gy14 in CsSGR protein which seems responsible for the differential anthracnose inoculation responses between Gy14 and 9930. Quantitative real-time PCR analysis indicated that CsSGR was significantly upregulated upon anthracnose pathogen inoculation in the susceptible 9930, while its expression was much lower in the resistant Gy14. Investigation of allelic diversities in natural cucumber populations revealed that the resistance allele in almost all improved cultivars or breeding lines of the U.S. origin was derived from PI 197087. This work reveals an unknown function for the highly conserved STAYGREEN (SGR) family genes for host disease resistance in plants.

Excitation Mechanisms of Near-Infrared Emission Lines in LINER Galaxies

NASA Astrophysics Data System (ADS)

Boehle, Anna

2017-01-01

I will present high spatial resolution, integral field spectroscopic observations of the nearby LINER (low ionization nuclear emission line region) galaxy NGC 404. LINERs are found at the centers of ~1/3 of galaxies within 40 Mpc, but their physical nature is not well understood. Although NGC 404 is thought to host a intermediate mass black hole at its center, it is unclear whether accretion onto the black hole or another mechanism such as shock excitation drives its LINER emission. We use the OSIRIS near-infrared integral field spectrograph at Keck Observatory behind laser guide star adaptive optics to map the strength and kinematics of [FeII], H2, and hydrogen recombination lines in the nucleus of NGC 404. These observations have a spatial pixel sampling of 0.5 pc and span the central 30 pc of the galaxy. We find that the ionized and molecular gas show differences in their morphology and kinematics on parsec scales. In particular, there are regions with line ratios of [FeII]/Pa-β that are much higher than previously seen in spatially integrated spectra, significantly restricting the possible excitation mechanisms of the near-infrared emission lines in this source. We are also applying these analysis techniques to 10 additional nearby LINERs, a part of a larger sample of 14 sources, to understand what drives the emission lines in these active galaxies. As a part of this program, I worked on the upgrade of the detector in the OSIRIS spectrograph, which has allowed observations for this survey obtained since January 2016 to be taken with increased instrument sensitivity of a factor of ~2 at J-band wavelengths (1.2 - 1.4 microns) and ~1.6 at H- and K-band wavelengths (1.5 - 2.4 microns). I will present results from the LINER survey, the OSIRIS detector upgrade, and also touch on related work using stellar orbits around the Milky Way supermassive black hole Sgr A* to constrain the mass and distance to our own Galactic Center.

Outward Motions of SiO Masers around VX Sgr

NASA Astrophysics Data System (ADS)

Su, J. B.; Shen, Z.-Q.; Chen, X.; Jiang, D. R.

2014-09-01

We report the proper motions of SiO maser features around VX Sgr from the two-epoch VLBA observations (2006 December 15 and 2007 August 19). The majority of maser feature activities show a trend of outward motions. It is consistent with our previous finding that the outflow may play an important role for SiO maser pumping.

Self-Guided Reading: Touch-Based Measures of Syntactic Processing

ERIC Educational Resources Information Center

Hatfield, Hunter

2016-01-01

A novel online reading methodology termed Self-Guided Reading (SGR) is examined to determine if it can successfully detect well-studied syntactic processing behaviours. In SGR, a participant runs their finger under masked text in order to reveal a sentence. It is therefore similar to self-paced reading in presentation of stimuli, but different in…

Feasibility of a Text-Based Smoking Cessation Intervention in Rural Older Adults

ERIC Educational Resources Information Center

Noonan, D.; Silva, S.; Njuru, J.; Bishop, T.; Fish, L. J.; Simmons, L. A.; Choi, S. H.; Pollak, K. I.

2018-01-01

Text-based interventions are effective for smoking cessation, but have not been tested in rural older adults. The purpose of this study was to compare the feasibility, acceptability and preliminary efficacy of a text-based Scheduled Gradual Reduction (SGR) program to a non-SGR text messaging support condition among rural older adults. Adults over…

DISCOVERY OF METHYL ACETATE AND GAUCHE ETHYL FORMATE IN ORION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tercero, B.; Cernicharo, J.; Lopez, A.

2013-06-10

We report on the discovery of methyl acetate, CH{sub 3}COOCH{sub 3}, through the detection of a large number of rotational lines from each one of the spin states of the molecule: AA species (A{sub 1} or A{sub 2}), EA species (E{sub 1}), AE species (E{sub 2}), and EE species (E{sub 3} or E{sub 4}). We also report, for the first time in space, the detection of the gauche conformer of ethyl formate, CH{sub 3}CH{sub 2}OCOH, in the same source. The trans conformer is also detected for the first time outside the Galactic center source SgrB2. From the derived velocity ofmore » the emission of methyl acetate, we conclude that it arises mainly from the compact ridge region with a total column density of (4.2 {+-} 0.5) Multiplication-Sign 10{sup 15} cm{sup -2}. The derived rotational temperature is 150 K. The column density for each conformer of ethyl formate, trans and gauche, is (4.5 {+-} 1.0) Multiplication-Sign 10{sup 14} cm{sup -2}. Their abundance ratio indicates a kinetic temperature of 135 K for the emitting gas and suggests that gas-phase reactions could participate efficiently in the formation of both conformers in addition to cold ice mantle reactions on the surface of dust grains.« less

A new low-B magnetar: Swift J1822.3-1606

NASA Astrophysics Data System (ADS)

Camero-Arranz, A.; Rea, N.; Israel, G. L.; Esposito, P.; Pons, J. A.; Mignani, R. P.; Turolla, R.; Zane, S.; Burgay, M.; Possenti, A.; Campana, S.; Enoto, T.; Gehrels, N.; Göğüş, E.; Götz, D.; Kouveliotou, C.; Makishima, K.; Mereghetti, S.; Oates, S. R.

2013-03-01

We report on the long term X-ray monitoring with Swift, RXTE, Suzaku, Chandra, and XMM-Newton of the outburst of the newly discovered magnetar Swift J1822.3-1606 (SGR 1822-1606), from the first observations soon after the detection of the short X-ray bursts which led to its discovery (July 2011), through the first stages of its outburst decay (April 2012). Our X-ray timing analysis finds the source rotating with a period of P = 8.43772016(2) s and a period derivative Ṗ = 8.3(2) × 10-14 ss-1, which entails an inferred dipolar surface magnetic field of B ≃ 2.7 × 1013 G at the equator. This measurement makes Swift J1822.3-1606 the second lowest magnetic field magnetar (after SGR 0418+5729; Rea et al. 2010). Following the flux and spectral evolution from the beginning of the outburst, we find that the flux decreased by about an order of magnitude, with a subtle softening of the spectrum, both typical of the outburst decay of magnetars. By modeling the secular thermal evolution of Swift J1822.3-1606, we find that the observed timing properties of the source, as well as its quiescent X-ray luminosity, can be reproduced if it was born with a poloidal and crustal toroidal fields of Bp ~ 1.5 × 1014 G and Btor ~ 7 × 1014 G, respectively, and if its current age is ~550 kyr (Rea et al. 2012).

A New Low Magnetic Field Magnetar: The 2011 Outburst of Swift J1822.3-1606

NASA Astrophysics Data System (ADS)

Rea, N.; Israel, G. L.; Esposito, P.; Pons, J. A.; Camero-Arranz, A.; Mignani, R. P.; Turolla, R.; Zane, S.; Burgay, M.; Possenti, A.; Campana, S.; Enoto, T.; Gehrels, N.; Göǧüş, E.; Götz, D.; Kouveliotou, C.; Makishima, K.; Mereghetti, S.; Oates, S. R.; Palmer, D. M.; Perna, R.; Stella, L.; Tiengo, A.

2012-07-01

We report on the long-term X-ray monitoring with Swift, RXTE, Suzaku, Chandra, and XMM-Newton of the outburst of the newly discovered magnetar Swift J1822.3-1606 (SGR 1822-1606), from the first observations soon after the detection of the short X-ray bursts which led to its discovery, through the first stages of its outburst decay (covering the time span from 2011 July until the end of 2012 April). We also report on archival ROSAT observations which detected the source during its likely quiescent state, and on upper limits on Swift J1822.3-1606's radio-pulsed and optical emission during outburst, with the Green Bank Telescope and the Gran Telescopio Canarias, respectively. Our X-ray timing analysis finds the source rotating with a period of P = 8.43772016(2) s and a period derivative \\dot{P}=8.3(2)\\times 10^{-14} s s-1, which implies an inferred dipolar surface magnetic field of B ~= 2.7 × 1013 G at the equator. This measurement makes Swift J1822.3-1606 the second lowest magnetic field magnetar (after SGR 0418+5729). Following the flux and spectral evolution from the beginning of the outburst, we find that the flux decreased by about an order of magnitude, with a subtle softening of the spectrum, both typical of the outburst decay of magnetars. By modeling the secular thermal evolution of Swift J1822.3-1606, we find that the observed timing properties of the source, as well as its quiescent X-ray luminosity, can be reproduced if it was born with a poloidal and crustal toroidal fields of Bp ~ 1.5 × 1014 G and B tor ~ 7 × 1014 G, respectively, and if its current age is ~550 kyr.

The Fossil Nuclear Outflow in the Central 30 pc of the Galactic Center

NASA Astrophysics Data System (ADS)

Hsieh, Pei-Ying; Ho, Paul T. P.; Hwang, Chorng-Yuan; Shimajiri, Yoshito; Matsushita, Satoki; Koch, Patrick M.; Iono, Daisuke

2016-11-01

We report a new 1 pc (30″) resolution CS(J=2-1) line map of the central 30 pc of the Galactic center (GC), made with the Nobeyama 45 m telescope. We revisit our previous study of an extraplanar feature called the polar arc (PA), which is a molecular cloud located above SgrA*, with a velocity gradient perpendicular to the galactic plane. We find that the PA can be traced back to the galactic disk. This provides clues to the launching point of the PA, roughly 6 × 106 years ago. Implications of the dynamical timescale of the PA might be related to the Galactic center lobe at parsec scale. Our results suggest that, in the central 30 pc of the GC, the feedback from past explosions could alter the orbital path of molecular gas down to the central tenth of a parsec. In the follow-up work of our new CS(J=2-1) map, we also find that, near systemic velocity, the molecular gas shows an extraplanar hourglass-shaped feature (HG-feature) with a size of ˜13 pc. The latitude-velocity diagrams show that the eastern edge of the HG-feature is associated with an expanding bubble B1, ˜7 pc away from SgrA*. The dynamical timescale of this bubble is ˜3 × 105 years. This bubble is interacting with the 50 km s-1 cloud. Part of the molecular gas from the 50 km s-1 cloud was swept away by the bubble to b=-0\\buildrel{\\circ}\\over{.} 2. The western edge of the HG-feature seems to be molecular gas entrained from the 20 km s-1 cloud toward the north of the galactic disk. Our results suggest a fossil explosion in the central 30 pc of the GC, a few 105 years ago.

Exploring Molecular Complexity in the Interstellar Medium with Alma

NASA Astrophysics Data System (ADS)

Belloche, Arnaud

2017-06-01

The search for complex organic molecules (COMs) in the interstellar medium (ISM) relies heavily on the progress made in the laboratory to record and characterize the rotational spectra of these molecules. Almost 200 different molecules have been identified in the ISM so far, in particular thanks to millimeter-wavelength observations of the star-forming molecular cloud core Sgr B2(N) in the Galactic Center region. The advent of the Atacama Large Millimeter/submillimeter Array (ALMA) has recently opened a new door to explore the molecular complexity of the ISM. Thanks to its high angular resolution, the spectral confusion of star-forming cores can be reduced, and its tremendous sensitivity allows astronomers to detect molecules of low abundance that could not be probed by previous generations of telescopes. I will present results of the EMoCA survey conducted toward Sgr B2(N) with ALMA. The main goal of this spectral line survey is to decipher the molecular content of Sgr B2(N) in order to test the predictions of astrochemical numerical simulations and gain insight into the chemical processes at work in the ISM. I will in particular report on the tentative detection of N-methylformamide, on the deuterium fractionation of COMs, and on the detection of a branched alkyl molecule in the ISM. The latter detection has unveiled a new domain in the structures available to the chemistry of star-forming regions and established a further connection to the COMs found in meteorites. A. Belloche, A. A. Meshcheryakov, R. T. Garrod et al. 2017, A&A, in press, DOI: 10.1051/0004-6361/201629724 A. Belloche, H. S. P. Müller, R. T. Garrod, and K. M. Menten 2016, A&A, 587, A91 A. Belloche, R. T. Garrod, H. S. P. Müller, and K. M. Menten 2014, Science, 345, 1584 R. T. Garrod, A. Belloche, H. S. P. Müller, and K. M. Menten 2017, A&A, in press, DOI: 10.1051/0004-6361/201630254.

VISTA variables in the Sagittarius dwarf spheroidal galaxy: pulsation-versus dust-driven winds on the giant branches

NASA Astrophysics Data System (ADS)

McDonald, I.; Zijlstra, A. A.; Sloan, G. C.; Kerins, E.; Lagadec, E.; Minniti, D.

2014-04-01

Variability is examined in over 2.6 million stars covering 11 square degrees of the core of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) from Visible and Infrared Survey Telescope for Astronomy Z-band observations. Generally, pulsation on the Sgr dSph giant branches appears to be excited by the internal κ mechanism. Pulsation amplitudes appear identical between red and asymptotic (red giant branch/asymptotic giant branch) giant stars, and between unreddened carbon and oxygen-rich stars at the same luminosity. The lack of correlation between infrared excess and variability among oxygen-rich stars indicates that pulsations do not contribute significantly to wind driving in oxygen-rich stars in the Sgr dSph, though the low amplitudes of these stars mean this may not apply elsewhere. The dust-enshrouded carbon stars have the highest amplitudes of the stars we observe. Only in these stars does an external κ-mechanism-driven pulsation seem likely, caused by variations in their more opaque carbon-rich molecules or dust. This may allow pulsation driving of winds to be effective in carbon stars. Variability can be simplified to a power law (A ∝ L/T2), as in other systems. In total, we identify 3026 variable stars (with rms variability of δZ ≳ 0.015 mag), of which 176 are long-period variables associable with the upper giant branches of the Sgr dSph. We also identify 324 candidate RR Lyrae variables in the Sgr dSph and 340 in the outer Galactic bulge.

Dusty cradles in a turbulent nursery: the SGR A east H II region complex at the galactic center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lau, R. M.; Herter, T. L.; Adams, J. D.

2014-10-20

We present imaging at 19, 25, 31, and 37 μm of the compact H II region complex G-0.02-0.07 located 6 pc in projection from the center of the Galaxy obtained with SOFIA using FORCAST. G-0.02-0.07 contains three compact H II regions (A, B, and C) and one ultra-compact H II region (D). Our observations reveal the presence of two faint, infrared sources located 23'' and 35'' to the east of region C (FIRS 1 and 2) and detect dust emission in two of the three 'ridges' of ionized gas west of region A. The 19/37 color temperature and 37 μmmore » optical depth maps of regions A-C are used to characterize the dust energetics and morphology. Regions A and B exhibit average 19/37 color temperatures of ∼105 K, and regions C and D exhibit color temperatures of ∼115 K and ∼130 K, respectively. Using the DustEM code, we model the SEDs of regions A-D and FIRS 1, all of which require populations of very small, transiently heated grains and large, equilibrium-heated grains. We also require the presence of polycyclic aromatic hydrocarbons in regions A-C in order to fit the 3.6, 4.5, 5.8, and 8.0 μm fluxes observed by Spitzer/IRAC. The location of the heating source for region A is determined by triangulation from distances and temperatures derived from DustEM models fit to SEDs of three different points around the region, and it is found to be displaced to the northeast of the center of curvature near the color temperature peak. Based on total luminosity, expected 1.90 μm fluxes, and proximity to the mid-IR color temperature peaks, we identify heating source candidates for regions A, B, and C. However, for region D, the observed fluxes at 1.87 and 1.90 μm of the previously proposed ionizing star are a factor of ∼40 times too bright to be the heating source and hence is likely just a star lying along the line of sight toward region D.« less

La Freccia Rossa: an IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate

NASA Astrophysics Data System (ADS)

Ravi, Vikram; Vedantham, Harish; Phinney, E. Sterl

2018-07-01

The dynamics of the high-velocity compact molecular cloud CO-0.40-0.22 have been interpreted as evidence for a ˜105 M⊙ black hole within 60 pc of Sgr A*. Recently, Oka et al. have identified a compact millimetre-continuum source, CO-0.40-0.22*, with this candidate black hole. Here we present a collation of radio and infrared data at this location. Australia Telescope Compact Array constraints on the radio spectrum, and the detection of a mid-infrared counterpart, are in tension with an Sgr A*-like model for CO-0.40-0.22* despite the comparable bolometric to the Eddington luminosity ratios under the intermediate-mass black hole interpretation. A protostellar-disc scenario is, however, tenable. CO-0.40-0.22(*) is positionally coincident with an arrowhead-shaped infrared-dark cloud (which we call the Freccia Rossa). If the VLSR ≈ 70 km s-1 systemic velocity of CO-0.40-0.22 is common to the entire Freccia Rossa system, we hypothesize that it is the remnant of a high-velocity cloud that has plunged into the Milky Way from the Galactic halo.

Initial evaluation of an interactive test of sentence gist recognition.

PubMed

Tye-Murray, N; Witt, S; Castelloe, J

1996-12-01

The laser videodisc-based Sentence Gist Recognition (SGR) test consists of sets of topically related sentences that are cued by short film clips. Clients respond to test items by selecting picture illustrations and may interact with the talker by using repair strategies when they do not recognize a test item. The two experiments, involving 40 and 35 adult subjects, respectively, indicated that the SGR may better predict subjective measures of speechreading and listening performance than more traditional audiologic sentence and nonsense syllable tests. Data from cochlear implant users indicated that the SGR accounted for a greater percentage of the variance for selected items of the Communication Profile for the Hearing-Impaired and the Speechreading Questionnaire for Cochlear-Implant Users than two other audiologic tests. As in previous work, subjects were most apt to ask the talker to repeat an utterance that they did not recognize than to ask the talker to restructure it. It is suggested that the SGR may reflect the interactive nature of conversation and provide a simulated real-world listening and/or speechreading task. The principles underlaying this test are consistent with the development of other computer technologies and concepts, such as compact discinteractive and virtual reality.

Detection With Rhessi of High Frequency X-ray Oscillations in the Tail of the 2004 Hyperflare From SGR 1806-20

NASA Technical Reports Server (NTRS)

Watts, Anna L.; Strohmayer, Tod E.

2005-01-01

The recent discovery of high frequency oscillations in giant flares from SGR 1806-20 and SGR 1900+14 may be the first direct detection of vibrations in a neutron star crust. If this interpretation is correct it offers a novel means of testing the neutron star equation of state, crustal breaking strain, and magnetic field configuration. Using timing data from RHESSI, we have confirmed the detection of a 92.5 Hz Quasi-Periodic Oscillation (QPO) in the tail of the SGR 1806-20 giant flare. We also find another, stronger, QPO at higher energies, at 626.5 Hz. Both QPOs are visible only at particular (but different) rotational phases, implying an association with a specific area of the neutron star surface or magnetosphere. At lower frequencies we confirm the detection of an 18 Hz QPO, at the same rotational phase as the 92.5 Hz QPO, and report the additional presence of a broad 26 Hz QPO. We are however unable to make a robust confirmation of the presence of a 30 Hz QPO, despite higher count rates. We discuss our results in the light of neutron star vibration models.

A Subarcsecond ALMA Molecular Line Imaging Survey of the Circumbinary, Protoplanetary Disk Orbiting V4046 Sgr

NASA Astrophysics Data System (ADS)

Kastner, Joel H.; Qi, C.; Dickson-Vandervelde, Annie; Forveille, Thierry; Hily-Blant, Pierre; Oberg, Karin; Wilner, David; Andrews, Sean; Gorti, Uma; Sacco, Germano; Rapson, Valerie; Principe, David

2018-01-01

We present a suite of ALMA interferometric molecular line and continuum images of the gas-rich circumbinary disk orbiting the nearby, young, short-period, solar-mass binary system V4046 Sgr (D ~ 73 pc; age ~20 Myr). These Cycle 2 and 3 ALMA observations of V4046 Sgr were undertaken in the 1.1 to 1.4 mm wavelength range (ALMA Band 6) with antenna configurations involving maximum baselines of several hundred meters, yielding subarcsecond-resolution images in more than a dozen molecular species and isotopologues. Collectively, these ALMA images serve to elucidate, on linear size scales of ~30-40 AU, the chemical structure of an evolved, circumbinary, protoplanetary disk.This research is supported by NASA Exoplanets program grant NNX16AB43G to RIT.

Simultaneous Chandra/EHT/NuSTAR Monitoring of Sgr A* Flares

NASA Astrophysics Data System (ADS)

Garmire, Gordon

2017-09-01

EHT will observe SgrA* at 0.85 mm during the period 2017 April 5-14 UT. These will be the first mm VLBI observations with sufficient effective area and angular resolution to produce time-resolved images of the event horizon of a black hole, enabling tests of general relativity in the strong gravity regime and a search for structural variability, especially during flares. Chandra Flight Ops has identified windows on four dates when Chandra can observe SgrA* uninterrupted for 33 ks simultaneous with EHT. NuSTAR will coordinate to observe simultaneously in these windows. This Cycle 19 observation will cover one of the four windows. The other three will be covered by splitting 100 ks of Cycle 18 time currently in ObsIDs 19726 and 19727 into three observations (Proposal 18620742).

Watching a Black Hole Feed: Sgr A* in the X-ray and Infrared

NASA Astrophysics Data System (ADS)

Fazio, Giovanni

2017-09-01

Black hole accretion drives extreme astrophysical phenomena in the universe. Sgr A*, the nearest supermassive black hole, is highly variable, but sparse data and short observations preclude determination of its emission physics. Despite enormous advances in accretion models in recent years, even the radiation mechanisms of Sgr A* are still unknown. Because the needed information is encoded in the time-dependent relationship between X-ray and IR emission, we propose four new epochs of Chandra monitoring with Spitzer at 4.5 microns. This will double the exposure time for X-ray flares where the NIR state is known, moving us out of the realm of small-number statistics and enabling diagnostics of the true X-ray/IR relationship. This will be the final chance for Chandra+Spitzer observations.

Investigating the Relativistic Motion of the Stars Near the Supermassive Black Hole in the Galactic Center

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parsa, M.; Eckart, A.; Shahzamanian, B.

The S-star cluster in the Galactic center allows us to study the physics close to a supermassive black hole, including distinctive dynamical tests of general relativity. Our best estimates for the mass of and the distance to Sgr A* using the three stars with the shortest period (S2, S38, and S55/S0-102) and Newtonian models are M {sub BH} = (4.15 ± 0.13 ± 0.57) × 10{sup 6} M {sub ⊙} and R {sub 0} = 8.19 ± 0.11 ± 0.34 kpc. Additionally, we aim at a new and practical method to investigate the relativistic orbits of stars in the gravitationalmore » field near Sgr A*. We use a first-order post-Newtonian approximation to calculate the stellar orbits with a broad range of periapse distance r {sub p} . We present a method that employs the changes in orbital elements derived from elliptical fits to different sections of the orbit. These changes are correlated with the relativistic parameter defined as ϒ ≡ r {sub s} / r {sub p} (with r {sub s} being the Schwarzschild radius) and can be used to derive ϒ from observational data. For S2 we find a value of ϒ = 0.00088 ± 0.00080, which is consistent, within the uncertainty, with the expected value of ϒ = 0.00065 derived from M {sub BH} and the orbit of S2. We argue that the derived quantity is unlikely to be dominated by perturbing influences such as noise on the derived stellar positions, field rotation, and drifts in black hole mass.« less

General relativistic magnetohydrodynamical κ-jet models for Sagittarius A*

NASA Astrophysics Data System (ADS)

Davelaar, J.; Mościbrodzka, M.; Bronzwaer, T.; Falcke, H.

2018-04-01

Context. The observed spectral energy distribution of an accreting supermassive black hole typically forms a power-law spectrum in the near infrared (NIR) and optical wavelengths, that may be interpreted as a signature of accelerated electrons along the jet. However, the details of acceleration remain uncertain. Aim. In this paper, we study the radiative properties of jets produced in axisymmetric general relativistic magnetohydrodynamics (GRMHD) simulations of hot accretion flows onto underluminous supermassive black holes both numerically and semi-analytically, with the aim of investigating the differences between models with and without accelerated electrons inside the jet. Methods: We assume that electrons are accelerated in the jet regions of our GRMHD simulation. To model them, we modify the electrons' distribution function in the jet regions from a purely relativistic thermal distribution to a combination of a relativistic thermal distribution and the κ-distribution function (the κ-distribution function is itself a combination of a relativistic thermal and a non-thermal power-law distribution, and thus it describes accelerated electrons). Inside the disk, we assume a thermal distribution for the electrons. In order to resolve the particle acceleration regions in the GRMHD simulations, we use a coordinate grid that is optimized for modeling jets. We calculate jet spectra and synchrotron maps by using the ray tracing code RAPTOR, and compare the synthetic observations to observations of Sgr A*. Finally, we compare numerical models of jets to semi-analytical ones. Results: We find that in the κ-jet models, the radio-emitting region size, radio flux, and spectral index in NIR/optical bands increase for decreasing values of the κ parameter, which corresponds to a larger amount of accelerated electrons. This is in agreement with analytical predictions. In our models, the size of the emission region depends roughly linearly on the observed wavelength λ, independently of the assumed distribution function. The model with κ = 3.5, ηacc = 5-10% (the percentage of electrons that are accelerated), and observing angle i = 30° fits the observed Sgr A* emission in the flaring state from the radio to the NIR/optical regimes, while κ = 3.5, ηacc < 1%, and observing angle i = 30° fit the upper limits in quiescence. At this point, our models (including the purely thermal ones) cannot reproduce the observed source sizes accurately, which is probably due to the assumption of axisymmetry in our GRMHD simulations. The κ-jet models naturally recover the observed nearly-flat radio spectrum of Sgr A* without invoking the somewhat artificial isothermal jet model that was suggested earlier. Conclusions: From our model fits we conclude that between 5% and 10% of the electrons inside the jet of Sgr A* are accelerated into a κ distribution function when Sgr A* is flaring. In quiescence, we match the NIR upper limits when this percentage is <1%.

ISO ammonia line absorption reveals a layer of hot gas veiling Sgr B2

NASA Astrophysics Data System (ADS)

Ceccarelli, C.; Baluteau, J.-P.; Walmsley, M.; Swinyard, B. M.; Caux, E.; Sidher, S. D.; Cox, P.; Gry, C.; Kessler, M.; Prusti, T.

2002-02-01

We report the first results of the unbiased spectral high resolution survey obtained towards Sgr B2 with the Long Wavelength Spectrometer on board ISO. The survey detected more than one hundreds lines from several molecules. Ammonia is the molecule with the largest number (21) of detected lines in the survey. We detected NH3 transitions from levels with energies from 45 to 500 cm-1. The detected transitions are from both para and ortho ammonia and metastable and non-metastable levels. All the ammonia lines are in absortion against the FIR continuum of Sgr B2. With such a large number of detected lines in such a large range of energy levels, we could very efficiently constrain the main parameters of the absorbing gas layer. The gas is at (700 +/- 100) K and has a density lower than 104 cm-3. The total NH3 column density in the layer is (3+/- 1) x 1016 cm-2, equally shared between ortho and para ammonia. Given the derived relatively high gas temperature and ammonia column density, our observations support the hypothesis previously proposed of a layer of shocked gas between us and Sgr B2. We also discuss previous observations of far infrared line absorption from other molecules, like H2O and HF, in the light of this hot absorbing layer. If the absorption is done by the hot absorbing layer rather than by the warm envelope surrounding Sgr B2, as was previously supposed in order to interpret the mentioned observations, the derived H2O and HF abundances are one order of magitude larger than previously estimated. Yet, the present H2O and HF observations do not allow one to disentangle the absorption from the hot layer against the warm envelope. Our conclusions are hence that care should be applied when interpreting the absorption observations in Sgr B2, as the hot layer clearly seen in the ammonia transitions may substantially contribute to the absorption. ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

A Critical Role of STAYGREEN/Mendel’s I Locus in Controlling Disease Symptom Development during Pseudomonas syringae pv tomato Infection of Arabidopsis1[W][OA

PubMed Central

Mecey, Christy; Hauck, Paula; Trapp, Marisa; Pumplin, Nathan; Plovanich, Anne; Yao, Jian; He, Sheng Yang

2011-01-01

Production of disease symptoms represents the final phase of infectious diseases and is a main cause of crop loss and/or marketability. However, little is known about the molecular basis of disease symptom development. In this study, a genetic screening was conducted to identify Arabidopsis (Arabidopsis thaliana) mutants that are impaired specifically in the development of disease symptoms (leaf chlorosis and/or necrosis) after infection with the bacterial pathogen Pseudomonas syringae pv tomato (Pst) DC3000. An ethyl methanesulfonate-induced Arabidopsis mutant (no chlorosis1 [noc1]) was identified. In wild-type plants, the abundance of chlorophylls decreased markedly after Pst DC3000 infection, whereas the total amount of chlorophylls remained relatively unchanged in the noc1 mutant. Interestingly, noc1 mutant plants also exhibited reduced disease symptoms in response to the fungal pathogen Alternaria brassicicola. Genetic and molecular analyses showed that the nuclear gene STAYGREEN (SGR; or Mendel’s I locus) is mutated (resulting in the aspartic acid to tyrosine substitution at amino acid position 88) in noc1 plants. Transforming wild-type SGR cDNA into the noc1 mutant rescued the chlorosis phenotype in response to Pst DC3000 infection. The SGR transcript was highly induced by Pst DC3000, A. brassicicola, or coronatine (COR), a bacterial phytotoxin that promotes chlorosis. The induction of SGR expression by COR is dependent on COI1, a principal component of the jasmonate receptor complex. These results suggest that pathogen/COR-induced expression of SGR is a critical step underlying the development of plant disease chlorosis. PMID:21994350

A spatial characterization of the Sagittarius dwarf galaxy tidal tails

DOE Office of Scientific and Technical Information (OSTI.GOV)

Newby, Matthew; Cole, Nathan; Newberg, Heidi Jo

2013-06-01

We measure the spatial density of F turnoff stars in the Sagittarius dwarf tidal stream, from Sloan Digital Sky Survey data, using statistical photometric parallax. We find a set of continuous, consistent parameters that describe the leading Sgr stream's position, direction, and width for 15 stripes in the north Galactic cap, and three stripes in the south Galactic cap. We produce a catalog of stars that has the density characteristics of the dominant leading Sgr tidal stream that can be compared with simulations. We find that the width of the leading (north) tidal tail is consistent with recent triaxial andmore » axisymmetric halo model simulations. The density along the stream is roughly consistent with common disruption models in the north, but possibly not in the south. We explore the possibility that one or more of the dominant Sgr streams has been misidentified, and that one or more of the ''bifurcated'' pieces is the real Sgr tidal tail, but we do not reach definite conclusions. If two dwarf progenitors are assumed, fits to the planes of the dominant and ''bifurcated'' tidal tails favor an association of the Sgr dwarf spheroidal galaxy with the dominant southern stream and the ''bifurcated'' stream in the north. In the north Galactic cap, the best fit Hernquist density profile for the smooth component of the stellar halo is oblate, with a flattening parameter q = 0.53, and a scale length of r {sub 0} = 6.73. The southern data for both the tidal debris and the smooth component of the stellar halo do not match the model fits to the north, although the stellar halo is still overwhelmingly oblate. Finally, we verify that we can reproduce the parameter fits on the asynchronous MilkyWay@home volunteer computing platform.« less

Optical Spectroscopy of the Classical Novae V339 Del (2013) and V5668 Sgr (2015 No. 2)

NASA Astrophysics Data System (ADS)

Wagner, R. Mark; Woodward, Charles E.; Starrfield, Sumner; Ilyin, Ilya; Strassmeier, Klaus G.; Page, Kim; Osborne, Julian P.; Beardmore, Andrew P.

2016-01-01

We report the results of optical spectroscopy of the gamma-ray classical novae V339 Del (2013) and V5668 Sgr (PNV J18365700-2855420/Nova Sgr 2015 No. 2) supplemented by UV and X-ray observations obtained with Swift. Our spectra were obtained with the Steward Observatory Bok 2.3 m telescope (+B&C), the MDM 2.4 m Hiltner telescope (+OSMOS), the 6.5 m MMT (+BlueChannel), and the 2 x 8.4 m Large Binocular Telescope (+MODS1 and PEPSI) between 2013 August and 2015 September. The PEPSI spectra cover all or part of the 384-907 nm spectral region at a resolution of up to 270,000 (1 km/s). This is the highest resolution available on any 8-10 m class telescope. V339 Del was discovered on 2015 August 14.58 by Itagaki at V about 6.8. This nova reached a peak magnitude of about 4.3 making it one of the brightest novae of this century. Because of its exceptional brightness it has been observed at a variety of wavelengths and by a host of observatories both on the ground and in space. V5668 Sgr was discovered on 2015 March 15.634 by Seach at a magnitude of 6.0. It subsequently reached a maximum brightness of about 4.0 in late March. High resolution PEPSI spectra obtained in early April show dramatic variations in the multi-component P Cygni-type line profiles. V5668 Sgr was observed to form dust in June thereafter fading to about 13th magnitude. Our recent observations show that it has now evolved into the nebular phase. SS acknowledges partial support from NSF and NASA grants to ASU. CEW acknowledges support from NASA.

The circumbinary dusty disk of upsilon Sgr revealed by mid-IR interferometric observations with the VLTI/MIDI

NASA Astrophysics Data System (ADS)

Bonneau, D.; Netolický, M.; Chesneau, O.; Harmanec, P.; Koubský, P.; Mourard, D.; Stee, P.

2008-11-01

The first mid-IR interferometric observations of a hydrogen-deficient binary star, υ Sgr, were carried out using the MIDI/VLTI instrument between April 2007 and May 2008. The dusty circumbinary envelope is resolved in the N band (8-13.5 μ m), and has a typical size of 20 x 14 mas. The calibrated fringe visibilities, the mid-IR spectrum and the SED were fitted using models computed with the radiative transfer code MC3D using several mixtures of carbon and silicate dust, in order to determine the geometry and chemical composition of the envelope. The best model we obtain is a geometrically thin and dense disk with an inner radius of R_{in} ≃ 6.0AU and a scale height h_{100} ≃ 3.5 AU. The inclination of the disk is i ≃ 50° and its position angle is PA ≃ 80°. The chemical composition of the dust is approximatelya ratio of 60% of carbon dust and 40% of silicate dust. We constrained for the first time the geometry and the chemistry of the circumbinary dusty envelope of υ Sgr. It is now clear that the components of υ Sgr are massive stars (> 10 M_⊙) and the results are compatible with evolutionary scenario proposed by Delgado & Thomas (1981) of a binary with massive components experiencing several phases of important mass transfer leading to the hydrogen-deficient primary star. However, complementary spectro-interferometric observations in the near infrared and the visible are mandatory to investigate the complex structure of the inner circumstellar environment and directly resolve the stellar components of the υ Sgr system.

XMM-Newton Proposal 03039101

NASA Astrophysics Data System (ADS)

Hernanz, Margarita

2004-10-01

Two recent galactic novae, V2487 Oph 1998 and V4633 Sgr 1998, have been detec- ted in both soft and hard X-rays with XMM. V2487 Oph showed an iron fluores- cent line only 2.7 yrs after its explosion, a clear signature of the very fast recovery of accretion, and V4633 Sgr displayed hard X-ray emission not clearly attributable to shocked ejecta or accretion. Longer observations are needed to do accurate timing and high resolution spectroscopy, essential to determine the main properties of the underlying cataclysmic variable in V2487 Oph (first nova seen in X-rays prior and after exploding) and to disentangle the origin of the hard X-rays from V4633 Sgr, through an analysis of the chemical compo- sition of the emitting thermal plasma, solar if accretion, non solar if ejecta.

Herschel observations of extraordinary sources: Analysis of the full Herschel/HIFI molecular line survey of sagittarius B2(N)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neill, Justin L.; Bergin, Edwin A.; Crockett, Nathan R.

2014-07-01

A sensitive broadband molecular line survey of the Sagittarius B2(N) star-forming region has been obtained with the Heterodyne Instrument for the Far-Infrared (HIFI) instrument on the Herschel Space Observatory, offering the first high spectral resolution look at this well-studied source in a wavelength region largely inaccessible from the ground (625-157 μm). From the roughly 8000 spectral features in the survey, a total of 72 isotopologues arising from 44 different molecules have been identified, ranging from light hydrides to complex organics, and arising from a variety of environments from cold and diffuse to hot and dense gas. We present a localmore » thermodynamic equilibrium (LTE) model to the spectral signatures of each molecule, constraining the source sizes for hot core species with complementary Submillimeter Array interferometric observations and assuming that molecules with related functional group composition are cospatial. For each molecule, a single model is given to fit all of the emission and absorption features of that species across the entire 480-1910 GHz spectral range, accounting for multiple temperature and velocity components when needed to describe the spectrum. As with other HIFI surveys toward massive star-forming regions, methanol is found to contribute more integrated line intensity to the spectrum than any other species. We discuss the molecular abundances derived for the hot core where the LTE approximation is generally found to describe the spectrum well, in comparison to abundances derived for the same molecules in the Orion KL region from a similar HIFI survey. Notably, we find significantly higher abundances of amine- and amide-bearing molecules (CH{sub 3}NH{sub 2}, CH{sub 2}NH, and NH{sub 2}CHO) toward Sgr B2(N) than Orion KL and lower abundances of some complex oxygen-bearing molecules (CH{sub 3}OCHO in particular). In addition to information on the chemical composition of the hot core, the strong far-infrared dust continuum allows a number of molecules to be detected in absorption in the Sgr B2(N) envelope for the first time at high spectral resolution, and we discuss the possible physical origin of the kinematic components observed in absorption. Additionally, from the detection of new HOCO{sup +} transitions in absorption compared to published HCO{sup +} isotopic observations, we discuss constraints on the gas-phase CO{sub 2} abundance and compare this to observations of the ice composition in the Galactic center region, and to CO{sub 2} abundance estimates toward other high-mass star-forming regions. The reduced HIFI spectral scan and LTE model are made available to the public as a resource for future investigations of star-forming regions in the submillimeter and far-infrared.« less

Narrow polarized components in the OH 1612-MHz maser emission from supergiant OH-IR sources

NASA Technical Reports Server (NTRS)

Cohen, R. J.; Downs, G.; Emerson, R.; Grimm, M.; Gulkis, S.; Stevens, G.

1987-01-01

High-resolution (300 Hz) OH 1612-MHz spectra of the supergiant OH-IR sources VY CMa, VX Sgr, IRC 10420, and NML Cyg are presented. Linewidths as small as 550 Hz (0.1 km/s) are found for narrow components in the spectra. The present results are consistent with current models for maser line-narrowing and for the physical properties in the OH maser regions. A significant degree of circular polarization is noted in many of the narrow components. The circular polarization suggests the presence of magnetic fields of about 1 mG in the circumstellar envelopes which would be strong enough to influence the outflow from the stars, and which may explain asymmetries found in the circumstellar envelopes.

Progress Report Abstracts. Oceanic Biology Program.

DTIC Science & Technology

1982-12-01

predominantly of myctophids and larval fishes of the genus Sebastolobus (having swimbladders). Our sampling efforts were concentrated on the 400m DSL...in collection of 7 individual animals of the genus , Nanomi sp. These animals were gently captured with the SGR and their oxygen consumption and...fishes of the genus , Sebastolobus altivelis, demersal fish as adults (Moser, 1974), were captured similarly at 600m with the SGR and their in situ

High-resolution VLBA Observations of Three 7 mm SiO Masers toward VX Sgr at Five Epochs

NASA Astrophysics Data System (ADS)

Su, J. B.; Shen, Z.-Q.; Chen, X.; Yi, Jiyune; Jiang, D. R.; Yun, Y. J.

2012-07-01

VX Sgr is a red supergiant at an adopted distance of 1.6 kpc with intense 43 GHz SiO maser emission. In this paper, we present the high-resolution very long baseline interferometry (VLBI) observations of SiO masers toward VX Sgr at five epochs. We used the Very Long Baseline Array to map the J = 1→0 (v = 1, 2) 28SiO masers and confirmed a ring-like structure. In the first two epochs, the v = 1 masers form a ring, but v = 2 maser spots residing only in the southern and northern regions do not form a complete ring. In the third epoch, the two masers are distributed in a ring structure and the v = 2 masers are a bit closer to the central star. In the last two epochs, many new maser spots appear and overlap each other. These overlapping maser spots can be related to the shock waves and reflect the collisional pumping. We compare the observations with the pumping models and speculate that the real pumping mechanism may be complex in VX Sgr and vary with time. The J = 1→0 (v = 0) 29SiO line emission is also detected, but is too weak to produce any VLBI map.

delta 15N and non-carbonate delta 13C values for two petroleum source rock reference materials and a marine sediment reference material

USGS Publications Warehouse

Dennen, Kristin O.; Johnson, Craig A.; Otter, Marshall L.; Silva, Steven R.; Wandless, Gregory A.

2006-01-01

Samples of United States Geological Survey (USGS) Certified Reference Materials USGS Devonian Ohio Shale (SDO-1), and USGS Eocene Green River Shale (SGR-1), and National Research Council Canada (NRCC) Certified Marine Sediment Reference Material (PACS-2), were sent for analysis to four separate analytical laboratories as blind controls for organic rich sedimentary rock samples being analyzed from the Red Dog mine area in Alaska. The samples were analyzed for stable isotopes of carbon (delta13Cncc) and nitrogen (delta15N), percent non-carbonate carbon (Wt % Cncc) and percent nitrogen (Wt % N). SDO-1, collected from the Huron Member of the Ohio Shale, near Morehead, Kentucky, and SGR-1, collected from the Mahogany zone of the Green River Formation are petroleum source rocks used as reference materials for chemical analyses of sedimentary rocks. PACS-2 is modern marine sediment collected from the Esquimalt, British Columbia harbor. The results presented in this study are, with the exceptions noted below, the first published for these reference materials. There are published information values for the elemental concentrations of 'organic' carbon (Wt % Corg measured range is 8.98 - 10.4) and nitrogen (Wt % Ntot 0.347 with SD 0.043) only for SDO-1. The suggested values presented here should be considered 'information values' as defined by the NRCC Institute for National Measurement Reference Materials and should be useful for the analysis of 13C, 15N, C and N in organic material in sedimentary rocks.

A new study of the interacting binary star V356 Sgr

NASA Technical Reports Server (NTRS)

Polidan, R. S.

1988-01-01

Results on V356 Sgr from IUE and Voyager ultraviolet (500 to 3200 A) observations obtained in 1986 and 1987, primarily during 2 total eclipses are presented. The eclipse of Aug. 15, 1986 was fully covered with IUE low dispersion images and 9 hr of Voyager UVS data. The eclipse of Mar. 25, 1987 was covered with IUE low dispersion images and 1 high dispersion SWP image. During both eclipses the total strength of the emission lines is found to be invariant. An uneclipsed UV continuum is detected at wavelengths shorter than 1500 A. The high dispersion SWP spectrum reveals that the emission lines are extremely broad, almost symmetrical emissions with weak, slightly blue shifted absorption components. No evidence of carbon, C I, C II, C III, or C IV, is seen in the emission or absorption spectrum of V356 Sgr in eclipse. Models for this binary system are presented.

Measuring the masses of intermediate polars with NuSTAR: V709 Cas, NY Lup, and V1223 Sgr

NASA Astrophysics Data System (ADS)

Shaw, A. W.; Heinke, C. O.; Mukai, K.; Sivakoff, G. R.; Tomsick, J. A.; Rana, V.

2018-05-01

The X-ray spectra of intermediate polars can be modelled to give a direct measurement of white dwarf mass. Here, we fit accretion column models to NuSTAR spectra of three intermediate polars; V709 Cas, NY Lup, and V1223 Sgr in order to determine their masses. From fits to 3-78 keV spectra, we find masses of M_WD=0.88^{+0.05}_{-0.04} M_{⊙}, 1.16^{+0.04}_{-0.02} M_{⊙}, and 0.75 ± 0.02 M⊙ for V709 Cas, NY Lup, and V1223 Sgr, respectively. Our measurements are generally in agreement with those determined by previous surveys of intermediate polars, but with typically a factor ˜2 smaller uncertainties. This work paves the way for an approved NuSTAR Legacy Survey of white dwarf masses in intermediate polars.

Testing General Relativity with the Shadow Size of Sgr A(*).

PubMed

Johannsen, Tim; Broderick, Avery E; Plewa, Philipp M; Chatzopoulos, Sotiris; Doeleman, Sheperd S; Eisenhauer, Frank; Fish, Vincent L; Genzel, Reinhard; Gerhard, Ortwin; Johnson, Michael D

2016-01-22

In general relativity, the angular radius of the shadow of a black hole is primarily determined by its mass-to-distance ratio and depends only weakly on its spin and inclination. If general relativity is violated, however, the shadow size may also depend strongly on parametric deviations from the Kerr metric. Based on a reconstructed image of Sagittarius A^{*} (Sgr A^{*}) from a simulated one-day observing run of a seven-station Event Horizon Telescope (EHT) array, we employ a Markov chain Monte Carlo algorithm to demonstrate that such an observation can measure the angular radius of the shadow of Sgr A^{*} with an uncertainty of ∼1.5  μas (6%). We show that existing mass and distance measurements can be improved significantly when combined with upcoming EHT measurements of the shadow size and that tight constraints on potential deviations from the Kerr metric can be obtained.

Burst and Persistent Emission Properties during the Recent Active Episode of the Anomalous X-Ray Pulsar 1E 1841-045

NASA Technical Reports Server (NTRS)

Lin, Lin; Kouveliotou, Chryssa; Gogus, Ersin; van der Horst, Alexander J.; Watts, Anna L.; Baring, Matthew G.; Kaneko, Yuki; Wijers, Ralph A. M. J.; Woods, Peter M.; Barthelmy, Scott;

The Marine Corps Physical Fitness Test: The Need to Replace it with a Combat Fitness Test

DTIC Science & Technology

2008-02-19

unforeseen emergencies.”1 Crossfit , a website-based workout program, has popularized the en vogue, yet relatively old concept of “functional fitness...Sports; 1996. <http://www.cdc.gov/nccdphp/sgr/sgr.htm> 2 Greg Glassman, “What is Fitness?” Crossfit Journal, October 2002, 1-2. 3 human...short, intense workouts aimed at increasing power, speed, and strength. Additionally, Crossfit explains the crossover between the three pathways

HIGH-RESOLUTION VLBA OBSERVATIONS OF THREE 7 mm SiO MASERS TOWARD VX Sgr AT FIVE EPOCHS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, J. B.; Shen, Z.-Q.; Chen, X.

2012-07-20

VX Sgr is a red supergiant at an adopted distance of 1.6 kpc with intense 43 GHz SiO maser emission. In this paper, we present the high-resolution very long baseline interferometry (VLBI) observations of SiO masers toward VX Sgr at five epochs. We used the Very Long Baseline Array to map the J = 1{yields}0 (v = 1, 2) {sup 28}SiO masers and confirmed a ring-like structure. In the first two epochs, the v = 1 masers form a ring, but v = 2 maser spots residing only in the southern and northern regions do not form a complete ring.more » In the third epoch, the two masers are distributed in a ring structure and the v = 2 masers are a bit closer to the central star. In the last two epochs, many new maser spots appear and overlap each other. These overlapping maser spots can be related to the shock waves and reflect the collisional pumping. We compare the observations with the pumping models and speculate that the real pumping mechanism may be complex in VX Sgr and vary with time. The J = 1{yields}0 (v = 0) {sup 29}SiO line emission is also detected, but is too weak to produce any VLBI map.« less

Consequences of intrauterine growth restriction on ventilatory and thermoregulatory responses to asphyxia and hypercapnia in the newborn guinea-pig.

PubMed

Tolcos, Mary; Rees, Sandra; McGregor, Hugh; Walker, David

2002-01-01

The purpose of this study was to determine the effects of prenatal growth restriction on the ventilatory and thermoregulatory responses to asphyxia and hypercapnia in the newborn guinea-pig. Spontaneously growth-restricted (SGR) animals born to unoperated dams, and growth-retarded (GR) neonates born to dams in which a uterine artery had been ligated at mid gestation, were studied and compared with control neonates. Ventilatory responses to progressive asphyxia and steady-state hypercapnia were tested at 3-6 days of age using a barometric plethysmograph. The animals were then killed and the brains prepared for histological and immunohistochemical analysis. During progressive asphyxia, SGR neonates (n = 5) had a significantly increased minute ventilation compared with both control (n = 6) and GR (n = 5) neonates. Rectal temperature fell significantly in GR and SGR neonates after progressive asphyxia, but was unchanged in control neonates. The ventilatory responses to steady-state hypercapnia were not different in the GR, SGR and control neonates. The immunoreactive expression of glial fibrillary acidic protein, tyrosine hydroxylase, substance P and met-enkephalin in the medulla was also not different between the three groups. It was concluded that prenatal growth restriction is associated with alterations in the respiratory and thermoregulatory responses to asphyxia and hypercapnia, with greater effects observed when in utero growth restriction arises spontaneously, compared with that produced experimentally over approximately the last half of gestation.

Orogen-scale along-strike continuity in quartz recrystallization microstructures adjacent to the Main Central Thrust: implications for deformation temperatures, strain rates and flow stresses

NASA Astrophysics Data System (ADS)

Law, Richard

2015-04-01

Traced for ~ 1500 km along the foreland edge of the Himalaya from NW India to Bhutan published reports indicate a remarkable along-strike continuity of quartz recrystallization microstructures in the footwall and hanging wall to the Main Central Thrust (MCT). Recrystallization in Lesser Himalayan Series (LHS) rocks in the footwall to the MCT is dominated by grain boundary bulging (BLG) microstructures, while recrystallization in Greater Himalayan Series (GHS) rocks in the hanging wall is dominated by grain boundary migration microstructures that traced structurally upwards transition in to the anatectic core of the GHS. In foreland-positioned high-strain rocks adjacent to the MCT recrystallization is dominated by subgrain rotation (SGR) with transitional BLG-SGR and SGR-GBM microstructures being recorded at structural distances of up to a few hundred meters below and above the MCT, respectively. Correlation with available information on temperatures of metamorphism indicated by mineral phase equilibria and RSCM data suggests that recrystallization in the structural zones dominated by BLG, SGR and GBM occurred at temperatures of ~ 350-450, 450-550 and 550- > 650 °C, respectively. It should be kept in mind, however, that these temperatures are likely to be 'close-to-peak' temperatures of metamorphism, whereas penetrative shearing and recrystallization may have continued during cooling. The dominance of SGR along the more foreland-positioned exposures of the MCT intuitively suggests that shearing occurred under a relatively restricted range of deformation temperatures and strain rates. Plotting the 'close-to-peak' 450-500 °C temperatures of metamorphism indicated for SGR-dominated rocks located at up to a few hundred meters below/above the MCT on the quartz recrystallization map developed by Stipp et al. (2002) indicates 'ball-park' strain rates of ~ 10-13 to 10-10 sec-1. However, only strain rates slower than 10-12 sec-1 on the MCT are likely to be compatible with know convergence rates between the Indian and Asian plates. If shearing continued during retrograde cooling while remaining in the SGR field, then the recrystallization map suggests that a significant drop in deformation temperature (> ~75-100 °C) would result in a decrease in strain rate. In general, however, the presence of a single recrystallization microstructure traced over a large (regional scale) distance does not necessarily mean that deformation temperature (or strain rate) remains constant but could, for example, indicate that spatial variations in deformation temperature are compensated for by changes in strain rate, with grain-scale deformation remaining within a particular recrystallization regime. Constant stress conditions plot along a straight line in the 1/T versus log strain rate space used in the quartz recrystallization mechanism map. This suggests that the observed along-strike consistency of SGR-dominated recrystallization microstructures may indicate near to constant stress boundary conditions (albeit with varying temperatures and strain rates) prevailing along what are now the more foreland-positioned exposures of the MCT. Extrapolation of the Hirth et al. (2001) flow law suggests a flow stress of ~ 30-50 MPa based on the deformation temperatures and strain rates inferred for foreland-positioned exposures of the MCT, in agreement with flow stresses estimated from recrystallized quartz grain size data.

Identification and analysis of novel genes involved in gravitropism of Arabidopsis thaliana.

NASA Astrophysics Data System (ADS)

Morita, Miyo T.; Tasaka, Masao; Masatoshi Taniguchi, .

2012-07-01

Gravitropism is a continuous control with regard to the orientation and juxtaposition of the various parts of the plant body in response to gravity. In higher plants, the relative directional change of gravity is mainly suscepted in specialized cells called statocytes, followed by signal conversion from physical information into physiological information within the statocytes. We have studied the early process of shoot gravitropism, gravity sensing and signaling process, mainly by molecular genetic approach. In Arabidopsis shoot, statocytes are the endodermal cells. sgr1/scarcrow (scr) and sgr7/short-root (shr) mutants fail to form the endodermis and to respond to gravity in their inflorescence stems. Since both SGR1/SCR and SGR7/SHR are transcriptional factors, at least a subset of their downstream genes can be expected to be involved in gravitropism. In addition, eal1 (endodermal-amyloplast less 1), which exhibits no gravitropism in inflorescence stem but retains ability to form endodermis, is a hypomorphic allele of sgr7/shr. Take advantage of these mutants, we performed DNA microarray analysis and compared gene expression profiles between wild type and the mutants. We found that approx. 40 genes were commonly down-regulated in these mutants and termed them DGE (DOWN-REGULATED GENE IN EAL1) genes. DGE1 has sequence similarity to Oryza sativa LAZY1 that is involved in shoot gravitropism of rice. DGE2 has a short region homologous to DGE1. DTL (DGE TWO-LIKE}) that has 54% identity to DGE2 is found in Arabidopsis genome. All three genes are conserved in angiosperm but have no known functional domains or motifs. We analyzed T-DNA insertion for these genes in single or multiple combinations. In dge1 dge2 dtl triple mutant, gravitropic response of shoot, hypocotyl and root dramatically reduced. Now we are carrying out further physiological and molecular genetic analysis of the triple mutant.

Giant Molecular Clouds with High Abundance of Atomic Carbon and Cyano Radical in the Milky Way's Central Molecular Zone

NASA Astrophysics Data System (ADS)

Tanaka, Kunihiko; Oka, Tomoharu; Nagai, Makoto; Kamegai, Kazuhisa

2015-08-01

The central 400 pc region of the Milky Way Galaxy is the closest galactic central region to us, providing a unique opportunity to detailedly investigate gas dynamics, star formation activity, and chemistry under the extreme environment of galactic centers, where the presence of bar, intense UV/cosmic-ray fluxes, high degree of turbulence may significantly affect those processes. We report the results of molecular line surveys toward the Milky Way's central molecular zone (CMZ) performed with the ASTE 10m telescope, the Mopra 22m telescope, and the Nobeyama 45 m telescope. With the observations of the 500 GHz [CI] fine structure line of atomic carbon (C0), we have found a molecular cloud structure with remarkably bright [CI] emission in the Sgr A comlex in the innermost 20 pc region. The [CI] cloud is more extended than the GMCs in the region, and appears to connect the northern part of the 50 kms-1 (M-0.02-0.07) and the circumnuclear disk (CND), though no corresponding structures are visible in other molecular lines. The [C0]/[CO] abundance ratio is measured to be 0.5-2, which is 2-10 times those measured to the clouds at larger Galactic radii. This high ratio is close to the values measured toward centers of galaxies with starburst and AGN, suggesting that the chemical state of the cloud is similar to that in those active galaxies. We have also found a large scale gradient of the cyano radical (CN) abundance toward the Galactic center in the innermost 100 pc radius, showing near the Sgr A complex. We suggest that the cloud with high C0 and CN abundance is a feature formed as a result of inward transfer of diffuse molecular gas by the bar potential in the inner Galaxy, in which PDR-like chemical composition remains preserved, and that thus the [CI] cloud could be deeply related to formation of the GMCs and star formation in the CMZ. We also discuss other possible mechanisms to enhance C0 and CN abundances, including the enhanced cosmic-ray dissociation ratio.

A New Low Magnetic Field Magnetar: The 2011 Outburst of Swift J1822.3-1606

NASA Technical Reports Server (NTRS)

Rea, N.; Israel, G.L.; Esposito, P.; Pons, J. A.; Camero-Arramz, A.; Mignani, R. P.; Turolla, R.; Zane, S..; Burgay, M.; Possenti, A.;

Polarization properties of bow shock sources close to the Galactic centre

NASA Astrophysics Data System (ADS)

Zajaček, M.; Karas, V.; Hosseini, E.; Eckart, A.; Shahzamanian, B.; Valencia-S., M.; Peissker, F.; Busch, G.; Britzen, S.; Zensus, J. A.

2017-12-01

Several bow shock sources were detected and resolved in the innermost parsec from the supermassive black hole in the Galactic centre. They show several distinct characteristics, including an excess towards mid-infrared wavelengths and a significant linear polarization as well as a characteristic prolonged bow-shock shape. These features give hints about the presence of a non-spherical dusty envelope generated by the bow shock. The Dusty S-cluster Object (also denoted as G2) shows similar characteristics and it is a candidate for the closest bow shock with a detected proper motion in the vicinity of Sgr A*, with the pericentre distance of only approx. 2000 Schwarzschild radii. However, in the continuum emission it is a point-like source and hence we use Monte Carlo radiative transfer modeling to reveal its possible three-dimensional structure. Alongside the spectral energy distribution, the detection of polarized continuum emission in the near-infrared Ks-band (2.2 micrometers) puts additional constraints on the geometry of the source.

Fermi GBM: Results from the First Year +

NASA Technical Reports Server (NTRS)

Wilson-Hodge, Colleen A.

2009-01-01

Gamma-ray Burst Monitor (GBM) has performed well in the first year+. GBM triggers 353 Gamma-ray Bursts (GRBs), 168 SGR events, 18 TGFs, and 1 solar flare to date. Short GRBs appear contracted in time and shifted to higher energy than long GRBs. Pulsed persistent emission from SGR 1550-5418 detected. TGFs are shorter, have higher average photon energies, and much higher count rates than GRBs. GBM monitoring of accreting pulsars provides long-term spin-histories. GBM Earth occultation monitoring complements Swift.

Detection of a weak maser emission pedestal associated with the SiO maser. [in variable late stars

NASA Technical Reports Server (NTRS)

Snyder, L. E.; Dickinson, D. F.; Brown, L. W.; Buhl, D.

1978-01-01

Results are reported for high-spectral-resolution observations of the v = 1, J = 1-0 SiO maser sources at 43,122.027 MHz (6.95 mm wavelength) associated with the variable stars Omega Cet, NML Tau, VY CMa, R Leo, W Hya, VX Sgr, NML Cyg, and R Cas. A weak underlying maser emission pedestal is clearly observed in the spectra of all but NML Cyg and R Cas. The data indicate that the underlying pedestal of SiO emission appears to originate in a shell-like region around the star, has a thermal appearance even though it must be due to weak maser emission, and appears to be part of the spectral signature of SiO maser emission from late-type stars. It is found that the center velocities of the pedestals may be used to determine stellar radial velocities. Observations of large-scale time variations in the intensity of the Ori A SiO maser and the detection of weak maser pedestals associated with each of the two strong emission-feature groups in Orion are also discussed. It is suggested that the Orion molecular cloud might contain two late-type long-period variable stars that may be semiregular variables.

A giant gamma-ray flare from the magnetar SGR 1806-20.

PubMed

Palmer, D M; Barthelmy, S; Gehrels, N; Kippen, R M; Cayton, T; Kouveliotou, C; Eichler, D; Wijers, R A M J; Woods, P M; Granot, J; Lyubarsky, Y E; Ramirez-Ruiz, E; Barbier, L; Chester, M; Cummings, J; Fenimore, E E; Finger, M H; Gaensler, B M; Hullinger, D; Krimm, H; Markwardt, C B; Nousek, J A; Parsons, A; Patel, S; Sakamoto, T; Sato, G; Suzuki, M; Tueller, J

2005-04-28

Two classes of rotating neutron stars-soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B approximately 10(15) G). SGRs occasionally become 'active', producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst. Here we report that SGR 1806-20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 x 10(46) erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard gamma-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.

Beating the confusion limit: the necessity of high angular resolution for probing the physics of Sagittarius A* and its environment: opportunities for LINC-NIRVANA (LBT), GRAVITY (VLTI) and and METIS (E-ELT)

NASA Astrophysics Data System (ADS)

Eckart, A.; Sabha, N.; Witzel, G.; Straubmeier, C.; Shahzamanian, B.; Valencia-S., M.; García-Marín, Macarena; Horrobin, M.; Moser, L.; Zuther, J.; Fischer, S.; Rauch, C.; Rost, S.; Iserlohe, C.; Yazici, S.; Smajic, S.; Wiest, M.; Araujo-Hauck, C.; Wank, I.

2012-07-01

The super-massive 4 million solar mass black hole (SMBH) SgrA* shows variable emission from the millimeter to the X-ray domain. A detailed analysis of the infrared light curves allows us to address the accretion phenomenon in a statistical way. The analysis shows that the near-infrared flux density excursions are dominated by a single state power law, with the low states of SgrA* are limited by confusion through the unresolved stellar background. We show that for 8-10m class telescopes blending effects along the line of sight will result in artificial compact star-like objects of 0.5-1 mJy that last for about 3-4 years. We discuss how the imaging capabilities of GRAVITY at the VLTI, LINC-NIRVANA at the LBT and METIS at the E-ELT will contribute to the investigation of the low variability states of SgrA*.

Fermi bubbles: the explosive nuclear activity of the Galaxy

NASA Astrophysics Data System (ADS)

Bland-Hawthorn, Joss

2015-08-01

The Galaxy's supermassive black hole (Sgr A*) is a hundred times closer than any other massive singularity. It is surrounded by a highly unstable gas disk so why is the black hole so peaceful at the present time? This mystery has led to a flurry of models in order to explain why Sgr A* is radiating far below (1 part in 10^8) the Eddington accretion limit. But has this always been so? Evidence is gathering that Sgr A* has been far more active in the recent past, on timescales of thousands of years and longer. The bipolar wind discovered by MSX, the gamma-ray bubbles discovered by Fermi-LAT, the WMAP haze, the positronium flash confirmed by INTEGRAL, are suggestive of something truly spectacular in the recent past. We present exciting new evidence that the Galactic Centre was a full blown "active galaxy" just two million years ago. The echo of this incredible event can be seen today imprinted across the Galaxy.

Simple preparation and highly selective detection of silver ions using an electrochemical sensor based on sulfur-doped graphene and a 3,3',5,5'-tetramethylbenzidine composite modified electrode.

PubMed

Fu, Yang; Yang, Yajie; Tuersun, Tayierjiang; Yu, Yuan; Zhi, Jinfang

2018-04-30

A novel electrochemical sensor based on sulfur (S)-doped graphene (S-Gr) and a 3,3',5,5'-tetramethylbenzidine (TMB) composite (S-Gr-TMB) modified glassy carbon (GCE) electrode for highly selective quantitative detection of silver ions (Ag+) were fabricated. The S-Gr-TMB composite was first prepared via electrostatic interaction between TMB and S-Gr and then, the composite was coated on the surface of GCE. The resultant S-Gr-TMB/GCE electrode showed a significant voltammetric response to Ag+ at 0.3 V vs. Ag/AgCl due to the synergistic effect of S-Gr and TMB. The sensor showed good linearity from 50 μM to 400 μM with a detection limit of 2.15 μM towards the determination of Ag+. In addition, after the addition of Fe3+ and other metal ions, including Al3+, Ca2+, Cd2+, Co2+, Cu2+, K+, Mg2+, Na+, Ni2+, Pb2+ and Zn2+, in the same concentration, the current signal remained almost unchanged, revealing that the proposed electrochemical sensor exhibited a high selectivity for Ag+, which solves the nonselective problem of TMB as a spectral probe. This enhanced detection performance is attributed to two factors: (1) S-Gr has excellent electrical conductivity; (2) the coupling interactions between Ag-S are speculated to result in strengthened enrichment for Ag and good selective performance.

VizieR Online Data Catalog: XMM-Newton and Chandra monitoring of Sgr A* (Ponti+, 2015)

NASA Astrophysics Data System (ADS)

Ponti, G.; de, Marco B.; Morris, M. R.; Merloni, A.; Munoz-Darias, T.; Clavel, M.; Haggard, D.; Zhang, S.; Nandra, K.; Gillessen, S.; Mori, K.; Neilsen, J.; Rea, N.; Degenaar, N.; Terrier, R.; Goldwurm, A.

2018-01-01

As of 2014 November 11 the XMM-Newton archive contains 37 public observations that can be used for our analysis of Sgr A*. In addition, we consider four new observations aimed at monitoring the interaction between the G2 object and Sgr A*, performed in fall 2014 (see Table A4). A total of 41 XMM-Newton data sets are considered in this work. All the 46 Chandra observations accumulated between 1999 and 2011 and analysed here are obtained with the ACIS-I camera without any gratings on (see Table A1). From 2012 onwards, data from the ACIS-S camera were also employed. The 2012 Chandra "X-ray Visionary Project" (XVP) is composed of 38 High-Energy Transmission Grating (HETG) observations with the ACIS-S camera at the focus (Nowak et al. 2012ApJ...759...95N; Neilsen et al. 2013ApJ...774...42N; 2015ApJ...799..199N; Wang et al. 2013Sci...341..981W; see Table A2). The first two observations of the 2013 monitoring campaign were performed with the ACIS-I instrument, while the ACIS-S camera was employed in all the remaining observations, after the outburst of SGR J1745-2900 on 2013 April 25. Three observations between 2013 May and July were performed with the HETG on, while all the remaining ones do not employ any gratings (see Table A2). (4 data files).

Anti-proliferative and pro-apoptotic effect of Smilax glabra Roxb. extract on hepatoma cell lines.

PubMed

Sa, Fei; Gao, Jian-Li; Fung, Kwok-Pui; Zheng, Ying; Lee, Simon Ming-Yuen; Wang, Yi-Tao

2008-01-10

Smilax glabra Roxb. (SGR) is the root of a traditional Chinese herb, referred to as tu fu ling in Chinese medicine. It is an inexpensive traditional Chinese medicine commonly used for the treatment of liver diseases, and a few studies have indicated that SGR has anti-hepatocarcinogenic and anti-cancer growth activities. In the current study, raw SGR plant was extracted with Accelerate Solvent Extractor, and the molecular mechanism by which S. glabra Roxb. extract (SGRE) has an anti-proliferative effect on the human hepatoma cell lines, HepG2 and Hep3B, was determined. We showed that SGRE inhibited HepG2 and Hep3B cell growth by causing cell-cycle arrest at either S phase or S/G2 transition and induced apoptosis, as evidenced by a DNA fragmentation assay. SGRE-induced apoptosis by alternation of mitochondrial transmembrane depolarization, release of mitochondrial cytochrome c, activation of caspase-3, and cleavage of poly(ADP-ribose) polymerase. The SGRE-mediated mitochondria-caspase dependent apoptotic pathway also involved activation of p38, JNK, and ERK mitogen-activated protein kinase signaling. Isometric compounds of astilbin (flavonoids) and smilagenin (saponin) have been identified as the main chemical constituents in SGRE by HPLC-MS/MS. These results have identified, for the first time, the biological activity of SGRE in HepG2 and Hep3B cells and should lead to further development of SGR for liver disease therapy.

A remarkable oxygen-rich asymptotic giant branch variable in the Sagittarius Dwarf Irregular Galaxy

NASA Astrophysics Data System (ADS)

Whitelock, Patricia A.; Menzies, John W.; Feast, Michael W.; Marigo, Paola

2018-01-01

We report and discuss JHKS photometry for Sgr dIG, a very metal-deficient galaxy in the Local Group, obtained over 3.5 years with the Infrared Survey Facility in South Africa. Three large amplitude asymptotic giant branch variables are identified. One is an oxygen-rich star that has a pulsation period of 950 d, which was until recently undergoing hot bottom burning, with Mbol ∼ -6.7. It is surprising to find a variable of this sort in Sgr dIG, given their rarity in other dwarf irregulars. Despite its long period the star is relatively blue and is fainter, at all wavelengths shorter than 4.5 μm, than anticipated from period-luminosity relations that describe hot bottom burning stars. A comparison with models suggests it had a main-sequence mass Mi ∼ 5 M⊙ and that it is now near the end of its asymptotic giant branch evolution. The other two periodic variables are carbon stars with periods of 670 and 503 d (Mbol ∼ -5.7 and -5.3). They are very similar to other such stars found on the asymptotic giant branch of metal-deficient Local Group galaxies and a comparison with models suggests Mi ∼ 3 M⊙. We compare the number of asymptotic giant branch variables in Sgr dIG to those in NGC 6822 and IC 1613, and suggest that the differences may be due to the high specific star formation rate and low metallicity of Sgr dIG.

Post-Keplerian perturbations of the orbital time shift in binary pulsars: an analytical formulation with applications to the galactic center

NASA Astrophysics Data System (ADS)

Iorio, Lorenzo

2017-07-01

We develop a general approach to analytically calculate the perturbations Δ δ τ _ {p} of the orbital component of the change δ τ _ {p} of the times of arrival of the pulses emitted by a binary pulsar p induced by the post-Keplerian accelerations due to the mass quadrupole Q_2, and the post-Newtonian gravitoelectric (GE) and Lense-Thirring (LT) fields. We apply our results to the so-far still hypothetical scenario involving a pulsar orbiting the supermassive black hole in the galactic center at Sgr A^*. We also evaluate the gravitomagnetic and quadrupolar Shapiro-like propagation delays δ τ _ {prop}. By assuming the orbit of the existing main sequence star S2 and a time span as long as its orbital period P_b, we obtain | Δ δ τ _ {p}^ {GE}| ≲ 10^3 {s}, | Δ δ τ _ {p}^ {LT}| ≲ 0.6 {s},| Δ δ τ _ {p}^{Q_2}| ≲ 0.04 {s}. Faster ( P_b= 5 {years}) and more eccentric ( e=0.97) orbits would imply net shifts per revolution as large as | < Δ δ τ _ {p}^ {GE}\\rangle | ≲ 10 {Ms}, | < Δ δ τ _ {p}^ {LT}\\rangle | ≲ 400 {s},| < Δ δ τ _ {p}^{Q_2}\\rangle | ≲ 10^3 {s}, depending on the other orbital parameters and the initial epoch. For the propagation delays, we have | δ τ _ {prop}^ {LT}| ≲ 0.02 {s}, | δ τ _ {prop}^{Q_2}| ≲ 1 μs. The results for the mass quadrupole and the Lense-Thirring field depend, among other things, on the spatial orientation of the spin axis of the Black Hole. The expected precision in pulsar timing in Sgr A^* is of the order of 100 μs, or, perhaps, even 1-10 μs. Our method is, in principle, neither limited just to some particular orbital configuration nor to the dynamical effects considered in the present study.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Broderick, Avery E.; Johannsen, Tim; Loeb, Abraham

The advent of the Event Horizon Telescope (EHT), a millimeter-wave very long baseline interferometric array, has enabled spatially resolved studies of the subhorizon-scale structure for a handful of supermassive black holes. Among these, the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), presents the largest angular cross section. Thus far, these studies have focused on measurements of the black hole spin and the validation of low-luminosity accretion models. However, a critical input in the analysis of EHT data is the structure of the black hole spacetime, and thus these observations provide the novel opportunitymore » to test the applicability of the Kerr metric to astrophysical black holes. Here we present the first simulated images of a radiatively inefficient accretion flow (RIAF) around Sgr A* employing a quasi-Kerr metric that contains an independent quadrupole moment in addition to the mass and spin that fully characterize a black hole in general relativity. We show that these images can be significantly different from the images of an RIAF around a Kerr black hole with the same spin and demonstrate the feasibility of testing the no-hair theorem by constraining the quadrupolar deviation from the Kerr metric with existing EHT data. Equally important, we find that the disk inclination and spin orientation angles are robust to the inclusion of additional parameters, providing confidence in previous estimations assuming the Kerr metric based on EHT observations. However, at present, the limits on potential modifications of the Kerr metric remain weak.« less

Hydrodynamic Simulations of the Inner Accretion Flow of Sagittarius A* Fueled By Stellar Winds

NASA Astrophysics Data System (ADS)

Ressler, S. M.; Quataert, E.; Stone, J. M.

2018-05-01

We present Athena++ grid-based, hydrodynamic simulations of accretion onto Sagittarius A* via the stellar winds of the ˜30 Wolf-Rayet stars within the central parsec of the galactic center. These simulations span ˜ 4 orders of magnitude in radius, reaching all the way down to 300 gravitational radii of the black hole, ˜32 times further in than in previous work. We reproduce reasonably well the diffuse thermal X-ray emission observed by Chandra in the central parsec. The resulting accretion flow at small radii is a superposition of two components: 1) a moderately unbound, sub-Keplerian, thick, pressure-supported disc that is at most (but not all) times aligned with the clockwise stellar disc, and 2) a bound, low-angular momentum inflow that proceeds primarily along the southern pole of the disc. We interpret this structure as a natural consequence of a few of the innermost stellar winds dominating accretion, which produces a flow with a broad distribution of angular momentum. Including the star S2 in the simulation has a negligible effect on the flow structure. Extrapolating our results from simulations with different inner radii, we find an accretion rate of ˜ a few × 10-8M⊙/yr at the horizon scale, consistent with constraints based on modeling the observed emission of Sgr A*. The flow structure found here can be used as more realistic initial conditions for horizon scale simulations of Sgr A*.

SGR 1822-1606 (Swift 1822.3-1606): Spin-down rate and inferred dipole field strength

NASA Astrophysics Data System (ADS)

Gogus, Ersin; Strohmayer, Tod; Kouveliotou, Chryssa

2011-07-01

We have been monitoring the new source Swift 1822.3-1606 (Cummings et al. GCN 12159) with RXTE. We acquired a total exposure of 20.6 ks in 5 pointings, spanning a time baseline of 5 days. We clearly detect the 8.44 s pulsations reported earlier (Pagani et al. ATel #3489, Gogus et al ATel #3491, Rea et al Atel #3501). We employed an epoch folding technique to determine the spin ephemeris. Our preliminary analysis reveal the spin period, P = 8.4377158(9) s and the spin-down rate, Pdot = 2.2(5) x 10-11 s/s (Epoch: 55758.5 MJD).

Weak Maser Emission of Methyl Formate toward Sagittarius B2(N) in the Green Bank Telescope PRIMOS Survey

NASA Astrophysics Data System (ADS)

Faure, A.; Remijan, A. J.; Szalewicz, K.; Wiesenfeld, L.

2014-03-01

A non-LTE radiative transfer treatment of cis-methyl formate (HCOOCH3) rotational lines is presented for the first time using a set of theoretical collisional rate coefficients. These coefficients have been computed in the temperature range 5-30 K by combining coupled-channel scattering calculations with a high accuracy potential energy surface for HCOOCH3-He. The results are compared to observations toward the Sagittarius B2(N) molecular cloud using the publicly available PRIMOS survey from the Green Bank Telescope. A total of 49 low-lying transitions of methyl formate, with upper levels below 25 K, are identified. These lines are found to probe a presumably cold (~30 K), moderately dense (~104 cm-3), and extended region surrounding Sgr B2(N). The derived column density of ~4 × 1014 cm-2 is only a factor of ~10 larger than the column density of the trans conformer in the same source. Provided that the two conformers have the same spatial distribution, this result suggests that strongly non-equilibrium processes must be involved in their synthesis. Finally, our calculations show that all detected emission lines with a frequency below 30 GHz are (collisionally pumped) weak masers amplifying the continuum of Sgr B2(N). This result demonstrates the importance and generality of non-LTE effects in the rotational spectra of complex organic molecules at centimeter wavelengths.

Timing Analysis of V404 Cyg during Its Brightest Outburst with INTEGRAL/SPI

NASA Astrophysics Data System (ADS)

Rodi, J.; Jourdain, E.; Roques, J. P.

2017-10-01

The outburst of V404 Cyg during the summer of 2015 reached unparalleled intensities at X-ray and soft gamma-ray energies with fluxes > 50 Crab in the 20-50 keV energy band. To date, studies in the hard X-ray/soft gamma-ray energy domain have focused primarily on the energy spectra. In this work, a timing analysis has been performed with INTEGRAL/SPI data in the 20-300 keV energy range for INTEGRAL revolution 1557, which corresponds to the brightest flare of V404 Cyg (on 2015 June 26). The power spectra are fit with broken power-law and multi-Lorentzian models and compared with previously reported results of V404 Cyg flaring activity from 1989 and 2015. Also, we took advantage of the good signal-to-noise ratio obtained above 70 keV to quantify the timing/fast-variability properties of the source as a function of energy. We then point out similarities of V404 Cyg with the black hole transient V4641 Sgr. Like V4641 Sgr, we found that the power spectra of V404 Cyg during high flux periods did not possess the expected flat-top feature typically seen in a hard spectral state. Interpretations are proposed in the framework of the fluctuating-propagation model to explain the observed properties.

Detection of Spectral Evolution in the Bursts Emitted During the 2008-2009 Active Episode of SGR J1550 - 5418

NASA Technical Reports Server (NTRS)

von Kienlin, Andreas; Gruber, David; Kouveliotou, Chryssa; Granot, Jonathan; Baring, Matthew G.; Gogus, Ersin; Huppenkothen, Daniela; Kaneko, Yuki; Lin, Lin; Watts, Anna L.;

Long-Term Spectral and Timing Behavior of Black Hole Candidate XTE J1908+094

NASA Technical Reports Server (NTRS)

Gogus, E.; Finger, M. H.; Kouveliotou, C.; Woods, P. M.; Patel, S. K.; Rupen, M.; Swank, J. H.; Markwardt, C. B.; Van Der Klis, M.

2003-01-01

The X-ray transient XTE J1908+094 was serendipitously discovered during RXTE ToO observations of SGR 1900+14 in February 2002. Following the discovery, RXTE routinely monitored the region. At the onset, the source was found in a spectrally low/hard state lasting for approximately 40 days, followed by a quick transition to the highhoft state. At the highest X-ray intensity level (seen on 2002 April 6), the source flux (2-10 keV) reached approximately 105 mCrab, then decayed rapidly. Overall outburst characteristics resemble the transient behavior of galactic black hole candidates. Here, we present the long term light curves, and detailed spectral and timing investigations of XTE J1098+094 using the RXTE/PCA data. We also report the results of Chandra ACIS observations which were performed during the decay phase.

Swift J1822.3-1606: refined X-ray timing and spectral parameters

NASA Astrophysics Data System (ADS)

Rea, N.; Esposito, P.; Israel, G. L.; Tiengo, A.; Zan, S.

2011-07-01

Between 2011 July 15-19 Swift-XRT continued its monitoring of the new SGR discovered by Swift-BAT, namely Swift J1822.3-1606 (Cummings et al. Atel #3488). Using the first four available Swift-XRT observations we find a best period of 8.437716(5)s. No evidence for a period derivative has been observed in the first days of monitoring, yielding a Pdot limit of about a few 10-10 s/s, still consistent with the SGR nature of this new transient.

Analysis of amyloplast dynamics involved in gravity sensing using a novel centrifuge microscope

NASA Astrophysics Data System (ADS)

Toyota, Masatsugu; Tasaka, Masao; Morita, Miyo T.

Plants sense gravity and change their growth orientation, a phenomenon known as gravitropism. According to the starch-statolith hypothesis, sedimentation of high-density starch-filled plastids (amyloplasts) within endodermal cells appears to be involved in gravity sensing of Arabidop-sis shoots. Recent studies suggest, however, that amyloplasts are never static but continu-ously show dynamic and complicated movements due to interaction with vacuole/cytoskeleton. Therefore, it remains unclear what movement/state of amyloplasts is required for gravity sens-ing. To address this critical issue, we analyzed gravitropism and amyloplast dynamics under hypergravity condition where sedimentation by gravity is more dominant than other movements. Segments of Arabidopsis inflorescence stem showed a gravitropism in response to hypergrav-ity (10g) that had been applied perpendicularly to the growth axis for 30 s in a conventional centrifuge, suggesting that amyloplast dynamics during this short time period is involved in gravity sensing. Real-time imaging of amyloplasts during the 10g stimulation was performed using a novel centrifuge microscope (NSK Ltd, Japan): all optical devices including objective lens, light source (LED) and CCD camera are mounted on an AC motor, enabling bright-field imaging with a temporal resolution of 30 frames/sec during rotation. Almost all amyloplasts started to move toward 10g and some reached the one side of endodermal cell within 30 s. These results clearly support the starch-statolith hypothesis that redistribution of amyloplasts to gravity is important for gravity sensing. Furthermore, we analyzed the shoot gravitropic mutant, sgr2, that has non-sedimentable amyloplasts and shows little gravitropism at 1g. An obvious gravitropism was induced by 30g for 5 min where amyloplasts were moved to the hyper-gravity but not by 10g where amyloplasts were not moved. These results not only suggest that gravity sensing of Arabidopsis inflorescence stems is triggered by the amyloplast redistribution resulting from the directional movement to gravity, but also provide a new interpretation of sgr2 that sgr2 has a gravity-sensing mechanism, which is inactivated at 1g probably due to non-sedimentable amyloplasts.

The Quest for Carbon Sequestration in the Southeastern United States

NASA Astrophysics Data System (ADS)

Knapp, C. C.; Akintunde, O. M.; Knapp, J. H.; Brantley, D.; Lakshmi, V.

2016-12-01

Eighty percent of the world's energy relies on fossil fuel and under increasingly stricter national and international regulations on greenhouse gas emissions, storage of CO2 in geologic repositories is a feasible and vital solution for near- and mid-term reduction of carbon emissions in any climate change mitigation strategy. The U.S. Environmental Protection Agency estimates that about 40% of anthropogenic CO2 emissions in the U.S. are generated in the southeastern United States, mostly from point sources. The Earth Sciences and Resources Institute and the Department of Earth and Ocean Sciences at the University of South Carolina have received $11M in Department of Energy funding to evaluate the feasibility of CO2 storage in saline formations of the Eastern North American Margin (ENAM) including (1) the Jurassic/Triassic (J/TR) sandstones of the buried South Georgia Rift basin (SGR; 2009-2014), and (2) Cretaceous and Cenozoic formations along the Mid- and South Atlantic seaboard (2015-2018). ENAM is a complex and regionally extensive mature Mesozoic passive margin rift system encompassing: (1) a large volume and regional extent of related magmatism known as the Central Atlantic Magmatic Province (CAMP), (2) a complete stratigraphic column that records the post-rift evolution in several basins, (3) preserved lithospheric-scale pre-rift structures including Paleozoic sutures, and (4) a wide range of geological, geochemical, and geophysical studies both onshore and offshore. Our analyses have included integration of 2- and 3-D seismic surveys with core samples and geophysical well logs leading to a detailed stratigraphic, structural, petrophysical, and injection simulation model showing the heterogeneity and highly complex tectonic evolution of the target reservoirs. Our study shows that (1) the SGR basin manifests distinct porosity-permeability regimes; (2) CAMP is much more limited spatially than previously thought; (3) fractured igneous rocks hold promise for CO2 storage in the SGR basin; (4) the Tr section was buried 2.8 km deeper than present depth, (5) transfer fault zones represent major conduit for leakage; (6) the South Atlantic seaboard is a major frontier area for CO2 sequestration based on extensive 2-D seismic data with limited well control.

FUSE Observations of the Active Interacting Binary RY Persei

NASA Astrophysics Data System (ADS)

Peters, G. J.; Polidan, R. S.

2003-12-01

RY Per (HD 17034, B4 V + F7 II-III, P=6.86 d) is a massive interacting binary (6.25 M⊙ + 1.60 M⊙, Olson & Plavec 1997, AJ, 113, 425) that displays a variable weak accretion disk that emits in Hα (Barai, et al., preprint). FUSE observations of this system, carried through in 2002 October at phases 0.20, 0.57, and 0.97 and during its total eclipse on 2002 December 8 are presented. The totality data were binned into two phase intervals: 0.0056-0.9976 (after second contact) and 0.0052-0.0089 (just before third contact). Both eclipse observations reveal broad, prominent emission lines of N III (UV1, λ λ 990-992 Å), O VI (UV1, λ λ 1032,1038 Å), N II (UV1, λ λ 1084-1086 Å), Si III (UV5, λ λ 1108,1109,1113 Å), Si IV(UV3, λ λ 1122,1138 Å), and Fe III (UV1, λ λ 1122-32 Å). Emission from C III (UV4, λ 1176 Å) seen during totality in FUSE observations of the Algol binaries V356 Sgr and TT Hya is conspicuously absent. C III (UV1, λ 977 Å) is also absent. This observation combined with the strong presence of N II, III emission suggests that material processed through the CNO cycle in the mass loser is now being transferred to the B star. The FUSE data imply that the emitting plasma is hot ( ˜100,000-300,000 K) and located above/below the orbital plane. The source of this apparent bipolar flow (also seen in V356 Sgr and TT Hya) may be the splash region detected near phase 0.5 in IUE observations of the N V resonance line, but absorption features from this region were not seen in the non-eclipse FUSE observations. A model for the circumstellar material in this system will be presented and the FUSE observations will be compared with those of V356 Sgr and TT Hya. GJP is grateful for support from NASA Grant NAG5-12253.

The GNSS Reflectometry Response to the Ocean Surface

NASA Astrophysics Data System (ADS)

Chang, Paul; Jelenak, Zorana; Soisuvarn, Seubson; Said, Faozi

2016-04-01

Global Navigation Satellite System - Reflectometry (GNSS-R) exploits signals of opportunity from the Global Navigation Satellite System (GNSS). GNSS transmitters continuously transmit navigation signals at L-band toward the earth's surface. The scattered power reflected off the earth's surface can be sensed by specially designed GNSS-R receivers. The reflected signal can then be used to glean information about the surface of the earth, such as ocean surface roughness, snow depth, sea ice extent, and soil moisture. The use of GNSS-R for ocean wind retrievals was first demonstrated from aircraft. On July 8 2014, the TechDemoSat-1 satellite (TDS-1) was launched by Surrey Satellite Technology, Ltd as a technology risk reduction mission into sun-synchronous orbit. This paper investigates the GNSS-R measurements collected by the Space GNSS Receiver-Remote Sensing Instrument (SGR-ReSI) on board the TDS-1 satellite. The sensitivity of the SGR-ReSI measurements to the ocean surface winds and waves are characterized. The effects of sea surface temperature, wind direction, and rain are also investigated. The SGR-ReSI measurements exhibited sensitivity through the entire range of wind speeds sampled in this dataset, up to 35 m/s. A significant dependence on the larger waves was observed for winds < 6 m/s. Additionally, an interesting dependence on SST was observed where the slope of the SGR-ReSI measurements is positive for winds < 5 m/s and reverses for winds > 5 m/s. There appeared to be very little wind direction signal, and investigation of the rain impacts found no apparent sensitivity in the data. These results are shown through the analysis of global statistics and examination of a few case studies. This released SGR-ReSI dataset provided the first opportunity to comprehensively investigate the sensitivity of satellite-based GNSS-R measurements to various ocean surface parameters. The upcoming NASA's Cyclone Global Navigation Satellite System (CYGNSS) satellite constellation will utilize a similar receiver to SGI-ReSI and thus this data provides valuable pre-launch knowledge for the CYGNSS mission.

Gravitational lensing of a star by a rotating black hole

NASA Astrophysics Data System (ADS)

Dokuchaev, V. I.; Nazarova, N. O.

2017-11-01

The gravitational lensing of a finite star moving around a rotating Kerr black hole has been numerically simulated. Calculations for the direct image of the star and for the first and second light echoes have been performed for the star moving with an orbital period of 3.22 h around the supermassive black hole SgrA* at the center of the Galaxy. The time dependences for the observed position of the star on the celestial sphere, radiation flux from the star, frequency of detected radiation, and major and minor semiaxes of the lensed image of the star have been calculated and plotted. The detailed observation of such lensing requires a space interferometer such as the Russian Millimetron project.

Systematic evaluation of sequential geostatistical resampling within MCMC for posterior sampling of near-surface geophysical inverse problems

NASA Astrophysics Data System (ADS)

Ruggeri, Paolo; Irving, James; Holliger, Klaus

2015-08-01

We critically examine the performance of sequential geostatistical resampling (SGR) as a model proposal mechanism for Bayesian Markov-chain-Monte-Carlo (MCMC) solutions to near-surface geophysical inverse problems. Focusing on a series of simple yet realistic synthetic crosshole georadar tomographic examples characterized by different numbers of data, levels of data error and degrees of model parameter spatial correlation, we investigate the efficiency of three different resampling strategies with regard to their ability to generate statistically independent realizations from the Bayesian posterior distribution. Quite importantly, our results show that, no matter what resampling strategy is employed, many of the examined test cases require an unreasonably high number of forward model runs to produce independent posterior samples, meaning that the SGR approach as currently implemented will not be computationally feasible for a wide range of problems. Although use of a novel gradual-deformation-based proposal method can help to alleviate these issues, it does not offer a full solution. Further, we find that the nature of the SGR is found to strongly influence MCMC performance; however no clear rule exists as to what set of inversion parameters and/or overall proposal acceptance rate will allow for the most efficient implementation. We conclude that although the SGR methodology is highly attractive as it allows for the consideration of complex geostatistical priors as well as conditioning to hard and soft data, further developments are necessary in the context of novel or hybrid MCMC approaches for it to be considered generally suitable for near-surface geophysical inversions.

Circulation and physical processes within the San Gabriel River Estuary during summer 2005

USGS Publications Warehouse

Rosenberger, Kurt J.; Xu, Jingping; Stein, Eric D.; Noble, Marlene A.; Gartner, Anne L.

2007-01-01

The Southern California Coastal Water Research Project (SCCWRP) is developing a hydrodynamic model of the SGR estuary, which is part of the comprehensive water-quality model of the SGR estuary and watershed investigated by SCCWRP and other local agencies. The hydrodynamic model will help understanding of 1) the exchange processes between the estuary and coastal ocean; 2) the circulation patterns in the estuary; 3) upstream natural runoff and the cooling discharge from PGS. Like all models, the SGR hydrodynamic model is only useful after it is fully calibrated and validated. In May 2005, SCCWRP requested the assistance of the U.S. geological Survey (USGS) Coastal and Marine Geology team (CMG) in collecting data on the hydrodynamic conditions in the estuary during the summer dry season. The summer was chosen for field data collection as this was assumed to be the season with the greatest potential for chronic degraded water quality due to low river flow and high thermal stratification within the estuary (due to both higher average air temperature and PGS output). Water quality can be degraded in winter as well, when higher river discharge events bring large volumes of water from the Los Angeles basin into the estuary. The objectives of this project were to 1) collect hydrodynamic data along the SGR estuary; 2) study exchange processes within the estuary through analysis of the hydrodynamic data; and 3) provide field data for model calibration and validation. As the data only exist for the summer season, the results herein only apply to summer conditions.

The role of electron heating physics in images and variability of the Galactic Centre black hole Sagittarius A*

NASA Astrophysics Data System (ADS)

Chael, Andrew; Rowan, Michael; Narayan, Ramesh; Johnson, Michael; Sironi, Lorenzo

2018-05-01

The accretion flow around the Galactic Centre black hole Sagittarius A* (Sgr A*) is expected to have an electron temperature that is distinct from the ion temperature, due to weak Coulomb coupling in the low-density plasma. We present four two-temperature general relativistic radiative magnetohydrodynamic (GRRMHD) simulations of Sgr A* performed with the code KORAL. These simulations use different electron heating prescriptions, motivated by different models of the underlying plasma microphysics. We compare the Landau-damped turbulent cascade model used in previous work with a new prescription we introduce based on the results of particle-in-cell simulations of magnetic reconnection. With the turbulent heating model, electrons are preferentially heated in the polar outflow, whereas with the reconnection model electrons are heated by nearly the same fraction everywhere in the accretion flow. The spectra of the two models are similar around the submillimetre synchrotron peak, but the models heated by magnetic reconnection produce variability more consistent with the level observed from Sgr A*. All models produce 230 GHz images with distinct black hole shadows which are consistent with the image size measured by the Event Horizon Telescope, but only the turbulent heating produces an anisotropic `disc-jet' structure where the image is dominated by a polar outflow or jet at frequencies below the synchrotron peak. None of our models can reproduce the observed radio spectral slope, the large near-infrared and X-ray flares, or the near-infrared spectral index, all of which suggest non-thermal electrons are needed to fully explain the emission from Sgr A*.

A methodological survey identified eight proposed frameworks for the adaptation of health related guidelines.

PubMed

Darzi, Andrea; Abou-Jaoude, Elias A; Agarwal, Arnav; Lakis, Chantal; Wiercioch, Wojtek; Santesso, Nancy; Brax, Hneine; El-Jardali, Fadi; Schünemann, Holger J; Akl, Elie A

2017-06-01

Our objective was to identify and describe published frameworks for adaptation of clinical, public health, and health services guidelines. We included reports describing methods of adaptation of guidelines in sufficient detail to allow its reproducibility. We searched Medline and EMBASE databases. We also searched personal files, as well manuals and handbooks of organizations and professional societies that proposed methods of adaptation and adoption of guidelines. We followed standard systematic review methodology. Our search captured 12,021 citations, out of which we identified eight proposed methods of guidelines adaptation: ADAPTE, Adapted ADAPTE, Alberta Ambassador Program adaptation phase, GRADE-ADOLOPMENT, MAGIC, RAPADAPTE, Royal College of Nursing (RCN), and Systematic Guideline Review (SGR). The ADAPTE framework consists of a 24-step process to adapt guidelines to a local context taking into consideration the needs, priorities, legislation, policies, and resources. The Alexandria Center for Evidence-Based Clinical Practice Guidelines updated one of ADAPTE's tools, modified three tools, and added three new ones. In addition, they proposed optionally using three other tools. The Alberta Ambassador Program adaptation phase consists of 11 steps and focused on adapting good-quality guidelines for nonspecific low back pain into local context. GRADE-ADOLOPMENT is an eight-step process based on the GRADE Working Group's Evidence to Decision frameworks and applied in 22 guidelines in the context of national guideline development program. The MAGIC research program developed a five-step adaptation process, informed by ADAPTE and the GRADE approach in the context of adapting thrombosis guidelines. The RAPADAPTE framework consists of 12 steps based on ADAPTE and using synthesized evidence databases, retrospectively derived from the experience of producing a high-quality guideline for the treatment of breast cancer with limited resources in Costa Rica. The RCN outlines five key steps strategy for adaptation of guidelines to the local context. The SGR method consists of nine steps and takes into consideration both methodological gaps and context-specific normative issues in source guidelines. We identified through searching personal files two abandoned methods. We identified and described eight proposed frameworks for the adaptation of health-related guidelines. There is a need to evaluate these different frameworks to assess rigor, efficiency, and transparency of their proposed processes. Copyright © 2017 Elsevier Inc. All rights reserved.

The 2004 Hyperflare from SGR 1806-20: Further Evidence for Global Torsional Vibrations

NASA Technical Reports Server (NTRS)

Strohmayer, Tod E.; Watts, Anna L.

2006-01-01

We report an analysis of the archival Rossi X-ray Timing Explorer (RXTE) data from the December 2004 hyperflare from SGR 1806-20. In addition to the approx. equal to 90 Hz QPO first discovered by Israel et al., we report the detection of higher frequency oscillations at approx. equal to 150, 625, and 1,835 Hz. In addition to these frequencies there are indications of oscillations at approx. equal to 720, and 2,384 Hz, but with lower significances. The 150 Hz QPO has a width (FWHM) of about 17 Hz, an average amplitude (rms) of 6.5%, and is detected in average power spectra centered on the rotational phase of the strongest peak in the pulse profile. This is approximately half a rotational cycle from the phase at which the 90 Hz QPO is strongly detected. The 625 Hz oscillation was first detected in an average power spectrum from nine successive cycles beginning approximately 180 s after the initial hard spike. It has a width (FWHM) of approx. equal to 2 Hz and an average amplitude (rms) during this interval of 9%. We find a strong detection of the 625 Hz oscillation in a pair of successive rotation cycles beginning about 230 s after the start of the flare. In these cycles we also detect the 1,835 Hz QPO with the 625 Hz oscillation. The rotational phase in which the 625 Hz &PO is detected is similar to that for the 90 Hz QPO, indeed, this feature is seen in the same average power spectrum. During the time the 625 Hz QPO is detected we also confirm the simultaneous presence of 30 and 92 Hz QPOs, first reported by Israel et al. The centroid frequency of the 625 Hz QPO detected with RXTE is within 1 Hz of the M 626 Hz oscillation recently found in RHESSI data from this hyperflare by Watts & Strohmayer, however, the two detections were made in different phase and energy intervals. Nevertheless, we argue that the two results likely represent detections of the same oscillation frequency intrinsic to the source, but we comment on some of the difficulties in making direct comparisons between the RXTE and RHESSI measurements

The Role of the Outer Boundary Condition in Accretion Disk Models: Theory and Application

NASA Astrophysics Data System (ADS)

Yuan, Feng; Peng, Qiuhe; Lu, Ju-fu; Wang, Jianmin

2000-07-01

In a previous paper, we find that the outer boundary conditions (OBCs) of an optically thin accretion flow play an important role in determining the structure of the flow. Here in this paper, we further investigate the influence of OBCs on the dynamics and radiation of the accretion flow on a more detailed level. Bremsstrahlung and synchrotron radiations amplified by Comptonization are taken into account, and two-temperature plasma assumption is adopted. The three OBCs we adopted are the temperatures of the electrons and ions and the specific angular momentum of the accretion flow at a certain outer boundary. We investigate the individual role of each of the three OBCs on the dynamical structure and the emergent spectrum. We find that when the general parameters such as the mass accretion rate M and the viscous parameter α are fixed the peak flux at various bands such as radio, IR, and X-ray can differ by as much as several orders of magnitude under different OBCs in our example. Our results indicate that the OBC is both dynamically and radiatively important and therefore should be regarded as a new ``parameter'' in accretion disk models. As an illustrative example, we further apply the above results to the compact radio source Sgr A* located at the center of our Galaxy. The advection-dominated accretion flow (ADAF) model has turned out to be a great success in explaining its luminosity and spectrum. However, there exists a discrepancy between the mass accretion rate favored by ADAF models in the literature and that favored by the three-dimensional hydrodynamical simulation, with the former being 10-20 times smaller than the latter. By seriously considering the outer boundary condition of the accretion flow, we find that because of the low specific angular momentum of the accretion gas the accretion in Sgr A* should belong to a new accretion pattern, which is characterized by the possession of a very large sonic radius. This accretion pattern can significantly reduce the discrepancy between the mass accretion rates. We argue that the accretion occurred in some detached binary systems; the core of nearby elliptical galaxies and active galactic nuclei very possibly belongs to this accretion pattern.

Implications for the Origin of GRB 051103 from LIGO Observations

NASA Technical Reports Server (NTRS)

Bizouard, M. A.; Dietz, A.; Guidi, G. M.; Was, M.; Camp, J. B.; Cannizzo, J.; Stroeer, A. S.; Blackburn, L.

2012-01-01

We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30. we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.

Implications for the Origin of GRB 051103 from LIGO Observations

NASA Astrophysics Data System (ADS)

Abadie, J.; Abbott, B. P.; Abbott, T. D.; Abbott, R.; Abernathy, M.; Adams, C.; Adhikari, R.; Affeldt, C.; Ajith, P.; Allen, B.; Allen, G. S.; Amador Ceron, E.; Amariutei, D.; Amin, R. S.; Anderson, S. B.; Anderson, W. G.; Arai, K.; Arain, M. A.; Araya, M. C.; Aston, S. M.; Atkinson, D.; Aufmuth, P.; Aulbert, C.; Aylott, B. E.; Babak, S.; Baker, P.; Ballmer, S.; Barker, D.; Barnum, S.; Barr, B.; Barriga, P.; Barsotti, L.; Barton, M. A.; Bartos, I.; Bassiri, R.; Bastarrika, M.; Bauchrowitz, J.; Behnke, B.; Bell, A. S.; Belopolski, I.; Benacquista, M.; Bertolini, A.; Betzwieser, J.; Beveridge, N.; Beyersdorf, P. T.; Bilenko, I. A.; Billingsley, G.; Birch, J.; Biswas, R.; Black, E.; Blackburn, J. K.; Blackburn, L.; Blair, D.; Bland, B.; Bock, O.; Bodiya, T. P.; Bogan, C.; Bondarescu, R.; Bork, R.; Born, M.; Bose, S.; Boyle, M.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Breyer, J.; Bridges, D. O.; Brinkmann, M.; Britzger, M.; Brooks, A. F.; Brown, D. A.; Brummitt, A.; Buonanno, A.; Burguet-Castell, J.; Burmeister, O.; Byer, R. L.; Cadonati, L.; Camp, J. B.; Campsie, P.; Cannizzo, J.; Cannon, K.; Cao, J.; Capano, C.; Caride, S.; Caudill, S.; Cavaglia, M.; Cepeda, C.; Chalermsongsak, T.; Chalkley, E.; Charlton, P.; Chelkowski, S.; Chen, Y.; Christensen, N.; Chua, S. S. Y.; Chung, S.; Chung, C. T. Y.; Clara, F.; Clark, D.; Clark, J.; Clayton, J. H.; Conte, R.; Cook, D.; Corbitt, T. R. C.; Cornish, N.; Costa, C. A.; Coughlin, M.; Coward, D. M.; Coyne, D. C.; Creighton, J. D. E.; Creighton, T. D.; Cruise, A. M.; Cumming, A.; Cunningham, L.; Culter, R. M.; Dahl, K.; Danilishin, S. L.; Dannenberg, R.; Danzmann, K.; Das, K.; Daudert, B.; Daveloza, H.; Davies, G.; Daw, E. J.; Dayanga, T.; DeBra, D.; Degallaix, J.; Dent, T.; Dergachev, V.; DeRosa, R.; DeSalvo, R.; Dhurandhar, S.; Di Palma, I.; Díaz, M.; Donovan, F.; Dooley, K. L.; Dorsher, S.; Douglas, E. S. D.; Drever, R. W. P.; Driggers, J. C.; Dumas, J.-C.; Dwyer, S.; Eberle, T.; Edgar, M.; Edwards, M.; Effler, A.; Ehrens, P.; Engel, R.; Etzel, T.; Evans, M.; Evans, T.; Factourovich, M.; Fairhurst, S.; Fan, Y.; Farr, B. F.; Fazi, D.; Fehrmann, H.; Feldbaum, D.; Finn, L. S.; Flanigan, M.; Foley, S.; Forsi, E.; Fotopoulos, N.; Frede, M.; Frei, M.; Frei, Z.; Freise, A.; Frey, R.; Fricke, T. T.; Friedrich, D.; Fritschel, P.; Frolov, V. V.; Fulda, P.; Fyffe, M.; Garcia, J.; Garofoli, J. A.; Gholami, I.; Ghosh, S.; Giaime, J. A.; Giampanis, S.; Giardina, K. D.; Gill, C.; Goetz, E.; Goggin, L. M.; González, G.; Gorodetsky, M. L.; Goßler, S.; Graef, C.; Grant, A.; Gras, S.; Gray, C.; Greenhalgh, R. J. S.; Gretarsson, A. M.; Grosso, R.; Grote, H.; Grunewald, S.; Guido, C.; Gupta, R.; Gustafson, E. K.; Gustafson, R.; Hage, B.; Hallam, J. M.; Hammer, D.; Hammond, G.; Hanks, J.; Hanna, C.; Hanson, J.; Harms, J.; Harry, G. M.; Harry, I. W.; Harstad, E. D.; Hartman, M. T.; Haughian, K.; Hayama, K.; Heefner, J.; Hendry, M. A.; Heng, I. S.; Heptonstall, A. W.; Herrera, V.; Hewitson, M.; Hild, S.; Hoak, D.; Hodge, K. A.; Holt, K.; Hong, T.; Hooper, S.; Hosken, D. J.; Hough, J.; Howell, E. J.; Hughey, B.; Husa, S.; Huttner, S. H.; Ingram, D. R.; Inta, R.; Isogai, T.; Ivanov, A.; Johnson, W. W.; Jones, D. I.; Jones, G.; Jones, R.; Ju, L.; Kalmus, P.; Kalogera, V.; Kandhasamy, S.; Kanner, J. B.; Katsavounidis, E.; Katzman, W.; Kawabe, K.; Kawamura, S.; Kawazoe, F.; Kells, W.; Kelner, M.; Keppel, D. G.; Khalaidovski, A.; Khalili, F. Y.; Khazanov, E. A.; Kim, N.; Kim, H.; King, P. J.; Kinzel, D. L.; Kissel, J. S.; Klimenko, S.; Kondrashov, V.; Kopparapu, R.; Koranda, S.; Korth, W. Z.; Kozak, D.; Kringel, V.; Krishnamurthy, S.; Krishnan, B.; Kuehn, G.; Kumar, R.; Kwee, P.; Landry, M.; Lantz, B.; Lastzka, N.; Lazzarini, A.; Leaci, P.; Leong, J.; Leonor, I.; Li, J.; Lindquist, P. E.; Lockerbie, N. A.; Lodhia, D.; Lormand, M.; Lu, P.; Luan, J.; Lubinski, M.; Lück, H.; Lundgren, A. P.; Macdonald, E.; Machenschalk, B.; MacInnis, M.; Mageswaran, M.; Mailand, K.; Mandel, I.; Mandic, V.; Marandi, A.; Márka, S.; Márka, Z.; Maros, E.; Martin, I. W.; Martin, R. M.; Marx, J. N.; Mason, K.; Matichard, F.; Matone, L.; Matzner, R. A.; Mavalvala, N.; McCarthy, R.; McClelland, D. E.; McGuire, S. C.; McIntyre, G.; McIver, J.; McKechan, D. J. A.; Meadors, G.; Mehmet, M.; Meier, T.; Melatos, A.; Melissinos, A. C.; Mendell, G.; Mercer, R. A.; Meshkov, S.; Messenger, C.; Meyer, M. S.; Miao, H.; Miller, J.; Mino, Y.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Miyakawa, O.; Moe, B.; Moesta, P.; Mohanty, S. D.; Moraru, D.; Moreno, G.; Mossavi, K.; Mow-Lowry, C. M.; Mueller, G.; Mukherjee, S.; Mullavey, A.; Müller-Ebhardt, H.; Munch, J.; Murphy, D.; Murray, P. G.; Nash, T.; Nawrodt, R.; Nelson, J.; Newton, G.; Nishizawa, A.; Nolting, D.; Nuttall, L.; O'Reilly, B.; O'Shaughnessy, R.; Ochsner, E.; O'Dell, J.; Ogin, G. H.; Oldenburg, R. G.; Osthelder, C.; Ott, C. D.; Ottaway, D. J.; Ottens, R. S.; Overmier, H.; Owen, B. J.; Page, A.; Pan, Y.; Pankow, C.; Papa, M. A.; Patel, P.; Pedraza, M.; Pekowsky, L.; Penn, S.; Peralta, C.; Perreca, A.; Phelps, M.; Pickenpack, M.; Pinto, I. M.; Pitkin, M.; Pletsch, H. J.; Plissi, M. V.; Podkaminer, J.; Pöld, J.; Postiglione, F.; Predoi, V.; Price, L. R.; Prijatelj, M.; Principe, M.; Privitera, S.; Prix, R.; Prokhorov, L.; Puncken, O.; Quetschke, V.; Raab, F. J.; Radkins, H.; Raffai, P.; Rakhmanov, M.; Ramet, C. R.; Rankins, B.; Mohapatra, S. R. P.; Raymond, V.; Redwine, K.; Reed, C. M.; Reed, T.; Reid, S.; Reitze, D. H.; Riesen, R.; Riles, K.; Roberts, P.; Robertson, N. A.; Robinson, C.; Robinson, E. L.; Roddy, S.; Rollins, J.; Romano, J. D.; Romie, J. H.; Röver, C.; Rowan, S.; Rüdiger, A.; Ryan, K.; Sakata, S.; Sakosky, M.; Salemi, F.; Salit, M.; Sammut, L.; Sancho de la Jordana, L.; Sandberg, V.; Sannibale, V.; Santamaría, L.; Santiago-Prieto, I.; Santostasi, G.; Saraf, S.; Sathyaprakash, B. S.; Sato, S.; Saulson, P. R.; Savage, R.; Schilling, R.; Schlamminger, S.; Schnabel, R.; Schofield, R. M. S.; Schulz, B.; Schutz, B. F.; Schwinberg, P.; Scott, J.; Scott, S. M.; Searle, A. C.; Seifert, F.; Sellers, D.; Sengupta, A. S.; Sergeev, A.; Shaddock, D. A.; Shaltev, M.; Shapiro, B.; Shawhan, P.; Shihan Weerathunga, T.; Shoemaker, D. H.; Sibley, A.; Siemens, X.; Sigg, D.; Singer, A.; Singer, L.; Sintes, A. M.; Skelton, G.; Slagmolen, B. J. J.; Slutsky, J.; Smith, R.; Smith, J. R.; Smith, M. R.; Smith, N. D.; Somiya, K.; Sorazu, B.; Soto, J.; Speirits, F. C.; Stein, A. J.; Steinlechner, J.; Steinlechner, S.; Steplewski, S.; Stefszky, M.; Stochino, A.; Stone, R.; Strain, K. A.; Strigin, S.; Stroeer, A. S.; Stuver, A. L.; Summerscales, T. Z.; Sung, M.; Susmithan, S.; Sutton, P. J.; Szokoly, G. P.; Talukder, D.; Tanner, D. B.; Tarabrin, S. P.; Taylor, J. R.; Taylor, R.; Thomas, P.; Thorne, K. A.; Thorne, K. S.; Thrane, E.; Thüring, A.; Tokmakov, K. V.; Torres, C.; Torrie, C. I.; Traylor, G.; Trias, M.; Tseng, K.; Ugolini, D.; Urbanek, K.; Vahlbruch, H.; Vaishnav, B.; Vallisneri, M.; Van Den Broeck, C.; van der Sluys, M. V.; van Veggel, A. A.; Vass, S.; Vaulin, R.; Vecchio, A.; Veitch, J.; Veitch, P. J.; Veltkamp, C.; Villar, A. E.; Vorvick, C.; Vyachanin, S. P.; Waldman, S. J.; Wallace, L.; Wanner, A.; Ward, R. L.; Wei, P.; Weinert, M.; Weinstein, A. J.; Weiss, R.; Wen, L.; Wen, S.; Wessels, P.; West, M.; Westphal, T.; Wette, K.; Whelan, J. T.; Whitcomb, S. E.; White, D.; Whiting, B. F.; Wilkinson, C.; Willems, P. A.; Williams, H. R.; Williams, L.; Willke, B.; Winkelmann, L.; Winkler, W.; Wipf, C. C.; Wiseman, A. G.; Woan, G.; Wooley, R.; Worden, J.; Yablon, J.; Yakushin, I.; Yamamoto, K.; Yamamoto, H.; Yang, H.; Yeaton-Massey, D.; Yoshida, S.; Yu, P.; Zanolin, M.; Zhang, L.; Zhang, Z.; Zhao, C.; Zotov, N.; Zucker, M. E.; Zweizig, J.; LIGO Collaboration; Bizouard, M. A.; Dietz, A.; Guidi, G. M.; Was, M.

2012-08-01

We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at a distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed γ-ray emission with a jet semi-angle of 30°, we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with >99% confidence. If the event occurred in M81, then our findings support the hypothesis that GRB 051103 was due to an SGR giant flare, making it one of the most distant extragalactic magnetars observed to date.

Detection of interstellar ethylene oxide (c-C2H4O).

PubMed

Dickens, J E; Irvine, W M; Ohishi, M; Ikeda, M; Ishikawa, S; Nummelin, A; Hjalmarson, A

1997-11-10

We report the identification of 10 transitions that support the detection of the small cyclic molecule ethylene oxide (c-C2H4O) in Sgr B2N. Although one of these transitions is severely blended, so that an accurate intensity and line width could not be determined, and two other lines are only marginally detected, we have done Gaussian fits to the remaining seven lines and have performed a rotation diagram analysis. Our results indicate a rotation temperature T(rot) = 18 K and a molecular column density N(c-C2H4O) = 3.3 x 10(14) cm-2, corresponding to a fractional abundance relative to molecular hydrogen of order 6 x 10(-11). This is a factor of more than 200 higher than the abundance for this molecule suggested by the "new standard" chemistry model of Lee, Bettens, & Herbst. This result suggests that grain chemistry might play an effective role in the production of c-C2H4O. No transitions of this molecule were detected in either Sgr B2M or Sgr B2NW.

Pumping Mechanisms for SiO Masers around VX Sgr

NASA Astrophysics Data System (ADS)

Su, J. B.; Shen, Z.-Q.; Chen, X.; Yi, Jiyune; Jiang, D. R.; Yun, Y. J.

2011-06-01

VX Sgr, a semi-regular variable, is a red giant star with intense SiO maser emission at 43 GHz. The pumping mechanism of the circumstellar SiO masers has been controversial for decades since its discovery. In order to pursue this long-standing problem further, we have carried out simultaneous VLBA observations of two 7 mm SiO masers at five epochs in about two years. We present relatively aligned υ = 1 and υ = 2, J = 1-0 SiO maser maps and discuss the dominant pumping mechanism, which may be epoch dependent or a combination of both mechanisms.

IRTF observations of the occultation of 28 Sgr by Saturn

NASA Technical Reports Server (NTRS)

Harrington, Joseph; Cooke, Maren L.; Forrest, William J.; Pipher, Judith L.; Dunham, Edward W.; Elliot, J. L.

1993-01-01

NASA's Mauna Kea IR Telescope Facility obtained an IR-imaging time series for the July 3, 1989 occultation of 28 Sgr by Saturn and its rings; the stellar signal is present in these images throughout the ring occultation event. These data are noted to vary systematically with respect to the Voyager data over large radius scales, perhaps due to stellar signal diffraction through the rings. The stellar diameter, which is projected to be about 20 km, placed most bending- and density-wave trains below measurable resolution. Masses and mean optical depths are presented for individual ring sections.

ERRATUM: Is SGR 1900+14 a Magnetar?

NASA Astrophysics Data System (ADS)

Marsden, D.; Rothschild, R. E.; Lingenfelter, R. E.

1999-09-01

In the Letter ``Is SGR 1900+14 a Magnetar?'' by D. Marsden, R. E. Rothschild, and R. E. Lingenfelter (ApJ, 520, L107 [1999]), there is a typographical error in Figure 1 that does not affect any of the scientific results of the Letter. The tick marks on the y-axis in this figure are mislabeled, indicating a wrong period for the peak in the χ2 distribution. The values of the period and period derivative quoted throughout the text are the correct values and are unaffected by the typographical error. The corrected figure appears below.

The sagittarius tidal stream and the shape of the galactic stellar halo

NASA Astrophysics Data System (ADS)

Newby, Matthew T.

The stellar halo that surrounds our Galaxy contains clues to understanding galaxy formation, cosmology, stellar evolution, and the nature of dark matter. Gravitationally disrupted dwarf galaxies form tidal streams, which roughly trace orbits through the Galactic halo. The Sagittarius (Sgr) dwarf tidal debris is the most dominant of these streams, and its properties place important constraints on the distribution of mass (including dark matter) in the Galaxy. Stars not associated with substructures form the "smooth" component of the stellar halo, the origin of which is still under investigation. Characterizing halo substructures such as the Sgr stream and the smooth halo provides valuable information on the formation history and evolution of our galaxy, and places constraints on cosmological models. This thesis is primarily concerned with characterizing the 3-dimensional stellar densities of the Sgr tidal debris system and the smooth stellar halo, using data from the Sloan Digital Sky Survey (SDSS). F turnoff stars are used to infer distances, as they are relatively bright, numerous, and distributed about a single intrinsic brightness (magnitude). The inherent spread in brightnesses of these stars is overcome through the use of the recently-developed technique of statistical photometric parallax, in which the bulk properties of a stellar population are used to create a probability distribution for a given star's distance. This was used to build a spatial density model for the smooth stellar halo and tidal streams. The free parameters in this model are then fit to SDSS data with a maximum likelihood technique, and the parameters are optimized by advanced computational methods. Several computing platforms are used in this study, including the RPI SUR Bluegene and the Milkyway home volunteer computing project. Fits to the Sgr stream in 18 SDSS data stripes were performed, and a continuous density profile is found for the major Sgr stream. The stellar halo is found to be strongly oblate (flattening parameter q=0.53). A catalog of stars consistent with this density profile is produced as a template for matching future disruption models. The results of this analysis favor a description of the Sgr debris system that includes more than one dwarf galaxy progenitor, with the major streams above and below the Galactic disk being separate substructures. Preliminary results for the minor tidal stream characterizations are presented and discussed. Additionally, a more robust characterization of halo turnoff star brightnesses is performed, and it is found that increasing color errors with distance result in a previously unaccounted for incompleteness in star counts as the SDSS magnitude limit is approached. These corrections are currently in the process of being implemented on MilkyWay home.

ORIGINS OF SCATTER IN THE RELATIONSHIP BETWEEN HCN 1-0 AND DENSE GAS MASS IN THE GALACTIC CENTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mills, Elisabeth A. C.; Battersby, Cara, E-mail: elisabeth.mills@sjsu.edu

We investigate the correlation of HCN 1-0 with gas mass in the central 300 pc of the Galaxy. We find that on the ∼10 pc size scale of individual cloud cores, HCN 1-0 is well correlated with dense gas mass when plotted as a log–log relationship. There is ∼0.75 dex of scatter in this relationship from clouds like Sgr B2, which has an integrated HCN 1-0 intensity of a cloud less than half its mass, and others that have HCN 1-0 enhanced by a factor of 2–3 relative to clouds of comparable mass. We identify the two primary sources ofmore » scatter to be self-absorption and variations in HCN abundance. We also find that the extended HCN 1-0 emission is more intense per unit mass than in individual cloud cores. In fact the majority (80%) of HCN 1-0 emission comes from extended gas with column densities below 7 × 10{sup 22} cm{sup −2}, accounting for 68% of the total mass. We find variations in the brightness of HCN 1-0 would only yield a ∼10% error in the dense gas mass inferred from this line in the Galactic center. However, the observed order of magnitude HCN abundance variations, and the systematic nature of these variations, warn of potential biases in the use of HCN as dense gas mass tracer in more extreme environments such as an active galactic nucleus and shock-dominated regions. We also investigate other 3 mm tracers, finding that HNCO is better correlated with mass than HCN, and might be a better tracer of cloud mass in this environment.« less

FRB as products of accretion disc funnels

NASA Astrophysics Data System (ADS)

Katz, J. I.

2017-10-01

The repeating FRB 121102, the only fast radio burst (FRB) with an accurately determined position, is associated with a variable persistent radio source. I suggest that an FRB originates in the accretion disc funnels of black holes. Narrowly collimated radiation is emitted along the wandering instantaneous angular momentum axis of accreted matter. This emission is observed as a fast radio burst when it sweeps across the direction to the observer. In this model, in contrast to neutron star (pulsar, RRAT or SGR) models, repeating FRBs do not have underlying periodicity and are co-located with persistent radio sources resulting from their off-axis emission. The model is analogous, on smaller spatial, lower mass and accretion rate and shorter temporal scales, to an active galactic nucleus (AGN), with FRB corresponding to blazars in which the jets point towards us. The small inferred black hole masses imply that FRBs are not associated with galactic nuclei.

Non-LTE model atmospheres for supersoft X-ray sources

NASA Astrophysics Data System (ADS)

Rauch, T.; Werner, K.

2010-02-01

In the last decade, X-ray observations of hot stellar objects became available with unprecedented resolution and S/N ratio. For an adequate interpretation, fully metal-line blanketed Non-LTE model-atmospheres are necessary. The Tübingen Non-LTE Model Atmosphere Package (TMAP) can calculate such model atmospheres at a high level of sophistication. Although TMAP is not especially designed for the calculation of spectral energy distributions (SEDs) at extreme photospheric parameters, it can be employed for the spectral analysis of burst spectra of novae like V4743 Sgr or line identifications in observations of neutron stars with low magnetic fields in low-mass X-ray binaries (LMXBs) like EXO 0748-676.

Application of the new comprehensive X-ray spectral model to the two brightest intermediate polars EX Hydrae and V1223 Sagittarii

NASA Astrophysics Data System (ADS)

Hayashi, Takayuki; Ishida, Manabu

2014-07-01

We applied the new comprehensive X-ray spectral model for the post-shock accretion column (PSAC) of the intermediate polars (IPs) constructed by Hayashi and Ishida to the Suzaku data of the two brightest IPs EX Hydrae and V1223 Sagittarii. The white dwarf (WD) mass and the specific accretion rate of EX Hya are estimated to be M_WD= 0.63_{-0.14}^{+0.17} M⊙ and a=0.049_{-0.035}^{+0.66} g cm-2 s-1. Our WD mass of EX Hya is greater than that of previous X-ray estimations (˜0.4-0.5 M⊙), where higher specific accretion rate than ours is assumed, and marginally consistent with 0.790 ± 0.026 M⊙ measured by Beuermann and Reinsch using a binary motion. On the other hand, with the aid of the PSAC height of V1223 Sgr hV1223 < 0.07RWD, we estimated M_WD= 0.87_{-0.06}^{+0.10} M_{⊙} and a > 2.0 g cm-2 s-1 for V1223 Sgr. We evaluated the fractional accreting area of EX Hya and V1223 Sgr at 0.0033_{-0.0030}^{+0.0067} and <0.007, respectively. Calculation of the hydrodynamical equations with these best-fitting parameters show that the PSAC height of EX Hya is 0.33 RWD = 2.8 × 108 cm. The maximum temperature of the EX Hya and V1223 Sgr are calculated at 18.0 keV and 43.1 keV, respectively. In EX Hya, the temperature distribution is flatter and the density at the top of the PSAC is smaller than those of the previous PSAC models because of its low specific accretion rate.

Modelling accretion disc and stellar wind interactions: the case of Sgr A.

PubMed

Christie, I M; Petropoulou, M; Mimica, P; Giannios, D

2016-07-01

Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disc, the ram and thermal pressures of the disc terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind. With the employment of numerical hydrodynamic simulations, this model is both verified and extended to a region prone to Kelvin-Helmholtz instabilities. Because the characteristic wind and stellar velocities are in ∼10 8  cm s -1 range, the shocked wind may produce detectable X-rays via thermal bremsstrahlung emission. The application of this model to the pericentre passage of S2, the brightest member of the S-cluster, shows that the shocked wind produces roughly a month long X-ray flare with a peak luminosity of L ≈ 4 × 10 33  erg s -1 for a stellar mass-loss rate, disc number density, and thermal pressure strength of [Formula: see text], n d  = 10 5  cm -3 , and α = 0.1, respectively. This peak luminosity is comparable to the quiescent X-ray emission detected from Sgr A* and is within the detection capabilities of current X-ray observatories. Its detection could constrain the density and thickness of the disc at a distance of ∼3000 gravitational radii from the supermassive black hole.

First Spectroscopic Studies and Detection in SgrB2 of 13C-DOUBLY Substitued Ethyl Cyanide

NASA Astrophysics Data System (ADS)

Margulès, L.; Motiyenko, R. A.; Guillemin, J.-C.; Müller, Holger S. P.; Belloche, Arnaud

2015-06-01

Ethyl cyanide (CH_3CH_2CN) is one of the most abundant complex organic molecules in the interstellar medium firstly detected in OMC-1 and Sgr B2 in 1977. The vibrationally excited states are enough populated under ISM conditions and could be detected. Apart from the deuterated ones, all mono-substituted isotopologues of ethyl cyanide (13C and 15N have been detected in the ISM. The detection of isotopologues in the ISM is important: it can give information about the formation process of complex organic molecules, and it is essential to clean the ISM spectra from the lines of known molecules in order to detect new ones. The 12C/13C ratio found in SgrB2: 20-30 suggests that the doubly 13C could be present in the spectral line survey recently obtained with ALMA (EMoCA), but no spectroscopic studies exist up to now. We measured and analyzed the spectra of the 13C-doubly-substitued species up to 1 THz with the Lille solid-state based spectrometer. The spectroscopic results and and the detection of the doubly 13C species in SgrB2 will be presented. This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI. This work was also done under ANR-13-BS05-0008-02 IMOLABS. Support by the Deutsche Forschungsgemeinschaft via SFB 956, project B3 is acknowledged D.~R.~Johnson, et al., Astrophys.~J. 1977, 218, L370 A.~Belloche, et al., A&A 2013, 559, A47 A.M.~Daly, et al., Astrophys.~J. 2013, 768, 81 K.~Demyk, et al. A&A 2007 466, 255 Margulès, et al. A&A 2009, 493, 565 Belloche et al. 2014, Science, 345, 1584

Confirmation and revision on the orbital period change of the possible type Ia supernova progenitor V617 Sagittarii

NASA Astrophysics Data System (ADS)

Shi, Guang; Qian, Sheng-Bang; Fernández Lajús, Eduardo

2014-02-01

This work reports new photometric results of eclipsing cataclysmic variable V617 Sagittarii (V617 Sgr). We analyzed the orbital period change of V617 Sgr by employing three new (since 2010) CCD eclipse timings along with all the available data from the literature. It was found that the orbital period of V617 Sgr undergoes an obvious long-term increase, which confirms the result revealed by Steiner et al. (2006). The rate of orbital period increase was calculated to be {dot{P}} = +2.14(0.05) × 10-7 d yr-1. This suggests the lifetime of the secondary star will end in a timescale of 0.97 × 106 yr faster than that predicted previously. In particular, a cyclic variation with a period of 4.5 yr and an amplitude of 2.3 min may appear in the O - C diagram. Dominated by the wind-accretion mechanism, high mass transfer from the low mass secondary to the white dwarf is expected to continue in the V Sge-type star V617 Sgr during its long-term evolution. The mass transfer rate |skew4dot{M}_{ tr}| was estimated to be in the range of about 2.2 × 10-7 to 5.2 × 10-7 M⊙ yr-1. Accordingly, the already massive (≥ 1.2 M⊙) white dwarf primary will process stable nuclear burning, accrete a fraction of the mass from its companion to reach the standard Chandrasekhar mass limit (≃ 1.38 M⊙), and ultimately produce a type Ia supernova (SN Ia) within about 4-8 × 105 yr or earlier.

The Newly Identified Subsurface Hazlehurst Formation and Implications for the Tectonic Evolution of the South Georgia Rift Basin, Southeastern U.S.

NASA Astrophysics Data System (ADS)

Cao, R.; Knapp, J. H.

2016-12-01

Integration of new 2-D seismic reflection profile with existing wells and potential field data from southeastern Georgia, USA provide exciting discovery of a new stratigraphic unit associated with the post-rift phase of the South Georgia Rift (SGR) basins. These data document an apparent reversal of rift basin asymmetry across the Warner Robins Transfer Zone, and the apparent presence of a new sub-horizontal stratigraphic unit (informally named the Hazlehurst Formation) which overlies with angular unconformity an inferred Triassic rift basin (Valdosta Basin), and sits below the regional Coastal Plain unconformity. Triassic rifting of the supercontinent Pangea left behind numerous extensional basins on what is now the eastern North American margin. The SGR is thought to be the most regionally extensive and best preserved of these basins, which were capped by thick basalt -flows of the Central Atlantic Magmatic Province (CAMP) and later buried beneath the Cretaceous and younger Coastal Plain section. Because it is buried beneath the Coastal Plain, the SGR is only known through relatively sparse drilling and geophysical methods. With these new seismic data acquired in 2013 near Hazlehurst, Georgia, we are able to put more constraints into the tectonic history of the basin. We test several hypotheses related to the SGR: (1) the "Transfer Zone" had to exist to transmit extensional strain between rift sub-basins with reverse polarities; (2) the newly identified sub-horizontal stratigraphic interval ("Hazlehurst Formation"), with a possible Jurassic age may represent a post-rift phase of regional subsidence; (3) the extent of this new unit appears to cover most of the coastal plain from eastern Mississippi to South Carolina. The result of this study suggests the previous inferred extent of the might need revision.

Constraining the spin and the deformation parameters from the black hole shadow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsukamoto, Naoki; Li, Zilong; Bambi, Cosimo, E-mail: tsukamoto@fudan.edu.cn, E-mail: zilongli@fudan.edu.cn, E-mail: bambi@fudan.edu.cn

2014-06-01

Within 5–10 years, very-long baseline interferometry (VLBI) facilities will be able to directly image the accretion flow around SgrA*, the super-massive black hole candidate at the center of the Galaxy, and observe the black hole ''shadow''. In 4-dimensional general relativity, the no-hair theorem asserts that uncharged black holes are described by the Kerr solution and are completely specified by their mass M and by their spin parameter a. In this paper, we explore the possibility of distinguishing Kerr and Bardeen black holes from their shadow. In Hioki and Maeda (2009), under the assumption that the background geometry is described bymore » the Kerr solution, the authors proposed an algorithm to estimate the value of a/M by measuring the distortion parameter δ, an observable quantity that characterizes the shape of the shadow. Here, we try to extend their approach. Since the Hioki-Maeda distortion parameter is degenerate with respect to the spin and possible deviations from the Kerr solution, one has to measure another quantity to test the Kerr black hole hypothesis. We study a few possibilities. We find that it is extremely difficult to distinguish Kerr and Bardeen black holes from the sole observation of the shadow, and out of reach for the near future. The combination of the measurement of the shadow with possible accurate radio observations of a pulsar in a compact orbit around SgrA* could be a more promising strategy to verify the Kerr black hole paradigm.« less

Evolving non-thermal electrons in simulations of black hole accretion

NASA Astrophysics Data System (ADS)

Chael, Andrew A.; Narayan, Ramesh; Saḑowski, Aleksander

2017-09-01

Current simulations of hot accretion flows around black holes assume either a single-temperature gas or, at best, a two-temperature gas with thermal ions and electrons. However, processes like magnetic reconnection and shocks can accelerate electrons into a non-thermal distribution, which will not quickly thermalize at the very low densities found in many systems. Such non-thermal electrons have been invoked to explain the infrared and X-ray spectra and strong variability of Sagittarius A* (Sgr A*), the black hole at the Galactic Center. We present a method for self-consistent evolution of a non-thermal electron population in the general relativistic magnetohydrodynamic code koral. The electron distribution is tracked across Lorentz factor space and is evolved in space and time, in parallel with thermal electrons, thermal ions and radiation. In this study, for simplicity, energy injection into the non-thermal distribution is taken as a fixed fraction of the local electron viscous heating rate. Numerical results are presented for a model with a low mass accretion rate similar to that of Sgr A*. We find that the presence of a non-thermal population of electrons has negligible effect on the overall dynamics of the system. Due to our simple uniform particle injection prescription, the radiative power in the non-thermal simulation is enhanced at large radii. The energy distribution of the non-thermal electrons shows a synchrotron cooling break, with the break Lorentz factor varying with location and time, reflecting the complex interplay between the local viscous heating rate, magnetic field strength and fluid velocity.

Probing the interstellar dust towards the Galactic Centre: dust-scattering halo around AX J1745.6-2901

NASA Astrophysics Data System (ADS)

Jin, Chichuan; Ponti, Gabriele; Haberl, Frank; Smith, Randall

2017-07-01

AX J1745.6-2901 is an X-ray binary located at only 1.45 arcmin from Sgr A⋆, showcasing a strong X-ray dust-scattering halo. We combine Chandra and XMM-Newton observations to study the halo around this X-ray binary. Our study shows two major thick dust layers along the line of sight (LOS) towards AX J1745.6-2901. The LOS position and NH of these two layers depend on the dust grain models with different grain size distributions and abundances. But for all the 19 dust grain models considered, dust layer-1 is consistently found to be within a fractional distance of 0.11 (mean value: 0.05) to AX J1745.6-2901 and contains only (19-34) per cent (mean value: 26 per cent) of the total LOS dust. The remaining dust is contained in layer-2, which is distributed from the Earth up to a mean fractional distance of 0.64. A significant separation between the two layers is found for all the dust grain models, with a mean fractional distance of 0.31. Besides, an extended wing component is discovered in the halo, which implies a higher fraction of dust grains with typical sizes ≲590 Å than considered in current dust grain models. Assuming AX J1745.6-2901 is 8 kpc away, dust layer-2 would be located in the Galactic disc several kpc away from the Galactic Centre (GC). The dust scattering halo biases the observed spectrum of AX J1745.6-2901 severely in both spectral shape and flux, and also introduces a strong dependence on the size of the instrumental point spread function and the source extraction region. We build xspec models to account for this spectral bias, which allow us to recover the intrinsic spectrum of AX J1745.6-2901 free from dust-scattering opacity. If dust layer-2 also intervenes along the LOS to Sgr A⋆ and other nearby GC sources, a significant spectral correction for the dust-scattering opacity would be necessary for all these GC sources.

The Vital Infrared to X-ray Link in the Sgr A* Accretion Flow

NASA Astrophysics Data System (ADS)

Fazio, Giovanni; Ashby, Matthew; Baganoff, Frederick; Becklin, Eric; Boyce, Hope; Carey, Sean; Gammie, Charles; Ghez, Andrea; Glaccum, William; Gurwell, Mark; Haggard, Daryl; Herrero-Illana, Ruben; Hora, Joseph; Ingalls, James; Lowrance, Patrick; Markoff, Sera; Marrone, Daniel; Morris, Mark; Narayan, Ramesh; Neilsen, Joseph; Ponti, Gabriele; Smith, Howard; Willner, Steven; Witzel, Gunther

2018-05-01

Black hole accretion drives extreme astrophysical phenomena in the universe. Sgr A*, the radiating counterpart of the nearest supermassive black hole, is highly variable, but sparse data and short observations have left its emission physics in question. Despite enormous advances in accretion models, physical description of the interacting radiation mechanisms is incomplete. The X-ray emission mechanism in particular remains unknown. Because the necessary information is contained in the time-dependent relation between X-ray and infrared emission, we have begun monitoring Sgr A* simultaneously with Chandra in X-rays and with Spitzer in the infrared. Defining the X-ray to infrared flux density ratio will allow the entire energy distribution to be understood. We therefore request two new 24-hour epochs of Spitzer monitoring at 4.5 microns simultaneous with Chandra time already approved. This will increase the exposure time for X-ray flares where the NIR state is known, moving us out of the realm of small-number statistics and enabling diagnostics of the true X-ray/IR ratio. Under current NASA plans, this will be the last chance for these valuable Spitzer+Chandra observations.

To the Galactic Virial Radius with Hyper Suprime-Cam

NASA Astrophysics Data System (ADS)

Deason, Alis J.; Belokurov, Vasily; Koposov, Sergey E.

2018-01-01

We exploit the exquisite, deep Hyper Suprime-Cam (HSC) imaging data to probe the Galactic halo out to 200 kpc. Using the ∼100 square degree, multiband photometry of the first HSC Wide survey data release, we identify blue horizontal branch (BHB) stars beyond 50 kpc in the halo. The presence of the Sagittarius (Sgr) stream in the HSC fields produces a notable excess of stars at the apocenter of the leading arm (∼50–60 kpc). For fields excluding Sgr, the BHB counts are consistent with a continuation of a ‑4 power law from the inner halo. However, we find that the majority of the non-Sgr BHB stars beyond 50 kpc reside in one 27 square degree HSC field called “VVDS.” Curiously, this field is located close to the Magellanic plane, and we hypothesize that the excess of stars between 50 and 200 kpc could be associated with distant Magellanic debris. Indeed, without the VVDS, there are very few BHBs in the remaining portions of the Galaxy probed by the HSC. Accordingly, this scarcity of tracers is consistent with a significant decline in stellar density beyond 50 kpc, with a power law of ‑4 or steeper.

The Metal-poor non-Sagittarius (?) Globular Cluster NGC 5053: Orbit and Mg, Al, and Si Abundances

NASA Astrophysics Data System (ADS)

Tang, Baitian; Fernández-Trincado, J. G.; Geisler, Doug; Zamora, Olga; Mészáros, Szabolcs; Masseron, Thomas; Cohen, Roger E.; García-Hernández, D. A.; Dell’Agli, Flavia; Beers, Timothy C.; Schiavon, Ricardo P.; Sohn, Sangmo Tony; Hasselquist, Sten; Robin, Annie C.; Shetrone, Matthew; Majewski, Steven R.; Villanova, Sandro; Schiappacasse Ulloa, Jose; Lane, Richard R.; Minnti, Dante; Roman-Lopes, Alexandre; Almeida, Andres; Moreno, E.

2018-03-01

Metal-poor globular clusters (GCs) exhibit intriguing Al–Mg anti-correlations and possible Si–Al correlations, which are important clues to decipher the multiple-population phenomenon. NGC 5053 is one of the most metal-poor GCs in the nearby universe and has been suggested to be associated with the Sagittarius (Sgr) dwarf galaxy, due to its similarity in location and radial velocity with one of the Sgr arms. In this work, we simulate the orbit of NGC 5053, and argue against a physical connection between Sgr and NGC 5053. On the other hand, the Mg, Al, and Si spectral lines, which are difficult to detect in the optical spectra of NGC 5053 stars, have been detected in the near-infrared APOGEE spectra. We use three different sets of stellar parameters and codes to derive the Mg, Al, and Si abundances. Regardless of which method is adopted, we see a large Al variation, and a substantial Si spread. Along with NGC 5053, metal-poor GCs exhibit different Mg, Al, and Si variations. Moreover, NGC 5053 has the lowest cluster mass among the GCs that have been identified to exhibit an observable Si spread until now.

(Sub)millimeter emission lines of molecules in born-again stars

NASA Astrophysics Data System (ADS)

Tafoya, D.; Toalá, J. A.; Vlemmings, W. H. T.; Guerrero, M. A.; De Beck, E.; González, M.; Kimeswenger, S.; Zijlstra, A. A.; Sánchez-Monge, Á.; Treviño-Morales, S. P.

2017-04-01

Context. Born-again stars provide a unique possibility to study the evolution of the circumstellar envelope of evolved stars in human timescales. Up until now, most of the observations of the circumstellar material in these stars have been limited to studying the relatively hot gas and dust. In other evolved stars, the emission from rotational transitions of molecules, such as CO, is commonly used to study the cool component of their circumstellar envelopes. Thus, the detection and study of molecular gas in born-again stars is of great importance when attempting to understand their composition and chemical evolution. In addition, the molecular emission is an invaluable tool for exploring the physical conditions, kinematics, and formation of asymmetric structures in the circumstellar envelopes of these evolved stars. However, up until now, all attempts to detect molecular emission from the cool material around born-again stars have failed. Aims: We searched for emission from rotational transitions of molecules in the hydrogen-deficient circumstellar envelopes of born-again stars to explore the chemical composition, kinematics, and physical parameters of the relatively cool gas. Methods: We carried out observations using the APEX and IRAM 30 m telescopes to search for molecular emission toward four well-studied born-again stars, V4334 Sgr, V605 Aql, A30, and A78, that are thought to represent an evolutionary sequence. Results: For the first time, we detected emission from HCN and H13CN molecules toward V4334 Sgr, and CO emission in V605 Aql. No molecular emission was detected above the noise level toward A30 and A78. The detected lines exhibit broad linewidths ≳150 km s-1, which indicates that the emission comes from gas ejected during the born-again event, rather than from the old planetary nebula. A first estimate of the H12CN/H13CN abundance ratio in the circumstellar environment of V4334 Sgr is ≈3, which is similar to the value of the 12C/13C ratio measured from other observations. We derived a rotational temperature of Trot = 13 ± 1 K, and a total column density of NHCN = 1.6 ± 0.1 × 1016 cm-2 for V4334 Sgr. This result sets a lower limit on the amount of hydrogen that was ejected into the wind during the born-again event of this source. For V605 Aql, we obtained a lower limit for the integrated line intensities I12CO/I13CO> 4. This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX) and IRAM 30 m telescopes. APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

An accreting black hole model for Sagittarius A(*). 2: A detailed study

NASA Technical Reports Server (NTRS)

Melia, Fulvio

1994-01-01

Sgr A(*) is a unique, compact radio source at the Galactic center whose characteristics suggest that it may be a massive (i.e., approximately 10(exp 6) solar mass) black hole accreting from an ambient wind in that region. Earlier (simplified) calculations suggested that its 10(exp 8) - 10(exp 20) Hz spectrum could be derived from bremsstrahlung and magnetic bremsstrahlung emission from plasma descending toward the event horizon at a rate of roughly 10(exp 22) g/s. Here, we introduce several significant improvements to the model, including (1) an exact treatment of the cyclotron/synchrotron emissivity that is valid for all temperatures, (2) the actual determination of the temperature distribution in the inflow, and (3) the effect on the spectrum should the accreting plasma have a residual angular momentum, possibly forming a disk at small radii. We find that the most likely value of the mass in this improved model is approximately equals 2 +/- 1 x 10(exp 6) solar mass, close to the range inferred earlier, but about a factor of 2 greater than the previous 'best-fit' number. The main reason for this difference is that the more realistic (new) formulation of the magnetic bremsstrahlung emissivity has fluctuations with frequency that decrease the overall line-of-sight intensity, thereby pointing to a slightly larger mass in order to account for the observed spectrum. We also find that a slight excess of angular momentum in the accreting gas may be necessary in order to account for the IR luminosity from this source. Such an excess is consistent with the results of ongoing three-dimensional simulations that will be reported elsewhere.

X-Ray and Radio Observations of the Magnetar SGR J1935+2154 during Its 2014, 2015, and 2016 Outbursts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Younes, George; Kouveliotou, Chryssa; Van der Horst, Alexander J.

We analyzed broadband X-ray and radio data of the magnetar SGR J1935+2154 taken in the aftermath of its 2014, 2015, and 2016 outbursts. The source soft X-ray spectrum <10 keV is well described with a blackbody+power-law (BB+PL) or 2BB model during all three outbursts. Nuclear Spectroscopic Telescope Array observations revealed a hard X-ray tail, with a PL photon index Γ = 0.9, extending up to 50 keV, with flux comparable to the one detected <10 keV. Imaging analysis of Chandra data did not reveal small-scale extended emission around the source. Following the outbursts, the total 0.5–10 keV flux from SGRmore » J1935+2154 increased in concordance to its bursting activity, with the flux at activation onset increasing by a factor of ∼7 following its strongest 2016 June outburst. A Swift /X-Ray Telescope observation taken 1.5 days prior to the onset of this outburst showed a flux level consistent with quiescence. We show that the flux increase is due to the PL or hot BB component, which increased by a factor of 25 compared to quiescence, while the cold BB component kT = 0.47 keV remained more or less constant. The 2014 and 2015 outbursts decayed quasi-exponentially with timescales of ∼40 days, while the stronger 2016 May and June outbursts showed a quick short-term decay with timescales of about four days. Our Arecibo radio observations set the deepest limits on the radio emission from a magnetar, with a maximum flux density limit of 14 μ Jy for the 4.6 GHz observations and 7 μ Jy for the 1.4 GHz observations. We discuss these results in the framework of the current magnetar theoretical models.« less

Determining Our Motion Through the Galaxy

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-12-01

Though we dont notice it from our point of view, were hurtling through space at breakneck speed and one of the contributors to our overall motion through the universe is the Suns revolutionaround the center of our galaxy. A recent study uses an unusual approach to measure the speed of this rotation.Moving While Sitting StillWe know that the Sun zips rapidly around the center of the Milky Way our orbitalspeed is somewhere around250 km/s, or 560,000 mph! Getting a precise measurement of this velocity is useful because we can combine it with the observed proper motion of Sgr A*, the black hole at the center of our galaxy, to determine the distance from us to the center of the Milky Way. This is an important baseline for lots of other measurements.Example particle orbits modeled within the galactic potential. The top panel represents a starwith zero angular momentum, which is scattered into a chaotic orbit after interacting with the galactic nucleus. [Hunt et al. 2016]But how can we measure the Suns revolutionspeed accurately? A team of scientists led by Jason Hunt (Dunlap Institute at University of Toronto, Canada) have suggested a unique approach to pin down this value: look for missing stars in the solar neighborhood.Missing StarsThe stars around us should exhibit a distribution of velocities describing their orbits about the galactic center but those stars with zero angular momentum should have plunged directly into the galactic center long ago. These stars would have been scattered onto chaotic halo orbits after their plunge, resulting in a dearth of stars with zero angular momentum around us today.By looking at the relative speeds of the stars moving around us, then, we should see a dip in the velocity distribution corresponding to the missing zero-angular-momentum stars. By noting the relative velocity at which that dip occurs, we cleverly reveal the negative of our motion around the galactic center.Velocity distribution for stars within 700 pc of the Sun. A dip in the distribution (marked with an arrow) is noticeable between 210 and 270 km/s. [Hunt et al. 2016]Where Are We and How Fast Are We Going?Hunt and collaborators use a combination of the first data release from ESAs Gaia mission and a star catalog from the Radial Velocity Experiment to examine the motions of a total of over 200,000 stars in the solar neighborhood. They find that there is indeed a lack of disk stars with velocities close to zero angular momentum. They then compare modeled stellar orbits to the data to estimate the relative speed at which the dip in the velocity distribution occurs.From this information, the authors obtain a measurement of 2399 km/s for the Suns revolutionvelocity around the galactic center. They combine this value with a proper motion measurement of Sgr A* to calculate the distance to the galactic center: 7.90.3 kpc (or about 26,000 light-years).Both of these measurements can be improved with future Gaia data releases, which will contain many orders of magnitude more stars. This clever technique, therefore, proves a useful way of better constraining our position and motion through the Milky Way.CitationJason A. S. Hunt et al 2016 ApJL 832 L25. doi:10.3847/2041-8205/832/2/L25

Continued X-ray Monitoring of Magnetar Candidate SWIFT J1822.3-1606

NASA Astrophysics Data System (ADS)

Scholz, P.; Livingstone, M. A.; Kaspi, V. M.

2011-08-01

We report on Swift/XRT and RXTE/PCA observations of the new 8.4-s Galactic magnetar candidate SWIFT J1822.3-1606, also referred to as SGR J1822.3-1606 (ATELs #3488, #3489, #3490, #3493, #3495, #3496, #3501, #3503, #3543). The persistent X-ray flux from the source continues to fade in ongoing XRT monitoring observations. For data in the MJD range 55757 to 55781, the best-fit power-law index, alpha, for the decay of the absorbed 1-10 keV flux is -0.47 ± 0.02, assuming a decay of functional form F(t) = F0 + F0*(t-T)^alpha, where T is the epoch of the Swift/BAT trigger (ATEL #3488).

What is the Magnetic Field of Magnetar Swift J1822.3-1606?

NASA Astrophysics Data System (ADS)

Kaspi, Victoria

2013-09-01

In recent years, the mean magnetic field of known magnetars has been lowered by discoveries of sources with magnetic fields < 1x10^14 G. In particular, Swift J1822.3-1606 and SGR 0418+5729 appear to have fields that are ~1x10^13 G. This begs the question of how low the true magnetic field distribution of magnetars stretches and whether it is in fact distinct from that of the main pulsar population. Here we propose to perform phase-coherent timing of Swift J1822.3-1606 with Chandra. With our proposed timing campaign we will be able to distinguish between ambiguous measurements now present in the literature and determine the true spin-inferred magnetic field of this interesting object.

The occultation of 28 Sgr by Saturn - Saturn pole position and astrometry

NASA Technical Reports Server (NTRS)

Hubbard, W. B.; Porco, C. C.; Hunten, D. M.; Rieke, G. H.; Rieke, M. J.; Mccarthy, D. W.; Haemmerle, V.; Clark, R.; Turtle, E. P.; Haller, J.

1993-01-01

Saturn's ring plane-defined pole position is presently derived from the geometry of Saturn's July 3, 1989 occultation of 28 Sgr, as indicated by the timings of 12 circular edges in the Saturn C-ring as well as the edges of the Encke gap and the outer edge of the Keeler gap. The edge timings are used to solve for the position angle and opening angle of the apparent ring ellipses; the internal consistency of the data set and the redundancy of stations indicates an absolute error of the order of 5 km. The pole position thus obtained is consistent with the pole and ring radius scale derived from Voyager occultation observations.

THE ARCHES CLUSTER: EXTENDED STRUCTURE AND TIDAL RADIUS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hosek, Matthew W. Jr.; Lu, Jessica R.; Anderson, Jay

At a projected distance of ∼26 pc from Sgr A*, the Arches cluster provides insight into star formation in the extreme Galactic center (GC) environment. Despite its importance, many key properties, such as the cluster’s internal structure and orbital history, are not well known. We present an astrometric and photometric study of the outer region of the Arches cluster ( R > 6.″25) using Hubble Space Telescope WFC3IR. Using proper motions, we calculate membership probabilities for stars down to F153M = 20 mag (∼2.5 M {sub ⊙}) over a 120″ × 120″ field of view, an area 144 times largermore » than previous astrometric studies of the cluster. We construct the radial profile of the Arches to a radius of 75″ (∼3 pc at 8 kpc), which can be well described by a single power law. From this profile we place a 3 σ lower limit of 2.8 pc on the observed tidal radius, which is larger than the predicted tidal radius (1–2.5 pc). Evidence of mass segregation is observed throughout the cluster, and no tidal tail structures are apparent along the orbital path. The absence of breaks in the profile suggests that the Arches has not likely experienced its closest approach to the GC between ∼0.2 and 1 Myr ago. If accurate, this constraint indicates that the cluster is on a prograde orbit and is located in front of the sky plane that intersects Sgr A*. However, further simulations of clusters in the GC potential are required to interpret the observed profile with more confidence.« less

Testing the Caustic Ring Dark Matter Halo Model Against Observations in the Milky Way

NASA Astrophysics Data System (ADS)

Dumas, Julie; Newberg, Heidi Jo; Niedzielski, Bethany; Susser, Adam; Thompson, Jeffery M.; Weiss, Jake; Lewis, Kim M.

2016-06-01

One prediction of axion dark matter models is they can form Bose-Einstein condensates and rigid caustic rings as a halo collapses in the non-linear regime. In this thesis, we undertake the first study of a caustic ring model for the Milky Way halo (Duffy & Sikivie 2008), paying particular attention to observational consequences. We first present the formalism for calculating the gravitational acceleration of a caustic ring halo. The caustic ring dark matter theory reproduces a roughly logarithmic halo, with large perturbations near the rings. We show that this halo can reasonably match the known Galactic rotation curve. We are not able to confirm or rule out an association between the positions of the caustic rings and oscillations in the observed rotation curve, due to insufficient rotation curve data. We explore the effects of dark matter caustic rings on dwarf galaxy tidal disruption with N-body simulations. Simulations of the Sagittarius (Sgr) dwarf galaxy in a caustic ring halo potential, with disk and bulge parameters that are tuned to match the Galactic rotation curve, match observations of the Sgr trailing tidal tails as far as 90 kpc from the Galactic center. Like the Navarro-Frenk-White (NFW) halo, they are, however, unable to match the leading tidal tail. None of the caustic, NFW, or triaxial logarithmic halos are able to simultaneously match observations of the leading and trailing arms of the Sagittarius stream. We further show that simulations of dwarf galaxies that move through caustic rings are qualitatively similar to those moving in a logarithmic halo. This research was funded by NSF grant AST 10-09670, the NASA-NY Space Grant, and the American Fellowship from AAUW.

Gas Cloud Accretion onto the SMBH SgrA* and Formation of Jet 4

NASA Astrophysics Data System (ADS)

Nishiyama, Shogo

2015-06-01

A dense gas cloud was detected to be rapidly approaching the Galactic supermassive black hole (SMBH) Sgr A*, and was 1,600 Schwarzschild radii from the SMBH at the pericenter of its eccentric orbit in Mar 2014. Ongoing tidal disruption has been observed, and cloud fragments are expected to accrete onto the SMBH on dynamical timescales, suggesting a jet formation in the following years. So we are carrying out daily monitoring observations of Sgr A* in near-infrared and radio wavelengths, and we propose quick follow-up observations with Subaru/Gemini. Br-gamma line emission maps obtained with Gemini/NIFS will be used to fine tune our 3D simulation to estimate how much mass accretes, and when the fragments accrete onto the SMBH. Polarimetric and astrometric signals from a jet taken with Subaru/HiCIAO and KaVA will be compared with the finely tuned simulation to understand the timescale of jet formation, and to investigate the correlation between the accreted mass of the cloud fragments and a luminosity of the newly-formed jet. Spectroscopic and imaging observations from 1.6 - 11 mum (Subaru/IRCS, COMICS) will also be conducted to understand processes responsible for near to mid-infrared emission during the accretion event.

The Sagittarius Dwarf Galaxy Survey (SDGS) - II. The stellar content and constraints on the star formation history

NASA Astrophysics Data System (ADS)

Bellazzini, M.; Ferraro, F. R.; Buonanno, R.

1999-08-01

A detailed study of the star formation history of the Sagittarius dwarf spheroidal galaxy is performed through the analysis of data from the Sagittarius Dwarf Galaxy Survey (SDGS). Accurate statistical decontamination of the SDGS colour-magnitude diagrams (CMDs) allows us to obtain many useful constraints on the age and metal content of the Sgr stellar populations in three different regions of the galaxy. A coarse metallicity distribution of Sgr stars is derived, ranging from [Fe/H]~-2.0 to [Fe/H]~-0.7, the upper limit being somewhat higher in the central region of the galaxy. A qualitative global fit to all the observed CMD features is attempted, and a general scheme for the star formation history of the Sgr dSph is derived. According to this scheme, star formation began at a very early time from a low metal content interstellar medium and lasted for severalGyr, coupled with progressive chemical enrichment. The star formation rate (SFR) had a peak from 8 to 10Gyr ago, when the mean metallicity was in the range -1.3<=[Fe/H]<=-0.7. After that maximum, the SFR rapidly decreased and a very low rate of star formation took place until ~1-0.5Gyr ago.

An X-ray Pulsar with a Superstrong Magnetic Field in the Soft Gamma-Ray Repeater SGR1806-20

NASA Technical Reports Server (NTRS)

Kouveliotou, C.; Dieters, S.; Strohmayer, T.; vanParadijs, J.; Fishman, G. J.; Meegan, C. A.; Hurley, K.; Kommers, J.; Smith, I.; Frail, D.;

Are sex steroids involved in the sexual growth dimorphism in Eurasian perch juveniles?

PubMed

Mandiki, S N M; Houbart, M; Babiak, I; Vandeloise, E; Gardeur, J N; Kestemont, P

2004-02-01

Individual growth and food intake were monitored in Eurasian perch (Perca fluviatilis L.) juveniles (13.5+/-3.4 g initial body weight) to determine whether androgens and estrogens may mediate sex-related growth differences. Fish were individually tagged with chips and implanted with cocoa butter containing 20 microg of either 17alpha-methyltestosterone (MT) or 17beta-estradiol (E(2)) per gram of fish body; controls were implanted with cocoa butter without hormones. All fish were bled at the end of the experiment for measurement of E(2) in females and testosterone (T) in males (MT was not measured) and triiodothyronine (T3) in both genders. Survival, gonadosomatic index and hepatosomatic index were not affected by steroid treatments. Relative food intake (RFI), feed efficiency (FE) and specific growth rate (SGR) were higher in females than in males in all treatments. MT treatment significantly lowered RIF, FE and SGR in both sexes, while E(2) treatment showed no significant effect on growth and feeding parameters. In contrast to E(2) and T concentrations, T3 levels were significantly and positively correlated with SGR and RFI. The results provide evidence that MT may affect sexually related growth dimorphism by decreasing food intake and FE in Eurasian perch.

A 149 min periodicity underlies the X-ray flaring of Sgr A*

NASA Astrophysics Data System (ADS)

Leibowitz, Elia

2018-03-01

In a paper in 2017, I have shown that 39 large X-ray flares of Sgr A* that were recorded by Chandra observatory in the year 2012 are concentrated preferably around tick marks of an equi-distance grid on the time axis. The period of this grid as found in that paper is 0.1033 d. In this work I show that the effect can be found among all the large X-ray flares recorded by Chandra and XMM - Newton along 15 yr. The mid-points of all the 71 large flares recorded between years 2000 and 2014 are also tightly grouped around tick marks of a grid with this period, or more likely, 0.1032 d. This result is obtained with a confidence level of at least 3.27σ and very likely of 4.62σ. I find also a possible hint that a similar grid is underlying IR flares of the object. I suggest that the pacemaker in the occurrences of the large X-ray flares of Sgr A* is a mass of the order of a low-mass star or a small planet, in a slightly eccentric Keplerian orbit around the SMBH at the centre of the Galaxy. The radius of this orbit is about 6.6 Schwarzschild radii of the BH.

Modeling SOFIA/FORCAST spectra of the classical nova V5568 Sgr with 3D pyCloudy

NASA Astrophysics Data System (ADS)

Calvén, Emilia; Helton, L. Andrew; Sankrit, Ravi

2017-06-01

We present our first results modelling Nova V5668 Sgr using the pseudo-3D photoionization code pyCloudy (Morisset 2013). V5668 Sgr is a classical nova of the FeII class (Williams et al. 2015; Seach 2015) showing signs of a bipolar flow (Banerjee et al. 2015). We construct a grid of models, which use hour-glass morphologies and a range of C, N, O and Ne abundances, to fit a suite of spectroscopic data in the near and mid-IR obtained between 82 to 556 days after outburst. The spectra were obtained using the FORCAST mid-IR instrument onboard the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA) and the 1.2m near-IR telescope of the Mount Abu Infrared Observatory. Additional photometric data from FORCAST, The STONY BROOK/SMARTS Atlas of (mostly) Southern Novae (Walter et al., 2012) and the American Association of Variable Star Observers (AAVSO) were used to supplement the spectral data to obtain the SED of the nova at different times during its evolution. The work presented here is the initial step towards developing a large database of 1D and 3D models that may be used to derive the elemental abundances and dust properties of classical novae.

Transcriptomic and metabolomic analyses identify a role for chlorophyll catabolism and phytoalexin during Medicago nonhost resistance against Asian soybean rust.

PubMed

Ishiga, Yasuhiro; Uppalapati, Srinivasa Rao; Gill, Upinder S; Huhman, David; Tang, Yuhong; Mysore, Kirankumar S

2015-08-12

Asian soybean rust (ASR) caused by Phakopsora pachyrhizi is a devastating foliar disease affecting soybean production worldwide. Understanding nonhost resistance against ASR may provide an avenue to engineer soybean to confer durable resistance against ASR. We characterized a Medicago truncatula-ASR pathosystem to study molecular mechanisms of nonhost resistance. Although urediniospores formed appressoria and penetrated into epidermal cells of M. truncatula, P. pachyrhizi failed to sporulate. Transcriptomic analysis revealed the induction of phenylpropanoid, flavonoid and isoflavonoid metabolic pathway genes involved in the production of phytoalexin medicarpin in M. truncatula upon infection with P. pachyrhizi. Furthermore, genes involved in chlorophyll catabolism were induced during nonhost resistance. We further characterized one of the chlorophyll catabolism genes, Stay-green (SGR), and demonstrated that the M. truncatula sgr mutant and alfalfa SGR-RNAi lines showed hypersensitive-response-like enhanced cell death upon inoculation with P. pachyrhizi. Consistent with transcriptomic analysis, metabolomic analysis also revealed the accumulation of medicarpin and its intermediate metabolites. In vitro assay showed that medicarpin inhibited urediniospore germination and differentiation. In addition, several triterpenoid saponin glycosides accumulated in M. truncatula upon inoculation with P. pachyrhizi. In summary, using multi-omic approaches, we identified a correlation between phytoalexin production and M. truncatula defense responses against ASR.

Dynamic recrystallization mechanisms and their transition in the Daling Thrust (DT) zone, Darjeeling-Sikkim Himalaya

NASA Astrophysics Data System (ADS)

Ghosh, Subhajit; Bose, Santanu; Mandal, Nibir; Dasgupta, Sujoy

2016-04-01

The Daling Thrust (DT) delineates a zone of intense shear localization in the Lesser Himalayan Sequence (LHS) of the Darjeeling-Sikkim Himalaya. From microstructural studies of deformed quartzite samples, we show a transition in the dynamic recrystallization mechanism with increasing distance from the DT, dominated by grain boundary bulging (BLG) recrystallization closest to the DT, and progressively replaced by sub-grain rotation (SGR) recrystallization away from the thrust. The transition is marked by a characteristic variation in the fractal dimension (D) of grain boundaries, estimated from the area-perimeter method. For the BLG regime, D ≈ 1.046, which decreases significantly to a value as low as 1.025 for the SGR regime. Using the available thermal data for BLG and SGR recrystallization, we infer increasing deformation temperatures away from the DT in the hanging wall. Based on the quartz piezometer our estimates reveal strong variations in the flow stress (59.00 MPa to 16.00 MPa) over a distance of 1.2 km from the DT. Deformation mechanism maps constructed for different temperatures indicate that the strain rates (10- 12 S- 1 to 10- 14 S- 1) comply with the geologically possible range. Finally, we present a mechanical model to provide a possible explanation for the cause of stress intensification along the DT.

Joint Meteorological Statistics of Observing Sites for the Event Horizon Telescope

NASA Astrophysics Data System (ADS)

Lope Córdova Rosado, Rodrigo Eduardo; Doeleman, Sheperd; Paine, Scott; Johnson, Michael; Event Horizon Telescope (EHT)

2018-01-01

The Event Horizon Telescope (EHT) aims to resolve the general relativistic shadow of Sgr A*, the supermassive black hole at the center of our galaxy, via Very Long Baseline Interferometry (VLBI) measurements with a multinational array of radio observatories. In order to optimize the scheduling of future observations, we have developed tools to model the atmospheric opacity at each EHT site using the past 10 years of Global Forecast System (GFS) data describing the atmospheric state. These tools allow us to determine the ideal observing windows for EHT observations and to assess the suitability and impact of new EHT sites. We describe our modeling framework, compare our models to in-situ measurements at EHT sites, and discuss the implications of weather limitations for planned extensions of the EHT to higher frequencies, as well as additional sites and observation windows.

Gas cloud G2 can illuminate the black hole population near the galactic center.

PubMed

Bartos, Imre; Haiman, Zoltán; Kocsis, Bence; Márka, Szabolcs

2013-05-31

Galactic nuclei are expected to be densely populated with stellar- and intermediate-mass black holes. Exploring this population will have important consequences for the observation prospects of gravitational waves as well as understanding galactic evolution. The gas cloud G2 currently approaching Sgr A* provides an unprecedented opportunity to probe the black hole and neutron star population of the Galactic nucleus. We examine the possibility of a G2-cloud-black-hole encounter and its detectability with current x-ray satellites, such as Chandra and NuSTAR. We find that multiple encounters are likely to occur close to the pericenter, which may be detectable upon favorable circumstances. This opportunity provides an additional important science case for leading x-ray observatories to closely follow G2 on its way to the nucleus.

Weak maser emission of methyl formate toward Sagittarius B2(N) in the green bank telescope PRIMOS survey

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faure, A.; Wiesenfeld, L.; Remijan, A. J.

A non-LTE radiative transfer treatment of cis-methyl formate (HCOOCH{sub 3}) rotational lines is presented for the first time using a set of theoretical collisional rate coefficients. These coefficients have been computed in the temperature range 5-30 K by combining coupled-channel scattering calculations with a high accuracy potential energy surface for HCOOCH{sub 3}-He. The results are compared to observations toward the Sagittarius B2(N) molecular cloud using the publicly available PRIMOS survey from the Green Bank Telescope. A total of 49 low-lying transitions of methyl formate, with upper levels below 25 K, are identified. These lines are found to probe a presumablymore » cold (∼30 K), moderately dense (∼10{sup 4} cm{sup –3}), and extended region surrounding Sgr B2(N). The derived column density of ∼4 × 10{sup 14} cm{sup –2} is only a factor of ∼10 larger than the column density of the trans conformer in the same source. Provided that the two conformers have the same spatial distribution, this result suggests that strongly non-equilibrium processes must be involved in their synthesis. Finally, our calculations show that all detected emission lines with a frequency below 30 GHz are (collisionally pumped) weak masers amplifying the continuum of Sgr B2(N). This result demonstrates the importance and generality of non-LTE effects in the rotational spectra of complex organic molecules at centimeter wavelengths.« less

Multiphase environment of compact galactic nuclei: the role of the nuclear star cluster

NASA Astrophysics Data System (ADS)

Różańska, A.; Kunneriath, D.; Czerny, B.; Adhikari, T. P.; Karas, V.

2017-01-01

We study the conditions for the onset of thermal instability in the innermost regions of compact galactic nuclei, where the properties of the interstellar environment are governed by the interplay of quasi-spherical accretion on to a supermassive black hole (SMBH) and the heating/cooling processes of gas in a dense nuclear star cluster (NSC). Stellar winds are the source of material for radiatively inefficient (quasi-spherical, non-magnetized) inflow/outflow on to the central SMBH, where a stagnation point develops within the Bondi-type accretion. We study the local thermal equilibrium to determine the parameter space that allows cold and hot phases in mutual contact to co-exist. We include the effects of mechanical heating by stellar winds and radiative cooling/heating by the ambient field of the dense star cluster. We consider two examples: the NSC in the Milky Way central region (including the gaseous mini-spiral of Sgr A*), and the ultracompact dwarf galaxy M60-UCD1. We find that the two systems behave in different ways because they are placed in different areas of parameter space in the instability diagram: gas temperature versus dynamical ionization parameter. In the case of Sgr A*, stellar heating prevents the spontaneous formation of cold clouds. The plasma from stellar winds joins the hot X-ray emitting phase and forms an outflow. In M60-UCD1, our model predicts spontaneous formation of cold clouds in the inner part of the galaxy. These cold clouds may survive since the cooling time-scale is shorter than the inflow/outflow time-scale.

Changing patterns of the long-term activity of the intermediate polar V1223 Sgr

NASA Astrophysics Data System (ADS)

Šimon, Vojtěch

2014-11-01

High and low states represent a large variety of features in the optical activity of some types of cataclysmic variables. Here, we examine them in the intermediate polar V1223 Sgr. We use the photographic observations from the Bamberg Observatory and from Garnavich and Szkody, and the CCD ASAS-3 and NSVS data. One plate or CCD image was usually obtained per night. These data span 78 years. We use the histograms of brightness to set the separation between the high and low states in V1223 Sgr at the level of 13.9 mag(B). The profile of this statistical distribution is dominated by a broad bump with the peak-to-peak amplitude of more than 1 mag(B). This is the result of co-adding various episodes of the high states, sometimes with the brightness varying on a timescale of months even during a single episode. The high state is not any uniquely defined level of brightness. Groups of the low states represent tails from such bumps rather than forming specific levels of brightness. The fuzzy boundaries of the bright side of the statistical distributions of brightness show that the system cannot find equilibrium of the mass transfer even in the high state. We show that V1223 Sgr underwent a large change of its high/low state activity; we ascribe it to the changes of the stellar activity of the donor. The episodes of the low states with mutually similar depth and profile were observed to recur with a cycle of 1092 days in the data mapping the years from 1999 to 2009; this behavior was discordant with the typical recurrence times present before. In our scenario, this cycle is driven by the changing aspect of some structure (e.g. a sequence of star spots migrating across the L1 point) on the donor. Because of the differential rotation of the donor, this configuration cyclically influences the mass flow to the accretion disk.

Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

NASA Astrophysics Data System (ADS)

Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

2014-02-01

The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

Imaging the Molecular Disk Orbiting the Twin Suns of V4046 Sgr

NASA Astrophysics Data System (ADS)

Rodriguez, David R.; Kastner, J. H.; Wilner, D. J.; Zuckerman, B.

2009-05-01

V4046 Sgr is a 12 Myr-old spectroscopic binary with a period of 2.4 days. At a distance of 73 pc (Torres et al. 2008), it is the second closest classical T Tauri star to the Earth after TW Hydra. Previously, rotational transitions of CO, HCO+, CN, and HCN were detected with the 30m IRAM telescope (Kastner et al. 2008). The double peaked CO profiles can be fit by a model invoking a Keplerian disk with outer radius of 250 AU that is viewed at an inclination of 35 degrees. The CO line profile was asymmetric, with the redshifted emission peak in both C-12 and C-13 brighter than the blueshifted peak. We have used the SMA to spatially resolve the J=2-1 CO emission line and the 230 GHz continuum. The CO channel maps show a disk consistent with Keplerian rotation. At the velocity of the redshifted emission peak, these observations reveal enhanced CO emission a few arcseconds to the southwest of the binary. A question arises as to whether this enhanced CO emission is associated with a third star in the system. According to the analysis of Tokovinin et al. (2006), the probability that a binary with a 2.4 day period has an associated tertiary star is essentially 100%. We searched archival Chandra and HST (ACS and NICMOS) images in the vicinity of V4046 Sgr to look for a star at the position of the enhanced CO emission. While there is a star in the HST ACS images approximately coincident with the enhanced CO emission, our preliminary analysis suggests that this star is not physically associated with V4046 Sgr. We will present a detailed discussion of the SMA results. This work has been partially supported by a NASA ADA grant to RIT and UCLA.

Sensitivity to dietary phosphorus limitation in native vs. invasive lineages of a New Zealand freshwater snail.

PubMed

Neiman, Maurine; Krist, Amy

2016-10-01

Why some species and lineages are more likely to be invasive than others is one of the most important unanswered questions in basic and applied biology. In particular, the relative contributions to the invasion process of factors like pre-adaptation to invasiveness in the native range, evolution post-colonization, and random vs. non-random sampling of colonist lineages remain unclear. We use a powerful common garden approach to address the potential for a role for sensitivity to nutrient limitation in determining the invasiveness of particular lineages of Potamopyrgus antipodarum, a New Zealand freshwater snail that has become globally invasive. We quantified specific growth rate (SGR), an important fitness-related trait in this species, under high phosphorus (P) vs. low-P conditions for a diverse set of native and invasive P. antipodarum. This experiment revealed that native-range P. antipodarum experience a more severe decline in SGR in low-P conditions relative to SGR in high-P conditions than their invasive range counterparts. Although these results suggest resilience to P limitation in invasive lineages, the absence of significant absolute differences in SGR between native and invasive lineages indicates that a straightforward connection between response to P limitation and invasiveness in P. antipodarum is unlikely. Regardless, our data demonstrate that invasive vs. native lineages of P. antipodarum exhibit consistently different responses to an important environmental variable that is rarely studied in the context of invasion success. Further studies directed at exploring and disentangling the roles of sampling effects, selection on preexisting variation, and evolution after colonization will be required to provide a comprehensive picture of the role (or lack thereof) of nutrient limitation in the global invasion of P. antipodarum, as well for as other invasive taxa. © 2016 by the Ecological Society of America.

The circumbinary dusty disk around the hydrogen-deficient binary star υ Sagittarii

NASA Astrophysics Data System (ADS)

Netolický, M.; Bonneau, D.; Chesneau, O.; Harmanec, P.; Koubský, P.; Mourard, D.; Stee, P.

2009-06-01

Aims: The aim of this paper is to determine the properties of the dusty environment of the hydrogen-deficient binary system υ Sgr, whose binary properties and other characteristics are poorly known. Methods: We obtained the first mid-IR interferometric observations of υ Sgr using the instrument MIDI of the VLTI used with different pairs of 1.8 m and 8 m telescopes. The calibrated visibilities, the N band spectrum, and the SED were compared with disk models computed with the MC3D code to determine the geometry and chemical composition of the envelope. Results: υ Sgr is unresolved with an 8 m telescope at 8.7 μm. We propose a disk model that agrees with the measured visibilities and the SED, consisting of a geometrically thin disk with an inner radius R_in = 6.0+0.5-1.5 AU and a scale height h100 = 3.5+2.0-1.5 AU. The chemical composition of the dust is approximately 60% of carbon dust and 40% of silicate dust, as a consequence of several episodes of mass transfers, whose chemistry was imprinted in the dust composition. We also constrain the inclination of the disk i = 50°+10°-20° and its orientation position angle PA = 80°+10°-5°. Conclusions: The mid-infrared interferometric observations of the binary star υ Sgr allowed us to constrain the geometry of the circumbinary dusty envelope. By defining the inclination and PA of the system with better accuracy than before, these observations restrict the parameter space for the orbital parameters and thus the nature of the stars orbiting in this system. Based on observations made with the Very Large Telescope Interferometer at Paranal Observatory under program 079.D-0115. Visibility data are only available in electronic form at the CDS website.

X-ray constraints on the number of stellar mass black holes in the inner parsec

NASA Astrophysics Data System (ADS)

Deegan, Patrick; Nayakshin, Sergei

2006-12-01

Due to dynamical friction stellar mass black holes should form a cusp in the inner parsec. Calculations [5, 6] show that approximately 20 thousand black holes would be present in a sphere with radius of about a parsec around Sgr A*. The presence of these objects opens up the possibility that they might be accreting ''cool'' gas (i.e. the Minispiral) as discussed by Morris [6]. Here we calculate the X-ray emission expected from these black holes as a method to constrain their population. We find that the data limits the total number of such black holes to around 10 - 20 thousand. Even a much smaller number of such black holes, i.e. 5 thousand, is sufficient to produce several sources with X-ray luminosity above Lx ~ 1033 erg s-1 at any one time. We suggest that some of the discrete X-ray sources observed by Muno [7] with Chandra in the inner parsec may be such ''fake X-ray binaries''.

Interstellar Antifreeze: Ethylene Glycol

NASA Technical Reports Server (NTRS)

Hollis, J. M.; Lovas, F. J.; Jewell, P. R.; Coudert, L. H.

2002-01-01

Interstellar ethylene glycol (HOCH2CH2,OH) has been detected in emission toward the Galactic center source Sagittarius B2(N-LMH) by means of several millimeter-wave rotational torsional transitions of its lowest energy conformer. The types and kinds of molecules found to date in interstellar clouds suggest a chemistry that favors aldehydes and their corresponding reduced alcohols-e.g., formaldehyde (H2CO)/methanol (CH3OH), acetaldehyde (CH3CHO)/ethanol (CH3CH2OH). Similarly, ethylene glycol is the reduced alcohol of glycolaldehyde (CH2OHCHO), which has also been detected toward Sgr B2(N-LMH). While there is no consensus as to how any such large complex molecules are formed in the interstellar clouds, atomic hydrogen (H) and carbon monoxide (CO) could form formaldehyde on grain surfaces, but such surface chemistry beyond that point is uncertain. However, laboratory experiments have shown that the gas-phase reaction of atomic hydrogen (H) and solid-phase CO at 10-20 K can produce formaldehyde and methanol and that alcohols and other complex molecules can be synthesized from cometary ice analogs when subject to ionizing radiation at 15 K. Thus, the presence of aldehyde/ reduced alcohol pairs in interstellar clouds implies that such molecules are a product of a low-temperature chemistry on grain surfaces or in grain ice mantles. This work suggests that aldehydes and their corresponding reduced alcohols provide unique observational constraints on the formation of complex interstellar molecules.

The supersoft X-ray source in V5116 Sagittarii. I. The high resolution spectra

NASA Astrophysics Data System (ADS)

Sala, G.; Ness, J. U.; Hernanz, M.; Greiner, J.

2017-05-01

Context. Classical nova explosions occur on the surface of an accreting white dwarf in a binary system. After ejection of a fraction of the envelope and when the expanding shell becomes optically thin to X-rays, a bright source of supersoft X-rays arises, powered by residual H burning on the surface of the white dwarf. While the general picture of the nova event is well established, the details and balance of accretion and ejection processes in classical novae are still full of unknowns. The long-term balance of accreted matter is of special interest for massive accreting white dwarfs, which may be promising supernova Ia progenitor candidates. Nova V5116 Sgr 2005b was observed as a bright and variable supersoft X-ray source by XMM-Newton in March 2007, 610 days after outburst. The light curve showed a periodicity consistent with the orbital period. During one third of the orbit the luminosity was a factor of seven brighter than during the other two thirds of the orbital period. Aims: In the present work we aim to disentangle the X-ray spectral components of V5116 Sgr and their variability. Methods: We present the high resolution spectra obtained with XMM-Newton RGS and Chandra LETGS/HRC-S in March and August 2007. Results: The grating spectrum during the periods of high-flux shows a typical hot white dwarf atmosphere dominated by absorption lines of N VI and N VII. During the low-flux periods, the spectrum is dominated by an atmosphere with the same temperature as during the high-flux period, but with several emission features superimposed. Some of the emission lines are well modeled with an optically thin plasma in collisional equilibrium, rich in C and N, which also explains some excess in the spectra of the high-flux period. No velocity shifts are observed in the absorption lines, with an upper limit set by the spectral resolution of 500 km s-1, consistent with the expectation of a non-expanding atmosphere so late in the evolution of the post-nova. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate

NASA Astrophysics Data System (ADS)

Mossoux, Enmanuelle; Grosso, Nicolas

2017-08-01

Context. X-ray flaring activity from the closest supermassive black hole Sagittarius A* (Sgr A*) located at the center of our Galaxy has been observed since 2000 October 26 thanks to the current generation of X-ray facilities. In a study of X-ray flaring activity from Sgr A* using Chandra and XMM-Newton public observations from 1999 to 2014 and Swift monitoring in 2014, it was argued that the "bright and very bright" flaring rate has increased from 2014 August 31. Aims: As a result of additional observations performed in 2015 with Chandra, XMM-Newton, and Swift (total exposure of 482 ks), we seek to test the significance and persistence of this increase of flaring rate and to determine the threshold of unabsorbed flare flux or fluence leading to any change of flaring rate. Methods: We reprocessed the Chandra, XMM-Newton, and Swift data from 1999 to 2015 November 2. From these data, we detected the X-ray flares via our two-step Bayesian blocks algorithm with a prior on the number of change points properly calibrated for each observation. We improved the Swift data analysis by correcting the effects of the target variable position on the detector and we detected the X-ray flares with a 3σ threshold on the binned light curves. The mean unabsorbed fluxes of the 107 detected flares were consistently computed from the extracted spectra and the corresponding calibration files, assuming the same spectral parameters. We constructed the observed distribution of flare fluxes and durations from the XMM-Newton and Chandra detections. We corrected this observed distribution from the detection biases to estimate the intrinsic distribution of flare fluxes and durations. From this intrinsic distribution, we determined the average flare detection efficiency for each XMM-Newton, Chandra, and Swift observation. We finally applied the Bayesian blocks algorithm on the arrival times of the flares corrected from the corresponding efficiency. Results: We confirm a constant overall flaring rate from 1999 to 2015 and a rise in the flaring rate by a factor of three for the most luminous and most energetic flares from 2014 August 31, I.e., about four months after the pericenter passage of the Dusty S-cluster Object (DSO)/G2 close to Sgr A*. In addition, we identify a decay of the flaring rate for the less luminous and less energetic flares from 2013 August and November, respectively, I.e., about 10 and 7 months before the pericenter passage of the DSO/G2 and 13 and 10 months before the rise in the bright flaring rate. Conclusions: The decay of the faint flaring rate is difficult to explain in terms of the tidal disruption of a dusty cloud since it occurred well before the pericenter passage of the DSO/G2, whose stellar nature is now well established. Moreover, a mass transfer from the DSO/G2 to Sgr A* is not required to produce the rise in the bright flaring rate since the energy saved by the decay of the number of faint flares during a long period of time may be later released by several bright flares during a shorter period of time.

Effects of propolis (Trigona sp.) extract supplementation on the growth and blood profile of Pangasius djambal

NASA Astrophysics Data System (ADS)

Nur, Firman M.; Nugroho, Rudy Agung; Fachmy, Syafrizal

2017-02-01

The study was conducted to examine the effects of propolis extract (PE) on the growth (G), growth rate (GR), specific growth rate (SGR) and blood profile (erythrocyte, leukocyte, and hemoglobin) of catfish (Pangasius djambal). five groups of fish with three replicates, containing 10 fish each group were fed various concentration of PE, viz 2 (P1), 4 (P2), 6 (P3), 8 (P4) and 10 (P5) g kg-1 of PE in a basal diet and compared to control (C) fish without PE at a rate 3% of body weight for 4 weeks. At the end of the trial, G, GR, SGR, and blood profile (erythrocyte, leukocyte, and hemoglobin) of all groups of fish were examined. The results showed that PE in the fish diet significantly increased G, GR, SGR, erythrocyte, hemoglobin while leukocyte was not affected by dietary any concentration of PE. The dietary 10 g kg-1 PE in the diet of fish showed the highest growth while the highest number of erythrocyte and hemoglobin activity was found in the fish fed 6 g kg-1 PE in the diet. These findings suggested that the inclusion of PE higher than 8 g kg-1 in the diet is beneficial to improve growth, growth rate, specific growth rate, erythrocyte and hemoglobin of Pangasius djambal.

The effects of season, aeration and light intensity on the performance of pacific whiteleg shrimp (Litopenaeus vannamei) polycultured with seaweed (Gracilaria verrucosa)

NASA Astrophysics Data System (ADS)

Susilowati, T.; Desrina; Hutabarat, J.; Anggoro, S.; Zainuri, M.; Sarjito; Basuki, F.; Yuniarti, T.

2018-04-01

This study was aimed to determine impact of stocking season, additional oxygen supply and light intensity on performance of pacific white leg shrimp (Litopenaeus vannamei) polycultured with seaweed Gracilaria verrucosa. Three sets of experiments were used and each experiment was conducted separately in 3 different season (factor W). Three factors and the interaction, that is, stocking seasons (W1: March-June;. W2 : July-October and W3 : November-February), Oxygen supply (O, with or without supply aeration of 6.5 ppm) and light intensity (with or without addition of light 640 lux) was observed. The experiment was conducted in 16 polyethilen net place in concrete tanks (1.2 m3). Shrimp (average weight 0.1 g and lenght 1.2 cm) with density 94 shrimp/m3 and seaweed 2.188 g/m3, cultured for 94 days. Data collected included absolute growth, specific growth rate (SGR), survival rate (SR) and biomass production of shrimp and seaweed. The result showed that culture period March to June, additonal light and suply DO gave the best result with shrimp absolute growth 13.23 g, SGR 5.09 %/day, SR 99.64 % and biomass production 1.256.36 g/m3. Absolute growth of G. verrucosa was 5.223.75g, SGR 268 %/day and biomass production 12.608.55 g/m3.

A Survey of CH3CN and HC3N in Protoplanetary Disks

NASA Astrophysics Data System (ADS)

Bergner, Jennifer B.; Guzmán, Viviana G.; Öberg, Karin I.; Loomis, Ryan A.; Pegues, Jamila

2018-04-01

The organic content of protoplanetary disks sets the initial compositions of planets and comets, thereby influencing subsequent chemistry that is possible in nascent planetary systems. We present observations of the complex nitrile-bearing species CH3CN and HC3N toward the disks around the T Tauri stars AS 209, IM Lup, LkCa 15, and V4046 Sgr as well as the Herbig Ae stars MWC 480 and HD 163296. HC3N is detected toward all disks except IM Lup, and CH3CN is detected toward V4046 Sgr, MWC 480, and HD 163296. Rotational temperatures derived for disks with multiple detected lines range from 29 to 73 K, indicating emission from the temperate molecular layer of the disk. V4046 Sgr and MWC 480 radial abundance profiles are constrained using a parametric model; the gas-phase CH3CN and HC3N abundances with respect to HCN are a few to tens of percent in the inner 100 au of the disk, signifying a rich nitrile chemistry at planet- and comet-forming disk radii. We find consistent relative abundances of CH3CN, HC3N, and HCN between our disk sample, protostellar envelopes, and solar system comets; this is suggestive of a robust nitrile chemistry with similar outcomes under a wide range of physical conditions.

[Effect of light intensity on the growth and digestive enzyme activity of juvenile sea cucumber Apostichopus japonicas under two kinds of culture methods].

PubMed

Wei, Zi-Zhong; Zhao, Wen

2014-01-01

The effects of light intensity (0, 1000, 2000 and 3000 1x) on the growth and digestive enzyme activity of juvenile sea cucumber Apostichopus japonicus under two kinds of culture methods (compound Chinese medicine preparation and microbial preparation) were studied. Results showed that the relative mass gain rate (WGR) and the specific growth rate (SGR) of juvenile sea cucumber were significantly affected by light intensity (P < 0.05) , and the orders of WGR and SGR (form high to low) of juvenile sea cucumber under different light intensities were 2000 1x > 1000 1x > 3000 1x > 0 1x. Under the same light intensity, the growth of juvenile sea cucumber under the two kinds of culture methods were significantly different (P < 0.05), with the WGR and SGR of the Chinese medicine treatment being greater than those of the microbial treatment. The light intensity also significantly affected the digestive enzyme activity of juvenile sea cucumber. The order of amylase and lipase activity was 2000 1x > 1000 1x > 3000 1x > 0 1x, while that of protease activity was 1000 1x > 2000 1x > 0 1x > 3000 1x. Under the same light intensity, the digestive enzyme activities of the Chinese medicine treatment were generally higher than those of the microbial treatment.