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1

Quiescent X-ray emission from an evolved brown dwarf ?  

E-print Network

I report on the X-ray detection of Gl569Bab. During a 25ksec Chandra observation the binary brown dwarf is for the first time spatially separated in X-rays from the flare star primary Gl569A. Companionship to Gl569A constrains the age of the brown dwarf pair to ~300-800 Myr. The observation presented here is only the second X-ray detection of an evolved brown dwarf. About half of the observing time is dominated by a large flare on Gl569Bab, the remainder is characterized by weak and non-variable emission just above the detection limit. This emission -- if not related to the afterglow of the flare -- represents the first detection of a quiescent corona on a brown dwarf, representing an important piece in the puzzle of dynamos in the sub-stellar regime.

B. Stelzer

2004-09-27

2

Comparison of the X-ray Emission from Two Quiescent Filament Eruptions  

NASA Astrophysics Data System (ADS)

Quiescent filament eruptions, solar eruptive events occurring outside of active regions, have yet to be studied in detail in the high-energy regime. Though similar to active region flares, quiescent filament eruptions typically occur in extended regions of relatively weak magnetic field strength and on longer time scales, allowing in-depth analyses to probe possible causes of the eruption. A previous study on a quiescent filament eruption on 2013 September 29 demonstrated the significance of emerging magnetic flux, which can perturb the magnetic structures that support the filament. We present a new solar eruptive event that occurred on 2014 November 1 on the southeast limb. This two-ribbon event occurred outside of any active regions and produced a coronal mass ejection with a velocity ~ 1800 km/s. Soft X-ray emission is observed by both GOES and RHESSI during the eruption, and the spatially resolved RHESSI data shows 3 - 9 keV emission correlated only with the eastward-expanding ribbon. Interaction between a compact, strong magnetic region and the eastern ribbon appears to be a likely catalyst of the X-ray flare. A similar interaction between magnetic structures appears to be responsible for the compact RHESSI X-ray source seen in the 2013 September 29 event. Our multiwavelength analyses of these quiescent filament eruptions and associated C-class flares will further our understanding of solar eruptive events.

Foord, Adi; Holman, Gordon D.

2015-04-01

3

The Soft Gamma Repeaters as Very Strongly Magnetized Neutron Stars. II. Quiescent Neutrino, X-Ray, and Alfven Wave Emission  

Microsoft Academic Search

We calculate the quiescent X-ray, neutrino, and Alfvén wave emission from a neutron star with a very strong magnetic field, Bdipole ˜ 1014-1015 G and Binterior (5-10) x 1015 G. These results are compared with observations of quiescent emission from the soft gamma repeaters and from a small class of anomalous X-ray pulsars that we have previously identified with such

Christopher Thompson; Robert C. Duncan

1996-01-01

4

X-ray and UV correlation in the quiescent emission of Cen X-4, evidence of accretion and reprocessing  

NASA Astrophysics Data System (ADS)

We conducted the first long-term (60 days), multiwavelength (optical, ultraviolet, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift observations, with the goal of understanding variability in the low mass X-ray binary Cen X-4 during quiescence. We found Cen X-4 to be highly variable in all energy bands on timescales from days to months, with the strongest quiescent variability a factor of 22 drop in the X-ray count rate in only 4 days. The X-ray, UV and optical (V band) emission are correlated on timescales down to less than 110 s. The shape of the correlation is a power law with index ? about 0.2-0.6. The X-ray spectrum is well fitted by a hydrogen NS atmosphere (kT = 59 - 80 eV) and a power law (with spectral index ? = 1.4 - 2.0), with the spectral shape remaining constant as the flux varies. Both components vary in tandem, with each responsible for about 50% of the total X-ray flux, implying that they are physically linked. We conclude that the X-rays are likely generated by matter accreting down to the NS surface. Moreover, based on the short timescale of the correlation, we also unambiguously demonstrate that the UV emission can not be due to either thermal emission from the stream impact point, or a standard optically thick, geometrically thin disc. The spectral energy distribution shows a small UV emitting region, too hot to arise from the accretion disk, that we identified as a hot spot on the companion star. Therefore, the UV emission is most likely produced by reprocessing from the companion star, indeed the vertical size of the disc is small and can only reprocess a marginal fraction of the X-ray emission. We also found the accretion disc in quiescence to likely be UV faint, with a minimal contribution to the whole UV flux.

Bernardini, F.; Cackett, E. M.; Brown, E. F.; D'Angelo, C.; Degenaar, N.; Miller, J. M.; Reynolds, M.; Wijnands, R.

2014-01-01

5

Strongly absorbed quiescent X-ray emission from the X-ray transient XTE J0421+56 (CI Cam) observed with XMM-Newton  

NASA Astrophysics Data System (ADS)

We have observed the X-ray transient XTE J0421+56 in quiescence with XMM-Newton. The observed spectrum is highly unusual being dominated by an emission feature at ~ 6.5 keV. The spectrum can be fit using a partially covered power-law and Gaussian line model, in which the emission is almost completely covered (covering fraction of 0.98 -0.06+0.02) by neutral material and is strongly absorbed with an \

Boirin, L.; Parmar, A. N.; Oosterbroek, T.; Lumb, D.; Orlandini, M.; Schartel, N.

2002-10-01

6

Resonant Cyclotron Scattering in Three Dimensions and the Quiescent Non-thermal X-ray Emission of Magnetars  

E-print Network

Although the surface of a magnetar is a source of bright thermal X-rays, its spectrum contains substantial non-thermal components. The X-ray emission is pulsed, with pulsed fractions that can be as high as ~ 70%. Several properties of magnetars indicate the presence of persistent, static currents flowing across the stellar surface and closing within the magnetosphere. The charges supporting these currents supply a significant optical depth to resonant cyclotron scattering in the 1-100 keV band. Here we describe a Monte Carlo approach to calculating the redistribution of thermal seed photons in frequency and angle by multiple resonant scattering in the magnetosphere. The calculation includes the full angular dependence of the cyclotron scattering cross section, the relativistic Doppler effect due to the motion of the charges, and allows for an arbitrary particle velocity distribution and magnetic field geometry. We construct synthetic spectra and pulse profiles for arbitrary orientations of the spin axis, magnetic axis, and line of sight, using a self-similar, twisted dipole field geometry, and assuming that the seed photons are supplied by single-temperature black body emission from the stellar surface. Pulse profiles and 1-10 keV spectra typical of AXPs are easily produced by this model, with pulsed fractions of ~ 50%. However, this model cannot reproduce the hard, rising energy spectra that are observed from SGRs during periods of activity, without overproducing the thermal emission peak. This suggests that the 1-100 keV emission of SGRs has a common origin with the hard X-ray emission detected from some AXPs above ~20 keV.

Rodrigo Fernandez; Christopher Thompson

2007-04-09

7

The Quiescent X-Ray Emission of Axps and Sgrs -- Powered by Accretion from a Fallback Disk  

NASA Astrophysics Data System (ADS)

Disk accretion as a means to explain the persistent and transient X-ray emission of anomalous X-ray pulsars (AXPs) has been first proposed by van Paradijs et al. 1995, by Chatterjee et al. 2000 and by Alpar 2001. This class of models was developed further in a series of papers of the Istanbul group (for a recent summary see Ertan et al. 2009), and can be applied to soft gamma ray repeaters (SGRs) as well, which have similar timing and spectral properties as AXPs. The required magnetic dipole fields to explain the temporal evolution of the neutron stars are in the range of 1012-1013 G. Highly super-Eddington bursts observed in SGRs, could be produced by the decay of super-strong magnetic fields (1014-1015 G) residing in localized multi-pole fields. The presence of magnetar multipole fields close to the surface of the star is compatible with the fallback disk model since the disk matter interacts with the magnetic dipole field.

Truemper, Joachim; Dennerl, Konrad; Kylafis, Nikos; Zezas, Andreas; Ertan, Ünal

2015-01-01

8

The long-term evolution of the X-ray pulsar XTE J1814-338: A receding jet contribution to the quiescent optical emission?  

NASA Astrophysics Data System (ADS)

Aims: We present a study of the quiescent optical counterpart of the accreting millisecond X-ray pulsar XTE J1814-338 that is aimed at unveiling the different components, which contribute to the quiescent optical emission of the system. Methods: We carried out multiband (BVR) orbital phase-resolved photometry of the system using the ESO Very Large Telescope (VLT) that is equipped with the FORS2 camera, covering about 70% of the 4.3 hour orbital period. Results: The optical light curves are consistent with a sinusoidal variability that are modulated with an orbital period with a semi-amplitude of 0.5-0.7 mag. They show evidence of a strongly irradiated companion star, which agrees with previous findings for this system. However, the observed colours cannot be accounted for by the companion star alone, suggesting the presence of an accretion disc during quiescence. The system seems to be fainter in all analysed bands compared to previous observations. The R band light curve displays a possible phase offset with respect to the B and V band. Through a combined fit of the multi-band light curve performed with a Markov chain Monte Carlo technique, we derive constraints on the companion star, disc fluxes, system distance, and companion star mass. Conclusions: The irradiation luminosity required to account for the observed day-side temperature of the companion star is consistent with the spin-down luminosity of a millisecond radio pulsar. Compared to our data with previous observations, which were collected over 5 years, the flux decrease and spectral evolution of the observed quiescent optical emission cannot be satisfactorily explained with the combined contribution of an irradiated companion star and of an accretion disc alone. The observed progressive flux decrease as the system gets bluer could be due to a continuum component that evolves towards a lower, bluer spectrum. While most of the continuum component is likely due to the disc, we do not expect it to become bluer in quiescence. Hence, we hypothesize that an additional component, such as synchrotron emission from a jet was significantly contributing in the data obtained earlier during quiescence and then progressively fading or moving its break frequency towards longer wavelengths. Based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 383.D-0730(A).

Baglio, M. C.; D'Avanzo, P.; Muñoz-Darias, T.; Breton, R. P.; Campana, S.

2013-11-01

9

X-ray emission from PTT stars  

NASA Astrophysics Data System (ADS)

We present preliminary results on new X-ray spectroscopic XMM/RGS observations of the visual binary nicknamed `Horace Horologii' (2RE J0241-53). The two stars are strong and very active X-ray emitters, and are members of an association of Post-T-Tauri stars. A detailed study (in particular in terms of chemical composition) is important for our understanding of the evolution from the T-Tauri phase, and to explain the origin of the X-ray emission in very young stars. The physical characteristics of the quiescent X-ray emission are described, and related to other stellar parameters such as photospheric abundances and the rotational period. Simultaneous ground-based optical spectroscopy and U-band photometric monitoring observations were obtained at the South African Astronomical Observatory.

del Zanna, G.; Bromage, G.; Foley, C.; Worters, H.; Mason, H.; Landini, M.

10

Monitoring X-Ray Emission from X-Ray Bursters  

NASA Technical Reports Server (NTRS)

The goal of this investigation was to use the All-Sky Monitor on the Rossi X-Ray Timing Explorer (RXTE) in combination with the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory to simultaneously measure the x-ray (2-12 keV) and hard x-ray (20-100 keV) emission from x-ray bursters. The investigation was successful. We made the first simultaneous measurement of hard and soft x-ray emission and found a strong anticorrelation of hard and soft x-ray emission from the X-Ray Burster 4U 0614+091. The monitoring performed under this investigation was also important in triggering target of opportunity observations of x-ray bursters made under the investigation hard x-ray emission of x-ray bursters approved for RXTE cycles 1 and 2. These observations lead to a number of papers on high-frequency quasi-periodic oscillations and on hard x-ray emission from the x-ray bursters 4U 0614+091 and 4U 1705-44.

Kaaret, Philip

1998-01-01

11

The Quiescent Counterpart of the Peculiar X-Ray Burster SAX J2224.9+5421  

NASA Astrophysics Data System (ADS)

SAX J2224.9+5421 is an extraordinary neutron star low-mass X-ray binary. It was discovered when it was exhibiting a ~= 10 s long thermonuclear X-ray burst, but it had faded to a 0.5-10 keV luminosity of L X <~ 8 × 1032(D/7.1 kpc)2 erg s-1 only ~= 8 hr later. It is generally assumed that neutron stars are quiescent (i.e., not accreting) at such intensity, raising questions about the trigger conditions of the X-ray burst and the origin of the faint persistent emission. We report on a sime51 ks XMM-Newton observation aimed at finding clues explaining the unusual behavior of SAX J2224.9+5421. We identify a likely counterpart that is detected at L X ~= 5 × 1031(D/7.1 kpc)2 erg s-1 (0.5-10 keV) and has a soft X-ray spectrum that can be described by a neutron star atmosphere model with a temperature of kT ? ~= 50 eV. This would suggest that SAX J2224.9+5421 is a transient source that was in quiescence during our XMM-Newton observation and experienced a very faint (ceasing) accretion outburst at the time of the X-ray burst detection. We consider one other potential counterpart that is detected at L X ~= 5 × 1032(D/7.1 kpc)2 erg s-1 and displays an X-ray spectrum that is best described by a power law with a photon index of ? ~= 1.7. Similarly hard X-ray spectra are seen for a few quiescent neutron stars and may be indicative of a relatively strong magnetic field or the occurrence of low-level accretion.

Degenaar, N.; Wijnands, R.; Miller, J. M.

2014-05-01

12

The quiescent state of the accreting X-ray pulsar SAX J2103.5+4545  

NASA Astrophysics Data System (ADS)

We present an X-ray timing and spectral analysis of the Be/X-ray binary SAX J2103.5+4545 at a time when the Be star's circumstellar disc had disappeared and thus the main reservoir of material available for accretion had extinguished. In this very low optical state, pulsed X-ray emission was detected at a level of LX ˜ 1033 erg s-1. This is the lowest luminosity at which pulsations have ever been detected in an accreting pulsar. The derived spin period is 351.13 s, consistent with previous observations. The source continues its overall long-term spin-up, which reduced the spin period by 7.5 s since its discovery in 1997. The X-ray emission is consistent with a purely thermal spectrum, represented by a blackbody with kT = 1 keV. We discuss possible scenarios to explain the observed quiescent luminosity and conclude that the most likely mechanism is direct emission resulting from the cooling of the polar caps, heated either during the most recent outburst or via intermittent accretion in quiescence.

Reig, P.; Doroshenko, V.; Zezas, A.

2014-12-01

13

THE QUIESCENT X-RAY PROPERTIES OF THE ACCRETING MILLISECOND X-RAY PULSAR AND ECLIPSING BINARY SWIFT J1749.4-2807  

SciTech Connect

Swift J1749.4-2807 is a transient neutron star low-mass X-ray binary that contains an accreting millisecond X-ray pulsar spinning at 518 Hz. It is the first of its kind that displays X-ray eclipses, which holds significant promise to precisely constrain the mass of the neutron star. We report on a {approx_equal} 105 ks long XMM-Newton observation performed when Swift J1749.4-2807 was in quiescence. We detect the source at a 0.5-10 keV luminosity of {approx_equal}1 Multiplication-Sign 10{sup 33}(D/6.7 kpc){sup 2} erg s{sup -1}. The X-ray light curve displays three eclipses that are consistent in orbital phase and duration with the ephemeris derived during outburst. Unlike most quiescent neutron stars, the X-ray spectrum can be adequately described with a simple power law, while a pure-hydrogen atmosphere model does not fit the data. We place an upper limit on the 0.01-100 keV thermal luminosity of the cooling neutron star of {approx}< 2 Multiplication-Sign 10{sup 33} erg s{sup -1} and constrain its temperature to be {approx}< 0.1 keV (for an observer at infinity). Timing analysis does not reveal evidence for X-ray pulsations near the known spin frequency of the neutron star or its first overtone with a fractional rms of {approx}< 34% and {approx}< 28%, respectively. We discuss the implications of our findings for dynamical mass measurements, the thermal state of the neutron star, and the origin of the quiescent X-ray emission.

Degenaar, N. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Patruno, A.; Wijnands, R., E-mail: degenaar@umich.edu [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands)

2012-09-10

14

X-ray line emission from Capella  

NASA Astrophysics Data System (ADS)

X-ray emission-line components from Mg, Si, S, and Fe are unambiguously detected from Capella with the solid-state spectrometer onboard the Einstein Observatory. The X-ray spectrum is inconsistent with an isothermal corona, and requires components between 6-million K and at least 24-million K for an adequate fit. An inhomogeneous corona in which the X-ray emitting plasma is confined to magnetically contained loops appears to be reconcilable with all of the experimental evidence.

Holt, S. S.; Boldt, E. A.; Serlemitsos, P. J.; White, N. E.; Becker, R. H.; Mushotzky, R. F.; Smith, B. W.

1979-11-01

15

X-ray Flare Associated with a Quiescent Filament Eruption and Coronal Mass Ejection  

NASA Astrophysics Data System (ADS)

To date, solar active regions are where most flares are found to occur. We present an analysis of multi-waveband observations of the large eruption of a 'quiescent' (outside of an active region) solar filament contemporaneous with X-ray emission. The eruption covers a 2-day time span, from 2013 September 29 to 2013 September 30. The event was observed using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the Solar Dynamics Observatory (SDO), and the Fermi Gamma-ray Space Telescope. Though not classified as a flare, the GOES class of the event was C1 and the X-ray light curves include a small impulsive-phase peak followed by a gradual-phase rise. The eruption produced a coronal mass ejection (CME) with a velocity of 1179 km/s. SDO Atmospheric Imaging Assembly (AIA) movies during the time span show that the filament lies outside any active region on the sun, and spans a length on the order of 600 arcseconds. Spatially resolved RHESSI emission during the gradual phase is found to come from an area along the post-eruption arcade, close to the westward expanding ribbon but confined to a length of only 150 arcseconds. No RHESSI emission is found along the eastward expanding ribbon. We infer the strength and geometry of the magnetic field during the eruption with the SDO Helioseismic and Magnetic Imager (HMI) and find a small (~ 100 arcseconds long) dipolar element within the filament channel that appears to be spatially correlated with the RHESSI emission. The dipolar element is observed to have magnetic field strengths as high as 1000 Gauss. The evolution of both the X-ray emission and AIA data support the notion that the flare was a consequence of magnetic reconnection between the dipole's magnetic field and the magnetic field supporting the filament. We conclude that solar eruptive events, which consist of both a flare and a CME, can occur outside active regions in association with a quiescent filament eruption if new, sufficiently strong magnetic flux emerges in the immediate area and reconnects with the filament's magnetic field.

Foord, Adi; Holman, Gordon D.

2015-01-01

16

THE X-RAY POLARIZATION SIGNATURE OF QUIESCENT MAGNETARS: EFFECT OF MAGNETOSPHERIC SCATTERING AND VACUUM POLARIZATION  

SciTech Connect

In the magnetar model, the quiescent non-thermal soft X-ray emission from anomalous X-ray pulsars and soft gamma repeaters is thought to arise from resonant Comptonization of thermal photons by charges moving in a twisted magnetosphere. Robust inference of physical quantities from observations is difficult, because the process depends strongly on geometry, and current understanding of the magnetosphere is not very deep. The polarization of soft X-ray photons is an independent source of information, and its magnetospheric imprint remains only partially explored. In this paper, we calculate how resonant cyclotron scattering would modify the observed polarization signal relative to the surface emission, using a multidimensional Monte Carlo radiative transfer code that accounts for the gradual coupling of polarization eigenmodes as photons leave the magnetosphere. We employ a globally twisted, self-similar, force-free magnetosphere with a power-law momentum distribution, assume a blackbody spectrum for the seed photons, account for general relativistic light deflection close to the star, and assume that vacuum polarization dominates the dielectric properties of the magnetosphere. The latter is a good approximation if the pair multiplicity is not much larger than unity. Phase-averaged polarimetry is able to provide a clear signature of the magnetospheric reprocessing of thermal photons and to constrain mechanisms generating the thermal emission. Phase-resolved polarimetry, in addition, can characterize the spatial extent and magnitude of the magnetospheric twist angle at {approx}100 stellar radii, and discern between uni- or bidirectional particle energy distributions, almost independently of every other parameter in the system. We discuss prospects for detectability with the Gravity and Extreme Magnetism (GEMS) mission.

Fernandez, Rodrigo; Davis, Shane W. [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States)

2011-04-01

17

X-ray emissions associated with thunderstorms  

NASA Astrophysics Data System (ADS)

We used an x-ray detector, including a NaI scintillator and a photomultiplier tube, to (1) compare x-ray emissions during thunderstorm and non-thunderstorm days and (2) examine x-ray emissions associated with specific lightning processes. X-ray data were acquired in 2010 and 2011 at the Lightning Observatory in Gainesville (LOG) [e.g., Mallick et al., 2011] in conjunction with corresponding electric field and electric field derivative waveforms (for thunderstorm days). Record length was 240 ms. The system was triggered on the electric field during thunderstorms and manually on non-thunderstorm days. The average x-ray rate on thunderstorm days, 124 counts per second, is higher than that, 95 counts per second, on non-thunderstorm days, and the difference is statistically significant. Non-thunderstorm days were defined as those with no thunderstorms within at least 15 km of LOG. X-ray emissions on these days are attributed to cosmic rays and natural Earth radioactivity. Fig. 1 shows average x-ray counts per second in different energy ranges for both thunderstorm and non-thunderstorm days. On July 31st, 2011, we recorded x-ray bursts associated with three close multiple-stroke natural lightning flashes along with their electric field and electric field derivative waveforms. These flashes transported negative charge to ground. The total number of bursts is six, and they are all apparently associated with stepped and dart-stepped leaders. Interestingly, some subsequent-stroke leaders are more prolific x-ray producers than first-stroke leaders. Also, for the same leader, some steps are accompanied by pronounced x-ray signals, while others are not. Reference Mallick, S. et al., On Remote Measurements of Lightning Peak Currents, XIV International Conference on Atmospheric Electricity (ICAE), August 08-12, 2011, Rio de Janeiro, Brazil.

Mallick, S.; Rakov, V. A.; Dwyer, J. R.; Hill, J. D.

2011-12-01

18

X-ray line emission from Capella  

NASA Astrophysics Data System (ADS)

X-ray emission line components from Mg, Si, S and Fe were unambiguously detected from Capella with the Solid-State Spectrometer onboard the Einstein Observatory. The X-ray spectrum is inconsistent with an isothermal corona, and requires components between 6,000,000 K and at least 24,000,000 K for an adequate fit. An inhomogeneous corona in which the X-ray emitting plasma is confined to magnetically-contained loops appears to be reconcilable with all of the experimental evidence.

Holt, S. S.; White, N. E.; Becker, R. H.; Boldt, E. A.; Mushotzky, R. F.; Serlemitsos, P. J.; Smith, B. W.

1979-06-01

19

ASCA Observation of the Quiescent X-ray Counterpart to SGR 1627-41  

NASA Technical Reports Server (NTRS)

We present a 2-10 keV ASCA (Advanced Satellite for Cosmology and Astrophysics) observation of the field around the soft gamma repeater SGR 1627-41. A quiescent X-ray source, whose position is consistent both with that of a recently discovered BeppoSAX X-ray source and with the Interplanetary Network localization for this soft gamma repeater, was detected in this observation. In 2-10 keV X-rays, the spectrum of the X-ray source may be fit equally well by a power-law, blackbody, or bremsstrahlung function, with unabsorbed flux equal to approximately 5 x 10(exp -12) ergs cm(exp -2) s(exp -1). We do not confirm a continuation of a fading trend in the flux, and we find no evidence for periodicity, both of which were noted in the earlier BeppoSAX observations.

Hurley, K.; Strohmayer, T.; Li, P.; Kouveliotou, C.; Woods, P.; VanParadijs, J.; Murakami, T.; Hartmann, D.; Smith, I.; Ando, M.

2002-01-01

20

Optical, Far-Infrared and X-ray Properties of the FIR quiescent SC Galaxy NGC 247  

NASA Astrophysics Data System (ADS)

We present a multi-wavelength study of the large Sc galaxy, NGC 247 in the Sculptor group. Optical (B, I and H? ) CCD, Far-Infrared (FIR) (IRAS 60 and 100microns), and X-ray (ROSAT PSPC, 0.2-2.4keV) images are combined to investigate local and global emission properties. NGC 247 is unique since it has the lowest LFIR, and FIR/B ratio of the large (D25B>8(') ) Sc's observed by IRAS. It may be considered the best example of a FIR quiescent galaxy, although its 60/100microns colour (dust temperature) is not abnormal for an Sc. There are 4-5 X-ray sources (LX ~ 5E37--3E38 erg s(-1) ) located in the disk of the galaxy. These sources are not coincident with the regions of 60microns emission, consistent with the interpretation that the X-ray sources are old population binary systems. Constraints are put on X-ray diffuse emission and source variability.

Mackie, G.; Ikebe, Y.; Fabbiano, G.; Kim, D.-W.

1994-05-01

21

X-ray emission processes in stars  

E-print Network

A decade of X-ray stellar observations with Chandra and XMM-Newton has led to significant advances in our understanding of the physical processes at work in hot (magnetized) plasmas in stars and their immediate environment, providing new perspectives and challenges, and in turn the need for improved models. The wealth of high-quality stellar spectra has allowed us to investigate, in detail, the characteristics of the X-ray emission across the HR diagram. Progress has been made in addressing issues ranging from classical stellar activity in stars with solar-like dynamos (such as flares, activity cycles, spatial and thermal structuring of the X-ray emitting plasma, evolution of X-ray activity with age), to X-ray generating processes (e.g. accretion, jets, magnetically confined winds) that were poorly understood in the pre-Chandra/XMM-Newton era. I discuss the progress made in the study of high energy stellar physics and its impact in a wider astrophysical context, focusing on the role of spectral diagnostics no...

Testa, Paola

2010-01-01

22

Coronal X-ray Emission from the Stellar Companions to Transiently Accreting Black Holes  

NASA Astrophysics Data System (ADS)

Many neutron stars and black holes are in binaries where the mass transfer rate onto the compact object is highly variable. X-ray observations of these transients in quiescence (Lx< 1034 \\ erg \\ s-1) have found that the binaries harboring black holes are much fainter than those that contain a neutron star. Narayan and collaborators postulated that the faint X-ray emission from black hole binaries was powered by an advection dominated accretion flow (ADAF). The subsequent ADAF modeling requires that an appreciable fraction of the constant Roche-lobe overflow into the outer disk proceeds into the black hole during ``quiescence''. A robust and nearly uniform quenching mechanism must then be hypothesized for the neutron star binaries, as comparably large accretion rates would lead to luminosities in excess of 1036 \\ erg \\ s-1 in quiescence. We explore an alternative explanation for the quiescent X-ray emission from the black hole systems: coronal emission from the rapidly rotating optical companion. This is commonly observed and well studied in other tidally locked binaries. We show that two of the three X-ray detected black hole binaries (A0620-00 and GRO J1655-40) exhibit X-ray fluxes entirely consistent with coronal emission, and predict expected levels of coronal emission from other black hole binaries. One black hole system (V404 Cyg) is too X-ray bright to be explained as coronal emission, and remains a candidate for ADAFs in quiescence. The quiescent X-ray emission from all of the neutron star binaries is far too bright for coronal emission. It might be that all SXT's have variable accretion rates in quiescence and that the basal quiescent X-ray flux is set by either coronal emission from the companion or -- when present -- by thermal emission from the neutron star.

Bildsten, L.; Rutledge, R. E.

2000-10-01

23

X-ray emission from Saturn  

E-print Network

We report the first unambiguous detection of X-ray emission originating from Saturn with a Chandra observation, duration 65.5 ksec with ACIS-S3. Beyond the pure detection we analyze the spatial distribution of X-rays on the planetary surface, the light curve, and some spectral properties. The detection is based on 162 cts extracted from the ACIS-S3 chip within the optical disk of Saturn. We found no evidence for smaller or larger angular extent. The expected background level is 56 cts, i.e., the count rate is (1.6 +- 0.2) 10^-3 cts/s. The extracted photons are rather concentrated towards the equator of the apparent disk, while both polar caps have a relative photon deficit. The inclination angle of Saturn during the observation was -27 degrees, so that the northern hemisphere was not visible during the complete observation. In addition, it was occulted by the ring system. We found a small but significant photon excess at one edge of the ring system. The light curve shows a small dip twice at identical phases, but rotational modulation cannot be claimed at a significant level. Spectral modeling results in a number of statistically, but not necessarily physically, acceptable models. The X-ray flux level we calculate from the best-fit spectral models is 6.8 10^-15 erg/cm^2/s (in the energy interval 0.1-2keV), which corresponds to an X-ray luminosity of 8.7 10^14 erg/s. A combination of scatter processes of solar X-rays requires a relatively high albedo favoring internal processes, but a definitive explanation remains an open issue.

J. -U. Ness; J. H. M. M. Schmitt; S. J. Wolk; K. Dennerl; V. Burwitz

2004-01-14

24

X-Ray Emission from "Uranium" Stars  

NASA Technical Reports Server (NTRS)

The project aims to secure XMM observations of two targets with extremely low abundances of the majority of heavy elements (e.g., log[Fe/H] $\\sim$-4), but that show absorption lines of uranium. The presence of an r-process element such as uranium requires a binary star system in which the companion underwent a supernova explosion. A binary star system raises the distinct possibility of the existence of a compact object, most likely a neutron star, in the binary, assuming it survived the supernova blast. The presence of a compact object then suggests X-ray emission if sufficient matter accretes to the compact object. The observations were completed less than one year ago following a series of reobservations to correct for significant flaring that occurred during the original observations. The ROSAT all-sky survey was used to report on the initial assessment of X-ray emission from these objects; only upper limits were reported. These upper limits were used to justify the XMM observing time, but with the expectation that upper limits would merely be pushed lower. The data analysis hinges critically on the quality and degree of precision with which the background is handled. During the past year, I have spent some time learning the ins and outs of XMM data analysis. In the coming year, I can apply that learning to the analysis of the 'uranium' stars.

Schlegel, Eric; Mushotzky, Richard (Technical Monitor)

2005-01-01

25

Constraints on relativistic jets in quiescent black hole X-ray binaries from broad-band spectral modelling  

NASA Astrophysics Data System (ADS)

The nature of black hole jets at the lowest detectable luminosities remains an open question, largely due to a dearth of observational constraints. Here, we present a new, nearly simultaneous broad-band spectrum of the black hole X-ray binary (BHXB) XTE J1118+480 at an extremely low Eddington ratio (LX ˜ 10-8.5LEdd). Our new spectral energy distribution (SED) includes the radio, near-infrared, optical, ultraviolet, and X-ray wavebands. XTE J1118+480 is now the second BHXB at such a low Eddington ratio with a well-sampled SED, thereby providing new constraints on highly sub-Eddington accretion flows and jets, and opening the door to begin comparison studies between systems. We apply a multizone jet model to the new broad-band SED, and we compare our results to previous fits to the same source using the same model at 4-5 decades higher luminosity. We find that after a BHXB transitions to the so-called quiescent spectral state, the jet base becomes more compact (by up to an order of magnitude) and slightly cooler (by at least a factor of 2). Our preferred model fit indicates that jet particle acceleration is much weaker after the transition into quiescence. That is, accelerated non-thermal particles no longer reach high enough Lorentz factors to contribute significant amounts of synchrotron X-ray emission. Instead, the X-ray waveband is dominated by synchrotron self-Compton emission from a population of mildly relativistic electrons with a quasi-thermal velocity distribution that are associated with the jet base. The corresponding (thermal) synchrotron component from the jet base emits primarily in the infrared through ultraviolet wavebands. Our results on XTE J1118+480 are consistent with broad-band modelling for A0620-00 (the only other comparably low Eddington ratio BHXB with a well-sampled SED) and for Sgr A* (the quiescent supermassive black hole at the Galactic centre). The above could therefore represent a canonical baseline geometry for accreting black holes in quiescence. We conclude with suggestions for future studies to further investigate the above scenario.

Plotkin, Richard M.; Gallo, Elena; Markoff, Sera; Homan, Jeroen; Jonker, Peter G.; Miller-Jones, James C. A.; Russell, David M.; Drappeau, Samia

2015-02-01

26

X-ray emission in heavy-ion collisons  

Microsoft Academic Search

Results from several investigations of the X-ray emission in heavy-ion collisions are presented. Areas covered include; spectra of K alpha X-rays from 64 MeV sulfur ions traveling in solids; foil-excited K alpha X-ray transitions in few-electron sulfur ions; high resolution study of the target thickness dependence of X-ray emmision from 65 MeV sulfur ions; dynamic screening of highly stripped sulfur

R. L. Watson

1980-01-01

27

X-Ray Emission in the Solar System  

NASA Astrophysics Data System (ADS)

Many objects in the solar system produce x-rays, including the Sun, Venus, Earth, Mars, Jupiter, and comets. A number of emission mechanisms account for this x-ray emission including scattering and fluorescence of solar x-rays, impact excitation of atoms and molecules by energetic electrons and ions, and by charge transfer of highly charged ions with neutrals. Atomic processes play a key role in all these emission mechanisms. A brief review is provided of x-ray sources in the solar system and the emission mechanisms that are thought to be responsible for this emission.

Cravens, T. E.

2002-10-01

28

X-ray emission from compact groups of galaxies  

NASA Technical Reports Server (NTRS)

The existence of very compact groups, or 'poor clusters,' of galaxies as a category of X-ray source is reported. By analogy with X-ray emission from clusters of galaxies, it is assumed that the extended X-ray emission is due to thermal bremsstrahlung from hot gas in the groups. The derived X-ray temperatures, luminosities, and sizes are similar to those for X-ray emitting, rich clusters of galaxies. It is inferred that these groups are in a late evolutionary stage because of the presence of a dominant galaxy, the absence of spiral galaxies, and the short cooling time inferred for 2A 0335 + 096.

Schwartz, D. A.; Schwarz, J.; Tucker, W.

1980-01-01

29

Deep Chandra/EVLA observations of the quiescent black hole X-ray binary XTE J1118+480  

NASA Astrophysics Data System (ADS)

We request coordinated Chandra/EVLA observations - to be complemented by IR-optical & UV monitoring - of the quiescent black hole X-ray binary XTE J1118+480, the one source for which we can realistically hope to secure a simultaneous radio/X-ray detection at the lowest luminosity levels. The system SED will be fitted with a radiative jet-corona model which has been successfully applied to higher Eddington ratio black hole X-ray binaries, enabling us to: i) measure and compare the jet vs. accretion radiated luminosity; ii) test the acceleration physics of jets over different accretion regimes. Concurrently, these observations will probe the empirical radio/X-ray correlation for hard and quiescent state sources down to the lowest Eddington ratios.

Gallo, Elena

2012-09-01

30

Quasi-monochromatic field-emission x-ray source  

SciTech Connect

By favoring the L-peak emission over the bremsstrahlung part, direct quasi-monochromatic soft x-ray emission has been obtained with a field emission (FE) x-ray source. The electron impact x-ray setup uses an arrayed cathode of carbon nanopearl FE tips as a stable cold electron source within a vacuum of 10{sup -6}-10{sup -7} Torr. The high brightness of the FE e-beam coupled with the array structure of the cold cathode allows a smoother control of the x-ray emission intensity. The wavelength of the x-ray source can be modified by the choice of target materials. Using Mo as the target material, the x-ray emission shows a peak centered at 2.45 keV with a monochromaticity between 75% and 55% and a FWHM in the range of 450 eV.

Diop, Babacar; Binh, Vu Thien [LPMCN, University of Lyon 1, Villeurbanne 69622 (France)

2012-09-15

31

X-Ray Emission from Protostellar Jets  

NASA Technical Reports Server (NTRS)

The goals of this program were to identify the termination shocks in several parsec-scale protostellar jets through the thermal soft X-rays emitted by the high-velocity terminal shock waves, and to assess the impact these outflows have on the surrounding interstellar and intercloud medium. The terminal shock waves that plow into the undisturbed interstellar medium may have shock velocities commensurate with the observed space motions of several hundred km s(exp -1). Such shocks will heat and ionize the interstellar medium, perhaps creating large ovoid bubbles of hot gas. Identifying the location of the terminal shocks in these outflows would also allow us to place constraints on the ages of these outflows, and hence the duration of the mass-loss phase that accompanies the formation of a star. We targeted four outflows where the outer optical shock waves are projected against low-extinction backgrounds. From the two dozen or so parsec-scale flows known, we chose those that have the highest velocities, brightest optical counterparts, and/or the richest concentration of shock waves in a small area on the sky. Four giant HH flows have been observed with the ROSAT HRI at Priority A for 30 ksec each. Results: Unfortunately, we failed to detect X-ray emission from the terminal bow shocks of the giant HH flows using the ROSAT HRI. The reasons are likely to be: (1) The shock velocities may be too low to emit in the soft X-rays. (2) The sensitivity of the HRI is too low to detect the diffuse emission. The fields that we observed were chosen to be low extinction sight-lines, with the consequence that the tenuous media into which the outer bow shocks are propagating produce low fluxes. Despite the failure to achieve the primary science goals, we have identified in each image a half a dozen or so point-source young stellar objects. The HRI images have been very useful for discerning potential outflow sources and are being combined with optical, near-IR, and radio imaging data of each outflow field. The first paper on L1551 NE is currently in preparation.

Morse, Jon A.; McCray, Dick; Bally, John; Devine, David

1998-01-01

32

Theory of x-ray emission of conjugated molecules  

Microsoft Academic Search

A theory of nonresonant x-ray emission spectra of conjugated molecules is presented. The role of relaxation effects on the spectral shape of x-ray emission is advanced and examined in detail for the transpolyenes. In some contrast to unconjugated systems, the relaxation of valence charge around the core hole is shown to influence the distribution of x-ray intensities significantly. Site and

Faris Gel’mukhanov; Li Yang

1996-01-01

33

X-Ray and Extreme Ultraviolet Emission from Comets  

Microsoft Academic Search

The discovery of high energy X-ray emission in 1996 from C\\/1996 B2 (Hyakutake) has created a surprising new class of X-ray emitting objects. The original discovery (Lisse et al., 1996) and subsequent detection of X-rays from 17 other comets (Table 1) have shown that the very soft (E < 1 keV) emission is due to an interaction between the solar

C. M. Lisse; T. E. Cravens

34

X-ray emission properties of galaxies in Abell 3128  

E-print Network

We use archival Chandra X-ray Observatory data to investigate X-ray emission from early-type galaxies in the rich z=0.06 cluster Abell 3128. By combining the X-ray count-rates from an input list of optically-selected galaxies, we obtain a statistical detection of X-ray flux, unbiased by X-ray selection limits. Using 87 galaxies with reliable Chandra data, X-ray emission is detected for galaxies down to M_B ~ -19.0, with only an upper limit determined for galaxies at M_B ~ -18.3. The ratio of X-ray to optical luminosities is consistent with recent determinations of the low-mass X-ray binary content of nearby elliptical galaxies. Taken individually, in contrast, we detect significant (3sigma) flux for only six galaxies. Of these, one is a foreground galaxy, while two are optically-faint galaxies with X-ray hardness ratios characteristic of active galactic nuclei. The remaining three detected galaxies are amongst the optically-brightest cluster members, and have softer X-ray spectra. Their X-ray flux is higher than that expected from X-ray binaries, by a factor 2-10; the excess suggests these galaxies have retained their hot gaseous haloes. The source with the highest L_X / L_B ratio is of unusual optical morphology with prominent sharp-edged shells. Notwithstanding these few exceptions, the cluster population overall exhibits X-ray properties consistent with their emission being dominated by X-ray binaries. We conclude that in rich cluster environments, interaction with the ambient intra-cluster medium acts to strip most galaxies of their hot halo gas.

Russell J. Smith

2003-07-15

35

Reabsorption of Soft X-Ray Emission at High X-Ray Free-Electron Laser Fluences  

NASA Astrophysics Data System (ADS)

We report on oxygen K-edge soft x-ray emission spectroscopy from a liquid water jet at the Linac Coherent Light Source. We observe significant changes in the spectral content when tuning over a wide range of incident x-ray fluences. In addition the total emission yield decreases at high fluences. These modifications result from reabsorption of x-ray emission by valence-excited molecules generated by the Auger cascade. Our observations have major implications for future x-ray emission studies at intense x-ray sources. We highlight the importance of the x-ray pulse length with respect to the core-hole lifetime.

Schreck, Simon; Beye, Martin; Sellberg, Jonas A.; McQueen, Trevor; Laksmono, Hartawan; Kennedy, Brian; Eckert, Sebastian; Schlesinger, Daniel; Nordlund, Dennis; Ogasawara, Hirohito; Sierra, Raymond G.; Segtnan, Vegard H.; Kubicek, Katharina; Schlotter, William F.; Dakovski, Georgi L.; Moeller, Stefan P.; Bergmann, Uwe; Techert, Simone; Pettersson, Lars G. M.; Wernet, Philippe; Bogan, Michael J.; Harada, Yoshihisa; Nilsson, Anders; Föhlisch, Alexander

2014-10-01

36

Reabsorption of soft x-ray emission at high x-ray free-electron laser fluences.  

PubMed

We report on oxygen K-edge soft x-ray emission spectroscopy from a liquid water jet at the Linac Coherent Light Source. We observe significant changes in the spectral content when tuning over a wide range of incident x-ray fluences. In addition the total emission yield decreases at high fluences. These modifications result from reabsorption of x-ray emission by valence-excited molecules generated by the Auger cascade. Our observations have major implications for future x-ray emission studies at intense x-ray sources. We highlight the importance of the x-ray pulse length with respect to the core-hole lifetime. PMID:25375708

Schreck, Simon; Beye, Martin; Sellberg, Jonas A; McQueen, Trevor; Laksmono, Hartawan; Kennedy, Brian; Eckert, Sebastian; Schlesinger, Daniel; Nordlund, Dennis; Ogasawara, Hirohito; Sierra, Raymond G; Segtnan, Vegard H; Kubicek, Katharina; Schlotter, William F; Dakovski, Georgi L; Moeller, Stefan P; Bergmann, Uwe; Techert, Simone; Pettersson, Lars G M; Wernet, Philippe; Bogan, Michael J; Harada, Yoshihisa; Nilsson, Anders; Föhlisch, Alexander

2014-10-10

37

From Radio to X-ray: The Quiescent Atmosphere of the dMe Flare Star EV Lacertae  

E-print Network

We report on multi-wavelength observations spanning radio to X-ray wavelengths of the M dwarf flare star, EV Lacertae, probing the characteristics of the outer atmospheric plasma from the upper chromosphere to the corona. We detect the star at a wavelength of 2 cm (15 GHz) for the first time. UV and FUV line profiles show evidence of nonthermal broadening, and the velocity width appear to peak at lower temperatures than in the Sun; this trend is confirmed in another active M dwarf flare star. Electron density measurements indicate nearly constant electron pressures between $\\log T=$5.2 and 6.4. At higher coronal temperatures, there is a sharp increase of two orders of magnitude in density (n$_{e}\\sim10^{13}$ cm$^{-3}$ at $\\log T=$6.9). X-ray, EUV, FUV and NUV spectra constrain the DEM from the upper chromosphere through the corona. The coronal pressures are inconsistent with the assumption of hydrostatic equilibrium, either through EM modeling or application of scaling laws, and imply large conductive loss rates and a large energy input at the highest temperatures. The timescales for radiative and conductive losses in EV Lac's upper atmosphere imply that significant continued heating must occur for the corona to maintain its quiescent properties. The high frequency radio detection requires the high temperature X-ray-emitting coronal plasma to be spatially distinct from the radio emission source. Length scales in the low-temperature corona are markedly larger than those in the high-temperature corona, further suggestions of an inhomogeneous mixture of thermal and nonthermal coronal plasma.

R. A. Osten; S. L. Hawley; J. Allred; C. M. Johns-Krull; A. Brown; G. M. Harper

2006-04-11

38

Low-luminosity X-ray sources and the Galactic ridge X-ray emission  

NASA Astrophysics Data System (ADS)

Using the XMM-Newton slew survey, we construct a hard-band selected sample of low-luminosity Galactic X-ray sources. Two source populations are represented, namely coronally active stars and binaries (ASBs) and cataclysmic variables (CVs), with X-ray luminosities collectively spanning the range 1028-34 erg s-1 (2-10 keV). We derive the 2-10 keV X-ray luminosity function (XLF) and volume emissivity of each population. Scaled to the local stellar mass density, the latter is found to be 1.08 ± 0.16 × 1028 and 2.5 ± 0.6 × 10^{27} {erg s}^{-1} M_{{?}}^{-1}, for the ASBs and CVs, respectively, which in total is a factor of 2 higher than previous estimates. We employ the new XLFs to predict the X-ray source counts on the Galactic plane at l = 28.5° and show that the result is consistent with current observational constraints. The X-ray emission of faint, unresolved ASBs and CVs can account for a substantial fraction of the Galactic ridge X-ray emission (GRXE). We discuss a model in which ˜80 per cent of the 6-10 keV GRXE intensity is produced in this way, with the remainder attributable to X-ray scattering in the interstellar medium and/or young Galactic source populations. Much of the hard X-ray emission attributed to the ASBs is likely to be produced during flaring episodes.

Warwick, R. S.

2014-11-01

39

X-RAY POINT-SOURCE POPULATIONS CONSTITUTING THE GALACTIC RIDGE X-RAY EMISSION  

SciTech Connect

Apparently diffuse X-ray emission has been known to exist along the central quarter of the Galactic Plane since the beginning of X-ray astronomy; this is referred to as the Galactic Ridge X-ray emission (GRXE). Recent deep X-ray observations have shown that numerous X-ray point sources account for a large fraction of the GRXE in the hard band (2-8 keV). However, the nature of these sources is poorly understood. Using the deepest X-ray observations made in the Chandra bulge field, we present the result of a coherent photometric and spectroscopic analysis of individual X-ray point sources for the purpose of constraining their nature and deriving their fractional contributions to the hard-band continuum and Fe K line emission of the GRXE. Based on the X-ray color-color diagram, we divided the point sources into three groups: A (hard), B (soft and broad spectrum), and C (soft and peaked spectrum). The group A sources are further decomposed spectrally into thermal and non-thermal sources with different fractions in different flux ranges. From their X-ray properties, we speculate that the group A non-thermal sources are mostly active galactic nuclei and the thermal sources are mostly white dwarf (WD) binaries such as magnetic and non-magnetic cataclysmic variables (CVs), pre-CVs, and symbiotic stars, whereas the group B and C sources are X-ray active stars in flares and quiescence, respectively. In the log N-log S curve of the 2-8 keV band, the group A non-thermal sources are dominant above Almost-Equal-To 10{sup -14} erg cm{sup -2} s{sup -1}, which is gradually taken over by Galactic sources in the fainter flux ranges. The Fe K{alpha} emission is mostly from the group A thermal (WD binaries) and the group B (X-ray active stars) sources.

Morihana, Kumiko [Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)] [Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Tsujimoto, Masahiro; Ebisawa, Ken [Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, 3-1-1 Yoshino-dai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)] [Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, 3-1-1 Yoshino-dai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Yoshida, Tessei, E-mail: morihana@crab.riken.jp [National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan)] [National Astronomical Observatory of Japan, 2-21-1, Osawa, Mitaka, Tokyo 181-8588 (Japan)

2013-03-20

40

Diffuse X-ray emission in spiral galaxies  

E-print Network

We compare the soft diffuse X-ray emission from Chandra images of 12 nearby intermediate inclination spiral galaxies to the morphology seen in Halpha, molecular gas, and mid-infrared emission. We find that diffuse X-ray emission is often located along spiral arms in the outer parts of spiral galaxies but tends to be distributed in a rounder morphology in the center. The X-ray morphology in the spiral arms matches that seen in the mid-infrared or Halpha and so implies that the X-ray emission is associated with recent active star formation. We see no strong evidence for X-ray emission trailing the location of high mass star formation in spiral arms. However, population synthesis models predict a high mechanical energy output rate from supernovae for a time period that is about 10 times longer than the lifetime of massive ionizing stars, conflicting with the narrow appearance of the arms in X-rays. The fraction of supernova energy that goes into heating the ISM must depend on environment and is probably higher near sites of active star formation. The X-ray estimated emission measures suggest that the volume filling factors and scale heights are high in the galaxy centers but low in the outer parts of these galaxies. The differences between the X-ray properties and morphology in the centers and outer parts of these galaxies suggest that galactic fountains operate in outer galaxy disks but that winds are primarily driven from galaxy centers.

K. Tyler; A. C. Quillen; A. La Page; G. H. Rieke

2003-08-06

41

X-ray emission from magnetic cataclysmic variables  

NASA Astrophysics Data System (ADS)

I present a brief review of the present status of X-ray emission from Magnetic Cataclysmic Variables (MCVs). A short introduction to the types of Cataclysmic Variables (CVs) is followed by a presentation of some of the properties of the two types of MCVs - Polars and Intermediate Polars (IPs) as seen in X-rays. Finally X-ray spectra of MCVs and future prospects of their studies are discussed.

Singh, K. P.

42

X-Ray Emission from Compact Sources  

SciTech Connect

This paper presents a review of the physical parameters of neutron stars and black holes that have been derived from X-ray observations. I then explain how these physical parameters can be used to learn about the extreme conditions occurring in regions of strong gravity, and present some recent evidence for relativistic effects seen in these systems. A glossary of commonly used terms and a short tutorial on the names of X-ray sources are also included.

Cominsky, L

2004-03-23

43

X-ray emission from high temperature plasmas  

NASA Technical Reports Server (NTRS)

The physical processes occurring in plasma focus devices were investigated with particular emphasis on X-ray emission. Topics discussed include: trajectories of high energy electrons; detection of ion trajectories; spatial distribution of neutron emission; space and time resolved emission of hard X-rays from a plasma focus; the staged plasma focus as a variation of the hypocloidal pinch; formation of current sheets in a staged plasma focus; and X-ray and neutron emission from a staged plasma focus. The possibility of operating dense plasma-focus type devices in multiple arrays beyond the scaling law for a single gun is discussed.

Harries, W. L.

1977-01-01

44

Evidence for Optical Flares in Quiescent Soft X-Ray Transients  

NASA Astrophysics Data System (ADS)

We present the results of high time resolution optical photometry of five quiescent soft X-ray transients (SXTs): V404 Cyg, A0620-00, J0422+32, GS 2000+25, and Cen X-4. We detect fast optical variations superposed on the secondary star's double-humped ellipsoidal modulation. The variability resembles typical flare activity and has amplitudes ranging from 0.06 to 0.6 mag. Flares occur on timescales of minutes to a few hours, with no dependency on orbital phase, and contribute ~19%-46% to the total veiling observed in the R band. We find that the observed level of flaring activity is veiled by the light of the companion star, and therefore, systems with cool companions (e.g., J0422+32) exhibit stronger variability. After correcting for this dilution, we do not find any correlation between the flaring activity and fundamental system parameters. We find no underlying coherent periods in the data, only quasi-periodic variations ranging between 30 and 90 minutes for the short-period SXTs and longer than 1 hr for V404 Cyg. The power-law index of the power spectra is consistent with what is observed at X-rays wavelengths, i.e., a 1/f distribution, which is compatible with the cellular automaton model. Our observed R'-band luminosities, which are in the range 1031-1033 ergs s-1, are too large to be due to chromospheric activity in the rapidly rotating companions. Since the typical timescale of the flares increases with orbital period, they are most likely produced in the accretion disk. The associated dynamical (Keplerian) timescales suggest that flares are produced at ~0.3Rd-0.7Rd. Possible formation mechanisms are magnetic loop reconnection events in the disk or, less likely, optical reprocessing of X-ray flares. In the former scenario, the maximum duration of the flares suggests that the outer disk is responsible for the flare events and so allows us to constrain the sharing timescale to ?~(5-6)?-1K.

Zurita, C.; Casares, J.; Shahbaz, T.

2003-01-01

45

Confirmation of IGR J01363 plus 6610 as a Be X-Ray Binary with Very Low Quiescent X-Ray Luminosity  

NASA Technical Reports Server (NTRS)

The field containing the candidate High Mass X-ray Binary IGR J01 363+6610 was observed by XMM-Newton on 2009 July 31 for 28 ks. A Be star was previously suggested as the possible counterpart of the INTEGRAL source, and although Chandra, during a 2007 observation, did not detect an X-ray source at the position of the Be star, we find a variable source (XMMU 101 3549.5+661243) with an average X-ray flux of 2 x 10(exp -13)ergs/sq cm/s (0.2-12 keV, unabsorbed) at this position with XMM-Newton. The spectrum of this source is consistent with a hard power law with a photon index of r = 1.4+/-0.3 and a column density of N(sub H) = (15(+0.7/-0.5)) x 10(exp 22)/sq cm (90% confidence errors). These results, along with our optical investigation of other X-ray sources in the field, make the association with the Be star very likely, and the 2 kpc distance estimate for the Be star indicates an X-ray luminosity of 9.1 x 10(exp 31) ergs/s. This is lower than typical for a Be X-ray binary, and the upper limit on the luminosity was even lower ( < 1.4 x 10(exp 3)ergs/s assuming the same spectral model) during the Chandra observation. We discuss possible implications of the very low quiescent luminosity for the physical properties of IGR 101363+6610.

Tomsick, John A.; Heinke, Craig; Halpern, Jules; Kaaret, Philip; Chaty, Sylvain; Rodriguez, Jerome; Bodaghee, Arash

2011-01-01

46

Intensive X-ray emission bursts during thunderstorms  

NASA Astrophysics Data System (ADS)

The intensive X-ray emission during thunderstorms was studied at a height of 3340 m above sea level. For the first time, short-time (1-5 min) bursts of X-ray emission were observed. The bursts are highly correlated over a wide space region (about 0.5 km). The main component of X-ray emission in bursts has energies between 50-80 keV. The observed bursts could be attributed to the bremsstrahlung determined by the runaway breakdown (RB) effect in the thundercloud's electric field. Ground-based observations of RB open a wide range of opportunities for the studies of fundamental processes in thunderstorms.

Chubenko, A. P.; Antonova, V. P.; Kryukov, S. Yu.; Piskal, V. V.; Ptitsyn, M. O.; Shepetov, A. L.; Vildanova, L. I.; Zybin, K. P.; Gurevich, A. V.

2000-10-01

47

X-ray emission from high temperature plasmas  

NASA Technical Reports Server (NTRS)

X-rays from a 25-hJ plasma focus apparatus were observed with pinhole cameras. The cameras consist of 0.4 mm diameter pinholes in 2 cm thick lead housing enclosing an X-ray intensifying screen at the image plane. Pictures recorded through thin aluminum foils or plastic sheets for X-ray energies sub gamma smaller than 15 keV show distributed X-ray emissions from the focussed plasma and from the anode surface. However, when thick absorbers are used, radial filamentary structure in the X-ray emission from the anode surface is revealed. Occasionally larger structures are observed in addition to the filaments. Possible mechanisms for the filamentary structure are discussed.

Harries, W. L.

1974-01-01

48

Ion Induced X-Ray Emission  

Microsoft Academic Search

This thesis deals with the L subshell ionisation of high atomic number targets by proton and He('+) ion bombardment, and the subsequent filling of that inner shell vacancy by the production of X-rays. The three L subshell ionisation cross sections for selected thin and thick targets between dysprosium and uranium are systematically studied and compared using these light ions in

David Damien Cohen

1984-01-01

49

Solar-stellar connection - the relationship between flaring rates, flare power, and quiescent X-ray background  

SciTech Connect

The flaring rates, flare powers, and quiescent X-ray luminosities of dMe (red dwarf) stars are compared with those of solar active regions. In dMe stars, these properties are found to be closely related, and this may have a significant influence on the understanding of the flare process and coronal heating. For example, a correlation between flare rate and quiescent X-ray luminosity suggests that both may be driven by similar processes on a differing scale. It is a natural extension of this work to investigate similar relationships for the sun. The results are mixed. The relationships between the various parameters are certainly not as clear for the sun as for the dMe stars. Some solar properties appear to vary in a manner similar to the dMe analysis, and some contradict the dMe case. The implications of this are discussed. 14 references.

Harrison, R.A.; Pearce, G.; Skumanich, A.

1988-09-01

50

X-Ray Emission from the Guitar Nebula  

NASA Technical Reports Server (NTRS)

We have detected weak soft X-ray emission from the pulsar wind nebula trailing the high-velocity star PSR 2224+65 (the "Guitar Nebula"). This X-ray flux gives evidence of gamma approximately 10(exp 7) eV particles in the pulsar wind and constrains the properties of the postshock flow. The X-ray emission is most easily understood if the shocked pulsar wind is partly confined in the nebula and if magnetic fields in this zone can grow to near-equipartition values.

Romani, Roger W.; Cordes, James M.; Yadigaroglu, I.-A.

1997-01-01

51

Accretion tomography with X-ray reverberation: Localizing the X-ray emission in AGN  

NASA Astrophysics Data System (ADS)

Relativistic X-ray reverberation has emerged as a powerful probe of the inner accretion systems. It relies on the simple principle of a primary X-ray source reflected by a Compton-thick partially ionized material. By measuring the delay as a function of energy in the iron K band at different variability time-scales, emission from different region sizes is separated. Here, I will review some of the recent reverberation results, and present our latest work from a long joint campaign to study the highly variable AGN MCG-5-23-16 with XMM-Newton, Suzaku and NuSTAR.

Zoghbi, A.

2014-07-01

52

X-ray emission from the outer planets: Albedo for scattering and fluorescence of solar X rays  

NASA Astrophysics Data System (ADS)

Soft X-ray emission has been observed from the low-latitude "disk" of both Jupiter and Saturn as well as from the auroral regions of these planets. The disk emission as observed by ROSAT, the Chandra X-Ray Observatory, and XMM-Newton appears to be uniformly distributed across the disk and to be correlated with solar activity. These characteristics suggest that the disk X rays are produced by (1) the elastic scattering of solar X rays by atmospheric neutrals and (2) the absorption of solar X rays in the carbon K-shell followed by fluorescent emission. The carbon atoms are found in methane molecules located below the homopause. In this paper we present the results of calculations of the scattering albedo for soft X rays. We also show the calculated X-ray intensity for a range of atmospheric abundances for Jupiter and Saturn and for a number of solar irradiance spectra. The model calculations are compared with recent X-ray observations of Jupiter and Saturn. We conclude that the emission of soft X rays from the disks of Jupiter and Saturn can be largely explained by the scattering and fluorescence of solar soft X rays. We suggest that measured X-ray intensities from the disk regions of Jupiter and Saturn can be used to constrain both the absolute intensity and the spectrum of solar X rays.

Cravens, T. E.; Clark, J.; Bhardwaj, A.; Elsner, R.; Waite, J. H.; Maurellis, A. N.; Gladstone, G. R.; Branduardi-Raymont, G.

2006-07-01

53

The correlation of solar flare hard X-ray bursts with Doppler blueshifted soft X-ray flare emission  

NASA Technical Reports Server (NTRS)

We have investigated the temporal correlation between hard X-ray bursts and the intensity of Doppler blueshifted soft X-ray spectral line emission. We find a strong correlation for many events that have intense blueshifted spectral signatures and some correlation in events with modest blueshifts. The onset of hard X-rays frequently coincides to within a few seconds with the onset of blueshifted emission. The peak intensity of blueshifted emission is frequently close in time to the peak of the hard X-ray emission. Decay rates of the blueshifted and hard X-ray emission are similar, with the decay of the blueshifted emission tending to lag behind the hard X-ray emission in some cases. There are, however, exceptions to these conclusions, and, therefore, the results should not be generalized to all flares. Most of the data for this work were obtained from instruments flown on the Japanese Yohkoh solar spacecraft.

Bentley, R. D.; Doschek, G. A.; Simnett, G. M.; Rilee, M. L.; Mariska, J. T.; Culhane, J. L.; Kosugi, T.; Watanabe, T.

1994-01-01

54

A Common Stochastic Process Rules Gamma-ray Burst Prompt Emission and X-ray Flares  

NASA Astrophysics Data System (ADS)

Prompt ?-ray and early X-ray afterglow emissions in gamma-ray bursts (GRBs) are characterized by a bursty behavior and are often interspersed with long quiescent times. There is compelling evidence that X-ray flares are linked to prompt ?-rays. However, the physical mechanism that leads to the complex temporal distribution of ?-ray pulses and X-ray flares is not understood. Here we show that the waiting time distribution (WTD) of pulses and flares exhibits a power-law tail extending over four decades with an index of about two and can be the manifestation of a common time-dependent Poisson process. This result is robust and is obtained on different catalogs. Surprisingly, GRBs with many (?slant 8) ?-ray pulses are very unlikely to be accompanied by X-ray flares after the end of the prompt emission (3.1? Gaussian confidence). These results are consistent with a simple interpretation: a hyperaccreting disk breaks up into one or a few groups of fragments, each of which is independently accreted with the same probability per unit time. Prompt ?-rays and late X-ray flares are nothing but different fragments being accreted at the beginning and at the end, respectively, following the very same stochastic process and likely the same mechanism.

Guidorzi, C.; Dichiara, S.; Frontera, F.; Margutti, R.; Baldeschi, A.; Amati, L.

2015-03-01

55

X-ray emission from the terrestrial magnetosheath  

E-print Network

and consequently emits a photon in the extreme ultraviolet or soft X{ray region of the spectrum. Recent higher reso- lution spectra of the cometary X{rays by Chandra [Lisse et al., 2001] and of the extreme ultraviolet emission (EUV) by the EUVE satellite... al., 2001]. 2. The Model The following expression, similar to the expression origi- nally applied to comets by Cravens [1997], is used to obtain the EUV and soft X{raypower density in the Earth's geo- corona: P X;ray = #11;n sw n H (eV cm ;3 s ;1...

Robertson, Ina Picket; Cravens, Thomas Edward

2003-04-29

56

The very soft X-ray emission of X-ray-faint early-type galaxies  

NASA Technical Reports Server (NTRS)

A recent reanaylsis of Einstein data, and new ROSAT observations, have revealed the presence of at least two components in the X-ray spectra of X-ray faint early-type galaxies: a relatively hard component (kT greater than 1.5 keV), and a very soft component (kT approximately 0.2-0.3 keV). In this paper we address the problem of the nature of the very soft component and whether it can be due to a hot interstellar medium (ISM), or is most likely originated by the collective emission of very soft stellar sources. To this purpose, hydrodynamical evolutionary sequences for the secular behavior of gas flows in ellipticals have been performed, varying the Type Ia supernovae rate of explosion, and the dark matter amount and distribution. The results are compared with the observational X-ray data: the average Einstein spectrum for six X-ray faint early-type galaxies (among which are NGC 4365 and NGC 4697), and the spectrum obtained by the ROSAT pointed observation of NGC 4365. The very soft component could be entirely explained with a hot ISM only in galaxies such as NGC 4697, i.e., when the depth of the potential well-on which the average ISM temperature strongly depends-is quite shallow; in NGC 4365 a diffuse hot ISM would have a temperature larger than that of the very soft component, because of the deeper potential well. So, in NGC 4365 the softest contribution to the X-ray emission comes certainly from stellar sources. As stellar soft X-ray emitters, we consider late-type stellar coronae, supersoft sources such as those discovered by ROSAT in the Magellanic Clouds and M31, and RS CVn systems. All these candidates can be substantial contributors to the very soft emission, though none of them, taken separately, plausibly accounts entirely for its properties. We finally present a model for the X-ray emission of NGC 4365, to reproduce in detail the results of the ROSAT pointed observation, including the Position Sensitive Proportional Counter (PSPC) spectrum and radial surface brightness distribution. The present data may suggest that the X-ray surface brightness is more extended than the optical profile. In this case, a straightforward explanation in terms of stellar sources could not be satisfactory. The available data can be better explained with three different contributions: a very soft component of stellar origin, a hard component from X-ray binaries, and an approximately 0.6 keV hot ISM. The latter can explain the extended X-ray surface brightness profile, if the galaxy has a dark-to-luminous mass ratio of 9, with the dark matter very broadly distributed, and a SN Ia explosive rate of approximately 0.6 the Tammann rate.

Pellegrini, S.; Fabbiano, G.

1994-01-01

57

X-ray emission of hot massive stars  

NASA Astrophysics Data System (ADS)

Massive hot stars are important cosmic engines that severely influence their environment by powerful stellar wind and strong ionizing radiation. Modern observations of X-ray emission from massive stars provide deep insight into the structure and dynamics of their winds and allow to study the very hot gas in wind blown bubbles. I will review the recent findings on X-ray emission from OB and Wolf-Rayet stars and massive star clusters. While our knowledge about the X-ray emission from massive stars is increasing, a small fraction of massive stars that have strong magnetic fields are often unusual in their X-ray light. Massive star clusters provide an excellent opportunity to study stellar feedback and the hot gas filling the intracluster medium. The most massive stars are often binaries where the stellar winds collide and produce X-ray or even gamma-ray radiation. Finally, I will discuss the progress towards an unified view of stellar winds in single stars and in high mass X-ray binaries.

Oskinova, L.

2014-07-01

58

ANS hard X-ray experiment development program. [emission from X-ray sources  

NASA Technical Reports Server (NTRS)

The hard X-ray (HXX) experiment is one of three experiments included in the Dutch Astronomical Netherlands Satellite, which was launched into orbit on 30 August 1974. The overall objective of the HXX experiment is the detailed study of the emission from known X-ray sources over the energy range 1.5-30keV. The instrument is capable of the following measurements: (1) spectral content over the full energy range with an energy resolution of approximately 20% and time resolution down to 4 seconds; (2) source time variability down to 4 milliseconds; (3) silicon emission lines at 1.86 and 2.00keV; (4) source location to a limit of one arc minute in ecliptic latitude; and (5) spatial structure with angular resolution of the arc minutes. Scientific aspects of experiment, engineering design and implementation of the experiment, and program history are included.

Parsignault, D.; Gursky, H.; Frank, R.; Kubierschky, K.; Austin, G.; Paganetti, R.; Bawdekar, V.

1974-01-01

59

Unresolved Soft X-Ray Emission from the Galactic Disk  

NASA Astrophysics Data System (ADS)

The soft X-ray sky below 1 keV is spatially smooth after subtracting the local structure. In high galactic latitude regions, emissions from faint unresolved extragalactic point sources, i.e., the Cosmic X-ray Background (CXB), are responsible for ~40 % of the soft X-ray emission in the ROSAT R45 band 0.44-1.0 keV) (McCammom et al. 2002). Since the interstellar X-ray absorption column density is high enough 10^22 cm^-2) to block the extragalactic X-ray photons below 1 keV totally in the galactic midplane, it is naturally expected that the X-ray surface brightness in the R45 band decreases by ~40 %. However, the R45 band surface brightness reduces only by ~20 % or less from high galactic latitude regions to the midplane regions. This issue has been known as the “M band problem” (McCammom & Sanders 1990; Cox 2005). M band itself is a name of the energy band which is almost the same as the ROSAT R45 band. Masui et al. (2009) discovered the existence of an unresolved emission in its energy spectrum from a region located in the midplane for the first time and this excess emission is considered to be partly filling the decrease of the extragalactic component in the midplane. Spectral analysis revealed that this excess emission is represented well by a thin thermal emission with a temperature of abount 0.8 keV. If this excess emission is an answer for the M band problem, this should be observed in other midplane regions. We searched for this excess emission using archival data of Suzaku which has the lowest and stable background and therefore is optimum for faint soft X-ray emissions. Systematic analysis for over 100 observations with the galactic latitude of |b| < 5 was conducted and finally we detected excess emissions successfully from different 11 regions in the midplane (Mitsuishi et al. in prep). Temperatures ranges from 0.6 keV to 1.3 keV with different intensities. Our results suggests that these excess emissions are distributed in the whole galactic disk region such as CXB and the Galactic ridge X-ray emission. The origin for these excess emissions is also discussed in this conference.

Mitsuishi, Ikuyuki; Sato, T.; Kimura, S.; Mitsuda, K.; Yamasaki, N. Y.; Takei, Y.; Ohashi, T.; McCammon, D.

2013-04-01

60

X-ray emission from natural and triggered lightning  

NASA Astrophysics Data System (ADS)

We report on x-ray observations of lightning made at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, FL. Using NaI(Tl)/photomultiplier tube detectors housed inside heavy aluminum boxes designed to keep out light, moisture and RF noise, we have measured x-ray emission from nearby natural lightning and rocket-triggered lightning. Electric fields and channel-base currents (for triggered lightning only) were also recorded. The x-ray emission most often occurs during the stepped and dart leader phases with possibly some emission occurring during the very beginning of the return strokes. The energy spectra for both natural and triggered lightning typically extend up to a few hundred keV, and the x-rays arrive in a sequence of discrete bursts, less than 1 microsecond in duration, with the stepped leader emission usually starting approximately 1 millisecond before the return stroke and the dart leader emission usually starting within about 100 microseconds of the return stroke. In this presentation, we will review observations made during the 2002 and 2003 seasons and present new results from the 2004 season, including new x-ray data from several natural lightning strikes. In addition, we will discuss the Thunderstorm Energetic Radiation Array (TERA), currently under construction at the ICLRT.

Dwyer, J. R.; Rassoul, H. K.; Al-Dayeh, M.; Caraway, L.; Wright, B.; Chrest, A.; Uman, M. A.; Rakov, V. A.; Rambo, K. J.; Jordan, D. M.; Jerauld, J.

2004-12-01

61

X-ray emission from two nearby millisecond pulsars  

NASA Technical Reports Server (NTRS)

This grant, titled 'X-Ray Emission from Two Nearby Millisecond Pulsars,' included ROSAT observations of the nearby pulsars PSR J2322+20 and PSR J2019+24. Neither was detected, although the observations were among the most sensitive ever made towards millisecond pulsars, reaching 1.5 x 10(exp 29) and 2.7 x 10(exp 29) erg s(exp -1) (0.1-2.4 keV), respectively. This is about, or slightly below, the predicted level of emission from the Seward and Wang empirical prediction, based on an extrapolation from slower pulsars. To understand the significance of this result, we have compared these limits with observations of four other millisecond pulsars, taken from the ROSAT archives. Except for the case of PSR B1821-21, where we identified a possible x-ray counterpart, only upper limits on x-ray flux were obtained. From these results, we conclude that x-ray emission beaming does not follow the same dependence on pulsar period as that of radio emission: while millisecond pulsars have beaming fractions near unity in the radio, x-ray emission is observed only for favorable viewing geometries.

Thorsett, S. E.

1994-01-01

62

X-ray and Radio emission from type IIP supernovae  

NASA Astrophysics Data System (ADS)

Type-IIP supernovae are common core collapse SNe but few have been detected in X-ray and radio. These radiation can be due to relativistic electrons and the high seed photon density of optical, UV and IR bands during the visual lightcurve plateau phase can affect the radio and X-ray emission. Supernova shocks can also produce thermal X-rays. Each process has unique signatures on radio/X-ray light curves and spectra. They can characterize the progenitors and the partial loss of their envelopes prior to the explosion, shedding light on the `red supergiant problem', the lack of more massive progenitors of observed type IIP SNe than 17 Msun that may end up in black holes. Requested observations and followup may constrain the properties of the radiating plasma in magnetic fields.

Ray, Alak

2011-09-01

63

The X-ray emission of Lyman break galaxies  

NASA Astrophysics Data System (ADS)

We present an analysis of the X-ray emission of a large sample of z ~ 3 Lyman break galaxies (LBGs), based on Chandra/ACIS observations of several LBG survey fields. A total of 24 LBGs are directly detected in the X-ray, approximately doubling the number of known detections. Thirteen of the LBGs have optical spectroscopic signatures of active galactic nucleus (AGN) activity, but almost all the other X-ray detections are also likely to host an accreting black hole based on their X-ray properties. The AGN exhibit a wide range in X-ray luminosity, from weak Seyferts to bright quasi-stellar objects (QSOs). An optical spectroscopy identified approximately one-third of the X-ray-detected sources as broad-line QSOs, one-third as narrow-line AGN (NLAGN) and one-third as normal star-forming LBGs. The fraction of X-ray-detected LBGs is 3 per cent, much lower than that which has been found for submillimetre-selected galaxies. Two galaxies have X-ray luminosities, spectra and fX/fopt values that are consistent with emission from star formation processes and are identified as candidate X-ray bright, pure starburst galaxies at z ~ 3. If powered solely by star formation, the sources would have star formation rates (SFRs) of 300-500 Msolar yr-1. X-ray spectral analysis of the LBGs shows a mean photon index of ? = 1.96, similar to local AGN. There is evidence for absorption in at least 40 per cent of the objects. Significantly more absorption is evident in the NLAGN, which is consistent with AGN unification schemes. After correction for absorption, the narrow- and broad-line objects show the same average luminosity. X-ray-detected LBGs, spectroscopically classified as normal galaxies, however, are less luminous in both soft and hard X-ray bands, indicating that the host galaxy is outshining any optical AGN signature. Turning to the X-ray emission from LBGs without direct detections, stacking the X-ray flux in the two deepest Chandra fields under consideration [the Hubble Deep Field-North (HDF-N) and Groth-Westphal Strip (GWS)] produced significant detections in each, although the GWS result was marginal. The detection in the HDF-N gives an X-ray-derived SFR of 42.4 +/- 7.8 Msolar yr-1 per LBG and, by comparing with the ultraviolet (UV) SFR, the implied UV extinction correction is 4.1 +/- 0.8. The LBG sample was split into three bins based on UV magnitude to examine the correlation between UV and X-ray emission: for the limited statistics available, there was no evidence of any correlation.

Laird, E. S.; Nandra, K.; Hobbs, A.; Steidel, C. C.

2006-11-01

64

Extended X-Ray Emission around Quasars at Intermediate Redshift  

NASA Technical Reports Server (NTRS)

We compare the optical to soft X-ray spectral energy distribution (SED) of a sample of bright low-redshift (0.048 less than z less than 0.155), radio-quiet quasars, with a range of thermal models which have been proposed to explain the optical/UV/soft X-ray quasar emission: (a) optically thin emission from an ionized plasma, (b) optically thick emission from the innermost regions of an accretion disk in Schwarzschild and Kerr geometries. We presented ROSAT PSPC observations of these quasars in an earlier paper. Here our goals are to search for the signature of thermal emission in the quasar SED, and to investigate whether a single component is dominating at different frequencies. We find that isothermal optically thin plasma models can explain the observed soft X-ray color and the mean OUV color. However, they predict an ultraviolet (1325 Angstrom) luminosity a factor of 3 to 10 times lower than observed. Pure disk models, even in a Kerr geometry, do not have the necessary flexibility to account for the observed OUV and soft X-ray luminosities. Additional components are needed both in the optical and in the soft X-rays (e.g. a hot corona can explain the soft X-ray color). The most constrained modification of pure disk models, is the assumption of an underlying power law component extending from the infrared (3 micrometers) to the X-ray. This can explain both the OUV and soft X-ray colors and luminosities and does not exceed the 3 micrometers luminosity, where a contribution from hot dust is likely to be important. We also discuss the possibility that the observed soft X-ray color and luminosity are dominated by reflection from the ionized surface of the accretion disk. While modifications of both optically thin plasma models and pure disk models might account for the observed SED, we do not find any strong evidence that the OUV bump and soft X-ray emission are one and the same component. Likewise, we do not find any strong argument which definitely argues in favor of thermal models.

Fiore, Fabrizio

1998-01-01

65

X-ray emission from colliding laser plasmas  

SciTech Connect

Colliding Au, CD and Ti-Cr plasmas have been generated by illuminating two opposing foils each with a {approximately} 100J, 0.5 nsec, 2{omega} Nd-glass laser beam from the Trident laser facility at Los Alamos. The plasmas are being used to study plasma interactions which span the parameter regime from interpenetrating to collisional stagnation. X-ray emission during the laser target interaction and the subsequent collision is used to diagnose the initial plasma conditions and the colliding plasma properties. X-ray instrumentation consists of a 100 ps gated x-ray pinhole imager, a time-integratcd bremsstrahlung x-ray spectrograph and a gated x-ray spectrograph used to record isoelectronic spectra from the Ti-Cr plasmas. The imager has obtained multi-frame images of the collision and therefore, a measure of the stagnation length which is a function of the ion charge state and density and a strong function of the electron temperature. Other instrumentation includes a Thomson scattering spectrometer with probe beam, neutron detectors used to monitor the CD coated foil collisions and an ion spectrometer. We will describe the current status of the experiments and current results with emphasis on the x-ray emission diagnostics. We will also briefly describe the modeling using Lasnex and ISIS, a particle-in-cell code with massless fluid electrons and inter particle (classical) collisions.

Wilke, M.; Obst, A.W.; Winske, D. [and others

1995-09-01

66

Synchrotron-Radiation Induced X-Ray Emission (SRIXE)  

SciTech Connect

Elemental analysis using emission of characteristic x rays is a well-established scientific method. The success of this analytical method is highly dependent on the properties of the source used to produce the x rays. X-ray tubes have long existed as a principal excitation source, but electron and proton beams have also been employed extensively. The development of the synchrotron radiation x-ray source that has taken place during the past 40 years has had a major impact on the general field of x-ray analysis. Even tier 40 years, science of x-ray analysis with synchrotron x-ray beams is by no means mature. Improvements being made to existing synchrotron facilities and the design and construction of new facilities promise to accelerate the development of the general scientific use of synchrotron x-ray sources for at least the next ten years. The effective use of the synchrotron source technology depends heavily on the use of high-performance computers for analysis and theoretical interpretation of the experimental data. Fortunately, computer technology has advanced at least as rapidly as the x-ray technology during the past 40 years and should continue to do so during the next decade. The combination of these technologies should bring about dramatic advances in many fields where synchrotron x-ray science is applied. It is interesting also to compare the growth and rate of acceptance of this particular research endeavor to the rates for other technological endeavors. Griibler [1997] cataloged the time required for introduction, diffusion,and acceptance of technological, economic, and social change and found mean values of 40 to 50 years. The introduction of the synchrotron source depends on both technical and non-technical factors, and the time scale at which this seems to be occurring is quite compatible with what is seen for other major innovations such as the railroad or the telegraph. It will be interesting to see how long the present rate of technological change and increase in scientific use can be maintained for the synchrotron x-ray source. A short summary of the present state of the synchrotron radiation-induced x-ray emission (SRIXE) method is presented here. Basically, SRIXE experiments can include any that depend on the detection. of characteristic x-rays produced by the incident x-ray beam born the synchrotron source as they interact with a sample. Thus, experiments done to measure elemental composition, chemical state, crystal, structure, and other sample parameters can be considered in a discussion of SRIXE. It is also clear that the experimentalist may well wish to use a variety of complementary techniques for study of a given sample. For this reason, discussion of computed microtomography (CMT) and x-ray diffraction is included here. It is hoped that this present discussion will serve as a succinct introduction to the basic ideas of SRIXE for those not working in the field and possibly help to stimulate new types of work by those starting in the field as well as by experienced practitioners of the art. The topics covered include short descriptions of (1) the properties of synchrotron radiation, (2) a description of facilities used for its production, (3) collimated microprobe, (4) focused microprobes, (5) continuum and monoenergetic excitation, (6) detection limits, (7) quantitation, (8) applications of SRIXE, (9) computed microtomography (CMT), and (10)chemical speciation using x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). An effort has been made to cite a wide variety of work from different laboratories to show the vital nature of the field.

Jones, Keith W.

1999-09-01

67

Numerical simulation of subpicosecond laser plasma x-ray emission  

Microsoft Academic Search

A one-dimensional hydrodynamic code, ION, which takes ionization kinetics into account, was elaborated and used for the calculation of x-ray emission from plasma produced by the action of a subpicosecond laser pulse onto a solid target in vacuum. Calculated intensities for aluminum target emission are in agreement with experimental and theoretical results of other authors. The simple model gives the

A. A. Andreev; I. V. Kurnin

1996-01-01

68

Discovery of Diffuse Hard X-ray Emission Around Jupiter  

NASA Astrophysics Data System (ADS)

Our discovery of diffuse hard (1-5 keV) X-ray emission around Jupiter is reported. Recent Chandra and XMM-Newton observations revealed several types of X-rays in the vicinity of Jupiter such as auroral and disk emission from Jupiter and faint diffuse X-rays from the Io Plasma Torus (see Bhardwaj et al. 2007 for review). To investigate possible diffuse hard X-ray emission around Jupiter with the highest sensitivity, we conducted data analysis of Suzaku XIS observations of Jupiter on Feb 2006. After removing satellite and planetary orbital motions, we detected a significant diffuse X-ray emission extending to 6 x 3 arcmin with the 1-5 keV X-ray luminosity of 3e15 erg/s. The emitting region very well coincided with the Jupiter's radiation belts and the bright spot seemed to move according to the Io's motion. The 1-5 keV X-ray spectrum was represented by a simple power law model with a photon index of 1.4. Such a flat continuum strongly suggests non-thermal origin. We hence examined three mechanisms: bremsstrahlung by keV electrons, synchrotron emission by TeV electrons, and inverse Compton scattering of solar photons by MeV electrons. The former two can be rejected because of the X-ray spectral shape and implausible existence of TeV electrons around Jupiter, respectively. The last possibility was found to be possible because tens MeV electrons, which have been confirmed in inner radiation belts (Bolton et al. 2002), can kick solar photons to the keV energy range and provide a simple power-law continuum. We estimated an average electron density from the X-ray luminosity assuming the oblate spheroid shaped emitting region with 8 x 8 x 4 Jovian radii. The necessary density was 0.02 1/cm3 for 50 MeV electrons. Hence, our results may suggest a new particle acceleration phenomenon related to Io.

Ezoe, Yuichiro; Ishikawa, K.; Ohashi, T.; Terada, N.; Miyoshi, Y.; Uchiyama, Y.

2009-09-01

69

Hard X-ray emission from Eta Carinae  

E-print Network

Context : If relativistic particle acceleration takes place in colliding-wind binaries, hard X-rays and gamma-rays are expected through inverse Compton emission, but to date these have never been unambiguously detected. Aims : To detect this emission, observations of Eta Carinae were performed with INTEGRAL, leveraging its high spatial resolution. Methods : Deep hard X-ray images of the region of Eta Car were constructed in several energy bands. Results : The hard X-ray emission previously detected by BeppoSax around Eta Car originates from at least 3 different point sources. The emission of Eta Car itself can be isolated for the first time, and its spectrum unambiguously analyzed. The X-ray emission of Eta Car in the 22-100 keV energy range is very hard (photon index around 1) and its luminosity is 7E33 erg/s. Conclusions : The observed emission is in agreement with the predictions of inverse Compton models, and corresponds to about 0.1% of the energy available in the wind collision. Eta Car is expected to be detected in the GeV energy range.

Jean-Christophe Leyder; Roland Walter; Gregor Rauw

2007-12-10

70

Study of Diffuse X-ray Emission in Globular Clusters  

NASA Technical Reports Server (NTRS)

This grant supported our analysis of ROSAT x-ray data on globular clusters. Although the grant title referred to our original ROSAT proposal (cycle 1) to study diffuse soft x-ray emission in three globulars (for which time was only granted in that original observing cycle for one cluster, 47 Tuc), the grant has also been maintained through several renewals and funding supplements to support our later ROSAT observations of point sources in globulars. The primary emphasis has been on the study of the dim sources, or low liuminosity globular cluster x-ray sources, which we had originally discovered with the Einstein Observatory and for which ROSAT provided the logical followup. In this Final Report, we summarize the Scientific Objectives of this investigation of both diffuse emission and dim sources in globular clusters and the Results Achieved; and finally the Papers Published.

Grindlay, Jonathan E.

1997-01-01

71

Detecting X-ray Emission from Cometary Atmospheres Using the Suzaku X-ray Imaging Spectrometer  

SciTech Connect

The Suzaku X-ray imaging spectrometer has been used to observe the X-ray emission from comets 73P/Schwassmann-Wachmann 3C and 8P/Tuttle. Comet 73P/Schwassmann-Wachmann 3C was observed during May and June of 2006, while it was near perihelion and passed within 0.1 AU of the Earth. Comet 8P/Tuttle was observed during January of 2008 when it was at its closest approach to the Earth at 0.25 AU, and again near perihelion at a distance of 0.5 Au from Earth. In the case of comet 73P/Schwassmann Wachmann 3C, the XIS spectra show line emission from highly charged oxygen and carbon ions as well as emission from what is most likely L-shell transitions from Mg, Si, and S ions. This line emission is caused by charge exchange recombination between solar wind ions and cometary neutrals, and can be used as a diagnostic of the solar wind. Here we present some of the results of the observation of the comet 73P/Schwassmann-Wachmann 3C.

Brown, G V; Beiersdorfer, P; Bodewits, D; Porter, F S; Ezoe, Y; Hamaguchi, K; Hanya, M; Itoh, M; Kilbourne, C A; Kohmura, T; Maeda, Y; Negoro, H; Tsuboi, Y; Tsunemi, H; Urata, Y

2009-11-16

72

High resolution spectroscopy of X-ray emission from high mass X-ray binaries  

Microsoft Academic Search

This article briefly reviews first the progress of spectroscopy in X-ray astronomy from proportional counters, a major instrument in early phase of X-ray astronomy, to gas scintillation proportional counters, X-ray CCD cameras, transmission and reflection gratings, and finally to X-ray micro-calorimeters. As a typical example of spectral features observed from high mass X-ray binaries (HMXBs), the spectra observed from Vela

F. Nagase; S. Watanabe

2006-01-01

73

Soft X-ray emissions by high current vacuum discharges  

Microsoft Academic Search

The authors have investigated the vacuum spark, which is utilized in the spectroscopic study of highly charged ions. One merit of the vacuum spark is its ability to produce a stable spot plasma between the electrodes. Another is its flexibility in selection of characteristic X-ray emission wavelengths, because many metals can be used for this purpose. To make a stable

H. Arita; K. Suzuki; Y. Kurosawa; K. Hirasawa

1989-01-01

74

X-RAY EMISSION ANALYSIS: SAMPLE LOSSES DURING EXCITATION  

EPA Science Inventory

Many samples of atmospheric aerosols and biological materials containing volatile or unstable species are now being examined by X-ray emission analysis, and loss of these species by sample heating is a critical consideration. The amount of heat energy deposited in a sample by the...

75

X-ray Emissions Detected From Elusive Cosmic Objects  

NASA Astrophysics Data System (ADS)

A type of celestial object that has long stumped astronomers has been found to emit X-rays, thus proving a theory of how the objects form. Dr. Steven Pravdo of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and other scientists have concluded that these objects, called Herbig Haro objects, are produced by high velocity shocks. Pravdo is the lead author of a paper published in the Oct. 18 issue of the journal Nature. Herbig Haro objects are found in regions where new stars are forming. They are nebulas, or dust and gas clouds. They form when high-velocity gas emitted from young stars collides with clouds of interstellar material. The collision heats the gas in the surrounding nebula to sufficiently high temperatures to produce X-rays. Observations for the past 20 years showed no evidence of X-ray emission from these objects, which are named for astronomers George Herbig and Guillermo Haro. Previous instruments lacked the resolution and sensitivity necessary to 'see' these X-rays. The discovery of the X-ray emissions was possible through the very powerful Advanced CCD Imaging Spectrometer on NASA's Chandra X-ray Observatory, which has been in orbit since 1999. On Oct. 8, 2000, astrophysicists used the instrument to study HH2, one of the brightest and closest Herbig Haro objects in the Orion Nebula. They determined that HH2 contains shock-heated material with a temperature of about 1 million degrees Kelvin. Pravdo and his team used three criteria to rule out the possibility that the emissions came from any other source. First, Chandra's high spatial resolution pinpointed the location of the X-rays at HH2. Second, the X-rays appeared to be covering a region bigger than a star. Third, the temperature of the X-rays was about 1 million degrees, cooler than nearby X-ray stars. One million degrees is about the temperature expected if material moving at about 300 kilometers per second (about 600,000 miles per hour) collides. At this speed, you could go from Los Angeles to San Diego and back in one second. The principal investigator of the Advanced CCD Imaging Spectrometer, Dr. Gordon Garmire of Pennsylvania State University, University Park, is a co-author of the paper. Other co-authors include Drs. Yohko Tsuboi, Yoshitomo Maeda and Eric Feigelson, all from Pennsylvania State University, and Dr. John Bally from the University of Colorado, Boulder. The Advanced CCD Imaging Spectrometer X-ray camera was developed for NASA by Pennsylvania State University and the Massachusetts Institute of Technology, Cambridge, Mass. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. 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. Images associated with this release are available on the World Wide Web at: http://chandra.harvard.edu AND http://chandra.nasa.gov The Chandra X-ray Observatory is managed for NASA by the Smithsonian Astrophysical Observatory, Cambridge, Mass. JPL is managed for NASA by the California Institute of Technology in Pasadena.

2001-10-01

76

Models for X-Ray Emission from Isolated Pulsars  

E-print Network

A model is proposed for the observed combination of power-law and thermal emission of keV X-rays from rotationally powered pulsars. For gamma-ray pulsars with accelerators very many stellar radii above the neutron star surface, 100 MeV curvature gamma-rays from $e^{-}$ or $e^{+}$ flowing starward out of such accelerators are converted to electron-positron pairs on closed field lines all around the star. These pairs strongly affect X-ray emission from near the star in two ways. (1) The pairs are a source of synchrotron emission immediately following their creation in regions where $B \\sim 10^{10}$ G. This emission, in the photon energy range 0.1 keV $\\lesssim E_{X} \\lesssim$ 5 MeV, has a power-law spectrum with energy index 0.5 and X-ray luminosity that depends on the backflow current, and is typically $\\sim 10^{33}$ \\lum. (2) The pairs ultimately form a cyclotron resonance ``blanket'' surrounding the star except for two holes along the open field line bundles which pass through it. In such a blanket the gravitational pull on electron-positron pairs toward the star is balanced by the hugely amplified push of outflowing surface emitted X-rays wherever cyclotron resonance occurs. Because of it the neutron star is surrounded by a leaky ``hohlraum'' of hot blackbody radiation with two small holes, which prevents direct X-ray observation of a heated polar cap of a gamma-ray pulsar. Weakly spin-modulated radiation from the blanket together with more strongly spin-modulated radiation from the holes through it would then dominate observed low energy (0.1--10 keV) emission. For non-gamma-ray pulsars, in which no such accelerators with their accompanying extreme relativistic backflow toward the star are ...

F. Y. -H. Wang; M. Ruderman; J. P. Halpern; T. Zhu

1997-11-24

77

The X-Ray Emission of Composite Galaxies  

NASA Astrophysics Data System (ADS)

We propose to observe 2 low-redshift galaxies classified as HII/Seyfert-2 composites, as their optical spectra have the characteristics of star-forming galaxies and very weak signatures of AGN activity. However their high X-ray luminosities (Lx 10^{42-43} erg/s) are typical of broad-line AGN. These objects are considered as nearby examples of the NELGS detected in deep surveys which produce a large fraction of the X-ray background. The Chandra observations will allows us to check whether our objects a) host a powerful point-like source and thus harbour a 'naked' AGN (with a weak or absent broad-line region) or a heavily obscured AGN or b) have extended X-ray emission and thus are among the most powerful star-forming galaxies in the Universe similar to those found at high redshifts.

Zezas, Andreas

2000-09-01

78

Ultrasoft transient X-ray emission from AGN  

E-print Network

We report some remarkable and unexpected results of optical/UV/X-ray follow-up observations of bright soft X-ray selected AGN from the ROSAT All-Sky-Survey. The majority of these AGN are rather anonymous Seyfert galaxies, mostly of the narrow-line Seyfert 1 subtype (nlSy1). We confirm the well-known X-ray variability by factors of a few. However, we also found strikingly different variability patterns: (i) a drop in the PSPC count rate by a factor of ~400 in WPVS007, (ii) a bolometrically dominant soft X-ray component decreasing in flux by a factor ~100 in IC 3599 accompanied by a decrease in optical emission line fluxes, and (iii) a drastic X-ray spectral change in RX J0134-42 from ultrasoft to a typical hard Seyfert spectrum. These dramatic variations occur within a (few) year(s), implying that the accretion flow in the immediate vicinity of the central black hole must have undergone a major change. We discuss possible physical explanations such as accretion disk instabilities or the tidal disruption of stars.

K. Mannheim; D. Grupe; K. Beuermann; H. -C. Thomas; H. H. Fink

1995-12-08

79

X-ray emission from Wolf-Rayet stars  

NASA Astrophysics Data System (ADS)

Seven bright Wolf-Rayet (WR) stars were observed with the Einstein X-ray observatory; four were detected. The 0.15-4 keV fluxes of the detected stars (and the upper limits for the others) are consistent with the ratio of X-ray to bolometric luminosities observed for other early-type stars. The X-ray spectra of WR stars are also similar to those of OB stars, with most of the photons emerging with energies less than 1 keV. These observations support the idea that X-ray emission in all hot stars is produced by shocks in the wind. The X-ray flux of one of the stars, HD 50896, varied by a factor of 2 within half an hour on two of the three days when it was observed. The possible origin of these variations is discussed; it is concluded that the companion of HD 50896 is either a black hole or a white dwarf remnant of a massive star.

White, Richard L.; Long, Knox S.

1986-11-01

80

Hard X-ray emission of Sco X-1  

NASA Astrophysics Data System (ADS)

We study hard X-ray emission of the brightest accreting neutron star Sco X-1 with INTEGRAL observatory. Up to now INTEGRAL have collected ˜4 Ms of deadtime corrected exposure on this source. We show that hard X-ray tail in time average spectrum of Sco X-1 has a power-law shape without cutoff up to energies ˜200-300 keV. An absence of the high energy cutoff does not agree with the predictions of a model, in which the tail is formed as a result of Comptonization of soft seed photons on bulk motion of matter near the compact object. The amplitude of the tail varies with time with factor more than 10 with the faintest tail at the top of the so-called flaring branch of its colour-colour diagram. We show that the minimal amplitude of the power-law tail is recorded when the component, corresponding to the innermost part of optically thick accretion disc, disappears from the emission spectrum. Therefore, we show that the presence of the hard X-ray tail may be related with the existence of the inner part of the optically thick disc. We estimate cooling time for these energetic electrons and show that they cannot be thermal. We propose that the hard X-ray tail emission originates as a Compton upscattering of soft seed photons on electrons, which might have initial non-thermal distribution.

Revnivtsev, Mikhail G.; Tsygankov, Sergey S.; Churazov, Eugene M.; Krivonos, Roman A.

2014-12-01

81

X-ray Emission from Thunderstorms and Lightning  

ScienceCinema

How lightning is initiated in the relatively low electric fields inside thunderclouds and how it can then propagate for tens of kilometers through virgin air are two of the great unsolved problems in the atmospheric sciences.  Until very recently it was believed that lightning was entirely a conventional discharge, involving only low-energy (a few eV) electrons.  This picture changed completely a few years ago with the discovery of intense x-ray emission from both natural cloud-to-ground lightning and rocket-triggered lightning.  This energetic emission cannot be produced by a conventional discharge, and so the presence of x-rays strongly implies that runaway breakdown plays a role in lightning processes.  During runaway breakdown, electrons are accelerated through air to nearly the speed of light by strong electric fields.  These runaway electrons then emit bremsstrahlung x-rays and gamma-rays during collisions with air.  Indeed, the x-ray and gamma-ray emission produced by runaway breakdown near the tops of thunderstorms is bright enough to be seen from outer space, 600 km away.  As a result, the physics used for decades to describe thunderstorm electrification and lightning discharges is incomplete and needs to be revisited. 

Joseph Dwyer

2010-01-08

82

X-ray Emission from Thunderstorms and Lightning  

SciTech Connect

How lightning is initiated in the relatively low electric fields inside thunderclouds and how it can then propagate for tens of kilometers through virgin air are two of the great unsolved problems in the atmospheric sciences. Until very recently it was believed that lightning was entirely a conventional discharge, involving only low-energy (a few eV) electrons. This picture changed completely a few years ago with the discovery of intense x-ray emission from both natural cloud-to-ground lightning and rocket-triggered lightning. This energetic emission cannot be produced by a conventional discharge, and so the presence of x-rays strongly implies that runaway breakdown plays a role in lightning processes. During runaway breakdown, electrons are accelerated through air to nearly the speed of light by strong electric fields. These runaway electrons then emit bremsstrahlung x-rays and gamma-rays during collisions with air. Indeed, the x-ray and gamma-ray emission produced by runaway breakdown near the tops of thunderstorms is bright enough to be seen from outer space, 600 km away. As a result, the physics used for decades to describe thunderstorm electrification and lightning discharges is incomplete and needs to be revisited.

Dwyer, Joseph (Florida Institute of Technology) [Florida Institute of Technology

2009-08-08

83

X-ray Emission from Thunderstorms and Lightning  

SciTech Connect

How lightning is initiated in the relatively low electric fields inside thunderclouds and how it can then propagate for tens of kilometers through virgin air are two of the great unsolved problems in the atmospheric sciences.  Until very recently it was believed that lightning was entirely a conventional discharge, involving only low-energy (a few eV) electrons.  This picture changed completely a few years ago with the discovery of intense x-ray emission from both natural cloud-to-ground lightning and rocket-triggered lightning.  This energetic emission cannot be produced by a conventional discharge, and so the presence of x-rays strongly implies that runaway breakdown plays a role in lightning processes.  During runaway breakdown, electrons are accelerated through air to nearly the speed of light by strong electric fields.  These runaway electrons then emit bremsstrahlung x-rays and gamma-rays during collisions with air.  Indeed, the x-ray and gamma-ray emission produced by runaway breakdown near the tops of thunderstorms is bright enough to be seen from outer space, 600 km away.  As a result, the physics used for decades to describe thunderstorm electrification and lightning discharges is incomplete and needs to be revisited. 

Joseph Dwyer

2009-07-08

84

A CHANGE IN THE QUIESCENT X-RAY SPECTRUM OF THE NEUTRON STAR LOW-MASS X-RAY BINARY MXB 1659-29  

SciTech Connect

The quasi-persistent neutron star low-mass X-ray binary MXB 1659-29 went into quiescence in 2001, and we have followed its quiescent X-ray evolution since. Observations over the first 4 yr showed a rapid drop in flux and temperature of the neutron star atmosphere, interpreted as cooling of the neutron star crust which had been heated during the 2.5 yr outburst. However, observations taken approximately 1400 and 2400 days into quiescence were consistent with each other, suggesting the crust had reached thermal equilibrium with the core. Here we present a new Chandra observation of MXB 1659-29 taken 11 yr into quiescence and 4 yr since the last Chandra observation. This new observation shows an unexpected factor of {approx}3 drop in count rate and change in spectral shape since the last observation, which cannot be explained simply by continued cooling. Two possible scenarios are that either the neutron star temperature has remained unchanged and there has been an increase in the column density, or, alternatively the neutron star temperature has dropped precipitously and the spectrum is now dominated by a power-law component. The first scenario may be possible given that MXB 1659-29 is a near edge-on system, and an increase in column density could be due to build-up of material in, and a thickening of, a truncated accretion disk during quiescence. But, a large change in disk height may not be plausible if standard accretion disk theory holds during quiescence. Alternatively, the disk may be precessing, leading to a higher column density during this latest observation.

Cackett, E. M. [Department of Physics and Astronomy, Wayne State University, 666 W. Hancock Street, Detroit, MI 48201 (United States); Brown, E. F. [Department of Physics and Astronomy, National Superconducting Cyclotron Laboratory, and the Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States); Cumming, A. [Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A 2T8 (Canada); Degenaar, N.; Miller, J. M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Fridriksson, J. K.; Wijnands, R. [Astronomical Institute ''Anton Pannekoek'', University of Amsterdam, Science Park 904, 1098-XH Amsterdam (Netherlands); Homan, J., E-mail: ecackett@wayne.edu [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139 (United States)

2013-09-10

85

A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements.  

PubMed

We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ?5 keV to ?10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10(6)-10(7) photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species. PMID:25430123

Seidler, G T; Mortensen, D R; Remesnik, A J; Pacold, J I; Ball, N A; Barry, N; Styczinski, M; Hoidn, O R

2014-11-01

86

A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements  

NASA Astrophysics Data System (ADS)

We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ˜5 keV to ˜10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 106-107 photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species.

Seidler, G. T.; Mortensen, D. R.; Remesnik, A. J.; Pacold, J. I.; Ball, N. A.; Barry, N.; Styczinski, M.; Hoidn, O. R.

2014-11-01

87

Quiescent thermal emission from neutron stars in LMXBs  

E-print Network

We monitored the quiescent thermal emission from neutron stars in low-mass X-ray binaries after active periods of intense activity in x-rays (outbursts). The theoretical modeling of the thermal relaxation of the neutron star crust may be used to establish constraints on the crust composition and transport properties, depending on the astrophysical scenarios assumed. We numerically simulated the thermal evolution of the neutron star crust and compared them with inferred surface temperatures for five sources: MXB 1659-29, KS 1731-260, EXO 0748-676, XTE J1701-462 and IGR J17480-2446. We find that the evolution of MXB 1659-29, KS 1731-260 and EXO 0748-676 can be well described within a deep crustal cooling scenario. Conversely, we find that the other two sources can only be explained with models beyond crustal cooling. For the peculiar emission of XTE J1701-462 we propose alternative scenarios such as residual accretion during quiescence, additional heat sources in the outer crust, and/or thermal isolation of the inner crust due to a buried magnetic field. We also explain the very recent reported temperature of IGR J17480-2446 with an additional heat deposition in the outer crust from shallow sources.

Anabela Turlione; Deborah N. Aguilera; José A. Pons

2015-02-19

88

Synchrotron X-ray emission from old pulsars  

NASA Astrophysics Data System (ADS)

We study the synchrotron radiation as the observed non-thermal emission by the X-ray satellites from old pulsars (?1-10 Myr) to investigate the particle acceleration in their magnetospheres. We assume that the power-law component of the observed X-ray spectra is caused by the synchrotron radiation from electrons and positrons in the magnetosphere. We consider two pair-production mechanisms of X-ray emitting particles, the magnetic and the photon-photon pair productions. High-energy photons, which ignite the pair production, are emitted via the curvature radiation of the accelerated particles. We use the analytical description for the radiative transfer and estimate the luminosity of the synchrotron radiation. We find that for pulsars with the spin-down luminosity Lsd ? 1033 erg s-1, the locations of the particle acceleration and the non-thermal X-ray emission are within ?107 cm from the centre of the neutron star, where the magnetic pair production occurs. For pulsars with the spin-down luminosity Lsd ? 1031 erg s-1 such as J0108-1431, the synchrotron radiation is difficult to explain the observed non-thermal component even if we consider the existence of the strong and small-scale surface magnetic field structures.

Kisaka, Shota; Tanaka, Shuta J.

2014-09-01

89

"X-Ray Transients in Star-Forming Regions" and "Hard X-Ray Emission from X-Ray Bursters"  

NASA Technical Reports Server (NTRS)

This grant funded work on the analysis of data obtained with the Burst and Transient Experiment (BATSE) on the Compton Gamma-Ray Observatory. The goal of the work was to search for hard x-ray transients in star forming regions using the all-sky hard x-ray monitoring capability of BATSE. Our initial work lead to the discovery of a hard x-ray transient, GRO J1849-03. Follow-up observations of this source made with the Wide Field Camera on BeppoSAX showed that the source should be identified with the previously known x-ray pulsar GS 1843-02 which itself is identified with the x-ray source X1845-024 originally discovered with the SAS-3 satellite. Our identification of the source and measurement of the outburst recurrence time, lead to the identification of the source as a Be/X-ray binary with a spin period of 94.8 s and an orbital period of 241 days. The funding was used primarily for partial salary and travel support for John Tomsick, then a graduate student at Columbia University. John Tomsick, now Dr. Tomsick, received his Ph.D. from Columbia University in July 1999, based partially on results obtained under this investigation. He is now a postdoctoral research scientist at the University of California, San Diego.

Halpern, Jules P.; Kaaret, Philip

1999-01-01

90

Possible association of a quiescent x-ray source with a gamma-ray burster  

SciTech Connect

We report on the first repeatedly detected statistically significant coincidence (chance probability {approx_equal}10{sup {minus}2}{endash}10{sup {minus}3}) between an X-ray source and a gamma-ray burst error box. We present three {ital ROSAT} observations of the field of the gamma-ray burst of 1992 May 1. The first, a 2000 s target of opportunity observation, was carried out 18 days after the burst. A weak X-ray source was identified, but with too few photons to determine its spectral characteristics. The second, a 30 ks PSPC observation, resulted in the detection of 118 net photons over the 0.07{endash}2.4 keV energy range. We find that the spectrum is consistent with thermal bremsstrahlung from a 7{times}10{sup 6} K plasma with about 10{sup 22} cm{sup {minus}2} HI column density. The unabsorbed flux is {approximately}9.4{times}10{sup {minus}13} ergscm{sup {minus}2}s{sup {minus}1} (corresponding absorbed flux 4.8{times}10{sup {minus}14} ergscm{sup {minus}2}s{sup {minus}1}). Analysis of the photon arrival times indicates that the source may be variable. Using the HI column density from the spectral fit, we set a lower limit to the source distance of at least several kpc; an extragalactic source cannot be ruled out. If the gamma-ray burst is indeed related to the X-ray source, its total energy output would have been at least 2{times}10{sup 37} ergs. The third observation, 6200 s with the HRI, defines a source error circle of 6{double_prime} radius. We discuss optical observations of this region, and consider various possibilities for the nature of the X-ray source. {copyright} {ital 1996 The American Astronomical Society.}

Hurley, K.; Li, P. [University of California, Space Sciences Laboratory, Berkeley, California 94720 (United States)] [University of California, Space Sciences Laboratory, Berkeley, California 94720 (United States); Smette, A. [Kapteyn Laboratorium, Postbus 800, NL-9700 AV Groningen (The Netherlands)] [Kapteyn Laboratorium, Postbus 800, NL-9700 AV Groningen (The Netherlands); Kouveliotou, C.; Fishman, G. [Marshall Space Flight Center ES 62, Huntsville, Alabama 35812 (United States)] [Marshall Space Flight Center ES 62, Huntsville, Alabama 35812 (United States); Laros, J. [University of Arizona, Department of Planetary Sciences, Tucson, Arizona 85721 (United States)] [University of Arizona, Department of Planetary Sciences, Tucson, Arizona 85721 (United States); Cline, T. [Goddard Space Flight Center, Code 661, Greenbelt, Maryland 20771 (United States)] [Goddard Space Flight Center, Code 661, Greenbelt, Maryland 20771 (United States); Fenimore, E. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545 (United States); Klebesadel, R. [1411 Servais Street, Green Bay, Wisconsin 54304 (United States)] [1411 Servais Street, Green Bay, Wisconsin 54304 (United States); Boer, M. [Centre d`Etude Spatiale des Rayonnements, B.P. 4346, 31029 Toulouse Cedex (France)] [Centre d`Etude Spatiale des Rayonnements, B.P. 4346, 31029 Toulouse Cedex (France); [Max-Planck-Institut fuer Extraterrestrische Physik, D 85740 Garching (Germany); Pedersen, H. [Copenhagen University Observatory, Oster Voldgade 3, Denmark 1350 Copenhagen (Denmark)] [Copenhagen University Observatory, Oster Voldgade 3, Denmark 1350 Copenhagen (Denmark); Niel, M. [Centre d`Etude Spatiale des Rayonnements, B.P. 4346, 31029 Toulouse Cedex (France)] [Centre d`Etude Spatiale des Rayonnements, B.P. 4346, 31029 Toulouse Cedex (France); Sommer, M. [Max-Planck-Institut fuer Extraterrestrische Physik, D 85740 Garching (Germany)] [Max-Planck-Institut fuer Extraterrestrische Physik, D 85740 Garching (Germany)

1996-06-01

91

X-ray emission from high temperature plasmas  

NASA Technical Reports Server (NTRS)

The bremsstrahlung X-rays from a plasma focus device were investigated with emphasis on the emission versus position, time, energy, and angle of emission. It is shown that low energy X-rays come from the plasma focus region, but that the higher energy components come from the anode. The emission is anisotropic, the low energy polar diagram resembling a cardioid, while the high energy emission is a lobe into the anode. The plasma parameters were considered indicating that even in the dense focus, the plasma is collisionless near the axis. By considering the radiation patterns of relativistic electrons a qualitative picture is obtained, which explains the measured polar diagrams, assuming the electrons that produce the X-rays have velocity vectors lying roughly in a cone between the point of focus and the anode. The average electron energy is about 3keV at the focus and about 10 keV on the anode surface. Results are consistent with the converging beam model of neutron production.

Harries, W. L.

1975-01-01

92

X-ray emission from clusters of galaxies  

NASA Technical Reports Server (NTRS)

Some X-ray spectral observations of approximately 30 clusters of galaxies from HEAO-1 are summarized. There exists strong correlations between X-ray luminosity, L(x), and temperature kT in the form L(x)alphaT to the 2.3 power. This result combined with the L(x) central galaxy density relation and the virial theorem indicates that the core dadius of the gas should be roughly independent of L(x) or KT and that more luminous clusters have a greater fraction of their virial mass in gas. The poor correlation of KT and optical velocity dispersion seems to indicate that clusters have a variety of equations of state. There is poor agreement between X-ray imaging observations and optical and X-ray spectral measures of the polytropic index. Most clusters show Fe emission lines with a strong indication that they all have roughly 1/2 solar abundance. The evidence for cooling in the cores of several clusters is discussed based on spectral observations with the Einstein solid state spectrometer.

Mushotzky, R. F.

1983-01-01

93

X-ray emission from clusters of galaxies  

NASA Technical Reports Server (NTRS)

Some X-ray spectral observations of approximately 30 clusters of galaxies from HEAO-1 are summarized. There exists strong correlation betwen X-ray luminosity, L(x), and temperature kT in the form L(x)alphaT to the 2.3 power. This result combined with the L(x) central galaxy density relation and the virial theorem indicates that the core dadius of the gas should be roughly independent of L(x) or Kt and that more luminous clusters have a greater fraction of their virial mass in gas. The poor correlation of KT and optical velocity dispersion seems to indicate that clusters have a variety of equations of state. There is poor agreement between X-ray imaging observations and optical and X-ray spectral measures of the polytropic index. Most clusters show Fe emission lines with a strong indication that they all have roughly 1/2 solar abundance. The evidence for cooling in the cores several clusters is discussed based on spectral observations with the Einstein solid state spectrometer.

Mushotzky, R. F.

1984-01-01

94

The X-ray emission of the polar BL Hydri  

NASA Astrophysics Data System (ADS)

We report on the analysis of the ASCA and BeppoSAX X-ray observations of the polar system BL Hyi, performed in October 94 and September 96, respectively. Emission from both poles is apparent from the folded light curves of both observations; the emission from the second pole varies from cycle to cycle, indicating non-stationary accretion there. The temperature of the post-shock region is estimated to be about 10 keV. Inclusion of both complex absorption and Compton reflection significantly improves the quality of the fit. No soft X-ray component is observed; the BeppoSAX/LECS upper limit to the soft component is in agreement with theoretical expectations for this low magnetic field system.

Matt, G.; Barcaroli, R.; Belloni, T.; Beuermann, K.; Bonnet-Bidaud, J. M.; de Martino, D.; Done, C.; Gänsicke, B. T.; Guainazzi, M.; Mouchet, M.; Mukai, K.

1998-06-01

95

Limits on diffuse X-ray emission from M101  

NASA Technical Reports Server (NTRS)

Observed limits on diffuse X-ray emission from M101 require that the temperature of any coronal or matrix hot gas which is radiating an appreciable part ( 10%) of the average supernova power be less than 10(5.7)K. Furthermore, the fraction of the galactic plane occupied by hot buttles similar to the one which apparently surrounds the Sun is at most 25% in the region between 10 kpc and 20 kpc from the galactic center.

Mccammon, D.; Sanders, W. T.

1984-01-01

96

The Large Scale X-Ray Emission from M87  

NASA Technical Reports Server (NTRS)

We describe asymmetrical features in a long exposure X-ray map of M87 made with the ROSAT High Resolution Imager (HRI). A bright triangular region is marked by a linear 'spur' along one edge. The structure of this spur suggests an interpretation of a tangential view of a shock front 18 kpc long. None of the brighter features are spatially coincident with radio or optical structures so we concur with earlier investigators that most of the emission arises from thermal processes.

Harris, D. E.; Biretta, J. A.; Junor, W.

1998-01-01

97

The Evolution of Coronal X-ray Emission  

E-print Network

;7 How do we infer the past properties of the Sun? The rotation-age connection The age-dependence of X1 The Evolution of Coronal X-ray Emission The Sun in Time Rob Jeffries Keele University NASA GSFC The Sun has been around for 4.6 Gyr. After 10-20 Myr as a pre-main sequence star it settled onto the ZAMS

98

Understanding The Physics Of X-ray Emission In Young Stars  

NASA Astrophysics Data System (ADS)

We present the analysis of Chandra X-ray observations of a sample of young stars, particularly T Tauri stars, in order to better understand the characteristics of the X-ray emitting plasmas of young stars and the physical mechanisms that produce that emission. Our sample includes Chandra High Energy Transmission Grating Spectroscopy (HETGS) relatively long integration, high spectral resolution data for nine young stars, including classical, weak-lined, and post-T Tauri stars as well as a young main sequence star. For five of these nine stars we observed significant flaring during the Chandra observing epochs. We extracted spectra for each observation, and for the observations with significant flaring, we extracted separate spectra for the flaring and quiescent epochs. From these spectra, we measured the line fluxes of the strongest emission lines, most notably the Hydrogen-like Lyman line and the He-like triplet (forbidden, intercombination, and resonance) lines for Si, Mg, and Ne as well as strong Fe lines. From these line flux measurements, we were able to infer densities and temperatures from line flux ratios sensitive to these properties. In general, the quiescent state observations have higher densities (as inferred by the density-sensitive R ratio) than the flaring state observations. By measuring elemental abundance ratios, we find that all the observations of the stars in our sample have a high Ne/Fe ratio, but only one, TW Hya in quiescence, shows an enhanced Ne/O ratio. This work was supported by a grant from NASA's Chandra X-ray Observatory.

Shukla, Sonali J.; Weintraub, D.

2010-01-01

99

Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness  

NASA Astrophysics Data System (ADS)

We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z < 1.3. However, their rest-frame ?2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with <~ 45 counts in the 3-24 keV band, and the other three are not detected. The hard X-ray (8-24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (?eff ? 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (gsim 33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

Luo, B.; Brandt, W. N.; Alexander, D. M.; Stern, D.; Teng, S. H.; Arévalo, P.; Bauer, F. E.; Boggs, S. E.; Christensen, F. E.; Comastri, A.; Craig, W. W.; Farrah, D.; Gandhi, P.; Hailey, C. J.; Harrison, F. A.; Koss, M.; Ogle, P.; Puccetti, S.; Saez, C.; Scott, A. E.; Walton, D. J.; Zhang, W. W.

2014-10-01

100

Rotation and X-ray emission from protostars  

E-print Network

The ASCA satellite has recently detected variable hard X-ray emission from two Class I protostars in the rho Oph cloud, YLW15 (IRS43) and WL6, with a characteristic time scale ~20h. In YLW15, the X-ray emission is in the form of quasi-periodic energetic flares, which we explain in terms of strong magnetic shearing and reconnection between the central star and the accretion disk. In WL6, X-ray flaring is rotationally modulated, and appears to be more like the solar-type magnetic activity ubiquitous on T Tauri stars. We find that YLW15 is a fast rotator (near break-up), while WL6 rotates with a significantly longer period. We derive a mass M_\\star ~ 2 M_\\odot and \\simlt 0.4 M_\\odot for the central stars of YLW15 and WL6 respectively. On the long term, the interactions between the star and the disk results in magnetic braking and angular momentum loss of the star. On time scales t_{br} ~ a few 10^5 yrs, i.e., of the same order as the estimated duration of the Class~I protostar stage. Close to the birthline there must be a mass-rotation relation, t_{br} \\simpropto M_\\star, such that stars with M_\\star \\simgt 1-2 M_\\odot are fast rotators, while their lower-mass counterparts have had the time to spin down. The rapid rotation and strong star-disk magnetic interactions of YLW15 also naturally explain the observation of X-ray ``superflares''. In the case of YLW15, and perhaps also of other protostars, a hot coronal wind (T~10^6 K) may be responsible for the VLA thermal radio emission. This paper thus proposes the first clues to the rotation status and evolution of protostars.

Thierry Montmerle; Nicolas Grosso; Yohko Tsuboi; Katsuji Koyama

1999-11-19

101

X-ray Emission and Reprocessing in AGNs  

NASA Astrophysics Data System (ADS)

In this review, I discuss the primary X-ray emission of radio-quiet AGN and the reprocessing of this radiation by both the accretion disc and distant matter. Recent results, mostly from XMM-Newton, are reviewed, and the major open issues discussed. I will first treat the innermost regions, with respect to both the primary emission and the reprocessing by the accretion disc (with particular emphasis on the strong gravity effects on the iron line profile). I will then discuss absorption and reprocessing by distant matter, and in particular the ``torus'' and the disc of the host galaxy.

Matt, G.

2007-10-01

102

OPTICAL EMISSION OF THE BLACK HOLE X-RAY TRANSIENT MAXI J1659-152 DURING QUIESCENCE  

SciTech Connect

We report on the optical detection of the black hole X-ray transient MAXI J1659-152 during its quiescent state. By using the Canada-France-Hawaii Telescope, we observed MAXI J1659-152 about seven months after the end of an X-ray outburst. The optical counterpart of MAXI J1659-152 is clearly detected with an r'-band magnitude of 23.6-23.8. The detection confirms that the optical emission of MAXI J1659-152 during quiescence is relatively bright compared to other black hole X-ray transients. This implies that the distance to MAXI J1659-152 is 4.6-7.5 kpc for an M2 dwarf companion star or 2.3-3.8 kpc for an M5 dwarf companion star. By comparing with other measurements, an M2 dwarf companion is more likely.

Kong, Albert K. H., E-mail: akong@phys.nthu.edu.tw [Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

2012-12-01

103

Hard X-ray Emission from the NGC 5044 Group  

NASA Astrophysics Data System (ADS)

Observations made with the Rossi X-ray Timing Explorer Proportional Counter Array (PCA) to constrain the hard X-ray emission in the NGC 5044 group are reported here. Modeling a combined PCA and ROSAT position sensitive proportional counter spectrum with a 0.5-15 keV energy range shows excess hard emission above 4 keV. Addition of a power-law component with a spectral index of 2.6-2.8 and a luminosity of 2.6 × 1042 erg s-1 within 700 kpc in the observed energy band removes these residuals. Thus, there is a detection of a significant non-thermal component that is 32% of the total X-ray emission. Point-source emission makes up at most 14% of the non-thermal emission from the NGC 5044 group. Therefore, the diffuse, point-source-subtracted, non-thermal component is (2.2-3.0) × 1042 erg s-1. The cosmic-ray electron energy density is 3.6 × 10-12 erg cm-3 and the average magnetic field is 0.034 ?G in the largest radio emitting region. The ratio of cosmic-ray electron energy density to magnetic field energy density, ~2.5 × 104, is significantly out of equipartition and is therefore atypical of radio lobes. In addition, the group's small size and low non-thermal energy density strongly contradicts the size-energy relationship found for radio lobes. Thus, it is unlikely related to the active galaxy and is most likely a relic of the merger. The energy in cosmic rays and magnetic field is consistent with simulations of cosmic-ray acceleration by merger shocks.

Henriksen, Mark J.

2011-01-01

104

Measurement of coronal X-ray emission lines from Capella  

NASA Technical Reports Server (NTRS)

The Einstein Observatory's Focal Plane Crystal Spectrometer has detected X-ray emission lines due to O VIII, Fe XVII, and Fe XX, from the binary star system Capella. Line luminosities are well fitted by an emitting plasma at a single temperature of 6.29 + or - 0.01 - 0.03 million K, and a volume emission measure of about 8.6 x 10 to the 52nd/cu cm, corresponding to the low temperature component previously observed. A high temperature component is undetectable, since the observed lines are not produced in plasma at temperatures above about 20 million K. Nearly isothermal plasma would be expected if many of the magnetically confined coronal loops have similar sizes and pressures, and a second population of longer loops would be required to account for the hotter component. An alternative interpretation of the observed X-ray line emission and upper limit is that the plasma contains a continuous distribution of emission measure versus temperature that rises sharply to 3 million K and then falls by nearly a decade to 16 million. An extrapolation of the loop sizes suggested by this alternative to hotter, longer loops may also account for the higher temperature emission.

Vedder, P. W.; Canizares, C. R.

1983-01-01

105

X-ray/UV variability and the origin of soft X-ray excess emission from II Zw 177  

NASA Astrophysics Data System (ADS)

We study a detailed broad-band X-ray/UV emission from the narrow line Seyfert 1 galaxy II Zw 177 based on two XMM-Newton and single Swift/XRT observations. Both XMM-Newton observations show the soft X-ray excess emission below 2 keV when the best-fit 2 - 10 keV power law is extrapolated down to 0.3 keV. We find the blurred reflection from an ionized accretion disc and Comptonized disc emission both describe the observed soft excess well. We find a remarkable trend of decreasing UV flux with increasing soft X-ray excess and power law emission. We suggest that this could be due to that the external edge of corona hide a fraction of accretion disk. Co-Author: Prof. Gulab C. Dewangan (IUCAA), Prof. Ranjeev Misra (IUCAA), Pramod Kumar (Nanded university)

Pal, Main

106

Chandra ACIS Observations of Jovian X-Ray Emission  

NASA Technical Reports Server (NTRS)

On November 25 and 26, 1999, the Chandra X-ray spacecraft conducted a set of four 19,000 sec observations of Jupiter. The ACIS-S instrument configuration was used for its good low energy efficiency and spatial resolution. An anomalous response was obtained which was subsequently attributed to strong jovian infrared radiation penetrating the detector and piling up spurious events across the entire X-ray range. However, the pre-observation establishment of an offsetting bias field has allowed the recovery of data from that portion of Jupiter's disc which remained within the elevated portion of the bias field during the observation. This ranges from fewer than 3000 sec to the entire observing time for about 10% of the planet. Auroral emission is seen near both poles in each observation. The northern aurora ia overall more intense than the southern, consistent with prior Einstein and ROSAT Observatory results. The southern aurora shows more modulation with Jupiter's rotation than the northern. Spatial resolution has been improved by at least a factor of two over prior measurements but convincing evidence of structure has not been seen. Lower latitude emission, first observed by ROSAT, is confirmed with flux levels averaging more than a factor of five below peak auroral values. Pronounced variation in the observed emission has occurred over the observing period. The spectral response extends from 0.24 keV, below which noise dominates, to about 1.2 keV. For all four observations the spectrum is clearly enhanced between 0.45 and 0.85 keV. This is apparently unequivocal evidence that Jupiter's X-ray emission is the result of oxygen and perhaps sulfur ions precipitating into the planet's atmosphere, where they undergo charge exchange interactions. The identification of specific transitions lines in the spectrum is among the ongoing efforts. A bremsstrahlung component has not yet been identified.

Garmire, Gordon; Elsner, Ronald; Feigelson, Eric; Ford, Peter; Gladstone, G. Randall; Hurley, Kevin; Metzger, Albert; Waite, J. Hunter, Jr.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

107

Detection of 17 GHz radio emission from X-ray-bright points  

NASA Technical Reports Server (NTRS)

Using observations made with the Nobeyama radio heliograph (NRH) at 17 GHz and the Yohkoh/SXT experiment, we report the first detection of 17 GHz signatures of coronal X-ray-bright points (XBPs). This is also the first reported detection of flaring bright points in microwaves. We have detected four BPs at 17 GHz out of eight identified in SXT data on 1992 July 31, for which we looked for 17 GHz emission. For one XBP located in a quiet mixed-polarity region, the peak times at 17 GHz and X-rays are very similar, and both are long-lasting-about 2 hr in duration. There is a second BP (located near an active region) which is most likely flaring also, but the time profiles in the two spectral domains are not similar. The other two 17 GHz BPs are quiescent with fluctuations superposed upon them. For the quiet region XBP, the gradual, long-lasting, and unpolarized emission suggests that the 17 GHz emission is thermal.

Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.

1994-01-01

108

X-ray Emission From Planets Venus and Mars: Theoretical Model and Numerical Simulations  

Microsoft Academic Search

Recently X-ray emission from non-magnetic planets Venus and Mars have been discovered by Chandra X-ray telescopes [1,2]. Analysis of observational data shows that either charge exchange model or fluorescent scattering of solar x-rays cannot explain the whole set of observational data. The premise of this paper is that x-ray emission of both planets is a combination of line k-shell radiation

P. Bryans; V. D. Shapiro; R. Bingham; M. Tourner

2003-01-01

109

Astrophysics Research Projects:Astrophysics Research Projects: massive star winds, x-ray emission, theoretical models,massive star winds, x-ray emission, theoretical models,  

E-print Network

Astrophysics Research Projects:Astrophysics Research Projects: massive star winds, x-ray emission, theoretical models,massive star winds, x-ray emission, theoretical models, spectroscopy, laboratory plasma-drivenhave powerful radiation-driven stellar windsstellar winds.. etaeta CarinaCarina #12;TheThe ChandraChandra X

Cohen, David

110

The X-ray Iron Emission from Tycho's Supernova Remnant  

E-print Network

We present the results of broadband fits to the X-ray spectrum of Tycho's supernova remnant obtained by the Solid-State Imaging Spectrometers on the ASCA Observatory. We use single-temperature, single-ionization-age, nonequilibrium ionization models to characterize the ejecta and the blast-shocked interstellar medium. Based on the Fe K emission at 6.5 keV, previous spectral studies have suggested that the Fe ejecta in this Type Ia remnant are stratified interior to the other ejecta. The ASCA data provide important constraints from the Fe L emission near 1 keV as well as the Fe K emission. We find that the simplest models, with emission from the ejecta and blast wave each at a single temperature and ionization age, severely underestimate the Fe K flux. We show that there is little Fe emission associated with the Si and S ejecta shell. The blast-shocked interstellar medium has abundances roughly 0.3 times the solar value, while the ejecta, with the exception of Fe, have relative abundances that are typical of Type Ia supernovae. The addition of another component of Fe emission, which we associate with ejecta, at a temperature at least two times higher and an ionization age $\\sim$ 100 times lower than the Si ejecta, does provide a good fit to the spectrum. This model is consistent with X-ray imaging results. Although fluorescent emission from dust in the remnant may contribute to the Fe K flux, we conclude that it is unlikely to dominate.

Una Hwang; John P. Hughes; Robert Petre

1997-12-17

111

DISCOVERY OF A CANDIDATE QUIESCENT LOW-MASS X-RAY BINARY IN THE GLOBULAR CLUSTER NGC 6553  

SciTech Connect

This paper reports the search for quiescent low-mass X-ray binaries (qLMXBs) in the globular cluster (GC) NGC 6553 using an XMM-Newton observation designed specifically for that purpose. We spectrally identify one candidate qLMXB in the core of the cluster, based on the consistency of the spectrum with a neutron star H-atmosphere model at the distance of NGC 6553. Specifically, the best-fit radius found using the three XMM European Photon Imaging Camera spectra is R{sub NS} = 6.3{sub -}0{sub .8}{sup +2.3} km (for M{sub NS} = 1.4 M{sub sun}) and the best-fit temperature is kT{sub eff} = 136{sub -34}{sup +21} eV. Both physical parameters are in accordance with typical values of previously identified qLMXBs in GC and in the field, i.e., R{sub NS} {approx} 5-20 km and kT{sub eff} {approx} 50-150 eV. A power-law (PL) component with a photon index {Gamma} = 2.1{sup +0.5}{sub -0.8} is also required for the spectral fit and contributes {approx}33% of the total flux of the X-ray source. A detailed analysis supports the hypothesis that the PL component originates from nearby sources in the core, unresolved with XMM. The analysis of an archived Chandra observation provides marginal additional support to the stated hypothesis. Finally, a catalog of all the sources detected within the XMM field of view is presented here.

Guillot, Sebastien; Rutledge, Robert E. [Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A-2T8 (Canada); Brown, Edward F. [Department of Physics and Astronomy, Michigan State University, 3250 Biomedical Physical Science Building, East Lansing, MI 48824-2320 (United States); Pavlov, George G. [Department of Physics and Astronomy, Pennsylvania State University, 512 Davey Lab, University Park, PA 16802 (United States); Zavlin, Vyacheslav E., E-mail: guillots@physics.mcgill.ca, E-mail: rutledge@physics.mcgill.ca [Space Science Laboratory, Universities Space Research Association, NASA MSFC VP62, Huntsville, AL 35805 (United States)

2011-09-10

112

X-ray Emission from Eta Carinae near Periastron in 2009: Origin of the X-ray Minimum  

NASA Astrophysics Data System (ADS)

X-ray emission from the supermassive binary system, Eta Carinae, declines sharply around periastron. This X-ray minimum has two distinct phases --- the lowest flux phase in the first ~3 weeks and a slightly brighter phase thereafter. In 2009, the Chandra X-ray Observatory monitored the first phase five times and found the lowest observed flux at ~1.9e-12 ergs cm-2 s-1 (3-8 keV). The spectral shape changed such that the hard band above ~4 keV dropped quickly at the beginning and the soft band flux gradually decreased to its lowest observed value in ~2 weeks. The hard band spectrum had begun to recover by that time. This spectral variation suggests that the shocked gas producing the hottest X-ray gas near the apex of the wind-wind collision (WWC) is blocked behind the dense inner wind of the primary star, which later occults slightly cooler gas downstream. Shocked gas previously produced by the system at earlier orbital phases is suggested to produce the faint residual X-ray emission seen when the emission near the apex is completely blocked by the primary wind. The brighter phase is probably caused by the re-appearance of the WWC plasma, whose emissivity significantly declined during the occultation. We interpret this to mean that the X-ray minimum is produced by a hybrid mechanism of an occultation and a decline in emissivity of the WWC shock. We constrain timings of superior conjunction and periastron based on these results.

Hamaguchi, Kenji; Corcoran, M. F.; Russell, C. M.; Pollock, A. M.; Gull, T. R.; Teodoro, M.; Madura, T.; Damineli, A.; Pittard, J. M.

2014-01-01

113

A Chandra survey of X-ray emission from radio jets: Correlations of the jet X-ray flux  

NASA Astrophysics Data System (ADS)

We have completed a Chandra survey for X-ray emission from 54 radio jets that are extended on arcsecond scales. These are in flat spectrum radio loud quasars and have redshifts in the range z=0.3 to z=2.1. We detect X-ray emission from 60% of the jets. The study reported here considers the straight part of the jet nearest to the quasar. The X-ray counting rate from this correlates very well to that from the quasar. Correlation with redshift, the jet radio flux, the radio core flux, or visual apparent magnitude is poor or non-existent.This research was supported by NASA contract NAS8-03060, SAO Grant GO9-0121B, and HST Grant HST-GO-11838.04-A

Schwartz, Daniel A.; Marshall, Herman L.; Worrall, Diana M.; Birkinshaw, Mark; Perlman, Eric S.; Lovell, Jim; Jauncey, David L.; Murphy, David William; Gelbord, Jonathan; Godfrey, Leith; Bicknell, Geoffrey V.

2015-01-01

114

X-ray emission from middle-aged pulsars  

E-print Network

We present a simple, unified model which accounts for properties of the X-ray emission from the three middle-aged pulsars PSR 1055-52, PSR 0656+14 and PSR 0630+18 (Geminga). The X-ray radiation from these objects is pulsed more strongly at energies above a transition point around 0.5 keV. In addition, the phase of the pulses shifts by about 80-100 degrees around the same point. Geminga also has the peculiarity that its pulsed fraction decreases in the 0.3-0.5 keV energy range, attaining a minimum near 0.5 keV. We show that a two-component hydrogen atmosphere is able to account for these disparate features. In our model, the hotter component is powered by particle bombardment and is restricted to the polar regions, while the cooler one covers the entire stellar surface. The two components also differ in their emission patterns, with the hard and soft contributions coming from areas radiating into fan and pencil beams, respectively.

Rosalba Perna; Jeremy Heyl; Lars Hernquist

2001-04-30

115

Response of the low ionosphere to X-ray and Lyman-? solar flare emissions  

NASA Astrophysics Data System (ADS)

Using soft X-ray measurements from detectors onboard the Geostationary Operational Environmental Satellite (GOES) and simultaneous high-cadence Lyman-? observations from the Large Yield Radiometer (LYRA) onboard the Project for On-Board Autonomy 2 (PROBA2) ESA spacecraft, we study the response of the lower part of the ionosphere, the D region, to seven moderate to medium-size solar flares that occurred in February and March of 2010. The ionospheric disturbances are analyzed by monitoring the resulting sub-ionospheric wave propagation anomalies detected by the South America Very Low Frequency (VLF) Network (SAVNET). We find that the ionospheric disturbances, which are characterized by changes of the VLF wave phase, do not depend on the presence of Lyman-? radiation excesses during the flares. Indeed, Lyman-? excesses associated with flares do not produce measurable phase changes. Our results are in agreement with what is expected in terms of forcing of the lower ionosphere by quiescent Lyman-? emission along the solar activity cycle. Therefore, while phase changes using the VLF technique may be a good indicator of quiescent Lyman-? variations along the solar cycle, they cannot be used to scale explosive Lyman-? emission during flares.

Raulin, Jean-Pierre; Trottet, GéRard; Kretzschmar, Matthieu; Macotela, Edith L.; Pacini, Alessandra; Bertoni, Fernando C. P.; Dammasch, Ingolf E.

2013-01-01

116

X-ray emission of A stars Coronae and wind shocks  

E-print Network

07.06.2013 3 / 17 #12;X-rays from A stars (main-sequence) X-ray 'dark zone' from mid A to mid B stars no stellar dynamo (no outer convection zone) stellar winds too weak to power X-ray emission many X-ray detections (10 % RASS, H¨unsch et al. 1998, Schr¨oder & Schmitt, 2007) classical explanation: 'hidden

Robrade, Jan

117

First Detection of Phase-dependent Colliding Wind X-ray Emission outside the Milky Way  

NASA Technical Reports Server (NTRS)

After having reported the detection of X-rays emitted by the peculiar system HD 5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first detection of apparently periodic X-ray emission from hot gas produced by the collision of winds in an evolved massive binary outside the Milky Way. It also provides the first X-ray monitoring of a Luminous Blue Variable only years after its eruption and shows that the source of the X-rays is not associated with the ejecta.

Naze, Yael; Koenigsberger, Gloria; Moffat, Anthony F. J.

2007-01-01

118

X-ray emission from young supernova remnants - Nonionization equilibrium abundances and emissivities  

NASA Technical Reports Server (NTRS)

X-ray line emission from hot, low-density plasma in young supernova remnants is strongly enhanced by departures from ionization equilibrium. The X-ray emission from a Sedov blast wave has been calculated using a nonequilibrium evolutionary treatment of the ionization structure, and the resulting spectrum has been fitted to HEAO 2 SSS data for Tycho's remnant. These models yield dramatically different elemental abundances for heavy elements (Ne, Mg, Si, S, Ar, Ca, and Fe), compared with two-temperature component equilibrium models of Becker et al. (1979, 1980). Nonequilibrium broad-band X-ray emissivities result in lower mass determinations for the supernova ejecta. Areas of further improvement of remnant X-ray modeling are suggested.

Shull, J. M.

1982-01-01

119

X-ray Emission from Megamaser Galaxy IC 2560  

E-print Network

Observation of the H2O megamaser galaxy IC 2560 with the Chandra Observatory reveals a complex spectrum composed of soft X-ray emission due to multi-temperature thermal plasma, and a hard continuum with strong emission lines. The continuum is most likely a Compton reflection (reprocessing) of primary emission that is completely absorbed at least up to 7 keV. The lines can be identified with fluorescence from Si, S and Fe in the lowest ionization stages. The equivalent widths of the Si and S lines are broadly compatible with those anticipated for reprocessing by optically thick cold plasma of Solar abundances, while the large equivalent width of the Fe line requires some overabundance of iron. A contribution to the line from a transmitted component cannot be ruled out, but the limits on the strength of the Compton shoulder make it less likely. From the bolometric luminosity of the nuclear region, we infer that the source radiates at 1 - 10% of its Eddington luminosity, for an adopted central mass of 3 million Solar masses. The overall spectrum is consistent with the hypotheses that the central engines powering the detected megamsers in accretion disks are obscured from direct view by the associated accretion disk material itself, and that there is a correlation between the occurrence of megamaser emission and Compton-thick absorption columns. For the 11 known galaxies with both column density measurements and maser emission believed to arise from accretion disks, eight AGN are Compton thick.

Greg Madejski; Chris Done; Piotr Zycki; Lincoln Greenhill

2005-10-06

120

Determination of total x-ray absorption coefficient using non-resonant x-ray emission  

Microsoft Academic Search

An alternative measure of x-ray absorption spectroscopy (XAS) called inverse partial fluorescence yield (IPFY) has recently been developed that, unlike conventional electron yield (EY) and fluorescence yield (FY) measurements, is both bulk sensitive and does not experience saturation or self-absorption effects. In this manuscript, we show that the angle dependence of IPFY can also provide a direct measure of the

A. J. Achkar; T. Z. Regier; E. J. Monkman; K. M. Shen; D. G. Hawthorn

2011-01-01

121

Charge Exchange-Induced X-Ray Emission from Comet C\\/1999 S4 (LINEAR)  

Microsoft Academic Search

Using soft x-ray observations of the bright new comet C\\/1999 S4 (LINEAR) with the Chandra x-ray observatory, we have detected x-ray line emission created by charge exchange between highly ionized solar wind minor ions and neutral gases in the comet's coma. The emission morphology was symmetrically crescent shaped and extended out to 300,000 kilometers from the nucleus. The emission spectrum

C. M. Lisse; D. J. Christian; K. Dennerl; K. J. Meech; R. Petre; H. A. Weaver; S. J. Wolk

2001-01-01

122

X-ray emission from Stephan's Quintet and other compact groups  

NASA Technical Reports Server (NTRS)

A search for X-ray emission from five compact groups of galaxies with the Einstein Observatory revealed detections from three groups. Soft, extended X-ray emission was observed in Stephan's Quintet, which is most likely caused by hot intracluster gas. This provides evidence for dynamical interaction among the group galaxies. X-ray emission from the group Arp 330 may also originate in hot intracluster gas. Stephan's Quintet and Arp 330 have the largest velocity dispersions among the groups studied, suggesting a correlation between high velocity and the release (or properties) of hot gas. X-ray emission from Arp 318 may originate in its member galaxies.

Bahcall, N. A.; Harris, D. E.; Rood, H. J.

1984-01-01

123

X-Ray Emission from Jupiter, Saturn, and Earth: A Short Review  

E-print Network

Jupiter, Saturn, and Earth - the three planets having dense atmosphere and a well developed magnetosphere - are known to emit X-rays. Recently, Chandra X-ray Observatory has observed X-rays from these planets, and XMM-Newton has observed them from Jupiter and Saturn. These observations have provided improved morphological, temporal, and spectral characteristics of X-rays from these planets. Both auroral and non-auroral (low-latitude) 'disk' X-ray emissions have been observed on Earth and Jupiter. X-rays have been detected from Saturn's disk, but no convincing evidence for X-ray aurora on Saturn has been observed. The non-auroral disk X-ray emissions from Jupiter, Saturn, and Earth, are mostly produced due to scattering of solar X-rays. X-ray aurora on Earth is mainly generated via bremsstrahlung from precipitating electrons and on Jupiter via charge exchange of highlyionized energetic heavy ions precipitating into the polar atmosphere. Recent unpublished work suggests that at higher (>2 keV) energies electron bremsstrahlung also plays a role in Jupiter's X-ray aurora. This paper summarizes the recent results of X-ray observations on Jupiter, Saturn, and Earth mainly in the soft energy (~0.1-2.0 keV) band and provides a comparative overview.

Anil Bhardwaj

2006-05-11

124

Two component X-ray emission from RS CVn binaries  

NASA Astrophysics Data System (ADS)

A summary of results from the solid state spectrometer on the Einstein Observatory for 7 RS CVn binaries is presented. The spectra of all require two emission components, evidenced by line emission characteristic of plasma at 4 to 8 x 10 to the 6th power and bremsstrahlung characteristic of 20 to 100 x 10 to the 6th power K. The data are interpreted in terms of magnetic coronal loops similar to those seen on the Sun, although with different characteristic parameters. The emission regions could be defined by separate magnetic structures. For pressure less than approximately 10 dynes/sq cm the low temperature plasma would be confined within the stellar radii, while the high temperature plasma would, for the synchronous close binaries, fill the binary orbits. However, for loop pressures exceeding 100 dynes/sq cm, the high temperature components would also be confined to within the stellar radii, in loops covering only small fractions of the stellar surfaces. While the radio properties and the occurrence of X-ray flares suggest the larger emission regions, the observations of time variations leave the ambiguity unresolved.

Swank, J. H.; White, N. E.; Holt, S. S.; Becker, R. H.

1980-11-01

125

X-Ray, UV, and Optical Observations of Supernova 2006bp with Swift: Detection of Early X-Ray Emission  

E-print Network

We present results on the X-ray and optical/UV emission from the type IIP SN 2006bp and the interaction of the SN shock with its environment, obtained with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on-board the Swift observatory. SN 2006bp is detected in X-rays at a 4.5 sigma level of significance in the merged XRT data from days 1 to 12 after the explosion. If the X-ray luminosity of (1.8+/-0.4)E39 ergs/s is caused by interaction of the SN shock with circumstellar material (CSM), deposited by a stellar wind from the progenitor's companion star, a mass-loss rate of ~E-05 M_sun/yr is inferred. The mass-loss rate is consistent with the non-detection in the radio with the VLA on days 2, 9, and 11 after the explosion and characteristic of a red supergiant progenitor with a mass around 12-15 M_sun prior to the explosion. In combination with a follow-up XMM-Newton observation obtained on day 21 after the explosion, an X-ray rate of decline with index 1.2+/-0.6 is inferred. Since no other SN has been detected in X-rays prior to the optical peak and since type IIP SNe have an extended 'plateau' phase in the optical, we discuss the scenario that the X-rays might be due to inverse Compton scattering of photospheric optical photons off relativistic electrons produced in circumstellar shocks. However, due to the high required value of the Lorentz factor (~10-100) we conclude that Inverse Compton scattering is an unlikely explanation for the observed X-ray emission. The fast evolution of the optical/ultraviolet spectral energy distribution and the spectral changes observed with Swift reveal the onset of metal line-blanketing and cooling of the expanding photosphere during the first few weeks after the outburst.

S. Immler; P. J. Brown; P. Milne; L. Dessart; P. A. Mazzali; W. Landsman; N. Gehrels; R. Petre; D. N. Burrows; J. A. Nousek; R. A. Chevalier; C. L. Williams; M. Koss; C. J. Stockdale; M. T. Kelley; K. W. Weiler; S. T. Holland; E. Pian; P. W. A. Roming; D. Pooley; K. Nomoto; J. Greiner; S. Campana; A. M. Soderberg

2007-03-29

126

The cosmic X-ray background-IRAS galaxy correlation and the local X-ray volume emissivity  

NASA Technical Reports Server (NTRS)

We have cross-correlated the galaxies from the IRAS 2 Jy redshift survey sample and the 0.7 Jy projected sample with the all-sky cosmic X-ray background (CXB) map obtained from the High Energy Astronomy Observatory (HEAO) 1 A-2 experiment. We have detected a significant correlation signal between surface density of IRAS galaxies and the X-ray background intensity, with W(sub xg) = (mean value of ((delta I)(delta N)))/(mean value of I)(mean value of N)) of several times 10(exp -3). While this correlation signal has a significant implication for the contribution of the local universe to the hard (E greater than 2 keV) X-ray background, its interpretation is model-dependent. We have developed a formulation to model the cross-correlation between CXB surface brightness and galaxy counts. This includes the effects of source clustering and the X-ray-far-infrared luminosity correlation. Using an X-ray flux-limited sample of active galactic nuclei (AGNs), which has IRAS 60 micrometer measurements, we have estimated the contribution of the AGN component to the observed CXB-IRAS galaxy count correlations in order to see whether there is an excess component, i.e., contribution from low X-ray luminosity sources. We have applied both the analytical approach and Monte Carlo simulations for the estimations. Our estimate of the local X-ray volume emissivity in the 2-10 keV band is rho(sub x) approximately = (4.3 +/- 1.2) x 10(exp 38) h(sub 50) ergs/s/cu Mpc, consistent with the value expected from the luminosity function of AGNs alone. This sets a limit to the local volume emissivity from lower luminosity sources (e.g., star-forming galaxies, low-ionization nuclear emission-line regions (LINERs)) to rho(sub x) less than or approximately = 2 x 10(exp 38) h(sub 50) ergs/s/cu Mpc.

Miyaji, Takamitsu; Lahav, Ofer; Jahoda, Keith; Boldt, Elihu

1994-01-01

127

Field Emission Arrays for Tomographic Medical X-Ray Imaging  

Microsoft Academic Search

X-ray imaging has been important to both medical and industrial applications for over 100 years. Tomographic X-ray imaging has evolved over the last several decades with improvements in x-ray detectors and computing capability. The ability to reconstruct high-resolution, three-dimensional anatomical images for the detection of tumors, blood clots, and bleeding has had a major impact in medicine. Tomographic imaging requires

P. R. Schwoebelt; C. E. Holland; C. A. Spindt

2006-01-01

128

Measurements of x-ray emission from rocket-triggered lightning  

Microsoft Academic Search

We report measurements of the x-ray emission from rocket-triggered lightning, made during the summer of 2003, using four instruments placed between 15 and 40 m from the lightning channels. X-rays were measured 0-80 mus just prior to and at the beginning of 73% of the 26 return strokes observed. The emission was composed of multiple, very brief bursts of x-rays

J. R. Dwyer; H. K. Rassoul; M. Al-Dayeh; L. Caraway; B. Wright; A. Chrest; M. A. Uman; V. A. Rakov; K. J. Rambo; D. M. Jordan; J. Jerauld; C. Smyth

2004-01-01

129

A Survey of X-ray Emission from Wolf-Rayet Stars  

Microsoft Academic Search

Previous X-ray studies of Wolf-Rayet (WR) stars have focused mainly on WR binary systems whose luminous high-temperature X-ray emission is thought to originate (at least partially) in colliding wind shocks between the two stars. Much less is known about the X-ray emission of putatively single WR stars, for which evidence of binarity is lacking. We present new results from an

Steve L. Skinner; S. Zhekov; M. Guedel; W. Schmutz; K. Sokal

2009-01-01

130

High Resolution Temporal and Spectral Monitoring of Eta Carinae's X-Ray Emission the June Eclipse  

NASA Technical Reports Server (NTRS)

The supermassive and luminous star Eta Carinae undergoes strong X-ray variations every 5.5 years when its 2-10 keV X-ray emission brightens rapidly with wild fluctuations before dropping by a factor of 100 to a minimum lasting 3 months. The most recent X-ray "eclipse" began in June 2003 and during this time Eta Carinae was intensely observed throughout the electromagnetic spectrum. Here we report the first results of frequent monitoring of the 2-10 keV band X-ray emission by the Rossi X-ray Timing Explorer along wit high resolution X-ray spectra obtained with the transmission gratings on the Chandra X-ray Observatory. We compare these observations to those results obtained during the previous X-ray eclipse in 1998, and interpret the variations in the X-ray brightness, in the amount of absorption, in the X-ray emission measure and in the K-shell emission lines in terms of a colliding wind binary model.

Corcoran, M. F.; Hamaguchi, K.; Henley, D.; Pittard, J. M.; Gull, T. R.; Davidson, K.; Swank, J. H.; Petre, R.; Ishibashi, K.

2004-01-01

131

The PG X-Ray QSO Sample: Links between the Ultraviolet-X-Ray Continuum and Emission Lines  

NASA Astrophysics Data System (ADS)

Two sets of relationships relate QSO UV to soft X-ray continua with the broad-line region. These are (i) the Baldwin relationships, which are inverse relationships between the broad-line equivalent width and the continuum luminosity, and (ii) Boroson & Green's optical ``Principal Component 1'' relationships, linking steeper soft X-ray spectra with narrower H? emission, stronger H? blue wings, stronger optical Fe II emission, and weaker [O III] ?5007 lines. In order to understand these relationships, we extended the spectra into the UV for 22 QSOs with high-quality soft X-ray spectra. These are from the complete sample of QSOs from the Bright Quasar Survey for which Laor et al. demonstrated strong luminosity and X-ray-optical Principal Component 1 relationships. We show that these extend to a whole new set of UV relationships: Principal Component 1 (in the sense of steeper X-ray spectra) is related to narrower C III] ?1909 lines, larger Si III] ?1892/C III] ?1909 ratios (a high-density indicator), stronger low-ionization lines, and weaker C IV ?1549 but stronger N V ?1240 lines. We speculate that high accretion rates are linked to high columns of dense (~1011 cm-3), nitrogen-enhanced, low-ionization gas from nuclear starbursts. Line width, inverse Fe II-[O III] and inverse Fe II-C IV relationships hint at the geometrical arrangement of this gas. These Principal Component 1 relationships appear to be independent of luminosity and therefore of the Baldwin relationships.

Wills, Beverley J.; Laor, A.; Brotherton, M. S.; Wills, D.; Wilkes, B. J.; Ferland, G. J.; Shang, Zhaohui

1999-04-01

132

X-ray Emission from Megamaser Galaxy IC 2560  

SciTech Connect

Observation of the H{sub 2}O megamaser galaxy IC 2560 with the Chandra Observatory reveals a complex spectrum composed of soft X-ray emission due to multi-temperature thermal plasma, and a hard continuum with strong emission lines. The continuum is most likely a Compton reflection (reprocessing) of primary emission that is completely absorbed at least up to 7 keV. The lines can be identified with fluorescence from Si, S and Fe in the lowest ionization stages. The equivalent widths of the Si and S lines are broadly compatible with those anticipated for reprocessing by optically thick cold plasma of Solar abundances, while the large equivalent width of the Fe line requires some overabundance of iron. A contribution to the line from a transmitted component cannot be ruled out, but the limits on the strength of the Compton shoulder make it less likely. From the bolometric luminosity of the nuclear region, we infer that the source radiates at 1-10% of its Eddington luminosity, for an adopted central mass of 3 x 10{sup 6} M{sub {circle_dot}}. The overall spectrum is consistent with the hypotheses that the central engines powering the detected megamsers in accretion disks are obscured from direct view by the associated accretion disk material itself, and that there is a correlation between the occurrence of megamaser emission and Compton-thick absorption columns. For the 11 known galaxies with both column density measurements and maser emission believed to arise from accretion disks, eight AGN are Compton thick.

Madejski, Greg; /SLAC /KIPAC, Menlo Park; Done, Chris; /Durham U.; Zycki, Piotr; /Warsaw, Copernicus Astron. Ctr.; Greenhill, Lincoln; /KIPAC, Menlo Park

2005-09-12

133

Internal Energy Dissipation of Gamma-Ray Bursts Observed with Swift: Precursors, Prompt Gamma-Rays, Extended Emission, and Late X-Ray Flares  

NASA Astrophysics Data System (ADS)

We jointly analyze the gamma-ray burst (GRB) data observed with Burst Alert Telescope (BAT) and X-ray Telescope on board the Swift mission to present a global view on the internal energy dissipation processes in GRBs, including precursors, prompt gamma-ray emission, extended soft gamma-ray emission, and late X-ray flares. The Bayesian block method is utilized to analyze the BAT light curves to identify various emission episodes. Our results suggest that these emission components likely share the same physical origin, which is the repeated activation of the GRB central engine. What we observe in the gamma-ray band may be a small part of more extended underlying activities. The precursor emission, which is detected in about 10% of Swift GRBs, is preferably detected in those GRBs that have a massive star core-collapse origin. The soft extended emission tail, on the other hand, is preferably detected in those GRBs that have a compact star merger origin. Bright X-ray emission is detected during the BAT quiescent phases prior to subsequent gamma-ray peaks, implying that X-ray emission may be detectable prior the BAT trigger time. Future GRB alert instruments with soft X-ray capability are essential for revealing the early stages of GRB central engine activities, and shedding light on jet composition and the jet launching mechanism in GRBs.

Hu, You-Dong; Liang, En-Wei; Xi, Shao-Qiang; Peng, Fang-Kun; Lu, Rui-Jing; Lü, Lian-Zhong; Zhang, Bing

2014-07-01

134

X-ray emission from charge exchange of highly-charged ions in atoms and molecules  

NASA Technical Reports Server (NTRS)

Charge exchange followed by radiative stabilization are the main processes responsible for the recent observations of X-ray emission from comets in their approach to the Sun. A new apparatus was constructed to measure, in collisions of HCIs with atoms and molecules, (a) absolute cross sections for single and multiple charge exchange, and (b) normalized X-ray emission cross sections.

Greenwood, J. B.; Williams, I. D.; Smith, S. J.; Chutjian, A.

2000-01-01

135

Eclipse and Collapse of the Colliding Wind X-ray Emission from Eta Carinae  

NASA Technical Reports Server (NTRS)

X-ray emission from the massive stellar binary system, Eta Carinae, drops strongly around periastron passage; the event is called the X-ray minimum. We launched a focused observing campaign in early 2009 to understand the mechanism of causing the X-ray minimum. During the campaign, hard X-ray emission (<10 keV) from Eta Carinae declined as in the previous minimum, though it recovered a month earlier. Extremely hard X-ray emission between 15-25 keV, closely monitored for the first time with the Suzaku HXD/PIN, decreased similarly to the hard X-rays, but it reached minimum only after hard X-ray emission from the star had already began to recover. This indicates that the X-ray minimum is produced by two composite mechanisms: the thick primary wind first obscured the hard, 2-10 keV thermal X-ray emission from the wind-wind collision (WWC) plasma; the WWC activity then decays as the two stars reach periastron.

Hamaguchi, Kenji; Corcoran, Michael F.

2012-01-01

136

Persistent X-ray emission from a gamma-ray burst source  

NASA Technical Reports Server (NTRS)

A quiescent X-ray source detected with the Einstein X-ray Observatory in a location consistent with that of an intense gamma ray burst is shown to be also consistent with the location of the 1928 optical transient, the likely optical counterpart of the gamma ray burst source GBS0117-29. The system appears to be underluminous in X-rays by a factor of 10; possible reasons for this are discussed. The observed X-ray flux would require an accretion rate of about 10 to the -14th (d/1 kpc/)-squared solar masses per year, which is probably too low to be consistent with published nuclear flash models for gamma bursts, unless the distance is substantially greater than about 1 kpc or the burst recurrence time is greater than about 50 yrs, or the accretion rate is highly variable. Such a long recurrence time appears to be inconsistent with the detection of the optical burst.

Grindlay, J. E.; Cline, T.; Desai, U. D.; Teegarden, B. J.; Pizzichini, G.; Evans, W. D.; Laros, J. G.; Hurley, K. C.; Niel, M.; Klebesadel, R. W.

1982-01-01

137

X-ray Tube Using a Graphene Flower Cloth Field Emission Cathode  

NASA Astrophysics Data System (ADS)

We have successfully fabricated a filament-less X-ray tube using a graphene flower cloth (GFC) field emission cathode. The GFC has numerous nanoprotrusions formed by self-standing graphene structures. The field emission current and the field enhancement factor ? were 500 µA and 5600, respectively. The stability of voltage defined as a variance coefficient (?/mean) of voltage was calculated to be 0.04% while maintaining the X-ray tube current of 300 µA. We applied our X-ray tube with the GFC field emitter to the X-ray fluorescence (XRF) analysis of stainless steel.

Iwai, Yusuke; Muramatsu, Kazuo; Tsuboi, Shougo; Jyouzuka, Atsuo; Nakamura, Tomonori; Onizuka, Yoshihiro; Mimura, Hidenori

2013-10-01

138

X-ray Emission From Sn Ia 1885a & 1985g?  

NASA Astrophysics Data System (ADS)

X-ray emission is expected from the explosion and subsequent evolution of a Type Ia supernova. The outgoing shock will run into circumstellar material from early phases of the progenitor's evolution and generate X-ray emission from the interaction. To date, Type Ia supernovae have not been convincingly detected as X-ray sources. A number of remnants in the Milky Way are X-ray sources (eg, SN1006, Tycho). The question of when Type Ia supernovae become X-ray-emitting remnants remains open. We analyze and discuss the available Chandra X-ray Observatory data on two old Type Ia supernovae, SN1885A in M31 and SN1986G in NGC 5128 (= Cen A).

Packard, Melody M.; Schlegel, E. M.; Patnaude, D.; Katsuda, S.; Petre, R.

2012-01-01

139

Detection of X-ray Emission from the Eastern Radio Lobe of PICTOR A  

E-print Network

The XMM-Newton satellite has revealed extended X-ray emission from the eastern radio lobe of the Fanaroff-Riley II Radio Galaxy Pictor A. The X-ray spectrum, accumulated on a region covering about half the entire radio lobe, is well described by both a thermal model and a power law. The X-ray emission could be thermal and produced by circum-galactic gas shocked by the expanding radio lobe or, alternatively, by Inverse Compton (IC) of cosmic microwave background photons by relativistic electrons in the lobe. The latter possibility seems to be supported by the good agreement between the lobe-average synchrotron radio index and the X-ray energy slope. However, if this is the case, the magnetic field, as deduced from the comparison of the IC X-ray and radio fluxes, is more than a factor 2 below the equipartition value estimated in the same X-ray region.

Paola Grandi; Matteo Guainazzi; Laura Maraschi; Raffaella Morganti; Roberto Fusco-Femiano; Mariateresa Fiocchi; Lucia Ballo; Fabrizio Tavecchio

2002-11-25

140

The oldest X-ray supernovae: X-ray emission from 1941C, 1959D, 1968D  

E-print Network

We have studied the X-ray emission from four historical Type-II supernovae (the newly-discovered 1941C in NGC 4631 and 1959D in NGC 7331; and 1968D, 1980K in NGC 6946), using Chandra ACIS-S imaging. In particular, the first three are the oldest ever found in the X-ray band, and provide constraints on the properties of the stellar wind and circumstellar matter encountered by the expanding shock at more advanced stages in the transition towards the remnant phase. We estimate emitted luminosities ~ 5 x 10^{37} erg/s for SN 1941C, ~ a few x 10^{37} erg/s for SN 1959D, ~ 2 x 10^{38} erg/s for SN 1968D, and ~ 4 x 10^{37} erg/s for SN 1980K, in the 0.3-8 keV band. X-ray spectral fits to SN 1968D suggest the presence of a harder component, possibly a power law with photon index ~ 2, contributing ~ 10^{37} erg/s in the 2-10 keV band. We speculate that it may be evidence of non-thermal emission from a Crab-like young pulsar.

Roberto Soria; Rosalba Perna

2008-05-09

141

Production of Loop-Top Hard X-Ray Emission  

NASA Technical Reports Server (NTRS)

The main goal of this work has been to understand the particle acceleration mechanism (or mechanisms) in impulsive solar flares, using hard X-ray observations of high spatial and spectral resolution. Several new observations, including the observations by YOHKOH that reveal emission from both footpoints and loop tops, have suggested to us that a model employing stochastic acceleration is the most likely candidate for explaining energetic particles in a majority (if not all) of impulsive flares. In this model, most of the flare energy is initially converted into plasma waves and turbulence, which in turn can accelerate particles from thermal to relativistic energies on sub-second timescales. This research has provided important tools for the interpretation of the high spectral and spatial resolution observations obtained from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) . In the course of our research, we have focused on two different (but possibly related) stochastic acceleration models: (1) a model that employs high-frequency whistler turbulence and concentrates on the energetic electrons, and (2) a model that employs low frequency MHD waves, and is able to accelerate both the ambient electrons and ions.

Miller, James A.; Seaquist, Valerie

2003-01-01

142

Femtosecond x-ray line emission from specially designed targets irradiated by short laser pulses  

Microsoft Academic Search

The invention of high-power ultra short pulse lasers has opened way to investigations aimed at creation of a new type of bright x-ray source for different applications including material science and time resolved x-ray diffraction for biology. The conversion efficiency of the laser energy incident onto a solid target into the x-ray emission depends on many factors, including the temporal

Alexander A. Andreev; Hidetoshi Nakano; Jiri Limpouch

2004-01-01

143

Electronic Structure of In2O3 from Resonant X-ray Emission Spectroscopy  

SciTech Connect

The valence and conduction band structures of In2O3 have been measured using a combination of valence band x-ray photoemission spectroscopy, O K-edge resonant x-ray emission spectroscopy, and O K-edge x-ray absorption spectroscopy. Excellent agreement is noted between the experimental spectra and O 2p partial density of states calculated within hybrid density functional theory. Our data are consistent with a direct band gap for In2O3.

Piper, L.; DeMasi, A; Cho, S; Smith, K; Fuchs, F; Bechstedt, F; Korber, C; Klein, A; Payne, D; Egdell, R

2009-01-01

144

X-ray emissivity from old stellar populations: a Local Group census  

NASA Astrophysics Data System (ADS)

We study the unresolved X-ray emission from three Local Group dwarf elliptical galaxies (NGC147, NGC185 and NGC205), which is thought to originate from a collection of weak X-ray sources primarily consisting of cataclysmic variables and coronally active binaries. The derived 0.5-2 keV X-ray emissivities (per unit stellar mass) of these dwarfs are comparable to that in the Solar neighborhood, but are significantly higher than the average cumulative emissivity of X-ray sources in four Galactic globular clusters, indicating a reduced binary fraction in the latter. Our results are also important for studies of the apparently diffuse X-ray emission in nearby normal galaxies.

Li, Zhiyuan

2014-11-01

145

Echo Emission From Dust Scattering and X-Ray Afterglows of Gamma-Ray Bursts  

E-print Network

We investigate the effect of X-ray echo emission in gamma-ray bursts (GRBs). We find that the echo emission can provide an alternative way of understanding X-ray shallow decays and jet breaks. In particular, a shallow decay followed by a "normal" decay and a further rapid decay of X-ray afterglows can be together explained as being due to the echo from prompt X-ray emission scattered by dust grains in a massive wind bubble around a GRB progenitor. We also introduce an extra temporal break in the X-ray echo emission. By fitting the afterglow light curves, we can measure the locations of the massive wind bubbles, which will bring us closer to finding the mass loss rate, wind velocity, and the age of the progenitors prior to the GRB explosions.

L. Shao; Z. G. Dai; N. Mirabal

2007-11-24

146

X-ray emission possibly coincident with the radio tail of PKS 0301 - 123  

NASA Technical Reports Server (NTRS)

X-ray, radio, and optical observations are reported for a very poor cluster of galaxies containing the radio source PKS 0301 - 123. A long, 100,000 second X-ray observation using the Einstein Observatory's IPC resulted in the serendipitous discovery of a peculiar extended X-ray morphology associated with the poor cluster. The X-ray emission is extended in the same direction and is approximately the same length as the radio-tailed source, PKS 0301 - 123, which was mapped at 6 and 20 cm with the VLA. Optical redshift observations with the KPNO IIDS on the 2.1 m telescope confirm the identification of the X-ray and radio emission with the poor cluster at z = 0.1. It is argued that the X-ray extension is unlikely to be a chance coincidence of a background source projected onto the foreground cluster. Therefore, four possible mechanisms which might physically link the X-ray and radio emission are considered: thermal bremsstrahlung from a cluster with a flattened potential well; inverse Compton scattering of the relativistic electrons in the radio source, X-ray synchrotron radiation; and heating the cluster gas by the turbulent wake of the radio galaxy. The prospects for future observations of such X-ray/radio coincidences are briefly discussed.

Burns, J. O.; Nelson, E. R.; White, R. A.; Gregory, S. A.

1985-01-01

147

X-ray emission from high temperature plasmas  

NASA Technical Reports Server (NTRS)

The physical processes occurring in plasma focus devices were studied. These devices produce dense high temperature plasmas, which emit X rays of hundreds of KeV energy and one to ten billion neutrons per pulse. The processes in the devices seem related to solar flare phenomena, and would also be of interest for controlled thermonuclear fusion applications. The high intensity, short duration bursts of X rays and neutrons could also possibly be used for pumping nuclear lasers.

Harries, W. L.

1976-01-01

148

Evidence of non-thermal X-ray emission from HH 80  

E-print Network

Protostellar jets appear at all stages of star formation when the accretion process is still at work. Jets travel at velocities of hundreds of km/s, creating strong shocks when interacting with interstellar medium. Several cases of jets have been detected in X-rays, typically showing soft emission. For the first time, we report evidence of hard X-ray emission possibly related to non-thermal processes not explained by previous models of the post-shock emission predicted in the jet/ambient interaction scenario. HH 80 is located at the south head of the jet associated to the massive protostar IRAS 18162-2048. It shows soft and hard X-ray emission in regions that are spatially separated, with the soft X-ray emission region situated behind the region of hard X-ray emission. We propose a scenario for HH 80 where soft X-ray emission is associated to thermal processes from the interaction of the jet with denser ambient matter and the hard X-ray emission is produced by synchrotron radiation at the front shock.

Lopez-Santiago, J; Bonito, R; Miceli, M; Albacete-Colombo, J F; Benaglia, P; de Castro, E

2013-01-01

149

EVIDENCE OF NON-THERMAL X-RAY EMISSION FROM HH 80  

SciTech Connect

Protostellar jets appear at all stages of star formation when the accretion process is still at work. Jets travel at velocities of hundreds of km s{sup –1}, creating strong shocks when interacting with the interstellar medium. Several cases of jets have been detected in X-rays, typically showing soft emission. For the first time, we report evidence of hard X-ray emission possibly related to non-thermal processes not explained by previous models of the post-shock emission predicted in the jet/ambient interaction scenario. HH 80 is located at the south head of the jet associated with the massive protostar IRAS 18162-2048. It shows soft and hard X-ray emission in regions that are spatially separated, with the soft X-ray emission region situated behind the region of hard X-ray emission. We propose a scenario for HH 80 where soft X-ray emission is associated with thermal processes from the interaction of the jet with denser ambient matter and hard X-ray emission is produced by synchrotron radiation at the front shock.

López-Santiago, J. [Instituto de Matemática Interdisciplinar, S. D. Astronomía y Geodesia, Facultad de Ciencias Matemáticas, Universidad Complutense de Madrid, E-28040 Madrid (Spain)] [Instituto de Matemática Interdisciplinar, S. D. Astronomía y Geodesia, Facultad de Ciencias Matemáticas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Peri, C. S.; Benaglia, P. [Instituto Argentino de Radioastronomía (IAR), CCT La Plata (CONICET), C.C.5, 1894 Villa Elisa, Buenos Aires (Argentina)] [Instituto Argentino de Radioastronomía (IAR), CCT La Plata (CONICET), C.C.5, 1894 Villa Elisa, Buenos Aires (Argentina); Bonito, R. [Dipartimento di Fisica e Chimica, Università di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy)] [Dipartimento di Fisica e Chimica, Università di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy); Miceli, M. [INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy)] [INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy); Albacete-Colombo, J. F. [Universidad Nacional del COMAHUE, Monseñor Esandi y Ayacucho, 8500 Viedma, Río Negro (Argentina)] [Universidad Nacional del COMAHUE, Monseñor Esandi y Ayacucho, 8500 Viedma, Río Negro (Argentina); De Castro, E. [Dpto. de Astrofísica y CC. de la Atmósfera, Universidad Complutense de Madrid, E-28040 Madrid (Spain)] [Dpto. de Astrofísica y CC. de la Atmósfera, Universidad Complutense de Madrid, E-28040 Madrid (Spain)

2013-10-20

150

Evidence of Non-thermal X-Ray Emission from HH 80  

NASA Astrophysics Data System (ADS)

Protostellar jets appear at all stages of star formation when the accretion process is still at work. Jets travel at velocities of hundreds of km s-1, creating strong shocks when interacting with the interstellar medium. Several cases of jets have been detected in X-rays, typically showing soft emission. For the first time, we report evidence of hard X-ray emission possibly related to non-thermal processes not explained by previous models of the post-shock emission predicted in the jet/ambient interaction scenario. HH 80 is located at the south head of the jet associated with the massive protostar IRAS 18162-2048. It shows soft and hard X-ray emission in regions that are spatially separated, with the soft X-ray emission region situated behind the region of hard X-ray emission. We propose a scenario for HH 80 where soft X-ray emission is associated with thermal processes from the interaction of the jet with denser ambient matter and hard X-ray emission is produced by synchrotron radiation at the front shock.

López-Santiago, J.; Peri, C. S.; Bonito, R.; Miceli, M.; Albacete-Colombo, J. F.; Benaglia, P.; de Castro, E.

2013-10-01

151

X-Ray Emission in the Heliosphere: Ion-Neutral Collisions as a Plasma Diagnostic  

NASA Astrophysics Data System (ADS)

The solar corona is the most powerful source of x-rays in the solar system but x-ray emission has also been observed from planets, including the Earth and Jupiter, from the Moon, from comets, and from interstellar gas entering the heliosphere. Astrophysical x-ray emission primarily comes from hot plasmas, such as in the million degree solar corona. The gas and plasma in planetary atmospheres are rather cold and the x-ray emission is driven by solar radiation and/or the solar wind. For example, x-rays from Venus come from the scattering and K-shell fluorescence of solar x-rays from the neutral atmosphere. Auroral x-ray emission at Earth and Jupiter is produced by energetic electron and ion precipitation from the magnetospheres into the atmospheres. Cometary and heliospheric x-ray emission is caused by charge transfer of high charge state solar wind ions (e.g., O7+, C6+,…) with neutral hydrogen and helium.An important source of solar system x-rays is the solar wind charge exchange (SWCX) mechanism. The solar wind originates in the hot solar corona and species heavier than helium (comprising about 0.1% of the gas) are highly-charged (e.g., O7+, C6+, Fe12+,….). Such ions undergo charge transfer collisions when they encounter neutral gas (e.g., cometary or interstellar gas or the Earth’s geocoronal hydrogen). The product ions are in highly-excited states and, subsequently, emit soft x-ray photons. The SWCX mechanism can explain the observed cometary x-ray emission and can also explain part of the soft x-ray background (the other part of which originates in the hot interstellar medium).The Earth has an extensive hot hydrogen exosphere, or geocorona, that is visible in scattered solar Lyman alpha. X-ray emission is produced in the magnetosheath due to the SWCX mechanism as the solar wind interacts with the exospheric gas. The most intense x-ray emission comes from the subsolar sheath region and from the cusp regions. Imaging of this emission by a spacecraft located outside the magnetosphere would provide a global view of the solar wind interaction with Earth including dayside magnetic reconnection processes.

Cravens, Tom; Sibeck, David; Collier, MIchael

2015-04-01

152

The 300 Kpc Long X-Ray Jet in PKS 1127-145, Z=1.18 Quasar: Constraining X-Ray Emission Models  

SciTech Connect

We present a {approx} 100 ksec Chandra X-ray observation and new VLA radio data of the large scale, 300 kpc long X-ray jet in PKS 1127-145, a radio loud quasar at redshift z=1.18. With this deep X-ray observation we now clearly discern the complex X-ray jet morphology and see substructure within the knots. The X-ray and radio jet intensity profiles are seen to be strikingly different with the radio emission peaking strongly at the two outer knots while the X-ray emission is strongest in the inner jet region. The jet X-ray surface brightness gradually decreases by an order of magnitude going out from the core. The new X-ray data contain sufficient counts to do spectral analysis of the key jet features. The X-ray energy index of the inner jet is relatively flat with {alpha}{sub x} = 0.66 {+-} 0.15 and steep in the outer jet with {alpha}{sub x} = 1.0 {+-} 0.2. We discuss the constraints implied by the new data on the X-ray emission models and conclude that ''one-zone'' models fail and at least a two component model is needed to explain the jet's broad-band emission. We propose that the X-ray emission originates in the jet proper while the bulk of the radio emission comes from a surrounding jet sheath. We also consider intermittent jet activity as a possible cause of the observed jet morphology.

Siemiginowska, Aneta; /Harvard-Smithsonian Ctr. Astrophys.; Stawarz, Lukasz; /Heidelberg Observ. /Jagiellonian U., Astron. Observ. /KIPAC, Menlo Park; Cheung, C.C.; /KIPAC,; Harris, D.E.; /Harvard-Smithsonian Ctr. Astrophys.; Sikora, Marek; /Warsaw, Copernicus Astron. Ctr.; Aldcroft, Thomas L.; /Harvard-Smithsonian Ctr. Astrophys.; Bechtold,; /Arizona U., Astron. Dept. - Steward Observ.

2006-11-20

153

DISCOVERY OF X-RAY EMISSION FROM YOUNG SUNS IN THE SMALL MAGELLANIC CLOUD  

SciTech Connect

We report the discovery of extended X-ray emission within the young star cluster NGC 602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-Ray Observatory. X-ray emission is detected from the cluster core area with the highest stellar density and from a dusty ridge surrounding the H II region. We use a census of massive stars in the cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to provide a significant contribution to the X-ray emission detected from the central area of the cluster. We therefore suggest that X-ray emission at the cluster core originates from an ensemble of low- and solar-mass pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be detected individually. We attribute the X-ray emission from the dusty ridge to the embedded tight cluster of the newborn stars known in this area from infrared studies. Assuming that the levels of X-ray activity in young stars in the low-metallicity environment of NGC 602a are comparable to their Galactic counterparts, then the detected spatial distribution, spectral properties, and level of X-ray emission are largely consistent with those expected from low- and solar-mass PMS stars and young stellar objects (YSOs). This is the first discovery of X-ray emission attributable to PMS stars and YSOs in the SMC, which suggests that the accretion and dynamo processes in young, low-mass objects in the SMC resemble those in the Galaxy.

Oskinova, L. M.; Hainich, R. [Institute for Physics and Astronomy, University Potsdam, D-14476 Potsdam (Germany)] [Institute for Physics and Astronomy, University Potsdam, D-14476 Potsdam (Germany); Sun, W.; Chen, Y. [Department of Astronomy, Nanjing University, Nanjing, 210093 Jiangsu (China)] [Department of Astronomy, Nanjing University, Nanjing, 210093 Jiangsu (China); Evans, C. J. [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)] [UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Henault-Brunet, V. [Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)] [Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Chu, Y.-H.; Gruendl, R. A. [Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801 (United States)] [Department of Astronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801 (United States); Gallagher, J. S. III [Department of Astronomy, University of Wisconsin-Madison, 5534 Sterling, 475 North Charter Street, Madison, WI 53706 (United States)] [Department of Astronomy, University of Wisconsin-Madison, 5534 Sterling, 475 North Charter Street, Madison, WI 53706 (United States); Guerrero, M. A. [Instituto de Astrofisica de Andalucia, IAA-CSIC, Glorieta de la Astronomia s/n, E-18008 Granada (Spain)] [Instituto de Astrofisica de Andalucia, IAA-CSIC, Glorieta de la Astronomia s/n, E-18008 Granada (Spain); Guedel, M. [Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, A-1180 Vienna (Austria)] [Department of Astrophysics, University of Vienna, Tuerkenschanzstrasse 17, A-1180 Vienna (Austria); Silich, S. [Instituto Nacional de Astrofisica Optica y Electronica, AP 51, 72000 Puebla (Mexico)] [Instituto Nacional de Astrofisica Optica y Electronica, AP 51, 72000 Puebla (Mexico); Naze, Y. [GAPHE, Departement AGO, Universite de Liege, Allee du 6 Aout 17, Bat. B5C, B-4000 Liege (Belgium)] [GAPHE, Departement AGO, Universite de Liege, Allee du 6 Aout 17, Bat. B5C, B-4000 Liege (Belgium); Reyes-Iturbide, J. [LATO-DCET/Universidade Estadual de Santa Cruz, Rodovia Jorge Amado, km 16, 45662-000 Ilheus, BA (Brazil)] [LATO-DCET/Universidade Estadual de Santa Cruz, Rodovia Jorge Amado, km 16, 45662-000 Ilheus, BA (Brazil)

2013-03-01

154

High energy X-ray emission driven by high voltage circuit system  

NASA Astrophysics Data System (ADS)

The x-rays are produced by high voltage discharge applied inside plasma source interaction chamber; the control circuit system of high voltage is composed of a power supply and a LC-inverter. The goal of the project is based on the production of x-rays by a plasma to increase the efficiency of a classic x-ray tube with hot filament. Preliminary results of high energy x-rays emission, the layout and simulation with p-spice of the high voltage system are presented.

Emilio, M. Di Paolo; Palladino, L.

2014-04-01

155

Exploring the Hard and Soft X-ray Emission of Magnetic Cataclysmic Variables  

NASA Astrophysics Data System (ADS)

A non-negligible fraction of galactic hard (>20 keV) X-ray sources were identified as CVs of the magnetic Intermediate Polar type in INTEGRAL, SWIFT and RXTE surveys, that suggests a still hidden but potentially important population of faint hard X-ray sources. Simbol-X has the unique potential to simultaneously characterize their variable and complex soft and hard X-ray emission thus allowing to understand their putative role in galactic populations of X-ray sources.

de Martino, D.; Anzolin, G.; Bonnet-Bidaud, J.-M.; Falanga, M.; Matt, G.; Mouchet, M.; Mukai, K.; Masetti, N.

2009-05-01

156

Observation of soft X-ray emission from the supernova remnant HB9  

NASA Technical Reports Server (NTRS)

The number of known X-ray emitting supernova remnants in our galaxy has significantly grown as a result of the soft X-ray survey by the HEAO-1 spacecraft. The HEAO-1 A-2 experiment has observed soft X-ray emission from the old supernova remnant HB9 which lies close to the previously identified X-ray source, Capella. Spectral data and the low optical obscuration in the direction of the remnant suggest that HB9 is a good candidate for detecting Fe XIV coronal forbidden-line emission. Mapping of the coronal line emission in association with the imaging X-ray data expected from HEAO-2 would allow the temperature profile of the emitting shell to be determined in a manner similar to that used by Tuohy, Nousek, and Garmire (1979) for the Cygnus Loop, which is in a similar evolutionary phase to HB9.

Tuohy, I. R.; Clark, D. H.; Garmire, G. P.

1979-01-01

157

A Search for X-ray emission from Saturn, Uranus and Neptune  

E-print Network

We present an analysis of X-ray observations of the trans-Jovian planets Saturn, Uranus and Neptune with the ROSAT PSPC in comparison with X-ray observations of Jupiter. For the first time a marginal X-ray detection of Saturn was found and 95% confidence upper limits for Uranus and Neptune were obtained. These upper limits show that Jupiter-like X-ray luminosities can be excluded for all three planets, while they are consistent assuming intrinsic Saturn-like X-ray luminosities. Similar X-ray production mechanisms on all trans-Jovian planets can therefore not be ruled out, and spectral shape and total luminosity observed from Saturn are consistent with thick-target bremsstrahlung caused by electron precipitation as occurring in auroral emission from the Earth.

Jan-Uwe Ness; Juergen H. M. M. Schmitt

2000-01-08

158

Hard X-ray and Infrared Emission from Apparently Single White Dwarfs  

E-print Network

The photospheric emission of a white dwarf (WD) is not expected to be detectable in hard X-rays or the mid-IR. Hard X-ray (~1 keV) emission associated with a WD is usually attributed to a binary companion; however, emission at 1 keV has been detected from three WDs without companions: KPD 0005+5106, PG 1159, and WD 2226-210. The origin of their hard X-ray emission is unknown, although it has been suggested that WD 2226-210 has a late-type companion whose coronal activity is responsible for the hard X-rays. Recent Spitzer observations of WD 2226-210 revealed mid-IR excess emission indicative of the existence of a dust disk. It now becomes much less clear whether WD 2226-210's hard X-ray emission originates from the corona of a late-type companion or from the accretion of the disk material. High-quality X-ray observations and mid-IR observations of KPD 0005+5106 and PG 1159 are needed to help us understand the origin of their hard X-ray emission.

Y. -H. Chu; R. A. Gruendl; M. A. Guerrero; K. Y. -L. Su

2007-01-01

159

Amplified x-ray emission from core-ionized diatomic molecules.  

PubMed

We predict high-gain x-ray lasing in molecular nitrogen by ultrafast core ionization with an x-ray free-electron laser source. To estimate the spectral and temporal output of this molecular x-ray laser, we solve generalized Maxwell-Bloch equations, keeping track of the electronic and nuclear degrees of freedom. The spectrum of the amplified x-ray emission shows a strong dependence on the gain-length product. Whereas the emission at small gain length is similar to the relatively broad x-ray fluorescence band, the spectrum is determined by a single frequency in the linear gain region. The vibrational wave packet dynamics during the x-ray emission process is examined. By preparation of the initial vibrational quantum state, the x-ray emission frequency can be tuned within the fluorescence band. The present scheme is applicable to other homo- and heteronuclear diatomic systems, thereby extending the spectral range of coherent x-ray radiation sources based on amplification on bound transitions. PMID:25166164

Kimberg, Victor; Rohringer, Nina

2013-01-25

160

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

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

161

Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-Ray (EDX) Spectroscopy  

E-print Network

system with 30 take-off angle for quantitative analysis, digital imaging, and X-ray mapping. The EDAXField Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-Ray (EDX) Spectroscopy of objective aperture. Dual SE detectors allow versatile imaging. The FE-SEM is equipped with fully digital

Gelfond, Michael

162

Upper limits on X-ray emission from two rotating radio transients  

E-print Network

X-ray emission from the enigmatic rotating radio transients (RRATs) offers a vital clue to understanding these objects and how they relate to the greater neutron star population. An X-ray counterpart to RRAT J1819?1458 is ...

Kaplan, D. L.

163

On the Early Time X-ray Spectra of Swift Afterglows I: Evidence for Anomalous Soft X-ray Emission  

E-print Network

We have conducted a thorough and blind search for emission lines in >70 Swift X-ray afterglows of total exposure ~10^7s. We find that most afterglows are consistent with pure power-laws plus extinction. Significant outliers to the population exist at the 5-10% level and have anomalously soft, possibly thermal spectra. Four bursts are singled out via possible detections of 2-5 lines: GRBs 060218, 060202, 050822, and 050714B. Alternatively, a blackbody model with kT~0.1-0.5 keV can describe the soft emission in each afterglow. The most significant soft component detections in the full data set of ~2000 spectra correspond to GRB060218/SN2006aj, with line significances ranging up to \\~20-sigma. A thermal plasma model fit to the data indicates that the flux is primarily due to L-shell transitions of Fe at ~ solar abundance. We associate (>4-sigma significant) line triggers in the 3 other events with K-shell transitions in light metals. We favor a model where the possible line emission in these afterglows arises from the mildly relativistic cocoon of matter surrounding the GRB jet as it penetrates and exits the surface of the progenitor star. The emitting material in each burst is at a similar distance \\~10^12--10^13 cm, a similar density ~10^17 cm^-3, and subject to a similar flux of ionizing radiation. The lines may correlate with the X-ray flaring. For the blackbody interpretation, the soft flux may arise from break out of the GRB shock or plasma cocoon from the progenitor stellar wind, as recently suggested for GRB060218 (Campana et al. 2006). Due to the low z of GRB060218, bursts faint in Gamma-rays with fluxes dominated by this soft X-ray component could outnumber classical GRBs 100-1.

Nathaniel R. Butler

2006-11-03

164

Discovery of X-ray emission from the protostellar jet L1551 IRS5 (HH 154)  

Microsoft Academic Search

We have for the first time detected X-ray emission associated with a protostellar jet, on the jet emanating from the L1551 IRS5 protostar. The IRS5 protostar is hidden behind a very large absorbing column density, making the direct observation of the jet's emission possible. The observed X-ray emission is likely associated with the shock ``working surface'', i.e. the interface between

Fabio Favata; C. V. M. Fridlund; G. Micela; S. Sciortino; A. A. Kaas

2002-01-01

165

On the Early Time X-ray Spectra of Swift Afterglows I: Evidence for Anomalous Soft X-ray Emission  

Microsoft Academic Search

We have conducted a thorough and blind search for emission lines in >70 Swift\\u000aX-ray afterglows of total exposure ~10^7s. We find that most afterglows are\\u000aconsistent with pure power-laws plus extinction. Significant outliers to the\\u000apopulation exist at the 5-10% level and have anomalously soft, possibly thermal\\u000aspectra. Four bursts are singled out via possible detections of 2-5 lines:

Nathaniel R. Butler

2006-01-01

166

Stellar Wind Induced Soft X-Ray Emission from Close-in Exoplanets  

NASA Astrophysics Data System (ADS)

In this Letter, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX), which produces soft X-ray emission, is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted as a result of the charge exchange between heavy ions in the solar wind and the atmospheric neutral particles. In the solar system, comets produce X-rays mostly through the SWCX mechanism, but it has also been shown to operate in the heliosphere, in the terrestrial magnetosheath, and on Mars, Venus, and the Moon. Since the number of emitted photons is proportional to the solar wind mass flux, this mechanism is not very effective for the solar system giants. Here we present a simple estimate of the X-ray emission intensity that can be produced by close-in extrasolar giant planets due to charge exchange with the heavy ions of the stellar wind. Using the example of HD 209458b, we show that this mechanism alone can be responsible for an X-ray emission of ?1022 erg s-1, which is 106 times stronger than the emission from the Jovian aurora. We discuss also the possibility of observing the predicted soft X-ray flux of hot Jupiters and show that despite high emission intensities they are unobservable with current facilities.

Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.; Holmström, M.; Zaitsev, V. V.; Lammer, H.

2015-02-01

167

A SEARCH FOR IRON EMISSION LINES IN THE CHANDRA X-RAY SPECTRA OF NEUTRON STAR LOW-MASS X-RAY BINARIES  

E-print Network

While iron emission lines are well studied in black hole systems, both in X-ray binaries and active galactic nuclei, there has been less of a focus on these lines in neutron star low-mass X-ray binaries (LMXBs). However, ...

Cackett, E. M.

168

X-ray Emission from Wolf-Rayet Nebulae  

NASA Astrophysics Data System (ADS)

We present the analysis of the hot plasma detected with XMM-Newton and Chandra X-ray observations toward the only two Wolf-Rayet bubbles so far detected: S 308 and NGC 6888. Both nebulae present spectra dominated by soft temperature plasmas of ˜10^{6} K with luminosities of L_{{X}}˜10^{33}-10^{34} erg s^{-1}, but with different X-ray-emitting plasma distribution. In the case of S 308 it presents a limb-brightened morphology, while in the case of NGC 6888, it shows three maxima localized at the Northeast and Southwest caps and another one extending toward the Northwest.

Toalá, J. A.; Guerrero, M. A.; Chu, Y.-H.; Gruendl, R. A.; Arthur, S. J.; Smith, R. C.; Snowden, S. L.

2013-05-01

169

A Comparison of X-Ray and Optical Emission in Cassiopeia A  

NASA Astrophysics Data System (ADS)

Broadband optical and narrowband Si XIII X-ray images of the young Galactic supernova remnant Cassiopeia A (Cas A) obtained over several decades are used to investigate spatial and temporal emission correlations on both large and small angular scales. The data examined consist of optical and near-infrared ground-based and Hubble Space Telescope images taken between 1951 and 2011, and of X-ray images from Einstein, ROSAT, and Chandra taken between 1979 and 2013. We find weak spatial correlations between the remnant's X-ray and optical emission features on large scales, but several cases of good optical/X-ray correlations on small scales for features which have brightened due to recent interactions with the reverse shock. We also find instances (1) where a time delay is observed between the appearance of a feature's optical and X-ray emissions, (2) of displacements of several arcseconds between a feature's X-ray and optical emission peaks, and (3) of regions showing no corresponding X-ray or optical emissions. To explain this behavior, we propose a highly inhomogeneous density model for Cas A's ejecta consisting of small, dense optically emitting knots (n ~102-3 cm-3) and a much lower density (n ~0.1-1 cm-3) diffuse X-ray emitting component often spatially associated with optical emission knots. The X-ray emitting component is sometimes linked to optical clumps through shock-induced mass ablation generating trailing material leading to spatially offset X-ray/optical emissions. A range of ejecta densities can also explain the observed X-ray/optical time delays since the remnant's ?5000 km s-1 reverse shock heats dense ejecta clumps to temperatures around 3 × 104 K relatively quickly, which then become optically bright while more diffuse ejecta become X-ray bright on longer timescales. Highly inhomogeneous ejecta as proposed here for Cas A may help explain some of the X-ray/optical emission features seen in other young core-collapse supernova remnants.

Patnaude, Daniel J.; Fesen, Robert A.

2014-07-01

170

Suzaku Detection of Diffuse Hard X-Ray Emission Outside Vela X  

NASA Technical Reports Server (NTRS)

Vela X is a large, 3 deg x 2 deg, radio-emitting pulsar wind nebula (PWN) powered by the Vela pulsar in the Vela supernova remnant. Using four Suzaku/XIS observations pointed just outside Vela X, we find hard X-ray emission extending throughout the fields of view. The hard X-ray spectra are well represented by a power-law. The photon index is measured to be constant at Gamma approximates 2.4, similar to that of the southern outer part of Vela X. The power-law flux decreases with increasing distance from the pulsar. These properties lead us to propose that the hard X-ray emission is associated with the Vela PWN. The larger X-ray extension found in this work strongly suggests that distinct populations relativistic electrons form the X-ray PWN and Vela X, as was recently inferred from multiwavelength spectral modeling of Vela X.

Katsuda, Satoru; Mori, Koji; Petre, Robert; Yamaguchi, Hiroya; Tsunemi, Hiroshi; Bocchino, Fabrizio; Bamba, Aya; Miceli, Marco; Hewitt, John W.; Temim, Tea; Uchida, Hiroyuki; Yoshii, Rie

2011-01-01

171

X-ray jets and nuclear emission in low redshift early-type galaxies  

NASA Astrophysics Data System (ADS)

Due to its high angular resolution, the Chandra Observatory has allowed the discovery and detailed study of extragalactic X-ray jets. Although supermassive black holes are regularly found in the cores of massive galaxies and X-ray emission is detected from ~80% of these, X-ray and radio jets are only detected in a small fraction of ``normal'' galaxies. X-ray jets are either single-sided or double-sided and, with only one possible exception, are found to have radio emission. However many radio jets are not detected in current X-ray observations. The expanding jets produce cavities in the surrounding hot gas in the galaxy halos. By determining how much gas has been pushed out of these cavities, we can determine the mechanical energy and power of the jet.

Jones, Christine; Forman, William; Churazov, Eugene; Nulsen, Paul

2015-03-01

172

X-Ray Emission from Ultraviolet Luminous Galaxies and Lyman Break Galaxies  

NASA Technical Reports Server (NTRS)

We present results from an XMM mini-survey of GALEX-selected Ultraviolet-Luminous Galaxies (UVLGs) that appear to include an interesting subset that are analogs to the distant (3X-ray emission of LBGs appear to be broadly similar to that of galaxies in the local Universe, possibly indicating similarity in the production of accreting binaries over large evolutionary timescales in the Universe. We have detected luminous X-ray emission from one UVLG that permits basic X-ray spectroscopic analysis, and have direct X-ray constraints on a total of 6 UVLGs. We find evidence for likely large scatter in the assumed X-ray/star-formation rate relation for LBGs.

Hornschemeier, Ann; Ptak, A. F.; Salim, S.; Heckman, T. P.; Overzier, R.; Mallery, R.; Rich, M.; Strickland, D.; Grimes, J.

2009-01-01

173

The Chandra Planetary Nebula Survey (CHANPLANS). II. X-Ray Emission from Compact Planetary Nebulae  

NASA Astrophysics Data System (ADS)

We present results from the most recent set of observations obtained as part of the Chandra X-ray observatory Planetary Nebula Survey (CHANPLANS), the first comprehensive X-ray survey of planetary nebulae (PNe) in the solar neighborhood (i.e., within ~1.5 kpc of the Sun). The survey is designed to place constraints on the frequency of appearance and range of X-ray spectral characteristics of X-ray-emitting PN central stars and the evolutionary timescales of wind-shock-heated bubbles within PNe. CHANPLANS began with a combined Cycle 12 and archive Chandra survey of 35 PNe. CHANPLANS continued via a Chandra Cycle 14 Large Program which targeted all (24) remaining known compact (R neb <~ 0.4 pc), young PNe that lie within ~1.5 kpc. Results from these Cycle 14 observations include first-time X-ray detections of hot bubbles within NGC 1501, 3918, 6153, and 6369, and point sources in HbDs 1, NGC 6337, and Sp 1. The addition of the Cycle 14 results brings the overall CHANPLANS diffuse X-ray detection rate to ~27% and the point source detection rate to ~36%. It has become clearer that diffuse X-ray emission is associated with young (lsim 5 × 103 yr), and likewise compact (R neb <~ 0.15 pc), PNe with closed structures and high central electron densities (ne >~ 1000 cm-3), and is rarely associated with PNe that show H2 emission and/or pronounced butterfly structures. Hb 5 is one such exception of a PN with a butterfly structure that hosts diffuse X-ray emission. Additionally, two of the five new diffuse X-ray detections (NGC 1501 and NGC 6369) host [WR]-type central stars, supporting the hypothesis that PNe with central stars of [WR]-type are likely to display diffuse X-ray emission.

Freeman, M.; Montez, R., Jr.; Kastner, J. H.; Balick, B.; Frew, D. J.; Jones, D.; Miszalski, B.; Sahai, R.; Blackman, E.; Chu, Y.-H.; De Marco, O.; Frank, A.; Guerrero, M. A.; Lopez, J. A.; Zijlstra, A.; Bujarrabal, V.; Corradi, R. L. M.; Nordhaus, J.; Parker, Q. A.; Sandin, C.; Schönberner, D.; Soker, N.; Sokoloski, J. L.; Steffen, M.; Toalá, J. A.; Ueta, T.; Villaver, E.

2014-10-01

174

Impulsive phase of flares in soft X-ray emission  

NASA Technical Reports Server (NTRS)

Observations using the bent crystal spectrometer instrument on the Solar Maximum Mission show that turbulence and blue-shifted motions are characteristic of the soft X-ray plasma during the impulsive phase of flares, and are coincident with the hard X-ray bursts observed by the hard X-ray burst spectrometer. A method for analysing the Ca XIX and Fe XXV spectra characteristic of the impulsive phase is presented. Nonthermal widths and blue-shifted components in the spectral lines of Ca XIX and Fe XXV indicate the presence of turbulent velocities exceeding 100 km/s and upward motions of 300-400 km/s. The April 10, May 9, and June 29, 1980 flares are studied. The April 10 flare has two separated footpoints bright in hard X-rays. Plasma heated to temperatures greater than ten million K rises from the footpoints. During the three minutes in which the evaporation process occurs an energy of 3.7 x 10 to the 30th ergs. This is consistent with the above figures, allowing for loss by radiation and conduction.

Antonucci, E.; Gabriel, A. H.; Acton, L. W.; Leibacher, J. W.; Culhane, J. L.; Rapley, C. G.; Doyle, J. G.; Machado, M. E.; Orwig, L. E.

1982-01-01

175

Soft X-ray emission in kink-unstable coronal loops  

NASA Astrophysics Data System (ADS)

Solar flares are associated with intense soft X-ray emission generated by the hot flaring plasma in coronal magnetic loops. We investigate the temporal, spectral and spatial evolution of the properties of the thermal X-ray emission produced in simulated kink-unstable magnetic flux-ropes. The numerical setup used consists of a highly twisted loop embedded in a region of uniform and untwisted background coronal magnetic field. The magnetic flux-rope reconnects with the background flux after the triggering of the kink instability and is then allowed to relax to a lower energy state. Strong ohmic heating leads to strong and quick heating (up to more than 15 MK), to a strong peak of X-ray emission and to the hardening of the thermal X-ray spectrum. The emission pattern is often filamentary and the amount of twist deduced from the X-ray emission alone is considerably lower than the maximum twist in the simulated flux-ropes. The flux-rope plasma becomes strongly multi-thermal during the flaring episode. The emission measure evolves into a bi-modal distribution as a function of temperature during the saturation phase, and later converges to the power-law distribution mathrm{EM}~ T(-4.2) (during the relaxation/cooling) phase. These soft X-ray emission properties are maintained for a large range of coronal magnetic field strength, plasma density and flux-rope twist values.

Pinto, Rui; Vilmer, Nicole; Brun, Allan Sacha

176

Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination  

NASA Technical Reports Server (NTRS)

The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory (LLNL) to study X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in existing experimental and theoretical understanding of this atomic physics process, and are needed to explain all or part of the observed X-ray emission from the soft X-ray background, stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae. Progress made during the first year of the grant is described, as is work planned for the second year.

Wargelin, B.

2002-01-01

177

Soft x ray emission from a gas-puff z-pinch plasma  

Microsoft Academic Search

Soft x ray emission or radiation was studied by using a gas-puff z-pinch device, which has no triggered switch. A PIN-photodiode covered by aluminum was used for the detection of soft x rays. Three kinds of spatial emission patterns were observed from measurement using a pinhole camera. Hot spots were observed near the middle of the discharge. In order to

S. Ueda; S. Maeda; H. Akiyama

1991-01-01

178

Discovery of Diffuse Hard X-Ray Emission Around Jupiter with Suzaku  

Microsoft Academic Search

We report the discovery of diffuse hard (1-5 keV) X-ray emission around Jupiter in a deep 160 ks Suzaku X-ray Imaging Spectrometer data. The emission is distributed over ~16 × 8 Jovian radius and spatially associated with the radiation belts and the Io Plasma Torus (IPT). It shows a flat power-law spectrum with a photon index of 1.4 ± 0.2

Yuichiro Ezoe; Kumi Ishikawa; Takaya Ohashi; Yoshizumi Miyoshi; Naoki Terada; Yasunobu Uchiyama; Hitoshi Negoro

2010-01-01

179

Upper Limits on the X-ray Emission of "Uranium" Stars  

E-print Network

A paper by Qian & Wasserburg suggests the optical absorption lines of uranium observed in the spectra of ultra-metal-poor stars (defined as [Fe/H] $<$-3) arise from contamination from a supernova in a binary star system. Assuming the binary survived the explosion, a collapsed compact object may be present and implying potential accretion processes with accompanying X-ray emission. Upper limits on X-ray emission from an accreting compact object are described here.

Eric M. Schlegel

2003-01-15

180

Spectral Diagnostics of Galactic and Stellar X-Ray Emission from Charge Exchange Recombination  

NASA Technical Reports Server (NTRS)

The proposed research uses the electron beam ion trap at the Lawrence Livermore National Laboratory to study the X-ray emission from charge-exchange recombination of highly charged ions with neutral gases. The resulting data fill a void in the existing experimental and theoretical data and are needed to explain all or part of the observed X-ray emission from the Galactic Ridge, solar and stellar winds, the Galactic Center, supernova ejecta, and photoionized nebulae.

Wargelin, B.

2003-01-01

181

Discovery of Oxygen Kalpha X-ray Emission from the Rings of Saturn  

E-print Network

Using the Advanced CCD Imaging Spectrometer (ACIS), the Chandra X-ray Observatory (CXO) observed the Saturnian system for one rotation of the planet (~37 ks) on 20 January, 2004, and again on 26-27 January, 2004. In this letter we report the detection of X-ray emission from the rings of Saturn. The X-ray spectrum from the rings is dominated by emission in a narrow (~130 eV wide) energy band centered on the atomic oxygen K-alpha fluorescence line at 0.53 keV. The X-ray power emitted from the rings in the 0.49-0.62 keV band is 84 MW, which is about one-third of that emitted from Saturn disk in the photon energy range 0.24-2.0 keV. Our analysis also finds a clear detection of X-ray emission from the rings in the 0.49-0.62 keV band in an earlier (14-15 April, 2003) Chandra ACIS observation of Saturn. Fluorescent scattering of solar X-rays from oxygen atoms in the H2O icy ring material is the likely source mechanism for ring X-rays, consistent with the scenario of solar photo-production of a tenuous ring oxygen atmosphere and ionosphere recently discovered by Cassini.

Anil Bhardwaj; Ronald F. Elsner; J. Hunter Waite, Jr.; G. Randall Gladstone; Thomas E. Cravens; Peter G. Ford

2005-05-19

182

Discovery of Oxygen Kalpha X-ray Emission from the Rings of Saturn  

NASA Technical Reports Server (NTRS)

Using the Advanced CCD Imaging Spectrometer (ACIS), the Chandra X-ray Observatory (CXO) observed the Saturnian system for one rotation of the planet (approx.37 ks) on 20 January, 2004, and again on 26-27 January, 2004. In this letter we report the detection of X-ray emission from the rings of Saturn. The X-ray spectrum from the rings is dominated by emission in a narrow (approx.130 eV wide) energy band centered on the atomic oxygen Ka fluorescence line at 0.53 keV. The X-ray power emitted from the rings in the 0.49-0.62 keV band is about one-third of that emitted from Saturn disk in the photon energy range 0.24-2.0 keV. Our analysis also finds a clear detection of X-ray emission from the rings in the 0.49-0.62 keV band in an earlier (14-15 April, 2003) Chandra ACIS observation of Saturn. Fluorescent scattering of solar X-rays from oxygen atoms in the H20 icy ring material is the likely source mechanism for ring X-rays, consistent with the scenario of solar photo-production of a tenuous ring oxygen atmosphere and ionosphere recently discovered by Cassini.

Bhardwaj, Anil; Elsner, Ronald F.; Waite, J. Hunter, Jr.; Gladstone, G Randall; Cravens, Thomas E.; Ford, Peter G.

2005-01-01

183

X-ray emission of hot subdwarf stars  

NASA Astrophysics Data System (ADS)

While several hot subdwarf stars have been deeply investigated in the optical and UV domain, only the sdO stars HD49798 and BD+37 442 have been detected at X-rays. In both cases the measured value of log(fx/fbol) is about -7, in agreement with the average value found in the standard OB stars: therefore it is interesting to investigate if this is a common property of the sdO stars. To this aim, we propose to observe with XMM-Newton the sdO stars BD+28 4211, BD+75 325, BD+37 1977 and BD-03 2179, since they are the best candidate to perform this type of search: they are optically bright (V = 9-10) and are characterized by a high temperature (Teff > 45000 K), thus implying an estimated X-ray flux high enough to be detectable with a XMM-Newton observation.

La Palombara, Nicola

2011-10-01

184

X-ray emission from clusters and groups of galaxies  

NASA Technical Reports Server (NTRS)

Recent major advances in x-ray imaging and spectroscopy of clusters have allowed the determination of their mass and mass profile out to approximately 1/2 the virial radius. In rich clusters, most of the baryonic mass is in the gas phase, and the ratio of mass in gas/stars varies by a factor of 2-4. The baryonic fractions vary by a factor of approximately 3 from cluster to cluster and almost always exceed 0.09 h50-[3/2] and thus are in fundamental conflict with the assumption of Omega = 1 and the results of big bang nucleosynthesis. The derived Fe abundances are 0.2-0.45 solar, and the abundances of O and Si for low redshift systems are 0.6-1.0 solar. This distribution is consistent with an origin in pure type II supernova. The amount of light and energy produced by these supernovae is very large, indicating their importance in influencing the formation of clusters and galaxies. The lack of evolution of Fe to a redshift of z approximately 0.4 argues for very early enrichment of the cluster gas. Groups show a wide range of abundances, 0.1-0.5 solar. The results of an x-ray survey indicate that the contribution of groups to the mass density of the universe is likely to be larger than 0.1 h50-2. Many of the very poor groups have large x-ray halos and are filled with small galaxies whose velocity dispersion is a good match to the x-ray temperatures.

Mushotzky, R.

1998-01-01

185

Generation Mechanisms UV and X-ray Emissions During SL9 Impact  

NASA Astrophysics Data System (ADS)

The purpose of this grant was to study the ultraviolet and X-ray emissions associated with the impact of comet Shoemaker-Levy 9 with Jupiter. The University of Michigan task was primarily focused on theoretical calculations. The NAGW-4788 subtask was to be largely devoted to determining the constraints placed by the X-ray observations on the physical mechanisms responsible for the generation of the X-rays. Author summarized below the ROSAT observations and suggest a physical mechanism that can plausibly account for the observed emissions. It is hoped that the full set of activities can be completed at a later date. Further analysis of the ROSAT data acquired at the time of the impact was necessary to define the observational constraints on the magnetospheric-ionospheric processes involved in the excitation of the X-ray emissions associated with the fragment impacts. This analysis centered around improvements in the pointing accuracy and improvements in the timing information. Additional pointing information was made possible by the identification of the optical counterparts to the X-ray sources in the ROSAT field-of-view. Due to the large number of worldwide observers of the impacts, a serendipitous visible plate image from an observer in Venezuela provided a very accurate location of the present position of the X-ray source, virtually eliminating pointing errors in the data. Once refined, the pointing indicated that the two observed X-ray brightenings that were highly correlated in time with the K and P2 events were brightenings of the X-ray aurora (as identified in images prior to the impact).Appendix A "ROSAT observations of X-ray emissions from Jupiter during the impact of comet Shoemaker-Levy 9' also included.

Waite, J. Hunter, Jr.

1997-01-01

186

Recurrent X-ray Emission Variations of Eta Carinae and the Binary Hypothesis  

NASA Technical Reports Server (NTRS)

Recent studies suggest that, the super-massive star eta Carinae may have a massive stellar companion (Damineli, Conti, and Lopes 1997), although the dense ejecta surrounding the star make this claim hard to test using conventional methods. Settling this question is critical for determining the current evolutionary state and future evolution of the star. We address this problem by an unconventional method: If eta Carinae is a binary, X-ray emission should be produced in shock waves generated by wind-wind collisions in the region between eta Carinae and its companion. Detailed X-ray monitoring of eta Carinae for more that) 2 years shows that the observed emission generally resembles colliding-wind X-ray emission, but with some significant discrepancies. Furthermore, periodic X-ray "flaring" may provide an additional clue to determine the presence of a companion star and for atmospheric pulsation in eta Carinae.

Ishibashi, K.; Corcoran, M. F.; Davidson, K.; Swank, J. H.; Petre, R.; Drake, S. A.; Damineki, A.; White, S.

1998-01-01

187

Gas flow and generation of x ray emission in WR+OB binaries  

NASA Technical Reports Server (NTRS)

The supersonic flow of the ionized gas in WR+OB binaries and X-ray generation are considered. X-ray emission is caused by gas heating up to temperatures of 10(exp 7) to 10(exp 8) K behind the front of shock waves. These are found in the collision of gas flowing out from the WR star with either the OB star's surface or the gas of the OB star's wind. The distribution of temperature and concentration behind the shock front are obtained. Using these distributions, the spectral power of bremsstrahlung X-ray emission of hot gas is calculated. Possible reasons that lead to a considerable difference between the observed parameters of X-ray emission of the WR binary of V 444 Cygni and the theoretically expected are discussed.

Usov, V. V.

1991-01-01

188

The Heliospheric Contribution to the Soft X-ray Background Emission  

NASA Astrophysics Data System (ADS)

The soft x-ray background observed from Earth contains contributions not only from outside the solar system such as the local bubble but contributions from within the solar system including from the interplanetary medium and from the terrestrial geocorona and magnetosheath. Great effort was spent on removing non- cosmic contamination from data collected during the ROSAT all-sky survey. Some of the contamination, however, was due to X-ray emission from solar wind charge exchange with interstellar and geocoronal neutrals. The time varying component of this contamination was removed, but the steady state component of this X-ray emission was not. We will present all-sky maps of the soft X-ray emission with the heliospheric component removed, which will allow a re-interpretation of the nature of the local interstellar bubble. We have calculated this steady statement component for and will discuss its contribution to the ¼ and ¾ keV all- sky survey maps.

Robertson, I. P.; Kuntz, K. D.; Collier, M. R.; Snowden, S. L.; Cravens, T. E.

2008-12-01

189

A unified model of accretion flows and X ray emission in low mass X ray binary systems  

NASA Technical Reports Server (NTRS)

Recent work on a unified model of accretion flows and X-ray emission in low mass X-ray binaries is summarized. In this model, a weakly magnetic neutron star accretes gas simultaneously from a Keplerian disk and a corona above the inner part of the disk. Photons are produced and escape through an approximately radial inflow of gas captured from the inner disk corona. Changes in the optical depths of the central corona and the radial flow may explain the Z-shaped hardness-intensity and color-color tracks observed in the most luminous sources. Numerical simulations show that the radial flow oscillates when the luminosity rises to within a few percent of the Eddington critical luminosity L sub E, and that the oscillation frequency is approximately 5 to 10 Hz if the radial flow develops approximately 300 km from the neutron star. The 10 to 20 Hz oscillations observed in Sco X-1 when it is on the flaring branch are discussed.

Lamb, F. K.

1989-01-01

190

High-resolution X-ray Emission Spectroscopy as a Microprobe Imaging Modality  

NASA Astrophysics Data System (ADS)

Hard x-ray microprobe beamlines at third generation light sources have made significant impacts in several fields of science and technology. Such facilities permit rapid 2-dimensional studies of multiphase materials on submicron length scales using a variety of pixel-by-pixel imaging modalities (e.g., x-ray diffraction, x-ray absorption near edge fine structure, or x-ray fluorescence). Here, we aim to expand hard x-ray microprobe imaging modalities to include high-resolution x-ray emission spectroscopy (XES). When performed at 1-eV resolution, such measurements can provide quite direct atomic-level information on ionic valence, spin, and local electronic and chemical environment. Ongoing work in our research group has improved the efficiency of XES via the development of a new type of compact and inexpensive x-ray spectrometer design, the "miniature x-ray spectrometer" or "miniXS" paradigm. We will report preliminary 2-dimensional XES studies of planar multiphase materials, with specific applications to samples of interest for geophysics and catalysis science.

Pacold, Joseph; Seidler, Gerald; Mattern, Brian; Haave, Matthew; Gordon, Robert

2011-03-01

191

Catalytic action of ? source on x-ray emission from plasma focus  

NASA Astrophysics Data System (ADS)

The influence of preionization around the insulator sleeve by a mesh-type ? source (Ni6328) for the x-ray emission from a (2.3-3.9 kJ) plasma focus device is investigated. Quantrad Si p-i-n diodes along with suitable filters are employed as time-resolved x-ray detectors and a multipinhole camera with absorption filters is used for time-integrated analysis. X-ray emission in 4? geometry is measured as a function of argon and hydrogen gas filling pressures with and without ? source at different charging voltages. It is found that the pressure range for the x-ray emission is broadened, x-ray emission is enhanced, and shot to shot reproducibility is improved with the ? source. With argon, the CuK? emission is estimated to be 27.14 J with an efficiency of 0.7% for ? source and 21.5 J with an efficiency of 0.55% without ? source. The maximum x-ray yield in 4? geometry is found to be about 68.90 J with an efficiency of 1.8% for ? source and 54.58 J with an efficiency of 1.4% without ? source. With hydrogen, CuK? emission is 11.82 J with an efficiency of 0.32% for ? source and 10.07 J with an efficiency of 0.27% without ? source. The maximum x-ray yield in 4? geometry is found to be 30.20 J with an efficiency of 0.77% for ? source and 25.58 J with an efficiency of 0.6% without ? source. The x-ray emission with Pb insert at the anode tip without ? source is also investigated and found to be reproducible and significantly high. The maximum x-ray yield is estimated to be 46.6 J in 4? geometry with an efficiency of 1.4% at 23 kV charging voltage. However, degradation of x-ray yield is observed when charging voltage exceeds 23 kV for Pb insert. From pinhole images it is observed that the x-ray emission due to the bombardment of electrons at the anode tip is dominant in both with and without ? source.

Ahmad, S.; Sadiq, Mehboob; Hussain, S.; Shafiq, M.; Zakaullah, M.; Waheed, A.

2006-01-01

192

X-rays from emission-line stars in the Herbig-Haro 1 region  

NASA Technical Reports Server (NTRS)

We have observed the region in Orion containing Herbig-Haro 1 as well as a number of young, active stars. This observation shows a similar X-ray morphology to that in the first X-ray imaging observation about 10 years ago. The ROSAT High Resolution Instrument with its approximately arcsecond spatial resolution allows us in most cases to make definite optical identifications of the 0.1-2.4 keV X-ray sources. New identifications with emission-line stars are made, and prior identifications using lower resolution observations are confirmed or corrected. The X-ray emission previously detected from the vicinity of HH-1 is not associated with HH-1 but with a known T Tauri star. The observed relationships among X-ray, optical line, and infrared excess emission do not simply fall into the suggested classifications for T Tauri or T Tauri-like stars. This could be an indication of another X-ray emission region such as accretion disks that add to the emission from the stellar atmospheres.

Pravdo, Steven H.; Angelini, Lorella

1993-01-01

193

A Study of the X-Ray Emission from Three Radio Pulsars  

NASA Technical Reports Server (NTRS)

The subject grant is for work on a study of x-ray emission from isolated pulsars. The purpose of the study was to: determine whether the pulsars were x-ray sources; and, if so, search for evidence of pulsations at the known radio period; and study the nature of the x-ray emission. Observation of the pulsar PSR 0355+54 were obtained, and the analysis of these data is complete. These results were reported at the 183rd AAS Meeting, and in a paper entitled 'X-Ray Emission from PSR 0355+54' which as published in the The Astrophysical Journal. Also obtained an approx. 3 ks PSPC observations of PSR 1642-03. A summary of the results from these data were reported in a Conference Proceedings for the 'New Horizon of X-ray Astronomy' symposium. In addition, as part of a study with a student from the SAO Summer Intern Program, I incorporated ROSAT archival data in an extended study of pulsar emission. These results were reported at the 185th AAS Meeting, and in a paper entitled 'Soft X-ray Emission from Selected Isolated Pulsars' which was published in The Astrophysical Journal (Letters).

Slane, Patrick O. (Principal Investigator)

1996-01-01

194

X-ray emission in collisions of highly charged I, Pr, Ho, and Bi ions with a W surface  

SciTech Connect

X-ray emission yields, which are defined as the total number of emitted x-ray photons per incident ion, and dissipated fractions of potential energies through x-ray emission have been measured for slow highly charged ions of I, Pr, Ho, and Bi colliding with a W surface. A larger amount of potential energy was consumed for the x-ray emission with increasing the atomic number and the charge state. The present measurements show that x-ray emission is one of the main decay channels of hollow atoms produced in collisions of very highly charged ions of heavy elements.

Watanabe, H.; Tona, M.; Ohtani, S. [Institute for Laser Science and Department of Applied Physics and Chemistry, University of Electro-Communications, Chofu, Tokyo 182-8585 (Japan); CREST, Japan Science and Technology Agency, Chofu, Tokyo 182-8585 (Japan); Sun, J.; Nakamura, N.; Yamada, C.; Yoshiyasu, N. [Institute for Laser Science and Department of Applied Physics and Chemistry, University of Electro-Communications, Chofu, Tokyo 182-8585 (Japan); Sakurai, M. [Department of Physics, Kobe University, Kobe, Hyogo, 657-8501 (Japan)

2007-06-15

195

Evolution of X-ray emission from young massive star clusters  

E-print Network

The evolution of X-ray emission from young massive star clusters is modeled, taking into account the emission from the stars as well as from the cluster wind. It is shown that the level and character of the soft (0.2-10 keV) X-ray emission change drastically with cluster age and are tightly linked with stellar evolution. Using the modern X-ray observations of massive stars we show that the correlation between bolometric and X-ray luminosity known for single O stars also holds for O+O and O+Wolf-Rayet (WR) binaries. The diffuse emission originates from the cluster wind heated by the kinetic energy of stellar winds and supernova explosions. To model the evolution of the cluster wind, the mass and energy yields from a population synthesis are used as input to a hydrodynamic model. It is shown that in a very young clusters the emission from the cluster wind is low. When the cluster evolves, WR stars are formed. Their strong stellar winds power an increasing X-ray emission of the cluster wind. Subsequent supernova explosions pump the level of diffuse emission even higher. Clusters at this evolutionary stage may have no X-ray bright stellar point sources, but a relatively high level of diffuse emission. A supernova remnant may become a dominant X-ray source, but only for a short time interval of a few thousand years. We retrieve and analyse Chandra and XMM-Newton observations of six massive star clusters located in the Large Magellanic Cloud. Our model reproduces the observed diffuse and point-source emission from these LMC clusters, as well as from the Galactic clusters Arches, Quintuplet and NGC 3603.

L. M. Oskinova

2005-05-25

196

ISOCAM Photometry of Narrow-Line X-ray Galaxies  

E-print Network

Mid-infrared photometry of the hosts of Narrow-Line X-ray Galaxies at 6 microns and 12 microns has been attempted with ISOCAM. No conclusive detections have been made. This implies that these are quiescent objects with little or no active star-formation. Neither X-ray binaries nor starburst-driven superwinds are consistent explanations for the X-ray emission in these objects. We conclude that these NLXGs are predominantly AGN-powered.

J. D. Law-Green; A. Zezas; M. J. Ward; C. Boisson

1998-12-23

197

Using the X-ray Emission Lines of Seyfert 2 AGN to Measure Abundance Ratios  

E-print Network

We measure the metal abundance ratios in the X-ray photoionized gas located near the narrow line region of a sample of Seyfert 2 AGN. The high-resolution X-ray spectra observed with the Chandra high- and low-energy transmission grating spectrometers are compared with models of the resonant scattering and recombination emission from a plasma in thermal balance, and with multiple temperature zones. The abundance ratios in the sample are close to the Solar values, with slight over-abundances of N in NGC 1068, and of Ne in NGC 4151. Our X-ray spectral models use fewer degrees of freedom than previous works.

Mario A. Jimenez-Garate; Toan Khu

2004-03-26

198

Stellar wind induced soft X-ray emission from close-in exoplanets  

E-print Network

In this paper, we estimate the X-ray emission from close-in exoplanets. We show that the Solar/Stellar Wind Charge Exchange Mechanism (SWCX) which produces soft X-ray emission is very effective for hot Jupiters. In this mechanism, X-ray photons are emitted as a result of the charge exchange between heavy ions in the solar wind and the atmospheric neutral particles. In the Solar System, comets produce X-rays mostly through the SWCX mechanism, but it has also been shown to operate in the heliosphere, in the terrestrial magnetosheath, and on Mars, Venus and Moon. Since the number of emitted photons is proportional to the solar wind mass flux, this mechanism is not very effective for the Solar system giants. Here we present a simple estimate of the X-ray emission intensity that can be produced by close-in extrasolar giant planets due to charge exchange with the heavy ions of the stellar wind. Using the example of HD~209458b, we show that this mechanism alone can be responsible for an X-ray emission of $\\approx 10...

Kislyakova, K G; Johnstone, C P; Holmström, M; Zaitsev, V V; Lammer, H

2015-01-01

199

Technique to obtain positron emission mammography images in registration with x-ray mammograms  

E-print Network

Technique to obtain positron emission mammography images in registration with x-ray mammograms of suspicious lesions or tumors. Our PEM-1 positron emission mammography system detects metabolic activity frame is visible on the film image. During a positron emission metabolic scan, detectors acquire a 49 59

Thompson, Chris

200

NuSTAR observation of the Galactic ridge X-ray emission  

NASA Astrophysics Data System (ADS)

The paradigm of the Galactic Ridge X-ray Emission (GRXE) or hard X-ray background of the Milky Way has been dramatically changed over the past years. The stellar origin of the GRXE has been strongly supported by morphological and spectral studies. The GRXE does not arise from the interaction of cosmic rays with the interstellar medium, as was believed before, but is associated with the (predominantly old) stellar population of the Galaxy, namely with hard X-ray emission from accreting white dwarfs and coronally active stars. I will present results of the GRXE spectral study with NuSTAR hard X-ray mission launched into the orbit in 2012. The GRXE measurements have been done in a part of the Galactic Center survey program 2012-2014. New data allow us to reconstruct both GRXE spatial distribution and broadband (3-80 keV) spectrum, providing another test for its interpretation.

Krivonos, Roman

201

Investigating the origin of the X-ray emission of Cyg OB2 #5  

NASA Astrophysics Data System (ADS)

Massive stars have strong winds, which collide in massive binaries, giving rise to hard and varying X-ray emission. Cyg OB2 #5 is such a case. It was recently found to be a quadruple system and changes in its X- ray emission indicate that X-rays arise in the wind-wind collision (WWC) between the close binary and the third star. In this context, X-rays are a crucial tool to constrain the orbital parameters, but available observations only probe two phases of the 6.7 yr orbit of the third star. A monitoring (one observation per year) is thus needed and we therefore request in this AO a short exposure observation (10 ks) to better understand this iconic system.

Cazorla, Constantin

2013-10-01

202

Soft X-Ray Emission and Charged Particles Beams from a Plasma Focus of Hundreds Joules  

SciTech Connect

In a new stage of characterization of our plasma focus devices of hundred and tens of joules (PF-400J and PF-50J), preliminary series of measurements on soft X-ray and ion beams have been performed in the device PF-400J (176-539 J, 880 nF, T/4 {approx}300 ns). The device was operated in hydrogen to 7 mbar of pressure . The temporal and spatial X-ray characteristics are investigated by means filtered PIN diodes and a multipinhole camera. Graphite collectors, operating in the bias ion collector mode, are used to estimate the characteristic ion energy using the time flight across the probe array. The time of the ion beam emission to be correlated with plasma emission events associated with the soft X-ray pulses detected by the probes. Temporal correlations between soft X-ray signals and ion beams are performed.

Silva, Patricio; Moreno, Jose; Soto, Leopoldo [Comision Chilena de Energia Nuclear, Casilla 188-D, Santiago (Chile); Pavez, Cristian [Comision Chilena de Energia Nuclear, Casilla 188-D, Santiago (Chile); Universidad de Concepcion, Facultad de Ciencias, Departamento de Fisica, Concepcion (Chile); Arancibia, Jaime [Universidad de Chile, Facultad de Ciencias, Departamento de Fisica, Santiago (Chile)

2006-12-04

203

Galactic Ridge X-ray Emission study with NuSTAR  

NASA Astrophysics Data System (ADS)

The paradigm of the Galactic Ridge X-ray Emission (GRXE) or hard X-ray background of the Milky Way has been dramatically changed over the past years. The stellar origin of the GRXE has been strongly supported by morphological and spectral studies with RXTE, INTEGRAL and Chandra observatories. The GRXE does not arise from the interaction of cosmic rays with the interstellar medium, as was believed before, but is associated with the (predominantly old) stellar population of the Galaxy, namely with hard X-ray emission from accreting white dwarfs and coronaly active stars. I will present results of the GRXE spectral study with NuSTAR hard X-ray mission launched into the orbit in 2012. The GRXE measurements have been done in a part of the Galactic Center survey program 2012-2014. New data allow us to reconstruct both GRXE spatial distribution and broadband (3-80 keV) spectrum, providing another test for its interpretation.

Krivonos, Roman; NuSTAR

2015-01-01

204

A carbon nanotube field emission multipixel x-ray array source for microradiotherapy application  

SciTech Connect

The authors report a carbon nanotube (CNT) field emission multipixel x-ray array source for microradiotherapy for cancer research. The developed multipixel x-ray array source has 50 individually controllable pixels and it has several distinct advantages over other irradiation source including high-temporal resolution (millisecond level), the ability to electronically shape the form, and intensity distribution of the radiation fields. The x-ray array was generated by a CNT cathode array (5x10) chip with electron field emission. A dose rate on the order of >1.2 Gy/min per x-ray pixel beam is achieved at the center of the irradiated volume. The measured dose rate is in good agreement with the Monte Carlo simulation result.

Wang Sigen [Department of Radiation Oncology, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Department of Physics and Astronomy, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Calderon, Xiomara; Peng Rui [Curriculum of Applied and Materials Sciences, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Schreiber, Eric C. [Department of Radiation Oncology, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Zhou, Otto [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Curriculum of Applied and Materials Sciences, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Chang, Sha [Department of Radiation Oncology, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Department of Physics and Astronomy, University of North Carolina at Chapel Hill, North Carolina 27599 (United States); Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, North Carolina 27599 (United States)

2011-05-23

205

Chandra Observations and Modeling of Geocoronal Charge Exchange X-Ray Emission During Solar Wind Gusts  

NASA Astrophysics Data System (ADS)

Solar wind charge exchange (SWCX) X-rays are emitted when highly charged solar wind ions such as O7+ collide with neutral gas. The best known examples of this occur around comets, but SWCX emission also arises in the Earth's tenuous outer atmosphere and throughout the heliosphere as neutral H and He from the interstellar medium flows into the solar system. This geocoronal and heliospheric emission comprises much of the soft X-ray background and is seen in every X-ray observation. Geocoronal emission, although usually weaker than heliospheric emission, arises within a few tens of Earth radii and therefore responds much more quickly (on time scales of less than an hour) to changes in solar wind intensity than the widely distributed heliospheric emission.We have studied a dozen Chandra observations when the flux of solar wind protons and O7+ ions was at its highest. These gusts of wind cause correspondingly abrupt changes in geocoronal SWCX X-ray emission,which may or may not be apparent in Chandra data depending on a given observation's line of sight through the magnetosphere. We compare observed changes in the X-ray background with predictions from a fully 3D analysis of SWCX emission based on magnetospheric simulations using the BATS-R-US model.

Kornbleuth, Marc; Wargelin, Bradford J.; Juda, Michael

2014-06-01

206

THERMAL X-RAY EMISSION FROM THE SHOCKED STELLAR WIND OF PULSAR GAMMA-RAY BINARIES  

SciTech Connect

Gamma-ray-loud X-ray binaries are binary systems that show non-thermal broadband emission from radio to gamma rays. If the system comprises a massive star and a young non-accreting pulsar, their winds will collide producing broadband non-thermal emission, most likely originated in the shocked pulsar wind. Thermal X-ray emission is expected from the shocked stellar wind, but until now it has neither been detected nor studied in the context of gamma-ray binaries. We present a semi-analytic model of the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries, and find that the thermal X-ray emission increases monotonically with the pulsar spin-down luminosity, reaching luminosities of the order of 10{sup 33} erg s{sup -1}. The lack of thermal features in the X-ray spectrum of gamma-ray binaries can then be used to constrain the properties of the pulsar and stellar winds. By fitting the observed X-ray spectra of gamma-ray binaries with a source model composed of an absorbed non-thermal power law and the computed thermal X-ray emission, we are able to derive upper limits on the spin-down luminosity of the putative pulsar. We applied this method to LS 5039, the only gamma-ray binary with a radial, powerful wind, and obtain an upper limit on the pulsar spin-down luminosity of {approx}6 Multiplication-Sign 10{sup 36} erg s{sup -1}. Given the energetic constraints from its high-energy gamma-ray emission, a non-thermal to spin-down luminosity ratio very close to unity may be required.

Zabalza, V.; Paredes, J. M. [Departament d'Astronomia i Meteorologia, Institut de Ciencies del Cosmos (ICC), Universitat de Barcelona (IEEC-UB), Marti i Franques 1, E08028 Barcelona (Spain); Bosch-Ramon, V., E-mail: vzabalza@am.ub.es [Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland)

2011-12-10

207

Weak Hard X-ray Emission from Broad Absorption Line Quasars Observed with NuSTAR: Evidence for Intrinsic X-ray Weakness  

NASA Astrophysics Data System (ADS)

We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z=0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z<1.3. However, their rest-frame 2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with <45 counts in the 3-24 keV band, and the other three are not detected. The hard X-ray (8-24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (? 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (>33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

Luo, Bin; Brandt, W. Niel; Alexander, David M; Stern, Daniel; Teng, Stacy H.; Arevalo, Patricia; Bauer, Franz E.; Boggs, Steven E.; Christensen, Finn; Comastri, Andrea; Craig, William W.; Farrah, Duncan; Gandhi, Poshak; Hailey, Charles James; Harrison, Fiona; Koss, Michael; Ogle, Patrick M.; Puccetti, Simonetta; Saez, Cristian; Scott, Amy; Walton, Dom; Zhang, William

2014-08-01

208

The Morphology of the X-ray Emission above 2 keV from Jupiter's Aurorae  

NASA Technical Reports Server (NTRS)

The discovery in XMM-Newton X-ray data of X-ray emission above 2 keY from Jupiter's aurorae has led us to reexamine the Chandra ACIS-S observations taken in Feb 2003. Chandra's superior spatial resolution has revealed that the auroral X-rays with E > 2 keV are emitted from the periphery of the region emitting those with E < 1 keV. We are presently exploring the relationship of this morphology to that of the FUV emission from the main auroral oval and the polar cap. The low energy emission has previously been established as due to charge exchange between energetic precipitating ions of oxygen and either sulfur or carbon. It seems likely to us that the higher energy emission is due to precipitation of energetic electrons, possibly the same population of electrons responsible for the FUV emission. We discuss our analysis and interpretation.

Elsner, R.; Branduardi-Raymont, G.; Galand, M.; Grodent, D.; Gladstone, G. R.; Waite, J. H.; Cravens, T.; Ford, P.

2007-01-01

209

Chemical effects in the satellites of X-ray emission spectra  

Microsoft Academic Search

The origins of satellites in X-ray emission spectra are classified into 1) multivacancy satellite 2) charge-transfer satellite and 3) molecular-orbital splitting satellite. The multivacancy satellites are strong for ionic compounds and weak for covalent compounds. However, for ionic compounds of level crossing, the satellites are weak due to the resonance hole transfer from the X-ray emitting atom to one of

Kawai Jun

1993-01-01

210

A model of hard X-rays emission from free expanding Plasma-Focus discharges  

NASA Astrophysics Data System (ADS)

A planar-piston model of the hard x-ray production in Plasma-Focus devices is presented. The model applies Von Karman approximations to represent the inner structure of the pinch. The hard x-ray emission is calculated assuming Bremsstrahlung from the collision on the anode base of an electron current running away from the pinch. The model was applied to analyse the experimental data of a small Plasma Focus without surrounding cathode, founding good agreement.

Fogliatto, E.; González, J.; Barbaglia, M.; Clausse, A.

2014-05-01

211

X-ray Emission from Pre-Main-Sequence Stars - Testing the Solar Analogy  

NASA Technical Reports Server (NTRS)

This LTSA award funded my research on the origin of stellar X-ray emission and the validity of the solar-stellar analogy. This research broadly addresses the relevance of our current understanding of solar X-ray physics to the interpretation of X-ray emission from stars in general. During the past five years the emphasis has been on space-based X-ray observations of very young stars in star-forming regions (T Tauri stars and protostars), cool solar-like G stars, and evolved high-mass Wolf-Rayet (WR) stars. These observations were carried out primarily with the ASCA and ROSAT space-based observatories (and most recently with Chandra), supplemented by ground-based observations. This research has focused on the identification of physical processes that are responsible for the high levels of X-ray emission seen in pre-main-sequence (PMS) stars, active cool stars, and WR stars. A related issue is how the X-ray emission of such stars changes over time, both on short timescales of days to years and on evolutionary timescales of millions of years. In the case of the Sun it is known that magnetic fields play a key role in the production of X-rays by confining the coronal plasma in loop-like structures where it is heated to temperatures of several million K. The extent to which the magnetically-confined corona interpretation can be applied to other X-ray emitting stars is the key issue that drives the research summarized here.

Skinner, Stephen L.

2000-01-01

212

Nonthermal X-ray emission from young Supernova Remnants  

E-print Network

The cosmic-ray spectrum up to the knee ($E\\sim 10^{15}$ eV) is attributed to acceleration processes taking place at the blastwaves which bound supernova remnants. Theoretical predictions give a similar estimate for the maximum energy which can be reached at supernova remnant shocks by particle acceleration. Electrons with energies of the order $\\sim 10^{15}$ eV should give a nonthermal X-ray component in young supernova remnants. Recent observations of SN1006 and G347.3-0.5 confirm this prediction. We present a method which uses hydrodynamical simulations to describe the evolution of a young remnant. These results are combined with an algorithm which simultaneously calculates the associated particle acceleration. We use the test particle approximation, which means that the back-reaction on the dynamics of the remnant by the energetic particles is neglected. We present synchrotron maps in the X-ray domain, and present spectra of the energies of the electrons in the supernova remnant. Some of our results can be compared directly with earlier semi-analytical work on this subject by Reynolds [1].

Eric van der Swaluw; Abraham Achterberg; Yves A. Gallant

2000-12-18

213

ChanPlaNS: Investigating the Diffuse X-ray Emission within Compact Planetary Nebulae  

NASA Astrophysics Data System (ADS)

We present highlights of results from the Chandra Planetary Nebula Survey (ChanPlaNS), the first comprehensive X-ray survey of planetary nebulae (PNe) in the solar neighborhood (i.e., within ~ 1.5 kpc of the Sun). We are finding that diffuse X-ray emission is restricted to compact (Rneb <~0.15 pc) nebulae; this characteristic size scale corresponds to a PN-shaping wind collision timescale of <~ 5 x 103 yr. Furthermore, we find that all ChanPlaNS PNe that display diffuse X-ray emission have closed structures and characteristic nebular densities ne >~ 1000 cm-3, while older, lower-n_e nebulae remain difficult to detect. This relationship between nebular density and energetic wind interactions suggests that optical spectroscopy of density-sensitive lines (e.g., [O II], [S II]) can be used to establish whether a PN might be in an active wind-collision phase. Of the diffuse X-ray detections, 100% (5/5) of PNe with [WR]-type central stars (CSPNe) within ~ 1.5 kpc have detected. We present preliminary results from 3D structural reconstructions of PNe that are designed to investigate the apparent systematic differences between the diffuse X-ray emission morphologies of [WR] and non-[WR] CSPNe, as well as the possibility of enhanced X-ray absorption due to photoionized and neutral nebular gas.

Freeman, Marcus; Montez, Rodolfo; Kastner, Joel H.; ChanPlaNS Team

2015-01-01

214

X-ray Emission from the Pre-planetary Nebula Henize 3-1475  

NASA Technical Reports Server (NTRS)

We report the first detection of X-ray emission in a pre-planetary nebula, He 3-1475. Pre-planetary nebulae are rare objects in the short transition stage between the asymptotic giant branch (AGB) and planetary nebula evolutionary phases, and He 3-1475, characterized by a remarkable S-shaped chain of optical knots, is one of the most noteworthy members of this class. Observations with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory show the presence of compact emission coincident with the brightest optical knot in this bipolar object, which is displaced from the central star by 2'.7 along the polar axis. Model fits to the X-ray spectrum indicate an X-ray temperature and luminosity, respectively, of (4.3-5.7) x 10(exp 6) K and (4 +/- 1.4) x 10(exp 31) (D/5 kpc)(exp 2) ergs s(exp -1) respectively. Our 3 sigma upper limit on the luminosity of compact X-ray emission from the central star in He 3-1475 is approximately equal to 5 x 10(exp 31) (D/5 kpc)(exp 2) ergs s(exp -1). The detection of X-rays in He 3-1475 is consistent with models in which fast collimated post-AGB outflows are crucial to the shaping of nebulae; we discuss such models in the context of our observations.

Sahai, Raghvendra; Kastner, Joel H.; Frank, Adam; Morris, Mark; Blackman, Eric G.

2003-01-01

215

The X-ray emission of the massive stars population in Cyg OB2  

NASA Astrophysics Data System (ADS)

Cygnus OB2 contains a wealth of massive stars of spectral types O, B and Wolf-Rayet. In the framework of a Chandra legacy program to study the X-ray emission from this important association, we have studied the X-ray properties of its massive stars population. We show that the O-stars in Cyg OB2 follow a well-defined scaling relation between their X-ray and bolometric luminosities: log(Lx/Lbol) = -7.2 ± 0.2. Except for the brightest O-star binaries, there is no general X-ray overluminosity due to colliding winds in O-star binaries. Roughly half of the known B-stars in the surveyed field are detected, but they fail to display a clear relationship between Lx and Lbol. Out of the three WR stars in Cyg OB2, probably only WR144 is itself responsible for the observed level of X-ray emission, at a very low log(Lx/Lbol) = -8.8 ± 0.2. The X-ray emission of the other two WR-stars (WR145 and 146) is most probably due to their O-type companion along with a moderate contribution from a wind-wind interaction zone.

Rauw, G.; Nazé, Y.; Wright, N.; Drake, J.; Guarcello, M.; Chandra Cygnus OB2 legacy survey Consortium

2014-07-01

216

Discovery of Diffuse Hard X-ray Emission in the Galactic Center  

NASA Astrophysics Data System (ADS)

The inner arcminutes of the Galaxy contain one of the highest concentration of high-energy sources in the Milky Way. The supermassive black hole, pulsar wind nebulae, supernova remnants, X-ray binaries, and hot interstellar gas are copious emitters of X-rays and gamma-rays. NuSTAR provides a view of the hard X-ray (3-79 keV) band, a critical bridge between the soft X-ray and gamma-ray emission, with unprecedented sub-arcminute angular resolution. I will present analysis of NuSTAR’s view of the Galactic Center above 20 keV, which reveals entirely new contributions to the emission from this region. The hard X-ray emission from the Galactic Center is dominated by a strong point-like source, spatially consistent with the ultra-high energy gamma-ray emission detected by HESS, and a previously undetected diffuse emission extending along the Galactic plane, consistent with unresolved emission from a large population of millisecond pulsars, unusually hot intermediate polars, or black hole binaries.

Perez, Kerstin

2014-08-01

217

X-ray and Molecular Emission from the TW Hya Association  

NASA Astrophysics Data System (ADS)

The X-ray emission from TW Hya, HD 98800, and the three other ``original'' members of the TW Hya Association (TWA) is central to the argument that this group likely represents an association of ``old'' T Tauri stars (Kastner et al. 1997, Science, 277, 67), and X-ray emission has pointed the way to the subsequent identification of additional candidate TWA star systems (Webb et al. 1999, ApJ, 512, L63; Sterzik et al. 1999, A&A 346, L41). We are now beginning to take advantage of the proximity and, hence, large X-ray fluxes of the TWA stars to explore the mechanisms underlying X-ray emission from and variability of T Tauri stars. Observations of TW Hya with the ASCA satellite indicate that its X-ray spectrum is well modeled by coronal emission (Kastner et al. 1999, ApJ, in press). The ASCA data show fluctuations in X-ray flux on timescales 1 hr, while comparison of ROSAT and ASCA spectra indicate variations in the column depth of X-ray absorbing material on the order of years, suggesting that a combination of short-lived flares and longer-term changes in obscuration are responsible for the optical variability of TW Hya. Pending observations of TW Hya by the Chandra X-ray Observatory and the X-ray Multimirror Mission satellite telescopes will shed further light on the nature and variability of its X-ray spectrum. The rich spectrum of radio molecular line emission from TW Hya (Kastner et al. 1997), combined with its bright submillimeter continuum emission, offers compelling evidence that TW Hya is surrounded by a dusty molecular disk that is viewed nearly pole-on. Although several other TWA systems (including certain recently identified members) are sources of dust continuum emission in the radio and infrared, TW Hya remains the only known molecular line source among the TWA stars. Given our rapidly improving knowledge of the distance, age, and membership of the TWA, the apparent lack of molecules around these stars provides ever more stringent constraints on the survival timescales of gaseous circumstellar disks and, hence, the formation timescales of Jovian planets (Zuckerman et al. 1995, Nature, 373, 494). We highlight future radio and infrared observations that should provide improved estimates of (or upper limits for) the gas masses of circumstellar disks surrounding TWA stars.

Kastner, J. H.

1999-12-01

218

On the Early Time X-ray Spectra of Swift Afterglows I: Evidence for Anomalous Soft X-ray Emission  

E-print Network

We have conducted a thorough and blind search for emission lines in >70 Swift X-ray afterglows of total exposure ~10^7s. We find that most afterglows are consistent with pure power-laws plus extinction. Significant outliers to the population exist at the 5-10% level and have anomalously soft, possibly thermal spectra. Four bursts are singled out via detections of 2-5 lines: GRBs 060218, 060202, 050822, and 050714B. The most significant soft component detections in the full data set of ~2000 spectra correspond to GRB060218/SN2006aj, with significances ranging up to ~20sigma. A thermal plasma model fit to the data indicates that the flux is primarily due to L-shell transitions of Fe at ~solar abundance. We associate (>4sigma significant) line emission from the 3 other events with K-shell transitions in light metals. We favor a model where the line emission in these afterglows arises from the mildly relativistic cocoon of matter surrounding the GRB jet as it penetrates and exits the surface of the progenitor sta...

Butler, N R

2006-01-01

219

AN XMM-NEWTON SURVEY OF THE SOFT X-RAY BACKGROUND. III. THE GALACTIC HALO X-RAY EMISSION  

SciTech Connect

We present measurements of the Galactic halo's X-ray emission for 110 XMM-Newton sight lines selected to minimize contamination from solar wind charge exchange emission. We detect emission from few million degree gas on {approx}4/5 of our sight lines. The temperature is fairly uniform (median = 2.22 Multiplication-Sign 10{sup 6} K, interquartile range = 0.63 Multiplication-Sign 10{sup 6} K), while the emission measure and intrinsic 0.5-2.0 keV surface brightness vary by over an order of magnitude ({approx}(0.4-7) Multiplication-Sign 10{sup -3} cm{sup -6} pc and {approx}(0.5-7) Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively, with median detections of 1.9 Multiplication-Sign 10{sup -3} cm{sup -6} pc and 1.5 Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively). The high-latitude sky contains a patchy distribution of few million degree gas. This gas exhibits a general increase in emission measure toward the inner Galaxy in the southern Galactic hemisphere. However, there is no tendency for our observed emission measures to decrease with increasing Galactic latitude, contrary to what is expected for a disk-like halo morphology. The measured temperatures, brightnesses, and spatial distributions of the gas can be used to place constraints on models for the dominant heating sources of the halo. We provide some discussion of such heating sources, but defer comparisons between the observations and detailed models to a later paper.

Henley, David B.; Shelton, Robin L., E-mail: dbh@physast.uga.edu [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

2013-08-20

220

Infrared Line Emission from Molecular Gas Heated by X-Rays and Energetic Electrons  

NASA Technical Reports Server (NTRS)

"I propose to carry out a detailed study using infrared observations (and in some cases, optical and ultraviolet observations) of dense interstellar gas exposed to intense fluxes of X-rays and/or energetic electrons. This is undoubtedly the dominant source of line emission for clouds exposed to X-rays from active galactic nuclei, supernova shocks, or embedded X-ray sources (e.g., X-ray binaries), or to high-temperature or relativistic electrons in galaxy clusters, near powerful radio sources, or supernova remnants. Detailed physical and chemical models of such clouds will be used to analyze infrared observations of the Great Annihilator X-ray source in the Galactic Center, cD galaxies in massive cooling flows, and the nuclei of Seyfert galaxies which will be obtained with the Infrared Space Observatory (ISO), UV and optical observations of the Crab Nebula obtained with the Hubble Space Telescope, and ground-based near-infrared observations of Seyfert nuclei. Results from this work will also be of great relevance to observations obtained with the Submillimeter Wave Astronomical Satellite (SWAS). In the first year of funding of this proposal, my chief collaborators (D.J. Hollenbach and A.G.G.M. Tielens, both of NASA Ames Research Center) and I concentrated on completing our models of the physical conditions in, and the resulting line emission from, dense gas irradiated by X-rays. As noted in the original proposal, some important physical processes were not yet thoroughly incorporated into our models at the time of submission. We completed our modeling of the physical conditions and line emission for essentially the entire range of parameter space (five orders of magnitude in X-ray flux to gas density ratio) occupied by typical dense interstellar clouds in which the gas is mostly neutral and X-rays are important for the ionization, chemistry, and thermal balance.

Maloney, Philip R.

1997-01-01

221

A study of X-ray and infrared emissions from dusty nonradiative shock waves  

NASA Technical Reports Server (NTRS)

We have constructed models that predict the dynamic evolution and infrared (IR) emission of grains behind nonradiative shock waves. We present a self-consistent treatment of the effect of grain destruction and heating on the ionization structure and X-ray emission of the postshock gas. Incorporating thermal sputtering, collisional heating, and deceleration of grains in the postshock flow, we predict the IR and X-ray fluxes from the dusty plasma as a function of swept-up column density. Heavy elements such as C, O, Mg, S, Si and Fe are initially depleted from the gas phase but are gradually returned as the grains are destroyed. The injected neutral atoms require some time to 'catch up' with the ionization state of the ambient gas. The nonequilibrium ionization state and gradient in elemental abundances in the postshock flow produces characteristic X-ray signatures that can be related to the age of the shock and amount of grain destruction. We study the effects of preshock density and shock velocity on the X-ray and IR emission from the shock. We show that the effects of graindestruction on the X-ray spectra of shock waves are substantial. In particular, temperatures derived from X-ray spectra of middle-aged remnants are likely to be overestimated by approximately 15% if cosmic abundances are assumed. Due to the long timescales for grain destruction in X-ray gases over a wide range of temperatures, we suggest that future X-ray spectra studies of supernova remnants be based on depleted abundances instead of cosmic abundances. Our model predictions agree reasonably well with IRAS and Einstein IPC observations of the Cygnus Loop.

Vancura, Olaf; Raymond, John C.; Dwek, Eli; Blair, William P; Long, Knox S.; Foster, Scott

1994-01-01

222

DISCOVERY OF SOFT X-RAY EMISSION FROM IO, EUROPA, AND THE IO PLASMA TORUS Ronald F. Elsner,1  

E-print Network

, Europa, Jupiter) -- X-rays: general 1. INTRODUCTION Imaging and spectral data from the infrared through invoked to explain Jupiter's X-ray aurora and cometary X-ray emission, and ion stripping by dust grains the extreme ultraviolet provide important information on the makeup of the surfaces and atmospheres

Johnson, Robert E.

223

X-ray Emission from Middle-Aged Gamma-Ray Pulsars  

E-print Network

Electrons/positrons produced in a pulsar magnetosphere emit synchrotron radiation, which is widely believed as the origin of the non-thermal X-ray emission detected from pulsars. Particles are produced by curvature photons emitted from accelerated particles in the magnetosphere. These curvature photons are detected as pulsed $\\gamma$-ray emissions from pulsars with age $\\lesssim10^6$ yr. Using $\\gamma$-ray observations and analytical model, we impose severe constraints on the synchrotron radiation as a mechanism of the non-thermal X-ray emission. In most middle-aged pulsars ($\\sim10^5-10^6$ yr) which photon-photon pair production is less efficient in their magnetosphere, we find that the synchrotron radiation model is difficult to explain the observed non-thermal X-ray emission.

Kisaka, Shota

2015-01-01

224

XMM Observations of X-Ray Emission from Supernovae  

NASA Technical Reports Server (NTRS)

Of the six proposed targets, only one observation was performed. The observation resulted in a 28ks observation of SN 1998S. At the time of writing the proposal, our target list only contained previously unknown X-ray supernovae. Between submission of the proposal and the actual observation, a Chandra DDT observation resulted in the detection of SN 1998S. Since SN 1998S was observed with Chandra five times before the XMM-Newton observation was made, the data did not yield enough new information to warrant a separate SN 1998S publication. The key science results of that observation were presented in a review article (by Immler and Lewin); the results were also presented at two conferences.

Immler, Stefan; Lewin, Walter

2003-01-01

225

Beamed and Unbeamed X-Ray Emission in FR1 Radio Galaxies  

NASA Technical Reports Server (NTRS)

The research exploited ROSAT's sensitivity, together with its spatial and spectral resolution, to separate X-ray emission components in the sources. Prior to ROSAT, the dominant X-ray emission mechanism in radio galaxies as a class was unclear, with correlations between the X-ray and radio emission used on one hand to argue for a nuclear origin for the X-rays, and on the other hand for a thermal origin. Our observations (normally between 10 and 25 ks in length) routinely detected the target sources, and demonstrated that both resolved (thermal) and unresolved X-ray emission are typically present. Highlights of our work included two of the first detections of high-power radio galaxies at high redshift, 3C 280 and 3C 220.1. When combined with the work of two other groups, we find that of the 38 radio galaxies at z > 0.6 in the 3CRR sample, 12 were observed in ROSAT pointed observations and 9 were detected with the four most significant detections exhibiting source extent, including 3C 280 and 3C 220.1. Moreover, we discovered extended emission around five 3CRR quasars at redshift greater than about 0.4, one of which is at z > 0.6. Unification predicts that the X-ray environments of powerful radio galaxies and quasars should be similar, and our results show that powerful radio sources are finding some of the highest-redshift X-ray clusters known to date, pointing to deep gravitational potential wells early in the Universe.

Worrall, Diana M.

2000-01-01

226

Generation of x-ray images using a CNT-based cathode as an field emission electron source  

Microsoft Academic Search

Summary form only given. Conventional X-ray source reveals several problems such as short lifetime, immovability with bulky size, and relatively low resolution. For solving these problems, laser based X-ray sources have been applied but they were insufficient for X-ray source because of its low conversion efficiency. Recently, O. Zhou et al., has developed a new X-ray emission method by using

H. Y. Choi; W. S. Chang; H. S. Kim; Y. H. Park; J. U. Kim

2006-01-01

227

Investigating the reflection contribution to the X-ray emission of Ton S180  

NASA Astrophysics Data System (ADS)

There is now growing evidence that the soft X-ray excess is almost ubiquitous among unobscured active galaxies. In spite of the various interpretations that have been considered in the past few years, the nature of this foremost spectral feature is not firmly established yet. In this context, we review from a reflection perspective the three highest quality X-ray observations of the narrow-line type 1 Seyfert galaxy Tonantzintla (Ton) S180, obtained by XMM-Newton and Suzaku. The X-ray spectrum of Ton S180 shows only moderate variations over a time span of several years, suggesting that the same physical process accounts for the bulk of the broad-band X-ray emission at the different epochs, and that the properties of the X-ray source are fairly stable. We have successfully applied in our spectral analysis a dual-reflector model, consisting of two separate components: one arises from the surface of the accretion disc, is highly ionized and blurred by relativistic effects; the other is cold, quite faint and can be associated with a distant reprocessor. Due to the strength and the nearly power-law shape of its soft excess emission, Ton S180 is one of the most challenging sources to test the X-ray reflection scenario. In this work we provide a clear illustration of the great potential and spectral flexibility of blurred reflection models, while discussing some of their current limitations and possible shortcomings.

Nardini, E.; Fabian, A. C.; Walton, D. J.

2012-07-01

228

On the Lack of Thermal Emission from the Quiescent Black Hole XTE J1118+480: Evidence for the Event Horizon  

Microsoft Academic Search

A soft component of thermal emission is very commonly observed from the surfaces of quiescent, accreting neutron stars. We searched with Chandra for such a surface component of emission from the dynamical black hole candidate XTE J1118+480 (=J1118), which has a primary mass M1~8 Msolar. None was found, as one would expect if the compact X-ray source is a bona

Jeffrey E. McClintock; Ramesh Narayan; George B. Rybicki

2004-01-01

229

Discovery of Diffuse Hard X-ray Emission associated with Jupiter  

NASA Astrophysics Data System (ADS)

Our discovery of diffuse hard (1-5 keV) X-ray emission around Jupiter is reported. Recent Chandra and XMM-Newton observations revealed several types of X-rays in the vicinity of Jupiter such as auroral and disk emission from Jupiter and faint diffuse X-rays from the Io Plasma Torus (see Bhardwaj et al. 2007 for review). To investigate possible diffuse hard X-ray emission around Jupiter with the highest sensitivity, we conducted data analysis of Suzaku XIS observations of Jupiter on Feb 2006. After removing satellite and planetary orbital motions, we detected a significant diffuse X-ray emission extending to ~6 x 3 arcmin with the 1-5 keV X-ray luminosity of ~3e15 erg/s. The emitting region very well coincided with the Jupiter's radiation belts. The 1-5 keV X-ray spectrum was represented by a simple power law model with a photon index of 1.4. Such a flat continuum strongly suggests non-thermal origin. Although such an emission can be originated from multiple background point sources, its possibility is quite low. We hence examined three mechanisms, assuming that the emission is truly diffuse: bremsstrahlung by keV electrons, synchrotron emission by TeV electrons, and inverse Compton scattering of solar photons by MeV electrons. The former two can be rejected because of the X-ray spectral shape and implausible existence of TeV electrons around Jupiter, respectively. The last possibility was found to be possible because tens MeV electrons, which have been confirmed in inner radiation belts (Bolton et al. 2002), can kick solar photons to the keV energy range and provide a simple power-law continuum. We estimated an average electron density from the X-ray luminosity assuming the oblate spheroid shaped emitting region with 8 x 8 x 4 Jovian radii. The necessary density was 0.02 1/cm3 for 50 MeV electrons. Hence, our results may suggest a new particle acceleration phenomenon around Jupiter.

Ezoe, Y.; Miyoshi, Y.; Ishikawa, K.; Ohashi, T.; Terada, N.; Uchiyama, Y.; Negoro, H.

2009-12-01

230

From Radio to X-ray: The Quiescent Atmosphere of the dMe Flare Star EV Lacertae  

E-print Network

We report on multi-wavelength observations spanning radio to X-ray wavelengths of the M dwarf flare star, EV Lacertae, probing the characteristics of the outer atmospheric plasma from the upper chromosphere to the corona. We detect the star at a wavelength of 2 cm (15 GHz) for the first time. UV and FUV line profiles show evidence of nonthermal broadening, and the velocity width appear to peak at lower temperatures than in the Sun; this trend is confirmed in another active M dwarf flare star. Electron density measurements indicate nearly constant electron pressures between $\\log T=$5.2 and 6.4. At higher coronal temperatures, there is a sharp increase of two orders of magnitude in density (n$_{e}\\sim10^{13}$ cm$^{-3}$ at $\\log T=$6.9). X-ray, EUV, FUV and NUV spectra constrain the DEM from the upper chromosphere through the corona. The coronal pressures are inconsistent with the assumption of hydrostatic equilibrium, either through EM modeling or application of scaling laws, and imply large conductive loss ra...

Osten, R A; Brown, A; Harper, G M; Hawley, S L; Johns-Krull, C M

2006-01-01

231

X-ray microanalysis of monovalent electrolyte contents of quiescent, proliferating as well as tumor rat hepatocytes.  

PubMed

Energy-dispersive X-ray microanalysis was carried out on normal and regenerating liver as well as on 3924 A hepatoma cells. Specimens were quickly removed from the sacrificed animals, frozen in liquid isopentane, fractured still in the frozen state and freeze-dried under vacuum. The dried samples were examined in secondary electron image mode, and the X-ray spectra were recorded by means of an EDAX 707A system. Sodium and chlorine contents were higher both in nuclei and cytoplasms of regenerating and tumor hepatocytes than in normal liver. Moreover, hepatoma cells showed higher sodium and chlorine contents than did normal proliferating hepatocytes. Potassium contents did not show any differences among the experimental models. The increased sodium content and the resulting increased Na:K ratios of proliferating normal and tumor cells were not due to a generalized increase of these parameters in all the cells, but to the presence of new cell populations with high Na content and high Na:K ratios. Findings of present work are consistent with the hypothesis that high sodium content is associated with mitogenesis. Moreover, the much higher concentration of sodium in tumor cells as compared with normal proliferating hepatocytes supports the hypothesis that the concentration of this ion is related to oncogenesis of hepatocytes. PMID:6652871

Pieri, C; Giuli, C; Bertoni-Freddari, C

1983-12-01

232

Modeling Diffuse X-ray Emission around the Galactic Center from Colliding Stellar Winds  

NASA Astrophysics Data System (ADS)

The Galactic center is a hotbed of astrophysical phenomena. The ~30 evolved massive stars orbiting the SMBH on scales <10" inject a large fraction of the matter that accretes onto the SMBH, and potentially creates large swaths of hot, X-ray emitting material around Sgr A* from their wind-wind collisions. Using the Gadget-2 SPH simulations of these evolved stars ejecting their winds over the last 1100 years from Cuadra et al. 2008, we solve the formal solution to the equation of radiative transfer for a grid of rays through the 6"x6" simulation volume to calculate the thermal X-ray emission from the diffuse hot gas. We then fold each of these energy-dependent pixel maps through the Chandra ACIS-S response function to directly compare with the recent 3Ms X-ray Visionary Program observations of the Galactic center (Wang et al. 2013). The model X-ray flux, in absolute units, agrees well with the observations just outside the SMBH (whose emission is not included in this modeling), indicating that the shocked wind material from the evolved massive stars is indeed the source of diffuse X-ray emission at the Galactic center. The emission of the IRS13 cluster, though, is overestimated by two orders of magnitude, indicating a potential revision in the cluster stellar parameters. We will conclude by discussing future work, such as implementing the 'pressure-entropy' formulation of SPH for this calculation and including O stars and closely orbiting binaries.

Russell, Christopher Michael Post; Cuadra, Jorge; Wang, Q. Daniel; Owocki, Stanley P.

2015-01-01

233

X-RAY EMISSION FROM SN 2004dj: A TALE OF TWO SHOCKS  

SciTech Connect

Type IIP (Plateau) supernovae are the most commonly observed variety of core-collapse events. They have been detected in a wide range of wavelengths from radio, through optical to X-rays. The standard picture of a Type IIP supernova has the blastwave interacting with the progenitor's circumstellar matter to produce a hot region bounded by a forward and a reverse shock. This region is thought to be responsible for most of the X-ray and radio emission from these objects. Yet the origin of X-rays from these supernovae is not well understood quantitatively. The relative contributions of particle acceleration and magnetic field amplification in generating the X-ray and radio emission need to be determined. In this work, we analyze archival Chandra observations of SN 2004dj, one of the nearest supernovae since SN 1987A, along with published radio and optical information. We determine the pre-explosion mass-loss rate, blastwave velocity, electron acceleration, and magnetic field amplification efficiencies. We find that a greater fraction of the thermal energy goes into accelerating electrons than into amplifying magnetic fields. We conclude that the X-ray emission arises out of a combination of inverse Compton scattering by non-thermal electrons accelerated in the forward shock and thermal emission from supernova ejecta heated by the reverse shock.

Chakraborti, Sayan; Yadav, Naveen; Ray, Alak [Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Colaba, Mumbai 400 005 (India); Smith, Randall [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Chandra, Poonam [Department of Physics, Royal Military College of Canada, Kingston, ON K7K 7B4 (Canada); Pooley, David, E-mail: schakraborti@fas.harvard.edu [Department of Physics, Sam Houston State University, Huntsville, TX (United States)

2012-12-20

234

Constraints on Off-Axis X-Ray Emission from Beamed GRBs  

E-print Network

We calculate the prompt x-ray emission as a function of viewing angle for beamed Gamma-Ray Burst (GRB) sources. Prompt x-rays are inevitable due to the less highly blueshifted photons emitted at angles greater than 1/gamma relative to the beam symmetry axis, where gamma is the expansion Lorentz factor. The observed flux depends on the combinations (gamma Delta theta) and (gamma theta_v), where (Delta theta) is the beaming angle and theta_v is the viewing angle. We use the observed source counts of gamma-ray-selected GRBs to predict the minimum detection rate of prompt x-ray bursts as a function of limiting sensitivity. We compare our predictions with the results from the Ariel V catalog of fast x-ray transients, and find that Ariel's sensitivity is not great enough to place significant constraints on gamma and (Delta theta). We estimate that a detector with fluence limit ~10^{-7} erg/cm^2 in the 2-10 keV channel will be necessary to distinguish between geometries. Because the x-ray emission is simultaneous with the GRB emission, our predicted constraints do not involve any model assumptions about the emission physics but simply follow from special-relativistic considerations.

Eric Woods; Abraham Loeb

1999-03-24

235

Soft X-ray emission in kink-unstable coronal loops  

NASA Astrophysics Data System (ADS)

Context. Solar flares are associated with intense soft X-ray emission generated by the hot flaring plasma in coronal magnetic loops. Kink-unstable twisted flux-ropes provide a source of magnetic energy that can be released impulsively and may account for the heating of the plasma in flares. Aims: We investigate the temporal, spectral, and spatial evolution of the properties of the thermal continuum X-ray emission produced in such kink-unstable magnetic flux-ropes and discuss the results of the simulations with respect to solar flare observations. Methods: We computed the temporal evolution of the thermal X-ray emission in kink-unstable coronal loops based on a series of magnetohydrodynamical numerical simulations. The numerical setup consisted of a highly twisted loop embedded in a region of uniform and untwisted background coronal magnetic field. We let the kink instability develop, computed the evolution of the plasma properties in the loop (density, temperature) without accounting for mass exchange with the chromosphere. We then deduced the X-ray emission properties of the plasma during the whole flaring episode. Results: During the initial (linear) phase of the instability, plasma heating is mostly adiabatic (as a result of compression). Ohmic diffusion takes over as the instability saturates, leading to strong and impulsive heating (up to more than 20 MK), to a quick enhancement of X-ray emission, and to the hardening of the thermal X-ray spectrum. The temperature distribution of the plasma becomes broad, with the emission measure depending strongly on temperature. Significant emission measures arise for plasma at temperatures higher than 9 MK. The magnetic flux-rope then relaxes progressively towards a lower energy state as it reconnects with the background flux. The loop plasma suffers smaller sporadic heating events, but cools down globally by thermal conduction. The total thermal X-ray emission slowly fades away during this phase, and the high-temperature component of the emission measure distribution converges to the power-law distribution EM ? T-4.2. The twist deduced directly from the X-ray emission patterns is considerably lower than the highest magnetic twist in the simulated flux-ropes. Movies associated to Figs. 4 and 5 are available in electronic form at http://www.aanda.org

Pinto, R. F.; Vilmer, N.; Brun, A. S.

2015-04-01

236

X-ray Spontaneous Emission Control By 1D-PBG Structure  

SciTech Connect

The control of the decay rate of an excited atom through the photonic mode density (PMD) was pointed out at radiofrequency by Purcell in 1946. Nowadays the development of sophisticated photonic band structures makes it possible to monitor the PMD at shorter radiation wavelengths and then to manipulate the spontaneous emission of atoms in the hard region of the electromagnetic spectrum especially in the visible domain. In this communication we study the possibility of monitoring the x-ray emission by means of one-dimensional photonic band structures such as periodic multilayer systems. Enhancement or inhibition of soft x-ray emissions seems now to be feasible by means of the state-of-the art in x-ray optics.

Andre, Jean-Michel; Jonnard, Philippe [Laboratoire de Chimie Physique-Matiere et Rayonnement, CNRS, Universite Paris 6, UMR 7614, 11 rue Pierre et Marie Curie, F-75231 Paris CEDEX 05 (France)

2010-04-06

237

X-ray emission from the PSR B1259--63 system near apastron  

E-print Network

The PSR B1259--63 system contains a 47 ms radio pulsar in a highly eccentric binary with a Be-star companion. Strongly time variable X-ray emission was reported from this system as the pulsar was near apastron in 1992-early 1993. The variability was primarily deduced from an apparent non-detection of the \\psr system during a first pre-apastron \\ros observation in February~1992. We have re-analyzed the \\ros observations of the \\psr system. Contrary to the results of a previous analysis, we find that the \\psr system was detected by \\ros during the first off-axis February~1992 observation. The intensity of the soft X-ray emission of the \\psr system before and after the 1992 apastron appears to vary at most by a factor $\\sim 2$. Our results sensibly constrain theoretical models of X-ray emission from the \\psr system.

J. Greiner; M. Tavani; T. Belloni

1995-01-26

238

U. radio emission from quiescent filaments  

NASA Technical Reports Server (NTRS)

Full-disk Very Large Array (VLA) synthesis maps of the quiet Sun indicate that filaments can be seen in emission at 91.6 cm wavelength; they are detected in absorption at shorter microwave wavelengths. The 91.6 cm emission has a brightness temperature of T sub B = 3 x 10(exp 5) K. It is hotter, wider and longer than the underlying filament detected at H alpha wavelengths, but the similarity between the shape, position, elongation and orientation of the radio and optical features suggests their close association. The 91.6 cm emission is attributed to the thermal-bremsstrahlung of a hot transition sheath that envelopes the H alpha filament and acts as an interface between the cool, dense H alpha filament and the hotter, rarefied corona. The transition sheath is seen in emission because of the lower optical depth of the corona at 90 cm wavelength, and the width of this sheet is 10(exp 9) cm. A power law gradient in pressure provides a better match to the observations than a constant pressure model; definitive tests of theoretical models await simultaneous multi-wavelength studies of filaments at different observing angles. When the thermal bremsstrahlung is optically thin, the magnetic field strength in the transition sheath can be inferred from the observed circular polarization. Variable physical parameters of the sheath, such as width, electron density, and electron temperature, can explain controversial reports of the detection of, or the failure to detect, the meter-wavelength counterpart of H alpha filaments.

Lang, Kenneth R.

1989-01-01

239

HARD X-RAY AND ULTRAVIOLET EMISSION DURING THE 2011 JUNE 7 SOLAR FLARE  

SciTech Connect

The relationship between X-ray and UV emission during flares, particularly in the context of quasi-periodic pulsations, remains unclear. To address this, we study the impulsive X-ray and UV emission during an eruptive flare on 2011 June 7 utilizing X-ray imaging from RHESSI and UV 1700 Å imaging from SDO/AIA. This event is associated with quasi-periodic pulsations in X-ray and possibly UV emission, as well as substantial parallel and perpendicular motion in the hard X-ray footpoints. The motion of the footpoints parallel to the flare ribbons is unusual; it reverses direction on at least two occasions. However, there is no associated short timescale motion of the UV bright regions. Over the same time interval, the footpoints also gradually move apart at v ? 12 km s{sup –1}, consistent with the gradual outward expansion of the UV ribbons and the standard flare model. Additionally, we find that the locations of the brightest X-ray and UV regions are different, particularly during the early portion of the flare impulsive phase, despite their integrated emission being strongly correlated in time. Correlation analysis of measured flare properties, such as the footpoint separation, flare shear, photospheric magnetic field, and coronal reconnection rate, reveals that—in the impulsive phase—the 25-50 keV hard X-ray flux is only weakly correlated with these properties, in contrast with previous studies. We characterize this event in terms of long-term behavior, where the X-ray non-thermal, thermal, and UV emission sources appear temporally and spatially consistent, and short-term behavior, where the emission sources are inconsistent and quasi-periodic pulsations are a dominant feature requiring explanation. We suggest that the short timescale behavior of hard X-ray footpoints and the nature of the observed quasi-periodic pulsations are determined by fundamental, as yet unobserved properties of the reconnection region and particle acceleration sites. This presents a challenge for current three-dimensional flare reconnection models.

Inglis, A. R.; Gilbert, H. R. [Solar Physics Laboratory, Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2013-11-01

240

Inverse Compton X-ray emission from the superluminal quasar 3C 345  

NASA Technical Reports Server (NTRS)

In quasars with strong radio cores, the inverse-Compton process is believed to be the dominant source X-ray emission. For objects with parsec-scale radio jets, simple models have predicted that components in the jet emerging from the quasar nucleus generate the observed X-ray emission. We have tested this hypothesis in detail for the quasar 3C 345 using a ROSAT X-ray observation in 1990 July, together with quasi-simultaneous very long base interferometry (VLBI) imaging of the parsec-scale jet at five frequencies. The ROSAT spectrum is well fitted by a power law with index alpha = -0.96 +/- -0.13, consistent with models in which the X-ray emission results from inverse-Compton scattering of radio radiation from high-energy electrons in compact components. We show that the radio properties of brightest `knot' in the jet (`C5') can be fitted with a homogeneous sphere model whose parameters require bulk relativistic motion of the emitting material; otherwise the predicted model whose parameters require bulk relativistic motion of the emitting material; otherwise the predicted inverse-Compton X-ray emission exceeds the observed flux. If C5 is the origin of the X-ray emission, then it has a Doppler factor delta = 7.5((sup +3 sub -2)). If the nucleus or other components contribute to the X-ray emission, then this becomes a firm lower limit to delta. The inhomogeneous jet model of Koenigl is a good fit both to the barely resolved (less than 1 pc) flat-spectrum nucleus in the radio, and also to the ROSAT X-ray spectrum. The synchrotron and inverse-Compton emitting fluid moves down a narrow cone (opening angle 2 phi approximately 5 deg) nucleus relativistically, with delta approximately 4.6. Doppler factors for the nucleus and C5, derived from our ROSAT observation, provide evidence for bulk relativistic motion in the jet. By combining these constraints with well-known superluminal motion of jet components, we can deduce geometry. For epoch 1990.5 we infer the Lorentz factor gamma = 7.5 ((sup +1.0 sub -1.5)) and angle to the line of sight theta = 8((sup +2 deg sub -3 deg)) for H(sub 0) = 100 km/s/Mpc. These values are the most reliable yet derived using this method, because of the near-simultaneity of our X-ray and VLBI observations and the quality of the multifrequency of VLBI images and component radio spectra.

Unwin, S. C.; Wehrle, A. E.; Urry, C. M.; Gilmore, D. M.; Barton, E. J.; Kjerulf, B. C.; Zensus, J. A.; Rabaca, C. R.

1994-01-01

241

Non-Detection of X-Ray Emission From Sterile Neutrinos in Stacked Galaxy Spectra  

E-print Network

We conduct a comprehensive search for X-ray emission lines from sterile neutrino dark matter, motivated by recent claims of unidentified emission lines in the stacked X-ray spectra of galaxy clusters and the centers of the Milky Way and M31. Since the claimed emission lines lie around 3.5 keV, we focus on galaxies and galaxy groups (masking the central regions), since these objects emit very little radiation above ~2 keV and offer a clean background against which to detect emission lines. We develop a formalism for maximizing the signal-to-noise of sterile neutrino emission lines by weighing each X-ray event according to the expected dark matter profile. In total, we examine 81 and 89 galaxies with Chandra and XMM-Newton respectively, totaling 15.0 and 14.6 Ms of integration time. We find no significant evidence of any emission lines, placing strong constraints on the mixing angle of sterile neutrinos with masses between 4.8-12.4 keV. In particular, if the 3.57 keV feature from Bulbul et al. (2014) were due to 7.1 keV sterile neutrino emission, we would have detected it at 4.4 sigma and 11.8 sigma in our two samples. Unlike previous constraints, our measurements do not depend on the model of the X-ray background or on the assumed logarithmic slope of the center of the dark matter profile.

Michael E. Anderson; Eugene Churazov; Joel N. Bregman

2014-08-21

242

X-ray emission from relativistically moving electron density cusps  

SciTech Connect

We report on novel methods to generate ultra-short, coherent, X-rays using a laserplasma interaction. Nonlinear interaction of intense laser pulses with plasma creates stable, specific structures such as electron cusps. For example, wake waves excited in an underdense plasma by an intense, short-pulse laser become dense and propagate along with the laser pulse. This is called a relativistic flying mirror. The flying mirror can reflect a counter-propagating laser pulse and directly convert it into high-frequency radiation, with a frequency multiplication factor of {approx} 4{gamma}{sup 2} and pulse shortening with the same factor. After the proof-of-principle experiments, we observed that the photon number generated in the flying mirror is close to the theoretical estimate. We present the details of the experiment in which a 9 TW laser pulse focused into a He gas jet generated the Flying Mirror, which partly reflected a 1 TW pulse, giving up to {approx} 10{sup 10} photons, 60 nJ (1.4 Multiplication-Sign 10{sup 12} photons/sr) in the XUV spectral region (12.8-22 nm).

Kando, M.; Pirozhkov, A. S.; Nakamura, T.; Hayashi, Y.; Kotaki, H.; Kawase, K.; Esirkepov, T. Zh.; Fukuda, Y.; Kiriyama, H.; Okada, H.; Daito, I.; Kameshima, T.; Mori, M.; Koga, J. K.; Daido, H.; Faenov, A. Ya.; Pikuz, T.; Ma, J.; Chen, L.-M.; Ragozin, E. N. [Japan Atomic Energy Agency (Japan); Osaka University (Japan); Joint Institute for High Temperature of the Russian Academy of Science, Moscow (Russian Federation); Institute of Physics, Chinese Academy of Sciences, Beijing (China); P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninsky prospekt 53, 119991 Moscow (Russian Federation); Japan Atomic Energy Agency and Graduate School for the Creation of New Photonics Industries (Japan); Ludwig-Maximilians-University (Germany); and others

2012-07-11

243

X-RAY EMISSION AND ABSORPTION FEATURES DURING AN ENERGETIC THERMONUCLEAR X-RAY BURST FROM IGR J17062-6143  

SciTech Connect

Type-I X-ray bursts are thermonuclear explosions occurring in the surface layers of accreting neutron stars. These events are powerful probes of the physics of neutron stars and their surrounding accretion flow. We analyze a very energetic type-I X-ray burst from the neutron star low-mass X-ray binary IGR J17062-6143 that was detected with Swift on 2012 June 25. The light curve of the {approx_equal}18 minute long X-ray burst tail shows an episode of {approx_equal}10 minutes during which the intensity is strongly fluctuating by a factor of {approx_equal}3 above and below the underlying decay trend on a timescale of seconds. The X-ray spectrum reveals a highly significant emission line around {approx_equal}1 keV, which can be interpreted as an Fe-L shell line caused by the irradiation of cold gas. We also detect significant absorption lines and edges in the Fe-K band, which are strongly suggestive of the presence of hot, highly ionized gas along the line of sight. None of these features are present in the persistent X-ray spectrum of the source. The timescale of the strong intensity variations, the velocity width of the Fe-L emission line (assuming Keplerian motion), and photoionization modeling of the Fe-K absorption features each independently point to gas at a radius of {approx_equal} 10{sup 3} km as the source of these features. The unusual X-ray light curve and spectral properties could have plausibly been caused by a disruption of the accretion disk due to the super-Eddington fluxes reached during the X-ray burst.

Degenaar, N.; Miller, J. M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Wijnands, R.; Altamirano, D. [Astronomical Institute ''Anton Pannekoek'', University of Amsterdam, Postbus 94249, 1090 GE Amsterdam (Netherlands); Fabian, A. C., E-mail: degenaar@umich.edu [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom)

2013-04-20

244

Testing the ionized disc reprocessing model for the soft X- ray emission of quasars  

NASA Astrophysics Data System (ADS)

One of the current explanations for the soft X-ray emission of active galactic nuclei (AGN) is reprocessing of the hard X-rays by partially ionized, optically thick matter. This idea is very appealing because it would explain the shape of the AGN soft X-ray spectrum in terms of atomic physics. While at present the reflection model correctly describes the soft X-ray spectra of a few low-luminosity Seyfert galaxies, it is not clear whether or not it can be applied to higher luminosity quasars. To investigate this issue quantitatively, we have fitted the high signal-to-noise ratio Position Sensitive Proportional Counter (PSPC) spectra of 11 AGN of different luminosities with a model consisting of a direct hard X-ray component, reflection from the ionized surface of an accretion disc and the direct thermal emission of the disc. We find that the AGN with an acceptable fit are a minority, and all have a low optical (and bolometric) luminosity, flat PSPC energy index alpha_PSPC and the flattest alpha_OX of the sample, while those with the worst fit all have high optical (and bolometric) luminosity, steep alpha_PSPC and the steepest alpha_OX of the sample. We conclude that either the reprocessing model is not correct and the form of the soft X-ray spectrum of AGN cannot be simply explained in terms of characteristic atomic features (i.e. highly ionized oxygen K-edges), or the origin of the soft X-ray emission of AGN is not `universal'.

Fiore, Fabrizio; Matt, Giorgio; Nicastro, Fabrizio

1997-01-01

245

X-Ray Emission from the Wolf-Rayet Bubble S 308  

NASA Technical Reports Server (NTRS)

The Wolf-Rayet (WR) bubble S 308 around the WR star HD 50896 is one of the only two WR bubbles known to possess X-ray emission. We present XMM-Newton observations of three fields of this WR bubble that, in conjunction with an existing observation of its Northwest quadrant (Chu et al. 2003), map most of the nebula. The X-ray emission from S 308 displays a limb-brightened morphology, with a 22' in size central cavity and a shell thickness of approx. 8'. This X-ray shell is confined by the optical shell of ionized material. The spectrum is dominated by the He-like triplets of N VI at approx.0.43 keV and O VII at approx.0.5 keV, and declines towards high energies, with a faint tail up to 1 keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T1 approx.1.1 x 10(exp 6) K, T2 approx.13 x 10(exp 6) K), with a total X-ray luminosity approx.3 x 10(exp 33) erg/s at the assumed distance of 1.8 kpc. Qualitative comparison of the X-ray morphology of S 308 with the results of numerical simulations of wind-blown WR bubbles suggests a progenitor mass of 40 Stellar mass and an age in the WR phase approx.20,000 yrs. The X-ray luminosity predicted by simulatioms including the effects of heat conduction is in agreement with the observations, however, the simulated X-ray spectrum indicates generally hotter gas than is derived from the observations. We suggest that non-equilibrium ionization (NEI) may provide an explanation for this discrepancy.

Toala, J. A.; Guerrero, M. A.; Chu, Y.-H.; Gruendl, R. A.; Arthur, S. J.; Smith, R. C.; Snowden, S. L.

2012-01-01

246

New Chandra observations of the jet in 3C273. 1. Softer X-ray than radio spectra and the X-ray emission mechanism  

SciTech Connect

The jet in 3C273 is a high-power quasar jet with radio, optical and X-ray emission whose size and brightness allow a detailed study of the emission processes acting in it. We present deep Chandra observations of this jet and analyze the spectral properties of the jet emission from radio through X-rays. We find that the X-ray spectra are significantly softer than the radio spectra in all regions of the bright part of the jet except for the first bright ''knot A'', ruling out a model in which the X-ray emission from the entire jet arises from beamed inverse-Compton scattering of cosmic microwave background photons in a single-zone jet flow. Within two-zone jet models, we find that a synchrotron origin for the jet's X-rays requires fewer additional assumptions than an inverse-Compton model, especially if velocity shear leads to efficient particle acceleration in jet flows.

Jester, Sebastian; /Fermilab; Harris, D.E.; /Smithsonian Astrophys. Observ.; Marshall, H.L.; /MIT, MKI; Meisenheimer, K.; /Heidelberg, Max Planck Inst. Astron.

2006-05-01

247

Search for X-ray emission from a sample of luminous O-type subdwarfs  

NASA Astrophysics Data System (ADS)

While many hot subdwarf stars have been deeply investigated in the optical and UV domain, only two sdO stars, HD49798 and BD+37 442, have been detected at X-rays. In both cases the observed emission shows a fast periodic modulation, indicating the presence of a WD or NS companion, likely powered by accretion. We propose the first systematic search for X-ray emission from a complete flux-limited sample of sdO stars, in order to constrain the presence of compact companions.

La Palombara, Nicola

2012-09-01

248

Formation and X-ray emission from hot bubbles in planetary nebulae  

NASA Astrophysics Data System (ADS)

We present 2D radiative-hydrodynamic simulations of the X-ray emission from hot bubbles in planetary nebulae (PNe). We particularly explore the effects of hydrodynamical mixing at the interface between the hot bubble and the cold nebular envelope, and its interplay with thermal conduction in the production of soft X-ray emission. The additional physical processes incorporated in our simulations add fine details to the inner nebular envelope in contact with the hot bubble, having implications on the PN optical morphology which are dependent on the initial stellar mass of the model.

Toala, J.; Arthur, S. J.

2014-04-01

249

Hard X-Ray Emission and the Ionizing Source in LINERs  

NASA Technical Reports Server (NTRS)

We report X-ray fluxes in the 2-10 keV band from LINERs (low-ionization nuclear emission-line regions) and low-luminosity Seyfert galaxies obtained with the ASCA satellite. Observed X-ray luminosities are in the range between 4 x 10(exp 39) and 5 x 10(exp 41) ergs/s, which are significantly smaller than that of the "classical" low-luminosity Seyfert 1 galaxy NGC 4051. We found that X-ray luminosities in 2-10 keV of LINERs with broad H.alpha emission in their optical spectra (LINER 1s) are proportional to their Ha luminosities. This correlation strongly supports the hypothesis that the dominant ionizing source in LINER 1s is photoionization by hard photons from low-luminosity AGNs. On the other hand, the X-ray luminosities of most LINERs without broad H.alpha emission (LINER 2s) in our sample are lower than LINER 1s at a given H.alpha luminosity. The observed X-ray luminosities in these objects are insufficient to power their H.alpha luminosities, suggesting that their primary ionizing source is other than an AGN, or that an AGN, if present, is obscured even at energies above 2 keV.

Terashima, Yuichi; Ho, Luis C.; Ptak, Andrew F.

2000-01-01

250

Field-emission-type x-ray source using carbon-nanofibers  

SciTech Connect

An x-ray irradiation system of field-emission type has been constructed using carbon-nanofibers (CNFs) grown on a palladium wire that is 50 {mu}m in diameter. The electron current emitted from the CNFs was approximately 1 mA and was stable within 10% for a long time t>5000 h. The electrons passing through a slit in the gate electrode were accelerated to the desired energy, and were made to impinge on the metal target (Ti, Cu, Mo, and W) for generating x rays. The x-rays transmitted through Be-window were characterized using energy analyzers and a dosimeter. At an acceleration voltage of V{sub a}=50 kV, the energy spectra of the x-rays were exclusively composed of characteristic signals except for the Mo-target, and the dose rates of x-rays were D=2.5-14 Gy/min, depending on the target metals. This system also provides sharp x-ray images of both biological and nonbiological materials.

Kita, S.; Watanabe, Y.; Ogawa, A.; Ogura, K.; Sakai, Y.; Matsumoto, Y.; Isokane, Y.; Okuyama, F. [Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Nakazato, T.; Otsuka, T. [Department of Musculoskeletal Medicine, Graduate School of Medical Sciences, Nagoya City University, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601 (Japan)

2008-03-15

251

On the Origin of X-Ray Emission from Late B-Type Stars  

NASA Astrophysics Data System (ADS)

No mechanism is known that produces X-rays in late B-type stars: they are not massive enough to drive strong stellar winds nor do they possess convective zones that could sustain a magnetic dynamo. Nevertheless their detection has been reported from virtually all X-ray satellites and has remained a mystery to date. Our adaptive optics observations with ADONIS at the ESO 3.6m telescope have revealed faint infrared objects near ~20 X-ray emitting B-type stars that could be late-type companions. Most of the B-type stars in our sample are young. Some are confirmed members of the Sco-Cen OB association (t ~ 10 Myrs). At this age late-type stars are still on the pre-main sequence (PMS) and are expected to be strong X-ray emitters. A subgroup of the IR sources (at separation of 1-6 arcsec) is resolvable with Chandra but none of the previous X-ray instruments. We observed these objects using Chandra/ACIS to check whether the new infrared sources could be responsible for the X-ray emission previously ascribed to the B-type star. Furthermore we used their JHK magnitudes in combination with PMS models to study their evolutionary state and examine whether they are physically connected to the B-type stars

Stelzer, Beate; Huelamo, Nuria; Hubrig, Swetlana; Zinnecker, Hans

252

An X-Ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies  

NASA Technical Reports Server (NTRS)

Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert. galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, and Ryde for the X-ray binary Cygnus X-1 and later applied to Seyfert galaxies by Zdziarski, Lubifiski, and Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum, and as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those which have been observed from these objects can, in principle, be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate which satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the heretofore poorly measured hard X-ray continuum above approximately 50 keV in type 1 Seyfert galaxies. Conversely, forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft gamma-ray telescopes, such as those aboard the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.

Chiang, James; White, Nicholas E. (Technical Monitor)

2002-01-01

253

X-ray Emission From Eta Carinae near Periastron in 2009 I: A Two State Solution  

NASA Technical Reports Server (NTRS)

X-ray emission from the supermassive binary system Eta Carinae declines sharply around periastron. This X-ray minimum has two distinct phases the lowest flux phase in the first 3 weeks and a brighter phase thereafter. In 2009, the Chandra X-ray Observatory monitored the first phase five times and found the lowest observed flux at 1.91012 ergs/sq cm/s (38 keV). The spectral shape changed such that the hard band above 4 keV dropped quickly at the beginning and the soft band flux gradually decreased to its lowest observed value in 2 weeks. The hard band spectrum had begun to recover by that time. This spectral variation suggests that the shocked gas producing the hottest X-ray gas near the apex of the wind-wind collision (WWC) is blocked behind the dense inner wind of the primary star, which later occults slightly cooler gas down-stream. Shocked gas previously produced by the system at earlier orbital phases is suggested to produce the faint residual X-ray emission seen when the emission near the apex is completely blocked by the primary wind. The brighter phase is probably caused by the re-appearance of the WWC plasma, whose emissivity significantly declined during the occultation. We interpret this to mean that the X-ray minimum is produced by a hybrid mechanism of an occultation and a decline in emissivity of the WWC shock. We constrain timings of superior conjunction and periastron based on these results.

Hamaguchi, Kenji; Corcoran, Michael F.; Russell, Christopher; Pollock, Andrew M. T.; Gull, Theodore R.; Teodoro, Mairan; Madura, Thomas I.; Damineli, Augusto; Pittard, Julian M.

2014-01-01

254

A search for diffuse X-ray emission from GeV-detected Galactic globular clusters  

NASA Astrophysics Data System (ADS)

Context. Recently, diffuse and extended sources in TeV ?-rays as well as in X-rays have been detected in the direction of the Galactic globular cluster (GC) Terzan 5. Remarkably, this is among the brightest GCs detected in the GeV regime. The nature of either the TeV or the diffuse X-ray signal from Terzan 5 is not yet settled. These emissions most likely indicate the presence of several non-thermal radiation processes in addition to those that give rise to the GeV signal. Aims: The aim of this work is to search for diffuse X-ray emission from all GeV-detected GCs where appropriate X-ray observations are available, and to compare the obtained results with the signal detected from Terzan 5. This study will help to determine whether Terzan 5 stands out among other GC or whether a whole population of globular clusters feature similar properties. Methods: After assessing all archival X-ray observations of GeV detected GCs, we analyzed the data of six Chandra observations pointed toward M 62, NGC 6388, NGC 6541, M 28, M 80, and NGC 6139. For each GC we characterized the diffuse X-ray emission using the same analysis techniques as for Terzan 5. To study the emission on the same relative scales we used the half-mass radius as a scale parameter to determine the extent of the potential emission region. Results: None of the six GCs show significant diffuse X-ray emission above the particle and diffuse Galactic X-ray background components. The derived upper limits allow to assess the validity of different models that were discussed in the interpretation of the multi-wavelength data of Terzan 5. A scenario based on synchrotron emission from relativistic leptons provided by the millisecond pulsar population cannot be securely rejected if a comparable magnetic field strength as in Terzan 5 is assumed for every GC. However, such a scenario seems to be unlikely for NGC 6388, and M 62. An inverse-Compton scenario relying on the presence of a putative GRB remnant with the same properties as proposed for Terzan 5 can be ruled out for all six GCs. Finally, the assumption that each GC hosts a source with the same luminosity as in Terzan 5 is ruled out for all GCs but NGC 6139.

Eger, P.; Domainko, W.

2012-04-01

255

Feedback from winds and supernovae in massive stellar clusters - II. X-ray emission  

NASA Astrophysics Data System (ADS)

The X-ray emission from a simulated massive stellar cluster is investigated. The emission is calculated from a 3D hydrodynamical model which incorporates the mechanical feedback from the stellar winds of three O stars embedded in a giant molecular cloud (GMC) clump containing 3240 M? of molecular material within a 4 pc radius. A simple prescription for the evolution of the stars is used, with the first supernova (SN) explosion at t = 4.4 Myr. We find that the presence of the GMC clump causes short-lived attenuation effects on the X-ray emission of the cluster. However, once most of the material has been ablated away by the winds, the remaining dense clumps do not have a noticeable effect on the attenuation compared with the assumed interstellar medium (ISM) column. We determine the evolution of the cluster X-ray luminosity, LX, and spectra, and generate synthetic images. The intrinsic X-ray luminosity drops from nearly 1034 erg s-1 while the winds are `bottled up', to a near-constant value of 1.7 × 1032 erg s-1 between t = 1 and 4 Myr. LX reduces slightly during each star's red supergiant stage due to the depressurization of the hot gas. However, LX increases to ?1034 erg s-1 during each star's Wolf-Rayet stage. The X-ray luminosity is enhanced by two to three orders of magnitude to ˜1037 erg s-1 for at least 4600 yr after each SN explosion, at which time the blast wave leaves the grid and the X-ray luminosity drops. The X-ray luminosity of our simulation is generally considerably fainter than predicted from spherically symmetric bubble models, due to the leakage of hot gas material through gaps in the outer shell. This process reduces the pressure within our simulation and thus the X-ray emission. However, the X-ray luminosities and temperatures which we obtain are comparable to similarly powerful massive young clusters.

Rogers, H.; Pittard, J. M.

2014-06-01

256

Solar Control on Jupiter's Equatorial X-ray Emissions: 26-29 November 2003 XMM-Newton Observation  

E-print Network

During November 26-29, 2003 XMM-Newton observed soft (0.2-2 keV) X-ray emission from Jupiter for 69 hours. The low-latitude X-ray disk emission of Jupiter is observed to be almost uniform in intensity with brightness that is consistent with a solar-photon driven process. The simultaneous lightcurves of Jovian equatorial X-rays and solar X-rays (measured by the TIMED/SEE and GOES satellites) show similar day-to-day variability. A large solar X-ray flare occurring on the Jupiter-facing side of the Sun is found to have a corresponding feature in the Jovian X-rays. These results support the hypothesis that X-ray emission from Jovian low-latitudes are solar X-rays scattered from the planet's upper atmosphere, and suggest that the Sun directly controls the non-auroral X-rays from Jupiter's disk. Our study also suggests that Jovian equatorial X-rays can be used to monitor the solar X-ray flare activity on the hemisphere of the Sun that is invisible to space weather satellites.

Anil Bhardwaj; Graziella Branduardi-Raymont; Ronald F. Elsner; G. Randall Gladstone; Gavin Ramsay; Pedro Rodriguez; Roberto Soria; J. Hunter Waite Jr.; Thomas E. Cravens

2005-04-29

257

Water maser emission from X-ray-heated circumnuclear gas in active galaxies  

NASA Technical Reports Server (NTRS)

We have modeled the physical and chemical conditions present within dense circumnuclear gas that is irradiated by X-rays from an active galactic nucleus. Over a wide range of X-ray fluxes and gas pressures, the effects of X-ray heating give rise to a molecular layer at temperatures of 400-1000 K within which the water abundance is large. The physical conditions within this molecular layer naturally give rise to collisionally pumped maser emission in the 6(sub 16) - 5(sub 23) 22 GHz transition of ortho-water, with predicted maser luminosities of 10(exp 2 +/- 0.5) solar luminosity per sq. pc of illuminated area. Given plausible assumptions about the geometry of the source and about the degree to which the maser emission is anisotropic, such surface luminosities are sufficient to explain the large apparent luminosities observed in water maser sources that are associated with active galactic nuclei.

Neufeld, David A.; Maloney, Philip R.; Conger, Sarah

1994-01-01

258

X-ray emission from old and intermediate age brown dwarfs  

E-print Network

According to the paradigm of solar-type dynamo action brown dwarfs should not exhibit magnetic activity as they are fully convective. Indeed, Halpha observations of ultracool field dwarfs indicate a decline of activity setting in near the substellar limit. X-ray emission traditionally serves as another means to examine magnetic activity on stars. The substellar regime can now be accessed with the new generation of X-ray instruments onboard XMM-Newton and Chandra. We report on two recent XMM-Newton observations of brown dwarfs in the Pleiades cluster and in the field aiming to constrain the age and effective temperature dependence of X-ray emission from substellar objects.

B. Stelzer; R. Neuhaeuser

2002-06-17

259

WEAK HARD X-RAY EMISSION FROM TWO BROAD ABSORPTION LINE QUASARS OBSERVED WITH NuSTAR: COMPTON-THICK ABSORPTION OR INTRINSIC X-RAY WEAKNESS?  

SciTech Connect

We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain Almost-Equal-To 400-600 hard X-ray ({approx}> 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N{sub H} {approx}< 10{sup 24} cm{sup -2}). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N{sub H} Almost-Equal-To 7 Multiplication-Sign 10{sup 24} cm{sup -2} if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe K{alpha} line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

Luo, B.; Brandt, W. N. [Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States); Alexander, D. M.; Hickox, R. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Harrison, F. A.; Fuerst, F.; Grefenstette, B. W.; Madsen, K. K. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Stern, D. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Bauer, F. E. [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Boggs, S. E.; Craig, W. W. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Christensen, F. E. [DTU Space-National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Comastri, A. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Fabian, A. C. [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom); Farrah, D. [Department of Physics, Virginia Tech, Blacksburg, VA 24061 (United States); Fiore, F. [Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio Catone (Italy); Hailey, C. J. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Matt, G. [Dipartimento di Matematica e Fisica, Universita degli Studi Roma Tre, via della Vasca Navale 84, I-00146 Roma (Italy); Ogle, P. [IPAC, California Institute of Technology, Mail Code 220-6, Pasadena, CA 91125 (United States); and others

2013-08-01

260

Weak Hard X-Ray Emission from Two Broad Absorption Line Quasars Observed with NuSTAR: Compton-thick Absorption or Intrinsic X-Ray Weakness?  

NASA Astrophysics Data System (ADS)

We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain ?400-600 hard X-ray (gsim 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N H <~ 1024 cm-2). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N H ? 7 × 1024 cm-2 if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe K? line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

Luo, B.; Brandt, W. N.; Alexander, D. M.; Harrison, F. A.; Stern, D.; Bauer, F. E.; Boggs, S. E.; Christensen, F. E.; Comastri, A.; Craig, W. W.; Fabian, A. C.; Farrah, D.; Fiore, F.; Fuerst, F.; Grefenstette, B. W.; Hailey, C. J.; Hickox, R.; Madsen, K. K.; Matt, G.; Ogle, P.; Risaliti, G.; Saez, C.; Teng, S. H.; Walton, D. J.; Zhang, W. W.

2013-08-01

261

X-ray emissivities from well characterized underdense, laser-heated gas targets  

NASA Astrophysics Data System (ADS)

We have performed experiments with laser-irradiated gas-filled targets that produce efficient, bright L-shell x-rays from Kr ions (h? ? 1.8keV). These experiments were carried out at the OMEGA laser (?=351nm) at the University of Rochester. Targets with different fill pressures yielded plasma electron densities in the range 3 to 5% n_Cr, where n_ Cr=9×10^21cm-3 for 3? light. The plasmas were well diagnosed with gated x-ray framing cameras, which show homogeneity of the x-ray emission, and 4? Thomson scattering, which shows the electron temperature at the center of the bag. The conversion efficiency of these targets is measured with an absolute-flux-calibrated Bragg crystal spectrometer. The results demonstrate record x-ray production. Detailed collisional-radiatve (CR) models for the emitted spectra have been made with the HULLAC suite of codes. The models fully account for the dielectronic recombination channels that determine the ionization balance for L-shell Kr ions. The charge-state distribution and detailed x-ray spectra are compared to the observed spectra. The resulting line-by-line CR emissivity from the model is compared to the measured x-ray output from the gas targets. X-ray radiative-cooling rates are benchmarked against measurements from plasmas with known temperature and density conditions. This work was performed under the auspices of the U.S. Department of Energy by UC Lawrence Livermore National Laboratory under contract No.W-7405-Eng-48.

Fournier, K. B.; Constantin, C.; Back, C. A.; Miller, M. C.; Suter, L. J.; Chung, H.-K.

2004-11-01

262

X-RAY EMISSION FROM NITROGEN-TYPE WOLF-RAYET STARS  

SciTech Connect

We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars obtained in a limited survey aimed at establishing the X-ray properties of WN stars across their full range of spectral subtypes. None of the detected stars is so far known to be a close binary. We report Chandra detections of WR 2 (WN2), WR 18 (WN4), and WR 134 (WN6), and an XMM-Newton detection of WR79a (WN9ha). These observations clearly demonstrate that both WNE and WNL stars are X-ray sources. We also discuss Chandra archive detections of the WN6h stars WR 20b, WR 24, and WR 136 and ROSAT non-detections of WR 16 (WN8h) and WR 78 (WN7h). The X-ray spectra of all WN detections show prominent emission lines and an admixture of cool (kT < 1 keV) and hot (kT > 2 keV) plasma. The hotter plasma is not predicted by radiative wind shock models and other as yet unidentified mechanisms are at work. Most stars show X-ray absorption in excess of that expected from visual extinction (A {sub V}), likely due to their strong winds or cold circumstellar gas. Existing data suggest a falloff in X-ray luminosity toward later WN7-9 subtypes, which have higher L {sub bol} but slower, denser winds than WN2-6 stars. This provides a clue that wind properties may be a more crucial factor in determining emergent X-ray emission levels than bolometric luminosity.

Skinner, Stephen L.; Sokal, Kimberly R. [Center for Astrophysics and Space Astronomy (CASA), University of Colorado, Boulder, CO 80309-0389 (United States); Zhekov, Svetozar A. [JILA, University of Colorado, Boulder, CO 80309-0440 (United States); Guedel, Manuel [Institute of Astronomy, ETH Zuerich, Wolfgang-Pauli-Str. 27, 8093 Zuerich (Switzerland); Schmutz, Werner [Physikalisch-Meteorologisches Observatorium Davos and World Radiation Center (PMOD/WRC), Dorfstrasse 33, CH-7260 Davos Dorf (Switzerland)], E-mail: Stephen.Skinner@colorado.edu

2010-03-15

263

X-ray Emission from Nitrogen-Type Wolf-Rayet Stars  

NASA Astrophysics Data System (ADS)

We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars obtained in a limited survey aimed at establishing the X-ray properties of WN stars across their full range of spectral subtypes. None of the detected stars is so far known to be a close binary. We report Chandra detections of WR 2 (WN2), WR 18 (WN4), and WR 134 (WN6), and an XMM-Newton detection of WR79a (WN9ha). These observations clearly demonstrate that both WNE and WNL stars are X-ray sources. We also discuss Chandra archive detections of the WN6h stars WR 20b, WR 24, and WR 136 and ROSAT non-detections of WR 16 (WN8h) and WR 78 (WN7h). The X-ray spectra of all WN detections show prominent emission lines and an admixture of cool (kT < 1 keV) and hot (kT > 2 keV) plasma. The hotter plasma is not predicted by radiative wind shock models and other as yet unidentified mechanisms are at work. Most stars show X-ray absorption in excess of that expected from visual extinction (A V), likely due to their strong winds or cold circumstellar gas. Existing data suggest a falloff in X-ray luminosity toward later WN7-9 subtypes, which have higher L bol but slower, denser winds than WN2-6 stars. This provides a clue that wind properties may be a more crucial factor in determining emergent X-ray emission levels than bolometric luminosity.

Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel; Schmutz, Werner; Sokal, Kimberly R.

2010-03-01

264

Quiescent Diffusive and Fumarolic Volcanic Bromocarbon Emissions  

NASA Astrophysics Data System (ADS)

Future scenarios of declining atmospheric burdens of Ozone Depleting Substances (ODS) such as halocarbons after phase-out following international regulation (Montreal Protocol) vary strongly depending on what contribution from natural sources is taken into account. In addition, current and pre-industrial global atmospheric budgets of ODS are poorly balanced by known natural and anthropogenic sources of halocarbons (Butler, 2000). Brominated halocarbons have a high Ozone Depletion Potential, Br is at least 40x as efficient as Cl in polar stratospheric ozone destruction (Solomon et al., 1992). CH3Br is the dominant Br carrier to the stratosphere with sources being ca.: 32% anthropogenic, 39% natural, but ca. 29% unaccounted for (WMO, 1998). Natural sources have been reviewed recently (Gribble, 2000, Butler, 2000), including magmatic inorganic (Bureau, 2000) and volcanic organic sources (Rassmussen et al., 1980; Schwandner et al., 2002). CH3Br and other bromocarbons have been reported in non-eruptive volcanic gases previously (Jordan et al., 2000; Schwandner et al., 2000). Due to its capability to extremely rapidly hydrolyse (Gan et al., 1995), CH3Br should not be sampled by the caustic soda bottle technique as used by Jordan et al. (2000) whose samples also show signs of air contamination, but by cryogenic separation of steam with subsequent sorbent trapping, as used by Isidorov (1990), Wahrenberger (1996) and Schwandner et al. (2000, 2001). To contribute significantly to the natural Br budget, volcanic gases would have to at least contain 2 ppmv (dry gas) CH3Br, scaled to a global CO2 emission of 66 Tgy-1 (Stoiber, 1995) based on CO2 flux to halocarbon concentration correlations (e.g. CFC-11: R2=0.91, Schwandner et al., 2002). However, CH3Br is not the only volcanogenic bromocarbon. Analysis of diffusive flank and crater degassing on Vulcano island (Italy) showed a strong diffusive component of CH3Br and C2H5Br emissions in 60-100°C hot pristine unvegetated volcanic "soil" close to high-temperature fumaroles. Other ODS found significantly above air, field and analytical system blanks include CH3Cl, CH3I, chlorophenols and chlorobenzenes. Abundances range from upper pptv to ppmv (e.g. CFC-11: max. 1200 pptv diffusive, 3700 pptv fumarolic/dry gas, dry air: 268 pptv). References\\ Bureau H. et al. (2000), EPSL 183 (1-2):51-60.\\Butler J.H. (2000), Nature 403:560-261.\\Gan J. Y. et al. (1995), J. Agric. Food Chem. 43:1361-1367.\\Gribble G. W. (2000), Environ. Sci. Pollut. Res. 7(1), 37-49.\\Isidorov V. A. et al. (1990), J. Atmos. Chem. 10(3):329-340.\\Jordan A. et al.(2000), ES&T 34:1122-1124.\\Rasmussen R. A. et al. (1980), EOS Transact. 61(6):67.\\Schwandner F. M. et al. (2000), J. Conf. Abs. 5(2):898.\\Schwandner F. M. et al. (2001), Chimia 55(7-8):590.\\Schwandner F.M. et al. (2002), Geoch. Soc. Spec. Publ. 8 (subm.).\\Solomon S. et al. (1992), JGR-A. 97:825-842.\\Stoiber R. E. (1995), In: A handbook of physical constants, AGU Reference Shelf 1:308-319.\\Wahrenberger C. et al. (1996), EOS Trans. 77(46):804.\\WMO (1998) Scientific assessment of ozone depletion. WMO Rep. No. 44, World Meteorological Organisation (WMO), Geneva.

Schwandner, F. M.; Gi?e, A. P.; Seward, T. M.; Hall, P. A.; Dietrich, V. J.

2002-12-01

265

Chandra Observation of an X-ray Flare at Saturn: Evidence for Direct Solar Control on Saturn's Disk X-ray Emissions  

E-print Network

Saturn was observed by Chandra ACIS-S on 20 and 26-27 January 2004 for one full Saturn rotation (10.7 hr) at each epoch. We report here the first observation of an X-ray flare from Saturn's non-auroral (low-latitude) disk, which is seen in direct response to an M6-class flare emanating from a sunspot that was clearly visible from both Saturn and Earth. Saturn's disk X-ray emissions are found to be variable on time scales of hours to weeks to months, and correlated with solar F10.7 cm flux. Unlike Jupiter, X-rays from Saturn's polar (auroral) region have characteristics similar to those from its disk. This report, combined with earlier studies, establishes that disk X-ray emissions of the giant planets Saturn and Jupiter are directly regulated by processes happening on the Sun. We suggest that these emissions could be monitored to study X-ray flaring from solar active regions when they are on the far side and not visible to Near-Earth space weather satellites.

Anil Bhardwaj; Ronald F. Elsner; J. Hunter Waite Jr; G. Randall Gladstone; Thomas E. Cravens; Peter G. Ford

2005-04-05

266

X-ray emission and absorption features during an energetic thermonuclear X-ray burst from IGR J17062-6143  

E-print Network

Type-I X-ray bursts are thermonuclear explosions occurring in the surface layers of accreting neutron stars. These events are powerful probes of the physics of neutron stars and their surrounding accretion flow. We analyze a very energetic type-I X-ray burst from the neutron star low-mass X-ray binary IGR J17062-6143 that was detected with Swift on 2012 June 25. The light curve of the ~18 min long X-ray burst tail shows an episode of ~10 min during which the intensity is strongly fluctuating by a factor of ~3 above and below the underlying decay trend, on a time scale of seconds. The X-ray spectrum reveals a highly significant emission line around ~1 keV, which can be interpreted as a Fe-L shell line caused by irradiation of cold gas. We also detect significant absorption lines and edges in the Fe-K band, which are strongly suggestive of the presence of hot, highly ionized gas along the line of sight. None of these features are present in the persistent X-ray spectrum of the source. The time scale of the stro...

Degenaar, N; Wijnands, R; Altamirano, D; Fabian, A C

2012-01-01

267

Hard X-ray diffuse emission from the Galactic Center seen by INTEGRAL  

E-print Network

We study the hard X-ray (20-100 keV) variability of the Galactic Center (GC) and of the nearby sources on the time scale of 1000 s. We find that 3 of the 6 hard X-ray sources detected by INTEGRAL within the central 1 degree of the Galaxy are not variable on this time scale: the GC itself (the source IGR J1745.6-2901) as well as the source 1E 1743.1-2843 and the molecular cloud Sgr B2. We put an upper limit of 5 x 10^{-12} erg/(cm^2 sec) (in 20 to 60 keV band) on the variable emission form the supermassive black hole (the source Sgr A*) which powers the activity of the GC(although we can not exclude the possibility of rare stronger flares). The non-variable 20-100 keV emission from the GC turns out to be the high-energy non-thermal tail of the diffuse hard ``8 keV'' component of emission from Sgr A region. Combining the XMM-Newton and INTEGRAL data we find that the size of the extended hard X-ray emission region is about 20 pc. The only physical mechanism of production of diffuse non-thermal hard X-ray flux, which does not contradict the multi-wavelength data on the GC, is the synchrotron emission from electrons of energies 10-100 TeV.

A. Neronov; M. Chernyakova; T. J. -L. Courvoisier; R. Walter

2005-06-18

268

Modeling of X-ray emissions produced by stepping lightning leaders  

NASA Astrophysics Data System (ADS)

Intense and brief bursts of X-ray emissions have been measured during the stepping process of both natural cloud-to-ground (CG) and rocket-triggered lightning flashes. In this paper, we investigate theoretically the energy spectra of X-rays produced by the bremsstrahlung emission of thermal runaway electrons accelerated in the inhomogeneous electric field produced around lightning leader tips. The X-ray energy spectrum depends on the physical properties of the associated lightning leaders. Consequently, X-ray measurements can be used for diagnostics of the electrical properties of lightning stepped leaders. We report simulation results of the photon energy spectra produced by 5 and 10 MV negative CG lightning discharges that would be measured from the ground using ideal detectors. We also quantify theoretically the radial dependence of X-ray energy spectra received at ground level during the leader stepping process. Moreover, it is found that the ground radiation generated in this process is harmless to humans.

Xu, Wei; Celestin, Sebastien; Pasko, Victor P.

2014-10-01

269

The nature of the prompt X-ray and radio emission from SN2002ap  

E-print Network

We report on the combined X-ray and radio observations of the type Ic SN 2002ap, using XMM-Newton ToO observation of M74 and the Giant Metrewave Radio Telescope (GMRT). We account for the presence of a nearby source in the pre-supernova Chandra field of view in our measurements of the X-ray flux (0.3 - 10 KeV) 5.2 days after the explosion. The X-ray spectrum is well fitted by a power law spectrum with photon index $\\alpha= 2.6$. Our results suggest that the prompt X-ray emission originates from inverse Compton scattering of photospheric thermal emission by energetic electrons. Radio observations with the GMRT at 610 MHz (8 days after the explosion) and 1420 MHz (70 days after the explosion) are combined with the high frequency VLA observations of SN 2002ap reported earlier, and the early radiospheric properties of SN 2002ap are compared with similar data from two other supernovae. Finally, the GMRT radio map reveals four other X-ray sources in the field of view of M74 with radio counterparts.

F. K. Sutaria; P. Chandra; S. Bhatnagar; A. Ray

2002-11-06

270

The Sun's X-ray Emission During the Recent Solar Minimum  

NASA Astrophysics Data System (ADS)

The Sun recently underwent a period of a remarkable lack of major activity such as large flares and sunspots, without equal since the advent of the space age a half century ago. A widely used measure of solar activity is the amount of solar soft X-ray emission, but until recently this has been below the threshold of the X-ray-monitoring Geostationary Operational Environmental Satellites (GOES). There is thus an urgent need for more sensitive instrumentation to record solar X-ray emission in this range. Anticipating this need, a highly sensitive spectrophotometer called Solar Photometer in X-rays (SphinX) was included in the solar telescope/spectrometer TESIS instrument package on the third spacecraft in Russia's Complex Orbital Observations Near-Earth of Activity of the Sun (CORONAS-PHOTON) program, launched 30 January 2009 into a near-polar orbit. SphinX measures X-rays in a band similar to the GOES longer-wavelength channel.

Sylwester, Janusz; Kowalinski, Mirek; Gburek, Szymon; Siarkowski, Marek; Kuzin, Sergey; Farnik, Frantisek; Reale, Fabio; Phillips, Kenneth J. H.

2010-02-01

271

Hard X-rays and Fluorescent Iron Emission from the Embedded Infrared Cluster in NGC 2071  

E-print Network

We present first results of XMM-Newton X-ray observations of the infrared cluster lying near the NGC 2071 reflection nebula in the Orion B region. This cluster is of interest because it is one of the closest regions known to harbor embedded high-mass stars. We report the discovery of hard X-ray emission from the dense central NGC 2071-IR subgroup which contains at least three high-mass young stellar objects (NGC 2071 IRS-1, IRS-2, and IRS-3). A prominent X-ray source is detected within 1 arcsecond of the infrared source IRS-1, which is thought to drive a powerful bipolar molecular outflow. The X-ray spectrum of this source is quite unusual compared to the optically thin plasma spectra normally observed in young stellar objects (YSOs). The spectrum is characterized by a hard broad-band continuum plus an exceptionally broad emission line at approximately 6.4 keV from neutral or near-neutral iron. The fluorescent Fe line likely originates in cold material near the embedded star (i.e. a disk or envelope) that is irradiated by the hard heavily-absorbed X-ray source.

Stephen L. Skinner; Audrey E. Simmons; Marc Audard; Manuel Guedel

2006-12-19

272

RX J1301.9+2747: A Highly Variable Seyfert Galaxy with Extremely Soft X-ray Emission  

E-print Network

In this paper we present a temporal and spectral analysis of X-ray data from the XMM and Chandra observations of the ultrasoft and variable Seyfert galaxy RX J1301.9+2747. In both observations the source clearly displays two distinct states in the X-ray band, a long quiescent state and a short flare (or eruptive) state which differs in count rates by a factor of 5--7. The transition from quiescent to flare state occurs in 1--2 ks. We have observed that the quiescent state spectrum is unprecedentedly steep with a photon index Gamma~7.1, and the spectrum of the flare state is flatter with Gamma~4.4. X-rays above 2 keV were not significantly detected in either state. In the quiescent state, the spectrum appears to be dominated by a black body component of temperature about ~30--40 eV, which is comparable to the expected maximum effective temperature from the inner accretion disk. The quiescent state however, requires an additional steep power-law, presumably arising from the Comptonization by transient heated el...

Sun, Luming; Wang, Tinggui

2013-01-01

273

Investigating the hard X-ray emission from the hottest Abell cluster A2163 with Suzaku  

NASA Astrophysics Data System (ADS)

Context. We present the results from Suzaku of the hottest Abell galaxy cluster A2163 at z = 0.2. Aims: To study the physics of gas heating in cluster mergers, we investigated hard X-ray emission from the merging cluster A2163, which hosts the brightest synchrotron radio halo. Methods: We analyzed hard X-ray emission spectra accumulated from two-pointed Suzaku observations. Non-thermal hard X-ray emission should result from the inverse Compton scattering of relativistic electrons by photons in the cosmic microwave background. To measure this emission, the dominant thermal emission in the hard X-ray band must be modeled in detail. To this end, we analyzed the combined broadband X-ray data of A2163 collected by Suzaku and XMM-Newton, assuming single- and multi-temperature models for thermal emission and the power-law model for non-thermal emission. Comparing the non-thermal hard X-ray flux to radio synchrotron emission, we also estimated the magnetic field in the cluster. Results: From the Suzaku data, we detected significant hard X-ray emission from A2163 in the 12-60 keV band at the 28? level (or at the 5.5? level if a systematic error of the non-X-ray background model is considered). The Suzaku HXD spectrum alone is consistent with the single-temperature thermal model of gas temperature kT = 14 keV. From the XMM-Newton data, we constructed a multi-temperature model including a very hot (kT = 18 keV) component in the north-east region. Incorporating the multi-temperature and the power-law models into a two-component model with a radio-band photon index, where ? = 2.18, the 12-60 keV energy flux of non-thermal emission is constrained within 5.3 ± 0.9 (±3.8) × 10-12 erg s-1cm-2 (the first and second errors refer to the 1? statistical and systematic uncertainties, respectively). The 90% upper limit of detected inverse Compton emission is marginal (FNT < 1.2 × 10-11 erg s-1cm-2 in the 12-60 keV band). The estimated magnetic field in A2163 is B > 0.098 ?G. While the present results represent a three-fold increase in the accuracy of the broadband (0.3-60 keV) spectral model of A2163, more sensitive hard X-ray observations are needed to decisively test for the presence of hard X-ray emission due to inverse Compton emission.

Ota, N.; Nagayoshi, K.; Pratt, G. W.; Kitayama, T.; Oshima, T.; Reiprich, T. H.

2014-02-01

274

X-ray emission from Hickson's compact groups of galaxies: Results from the ROSAT All-Sky Survey  

Microsoft Academic Search

We report on the detection of X-ray emission from 11 of Hickson's compact groups of galaxies (HCGs) in the ROSAT All-Sky Survey (RASS). One of these is clearly part of a much richer system with an X-ray luminosity comparable to that of Abell clusters. With two order detections, the X-ray emission is dominated by pointlike and spectrally soft sources which

Harald Ebeling; Wolfgang Voges; Hans Boehringer

1994-01-01

275

Intense Non-Linear Soft X-Ray Emission from a Hydride Target during Pulsed D Bombardment  

Microsoft Academic Search

Radiation emission from low-energy nuclear radiation (LENR) electrodes (both charged-particle and X-rays) represents an important feature of LENR in general. Here, calibration, measurement techniques, and soft X-ray emission results from deuterium bombardment of a Pd target (cathode) placed in a pulsed deuterium glow discharge (PGD) are described. An X-ray intensity of 13.4 mW\\/cm2 and a dose of 3.3 muJ\\/cm2 were

George H. Miley; Yang Yang; Andrei Lipson; Munima Haque; Ian Percel; Michael Romer

2006-01-01

276

RX J1301.9+2747: A HIGHLY VARIABLE SEYFERT GALAXY WITH EXTREMELY SOFT X-RAY EMISSION  

SciTech Connect

In this paper we present a temporal and spectral analysis of X-ray data from XMM-Newton and Chandra observations of the ultrasoft and variable Seyfert galaxy RX J1301.9+2747. In both observations the source clearly displays two distinct states in the X-ray band: a long quiescent state and a short flare (or eruptive) state which differs in count rates by a factor of 5-7. The transition from the quiescent to the flare state occurs in 1-2 ks. We have observed that the quiescent state spectrum is unprecedentedly steep with a photon index {Gamma} {approx} 7.1, and the spectrum of the flare state is flatter with {Gamma} {approx} 4.4. X-rays above 2 keV were not significantly detected in either state. In the quiescent state, the spectrum appears to be dominated by a blackbody component of temperature about {approx}30-40 eV, which is comparable to the expected maximum effective temperature from the inner accretion disk. The quiescent state, however, requires an additional steep power law, presumably arising from Comptonization by transient heated electrons. The optical spectrum from the Sloan Digital Sky Survey shows Seyfert-like narrow lines for RX J1301.9+2747, while Hubble Space Telescope imaging reveals a central point source for the object. In order to precisely determine the hard X-ray component, future longer X-ray observations are required. This will help constrain the accretion disk model for RX J1301.9+2747, and shed new light on the characteristics of the corona and accretion flows around black holes.

Sun Luming; Shu Xinwen; Wang Tinggui, E-mail: lmsun@mail.ustc.edu.cn, E-mail: xwshu@mail.ustc.edu.cn, E-mail: twang@ustc.edu.cn [CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2013-05-10

277

The Detection of Circumnuclear X-Ray Emission from the Seyfert Galaxy NGC 3516  

NASA Technical Reports Server (NTRS)

We present the first high-resolution, X-ray image of the circumnuclear regions of the Seyfert 1 galaxy NGC 3516, using the Chandra X-ray Observatory (CXO). All three of the CXO observations reported were performed with one of the two grating assemblies in place, and here we restrict our analysis to undispersed photons (i.e. those detected in the zeroth-order). A previously-unknown X-ray source is detected approximately 6 arcsec (1.1h(sub 75)(exp -1) kpc) NNE of the nucleus (position angle approximately 29 degrees) which we designate CXOU 110648.1 + 723412. Its spectrum can be characterized as a power law with a photon index (Gamma) approximately 1.8 - 2.6, or as thermal emission with a temperature kT approximately 0.7 - 3 keV. Assuming a location within NGC 3516, isotropic emission implies a luminosity L approximately 2 - 8 x 10(exp 39)h(sub 75)(exp-2) erg s(exp -1) in the 0.4 - 2 keV band. If due to a single point source, the object is super-Eddington for a 1.4 solar mass neutron star. However, multiple sources or a small, extended source cannot be excluded using the current data. Large-scale extended S-ray emission is also detected out to approximately 10 arcsec (approximately 2h(sub 75)(exp -1) kpc) from the nucleus to the NE and SW, and is approximately aligned with the morphologies of the radio emission and extended narrow emission line region (ENLR). The mean luminosity of this emission is 1 - 5 x 10(exp 37)h(sub 75)(exp -2) erg s(exp -1) arcsec(exp -2), in the 0.4 - 2 keV band. Unfortunately the current data cannot usefully constrain its spectrum. These results are consistent with earlier suggestions of circumnuclear X-ray emissi in NGC 3516 based on ROSAT observations, and thus provide the first clear detection of extended X-ray emission in a Seyfert 1.0 galaxy. If the extended emission is due to scattering of the nuclear X-ray continuum, then the pressure in the X-ray emitting gas is at least two orders of magnitude too small to provide the confining medium for the ENLR clouds.

George, I. M.; Turner, T. J.; Netzer, H.; Kraemer, S. B.; Ruiz, J.; Chelouche, D.; Crenshaw, D. M.; Yaqoob, T.; Nandra, K.; Mushotzky, R. F.; White, Nicholas E. (Technical Monitor)

2001-01-01

278

Quantitative Analysis of the Resolved X-ray Emission Line Profiles of O Stars  

E-print Network

, absorbs more radiation, and is further accelerated... #12;The line-driven instability (LDI) should lead to shock-heating and X-ray emission 1-D rad-hydro simulation of the LDI #12;A snapshot at a single time from the same simulation. Note the shock fronts. Most of the wind mass is in dense inter-shock regions

Cohen, David

279

Implications of the non-detection of X-ray emission from HD 149427  

NASA Astrophysics Data System (ADS)

HD 149427 is a very enigmatic object. It has been classified either as a planetary nebula or as a D'-type symbiotic star. Its distance is also highly uncertain. Furthermore, HD 149427 is a potential jet source. We report the non-detection of X-ray emission from HD 149427 and explore the implications to its nature. We observed the object with XMM-Newton with an effective exposure time of 33.5 ks. The upper limit for the flux of the X-ray emission in the soft band (<2 keV) is 10^-15 erg s^-1 cm^-2, while in the hard band (>2 keV) it is about 10^-14 erg s^-1 cm^-2. We discuss the implication of our results in light of the possible natures of HD 149427 - being a planetary nebula or a symbiotic star, close or very distant. The derived upper limits on the mass accretion rate of the white dwarf are untypical for symbiotic stars and may favor the picture of HD 149427 being a young PN. HD 149427 might be a symbiotic star in hibernation - if a symbiotic star at all. We estimate the possible mass-loss rate and kinetic luminosity of the jet and find no contradiction with our upper limit of soft X-ray emission. Therefore the jet may be still present but it was too faint to be detected via soft X-ray emission.

Stute, M.; Luna, G. J. M.

2011-11-01

280

THE MULTIELEMENTAL ANALYSIS OF DRINKING WATER USING PROTON-INDUCED X-RAY EMISSION (PIXE)  

EPA Science Inventory

A new, rapid, and economical method for the multielemental analysis of drinking water samples is described. The concentrations of 76 elements heavier than aluminum are determined using proton-induced x-ray emission (PIXE) technology. The concentration of sodium is evaluated using...

281

The X-ray emission of Compton-thick Seyfert 2 galaxies.  

NASA Astrophysics Data System (ADS)

The author briefly summarizes some theoretical and observational results on the X-ray emission of Compton-thick Seyfert 2 galaxies, i.e. sources in which the obscuring torus is optically thick to Compton scattering (NH ? 1024cm-2).

Matt, G.

1996-02-01

282

Effects of weak vacuum on triboelectric charging and x-ray emissions of colliding particles.  

E-print Network

Effects of weak vacuum on triboelectric charging and x-ray emissions of colliding particles. Tyler and become oppositely charged. Triboelectricity is a poorly-understood phenomenon, and scientists do not even, and humidity inversely affects triboelectric charging. One possible explanation

Anlage, Steven

283

Disentangling X-Ray Emission Processes in Vela-Like Pulsars  

NASA Technical Reports Server (NTRS)

We present a deep observation with the X-Ray Multimirror Mission of PSR B1823-13, a young pulsar with similar properties to the Vela pulsar. We detect two components to the X-ray emission associated with PSR B1823-13: an elongated core of extent 30 min immediately surrounding the pulsar embedded in a fainter, diffuse component of emission 5 sec in extent, seen only on the southern side of the pulsar. The pulsar itself is not detected, either as a point source or through its pulsations. Both components of the X-ray emission are well fitted by a power-law spectrum, with photon index Gamma approx. 1.6 and X-ray luminosity (0.5-10 keV) L(sub X) approx. 9 x 10(exp 32) ergs/s for the core and Gamma approx. 2.3 and L(sub X) approx. 3 x 10(exp 33) ergs/s for the diffuse emission, for a distance of 4 kpc. We interpret both components of emission as corresponding to a pulsar wind nebula, which we designate G18.0-0.7. We argue that the core region represents the wind termination shock of this nebula, while the diffuse component indicates the shocked downstream wind. We propose that the asymmetric morphology of the diffuse emission with respect to the pulsar is the result of a reverse shock from an associated supernova remnant, which has compressed and distorted the pulsar-powered nebula. Such an interaction might be typical for pulsars at this stage in their evolution. The associated supernova remnant is not detected directly, most likely being too faint to be seen in existing X-ray and radio observations.

Gaensler, Bryan; Mushotzky, Richard (Technical Monitor)

2003-01-01

284

The Relationship Between Solar Radio and Hard X-Ray Emission  

NASA Technical Reports Server (NTRS)

This review discusses the complementary relationship between radio and hard Xray observations of the Sun using primarily results from the era of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A primary focus of joint radio and hard X-ray studies of solar flares uses observations of nonthermal gyrosynchrotron emission at radio wavelengths and bremsstrahlung hard X-rays to study the properties of electrons accelerated in the main flare site, since it is well established that these two emissions show very similar temporal behavior. A quantitative prescription is given for comparing the electron energy distributions derived separately from the two wavelength ranges: this is an important application with the potential for measuring the magnetic field strength in the flaring region, and reveals significant differences between the electrons in different energy ranges. Examples of the use of simultaneous data from the two wavelength ranges to derive physical conditions are then discussed, including the case of microflares, and the comparison of images at radio and hard X-ray wavelengths is presented. There have been puzzling results obtained from observations of solar flares at millimeter and submillimeter wavelengths, and the comparison of these results with corresponding hard X-ray data is presented. Finally, the review discusses the association of hard X-ray releases with radio emission at decimeter and meter wavelengths, which is dominated by plasma emission (at lower frequencies) and electron cyclotron maser emission (at higher frequencies), both coherent emission mechanisms that require small numbers of energetic electrons. These comparisons show broad general associations but detailed correspondence remains more elusive.

White, S. M.; Benz, A. O.; Christe, S.; Farnik, F.; Kundu, M. R.; Mann, G.; Ning, Z.; Raulin, J.-P.; Silva-Valio, A. V. R.; Saint-Hilaire, P.; Vilmer, N.; Warmuth, A.

2011-01-01

285

10 micron detection of the hard X-ray transient GRO J0422+32: Free-free emission from an X-ray-driven accretion disk wind?  

NASA Technical Reports Server (NTRS)

We report the detection of 10 micrometer emission from the transient low-mass X-ray binary (LMXB) and optical nova GRO J0422+32 near the maximum of its outburst. We discuss this result in terms of (1) a 'standard' model according to which low-energy radiation of LMXB is caused by reprocessing of X-rays in an accretion disk; (2) emission from a cool secondary star; (3) emission from dust grains heated by the transient X-rays, and (4) free-free emission from an X-ray-driven wind from the accretion disk. Only the fourth alternative provides a viable explanation for the observed 10 micrometer emission, with a mass-loss rate in the disk wind that may be substantially higher than the rate of accretion onto the compact star. The presence of such a wind may have a profound effect on the evolution of the binary, and contribute to the solution of the 'birthrate problem' of millisecond ratio pulsars.

Paradijs, Van J.; Telesco, C. M.; Kouveliotou, C.; Fishman, G. J.

1994-01-01

286

What's important at z>5? X-ray Emission from Starbursts!  

NASA Astrophysics Data System (ADS)

There has recently been quite a bit of excitement on the role of X-ray emission from galaxies in reionization. It turns out that the X-ray output from X-ray binaries and hot gas are both likely important and may rival the ionizing output of AGN at z>5, particularly for Hydrogen reionization. Here we present our research on constraining the X-ray SED of high-redshift galaxies using an important local universe analog population, the Lyman Break Galaxy Analogs. We have established a relationship between the 2-10 keV X-ray luminosity, assumed to originate from X-ray binaries (XRBs), and star formation rate (SFR) in rest-frame UV-selected galaxies across cosmic time -- ranging from Lyman break galaxies (LBGs) in the early Universe (z=1.5-4) to Lyman break analogs (LBAs) in the present-day Universe ( 0.1). We present results from the 4Ms Chandra Deep Field South (CDF-S) observations of ~4000 z=1.5-4 LBGs as well as in-depth studies of a sample of six nearby GALEX-selected 0.1 LBAs, which are individually X-ray detected. Both populations may yield a larger output in collective HMXB luminosity per unit SFR than that observed in local (z=0) star-forming galaxies. We also discuss the properties of the hot gas in these galaxies, particularly what we hope to learn with next generation facilities such as the Athena calorimeter.

Hornschemeier, Ann E.; Basu-Zych, Antara; Yukita, Mihoko; Mineo, Stefano; Lehmer, Bret; Ptak, Andrew; Fragos, Tassos; Zezas, Andreas

2014-08-01

287

Old Isolated Accreting Neutron Stars: The Diffuse X--ray Emission From The Galactic Center  

E-print Network

The contribution of weakly--magnetized ($B\\sim 10^9$ G) neutron stars accreting the interstellar medium to the diffuse X--ray emission observed in the Galactic Center is investigated. It is shown that, under rather conservative assumptions about the neutron stars and gas distributions, the accretion luminosity can account for a sizable fraction, possibly most, of the detected X--ray flux in the 2.5--7 keV band. In particular, model results are compared with {\\it Granat\\/} data and show a general agreement in both the flux energy and radial distributions.

Silvia Zane; Roberto Turolla; Aldo Treves

1996-05-14

288

Measurement of the Radius of Neutron Stars with High Signal-to-noise Quiescent Low-mass X-Ray Binaries in Globular Clusters  

NASA Astrophysics Data System (ADS)

This paper presents the measurement of the neutron star (NS) radius using the thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular clusters (GCs). Recent observations of NSs have presented evidence that cold ultra dense matter—present in the core of NSs—is best described by "normal matter" equations of state (EoSs). Such EoSs predict that the radii of NSs, R NS, are quasi-constant (within measurement errors, of ~10%) for astrophysically relevant masses (M NS>0.5 M ?). The present work adopts this theoretical prediction as an assumption, and uses it to constrain a single R NS value from five qLMXB targets with available high signal-to-noise X-ray spectroscopic data. Employing a Markov chain Monte-Carlo approach, we produce the marginalized posterior distribution for R NS, constrained to be the same value for all five NSs in the sample. An effort was made to include all quantifiable sources of uncertainty into the uncertainty of the quoted radius measurement. These include the uncertainties in the distances to the GCs, the uncertainties due to the Galactic absorption in the direction of the GCs, and the possibility of a hard power-law spectral component for count excesses at high photon energy, which are observed in some qLMXBs in the Galactic plane. Using conservative assumptions, we found that the radius, common to the five qLMXBs and constant for a wide range of masses, lies in the low range of possible NS radii, R_NS =9.1^{+ 1.3}_{- 1.5} \\,km (90%-confidence). Such a value is consistent with low-R NS equations of state. We compare this result with previous radius measurements of NSs from various analyses of different types of systems. In addition, we compare the spectral analyses of individual qLMXBs to previous works.

Guillot, Sebastien; Servillat, Mathieu; Webb, Natalie A.; Rutledge, Robert E.

2013-07-01

289

Optical emission from cooling flows in distant x ray clusters of galaxies  

NASA Technical Reports Server (NTRS)

Although the Einstein satellite detected cooling flows in the x ray emission from clusters of galaxies 10 years ago, the understanding of these flows remains incomplete. The x ray emitting gas in the centers of these clusters is so dense that its cooling time is shorter than a Hubble time. Thus gas may cool and flow into the center of the cluster. This cooling gas is thermally unstable and should quickly become inhomogeneous. Optical filamentation (1-100 kpc scales) often appears near the centers of nearby clusters containing cooling flows, usually within the central galaxies accreting the gas. Indeed, only clusters with well-developed cooling flows seem to possess highly luminous, emission-line nebulae. Researchers present here some results of preliminary observational and theoretical studies of this class of emission-line objects. Researchers observed a complete, x ray selected sample of 25 distant clusters of galaxies extracted from the Einstein Extended Medium Sensitivity Survey. They discovered luminous extended H alpha emission in 10 of these clusters. Thus at least 40 percent of the clusters in the sample contain cool gas. If we crudely compare the sample to that of Arnaud (1988), in which approx. 40 percent of his 104 x ray clusters have cooling flows, the result implies that cooling flows may actually be a more common phenomenon in the past than in the present. The connection between the cooling flow and the H alpha emission is a mystery. The straightforward calculation of 1 (photoionization) to 3 (shocks) recombinations per H atom in the cooling flow gives mass infall rates 3 to 100 times greater than M derived from x ray observations. Researchers have made some preliminary theoretical calculations in an attempt to resolve this problem.

Donahue, Megan; Stocke, John T.; Voit, G. Mark; Gioia, Isabella

1990-01-01

290

The X-ray emission of the sdO star BD+37 1977  

NASA Astrophysics Data System (ADS)

While several hot subdwarf stars have been deeply investigated in the optical and UV domain, up to very recent times only the sdO stars HD49798 and BD+37 442 had been detected at X-rays. Both sources are characterized by comparable spectral and timing properties; in particular, the flux shows a fast periodic modulation, likely due to wind accretion from the sdO star onto a WD or NS companion. In the latest months the first systematic search for X-ray emission from a complete flux-limited sample of sdO stars, performed by Chandra, has provided a detection also of the sdO star BD+37 1977. Now we propose to observe this star with XMM: our aim is to characterize in detail its spectral X-ray properties and to investigate if it is intrinsic or due to an accreting compact companion.

La Palombara, Nicola

2013-10-01

291

X-ray Emission from Supernovae in Dense Circumstellar Matter Environments: a Search for Collisionless Shocks  

NASA Technical Reports Server (NTRS)

The optical light curve of some supernovae (SNe) may be powered by the outward diffusion of the energy deposited by the explosion shock (the so-called shock breakout) in optically thick (Tau approx > 30) circumstellar matter (CSM). Recently, it was shown that the radiation-mediated and radiation-dominated shock in an optically thick wind must transform into a collisionless shock and can produce hard X-rays. The X-rays are expected to peak at late times, relative to maximum visible light. Here we report on a search, using Swift/XRT and Chandra, for X-ray emission from 28 SNe that belong to classes whose progenitors are suspected to be embedded in dense CSM. Our sample includes 19 Type IIn SNe, one Type Ibn SN, and eight hydrogen-poor superluminous SNe (SLSN-I such as SN 2005ap). Two SNe (SN 2006jc and SN 2010jl) have X-ray properties that are roughly consistent with the expectation for X-rays from a collisionless shock in optically thick CSM. However, the X-ray emission from SN 2006jc can also be explained as originating in an optically thin region. Thus, we propose that the optical light curve of SN 2010jl is powered by shock breakout in CSM. We suggest that two other events (SN 2010al and SN 2011ht) were too X-ray bright during the SN maximum optical light to be explained by the shock-breakout model.We conclude that the light curves of some, but not all, SNe IIn/Ibn are powered by shock breakout in CSM. For the rest of the SNe in our sample, including all of the SLSN-I events, our X-ray limits are not deep enough and were typically obtained too early (i.e., near the SN maximum light) for definitive conclusions about their nature. Late-time X-ray observations are required in order to further test whether these SNe are indeed embedded in dense CSM. We review the conditions required for a shock breakout in a wind profile. We argue that the timescale, relative to maximum light, for the SN to peak in X-rays is a probe of the column density and the density profile above the shock region. In SNe whose X-ray emission slowly rises, and peaks at late times, the optical light curve is likely powered by the diffusion of shock energy in a dense CSM. We note that if the CSM density profile falls faster than a constant-rate wind-density profile, then X-rays may escape at earlier times than estimated for the wind-profile case. Furthermore, if the CSM has a region in which the density profile is very steep relative to a steady wind-density profile, or if the CSM is neutral, then the radio free-free absorption may be sufficiently low for radio emission to be detected.

Ofek, E. O.; Fox, D.; Cenko, Stephen B.; Sullivan, M; Gnat, O.; Frail, D. A.; Horesh, A.; Corsi, A.; Quimby, R. M.; Gehrels, N.; Kulkarni, S. R.; Gal-Yam, A.; Nugent, P. E.; Yaron, O.; Fillippenko, A. V; Kasliwal, M. M.; Bildsten, L.; Bloom, J. S.; Poznanski, D.; Arcavi, I.; Laher, R. R.; Levitan, D.; Sesar, B.; Surace, J..

2013-01-01

292

X-ray emission of brown dwarfs: Towards constraining the dependence on age, luminosity, and temperature  

E-print Network

Three brown dwarfs in different evolutionary stages have been observed with the Chandra X-ray Observatory. Combining the new observations with previous studies presented in the literature yields a brown dwarf sample that reaches well down into the cooling phase of brown dwarfs, allowing to investigate the possible influence of effective temperature on X-ray activity. Combining our results with published data allows us to consider a subsample of high-mass brown dwarfs (with 0.05-0.07 Msun), and another one characterized by similar effective temperature (with 2400-2800 K). Our findings support the idea that effective temperature plays a critical role for the X-ray activity in brown dwarfs. This underlines an earlier suggestion based on observations of chromospheric Ha emission in ultracool dwarfs that the low ionization fraction in the cool brown dwarf atmospheres may suppress magnetic activity.

B. Stelzer; G. Micela; E. Flaccomio; R. Neuhaeuser; R. Jayawardhana; ;; - Uni Palermo; - OA Palermo; - Uni Jena; - Uni Toronto

2005-11-07

293

X-ray emission processes in stars and their immediate environment.  

PubMed

A decade of X-ray stellar observations with Chandra and XMM-Newton has led to significant advances in our understanding of the physical processes at work in hot (magnetized) plasmas in stars and their immediate environment, providing new perspectives and challenges, and in turn the need for improved models. The wealth of high-quality stellar spectra has allowed us to investigate, in detail, the characteristics of the X-ray emission across the Hertzsprung-Russell (HR) diagram. Progress has been made in addressing issues ranging from classical stellar activity in stars with solar-like dynamos (such as flares, activity cycles, spatial and thermal structuring of the X-ray emitting plasma, and evolution of X-ray activity with age), to X-ray generating processes (e.g., accretion, jets, magnetically confined winds) that were poorly understood in the preChandra/XMM-Newton era. I will discuss the progress made in the study of high energy stellar physics and its impact in a wider astrophysical context, focusing on the role of spectral diagnostics now accessible. PMID:20360562

Testa, Paola

2010-04-20

294

DISCOVERY OF X-RAY EMISSION IN THE OLD CLASSICAL NOVA DK LACERTAE  

SciTech Connect

We report the discovery of X-ray emission at the position of the old classical nova DK Lacertae using the Swift satellite. Three observations were conducted using the X-Ray Telescope 62 years after the discovery of the nova, yielding 46 source signals in an exposure time of 4.8 ks. A background-subtracted count rate was 9 {+-} 2 Multiplication-Sign 10{sup -3} counts s{sup -1}, corresponding to a detection significance level of 5{sigma}. The X-ray spectrum was characterized by a continuum extending up to about 7 keV, which can be modeled by a power-law component with a photon index of 1.4-5.6, or by a thermal bremsstrahlung component with a temperature of 0.7-13.3 keV, convolved with interstellar absorption with an equivalent hydrogen column density of 0.3-2.4 Multiplication-Sign 10{sup 22} cm{sup -2}. Assuming a distance of 3900 pc to the source, the luminosity was 10{sup 32}-10{sup 34} erg s{sup -1} in the 0.3-10 keV energy band. The origin of X-rays is considered to be either mass accretion on the white dwarf or adiabatic shocks in nova ejecta, with the former appearing much more likely. In either case, DK Lacertae represents a rare addition to the exclusive club of X-ray emitting old novae.

Takei, D.; Drake, J. J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Sakamoto, T., E-mail: dtakei@head.cfa.harvard.edu [Department of Physics and Mathematics, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara-shi, Kanagawa 252-5258 (Japan)

2013-01-01

295

Multiplexing radiography based on carbon nanotube field emission X-ray technology  

NASA Astrophysics Data System (ADS)

State-of-the-art tomographic imaging technique is based upon of simple serial imaging scheme. The tomographic scanners collect the projection images sequentially in the time domain, by a step-and-shoot process using a single-pixel x-ray source. The inefficient serial data collection scheme severely limits the data collection speed, which is critical for imaging of objects in rapid motion such as for diagnosis of cardiovascular diseases, CT fluoroscopy, and airport luggage inspection. Further improvement of the speed demands an increasingly high x-ray peak workload and gantry rotation speed, both of which have approached the engineering limits. Multiplexing technique, which has been widely adopted in communication devices and in certain analytical instruments, holds the promise to significantly increase the data throughput. It however, has not been applied to x-ray radiography, mainly due to limitations of the current x-ray source technology. Here we report a method for frequency multiplexing radiography (FMR) based on the frequency multiplexing principle and the carbon nanotube field emission x-ray technology. We show the feasibility of multiplexing radiography that enables simultaneous collection of multiple projection images. It has the potential to significantly increase the imaging speed for tomographic imaging without compromising the imaging quality.

Zhang, J.; Yang, G.; Lee, Y.; Chang, S.; Lu, J. P.; Zhou, O.

2007-03-01

296

The origin of the puzzling hard X-ray emission of $\\gamma$ Cassiopeiae  

E-print Network

Massive B and Be stars produce X-rays from shocks in high velocity winds with temperatures of a few million degrees and maximum X-ray luminosities of $\\approx$ 10$^{31}$ erg/s. Surprisingly, a sub-group of early Be stars exhibits > 20 times hotter X-ray temperatures and > 10 times higher X-ray luminosities than normal. This group of Be stars, dubbed Gamma-Cas analogs, contains about 10 known objects. The origin of this bizarre behavior has been extensively debated in the past decades. Two mechanisms have been put forward, accretion of circumstellar disk matter onto an orbiting white dwarf, or magnetic field interaction between the star and the circumstellar disk (Smith & Robinson 1999). We show here that the X-ray and optical emissions of the prototype of the class, Gamma-Cas, are very well correlated on year time scales with no significant time delay. Since the expected migration time from internal disk regions that emit most of the optical flux to the orbit of the companion star is of several years, the...

Motch, Christian; Smith, Myron A

2015-01-01

297

X-ray Emission from Nitrogen-Type Wolf-Rayet Stars  

E-print Network

We summarize new X-ray detections of four nitrogen-type Wolf-Rayet (WR) stars obtained in a limited survey aimed at establishing the X-ray properties of WN stars across their full range of spectral subtypes. None of the detected stars is so far known to be a close binary. We report Chandra detections of WR 2 (WN2), WR 18 (WN4), and WR 134 (WN6), and an XMM-Newton detection of WR79a (WN9ha). These observations clearly demonstrate that both WNE and WNL stars are X-ray sources. We also discuss Chandra archive detections of the WN6h stars WR 20b, WR 24, and WR 136 and ROSAT non-detections of WR 16 (WN8h) and WR 78 (WN7h). The X-ray spectra of all WN detections show prominent emission lines and an admixture of cool (kT 2 keV) plasma. The hotter plasma is not predicted by radiative wind shock models and other as yet unidentified mechanisms are at work. Most stars show X-ray absorption in excess of that expected from visual extinction (Av), likely due to their strong winds or cold circumstellar gas. Existing data s...

Skinner, S L; Guedel, M; Schmutz, W; Sokal, K R

2009-01-01

298

X-ray emission processes in stars and their immediate environment  

PubMed Central

A decade of X-ray stellar observations with Chandra and XMM-Newton has led to significant advances in our understanding of the physical processes at work in hot (magnetized) plasmas in stars and their immediate environment, providing new perspectives and challenges, and in turn the need for improved models. The wealth of high-quality stellar spectra has allowed us to investigate, in detail, the characteristics of the X-ray emission across the Hertzsprung-Russell (HR) diagram. Progress has been made in addressing issues ranging from classical stellar activity in stars with solar-like dynamos (such as flares, activity cycles, spatial and thermal structuring of the X-ray emitting plasma, and evolution of X-ray activity with age), to X-ray generating processes (e.g., accretion, jets, magnetically confined winds) that were poorly understood in the preChandra/XMM-Newton era. I will discuss the progress made in the study of high energy stellar physics and its impact in a wider astrophysical context, focusing on the role of spectral diagnostics now accessible. PMID:20360562

Testa, Paola

2010-01-01

299

The X-ray spectrum and time variability of narrow emission line galaxies  

NASA Technical Reports Server (NTRS)

X-ray spectral and temporal observations are reported for six narrow emission line galaxies (NELGs), all of which are fitted by power-law X-ray spectra of energy slope 0.8 and have column densities in the line of sight greater than 1 x 10 to the 22nd atoms/sq cm. Three of the objects, NGC 526a, NGC 2110 and MCG-5-23-16 are variable in their X-ray flux, and the latter two, along with NGC 5506 and NGC 7582, showed detectable variability in at least one observation. The measured X-ray properties of these NELGs, which also included NGC 2992, strongly resemble those of previously-measured type 1 Seyferts of the same X-ray luminosity and lead to the conclusion of great similarity between the NELGs and low-luminosity type 1 Seyferts. The implications of these observations for the optical line-emitting region structure of these galaxies are discussed.

Mushotzky, R.

1981-01-01

300

Chandra X-ray Grating Spectrometry of Eta Carinae near X-ray Minimum: I. Variability of the Sulfur and Silicon Emission Lines  

NASA Technical Reports Server (NTRS)

We report on variations in important X-ray emission lines in a series of Chandra grating spectra of the supermassive colliding wind binary star eta Car, including key phases around the X-ray minimum/periastron passage in 2003.5. The X-rays arise from the collision of the slow, dense wind of eta Car with the fast, low-density wind of an otherwise hidden companion star. The X-ray emission lines provide the only direct measure of the flow dynamics of the companion's wind along the wind-wind collision zone. We concentrate here on the silicon and sulfur lines, which are the strongest and best resolved lines in the X-ray spectra. Most of the line profiles can be adequately fit with symmetric Gaussians with little significant skewness. Both the silicon and sulfur lines show significant velocity shifts and correlated increases in line widths through the observations. The R = forbidden-to-intercombination ratio from the Si XIII and S XV triplets is near or above the low-density limit in all observations, suggesting that the line-forming region is > 1.6 stellar radii from the companion star, and that the emitting plasma may be in a non-equilibrium state. We show that simple geometrical models cannot simultaneously fit both the observed centroid variations and changes in line width as a function of phase. We show that the observed profiles can be fitted with synthetic profiles with a reasonable model of the emissivity along the wind-wind collision boundary. We use this analysis to help constrain the line formation region as a function of orbital phase, and the orbital geometry. Subject headings: X-rays: stars -stars: early-type-stars: individual (q Car)

Henley, D. B.; Corcoran, M. F.; Pittard, J. M.; Stevens, I. R.; Hamaguchi, K.; Gull, T. R.

2008-01-01

301

X-ray emission from galaxies - The distribution of low-luminosity X-ray sources in the Galactic Centre region  

NASA Astrophysics Data System (ADS)

We report a study of the extended X-ray emission observed in the Galactic Centre (GC) region based on archival XMM-Newton data. The GC diffuse emission can be decomposed into three distinct components: the emission from low-luminosity point sources; the fluorescence of (and reflection from) dense molecular material; and soft (kT ~1 keV), diffuse thermal plasma emission most likely energised by supernova explosions. Here, we examine the emission due to unresolved point sources. We show that this source component accounts for the bulk of the 6.7-keV and 6.9-keV line emission. We fit the surface brightness distribution evident in these lines with an empirical 2-d model, which we then compare with a prediction derived from a 3-d mass model for the old stellar population in the GC region. We find that the X-ray surface brightness declines more rapidly with angular offset from Sgr A* than the mass-model prediction. One interpretation is that the X-ray luminosity per solar mass characterising the GC source population is increasing towards the GC. Alternatively, some refinement of the mass-distribution within the nuclear stellar disc may be required. The unresolved X-ray source population is most likely dominated by magnetic CVs. We use the X-ray observations to set constraints on the number density of such sources in the GC region. Our analysis does not support the premise that the GC is pervaded by very hot (~ 7.5 keV) thermal plasma, which is truly diffuse in nature.

Heard, Victoria; Warwick, Robert

2012-09-01

302

X-Ray Emission from the Wolf-Rayet Bubble S 308  

NASA Astrophysics Data System (ADS)

The Wolf-Rayet (WR) bubble S 308 around the WR star HD 50896 is one of the only two WR bubbles known to possess X-ray emission. We present XMM-Newton observations of three fields of this WR bubble that, in conjunction with an existing observation of its northwest quadrant, map most of the nebula. The X-ray emission from S 308 displays a limb-brightened morphology, with a central cavity ~22' in size and a shell thickness of ~8'. This X-ray shell is confined by the optical shell of ionized material. The spectrum is dominated by the He-like triplets of N VI at 0.43 keV and O VII at 0.57 keV, and declines toward high energies, with a faint tail up to 1 keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T 1 ~ 1.1 × 106 K, T 2 ~ 13 × 106 K), with a total X-ray luminosity ~2 × 1033 erg s-1 at the assumed distance of 1.5 kpc. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA.

Toalá, J. A.; Guerrero, M. A.; Chu, Y.-H.; Gruendl, R. A.; Arthur, S. J.; Smith, R. C.; Snowden, S. L.

2012-08-01

303

Charge Exchange Induced X-Ray Emission of Fe XXVI and Fe XXV  

NASA Astrophysics Data System (ADS)

Charge exchange is a vital process to consider in the modeling of X-ray spectra obtained by the Chandra, XMM Newton and Suzaku X-ray Space Observatories. The process is largely relevant in many astrophysical environments including comets (whose emission is primarily a product of charge exchange alone), the heliosphere, astropheres of stars, supernova remnants, the Galactic Center and the Galactic Ridge. The understanding of the X-ray spectra produced by these environments is crippled by the current lack of atomic and molecular data- especially for charge exchange. Here, we apply the Landau-Zener method to calculate total, n-resolved, n?-resolved and S-resolved cross sections for Fe26+ and Fe25+ collisions with H, He, H2, N2, H2O and CO. Using this data in a cascade model for X-ray emission, theoretical spectra for each system are predicted. The resulting spectra are then compared to experimental data for Fe26+ and Fe25+ collisions with N2. Fe XXVI and Fe XXV have been selected for study as iron emission lines have been detected in the galactic plane. Further, these systems illustrate computational difficulties for high projectile charges. In the Landau-Zener calculations, several ?-distribution models have been tested for the electron capture by the bare ion, Fe26+. Quantum defect methods are also employed to estimate excitation energies and transition probabilities for high-lying Rydberg levels of the He-like Fe24+.

Mullen, Patrick Dean; Cumbee, Renata; Lyons, David; Stancil, Phillip C.; B. J. Wargelin

2015-01-01

304

Detection of X-ray Emission From Galaxies Inside The Bootes Void  

NASA Technical Reports Server (NTRS)

We report the x-ray properties of Bootes void galaxies detected by the ROSAT All-Sky Survey (RASS). By searching the fields of 26 radio and 27 emission-line-selected void galaxies, we have detected 9 x-ray emitting void galaxies at >2.7-sigma confidence level. Five of these 9 galaxies are in the IP,AS subsample. We expect 2 detections at the redshift of the Bootes void based on previous positional cross-correlation studies of the RASS and IRAS Point Source Catalogue sources. Three of the x-ray emitting galaxies are AGNs (IRAS14288+5255, Mrk845, and IRAS 15195+5050), and the remaining 6 are all likely emission line galaxies (PC1357+4641, CG547, CG922, IRAS14SOO+4804, CG637, and IRAS15092+3940). The far infrared flux levels of the AGN sources implies most of the observed x-ray emissivity is from starburst activity. We have carried out timing and spectral analysis for the narrow-line Seyfert 1 galaxy Mrk845. Poor statistics prevents detailed analysis of the remaining sources. only two galaxies in our sample, BHI 1514+3819 and FSS 1515+3823, were observed during ROSAT pointed observations resulting in a nondetection at the 1-sigma level.

Kim, Chulhee; Boller, Thomas; Ghosh, Kajal K.; Swartz, Douglas A.; Ramsey, Brian D.; Rose, M. Franklin (Technical Monitor)

2000-01-01

305

Detection of X-Ray Emission from Galaxies Inside the Bootes Void  

NASA Technical Reports Server (NTRS)

We report the X-ray properties of Bootes void galaxies detected by the ROSAT All-Sky Survey (RASS). By searching the fields of 26 radio and 27 emission-line-selected void galaxies, we have detected nine X-ray-emitting void galaxies at greater than 2.7 sigma confidence level. Five of these nine galaxies are in the IRAS subsample. Two of the IRAS galaxies were previously identified in positional cross-correlation studies of the RASS and IRAS Point Source Catalogue sources. Three of the X-ray-emitting galaxies are active galactic nuclei (AGNs; IRAS 14288+5255, Mrk 845, and IRAS 15195+5050), three are emission-line galaxies (PC 1357+4641, CG 547, and CG 922), and the remaining three are of unknown spectral type (IRAS 14500+4804, CG 637, and MAS 15092+3940). The far-infrared flux levels of the AGN sources imply that most of the observed X-ray emissivity is from starburst activity. We have carried out timing and spectral analysis for the Seyfert 1 galaxy Mrk 845. Poor statistics prevents detailed analysis of the remaining sources. Only two galaxies in our sample, BHI 1514+3819 and FSS 1515+3823, were observed during ROSAT pointed observations resulting in a nondetection at the 1 sigma level.

Kim, Chulhee; Boller, T.; Ghosh, K.; Swartz, Douglas A.; Ramsey, Brian D.

2001-01-01

306

Twenty-two emission-line AGNs from the HEAO-1 X-ray survey  

NASA Technical Reports Server (NTRS)

We report 22 emission-line AGN as bright, hard X-ray sources. All of them appear to be new classifications with the exception of one peculiar IRAS source which is a known quasar and has no published spectrum. This sample exhibits a rich diversity in optical spectral properties and luminosities, ranging from a powerful broad-absorption-line quasar to a weak nucleus embedded in a nearby NGC galaxy. Two cases confer X-ray luminosities in excess of 10 exp 47 erg/s. However, there is a degree of uncertainty in the X-ray identification for the AGN fainter than V about 16.5. Optically, several AGN exhibit very strong Fe II emission. One Seyfert galaxy with substantial radio flux is an exception to the common association of strong Fe II emission and radio-quiet AGN. The previously recognized IRAS quasar shows extreme velocities in the profiles of the forbidden lines; the 0 III pair is broadened to the point that the lines are blended. Several of these AGN show evidence of intrinsic obscuration, illustrating the effectiveness of hard X-ray surveys in locating AGN through high column density.

Remillard, R. A.; Bradt, H. V. D.; Brissenden, R. J. V.; Buckley, D. A. H.; Roberts, W.; Schwartz, D. A.; Stroozas, B. A.; Tuohy, I. R.

1993-01-01

307

RECONNECTION ELECTRIC FIELD AND HARDNESS OF X-RAY EMISSION OF SOLAR FLARES  

SciTech Connect

Magnetic reconnection is believed to be the prime mechanism that triggers solar flares and accelerates electrons up to energies of MeV. In the classical two-dimensional reconnection model, the separation motion of chromospheric ribbons, manifests the successive reconnection that takes place higher up in the corona. Meanwhile, downward traveling energetic electrons bombard the dense chromosphere and create hard X-ray (HXR) emissions, which provide a valuable diagnostic of electron acceleration. Analyses of ribbon dynamics and the HXR spectrum have been carried out separately. In this Letter, we report a study of the comparison of reconnection electric field measured from ribbon motion and hardness (spectral index) of X-ray emission derived from X-ray spectrum. Our survey of the maximum average reconnection electric field and the minimum overall spectral index for 13 two-ribbon flares shows that they are strongly anticorrelated. The former is also strongly correlated with flare magnitude measured using the peak flux of soft X-ray emissions. These provide strong support for electron acceleration models based on the electric field generated at reconnecting current sheet during flares.

Liu Chang; Wang Haimin [Space Weather Research Laboratory, Center for Solar-Terrestrial Research, New Jersey Institute of Technology, University Heights, Newark, NJ 07102 (United States)], E-mail: chang.liu@njit.edu, E-mail: haimin@flare.njit.edu

2009-05-01

308

The Heliospheric Contribution to the Soft X-ray Background Emission  

NASA Astrophysics Data System (ADS)

The soft X-ray background observed from Earth contains contributions not only from outside the solar system such as the local bubble but also contributions from within the solar system, including contributions from the interplanetary medium, from the terrestrial geocorona, and from the magnetosheath. Great effort was spent on removing non-cosmic contamination from data collected during the ROSAT all-sky survey. Some of the contamination is the X-ray emission produced from charge exchange of solar wind ions with interstellar and geocoronal neutral gas. The time-varying component of this contamination was removed for the ROSAT survey, but the steady-state component was not. In this chapter, we present ROSAT 1/4-keV and 3/4-keV band all-sky maps of the cosmic soft X-ray emission with the steady state heliospheric and geocoronal components removed via modeling procedures. These new determinations of the ``true'' cosmic background X-ray emission will allow a re-interpretation of the nature of the local hot bubble. In particular, the thermal pressure of the bubble gas must be about a factor of two less than the pressures deduced from the original ROSAT all-sky survey.

Robertson, Ina P.; Kuntz, Kip D.; Collier, Michael R.; Cravens, Thomas E.; Snowden, Steven L.

2009-08-01

309

The evolution of planetary nebulae. V. The diffuse X-ray emission  

NASA Astrophysics Data System (ADS)

Context: Observations with space-borne X-ray telescopes revealed the existence of soft, diffuse X-ray emission from the inner regions of planetary nebulae. Although the existing images support the idea that this emission arises from the hot shocked central-star wind which fills the inner cavity of a planetary nebula, existing models have difficulties to explain the observations consistently. Aims: We investigate how the inclusion of thermal conduction changes the physical parameters of the hot shocked wind gas and the amount of X-ray emission predicted by time-dependent hydrodynamical models of planetary nebulae with central stars of normal, hydrogen-rich surface composition. Methods: We upgraded our 1D hydrodynamics code NEBEL by to account for energy transfer due to heat conduction, which is of importance at the interface separating the hot shocked wind gas (“hot bubble”) from the much cooler nebular material. With this new version of NEBEL we recomputed a selection of our already existing hydrodynamical sequences and obtained synthetic X-ray spectra for representative models along the evolutionary tracks by means of the freely available CHIANTI package. Results: Heat conduction leads to lower temperatures and higher densities within a bubble and brings the physical properties of the X-ray emitting domain into close agreement with the values derived from observations. The amount of X-rays emitted during the course of evolution depends on the energy dumped into the bubble by the fast stellar wind, on the efficiency of “evaporating” cool nebular gas via heat conduction, and on the bubble's expansion rate. We find from our models that the X-ray luminosity of a planetary nebula increases during its evolution across the HR diagram until stellar luminosity and wind power decline. Depending on the central-star mass and the evolutionary phase, our models predict X-ray [ 0.45-2.5 keV] luminosities between 10-8 and 10-4 of the stellar bolometric luminosities, in good agreement with the observations. Less than 1% of the wind power is radiated away in this X-ray band. Although temperature, density, and also the mass of the hot bubble is significantly altered by heat conduction, the dynamics of the whole system remains practically the same. Conclusions: Heat conduction allows the construction of nebular models which predict the correct amount of X-ray emission and at the same time are fully consistent with the observed mass-loss rate and wind speed. Thermal conduction must be considered as a viable physical process for explaining the diffuse X-ray emission from planetary nebulae with closed inner cavities. Magnetic fields must then be absent or extremely weak. Dedicated to the memory of M. Perinotto, a dear friend and esteemed colleague who died unexpectedly and much too early on August 15, 2007.

Steffen, M.; Schönberner, D.; Warmuth, A.

2008-10-01

310

Proton-induced X-ray and gamma ray emission analysis of biological samples  

NASA Astrophysics Data System (ADS)

A 4.1 MeV external proton beam was employed to simultaneously induce X-ray emission (PIXE) and gamma ray emission (PIGE) in biological samples that included human colostrum, spermatozoa, teeth, tree-rings, and follicular fluids. The analytical method was developed to simultaneously determine the elements lithium (Z = 3) through uranium (Z = 92) in the samples. PIXE-PIGE experimental design is described as well as applications in environmental and medical fields.

Hall, Gene S.; Navon, Eliahu

1986-04-01

311

INTRAGROUP AND GALAXY-LINKED DIFFUSE X-RAY EMISSION IN HICKSON COMPACT GROUPS  

SciTech Connect

Isolated compact groups (CGs) of galaxies present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups (HCGs) observed with the Chandra X-Ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of vigourous star formation or activity in the galaxy nucleus, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the L{sub X} -T relationship from clusters within the errors, while HCGs 16 and 31 are consistent with the cluster L{sub X} -{sigma} relation, though this is likely coincidental given that the hot gas in these two systems is largely due to star formation. We find that L{sub X} increases with decreasing group H I to dynamical-mass ratio with tentative evidence for a dependence in X-ray luminosity on H I morphology whereby systems with intragroup H I indicative of strong interactions are considerably more X-ray luminous than passively evolving groups. We also find a gap in the L{sub X} of groups as a function of the total group specific star formation rate. Our findings suggest that the hot gas in these groups is not in hydrostatic equilibrium and these systems are not low-mass analogs of rich groups or clusters, with the possible exception of HCG 62.

Desjardins, Tyler D.; Gallagher, Sarah C. [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada)] [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada); Tzanavaris, Panayiotis; Hornschemeier, Ann E. [Laboratory for X-ray Astrophysics, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)] [Laboratory for X-ray Astrophysics, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Mulchaey, John S. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)] [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Brandt, William N.; Charlton, Jane C.; Garmire, Gordon P.; Gronwall, Caryl; Konstantopoulos, Iraklis S. [Department of Astronomy and Astrophysics, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802 (United States)] [Department of Astronomy and Astrophysics, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802 (United States); Johnson, Kelsey E. [Department of Astronomy, University of Virginia, P.O. Box 3813, Charlottesville, VA 22904 (United States)] [Department of Astronomy, University of Virginia, P.O. Box 3813, Charlottesville, VA 22904 (United States); Zabludoff, Ann I., E-mail: tdesjar@uwo.ca [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 95721 (United States)

2013-02-15

312

Intragroup and Galaxy-linked Diffuse X-ray Emission In Hickson Compact Groups  

NASA Technical Reports Server (NTRS)

Isolated compact groups (CGs) of galaxies present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups (HCGs) observed with the Chandra X-Ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of vigourous star formation or activity in the galaxy nucleus, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the L(sub X-Tau) relationship from clusters within the errors, while HCGs 16 and 31 are consistent with the cluster L(sub X-sigma) relation, though this is likely coincidental given that the hot gas in these two systems is largely due to star formation. We find that L(sub X) increases with decreasing group Hi to dynamical-mass ratio with tentative evidence for a dependence in X-ray luminosity on Hi morphology whereby systems with intragroup Hi indicative of strong interactions are considerably more X-ray luminous than passively evolving groups. We also find a gap in the L(sub X) of groups as a function of the total group specific star formation rate. Our findings suggest that the hot gas in these groups is not in hydrostatic equilibrium and these systems are not low-mass analogs of rich groups or clusters, with the possible exception of HCG 62.

Desjardins, Tyler D.; Gallagher, Sarah C.; Tzanavaris, Panayiotis; Mulchaey, John S.; Brandt, William N.; Charlton, Jane C.; Garmire, Gordon P.; Gronwall, Caryl; Cardiff, Ann; Johnson, Kelsey E.; Konstantopoulos, Iraklis, S.; Zabludoff, Ann I.

2013-01-01

313

Non-Detection of X-Ray Emission From Sterile Neutrinos in Stacked Galaxy Spectra  

E-print Network

We conduct a comprehensive search for X-ray emission lines from sterile neutrino dark matter, motivated by recent claims of unidentified emission lines in the stacked X-ray spectra of galaxy clusters and the centers of the Milky Way and M31. Since the claimed emission lines lie around 3.5 keV, we focus on galaxies and galaxy groups (masking the central regions), since these objects emit very little radiation above ~2 keV and offer a clean background against which to detect emission lines. We develop a formalism for maximizing the signal-to-noise of sterile neutrino emission lines by weighing each X-ray event according to the expected dark matter profile. In total, we examine 81 and 89 galaxies with Chandra and XMM-Newton respectively, totaling 15.0 and 14.6 Ms of integration time. We find no significant evidence of any emission lines, placing strong constraints on the mixing angle of sterile neutrinos with masses between 4.8-12.4 keV. In particular, if the 3.57 keV feature from Bulbul et al. (2014) were due t...

Anderson, Michael E; Bregman, Joel N

2014-01-01

314

The X-ray eclipse of OY Car resolved with XMM-Newton: X-ray emission from the polar regions of the white dwarf  

E-print Network

We present the XMM-Newton X-ray eclipse lightcurve of the dwarf nova OY Car. The eclipse ingress and egress are well resolved for the first time in any dwarf nova placing strong constraints on the size and location of the X-ray emitting region. We find good fits to a simple linear eclipse model, giving ingress/egress durations of 30+/-3 sec. Remarkably this is shorter than the ingress/egress duration of the sharp eclipse in the optical as measured by Wood et al. (1989) and ascribed to the white dwarf (43+/-2 sec). We also find that the X-ray eclipse is narrower than the optical eclipse by 14+/-2 sec, which is precisely the difference required to align the second and third contact points of the X-ray and optical eclipses. We discuss these results and conclude that X-ray emission in OY Car most likely arises from the polar regions of the white dwarf. Our data were originally reported by Ramsay et al (2001), but they did not make a quantitative measurement of eclipse parameters. We have also corrected important timing anomalies present in the data available at that time.

Peter J. Wheatley; Richard G. West

2003-07-24

315

Synchrotron radiation based micro X-ray fluorescence analysis of the calibration samples used in surface sensitive total reflection and grazing emission X-ray fluorescence techniques  

NASA Astrophysics Data System (ADS)

Total reflection X-ray fluorescence (TXRF) and grazing emission X-ray fluorescence (GEXRF) are surface sensitive techniques and can be used for detailed surface studies of different materials, including ultra-low concentration contamination or the lateral and depth distributions of elements. The calibration procedure typically used involves placing a micro-droplet (˜?l) of the standard solution onto a silicon wafer (or quartz backing). After evaporation of the solvent, the residual amount of elements is used as a reference standard. Knowledge of the distribution of residue material on the substrate surface is crucial for precise quantification. In the present work the investigation of the lateral distribution of elements in the multielemental calibrating samples, containing the 23 most commonly studied elements, by using the synchrotron radiation based micro X-ray fluorescence is presented. The goal of this project was the study of a uniformity of the elemental distributions and determination of the residual elements morphology depending on the temperature of the drying process. The X-ray images were compared with optical and SEM images. Paper presents in details the experimental setup, sample preparation procedures, measurements and results. In the analysis of the X-ray images of the sample dried in high temperature the censoring approach was applied improving the quality of statistical analysis. The information on the elements distribution in the calibrating samples can be useful for developing more accurate calibration procedures applied in quantitative analysis of surface sensitive TXRF and GEXRF techniques.

Kubala-Kuku?, A.; Bana?, D.; Pajek, M.; Szlachetko, J.; Jagodzi?ski, P.; Susini, J.; Salomé, M.

2013-12-01

316

Making use of x-ray optical effects in photoelectron-, Auger electron-, and x-ray emission spectroscopies: Total reflection, standing-wave excitation, and resonant effects  

SciTech Connect

We present a general theoretical methodology and related open-access computer program for carrying out the calculation of photoelectron, Auger electron, and x-ray emission intensities in the presence of several x-ray optical effects, including total reflection at grazing incidence, excitation with standing-waves produced by reflection from synthetic multilayers and at core-level resonance conditions, and the use of variable polarization to produce magnetic circular dichroism. Calculations illustrating all of these effects are presented, including in some cases comparisons to experimental results. Sample types include both semi-infinite flat surfaces and arbitrary multilayer configurations, with interdiffusion/roughness at their interfaces. These x-ray optical effects can significantly alter observed photoelectron, Auger, and x-ray intensities, and in fact lead to several generally useful techniques for enhancing surface and buried-layer sensitivity, including layer-resolved densities of states and depth profiles of element-specific magnetization. The computer program used in this study should thus be useful for a broad range of studies in which x-ray optical effects are involved or are to be exploited in next-generation surface and interface studies of nanoscale systems.

Yang, S.-H. [IBM Almaden Research Center, San Jose, California 95120 (United States); Gray, A. X. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94740 (United States); Department of Physics, University of California at Davis, Davis, California 95616 (United States); Stanford Institute for Materials and Energy Science, Stanford University and SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Kaiser, A. M. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94740 (United States); Department of Physics, University of California at Davis, Davis, California 95616 (United States); Peter Grunberg Institute, PGI-6, Forschungszentrum Juelich, 52425 Juelich (Germany); Mun, B. S. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Department of Applied Physics, Hanyang University, Ansan, Gyeonggi 426-791 (Korea, Republic of); Sell, B. C. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94740 (United States); Department of Physics, University of California at Davis, Davis, California 95616 (United States); Department of Physics, Otterbein College, Westerville, Ohio 43081 (United States); Kortright, J. B. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94740 (United States); Fadley, C. S. [Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94740 (United States); Department of Physics, University of California at Davis, Davis, California 95616 (United States)

2013-02-21

317

EVIDENCE FOR ELEVATED X-RAY EMISSION IN LOCAL LYMAN BREAK GALAXY ANALOGS  

SciTech Connect

Our knowledge of how X-ray emission scales with star formation at the earliest times in the universe relies on studies of very distant Lyman break galaxies (LBGs). In this paper, we study the relationship between the 2-10 keV X-ray luminosity (L{sub X}), assumed to originate from X-ray binaries (XRBs), and star formation rate (SFR) in ultraviolet (UV) selected z < 0.1 Lyman break analogs (LBAs). We present Chandra observations for four new Galaxy Evolution Explorer selected LBAs. Including previously studied LBAs, Haro 11 and VV 114, we find that LBAs demonstrate L{sub X}/SFR ratios that are elevated by {approx}1.5{sigma} compared to local galaxies, similar to the ratios found for stacked LBGs in the early universe (z > 2). Unlike some of the composite LBAs studied previously, we show that these LBAs are unlikely to harbor active galactic nuclei, based on their optical and X-ray spectra and the spatial distribution of the X-rays in three spatially extended cases. Instead, we expect that high-mass X-ray binaries (HMXBs) dominate the X-ray emission in these galaxies, based on their high specific SFRs (sSFRs {identical_to} SFR/M{sub *} {>=} 10{sup -9} yr{sup -1}), which suggest the prevalence of young stellar populations. Since both UV-selected populations (LBGs and LBAs) have lower dust attenuations and metallicities compared to similar samples of more typical local galaxies, we investigate the effects of dust extinction and metallicity on the L{sub X}/SFR for the broader population of galaxies with high sSFRs (>10{sup -10} yr{sup -1}). The estimated dust extinctions (corresponding to column densities of N{sub H} < 10{sup 22} cm{sup -2}) are expected to have insignificant effects on observed L{sub X}/SFR ratio for the majority of galaxy samples. We find that the observed relationship between L{sub X}/SFR and metallicity appears consistent with theoretical expectations from XRB population synthesis models. Therefore, we conclude that lower metallicities, related to more luminous HMXBs such as ultraluminous X-ray sources, drive the elevated L{sub X}/SFR observed in our sample of z < 0.1 LBAs. The relatively metal-poor, active mode of star formation in LBAs and distant z > 2 LBGs may yield higher total HMXB luminosity than found in typical galaxies in the local universe.

Basu-Zych, Antara R.; Lehmer, Bret D.; Hornschemeier, Ann E.; Ptak, Andrew F. [NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Goncalves, Thiago S. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antonio 43, Saude, Rio de Janeiro-RJ, CEP 22240-060 (Brazil); Fragos, Tassos [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Heckman, Timothy M. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Overzier, Roderik A. [Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States); Schiminovich, David, E-mail: antara.r.basu-zych@nasa.gov [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)

2013-09-10

318

Soft X-ray emissions of Si IX in Procyon  

E-print Network

An analysis of $n=3 \\to 2$ transition lines of carbon-like silicon reveals that some ratios of line intensities are sensitive to the electron density. The ratio between two group of $3d\\to2p$ transition lines at 55.246 \\AA and 55.346 \\AA is a good $n_{\\rm e}$-diagnostic technique, due to its insensitivity to the electron temperature. Using this property, a lower limit of the density of 0.6$\\times10^8$cm$^{-3}$ is derived for Procyon, which is consistent with that constrained by C V and Si X emissions. Significant discrepancies in ratios of $3s\\to2p$ lines to $3d\\to2p$ lines between theoretical predictions and observed values, are found, by the spectral analysis of Procyon observed with the {\\it Chandra} High Resolution Transmission Grating spectra. The difference exceeding a factor of 3, cannot be explained by the uncertainty of atomic data. The opacity effect is also not a choice as reported by Ness and co-workers. For the $3s\\to2p$ line at 61.611 \\AA, present work indicates that the large discrepancy may be due to the contamination from a S VIII line at 61.645 \\AA . For the lines at 61.702 and 61.846 \\AA, we suggest that the discrepancies may be attributed to contaminations of unknown lines.

Guiyun Liang; Gang Zhao

2006-08-07

319

Shock-generated X-ray emission in radiatively driven winds - A model for Tau Scorpii  

NASA Technical Reports Server (NTRS)

A one-dimensional radiation-hydrodynamics code is used to numerically investigate the structure and evolution of shocks in the winds of hot stars. Results are presented for the specific case of Tau Sco, a well-studied main-sequence B star for which there are X-ray data from the Einstien satellite's Solid State Spectrometer. A phenomenological radiative acceleration term and a mass-loss rate consistent with UV observations, are used to determine the time dependence of the temperatures within and X-ray emission from an isolated shock region. The driving acceleration leads to the formation of a two-component shock zone with 'forward' and 'reverse' shocks, each with their own characteristic temperature. A denser cold region forms between the two shocks, which could potentially account for the presence of narrow absorption features that are observed in the UV P Cygni profiles of many hot stars. The X-ray emission spectra from the shocks in the calculations are in good general agreement with two-temperature model fits to Einstein X-ray observations.

Macfarlane, Joseph J.; Cassinelli, Joseph P.

1989-01-01

320

Revealing the hitherto hidden X-ray emission from shell-type supernova remnant Kes 32  

NASA Astrophysics Data System (ADS)

I will show results from Chandra ACIS-I observations of Kes 32 (G332.+0.1). A supernova remnant of 8arcmin size, that has never been imaged in X-rays before, largely as it was too obscured at low energies, and is situated in a complex region of the galaxy. Chandra reveals that the X-ray morphology is similar to the radio morphology, although the shell seems to have a slightly smaller radius than indicated by the radio map. The X-ray spectrum, although of poor quality, does reveal strong Silicon, Sulfur, and Argon lines, proving that the emission is at least partially described by thermal emission. Both its morphology and spectrum therefore suggest that this object is an older version of a typical shell-type remnant like Cas A. This work is supported by the NASA through Chandra Postdoctoral Fellowship Award Number PF0-10011 and by Chandra Award GO1-2059X issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-39073.

Vink, J.

2003-03-01

321

Thermal disc emission from a rotating black hole: X-ray polarization signatures  

NASA Astrophysics Data System (ADS)

Thermal emission from the accretion disc around a black hole can be polarized, due to Thomson scattering in a disc atmosphere. In Newtonian space, the polarization angle must be either parallel or perpendicular to the projection of the disc axis on the sky. As first pointed out by Stark and Connors in 1977, General Relativity effects strongly modify the polarization properties of the thermal radiation as observed at infinity. Among these effects, the rotation of the polarization angle with energy is particularly useful as a diagnostic tool. In this paper, we extend the Stark and Connors calculations by including the spectral hardening factor, several values of the optical depth of the scattering atmosphere and rendering the results to the expected performances of planned X-ray polarimeters. In particular, to assess the perspectives for the next generation of X-ray polarimeters, we consider the expected sensitivity of the detectors on board the planned POLARIX and International X-ray Observatory missions. We assume the two cases of a Schwarzschild and an extreme Kerr black hole with a standard thin disc and a scattering atmosphere. We compute the expected polarization degree and the angle as functions of the energy as they could be measured for different inclinations of the observer, optical thickness of the atmosphere and different values of the black hole spin. We assume the thermal emission dominates the X-ray band. Using the flux level of the microquasar GRS 1915+105 in the thermal state, we calculate the observed polarization.

Dov?iak, M.; Muleri, F.; Goosmann, R. W.; Karas, V.; Matt, G.

2008-11-01

322

High-sensitivity search for transient solar X-ray emission with NuSTAR  

NASA Astrophysics Data System (ADS)

We present the first results of a search for transient X-ray emission in quiet solar regions with the NuSTAR astrophysics satellite. Transient brightenings of 1024-1027 ergs, or "nanoflares," have been observed as thermal emission in EUV and soft X-rays, but never in hard X-rays (HXRs) due to lack of sensitivity. Frequent nanoflares could account for a significant fraction of the energy release needed to heat the corona to >1 MK. NuSTAR directly images X-rays from ~2-80 keV, with much higher sensitivity than dedicated solar HXR instruments. More importantly it can point at the Sun without suffering damage, a rare capability for an astrophysics instrument. We have developed an algorithm to search the NuSTAR data in space and time for transient events, while taking into account instrumental and systematic effects. Preliminary analysis yields a sensitivity to events ~0.001 times as bright as an “typical” RHESSI microflare (Hannah et al. 2008), for linear scaling and event duration of 10 seconds. Future observations at full-Sun flux levels below GOES ~B5 will increase our sensitivity by an order of magnitude or more.

Marsh, Andrew; Hannah, Iain; Glesener, Lindsay; Smith, David M.; Grefenstette, Brian; Madsen, Kristin; Krucker, Sam; Hudson, Hugh; White, Stephen; Caspi, Amir; Christe, Steven; Shih, Albert; Mewaldt, Richard; Pivovaroff, Michael; Vogel, Julia

2015-04-01

323

Chandra detection of extended X-ray emission from the recurrent nova RS Ophiuchi  

E-print Network

Radio, infrared, and optical observations of the 2006 eruption of the symbiotic recurrent nova RS Ophiuchi (RS Oph) showed that the explosion produced non-spherical ejecta. Some of this ejected material was in the form of bipolar jets to the east and west of the central source. Here we describe Xray observations taken with the Chandra X-ray Observatory one and a half years after the beginning of the outburst that reveal narrow, extended structure with a position angle of approximately 300 degrees (east of north). Although the orientation of the extended feature in the X-ray image is consistent with the readout direction of the CCD detector, extensive testing suggests that the feature is not an artifact. Assuming it is not an instrumental effect, the extended X-ray structure shows hot plasma stretching more than 1,900 AU from the central binary (taking a distance of 1.6 kpc). The X-ray emission is elongated in the northwest direction - in line with the extended infrared emission and some minor features in the ...

Luna, G J M; Sokoloski, J L; Mukai, K; Kästner, J H

2009-01-01

324

Discovery of X-ray and Extreme Ultraviolet Emission from Comet C\\/Hyakutake 1996 B2  

Microsoft Academic Search

During its close approach to Earth, comet C\\/Hyakutake 1996 B2 was observed at extreme ultraviolet and x-ray wavelengths with the Rontgen X-ray Satellite and Rossi X-ray Timing Explorer. The emission morphology was symmetric with respect to a vector from the comet's nucleus toward the sun, but not symmetric around the direction of motion of the comet with respect to interplanetary

C. M. Lisse; K. Dennerl; J. Englhauser; M. Harden; F. E. Marshall; M. J. Mumma; R. Petre; J. P. Pye; M. J. Ricketts; J. Schmitt; J. Trumper; R. G. West

1996-01-01

325

X-ray emission from an adolescent classical T Tauri star  

NASA Astrophysics Data System (ADS)

We propose to perform high-resolution X-ray spectroscopy of MP Muscae, a classical T Tauri star with an age of about 10 Myr, and hence quite old for its class. In fact, MP Mus is the only known star of this age with evidence of an accretion disk, found in a survey of the Lower Centaurus-Crux subgroup in the Scorpius- Centaurus association. Moreover, this star also shows evidence of a cold dusty disk, as indicated by excess emission at IR and mm wavelengths. The proposed observation will allow us to address several issues concerning the evolution of the X-ray emission in pre-main-sequence stars, the mechanism(s) of such emission, the element abundances of the emitting plasma, and the influence of high-energy radiation on the surrounding medium where planetary formation is likely occurring.

Maggio, Antonio

2005-10-01

326

Search for X-Ray Emission in the Nearest Known Brown Dwarf  

NASA Technical Reports Server (NTRS)

The XMM observation were obtained on 2001 January 07-08 for 51767 s. The Optical Monitor (OM) was used with the V filter for 4 exposures of 5000 s each in imaging mode. We used the data given by the OM to confirm the presence of the source in the field of view. The European Photon Imaging Camera (EPIC) MOS 1 and MOS2 were used 48724 s each in prime full window mode with 2.5 s time resolution. The EPIC PN was used 46618 s in prime full window mode with 73.4 ms time resolution. The X-ray source closest to the expected position of our target is offset by delta R.A=2.5 arcsec and delta Dec=-28.37 arcsec. This offset is high in comparison with the 0.4 arcsec observed with the optical data. So at this point we already knew that the target was not detected. To confirm that conclusion, we performed the identification of all X-ray sources in the field of view by comparing source to source our image with the one obtained by Rutledge et al. with Chandra. This allowed us to identify all the X-ray sources in our field of view in an area of 20 arcsec times 10 arcsec centered on the expected coordinates of LP944-20. We were then able to conclude that the target was not detected during this observation. This result allowed us to determine a new and better 3 sigma upper limit of X-Ray emission for this object. We have also derived duty cycles for X-ray flares as a function of X-ray luminosity by comparing the XMM data with Chandra and ROSAT data. One student has been supported with the grant during four months (Herve Bouy). A Sun workstation was purchased for him.

Martin, Eduardo

2003-01-01

327

Using Poisson statistics to analyze supernova remnant emission in the low counts X-ray regime  

NASA Astrophysics Data System (ADS)

We utilize a Poisson likelihood in a maximum likelihood statistical analysis to analyze X-ray spectragraphic data. Specifically, we examine four extragalactic supernova remnants (SNR). IKT 5 (SNR 0047-73.5), IKT 25 (SNR 0104-72.3), and DEM S 128 (SNR 0103-72.4) which are designated as Type Ia in the literature due to their spectra and morphology. This is troublesome because of their asymmetry, a trait not usually associated with young Type Ia remnants. We present Chandra X-ray Observatory data on these three remnants, and perform a maximum likelihood analysis on their spectra. We find that the X-ray emission is dominated by interactions with the interstellar medium. In spite of this, we find a significant Fe overabundance in all three remnants. Through examination of radio, optical, and infrared data, we conclude that these three remnants are likely not "classical" Type Ia SNR, but may be examples of so-called "prompt" Type Ia SNR. We detect potential point sources that may be members of the progenitor systems of both DEM S 128 and IKT 5, which could suggest a new subclass of prompt Type Ia SNR, Fe-rich CC remnants. In addition, we examine IKT 18. This remnant is positionally coincident with the X-ray point source HD 5980. Due to an outburst in 1994, in which its brightness changed by 3 magnitudes (corrsponding to an increase in luminosity by a factor of 16) HD 5980 was classified as a luminous blue variable star. We examine this point source and the remnant IKT 18 in the X-ray, and find that its non-thermal photon index has decreased from 2002 to 2013, corresponding to a larger proportion of more energetic X-rays, which is unexpected.

Roper, Quentin Jeffrey

328

Chandra Observations of Extended X-Ray Emission in ARP 220  

NASA Technical Reports Server (NTRS)

We resolve the extended X-ray emission from the prototypical ultraluminous infrared galaxy Arp 220. Extended, faint, edge-brightened, soft X-ray lobes outside the optical galaxy are observed to a distance of 1CL 15 kpc on each side of the nuclear region. Bright plumes inside the optical isophotes coincide with the optical line emission and extend 1 1 kpc from end to end across the nucleus. The data for the plumes cannot be fitted by a single-temperature plasma and display a range of temperatures from 0.2 to 1 keV. The plumes emerge from bright, diffuse circumnuclear emission in the inner 3 kpc centered on the Ha peak, which is displaced from the radio nuclei. There is a close morphological correspondence between the Ha and soft X-ray emission on all spatial scales. We interpret the plumes as a starburst-driven superwind and discuss two interpretations of the emission from the lobes in the context of simulations of the merger dynamics of Arp 220.

McDowell, J. C.; Clements, D. L.; Lamb, S. A.; Shaked, S.; Hearn, N. C.; Colina, L.; Mundell, C.; Borne, K.; Baker, A. C.; Arribas, S.

2003-01-01

329

X-Ray Emission from Supernovae in Dense Circumstellar Matter Environments: A Search for Collisionless Shock  

NASA Technical Reports Server (NTRS)

The optical light curve of some supernovae (SNe) may be powered by the outward diffusion of the energy deposited by the explosion shock (so-called shock breakout) in optically thick (tau approx > 30) circumstellar matter (CSM). Recently, it was shown that the radiation-mediated and -dominated shock in an optically thick wind must transform into 8. collisionless shock and can produce hard X-rays. The X-rays are expected to peak at late times, relative to maximum visible light. Here we report on a search, using Swift-XRT and Chandra, for X-ray emission from 28 SNe that belong to classes whose progenitors are suspected to be embedded in dense CSM. Our sample includes 19 type-IIn SNe, one type-Ibn SN and eiht hydrogen-poor super-luminous SNe (SLSN-I; SN 2005ap like). Two SNe (SN 2006jc and SN 2010jl) have X-ray properties that are roughly consistent with the expectation for X-rays from a collisionless shock in optically thick CSl\\l. Therefore, we suggest that their optical light curves are powered by shock breakout in CSM. We show that two other events (SN 2010al and SN 2011ht) were too X-ray bright during the SN maximum optical light to be explained by the shock breakout model. We conclude that the light curves of some, but not all, type-IIn/Ibn SNe are powered by shock breakout in CSM. For the rest of the SNe in our sample, including all the SLSN-I events, our X-ray limits are not deep enough and were typically obtained at too early times (i.e., near the SN maximum light) to conclude about their nature. Late time X-ray observations are required in order to further test if these SNe are indeed embedded in dense CSM. We review the conditions required for a shock breakOut in a wind profile. We argue that the time scale, relative to maximum light, for the SN to peak in X-rays is a probe of the column density and the density profile above the shock region. The optical light curves of SNe, for which the X-ray emission peaks at late times, are likely powered by the diffusion of shock energy from a dense CSM. We note that if the CSM density profile falls faster than a constant-rate wind density profile, then X-rays may escape at earlier times than estimated for the wind profile case. Furthermore, if the CSM have a region in which the density profile is very steep, relative to a steady wind density profile, or the CSM is neutral, then the radio free-free absorption may be low enough, and radio emission may be detected.

Ofek, E.O; Fox, D.; Cenko, B.; Sullivan, M.; Gnat, O.; Frail A.; Horesh, A.; Corsi, A; Quimby, R. M.; Gehrels, N.; Kulkarni, S. R.; Gal-Yam, A.; Nugent, P. E.; Yaron, O.; Filippenko, A. V.; Kasliwal, M. M.; Bildsten, L.; Bloom, J. S.; Poznanski, D; Arcavi, L.; Laher, R. R.; Levitan, D.; Sesar, B.; Surace, J.

2012-01-01

330

Possible Charge-Exchange X-Ray Emission in the Cygnus Loop Detected with Suzaku  

NASA Technical Reports Server (NTRS)

X-ray spectroscopic measurements of the Cygnus Loop supernova remnant indicate that metal abundances throughout most of the remnant s rim are depleted to approx.0.2 times the solar value. However, recent X-ray studies have revealed in some narrow regions along the outermost rim anomalously "enhanced" abundances (up to approx. 1 solar). The reason for these anomalous abundances is not understood. Here, we examine X-ray spectra in annular sectors covering nearly the entire rim of the Cygnus Loop using Suzaku (21 pointings) and XMM-Newton (1 pointing). We find that spectra in the "enhanced" abundance regions commonly show a strong emission feature at approx.0.7 keV. This feature is likely a complex of He-like O K(gamma + delta + epsilon), although other possibilities cannot be fully excluded. The intensity of this emission relative to He-like O K(alpha) appears to be too high to be explained as thermal emission. This fact, as well as the spatial concentration of the anomalous abundances in the outermost rim, leads us to propose an origin from charge-exchange processes between neutrals and H-like O. We show that the presence of charge-exchange emission could lead to the inference of apparently "enhanced" metal abundances using pure thermal emission models. Accounting for charge-exchange emission, the actual abundances could be uniformly low throughout the rim. The overall abundance depletion remains an open question. Subject headings: ISM: abundances ISM: individual objects (Cygnus Loop) ISM: supernova remnants X-rays: ISM atomic processes

Katsuda, Satoru; Tsunemi, Hiroshi; Mori, Koji; Uchida, Hiroyuki; Kosugi, Hiroko; Kimura, Masashi; Nakajima, Hiroshi; Takakura, Satoru; Petre, Robert; Hewitt. John W.; Yamaguchi, Hiroya

2011-01-01

331

Suzaku Observations of the Diffuse X-Ray Emission across the Fermi Bubbles' Edges  

NASA Astrophysics Data System (ADS)

We present Suzaku X-ray observations along two edge regions of the Fermi Bubbles, with eight ~= 20 ks pointings across the northern part of the North Polar Spur (NPS) surrounding the north bubble and six across the southernmost edge of the south bubble. After removing compact X-ray features, diffuse X-ray emission is clearly detected and is well reproduced by a three-component spectral model consisting of unabsorbed thermal emission (temperature kT ~= 0.1 keV) from the Local Bubble, absorbed kT ~= 0.3 keV thermal emission related to the NPS and/or Galactic halo (GH), and a power-law component at a level consistent with the cosmic X-ray background. The emission measure (EM) of the 0.3 keV plasma decreases by ~= 50% toward the inner regions of the northeast bubble, with no accompanying temperature change. However, such a jump in the EM is not clearly seen in the south bubble data. While it is unclear whether the NPS originates from a nearby supernova remnant or is related to previous activity within or around the Galactic center, our Suzaku observations provide evidence that suggests the latter scenario. In the latter framework, the presence of a large amount of neutral matter absorbing the X-ray emission as well as the existence of the kT ~= 0.3 keV gas can be naturally interpreted as a weak shock driven by the bubbles' expansion in the surrounding medium, with velocity v exp ~ 300 km s-1 (corresponding to shock Mach number {M} \\simeq 1.5), compressing the GH gas to form the NPS feature. We also derived an upper limit for any non-thermal X-ray emission component associated with the bubbles and demonstrate that, in agreement with the aforementioned findings, the non-thermal pressure and energy estimated from a one-zone leptonic model of its broadband spectrum, are in rough equilibrium with that of the surrounding thermal plasma.

Kataoka, J.; Tahara, M.; Totani, T.; Sofue, Y.; Stawarz, ?.; Takahashi, Y.; Takeuchi, Y.; Tsunemi, H.; Kimura, M.; Takei, Y.; Cheung, C. C.; Inoue, Y.; Nakamori, T.

2013-12-01

332

Accretion and Outflows in X-ray Binaries: What's Really Going on During X-ray Quiescence  

NASA Astrophysics Data System (ADS)

X-ray binaries, consisting of a star and a stellar-mass black hole, are wonderful laboratories for studying accretion and outflows. They evolve on timescales quite accessible to us, unlike their supermassive cousins, and allow the possibility of gaining a deeper understanding of these two common astrophysical processes. Different wavelength regimes reveal different aspects of the systems: radio emission is largely generated by outflows and jets, X-ray emission by inner accretion flows, and optical/infrared (OIR) emission by the outer disk and companion star. The search for relationships between these different wavelengths is thus an area of active research, aiming to reveal deeper connections between accretion and outflows.Initial evidence for a strong, tight correlation between radio and X-ray emission has weakened as further observations and newly-discovered sources have been obtained. This has led to discussions of multiple tracks or clusters, or the possibility that no overall relation exists for the currently-known population of X-ray binaries. Our ability to distinguish among these options is hampered by a relative lack of observations at lower luminosities, and especially of truly X-ray quiescent (non-outbursting) systems. Although X-ray binaries spend the bulk of their existence in quiescence, few quiescent sources have been observed and multiple observations of individual sources are largely nonexistent. Here we discuss new observations of the lowest-luminosity quiescent X-ray binary, A0620-00, and the place this object occupies in investigations of the radio/X-ray plane. For the first time, we also incorporate simultaneous OIR data with the radio and X-ray data.In December 2013 we took simultaneous observations of A0620-00 in the X-ray (Chandra), the radio (EVLA), and the OIR (SMARTS 1.3m). These X-ray and radio data allowed us to investigate similarities among quiescent X-ray binaries, and changes over time for this individual object, in the radio/X-ray plane. In addition, our OIR observations allowed us to examine the radio and X-ray information in relation to the different OIR states of behavior (passive and active) known to exist during X-ray quiescence.

MacDonald, Rachel K. D.; Bailyn, Charles D.; Buxton, Michelle

2015-01-01

333

A von Hamos x-ray spectrometer based on a segmented-type diffraction crystal for single-shot x-ray emission spectroscopy and time-resolved resonant inelastic x-ray scattering studies  

SciTech Connect

We report on the design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry. The spectrometer is equipped with a segmented-type crystal for x-ray diffraction and provides an energy resolution in the order of 0.25 eV and 1 eV over an energy range of 8000 eV-9600 eV. The use of a segmented crystal results in a simple and straightforward crystal preparation that allows to preserve the spectrometer resolution and spectrometer efficiency. Application of the spectrometer for time-resolved resonant inelastic x-ray scattering and single-shot x-ray emission spectroscopy is demonstrated.

Szlachetko, J. [Paul Scherrer Institut, 5232 Villigen PSI (Switzerland); Institute of Physics, Jan Kochanowski University, 25-406 Kielce (Poland); Nachtegaal, M.; Boni, E. de; Willimann, M.; Safonova, O.; Sa, J.; Smolentsev, G.; Szlachetko, M.; Bergamaschi, A.; Schmitt, B.; David, C.; Luecke, A. [Paul Scherrer Institut, 5232 Villigen PSI (Switzerland); Bokhoven, J. A. van [Paul Scherrer Institut, 5232 Villigen PSI (Switzerland); Institute for Chemical and Bioengineering, ETH Zurich, 8093 Zuerich (Switzerland); Dousse, J.-Cl.; Hoszowska, J.; Kayser, Y. [Department of Physics, University of Fribourg, 1700 Fribourg (Switzerland); Jagodzinski, P. [University of Technology, Kielce (Poland)

2012-10-15

334

Diffuse X-Ray Emission from the Superbubbles N70 and N185 in the Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

We present a study of the diffuse X-ray emission from superbubbles (SBs) N70 (DEM L301) and N185 (DEM L25) located in the Large Magellanic Cloud, based on data from the XMM-Newton Satellite. We obtained spectra and images of these objects in the soft X-ray energy band. These X-ray spectra were fitted by a thermal plasma model, with temperatures of 2.6× {{10}6} K and 2.3× {{10}6} K, for N70 and N185, respectively. For N70, images show that X-ray emission comes from the inner regions of the SB when we compare the distribution of the X-ray and the optical emission, while for N185, the X-ray emission is partially confined by the optical shell. We suggest that the observed X-ray emission is caused by shock-heated gas, inside of the optical shells. We also obtained X-ray luminosities which exceed the values predicted by the standard analytical model. This fact shows that, in addition to the winds of the interior stars, it is necessary to consider another ingredient in the description, such as a supernova explosion, as has been proposed in previous numerical models.

Reyes-Iturbide, J.; Rosado, M.; Rodríguez-González, A.; Velázquez, P. F.; Sánchez-Cruces, M.; Ambrocio-Cruz, P.

2014-11-01

335

Diffuse Hard X-Ray Emission in Starburst Galaxies as Synchrotron from Very High Energy Electrons  

NASA Astrophysics Data System (ADS)

The origin of the diffuse hard X-ray (2-10 keV) emission from starburst galaxies is a long-standing problem. We suggest that synchrotron emission of 10-100 TeV electrons and positrons (e ±) can contribute to this emission, because starbursts have strong magnetic fields. We consider three sources of e ± at these energies: (1) primary electrons directly accelerated by supernova remnants, (2) pionic secondary e ± created by inelastic collisions between cosmic ray (CR) protons and gas nuclei in the dense interstellar medium of starbursts, and (3) pair e ± produced between the interactions between 10 and 100 TeV ?-rays and the intense far-infrared (FIR) radiation fields of starbursts. We create one-zone steady-state models of the CR population in the Galactic center (R <= 112 pc), NGC 253, M82, and Arp 220's nuclei, assuming a power-law injection spectrum for electrons and protons. We consider different injection spectral slopes, magnetic field strengths, CR acceleration efficiencies, and diffusive escape times, and include advective escape, radiative cooling processes, and secondary and pair e ±. We compare these models to extant radio and GeV and TeV ?-ray data for these starbursts, and calculate the diffuse synchrotron X-ray and inverse Compton (IC) luminosities of these starbursts in the models which satisfy multiwavelength constraints. If the primary electron spectrum extends to ~PeV energies and has a proton/electron injection ratio similar to the Galactic value, we find that synchrotron emission contributes 2%-20% of their unresolved, diffuse hard X-ray emission. However, there is great uncertainty in this conclusion because of the limited information on the CR electron spectrum at these high energies. IC emission is likewise a minority of the unresolved X-ray emission in these starbursts, from 0.1% in the Galactic center to 10% in Arp 220's nuclei, with the main uncertainty being the starbursts' magnetic field. We also model generic starbursts, including submillimeter galaxies, in the context of the FIR-X-ray relation, finding that anywhere between 0% and 16% of the total hard X-ray emission is synchrotron for different parameters, and up to 2% in the densest starbursts assuming an E -2.2 injection spectrum and a diffusive escape time of 10 Myr (E/3 GeV)-1/2 (h/100 pc). Neutrino observations by IceCube and TeV ?-ray data from HESS, VERITAS, and CTA can further constrain the synchrotron X-ray emission of starbursts. Our models do not constrain the possibility of hard, second components of primary e ± from sources like pulsars in starbursts, which could enhance the synchrotron X-ray emission further.

Lacki, Brian C.; Thompson, Todd A.

2013-01-01

336

Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas  

NASA Technical Reports Server (NTRS)

There is a general agreement that the conspicuous extranuclear X-ray, optical-line, and radio-contiuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyze the interaction of the wind with a two-component disk-halo ambient interstellar medium and argue that this two-component representation is crucial for adequate modeling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the X-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex 'filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions r elated to the origin and development of the 'filaments'. The filament parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A 'mild' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk and halo gas without strongly affecting the gaseous disk, thus creating conditions for virtually free vertical escape of the hot gas at the later, much more violent supernova-dominated phases of the starburst. We calculate the luminosity, mass, and effective temperature of the X-ray emitting gas in the 'soft' (0.1 to 0.7 keV, 0.7 to 2.2 keV, and 0.1 to 2.2 keV) and 'hard' (1.6 to 8.3 keV) energy bands and estimate the contribution of different gaseous components to the X-ray flux in these bands. Analysis of these parameters enables us to make conclusions regarding the nature of the X-ray-emitting material. We have inferred that the bulk of the soft thermal X-ray emission from starbursts arises in the wind-shocked material of the disk and halo gas rather than in the wind material itself. This enables us to predict that the integrated soft X-ray spectra of starbursts need not show an overabundance of heavy elements which are believed to be produced copiously in the centers of starbursts. Unlike soft X-ray emission, the hard component of thermal X-ray emission is found to originate in the wind material ejected from the starburst region. However, the derived ratio of hard-to-soft X-ray luminosities is too small compared to that observed in starbursts. We conclude therefore that the observed hard X-ray emission of starbursts is probably not associated with the thermal emission of hot wind or ambient shocked gas. Typical temperatures of the bulk of the soft X-ray-emitting material in our very different models have been found to agree well with the ones estimated on the basis of the ROSAT data for the soft component of X-ray emission of nearby starbursts. We predict that temperatures of the extranuclear soft X-ray-emitting gas in starburst galaxies with heavy element abundances near solar should be close to T(sub Xs = 2 to 5 x 10(exp 6)K.

Suchkov, Anatoly A.; Balsara, Dinshaw S.; Heckman, Timothy M.; Leitherner, Claus

1994-01-01

337

Iron line and diffuse hard X-ray emission from the starburst galaxy M82  

E-print Network

We examine the properties of the diffuse hard X-ray emission in the classic starburst galaxy M82. We use new Chandra ACIS-S observations in combination with reprocessed archival Chandra ACIS-I and XMM-Newton observations. We find E~6.7 keV Fe He-alpha emission is present in the central |r| iron line fluxes in the 2004 April 21 XMM-Newton observation are consistent with those of the Chandra-derived diffuse component, but in the 2001 May 6 XMM-Newton observation they are significantly higher and also both E=6.4 and E=6.9 keV iron lines are detected. We attribute the excess iron line emission to the Ultra-Luminous X-ray source in its high state. In general the iron K-shell luminosity of M82 is dominated by the diffuse component. The total X-ray luminosity of the diffuse hard X-ray emission (corrected for emission by unresolved low luminosity compact objects) is L_X ~ 4.4 x 10^39 erg/s in the E=2-8 keV energy band, and the 6.7 keV iron line luminosity is L_X ~ (1.1 -- 1.7) x 10^38 erg/s. The 6.7 keV iron line luminosity is consistent with that expected from the previously unobserved metal-enriched merged supernova ejecta that is thought to drive the larger-scale galactic superwind. The iron line luminosity implies a thermal pressure within the starburst region of P/k ~ 2 x 10^7 K/cm^3, which is consistent with independent observational estimates of the starburst region pressure [Abstract abridged].

D. K. Strickland; T. M. Heckman

2006-11-28

338

GRB 060607A: A GRB with Bright Asynchronous Early $X$-ray and Optical Emissions  

E-print Network

The early optical emission of the moderately high redshift ($z=3.08$) GRB 060607A shows a remarkable broad and strong peak with a rapid rise and a relatively slow power-law decay. It is not coincident with the strong early-time flares seen in the X-ray and gamma-ray energy bands. There is weak evidence for variability superposed on this dominant component in several optical bands that can be related to flares in high energy bands. While for a small number of GRBs, well-sampled optical flares have been observed simultaneously with X-ray and gamma ray pulses, GRB 060607A is one of the few cases where the early optical emission shows no significant evidence for correlation with the prompt emission. In this work we first report in detail the broad band observations of this burst by Swift. Then by applying a simple model for the dynamics and the synchrotron radiation of a relativistic shock, we show that the dominant component of the early emissions in optical wavelengths has the same origin as the tail emission produced after the main gamma ray activity. The most plausible explanation for the peak in the optical light curve seems to be the cooling of the prompt after the main collisions, shifting the characteristic synchrotron frequency to the optical bands. It seems that the cooling process requires a steepening of the electron energy distribution and/or a break in this distribution at high energies. The sharp break in the X-ray light curve at few thousands of seconds after the trigger, is not observed in the IR/optical/UV bands, and therefore can not be a jet break. Either the X-ray break is due to a change in the spectrum of the accelerated electrons or the lack of an optical break is due to the presence of a related delayed response component (Abbreviated).

Houri Ziaeepour; Stephen T. Holland; Patricia T. Boyd; Kim L. Page; Samantha Oates; Craig B. Markwardt; Peter Meszaros; Neil Gehrels; Francis E. Marshall; Jay Cummings; Mike Goad

2007-12-19

339

Intragroup and Galaxy-Linked Diffuse X-ray Emission in Hickson Compact Groups  

E-print Network

Isolated compact groups of galaxies (CGs) present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups observed with the Chandra X-ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of star formation or AGN activity, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the Lx-T relationship from clusters within the errors, while HCGs 16 and 31 are co...

Desjardins, Tyler D; Tzanavaris, Panayiotis; Mulchaey, John S; Brandt, William N; Charlton, Jane C; Garmire, Gordon P; Gronwall, Caryl; Hornschemeier, Ann E; Johnson, Kelsey E; Konstantopoulos, Iraklis S; Zabludoff, Ann I

2012-01-01

340

A novel paradigm for short gamma-ray bursts with extended X-ray emission  

E-print Network

The merger of a binary of neutron stars provides natural explanations for many of the features of short gamma-ray bursts (SGRBs), such as the generation of a hot torus orbiting a rapidly rotating black hole, which can then build a magnetic jet and provide the energy reservoir to launch a relativistic outflow. Yet, this scenario has problems explaining the recently discovered long-term and sustained X-ray emission associated with the afterglows of a subclass of SGRBs. We propose a new model that explains how an X-ray afterglow can be sustained by the product of the merger and how the X-ray emission is produced before the corresponding emission in the gamma-band, although it is observed to follow it. Overall, our paradigm combines in a novel manner a number of well-established features of the emission in SGRBs and results from simulations. Because it involves the propagation of an ultra-relativistic outflow and its interaction with a confining medium, the paradigm also highlights a unifying phenomenology between short and long GRBs.

Luciano Rezzolla; Pawan Kumar

2015-01-21

341

X-ray Emission from Charge Exchange in the Cygnus Loop SNR  

E-print Network

The Cygnus Loop has been the focus of substantial debate concerning the contribution of charge exchange (CX) to supernova remnant (SNR) X-ray emission. We take advantage of a distinct feature of CX, enhanced K{\\alpha} forbidden line emission, and employ the energy centroid of the OVII K{\\alpha} triplet as a diagnostic. Based on X-ray spectra extracted from an extensive set of Suzaku observations, we measure the energy centroid shifts of the triplet on and off the shock rim of the remnant. We find that enhanced forbidden to resonance line emission exists throughout much of the rim and this enhancement azimuthally correlates with non-radiative H{\\alpha} filaments, a tracer of strong neutral-plasma interaction in the optical. We also show that alternative mechanisms cannot explain the enhancement observed. These results demonstrate the need to model the CX contribution to the X-ray emission of SNRs, particularly for shocks propagating in a partially neutral medium. Such modeling may be critically important to th...

Roberts, Shawn R

2015-01-01

342

A Novel Paradigm for Short Gamma-Ray Bursts With Extended X-Ray Emission  

NASA Astrophysics Data System (ADS)

The merger of a binary of neutron stars provides natural explanations for many of the features of short gamma-ray bursts (SGRBs), such as the generation of a hot torus orbiting a rapidly rotating black hole, which can then build a magnetic jet and provide the energy reservoir to launch a relativistic outflow. However, this scenario has problems explaining the recently discovered long-term and sustained X-ray emission associated with the afterglows of a subclass of SGRBs. We propose a new model that explains how an X-ray afterglow can be sustained by the product of the merger and how the X-ray emission is produced before the corresponding emission in the gamma-band, though it is observed to follow it. Overall, our paradigm combines in a novel manner a number of well-established features of the emission in SGRBs and results from simulations. Because it involves the propagation of an ultra-relativistic outflow and its interaction with a confining medium, the paradigm also highlights a unifying phenomenology between short and long GRBs.

Rezzolla, Luciano; Kumar, Pawan

2015-04-01

343

Evidence for X-ray emission from superclusters of galaxies determined from Uhuru  

NASA Technical Reports Server (NTRS)

X-ray emission from three class 2 clusters of rich clusters of galaxies has been detected. A definition for these objects based in part on Abell's (1961) description is used, and 12 candidate superclusters of distance class 5 and six clusters are found within the area of sky covered by the 4U catalog. The probability that these three X-ray sources accidentally coincide with the superclusters is less than 0.003. Equally low probabilities are found that the X-ray emission is due to either a single luminous cluster or to the combined emission of all members of the supercluster. A possible explanation of these sources is thermal bremsstrahlung emission from a hot tenuous gas pervading the supercluster. The mass of the gas can be as much as 10 times the mass of the galaxies in the supercluster and comparable to the virial mass necessary to bind the supercluster gravitationally. Should such regions of enhanced gas density be found to be associated with all groups of clusters (multiplicity of at least 2), this gas may provide a significant fraction of the mass required to close the universe.

Murray, S. S.; Forman, W.; Jones, C.; Giacconi, R.

1978-01-01

344

Depth-resolved soft x-ray photoelectron emission microscopy in nanostructures via standing-wave excited photoemission  

SciTech Connect

We present an extension of conventional laterally resolved soft x-ray photoelectron emission microscopy. A depth resolution along the surface normal down to a few {angstrom} can be achieved by setting up standing x-ray wave fields in a multilayer substrate. The sample is an Ag/Co/Au trilayer, whose first layer has a wedge profile, grown on a Si/MoSi2 multilayer mirror. Tuning the incident x-ray to the mirror Bragg angle we set up standing x-ray wave fields. We demonstrate the resulting depth resolution by imaging the standing wave fields as they move through the trilayer wedge structure.

Kronast, F.; Ovsyannikov, R.; Kaiser, A.; Wiemann, C.; Yang, S.-H.; Locatelli, A.; Burgler, D.E.; Schreiber, R.; Salmassi, F.; Fischer, P.; Durr, H.A.; Schneider, C.M.; Eberhardt, W.; Fadley, C.S.

2008-11-24

345

Correlated optical and X-ray variability in CTTS - Indications of absorption-modulated emission  

E-print Network

Optical and X-ray emission from classical T Tauri stars (CTTSs) has long been known to be highly variable. Our long, uninterrupted optical observation of the NGC2264 region with CoRoT allows the optical variability in CTTS to be studied with unprecedented accuracy and time coverage. Two short Chandra observations obtained during the CoRoT pointing with a separation of 16 days allow us to study whether there is a correlation between optical and X-ray variability on this timescale, thus probing the physical mechanisms driving the variability in both bands. We have computed the optical and X-ray fractional variability between the two 30 ks duration windows covered by both the Chandra and CoRoT observations, for a sample of classical and weak line T Tauri stars (WTTSs) in NGC2264. A scatter plot clearly shows that the variability of CTTSs in the optical and soft X-ray (0.5-1.5 keV) bands is correlated, while no correlation is apparent in the hard (1.5-8.0 keV) band. Also, no correlation in either band is present ...

Flaccomio, E; Favata, F; Alencar, S P H

2010-01-01

346

Experimental study of hard-X ray emission from laboratory sparks  

NASA Astrophysics Data System (ADS)

We present the characterization of hard-X rays produced by meter-long laboratory sparks carried out at the high-voltage laboratory of RSE, Milano, Italy. Sparks are known to emit X-rays when positive and negative streamers connect, before breakdown. Numerical simulations suggest that X-rays are produced by Bremsstrahlung in air by electrons accelerated to the runaway regime in the high electric field at the streamers tip. Positive meter-long discharges are produced by a Marx generator loaded by a meter-long air gap formed by a spherical anode and a conical-shaped cathode. Maximum voltage at breakdown is about 1 MV. We investigate the production of X-rays by means of an array of scintillation detectors deployed around the cathode. Each detector is a 2'' NaI(Tl) scintillating crystal coupled to a photomultiplier tube (PMT). Each detector is battery-powered and enclosed in a metallic housing for EM shielding. Analog signal output is trasmitted to a shielded control room by means of optical fibre tranceivers, and then collected by a fast digitizer. We present the experimental setup and first results concerning detection efficiency, energy spectra, and geometrical distribution of the emission.

Marisaldi, Martino; Rizzi, Rolando; Levi, Giuseppe; Malgesini, Roberto; Villa, Andrea; Mazza, Paolo; Labanti, Claudio; Fuschino, Fabio; Campana, Riccardo; Bianchini, David; Brancaccio, Rossella; Montanari, Alessandro; Patrizii, Laura

2014-05-01

347

Electrochemical flowcell for in-situ investigations by soft x-ray absorption and emission spectroscopy.  

PubMed

A new liquid flow-cell designed for electronic structure investigations at the liquid-solid interface by soft X-ray absorption and emission spectroscopy is presented. A thin membrane serves simultaneously as a substrate for the working electrode and solid state samples as well as for separating the liquid from the surrounding vacuum conditions. In combination with counter and reference electrodes this approach allows in-situ studies of electrochemical deposition processes and catalytic reactions at the liquid-solid interface in combination with potentiostatic measurements. As model system in-situ monitoring of the deposition process of Co metal from a 10 mM CoCl2 aqueous solution by X-ray absorption and emission spectroscopy is presented. PMID:25362384

Schwanke, C; Golnak, R; Xiao, J; Lange, K M

2014-10-01

348

Angular Distribution of Argon Ions and X-Ray Emissions in the Apf Plasma Focus Device  

NASA Astrophysics Data System (ADS)

Angular distribution of ion beam emission from an argon gas-filled plasma focus devices has been investigated using an array of five Faraday cups. The argon ion beam emission is found to be highly pressure-dependent and reaches its maximum at the pressure of 1 torr. The ions flux decreased as the working pressure increased; the maximum ion density at 1 torr was estimated to be around 9.24 × 1024 ions/steradian. Also, the study on the angular distribution of X-rays has been carried out using TLD-100 dosimeters. The intensity of ions reduced significantly at angles higher than ±11° but the X-ray distribution was bimodal, peaked approximately at ±15°.

Etaati, G. R.; Amrollahi, R.; Habibi, M.; Baghdadi, R.

2011-04-01

349

Spatial and temporal evolution of soft and hard X-ray emission in a solar flare  

NASA Technical Reports Server (NTRS)

Hard X-ray burst spectrometer and imaging spectrometer data are used to study the spatial and temporal characteristics of the 3.5-30.0 keV emission in an Apr. 10, 1980 solar flare. It is found that: (1) continuous energy release is needed to sustain the increase of the emission through the flare's rising phase, before and after the impulsive phase in hard X-rays, and the release is characterized by the production of 50 million-150 million K thermal regions within the flare loop structures; (2) the observational parameters which characterize the impulsive burst indicate that it is probably associated with nonthermal processes, such as particle acceleration; and (3) the continuous energy release is associated with strong chromospheric evaporation, in view of spectral line behavior. Both particle acceleration and chromospheric evaporation stop just before flare maximum, and the subsequent evolution is probably governed by the radiative cooling of the flare plasma.

Machado, M. E.; Duijveman, A.; Dennis, B. R.

1982-01-01

350

Electrochemical flowcell for in-situ investigations by soft x-ray absorption and emission spectroscopy  

SciTech Connect

A new liquid flow-cell designed for electronic structure investigations at the liquid-solid interface by soft X-ray absorption and emission spectroscopy is presented. A thin membrane serves simultaneously as a substrate for the working electrode and solid state samples as well as for separating the liquid from the surrounding vacuum conditions. In combination with counter and reference electrodes this approach allows in-situ studies of electrochemical deposition processes and catalytic reactions at the liquid-solid interface in combination with potentiostatic measurements. As model system in-situ monitoring of the deposition process of Co metal from a 10 mM CoCl{sub 2} aqueous solution by X-ray absorption and emission spectroscopy is presented.

Schwanke, C.; Lange, K. M., E-mail: Kathrin.lange@helmholtz-berlin.de [Helmholtz-Zentrum Berlin für Materialien und Energie, Institute of Solar Fuels, Albert-Einstein-Straße 15, 12489 Berlin (Germany); Golnak, R.; Xiao, J. [Helmholtz-Zentrum Berlin für Materialien und Energie, Institute of Methods for Material Development, Albert-Einstein-Straße 15, 12489 Berlin (Germany)

2014-10-15

351

THE EFFECT OF POROSITY ON X-RAY EMISSION-LINE PROFILES FROM HOT-STAR WINDS Stanley P. Owocki  

E-print Network

THE EFFECT OF POROSITY ON X-RAY EMISSION-LINE PROFILES FROM HOT-STAR WINDS Stanley P. Owocki Bartol be explained by the possibly porous nature of their spatially structured stellar winds. Such porosity could effectively reduce the bound-free absorption of X-rays emitted by embedded wind shocks, and thus allow a more

Cohen, David

352

Depth-resolved soft x-ray photoelectron emission microscopy in nanostructures via standing-wave excited photoemission  

E-print Network

Depth-resolved soft x-ray photoelectron emission microscopy in nanostructures via standing-wave by using standing-wave excitation. The sample is a Ag/Co/Au trilayer, grown on a Si/MoSi2 multilayer mirror a standing x-ray wave field in the multilayer and the trilayer wedge structure. We demonstrate the resulting

Fadley, Charles

353

X-RAY EMISSION FROM NEUTRON STARS:. Some personal reflections and recent developments  

NASA Astrophysics Data System (ADS)

After a few remarks about the early history of the subject we present a short review of the present observational situation regarding the X-ray emission from isolated neutron stars. In total 32 objects have been detected with ROSAT, the majority of which are radio pulsars showing non -thermal (magnetospheric) emission. For three radio pulsars and three point sources in SNRs thermal emission has been seen which probably comes from the photospheric of the cooling neutron star. A third class comprising the objects represents neutron stars according matter from the interstellar medium.

Trümper, Joachim

2000-09-01

354

X-ray continuum emission spectroscopy from hot dense matter at Gbar pressures  

NASA Astrophysics Data System (ADS)

We have measured the time-resolved x-ray continuum emission spectrum of ˜30 times compressed polystyrene created at stagnation of spherically convergent shock waves within the Gbar fundamental science campaign at the National Ignition Facility. From an exponential emission slope between 7.7 keV and 8.1 keV photon energy and using an emission model which accounts for reabsorption, we infer an average electron temperature of 375 ± 21 eV, which is in good agreement with HYDRA-1D simulations.

Kraus, D.; Döppner, T.; Kritcher, A. L.; Bachmann, B.; Chapman, D. A.; Collins, G. W.; Glenzer, S. H.; Hawreliak, J. A.; Landen, O. L.; Ma, T.; Le Pape, S.; Neumayer, P.; Swift, D. C.; Falcone, R. W.

2014-11-01

355

X-ray continuum emission spectroscopy from hot dense matter at Gbar pressures.  

PubMed

We have measured the time-resolved x-ray continuum emission spectrum of ?30 times compressed polystyrene created at stagnation of spherically convergent shock waves within the Gbar fundamental science campaign at the National Ignition Facility. From an exponential emission slope between 7.7 keV and 8.1 keV photon energy and using an emission model which accounts for reabsorption, we infer an average electron temperature of 375 ± 21 eV, which is in good agreement with HYDRA-1D simulations. PMID:25430182

Kraus, D; Döppner, T; Kritcher, A L; Bachmann, B; Chapman, D A; Collins, G W; Glenzer, S H; Hawreliak, J A; Landen, O L; Ma, T; Le Pape, S; Neumayer, P; Swift, D C; Falcone, R W

2014-11-01

356

MEASUREMENT OF THE RADIUS OF NEUTRON STARS WITH HIGH SIGNAL-TO-NOISE QUIESCENT LOW-MASS X-RAY BINARIES IN GLOBULAR CLUSTERS  

SciTech Connect

This paper presents the measurement of the neutron star (NS) radius using the thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular clusters (GCs). Recent observations of NSs have presented evidence that cold ultra dense matter-present in the core of NSs-is best described by ''normal matter'' equations of state (EoSs). Such EoSs predict that the radii of NSs, R{sub NS}, are quasi-constant (within measurement errors, of {approx}10%) for astrophysically relevant masses (M{sub NS}>0.5 M{sub Sun }). The present work adopts this theoretical prediction as an assumption, and uses it to constrain a single R{sub NS} value from five qLMXB targets with available high signal-to-noise X-ray spectroscopic data. Employing a Markov chain Monte-Carlo approach, we produce the marginalized posterior distribution for R{sub NS}, constrained to be the same value for all five NSs in the sample. An effort was made to include all quantifiable sources of uncertainty into the uncertainty of the quoted radius measurement. These include the uncertainties in the distances to the GCs, the uncertainties due to the Galactic absorption in the direction of the GCs, and the possibility of a hard power-law spectral component for count excesses at high photon energy, which are observed in some qLMXBs in the Galactic plane. Using conservative assumptions, we found that the radius, common to the five qLMXBs and constant for a wide range of masses, lies in the low range of possible NS radii, R{sub NS}=9.1{sup +1.3}{sub -1.5} km (90%-confidence). Such a value is consistent with low-R{sub NS} equations of state. We compare this result with previous radius measurements of NSs from various analyses of different types of systems. In addition, we compare the spectral analyses of individual qLMXBs to previous works.

Guillot, Sebastien; Rutledge, Robert E. [Department of Physics, McGill University, 3600 rue University, Montreal, QC, H2X-3R4 (Canada); Servillat, Mathieu [Laboratoire AIM (CEA/DSM/IRFU/SAp, CNRS, Universite Paris Diderot), CEA Saclay, Bat. 709, F-91191 Gif-sur-Yvette (France); Webb, Natalie A., E-mail: guillots@physics.mcgill.ca, E-mail: rutledge@physics.mcgill.ca [Universite de Toulouse, UPS-OMP, IRAP, Toulouse (France)

2013-07-20

357

X-rays emission from a compact diode energized by capacitor discharge  

NASA Astrophysics Data System (ADS)

X-ray emission from a compact diode consisting of a sharp edged cathode and flat anode of copper and lead, energized by simple capacitor discharge is reported. With a sewing machine needle cathode, and lead target, the generation efficiency upto 0.4% is obtained. The efficiency is expected to enhance further with the increase in discharge energy, charging voltage and reducing the parasitic inductance.

Zakaullah, M.; Ahmed, S.; Hussain, S.; Afzal, M.; Waheed, A.

2005-01-01

358

New findings on the X-ray emission from Wolf-Rayet nebulae  

NASA Astrophysics Data System (ADS)

We present the most recent results from XMM-Newton and Chandra observations on the only 4 Wolf-Rayet (WR) nebulae observed to date. Given the limited number of observations and different morphological and spectral characteristics, there still no fully understanding of the reason why only two of them harbor diffuse X-ray emission. There is an apparent correlation between the central star properties and the existence of hot gas inside the nebulae but strong statements cannot be done.

Toala, J.; Guerrero, M.; Chu, Y.; Gruendl, R.; Arthur, S.

2014-07-01

359

Resolved X-ray emission line profiles Clumping in Hot Star Winds  

E-print Network

Resolved X-ray emission line profiles Clumping in Hot Star Winds W.-R. Hamann, A. Feldmeier & L and wind porosity. We find that reducing the mass-loss rate of Pup by roughly a factor of four, to 1.5 Ã? 10-6 M yr-1 , enables simple non-porous wind models to provide good fits to the data. If

Cohen, David

360

Correlated optical and X-ray variability in CTTS. Indications of absorption-modulated emission  

Microsoft Academic Search

Aims: Optical and X-ray emission from classical T Tauri stars (CTTSs) has long been known to be highly variable. Our long, uninterrupted optical observation of the NGC 2264 region with CoRoT [The CoRoT space mission was developed and is operated by the French space agency CNES, with participation of ESA's RSSD and Science Programs, Austria, Belgium, Brazil, Germany, and Spain.

E. Flaccomio; G. Micela; F. Favata; S. P. H. Alencar

2010-01-01

361

Site determination of oxygen in B6O by oxygen Kalpha x-ray-emission spectroscopy  

Microsoft Academic Search

An electron-excited x-ray-emission spectrum of oxygen Kalpha is presented for boron suboxide B6O (isostructural with B13C2). The spectrum is compared with those calculated by the discrete-variation Xalpha (DV-Xalpha) method with various O-O distances as an adjustable parameter in the fixed icosahedral B12 framework. The observed spectrum is reproduced well when the O-O distance is in the range 2.5-3.5 Å. This

J. Kawai; K. Maeda; I. Higashi; M. Takami; Y. Hayasi; M. Uda

1990-01-01

362

Bulk band gaps in divalent hexaborides: A soft x-ray emission study  

SciTech Connect

Boron K-edge soft x-ray emission and absorption are used to address the fundamental question of whether divalent hexaborides are intrinsic semimetals or defect-doped bandgap insulators. These bulk sensitive measurements, complementary and consistent with surface-sensitive angle-resolved photoemission experiments, confirm the existence of a bulk band gap and the location of the chemical potential at the bottom of the conduction band.

Denlinger, Jonathan D.; Gweon, Gey-Hong; Allen, James W.; Bianchi, Andrea D.; Fisk, Zachary

2001-10-03

363

On the Integrated Spectrum of the X-ray Binaries and the Origin of Soft X-ray Emission from the Bulge of M31  

E-print Network

Using ROSAT PSPC data, we have performed several tests aimed at understanding the origin of the soft X-ray spectral component detected from the bulge of M31. We find that a significant soft component in the spectrum of the bulge is spatially correlated with the unresolved X-ray emission near the core of M31, which is probably a hot interstellar medium or perhaps a population of multiple faint sources. For the first time, we extracted the spectrum of this unresolved emission, by removing point sources dominating the integral spectrum of the bulge, and found it to be responsible for the most of soft excess. A soft spectral component is not at all needed to fit the point source spectrum that remains after subtracting the unresolved emission. The integral spectra of bright point sources, both inside and outside of the M31 bulge, can be fitted with a single power-law in the ROSAT band. Our analysis rules out the previous suggestion that all bulge emission in M31 may be generated by low mass X-ray binaries (Irwin & Bregman, 1999).

Konstantin N. Borozdin; William C. Priedhorsky

2000-09-06

364

X-ray photo-emission and energy dispersive spectroscopy of HA coated titanium  

SciTech Connect

The purpose of this study was to determine the chemical composition changes of hydroxyapatite (HA) coated titanium using surface analysis (x-ray photo-emission) and bulk analysis (energy dispersive spectroscopy). The specimens examined were controls, 30 minutes and 3 hours aged specimens in distilled water or 0.2M sodium phosphate buffer (pH 7.2) at room temperature. Each x-ray photo-emission cycle consisted of 3 scans followed by argon sputtering for 10 minutes for a total of usually 20 cycles, corresponding to a sampling depth of {approximately} 1500 {angstrom}. The energy dispersive spectroscopy analysis was on a 110 by 90 {mu}m area for 500 sec. Scanning electron microscopy examination showed crystal formation (3P{sub 2}O{sub 5}*2CAO*?H{sub 2}O by energy dispersive spectroscopy analysis) on the HA coating for the specimens aged in sodium phosphate buffer. The x-ray photo-emission results indicated the oxidation effect of water on the titanium (as TiO{sub 2}) and the effect of the buffer to increase the surface concentration of phosphorous. No differences in the chemical composition were observed by energy dispersive spectroscopy analysis. The crystal growth was only observed for the sodium phosphate buffer specimens and only on the HA surface.

Drummond, J.L.; Steinberg, A.D. [Univ. of Illinois, Chicago, IL (United States); Krauss, A.R. [Argonne National Lab., IL (United States)] [and others

1997-08-01

365

Static and Dynamic Modeling of a Solar Active Region. I: Soft X-Ray Emission  

E-print Network

Recent simulations of solar active regions have shown that it is possible to reproduce both the total intensity and the general morphology of the high temperature emission observed at soft X-ray wavelengths using static heating models. There is ample observational evidence, however, that the solar corona is highly variable, indicating a significant role for dynamical processes in coronal heating. Because they are computationally demanding, full hydrodynamic simulations of solar active regions have not been considered previously. In this paper we make first application of an impulsive heating model to the simulation of an entire active region, AR8156 observed on 1998 February 16. We model this region by coupling potential field extrapolations to full solutions of the time-dependent hydrodynamic loop equations. To make the problem more tractable we begin with a static heating model that reproduces the emission observed in 4 different \\textit{Yohkoh} Soft X-Ray Telescope (SXT) filters and consider dynamical heating scenarios that yield time-averaged SXT intensities that are consistent with the static case. We find that it is possible to reproduce the total observed soft X-ray emission in all of the SXT filters with a dynamical heating model, indicating that nanoflare heating is consistent with the observational properties of the high temperature solar corona.

Harry P. Warren; Amy R. Winebarger

2006-09-01

366

XMM-Newton observations of X-ray emission from Jupiter  

E-print Network

We present the results of two XMM-Newton observations of Jupiter carried out in 2003 for 100 and 250 ks (or 3 and 7 planet rotations) respectively. X-ray images from the EPIC CCD cameras show prominent emission from the auroral regions in the 0.2 - 2.0 keV band: the spectra are well modelled by a combination of emission lines, including most prominently those of highly ionised oxygen (OVII and OVIII). In addition, and for the first time, XMM-Newton reveals the presence in both aurorae of a higher energy component (3 - 7 keV) which is well described by an electron bremsstrahlung spectrum. This component is found to be variable in flux and spectral shape during the Nov. 2003 observation, which corresponded to an extended period of intense solar activity. Emission from the equatorial regions of Jupiter's disk is also observed, with a spectrum consistent with that of solar X-rays scattered in the planet's upper atmosphere. Jupiter's X-rays are spectrally resolved with the RGS which clearly separates the prominent OVII contribution of the aurorae from the OVIII, FeXVII and MgXI lines, originating in the low-latitude disk regions of the planet.

G. Branduardi-Raymont; A. Bhardwaj; R. F. Elsner; G. R. Gladstone; G. Ramsay; P. Rodriguez; R. Soria; J. H. Waite, Jr; T. E. Cravens

2005-12-09

367

Non-thermal emissions from accreting X-ray binary pulsars  

NASA Astrophysics Data System (ADS)

We study non-thermal emissions from cascade processes in accreting X-ray binary pulsars. In the framework of the magnetospheric gap model, we consider three photon fields, which are respectively from the polar cap of a pulsar, its surrounding accretion disk and a massive companion star with a circumstellar disk, to shield the gap. The gap-accelerated ultra-relativistic electrons emit high-energy photons via curvature radiation and an inverse Compton scattering process, in which part of these high-energy photons absorbed by interactions with the surrounding photon fields can facilitate the following electromagnetic cascades. We first carry out numerical calculations of the cascade processes in order to obtain the predicted emission spectra. As an example, we subsequently apply this model to reproduce observations of LS I +61° 303. We find that the results can fit observations ranging from hard X-ray to ?-ray bands. In particular, they can explain the spectral cutoff feature at a few GeV. Finally, we suggest that the emissions detected by the Fermi Large Area Telescope from X-ray binary pulsars originate in the magnetosphere region of the pulsar.

Zhang, Jian-Fu; Jin, Hui; Dong, Ai-Jun

2014-03-01

368

Changes in the X-Ray Emission from the Magnetar Candidate 1E 2259+586 During its 2002 Outburst  

NASA Technical Reports Server (NTRS)

An outburst of more than 80 individual bursts, similar to those seen from Soft Gamma Repeaters (SGRs), was detected from the anomalous X-ray pulsar (AXP) 1E 2259+586 in 2002 June. Coincident with this burst activity were gross changes in the pulsed flux, persistent flux, energy spectrum, pulse profile, and spin-down of the underlying X-ray source. We present Rossi X-Ray Timing Explorer and X-Ray Multi-Mirror Mission observations of 1E 2259+586 that show the evolution of the aforementioned source parameters during and following this episode and identify recovery timescales for each. Specifically, we observe an X-ray flux increase (pulsed and phase-averaged) by more than an order of magnitude having two distinct components. The first component is linked to the burst activity and decays within approx. 2 days, during which the energy spectrum is considerably harder than during the quiescent state of the source. The second component decays over the year following the glitch according to a power law in time with an exponent -0.22 +/- 0.01. The pulsed fraction decreased initially to approx. 15% rms but recovered rapidly to the preoutburst level of approx. 23% within the first 3 days. The pulse profile changed significantly during the outburst and recovered almost fully within 2 months of the outburst. A glitch of size Delta(sib (nu)max) = (4.24 +/- 0.11) x 10(exp -6) was observed in 1E 2259+586, which preceded the observed burst activity. The glitch could not be well fitted with a simple partial exponential recovery. An exponential rise of approx. 20% of the frequency jump with a timescale of approx. 14 days results in a significantly better fit to the data; however, contamination from a systematic drift in the phase of the pulse profile cannot be excluded. A fraction of the glitch (approx. 19%) was recovered in a quasi-exponential manner having a recovery timescale of approx. 16 days. The long-term postglitch spin-down rate decreased in magnitude relative to the preglitch value. The changes in the source properties of 1E 2259+586 during its 2002 outburst are shown to be qualitatively similar to changes seen during or following burst activity in two SGRs, thus further solidifying the common nature of SGRs and AXP's as magnetars. The changes in persistent emission properties of 1E 2259+586 suggest that the star underwent a plastic deformation of the crust that simultaneously impacted the superfluid interior (crustal and possibly core superfluid) and the magnetosphere. Finally, the changes in persistent emission properties coincident with burst activity in 1E 2259+586 enabled us to infer previous burst-active episodes from this and other AXP's. The nondetection of these outbursts by all-sky gamma-ray instruments suggests that the number of active magnetar candidates in our Galaxy is larger than previously thought.

Woods, P. M.; Kaspi, V. M.; Thompson, C.; Gavrill, F. P.; Marshall, H. L.; Chakrabarty, D.; Flanagan, K.; Heyl, J.; Hernquist, L.

2004-01-01

369

Physical Conditions in the X-Ray Emission-line Gas in NGC 1068  

NASA Astrophysics Data System (ADS)

We present a detailed, photoionization modeling analysis of XMM-Newton/Reflection Grating Spectrometer observations of the Seyfert 2 galaxy NGC 1068. The spectrum, previously analyzed by Kinkhabwala et al., reveals a myriad of soft X-ray emission lines, including those from H- and He-like carbon, nitrogen, oxygen, and neon, and M- and L-shell iron. As noted in the earlier analysis, based on the narrowness of the radiative recombination continua, the electron temperatures in the emission-line gas are consistent with photoionization, rather than collisional ionization. The strengths of the carbon and nitrogen emission lines, relative to those of oxygen, suggest unusual elemental abundances, which we attribute to the star formation history of the host galaxy. Overall, the emission lines are blueshifted with respect to systemic, with radial velocities ~160 km s-1, similar to that of [O III] ?5007, and thus consistent with the kinematics and orientation of the optical emission-line gas and, hence, likely part of an active galactic nucleus driven outflow. We were able to achieve an acceptable fit to most of the strong emission lines with a two-component photoionization model, generated with CLOUDY. The two components have ionization parameters and column densities of logU = -0.05 and 1.22 and logN H = 20.85 and 21.2 and covering factors of 0.35 and 0.84, respectively. The total mass of the X-ray gas is roughly an order of magnitude greater than the mass of ionized gas determined from optical and near-IR spectroscopy, which indicates that it may be the dominant component of the narrow-line region. Furthermore, we suggest that the medium that produces the scattered/polarized optical emission in NGC 1068 possesses similar physical characteristics to those of the more highly ionized of the X-ray model components.

Kraemer, S. B.; Sharma, N.; Turner, T. J.; George, Ian M.; Crenshaw, D. Michael

2015-01-01

370

Spectral Study of the Galactic Ridge X-Ray Emission with Suzaku  

NASA Astrophysics Data System (ADS)

In order to carry out a precise spectral study of the Galactic Ridge X-ray Emission using Suzaku, we have observed a typical Galactic plane field at (l,b) = (28°46, -0°20), which is already deeply observed with Chandra, and known to be devoid of bright X-ray point sources. Thanks to the low background and high spectral resolution of Suzaku, we were able to resolve three narrow iron K-emission lines from low-ionized (6.41keV), helium-like (6.67keV), and hydrogenic ions (7.00keV). The cosmic-ray ion charge-exchange model or the non-equilibrium ionization plasma model are unlikely to explain these line features, since they require either broad emission lines or lines at intermediate ionization states. Collisional ionization equilibrium plasma is the likely origin for the 6.67keV and 7.00keV lines; however, the origin of the 6.41keV line, which is due to fluorescence from cold material, has not been elucidated. We could also precisely measure the absolute X-ray surface brightness in the direction of the Galactic plane. Excluding point sources brighter than ˜2×10-13 ergs-1 cm-2 (2-10keV), the total surface brightness on the Galactic plane is ˜6.1×10-11 ergs-1 cm-2 deg-2 (2--10keV), including the contribution of the cosmic X-ray background, which is estimated to be ˜1.3×10-11 ergs-1 cm-2 deg-2.

Ebisawa, Ken; Yamauchi, Shigeo; Tanaka, Yasuo; Koyama, Katsuji; Ezoe, Yuichiro; Bamba, Aya; Kokubun, Motohide; Hyodo, Yoshiaki; Tsujimoto, Masahiro; Takahashi, Hiromitsu

2008-01-01

371

X-ray emission from star-forming galaxies - signatures of cosmic rays and magnetic fields  

NASA Astrophysics Data System (ADS)

The evolution of magnetic fields in galaxies is still an open problem in astrophysics. In nearby galaxies the far-infrared-radio correlation indicates the coupling between magnetic fields and star formation. The correlation arises from the synchrotron emission of cosmic ray electrons travelling through the interstellar magnetic fields. However, with an increase of the interstellar radiation field (ISRF), inverse Compton scattering becomes the dominant energy loss mechanism of cosmic ray electrons with a typical emission frequency in the X-ray regime. The ISRF depends on the one hand on the star formation rate and becomes stronger in starburst galaxies, and on the other hand increases with redshift due to the higher temperature of the cosmic microwave background. With a model for the star formation rate of galaxies, the ISRF, and the cosmic ray spectrum, we can calculate the expected X-ray luminosity resulting from the inverse Compton emission. Except for galaxies with an active galactic nucleus the main additional contribution to the X-ray luminosity comes from X-ray binaries. We estimate this contribution with an analytical model as well as with an observational relation, and compare it to the pure inverse Compton luminosity. Using data from the Chandra Deep Field Survey and far-infrared observations from Atacama Large Millimeter/Submillimeter Array, we then determine upper limits for the cosmic ray energy. Assuming that the magnetic energy in a galaxy is in equipartition with the energy density of the cosmic rays, we obtain upper limits for the magnetic field strength. Our results suggest that the mean magnetic energy of young galaxies is similar to the one in local galaxies. This points towards an early generation of galactic magnetic fields, which is in agreement with current dynamo evolution models.

Schober, J.; Schleicher, D. R. G.; Klessen, R. S.

2015-01-01

372

TRANSIENT EXTREMELY SOFT X-RAY EMISSION FROM THE UNUSUALLY BRIGHT CATACLYSMIC VARIABLE IN THE GLOBULAR CLUSTER M3: A NEW CV X-RAY LUMINOSITY RECORD?  

SciTech Connect

We observed the accreting white dwarf (WD) 1E1339.8+2837 (1E1339) in the globular cluster M3 in 2003 November, 2004 May, and 2005 January, using the Chandra ACIS-S detector. The source was observed in 1992 to possess traits of a supersoft X-ray source (SSS), with a 0.1-2.4 keV luminosity as large as 2 x 10{sup 35} erg s{sup -1}, after which time the source's luminosity fell by roughly two orders of magnitude, adopting a hard X-ray spectrum more typical of cataclysmic variables (CVs). Our observations confirm 1E1339's hard CV-like spectrum, with photon index {Gamma} = 1.3 {+-} 0.2. We found 1E1339 to be highly variable, with a 0.5-10 keV luminosity ranging from (1.4 {+-} 0.3) x 10{sup 34} erg s{sup -1} to 8.5{sup +4.9}{sub -4.6} x 10{sup 32} erg s{sup -1}, with 1E1339's maximum luminosity being perhaps the highest yet recorded for hard X-ray emission from a WD. In 2005 January, 1E1339 displayed substantial low-energy emission below {approx}0.3 keV. Although current Chandra responses cannot properly model this emission, its bolometric luminosity appears comparable to or greater than that of the hard spectral component. This raises the possibility that the supersoft X-ray emission seen from 1E1339 in 1992 may have shifted to the far-UV.

Stacey, W. S.; Heinke, C. O. [Physics Department, University of Alberta, 11322-89 Avenue, Edmonton, AB T6G 2G7 (Canada); Elsner, R. F.; Weisskopf, M. C. [NASA Marshall Space Flight Center, VP62, Huntsville, AL 35812 (United States); Edmonds, P. D.; Grindlay, J. E., E-mail: heinke@ualberta.ca [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2011-05-01

373

Dynamics of the Upper Atmosphere X-ray Emission during the 23rd Solar Cycle  

NASA Astrophysics Data System (ADS)

Long-term observations with the RPS-1instrument on the CORONAS-F satellite (July 2001 to December 2005) permitted the evaluation of the low energy 3.0-31.5 keV X-ray emission flux radiated by the upper nocturnal atmosphere. This emission mostly results from the bremsstrahlung radiation from magnetospheric electrons. The entire nocturnal atmosphere emits energy in the range of 3 to 5 keV, especially in the southern hemisphere, over the Pacific and Indian ocean areas. In the northern hemisphere, the brightest emission from the atmo-sphere is observed at high latitudes in the region of Earth's radiation belt (ERB). In lower northern latitudes, the X-ray emission intensity is rather weak especially during the summer, and on 5-8 keV maps there are regions where there are no discernible emissions. At energies higher than 8 keV, only areas over the South-Atlantic magnetic anomaly and ERB at high latitudes are distinctly observed. This emission is produced by X-rays arising from interactions of ERB particles, descending to the altitude of 500 km in their bounce motion with the am-bient atmospheric matter, and by direct ERB particles passing through the lateral walls and entrance window of the detector (electrons with energies higher than 100 keV and protons with energies higher than 3 MeV). In order to determine the source mechanisms of soft X-rays in the energy range 3 to 8 keV from regions in the ERB, we studied the relationship between the seasonal variation of the X-ray atmospheric radiation and phases of the solar activity cycle. The global monthly, six-monthly, and yearly-averaged X-ray flux distributions were statistically determined for the five-year duration of the CORONAS-F mission. From these distributions, it is possible to infer about the influence of the phase of the solar activity and seasonal effects on the fluxes with energy in the range of 3 to 8 keV. Analysis of these data revealed important regularities in the behavior of this emission. We noted that the emission decreased about 10 times from 2001 to 2005, i.e. from maximum to almost minimum of the solar activity cycle 23 when mean annual values of sunspot number decreased from 110.6 to 28.9. Some compact terrestrial sources of unknown origin located outside of ERB zones were detected. Also, X-rays flux distributions out of ERB were obtained during five strong geomagnetic storms that oc-curred during the CORONAS-F mission on November 6 and 24, 2001; October 28 to November 4, 2003; November 20, 2004; and May15, 2005. (To the memory of V.M. Pankov and V.L. Prokhin, colleagues and coworkers in the Coronas-F mission.)

Pugacheva, Galina; Gusev, Anatoly; Martin, Inácio M.; Spjeldvik, Walther

374

Some Like It Hot: The X-Ray Emission of the Giant Star YY Mensae  

NASA Astrophysics Data System (ADS)

We present an analysis of the X-ray emission of the rapidly rotating giant star YY Mensae observed by Chandra HETGS and XMM-Newton. The high-resolution spectra display numerous emission lines of highly ionized species; Fe XVII to Fe XXV lines are detected, together with H-like and He-like transitions of lower Z elements. Although no obvious flare was detected, the X-ray luminosity changed by a factor of 2 between the XMM-Newton and Chandra observations taken 4 months apart (from logLX~32.2 to 32.5 ergs s-1, respectively). The coronal abundances and the emission measure distribution have been derived from three different methods using optically thin collisional ionization equilibrium models, which is justified by the absence of opacity effects in YY Men as measured from line ratios of Fe XVII transitions. The abundances show a distinct pattern as a function of the first ionization potential (FIP), suggestive of an inverse FIP effect as seen in several active RS CVn binaries. The low-FIP elements (<10 eV) are depleted relative to the high-FIP elements; when compared to its photospheric abundance, the coronal Fe abundance also appears depleted. We find a high N abundance in YY Men's corona, which we interpret as a signature of material processed in the CNO cycle and dredged up in the giant phase. The corona is dominated by a very high temperature (20-40 MK) plasma, which places YY Men among the magnetically active stars with the hottest coronae. Lower temperature plasma also coexists, albeit with much lower emission measure. Line broadening is reported in some lines, with a particularly strong significance in Ne X Ly?. We interpret such broadening as Doppler thermal broadening, although rotational broadening due to X-ray-emitting material high above the surface could be present as well. We use two different formalisms to discuss the shape of the emission measure distribution. The first one infers the properties of coronal loops, whereas the second formalism uses flares as a statistical ensemble. We find that most of the loops in the corona of YY Men have their maximum temperature equal to or slightly larger than about 30 MK. We also find that small flares could contribute significantly to the coronal heating in YY Men. Although there is no evidence of flare variability in the X-ray light curves, we argue that YY Men's distance and X-ray brightness do not allow us to detect flares with peak luminosities LX<=1031 ergs s-1 with current detectors.

Audard, Marc; Telleschi, Alessandra; Güdel, Manuel; Skinner, Stephen L.; Pallavicini, Roberto; Mitra-Kraev, Urmila

2004-12-01

375

On binary-driven hypernovae and their nested late X-ray emission  

NASA Astrophysics Data System (ADS)

Context. The induced gravitational collapse (IGC) paradigm addresses the very energetic (1052-1054 erg) long gamma-ray bursts (GRBs) associated to supernovae (SNe). Unlike the traditional "collapsar" model, an evolved FeCO core with a companion neutron star (NS) in a tight binary system is considered as the progenitor. This special class of sources, here named "binary-driven hypernovae" (BdHNe), presents a composite sequence composed of four different episodes with precise spectral and luminosity features. Aims: We first compare and contrast the steep decay, the plateau, and the power-law decay of the X-ray luminosities of three selected BdHNe (GRB 060729, GRB 061121, and GRB 130427A). Second, to explain the different sizes and Lorentz factors of the emitting regions of the four episodes, for definiteness, we use the most complete set of data of GRB 090618. Finally, we show the possible role of r-process, which originates in the binary system of the progenitor. Methods: We compare and contrast the late X-ray luminosity of the above three BdHNe. We examine correlations between the time at the starting point of the constant late power-law decay t*a, the average prompt luminosity ? Liso ?, and the luminosity at the end of the plateau La. We analyze a thermal emission (~ 0.97-0.29 keV), observed during the X-ray steep decay phase of GRB 090618. Results: The late X-ray luminosities of the three BdHNe, in the rest-frame energy band 0.3-10 keV, show a precisely constrained "nested" structure. In a space-time diagram, we illustrate the different sizes and Lorentz factors of the emitting regions of the three episodes. For GRB 090618, we infer an initial dimension of the thermal emitter of ~ 7 × 1012 cm, expanding at ? ? 2. We find tighter correlations than the Dainotti-Willingale ones. Conclusions: We confirm a constant slope power-law behavior for the late X-ray luminosity in the source rest frame, which may lead to a new distance indicator for BdHNe. These results, as well as the emitter size and Lorentz factor, appear to be inconsistent with the traditional afterglow model based on synchrotron emission from an ultra-relativistic (? ~ 102-103) collimated jet outflow. We argue, instead, for the possible role of r-process, originating in the binary system, to power the mildly relativistic X-ray source.

Ruffini, R.; Muccino, M.; Bianco, C. L.; Enderli, M.; Izzo, L.; Kovacevic, M.; Penacchioni, A. V.; Pisani, G. B.; Rueda, J. A.; Wang, Y.

2014-05-01

376

Thermal and Nonthermal X-ray Emission from the Forward Shock in Tycho's Supernova Remnant  

NASA Technical Reports Server (NTRS)

We present Chandra CCD images of Tycho's supernova remnant that delineate its outer shock, seen as a thin, smooth rim along the straight northeastern edge and most of the circular western half. The images also show that the Si and S ejecta are highly clumpy, and have reached the forward shock at numerous locations. Most of the X-ray spectra that we examine along the rim show line emission from Si and S, which in some cases must come from ejecta; the continuum is well represented by either thermal or nonthermal models. In the case that the continuum is assumed to be thermal, the temperatures at the rim are all similar at about 2 keV, and the ionization ages are very low because of the overall weakness of the line emission. Assuming shock velocities inferred from radio and X-ray expansion measurements, these temperatures are substantially below those expected for equilibration of the electron and ion temperatures; electron to mean temperature ratios of approximately less than 0.1 - 0.2 indicate at most modest collisionless heating of the electrons at the shock. The nonthermal contribution to these spectra may be important, however, and may account for as many as half of the counts in the 4-6 keV energy range, based on an extrapolation of the hard X-ray spectrum above 10 keV.

Hwang, Una; Decourchelle, Anne; Holt, Stephen S.; Petre, Robert; White, Nicholas E. (Technical Monitor)

2002-01-01

377

SCO X-1: Origin of the radio and hard X-ray emissions  

NASA Technical Reports Server (NTRS)

The consequences of models for the central radio source and the hard X-ray ( 30 keV) emitting region in Sco X-1 are examined. It was found that the radio emission could result from noncoherent synchrotron radiation and that the X-rays may be produced by bremsstrahlung. It is shown that both mechanisms require a mass outflow from Sco X-1. The radio source is located at r approximately 3x10 to the 12th power cm from the center of the star, and its linear dimensions do not exceed 3x10 to the 13th power cm. The magnetic field in the radio source is on the order of 1 gauss. If the hard X-rays are produced by thermal bremsstrahlung, their source is located at 10 to the 9th power approximately r approximately 5x10 to the 9th power cm, the temperature is 2x10 to the 9th power K, and the emission measure is 2x10 to the 56th power/cu cm. This hot plasma loses energy inward by conduction and outward by supersonic expansion. The rates of energy loss for both processes are about 10 to the 36th power erg/s, comparable to the total luminosity of Sco X-1.

Ramaty, R.; Cheng, C. C.; Tsuruta, S.

1973-01-01

378

Accelerated electrons and hard X-ray emission from X-pinches  

NASA Astrophysics Data System (ADS)

The generation of accelerated electrons in the X-pinch minidiode is studied experimentally. It is well known that the explosion of an X-pinch consisting of two or more wires is accompanied by the formation of a minidiode, in which electrons are accelerated. The subsequent slowing down of electrons in the products of wire explosion causes the generation of hard X-ray (HXR) emission with photon energies higher than 10 keV. In this work, the spatial and temporal characteristics of X-pinch HXR emission are studied, the specific features of HXR generation are discussed, and the capability of applying this radiation to point-projection X-ray imaging of various plasma and biological objects is considered. The parameters of the electron beam produced in the X-pinch are measured using a Faraday cup and X-ray diagnostics. The experiments were performed with the XP generator (550 kA, 100 ns) at Cornell University (United States) and the BIN generator (270 kA, 150 ns) at the Lebedev Physical Institute (Russia).

Shelkovenko, T. A.; Pikuz, S. A.; Mingaleev, A. R.; Agafonov, A. V.; Romanova, V. M.; Ter-Oganes'yan, A. E.; Tkachenko, S. I.; Blesener, I. C.; Mitchell, M. D.; Chandler, K. M.; Kusse, B. R.; Hammer, D. A.

2008-09-01

379

The Heliospheric Contribution to the Soft X-Ray Background Emission  

NASA Astrophysics Data System (ADS)

The soft x-ray background observed from Earth contains contributions not only from outside the solar system such as the local bubble but contributions from within the solar system including from the interplanetary medium and from the terrestrial geocorona. Great effort was spent on removing non-cosmic contamination from data collected during the ROSAT all-sky survey. Some of the contamination, however, was due to x-ray emission from solar wind charge exchange with interstellar and geocoronal neutrals. The time varying component of this contamination was removed but the steady state component was not. In this paper we will discuss our method of calculating the steady state component of solar wind charge exchange contamination and will present all-sky maps of the soft x-ray emission with this steady state component removed, which will allow for a re-interpretation of the nature of the local interstellar bubble. This method also can be used to obtain information on solar wind fluxes and on solar wind composition at different locations throughout the heliosphere.

Robertson, Ina P.; Kuntz, Kip D.; Collier, Michael R.; Cravens, Thomas E.; Snowden, Steven L.

2010-03-01

380

THE BURSTY NATURE OF SOLAR FLARE X-RAY EMISSION. II. THE NEUPERT EFFECT  

SciTech Connect

We carry out a novel statistical test of the Neupert effect based on multifractal spectra. The multifractal spectrum is the number distribution of the strengths (i.e., the Hölder exponents) of bursts in a signal. This is tested on simulations and carried out on RHESSI X-ray data from a well observed GOES X4.8 magnitude flare. The multifractal spectra is ideally suited to quantifying the relative smooth and bursty signals typically found in (thermal) soft X-ray and (non-thermal) hard X-ray data of solar flares. We show that light curves from all energies between 3 keV and 25 keV are statistically similar, suggesting that all these signals are dominated by the same (presumably thermal) emission. Emission lying between 25 keV and 100 keV probably contains some contribution from both thermal and non-thermal sources. The multifractal spectrum of a signal and that of its (cumulative) temporal integration are statistically similar (i.e., low residuals upon subtraction), but shifted by one in the peak Hölder exponent. We find the pairs of 3-6 keV and 100-300 keV emissions, the 6-12 keV and 100-300 keV emissions and the 12-25 keV and 100-300 keV emissions are all consistent with the Neupert effect. The best agreement with the Neupert effect is between the 12-25 keV and 100-300 keV pair, although possibly with some secondary source of thermal emission present.

McAteer, R. T. James [Department of Astronomy, New Mexico State University, MSC 4500, NM 88003-8001 (United States); Bloomfield, D. Shaun, E-mail: mcateer@nmsu.edu [Astrophysics Research Group, School of Physics, Trinity College Dublin, College Green, Dublin 2 (Ireland)

2013-10-20

381

Chemical Analysis of Impurity Boron Atoms in Diamond Using Soft X-ray Emission Spectroscopy  

SciTech Connect

To analyze the local structure and/or chemical states of boron atoms in boron-doped diamond, which can be synthesized by the microwave plasma-assisted chemical vapor deposition method (CVD-B-diamond) and the temperature gradient method at high pressure and high temperature (HPT-B-diamond), we measured the soft X-ray emission spectra in the CK and BK regions of B-diamonds using synchrotron radiation at the Advanced Light Source (ALS). X-ray spectral analyses using the fingerprint method and molecular orbital calculations confirm that boron atoms in CVD-B-diamond substitute for carbon atoms in the diamond lattice to form covalent B-C bonds, while boron atoms in HPT-B-diamond react with the impurity nitrogen atoms to form hexagonal boron nitride. This suggests that the high purity diamond without nitrogen impurities is necessary to synthesize p-type B-diamond semiconductors.

Muramatsu, Yasuji; Iihara, Junji; Takebe, Toshihiko; Denlinger, Jonathan D.

2008-03-29

382

MCNP Simulation to Hard X-Ray Emission of KSU Dense Plasma Focus Machine  

E-print Network

The MCNP program used to simulate the hard x-ray emission from KSU dense plasma focus device, an electron beam spectrum of maximum energy 100 keV was used to hit anode target. The bremsstrahlung radiation was measured using the F2 tally functions on the chamber walls and on a virtual sphere surrounding the machine, the radiation spectrum was recorded for various anode materials like tungsten, stainless steel and molybdenum. It was found that tungsten gives the best and the most intense radiation for the same electron beam. An aluminum filter of thickness 2mm and 4mm was used to cutoff the lower energy band from the x-ray spectrum. It was found that the filters achieved the mission and there is no distinct difference in between.

Mohamed, Amgad E

2015-01-01

383

Computer modeling of X-ray emission and absorption in the context of hot star winds  

NASA Astrophysics Data System (ADS)

In support of ongoing studies of the X-ray emission from hot stars, we have been working on simulations of the X-ray output from mixtures of plasmas at wide ranges of temperature. These simulations have been carried out using the Spect3D, Spect3D Visualizer, and Plasma Grid Generator programs developed by Prism Computational Sciences. The Spect3D code allows construction of a plasma of arbitrary geometry and composition, and can then be used to calculate the observed spectrum for any direction of observation. Our initial studies have concentrated on simple geometric situations to build the foundations for more complicated spherical geometries. While the initial simulations used a mixture of hydrogen, helium, and oxygen, later simulations are including all important elements in their astrophysical abundances. We acknowledge support from Research Corporation, NASA grant GO4-5015B, and the University of Wisconsin-Eau Claire.

Abing, C. B.; Miller, N. A.

2005-12-01

384

X-ray Fluorescence Emission Tomography (XFET) with Novel Imaging Geometries – A Monte Carlo Study  

PubMed Central

This paper presents a feasibility study for using two new imaging geometries for synchrotron X-ray fluorescence emission tomography (XFET) applications. In the proposed approaches, the object is illuminated with synchrotron X-ray beams of various cross-sectional dimensions. The resultant fluorescence photons are detected by high-resolution imaging-spectrometers coupled to collimation apertures. To verify the performance benefits of the proposed methods over the conventional line-by-line scanning approach, we have used both Monte Carlo simulations and an analytical system performance index to compare several different imaging geometries. This study has demonstrated that the proposed XFET approach could lead to a greatly improved imaging speed, which is critical for making XFET a practical imaging modality for a wide range of applications. PMID:22228913

Meng, L. J.; Li, Nan; La Riviere, P. J.

2011-01-01

385

On the persistent X-ray emission from the soft gamma-ray repeaters  

E-print Network

It is suggested that the persistent X-ray emission from the soft gamma-ray repeaters is the thermal radiation of neutron stars which is enhanced by a factor of 10 or more due to the effect of a very strong magnetic field on the thermal structure of the neutron star envelope. For the thermal luminosity to be consistent with the persistent X-ray luminosity, the field strength at the neutron star surface has to be of the order of $10^{15}$ G. If it is confirmed that the soft gamma-ray repeaters are neutron stars with negligible accretion, then the presence of such a strong magnetic field is inevitable.

V. V. Usov

1996-12-10</