Detecting axion stars with radio telescopes

NASA Astrophysics Data System (ADS)

Bai, Yang; Hamada, Yuta

2018-06-01

When axion stars fly through an astrophysical magnetic background, the axion-to-photon conversion may generate a large electromagnetic radiation power. After including the interference effects of the spacially-extended axion-star source and the macroscopic medium effects, we estimate the radiation power when an axion star meets a neutron star. For a dense axion star with 10-13M⊙, the radiated power is at the order of 1011W ×(100 μeV /ma) 4(B /1010Gauss) 2 with ma as the axion particle mass and B the strength of the neutron star magnetic field. For axion stars occupy a large fraction of dark matter energy density, this encounter event with a transient O (0.1s) radio signal may happen in our galaxy with the averaged source distance of one kiloparsec. The predicted spectral flux density is at the order of μJy for a neutron star with B ∼1013 Gauss. The existing Arecibo, GBT, JVLA and FAST and the ongoing SKA radio telescopes have excellent discovery potential of dense axion stars.

Fermi LAT detection of GeV flares from blazars PKS 0458-02 and B2 1144+40

NASA Astrophysics Data System (ADS)

Antolini, Elisa; Buson, Sara

2014-03-01

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from two sources positionally consistent with the flat spectrum radio quasars PKS 0458-02 (also known as 2FGL J0501.2-0155, Nolan et al. 2012 ApJS, 199, 31) and B2 1144+40 (also known as S4 1144+40 and 2FGL J1146.9+4000). PKS 0458-02 has the radio coordinates RA=05h01m12.8098s, Dec=-1d59m14.255s (J2000, Johnston et al.

THE LOW-FREQUENCY RADIO CATALOG OF FLAT-SPECTRUM SOURCES

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

Massaro, F.; Giroletti, M.; D'Abrusco, R.

A well known property of the γ-ray sources detected by Cos-B in the 1970s, by the Compton Gamma-Ray Observatory in the 1990s, and recently by the Fermi observations is the presence of radio counterparts, particularly for those associated with extragalactic objects. This observational evidence is the basis of the radio-γ-ray connection established for the class of active galactic nuclei known as blazars. In particular, the main spectral property of the radio counterparts associated with γ-ray blazars is that they show a flat spectrum in the GHz frequency range. Our recent analysis dedicated to search blazar-like candidates as potential counterparts formore » the unidentified γ-ray sources allowed us to extend the radio-γ-ray connection in the MHz regime. We also showed that blazars below 1 GHz maintain flat radio spectra. Thus, on the basis of these new results, we assembled a low-frequency radio catalog of flat-spectrum sources built by combining the radio observations of the Westerbork Northern Sky Survey and of the Westerbork in the southern hemisphere catalog with those of the NRAO Very Large Array Sky survey (NVSS). This could be used in the future to search for new, unknown blazar-like counterparts of γ-ray sources. First, we found NVSS counterparts of Westerbork Synthesis Radio Telescope radio sources, and then we selected flat-spectrum radio sources according to a new spectral criterion, specifically defined for radio observations performed below 1 GHz. We also described the main properties of the catalog listing 28,358 radio sources and their logN-logS distributions. Finally, a comparison with the Green Bank 6 cm radio source catalog was performed to investigate the spectral shape of the low-frequency flat-spectrum radio sources at higher frequencies.« less

VizieR Online Data Catalog: WISE data for radio-loud AGN complete samples (Gurkan+, 2014)

NASA Astrophysics Data System (ADS)

Gurkan, G.; Hardcastle, M. J.; Jarvis, M. J.

2014-11-01

The 3CRR, 2Jy, 6CE and 7CE samples were chosen for our analysis. We used the revised subsample of the 3CR catalogue of radio sources (Bennett, 1962MNRAS.125...75B), which have flux densities greater than 10.9Jy at 178MHz (Laing, Riley & Longair, 1983MNRAS.204..151L, Cat. J/MNRAS.204.151). There are 172 sources with 0.0029

Investigation on the Frequency Allocation for Radio Astronomy at the L Band

NASA Astrophysics Data System (ADS)

Abidin, Z. Z.; Umar, R.; Ibrahim, Z. A.; Rosli, Z.; Asanok, K.; Gasiprong, N.

2013-09-01

In this paper, the frequency allocation reserved for radio astronomy in the L band set by the International Telecommunication Union (ITU), which is between 1400 and 1427 MHz, is reviewed. We argue that the nearby frequencies are still very important for radio astronomers on the ground by investigating radio objects (H i sources) around 1300-1500 MHz. The L-band window is separated into a group of four windows, namely 1400-1427 MHz (window A), 1380-1400 MHz (window B), 1350-1380 MHz (window C), and 1300-1350 MHz (window D). These windows are selected according to their redshifts from a rest frequency for hydrogen spectral line at 1420.4057 MHz. Radio objects up to z ≈ 0.1 or frequency down to 1300 MHz are examined. We argue that since window B has important radio objects within the four windows, this window should also be given to radio astronomy. They are galaxies, spiral galaxies, and galaxy clusters. This underlines the significance of window B for radio astronomers on the ground. By investigating the severeness of radio frequency interference (RFI) within these windows, we have determined that window B still has significant, consistent RFI. The main RFI sources in the four windows have also been identified. We also found that the Department of Civil Aviation of Malaysia is assigned a frequency range of 1215-1427 MHz, which is transmitted within the four windows and inside the protected frequency for radio astronomy. We also investigated the RFI in the four windows on proposed sites of future radio astronomy observatories in Malaysia and Thailand and found the two best sites as Universiti Pendidikan Sultan Idris (UPSI) and Ubon Ratchathani, respectively. It has also been determined that RFI in window B increases with population density.

DISCOVERY OF EXTENDED AND VARIABLE RADIO STRUCTURE FROM THE GAMMA-RAY BINARY SYSTEM PSR B1259-63/LS 2883

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

Moldon, Javier; Ribo, Marc; Paredes, Josep M.

2011-05-01

PSR B1259-63 is a 48 ms pulsar in a highly eccentric 3.4 year orbit around the young massive star LS 2883. During the periastron passage the system displays transient non-thermal unpulsed emission from radio to very high energy gamma rays. It is one of the three galactic binary systems clearly detected at TeV energies, together with LS 5039 and LS I +61 303. We observed PSR B1259-63 after the 2007 periastron passage with the Australian Long Baseline Array at 2.3 GHz to trace the milliarcsecond (mas) structure of the source at three different epochs. We have discovered extended and variablemore » radio structure. The peak of the radio emission is detected outside the binary system near periastron, at projected distances of 10-20 mas (25-45 AU assuming a distance of 2.3 kpc). The total extent of the emission is {approx}50 mas ({approx}120 AU). This is the first observational evidence that non-accreting pulsars orbiting massive stars can produce variable extended radio emission at AU scales. Similar structures are also seen in LS 5039 and LS I +61 303, in which the nature of the compact object is unknown. The discovery presented here for the young non-accreting pulsar PSR B1259-63 reinforces the link with these two sources and supports the presence of pulsars in these systems as well. A simple kinematical model considering only a spherical stellar wind can approximately trace the extended structures if the binary system orbit has a longitude of the ascending node of {Omega} {approx} -40{sup 0} and a magnetization parameter of {sigma} {approx} 0.005.« less

Finding the rarest objects in the universe: A new, efficient method for discovering BL Lacertae objects

NASA Technical Reports Server (NTRS)

Stocke, John; Perlman, Eric; Granados, Arno; Schachter, Jonathan; Elvis, Martin; Urry, Meg; Impey, Chris; Smith, Paul

1993-01-01

We present a new, efficient method for discovering new BL Lac Objects based upon the results of the Einstein Extended Medium Sensitivity Survey (EMSS). We have found that all x-ray selected BL Lacs are radio emitters, and further, that in a 'color-color' diagram (radio/optical and optical/x-ray) the BL Lac Objects occupy an area distinct from both radio loud quasars and the radio quiet QSOs and Seyferts which dominate x-ray selected samples. After obtaining radio counterparts via VLA 'snapshot' observations of a large sample of unidentified x-ray sources, the list of candidates is reduced. These candidates then can be confirmed with optical spectroscopy and/or polarimetry. Since greater than 70 percent of these sources are expected to be BL Lacs, the optical observations are very efficient. We have tested this method using unidentified sources found in the Einstein Slew Survey. The 162 Slew Survey x-ray source positions were observed with the VLA in a mixed B/C configuration at 6 cm resulting in 60 detections within 1.5 position error circle radii. These x-ray/optical/radio sources were then plotted, and 40 BL Lac candidates were identified. To date, 10 candidates have been spectroscopically observed resulting in 10 new BL Lac objects! Radio flux, optical magnitude, and polarization statistics (obtained in white light with the Steward Observatory 2.3 m CCD polarimeter) for each are given.

An X-ray Observation of the L1251 Dark Cloud

NASA Technical Reports Server (NTRS)

Simon, Theodore

2006-01-01

An X-ray image of the L1251 dark cloud in Cepheus was obtained with the XMM-Newton telescope. More than three dozen sources were detected above a 3 delta limit in X-ray luminosity of L(sub X = 10(exp 29) ergs/s. Among the detections are eight optically visible T Tauri stars, which had been identified in earlier work from their emission at H(alpha). The two strongest X-ray sources have steady luminosities of L(sub X) approx. 10(exp 31) ergs/s and are at the saturation limit for X-ray activity in late-type stars, L(sub X)/L(sub bol) approx. 10(exp -3). X-ray emission was also observed from two CO emission cores in L1251, core C (L1251A) and core E (L1251B). Both regions contain high-velocity molecular gas, bright IRAS sources (Class I protostars), thermal radio sources, and Herbig-Haro (HH) jets. In L1251A strong X-ray emission was discovered in close proximity to the near-inbred and radio source IRSA/VLA 7 and to IRAS 22343+7501. IRSA/VLA 7 thus appears to be the most likely source of the molecular and HH outflows in L1251A. In L1251B X-ray emission was observed from a visible T Tauri star, KP2-44, which is thought to be the driving source for HH 189. Also reported is the tentative detection of X-ray emission from VLA 3, a thermal radio continuum source in L1251B that is closely associated with the extreme Class I protostar IRAS 22376+7455.

Interstellar molecules and dense clouds.

NASA Technical Reports Server (NTRS)

Rank, D. M.; Townes, C. H.; Welch, W. J.

1971-01-01

Current knowledge of the interstellar medium is discussed on the basis of recent published studies. The subjects considered include optical identification of interstellar molecules, radio molecular lines, interstellar clouds, isotopic abundances, formation and disappearance of interstellar molecules, and interstellar probing techniques. Diagrams are plotted for the distribution of galactic sources exhibiting molecular lines, for hydrogen molecule, hydrogen atom and electron abundances due to ionization, for the densities, velocities and temperature of NH3 in the direction of Sagitarius B2, for the lower rotational energy levels of H2CO, and for temporal spectral variations in masing H2O clouds of the radio source W49. Future applications of the maser and of molecular microscopy in this field are visualized.

Long-Term Stability of Radio Sources in VLBI Analysis

NASA Technical Reports Server (NTRS)

Engelhardt, Gerald; Thorandt, Volkmar

2010-01-01

Positional stability of radio sources is an important requirement for modeling of only one source position for the complete length of VLBI data of presently more than 20 years. The stability of radio sources can be verified by analyzing time series of radio source coordinates. One approach is a statistical test for normal distribution of residuals to the weighted mean for each radio source component of the time series. Systematic phenomena in the time series can thus be detected. Nevertheless, an inspection of rate estimation and weighted root-mean-square (WRMS) variations about the mean is also necessary. On the basis of the time series computed by the BKG group in the frame of the ICRF2 working group, 226 stable radio sources with an axis stability of 10 as could be identified. They include 100 ICRF2 axes-defining sources which are determined independently of the method applied in the ICRF2 working group. 29 stable radio sources with a source structure index of less than 3.0 can also be used to increase the number of 295 ICRF2 defining sources.

A New Fundamental Plane for Radiatively Efficient Black-hole Sources

NASA Astrophysics Data System (ADS)

Dong, Ai-Jun; Wu, Qingwen; Cao, Xiao-Feng

2014-06-01

In recent years, it has been found that several low/hard states of X-ray binaries (XRBs) follow an "outliers" track in the radio-X-ray correlation (L_R\\propto L_X^{b} and b ~ 1.4), which is much steeper than the former universal track with b ~ 0.6. In this work, we compile a sample of bright radio-quiet active galactic nuclei (AGNs) and find that their hard X-ray photon indices and Eddington ratios are positively correlated, which is similar to that of XRB outliers, where both bright AGNs and XRB outliers have bolometric Eddington ratios >~ 1%L Edd (L Edd is Eddington luminosity). The Eddington-scaled radio-X-ray correlation of these AGNs is also similar to that of XRB outliers, which has the form of L 5 GHz/L Eddvprop(L 2-10 keV/L Edd) c with c ~= 1.59 and 1.53 for AGNs and XRBs, respectively. Both the positively correlated X-ray spectral evolution and the steeper radio-X-ray correlation can be regulated by a radiatively efficient accretion flow (e.g., disk-corona). Based on these similarities, we further present a new fundamental plane for XRB outliers and bright AGNs in black-hole (BH) mass, radio, and X-ray luminosity space: log L_R=1.59^{+0.28}_{-0.22} log L_X- 0.22^{+0.19}_{-0.20}log M_BH-28.97^{+0.45}_{-0.45} with a scatter of σR = 0.51 dex. This fundamental plane is suitable for radiatively efficient BH sources, while the former plane proposed by Merloni et al. and Falcke et al. may be most suitable for radiatively inefficient sources.

A radio monitoring survey of ultra-luminous X-ray sources

NASA Astrophysics Data System (ADS)

Körding, E.; Colbert, E.; Falcke, H.

2005-06-01

We present the results of a radio monitoring campaign to search for radio emission from nearby ultra-luminous X-ray sources (ULXs). These sources are bright off-nuclear X-ray point sources with luminosities exceeding LX > 1039 erg s-1. A well-defined sample of the 9 nearest ULXs has been monitored eight times over 5 months with the Very Large Array in A and B configuration. Our limiting sensitivity is ≈0.15 mJy (4σ) for radio flares and ≈60 μJy for continuous emission. In M 82 two ULXs seem to have coincident compact radio sources, which are probably supernova remnants. No continuous or flaring radio emission has been detected from any other ULX. Thus, ULXs do not generally emit steady-state radio emission above radio powers of 1.5 × 1017 W/Hz. The non-detections of the continuous emission are consistent with beamed or unbeamed radio emission from accreting black holes of ≤ 103 M⊙ based on the radio/X-ray correlation. Other published radio detections (M 82, NGC 5408) are also discussed in this context. Both detections are significantly above our detection limit. If ULXs have flaring radio emission above 4 × 1017 W/Hz we can give an upper limit on the duty cycle of the flares of 6%. This upper limit is in agreement with the observed number of flares in Galactic radio transients. Additionally we present a yet unreported radio double structure in the nearby low-luminosity AGN NGC 4736.

Milliarcsecond Imaging of the Radio Emission from the Quasar with the Most Massive Black Hole at Reionization

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

Wang, Ran; Wu, Xue-Bing; Jiang, Linhua

We report Very Long Baseline Array (VLBA) observations of the 1.5 GHz radio continuum emission of the z = 6.326 quasar SDSS J010013.02+280225.8 (hereafter J0100+2802). J0100+2802 is by far the most optically luminous and is a radio-quiet quasar with the most massive black hole known at z > 6. The VLBA observations have a synthesized beam size of 12.10 mas ×5.36 mas (FWHM), and detected the radio continuum emission from this object with a peak surface brightness of 64.6 ± 9.0 μ Jy beam{sup −1} and a total flux density of 88 ± 19 μ Jy. The position of themore » radio peak is consistent with that from SDSS in the optical and Chandra in the X-ray. The radio source is marginally resolved by the VLBA observations. A 2D Gaussian fit to the image constrains the source size to (7.1 ± 3.5) mas × (3.1 ± 1.7) mas. This corresponds to a physical scale of (40 ± 20) pc × (18 ± 10) pc. We estimate the intrinsic brightness temperature of the VLBA source to be T {sub B} = (1.6 ± 1.2) × 10{sup 7} K. This is significantly higher than the maximum value in normal star-forming galaxies, indicating an active galactic nucleus (AGN) origin for the radio continuum emission. However, it is also significantly lower than the brightness temperatures found in highest-redshift radio-loud quasars. J0100+2802 provides a unique example for studying the radio activity in optically luminous and radio-quiet AGNs in the early universe. Further observations at multiple radio frequencies will accurately measure the spectral index and address the dominant radiation mechanism of the radio emission.« less

Search for the Identification of 3EG J1835+5918: Evidence for a New Type of High-Energy Gamma-Ray Source

NASA Technical Reports Server (NTRS)

Mirabal, N.; Halpern, Jules P.; Eracleous, M.; Becker, R. H.; Oliversen, Ronald (Technical Monitor)

2001-01-01

The EGRET source 3EG J1835+5918 is the brightest and most accurately positioned of the as-yet unidentified high-energy gamma-ray sources at high Galactic latitude (l, b = 89 deg, 25 deg). We present a multiwavelength study of the region around it, including X-ray, radio, and optical imaging surveys, as well as optical spectroscopic classification of most of the active objects in this area. Identifications are made of all but one of the ROSAT and ASCA sources in this region to a flux limit of approximately 5 x 10(exp -14) erg/sq cm s, which is 10(exp -4) of the gamma-ray flux. The identified X-ray sources in or near the EGRET error ellipse are radio-quiet QSOs, a galaxy cluster, and coronal emitting stars. We also find eight quasars using purely optical color selection, and we have monitored the entire field for variable optical objects on short and long time scales without any notable discoveries. The radio sources inside the error ellipse are all fainter than 4 mJy at 1.4 GHz. There are no flat-spectrum radio sources in the vicinity; the brightest neighboring radio sources are steep-spectrum radio galaxies or quasars. Since no blazar-like or pulsar-like candidate has been found as a result of these searches, 3EG J1835+5918 must be lacking one or more of the physically essential attributes of these known classes of gamma-ray emitters. If it is an AGN it lacks the beamed emission radio of blazars by at least a factor of 100 relative to identified EGRET blazars. If it is an isolated neutron star, it lacks the steady thermal X-rays from a cooling surface and the magnetospheric non-thermal X-ray emission that is characteristic of all EGRET pulsars. If a pulsar, 3EG J1835+5918 must be either older or more distant than Geminga, and probably an even more efficient or beamed gamma-ray engine. One intermittent ROSA T source falls on a blank optical field to a limit of B greater than 23.4, V greater than 23.3, and R greater than 22.5. In view of this conspicuous absence, RX J1836-2+5925 should be examined further as a candidate for identification with 3EG J1835+5918 and possibly the prototype of a new class of high-energy gamma-ray source.

Study of the molecular and ionized gas in a possible precursor of an ultra-compact H II region

NASA Astrophysics Data System (ADS)

Ortega, M. E.; Paron, S.; Giacani, E.; Celis Peña, M.; Rubio, M.; Petriella, A.

2017-10-01

Aims: We aim to study the molecular and the ionized gas in a possible precursor of an ultra-compact H II region to contribute to the understanding of how high-mass stars build-up their masses once they have reached the zero-age main sequence. Methods: We carried out molecular observations toward the position of the Red MSX source G052.9221-00.4892, using the Atacama Submillimeter Telescope Experiment (ASTE; Chile) in the 12CO J = 3-2, 13CO J = 3-2, C18O J = 3-2, and HCO+J = 4-3 lines with an angular resolution of about 22''. We also present radio continuum observations at 6 GHz carried out with the Jansky Very Large Array (JVLA; USA) interferometer with a synthesized beam of 4.8 arcsec × 4.1 arcsec. The molecular data were used to study the distribution and kinematics of the molecular gas, while the radio continuum data were used to characterize the ionized gas in the region. Combining these observations with public infrared data allowed us to inquire about the nature of the source. Results: The analysis of the molecular observations reveals the presence of a kinetic temperature and H2 column density gradients across the molecular clump in which the Red MSX source G052.9221-00.4892 is embedded, with the hotter and less dense gas in the inner region. The 12CO J = 3-2 emission shows evidence of misaligned massive molecular outflows, with the blue lobe in positional coincidence with a jet-like feature seen at 8 μm. The radio continuum emission shows a slightly elongated compact radio source, with a flux density of about 0.9 mJy, in positional coincidence with the Red MSX source. The polar-like morphology of this compact radio source perfectly matches the hourglass-like morphology exhibited by the source in the Ks band. Moreover, the axes of symmetry of the radio source and the near-infrared nebula are perfectly aligned. Thus, based on the presence of molecular outflows, the slightly elongated morphology of the compact radio source matching the hourglass-like morphology of the source at the Ks band, and the lack of evidence of collimated jets in the near-infrared spectrum, one interpretation for the nature of the source, is that the Red MSX source G052.9221-00.4892 could be transiting a hyper-compact H II region phase, in which the young central star emits winds and ionizing radiation through the poles. On the other hand, according to a comparison between the Brγ intensity and the radio flux density at 6 GHz, the source would be in a more evolved evolutionary stage of an optically thin UC H II region in photoionization equilibrium. If this is the case, from the radio continuum emission, we can conjecture upon the spectral type of its exciting star which would be a B0.5V.

Complete identification of the Parkes half-Jansky sample of GHz peaked spectrum radio galaxies

NASA Astrophysics Data System (ADS)

de Vries, N.; Snellen, I. A. G.; Schilizzi, R. T.; Lehnert, M. D.; Bremer, M. N.

2007-03-01

Context: Gigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be the young counterparts of classical extended radio sources. Statistically complete samples of GPS sources are vital for studying the early evolution of radio-loud AGN and the trigger of their nuclear activity. The "Parkes half-Jansky" sample of GPS radio galaxies is such a sample, representing the southern counterpart of the 1998 Stanghellini sample of bright GPS sources. Aims: As a first step of the investigation of the sample, the host galaxies need to be identified and their redshifts determined. Methods: Deep R-band VLT-FORS1 and ESO 3.6 m EFOSC II images and long slit spectra have been taken for the unidentified sources in the sample. Results: We have identified all twelve previously unknown host galaxies of the radio sources in the sample. Eleven have host galaxies in the range 21.0 < RC < 23.0, while one object, PKS J0210+0419, is identified in the near infrared with a galaxy with Ks = 18.3. The redshifts of 21 host galaxies have been determined in the range 0.474 < z < 1.539, bringing the total number of redshifts to 39 (80%). Analysis of the absolute magnitudes of the GPS host galaxies show that at z>1 they are on average a magnitude fainter than classical 3C radio galaxies, as found in earlier studies. However their restframe UV luminosities indicate that there is an extra light contribution from the AGN, or from a population of young stars. Based on observations collected at the European Southern Observatory Very Large Telescope, Paranal, Chile (ESO prog. ID No. 073.B-0289(B)) and the European Southern Observatory 3.6 m Telescope, La Silla, Chile (prog. ID No. 073.B-0289(A)). Appendices are only available in electronic form at http://www.aanda.org

A circumstellar molecular gas structure associated with the massive young star Cepheus A-HW 2

NASA Technical Reports Server (NTRS)

Torrelles, Jose M.; Rodriguez, Luis F.; Canto, Jorge; Ho, Paul T. P.

1993-01-01

We report the detection via VLA-D observations of ammonia of a circumstellar high-density molecular gas structure toward the massive young star related to the object Cepheus A-HW 2, a firm candidate for the powering source of the high-velocity molecular outflow in the region. We suggest that the circumstellar molecular gas structure could be related to the circumstellar disk previously suggested from infrared, H2O, and OH maser observations. We consider as a plausible scenario that the double radio continuum source of HW 2 could represent the ionized inner part of the circumstellar disk, in the same way as proposed to explain the double radio source in L1551. The observed motions in the circumstellar molecular gas can be produced by bound motions (e.g., infall or rotation) around a central mass of about 10-20 solar masses (B0.5 V star or earlier).

Steep radio spectra in high-redshift radio galaxies

NASA Technical Reports Server (NTRS)

Krolik, Julian H.; Chen, Wan

1991-01-01

The generic spectrum of an optically thin synchrotron source steepens by 0.5 in spectral index from low frequencies to high whenever the source lifetime is greater than the energy-loss timescale for at least some of the radiating electrons. Three effects tend to decrease the frequency nu(b) of this spectral bend as the source redshift increases: (1) for fixed bend frequency nu* in the rest frame, nu(b) = nu*/(1 + z); (2) losses due to inverse Compton scattering the microwave background rise with redshift as (1 + z) exp 4, so that, for fixed residence time in the radiating region, the energy of the lowest energy electron that can cool falls rapidly with increasing redshift; and (3) if the magnetic field is proportional to the equipartition field and the emitting volume is fixed or slowly varying, flux-limited samples induce a selection effect favoring low nu* at high z because higher redshift sources require higher emissivity to be included in the sample, and hence have stronger implied fields and more rapid synchrotron losses. A combination of these effects may explain the trend observed in the 3CR sample for higher redshift radio galaxies to have steeper spectra, and the successful use of ultrasteep spectrum surveys to locate high-redshift galaxies.

FARADAY ROTATION STRUCTURE ON KILOPARSEC SCALES IN THE RADIO LOBES OF CENTAURUS A

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

Feain, I. J.; Ekers, R. D.; Norris, R. P.

2009-12-10

We present the results of an Australia Telescope Compact Array 1.4 GHz spectropolarimetric aperture synthesis survey of 34 deg{sup 2} centered on Centaurus A-NGC 5128. A catalog of 1005 extragalactic compact radio sources in the field to a continuum flux density of 3 mJy beam{sup -1} is provided along with a table of Faraday rotation measures (RMs) and linear polarized intensities for the 28% of sources with high signal to noise in linear polarization. We use the ensemble of 281 background polarized sources as line-of-sight probes of the structure of the giant radio lobes of Centaurus A. This is themore » first time such a method has been applied to radio galaxy lobes and we explain how it differs from the conventional methods that are often complicated by depth and beam depolarization effects. Assuming a magnetic field strength in the lobes of 1.3 B {sub 1} muG, where B {sub 1} = 1 is implied by equipartition between magnetic fields and relativistic particles, the upper limit we derive on the maximum possible difference between the average RM of 121 sources behind Centaurus A and the average RM of the 160 sources along sightlines outside Centaurus A implies an upper limit on the volume-averaged thermal plasma density in the giant radio lobes of (n{sub e} ) < 5 x 10{sup -5} B {sup -1} {sub 1} cm{sup -3}. We use an RM structure function analysis and report the detection of a turbulent RM signal, with rms sigma{sub RM} = 17 rad m{sup -2} and scale size 0.{sup 0}3, associated with the southern giant lobe. We cannot verify whether this signal arises from turbulent structure throughout the lobe or only in a thin skin (or sheath) around the edge, although we favor the latter. The RM signal is modeled as possibly arising from a thin skin with a thermal plasma density equivalent to the Centaurus intragroup medium density and a coherent magnetic field that reverses its sign on a spatial scale of 20 kpc. For a thermal density of n {sub 1} 10{sup -3} cm{sup -3}, the skin magnetic field strength is 0.8 n {sup -1} {sub 1} muG.« less

A low frequency RFI monitoring system

NASA Astrophysics Data System (ADS)

Amiri, Shahram; Shankar, N. Udaya; Girish, B. S.; Somashekar, R.

Radio frequency interference (RFI) is a growing problem for research in radio astronomy particularly at wavelengths longer than 2m. For satisfactory operation of a radio telescope, several bands have been protected for radio astronomy observations by the International Telecommunication Union. Since the radiation from cosmic sources are typically 40 to 100 dB below the emission from services operating in unprotected bands, often the out-of-band emission limits the sensitivity of astronomical observations. Moreover, several radio spectral emissions from cosmic sources are present in the frequency range outside the allocated band for radio astronomy. Thus monitoring of RFI is essential before building a receiver system for low frequency radio astronomy. We describe the design and development of an RFI monitoring system operating in the frequency band 30 to 100 MHz. This was designed keeping in view our proposal to extend the frequency of operation of GMRT down to 40 MHz. The monitor is a PC based spectrometer recording the voltage output of a receiver connected to an antenna, capable of digitizing the low frequency RF directly with an 8 bit ADC and sampling bandwidths up to 16 MHz. The system can operate continuously in almost real-time with a loss of only 2% of data. Here we will present the systems design aspects and the results of RFI monitoring carried out at the Raman Research Institute, Bangalore and at the GMRT site in Khodad.

Broadband Spectral Modeling of the Extreme Gigahertz-peaked Spectrum Radio Source PKS B0008-421

NASA Astrophysics Data System (ADS)

Callingham, J. R.; Gaensler, B. M.; Ekers, R. D.; Tingay, S. J.; Wayth, R. B.; Morgan, J.; Bernardi, G.; Bell, M. E.; Bhat, R.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Deshpande, A. A.; Ewall-Wice, A.; Feng, L.; Greenhill, L. J.; Hazelton, B. J.; Hindson, L.; Hurley-Walker, N.; Jacobs, D. C.; Johnston-Hollitt, M.; Kaplan, D. L.; Kudrayvtseva, N.; Lenc, E.; Lonsdale, C. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Pindor, B.; Prabu, T.; Procopio, P.; Riding, J.; Srivani, K. S.; Subrahmanyan, R.; Udaya Shankar, N.; Webster, R. L.; Williams, A.; Williams, C. L.

2015-08-01

We present broadband observations and spectral modeling of PKS B0008-421 and identify it as an extreme gigahertz-peaked spectrum (GPS) source. PKS B0008-421 is characterized by the steepest known spectral slope below the turnover, close to the theoretical limit of synchrotron self-absorption, and the smallest known spectral width of any GPS source. Spectral coverage of the source spans from 0.118 to 22 GHz, which includes data from the Murchison Widefield Array and the wide bandpass receivers on the Australia Telescope Compact Array. We have implemented a Bayesian inference model fitting routine to fit the data with internal free-free absorption (FFA), single- and double-component FFA in an external homogeneous medium, FFA in an external inhomogeneous medium, or single- and double-component synchrotron self-absorption models, all with and without a high-frequency exponential break. We find that without the inclusion of a high-frequency break these models cannot accurately fit the data, with significant deviations above and below the peak in the radio spectrum. The addition of a high-frequency break provides acceptable spectral fits for the inhomogeneous FFA and double-component synchrotron self-absorption models, with the inhomogeneous FFA model statistically favored. The requirement of a high-frequency spectral break implies that the source has ceased injecting fresh particles. Additional support for the inhomogeneous FFA model as being responsible for the turnover in the spectrum is given by the consistency between the physical parameters derived from the model fit and the implications of the exponential spectral break, such as the necessity of the source being surrounded by a dense ambient medium to maintain the peak frequency near the gigahertz region. This implies that PKS B0008-421 should display an internal H i column density greater than 1020 cm-2. The discovery of PKS B0008-421 suggests that the next generation of low radio frequency surveys could reveal a large population of GPS sources that have ceased activity, and that a portion of the ultra-steep-spectrum source population could be composed of these GPS sources in a relic phase.

Toward Understanding the Fanaroff-Riley Dichotomy in Radio Source Morphology and Power

NASA Astrophysics Data System (ADS)

Baum, Stefi A.; Zirbel, Esther L.; O'Dea, Christopher P.

1995-09-01

In Paper I we presented the results of a study of the interrelationships between host galaxy magnitude, optical line luminosity, and radio luminosity in a large sample of Fanaroff-Riley classes 1 and 2 (FR 1 and FR 2) radio galaxies. We report several important differences between the FR 1 and FR 2 radio galaxies. At the same host galaxy magnitude or radio luminosity, the FR 2's produce substantially more optical line emission (by roughly an order of magnitude or more) than do FR 1's. Similarly, FR 2 sources produce orders of magnitude more line luminosity than do radio-quiet galaxies of the same optical magnitude, while FR 1 sources and radio-quiet galaxies of the same optical magnitude produce similar line luminosities. Combining these results with previous results from the literature, we conclude that while the emission-line gas in the FR 2's is indeed photoionized by a nuclear UV continuum source from the AGN, the emission-line gas in the FR 1's may be energized predominantly by processes associated with the host galaxy itself. The apparent lack of a strong UV continuum source from the central engine in FR 1 sources can be understood in two different ways. In the first scenario, FR l's are much more efficient at covering jet bulk kinetic energy into radio luminosity than FR 2's, such that an FR 1 has a much lower bolometric AGN luminosity (hence nuclear UV continuum source) than does an FR 2 of the same radio luminosity. We discuss the pros and cons of this model and conclude that the efficiency differences needed between FR 2 and FR 1 radio galaxies are quite large and may lead to difficulties with the interpretation since it would suggest that FR 2 radio source deposit very large amounts of kinetic energy into the ISM Intracluster Medium. However, this interpretation remains viable. Alternatively, it may be that the AGNs in FR 1 sources simply produce far less radiant UV energy than do those in FR 2 sources. That is, FR 1 sources may funnel a higher fraction of the total energy output from the AGNs into jet kinetic energy versus radiant energy than do FR 2 sources. If this interpretation is correct, then this suggests that there is a fundamental difference in the central engine and/or in the immediate "accretion region" around the engine in FR 1 and FR 2 radio galaxies. We note also the absence of FR 1 sources with nuclear broad line regions and suggest that the absence of the BLR is tied to the absence of the "isotropic" nuclear UV continuum source in FR 1 sources. We put forth the possibility that the FR 1/FR 2 dichotomy (i.e., the observed differences in the properties of low- and high-power radio sources) is due to qualitative differences in the structural properties of the central engines in these two types of sources. Following early work by Rees et al. (1982), we suggest the possibility that FR 1 sources are produced when the central engine is fed at a lower accretion rate, leading to the creation of a source in which the ratio of radiant to jet bulk kinetic energy is low, while FR 2 sources are produced when the central engine is fed at a higher accretion rate, causing the central engine to deposit a higher fraction of its energy in radiant energy. We further suggest the possibility that associated differences in the spin properties of the central black hole between FR 1 (lower spin) and FR 2 (higher spin) sources may be responsible for the different collimation properties and Mach numbers of the jets produced by these two types of radio-loud galaxies. This scenario, although currently clearly speculative, is nicely consistent with our current picture of the triggering, feeding, environments, and evolution of powerful radio galaxies. This model allows for evolution of these properties with time for example, the mass accretion rate and BH spin may decline with time causing an FR 2 radio source or quasar to evolve into a FR 1 radio source.

Discovery of large-scale diffuse radio emission in low-mass galaxy cluster Abell 1931

NASA Astrophysics Data System (ADS)

Brüggen, M.; Rafferty, D.; Bonafede, A.; van Weeren, R. J.; Shimwell, T.; Intema, H.; Röttgering, H.; Brunetti, G.; Di Gennaro, G.; Savini, F.; Wilber, A.; O'Sullivan, S.; Ensslin, T. A.; De Gasperin, F.; Hoeft, M.

2018-07-01

Extended, steep-spectrum radio synchrotron sources are pre-dominantly found in massive galaxy clusters as opposed to groups. LOFAR Two-Metre Sky Survey images have revealed a diffuse, ultra-steep-spectrum radio source in the low-mass cluster Abell 1931. The source has a fairly irregular morphology with the largest linear size of about 550 kpc. The source is only seen in LOFAR observations at 143 MHz and Giant Metre Radio Telescope observations at 325 MHz. The spectral index of the total source between 143 and 325 MHz is α _{143}^{325} = -2.86 ± 0.36. The source remains invisible in Very Large Array (1-2 GHz) observations as expected given the spectral index. Chandra X-ray observations of the cluster revealed a bolometric luminosity of LX = (1.65 ± 0.39) × 1043 erg s-1 and a temperature of 2.92_{-0.87}^{+1.89} keV which implies a mass of around ˜1014 M⊙. We conclude that the source is a remnant radio galaxy that has shut off around 200 Myr ago. The brightest cluster galaxy, a radio-loud elliptical galaxy, could be the source for this extinct source. Unlike remnant sources studied in the literature, our source has a steep spectrum at low radio frequencies. Studying such remnant radio galaxies at low radio frequencies is important for understanding the scarcity of such sources and their role in feedback processes.

Discovery of large-scale diffuse radio emission in low-mass galaxy cluster Abell 1931

NASA Astrophysics Data System (ADS)

Brüggen, M.; Rafferty, D.; Bonafede, A.; van Weeren, R. J.; Shimwell, T.; Intema, H.; Röttgering, H.; Brunetti, G.; Di Gennaro, G.; Savini, F.; Wilber, A.; O'Sullivan, S.; Ensslin, T. A.; De Gasperin, F.; Hoeft, M.

2018-04-01

Extended, steep-spectrum radio synchrotron sources are pre-dominantly found in massive galaxy clusters as opposed to groups. LOFAR Two-Metre Sky Survey images have revealed a diffuse, ultra-steep spectrum radio source in the low-mass cluster Abell 1931. The source has a fairly irregular morphology with a largest linear size of about 550 kpc. The source is only seen in LOFAR observations at 143 MHz and GMRT observations at 325 MHz. The spectral index of the total source between 143 MHz and 325 MHz is α _{143}^{325} = -2.86 ± 0.36. The source remains invisible in Very Large Array (1-2 GHz) observations as expected given the spectral index. Chandra X-ray observations of the cluster revealed a bolometric luminosity of LX = (1.65 ± 0.39) × 1043 erg s-1 and a temperature of 2.92_{-0.87}^{+1.89} keV which implies a mass of around ˜1014M⊙. We conclude that the source is a remnant radio galaxy that has shut off around 200 Myr ago. The brightest cluster galaxy, a radio-loud elliptical galaxy, could be the source for this extinct source. Unlike remnant sources studied in the literature, our source has a steep spectrum at low radio frequencies. Studying such remnant radio galaxies at low radio frequencies is important for understanding the scarcity of such sources and their role in feedback processes.

The Mitigation of Radio Noise and Interference from On-Site Sources at Radio Receiving Sites

DTIC Science & Technology

2009-11-01

are rated to handle the maximum signal, noise, and interference power applied to them. All signal splitters and other components that contain ferrite ...other sources on the campus. 83 A.1.5 Data Recording Until a few years ago, data was recorded by freezing the operation of the 7200B display

New redshift determinations for three 3C radio sources.

NASA Astrophysics Data System (ADS)

Reynaldi, V.

2017-01-01

I report the new redshift determinations of three radio sources 3C 196.1, 3C 268.2 and 3C 303.1 by using GMOS/Gemini North long-slit optical spectroscopy. The details of the observations are summarized in the following table (the B600 grating was used for the three observations): Object | RA(J2000) | DEC(J2000) | Date of obs. | width-slit(arcsec) | PA(deg) | Exp.Time(sec) 3C 196.1 | 8:15:27.8 | -03:08:27 | Mar 2012 | 0.5 | 50 | 2560 3C 268.2| |12:00:59.1 | 31:33:28 | Feb 2011 | 0.5 | 165 | 2576 3C 303.1 | 14:43:14.5 | 77:07:28 | Feb 2012 | 1 | 145 | 2560 The three of the sources have extended regions of ionized gas that do not obey a spherical distribution.

PROBING DYNAMICS OF ELECTRON ACCELERATION WITH RADIO AND X-RAY SPECTROSCOPY, IMAGING, AND TIMING IN THE 2002 APRIL 11 SOLAR FLARE

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

Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.

Based on detailed analysis of radio and X-ray observations of a flare on 2002 April 11 augmented by realistic three-dimensional modeling, we have identified a radio emission component produced directly at the flare acceleration region. This acceleration region radio component has distinctly different (1) spectrum, (2) light curves, (3) spatial location, and, thus, (4) physical parameters from those of the separately identified trapped or precipitating electron components. To derive evolution of physical parameters of the radio sources we apply forward fitting of the radio spectrum time sequence with the gyrosynchrotron source function with five to six free parameters. At themore » stage when the contribution from the acceleration region dominates the radio spectrum, the X-ray- and radio-derived electron energy spectral indices agree well with each other. During this time the maximum energy of the accelerated electron spectrum displays a monotonic increase with time from {approx}300 keV to {approx}2 MeV over roughly one minute duration indicative of an acceleration process in the form of growth of the power-law tail; the fast electron residence time in the acceleration region is about 2-4 s, which is much longer than the time of flight and so requires a strong diffusion mode there to inhibit free-streaming propagation. The acceleration region has a relatively strong magnetic field, B {approx} 120 G, and a low thermal density, n{sub e} {approx}< 2 Multiplication-Sign 10{sup 9} cm{sup -3}. These acceleration region properties are consistent with a stochastic acceleration mechanism.« less

Radio continuum of galaxies with H2O megamaser disks: 33 GHz VLA data

NASA Astrophysics Data System (ADS)

Kamali, F.; Henkel, C.; Brunthaler, A.; Impellizzeri, C. M. V.; Menten, K. M.; Braatz, J. A.; Greene, J. E.; Reid, M. J.; Condon, J. J.; Lo, K. Y.; Kuo, C. Y.; Litzinger, E.; Kadler, M.

2017-09-01

Context. Galaxies with H2O megamaser disks are active galaxies in whose edge-on accretion disks 22 GHz H2O maser emission has been detected. Because their geometry is known, they provide a unique view into the properties of active galactic nuclei. Aims: The goal of this work is to investigate the nuclear environment of galaxies with H2O maser disks and to relate the maser and host galaxy properties to those of the radio continuum emission of the galaxy. Methods: The 33 GHz (9 mm) radio continuum properties of 24 galaxies with reported 22 GHz H2O maser emission from their disks are studied in the context of the multiwavelength view of these sources. The 29-37 GHz Ka-band observations are made with the Karl Jansky Very Large Array in B, CnB, or BnA configurations, achieving a resolution of 0.2-0.5 arcsec. Hard X-ray data from the Swift/BAT survey and 22 μm infrared data from WISE, 22 GHz H2O maser data and 1.4 GHz data from NVSS and FIRST surveys are also included in the analysis. Results: Eighty-seven percent (21 out of 24) galaxies in our sample show 33 GHz radio continuum emission at levels of 4.5-240σ. Five sources show extended emission (deconvolved source size larger than 2.5 times the major axis of the beam), including one source with two main components and one with three main components. The remaining detected 16 sources (and also some of the above-mentioned targets) exhibit compact cores within the sensitivity limits. Little evidence is found for extended jets (>300 pc) in most sources. Either they do not exist, or our chosen frequency of 33 GHz is too high for a detection of these supposedly steep spectrum features. In NGC 4388, we find an extended jet-like feature that appears to be oriented perpendicular to the H2O megamaser disk. NGC 2273 is another candidate whose radio continuum source might be elongated perpendicular to the maser disk. Smaller 100-300 pc sized jets might also be present, as is suggested by the beam-deconvolved morphology of our sources. Whenever possible, central positions with accuracies of 20-280 mas are provided. A correlation analysis shows that the 33 GHz luminosity weakly correlates with the infrared luminosity. The 33 GHz luminosity is anticorrelated with the circular velocity of the galaxy. The black hole masses show stronger correlations with H2O maser luminosity than with 1.4 GHz, 33 GHz, or hard X-ray luminosities. Furthermore, the inner radii of the disks show stronger correlations with 1.4 GHz, 33 GHz, and hard X-ray luminosities than their outer radii, suggesting that the outer radii may be affected by disk warping, star formation, or peculiar density distributions.

Radio detections of southern ultracool dwarfs

NASA Astrophysics Data System (ADS)

Lynch, C.; Murphy, T.; Ravi, V.; Hobbs, G.; Lo, K.; Ward, C.

2016-04-01

We report the results of a volume-limited survey using the Australia Telescope Compact Array to search for transient and quiescent radio emission from 15 Southern hemisphere ultracool dwarfs. We detect radio emission from 2MASSW J0004348-404405 increasing the number of radio loud ultracool dwarfs to 22. We also observe radio emission from 2MASS J10481463-3956062 and 2MASSI J0339352-352544, two sources with previous radio detections. The radio emission from the three detected sources shows no variability or flare emission. Modelling this quiescent emission we find that it is consistent with optically thin gyrosynchrotron emission from a magnetosphere with an emitting region radius of (1-2)R*, magnetic field inclination 20°-80°, field strength ˜10-200 G, and power-law electron density ˜104-108 cm-3. Additionally, we place upper limits on four ultracool dwarfs with no previous radio observations. This increases the number of ultracool dwarfs studied at radio frequencies to 222. Analysing general trends of the radio emission for this sample of 15 sources, we find that the radio activity increases for later spectral types and more rapidly rotating objects. Furthermore, comparing the ratio of the radio to X-ray luminosities for these sources, we find 2MASS J10481463-3956062 and 2MASSI J0339352-352544 violate the Güdel-Benz relation by more than two orders of magnitude.

Effects of the turbulent ISM on radio observations of quasars

NASA Astrophysics Data System (ADS)

Gabányi, Krisztina; Britzen, S.; Krichbaum, T. P.; Bach, U.; Fuhrmann, L.; Kraus, A.; Witzel, A.; Zensus, J. A.

In radio bands, the study of compact radio sources can be affected by propagation effects introduced by the interstellar medium, usually attributed to the presence of turbulent intervening plasma along the line of sight. Here, two of such effects are presented. The line of sight of B 2005+403 passes through the heavily scattered region of Cygnus causing substantial angular broadening of the source images obtained at frequencies between 0.6 GHz and 8 GHz. At higher frequencies, however, the intrinsic source structure shines through. Therefore, multi-frequency VLBI observations allow to study the characteristics of the intervening material, the source morphology and the interplay between them in forming the observed image.

Multifrequency VLA observations of PKS 0745 - 191 - The archetypal 'cooling flow' radio source?

NASA Technical Reports Server (NTRS)

Baum, S. A.; O'Dea, C. P.

1991-01-01

Ninety-, 20-, 6- and 2-cm VLA observations of the high-radio-luminosity cooling-flow radio source PKS 0745 - 191 are presented. The radio source was found to have a core with a very steep spectrum (alpha is approximately -1.5) and diffuse emission with an even steeper spectrum (alpha is approximately -1.5 to -2.3) without clear indications of the jets, hotspots, or double lobes found in the other radio sources of comparable luminosity. It is inferred that the energy to power the radio source comes from the central engine, but the source's structure may be heavily influenced by the past history of the galaxy and the inflowing intracluster medium. It is shown that, while the radio source is energetically unimportant for the cluster as a whole, it is important on the scale of the cooling flow. The mere existence of cosmic rays and magnetic fields within a substantial fraction of the volume inside the cooling radius has important consequences for cooling-flow models.

Milky Way scattering properties and intrinsic sizes of active galactic nuclei cores probed by very long baseline interferometry surveys of compact extragalactic radio sources

NASA Astrophysics Data System (ADS)

Pushkarev, A. B.; Kovalev, Y. Y.

2015-10-01

We have measured the angular sizes of radio cores of active galactic nuclei (AGNs) and analysed their sky distributions and frequency dependences to study synchrotron opacity in AGN jets and the strength of angular broadening in the interstellar medium. We have used archival very long baseline interferometry (VLBI) data of more than 3000 compact extragalactic radio sources observed at frequencies, ν, from 2 to 43 GHz to measure the observed angular size of VLBI cores. We have found a significant increase in the angular sizes of the extragalactic sources seen through the Galactic plane (|b| ≲ 10°) at 2, 5 and 8 GHz, about one-third of which show significant scattering. These sources are mainly detected in directions to the Galactic bar, the Cygnus region and a region with galactic longitudes 220° ≲ l ≲ 260° (the Fitzgerald window). The strength of interstellar scattering of the AGNs is found to correlate with the Galactic Hα intensity, free-electron density and Galactic rotation measure. The dependence of scattering strengths on source redshift is insignificant, suggesting that the dominant scattering screens are located in our Galaxy. The observed angular size of Sgr A* is found to be the largest among thousands of AGNs observed over the sky; we discuss possible reasons for this strange result. Excluding extragalactic radio sources with significant scattering, we find that the angular size of opaque cores in AGNs scales typically as ν-1, confirming predictions of a conical synchrotron jet model with equipartition.

Source Localization in a Cognitive Radio Environment Consisting of Frequency and Spatial Mobility

DTIC Science & Technology

2011-12-01

are designed to track position over time using a wireless RF sensor network, such as Kalman filtering [13]. 74 THIS PAGE INTENTIONALLY LEFT BLANK...Radio,” Proceedings of the IEEE, vol. 97, no. 4, pp. 612–625, Apr. 2009. 80 [12] J. B. Bernthal, T. X. Brown , D. N. Hatfield, D. C. Sicker, P. A... Kalman Filtering in Wireless Sensor Networks,” IEEE Control Systems, vol. 30, no. 2, pp. 66–86, April 2010. [14] J. Nemeroff, L. Garcia, D

VLA observations of A and B stars with kilogauss magnetic fields

NASA Technical Reports Server (NTRS)

Drake, S. A.; Abbott, D. C.; Linsky, J. L.; Bieging, J. H.; Churchwell, E.

1985-01-01

The serendipitous discovery that the star Sigma Ori E is a 3.5 mJy radio continuum source at 6 cm has stimulated a radio survey of other early-type stars with strong magnetic fields. No Ap stars have been detected of the eight observed, with typical 3-sigma upper limits of 0.5 mJy at 2 cm. Of the six Bp stars examined, only HR 1890, a helium-strong star, was detected. Possible emission mechanisms for the observed radio emission are discussed, and it is concluded that nonthermal emission seems the most plausible, on the basis of the present data.

The early ultraviolet, optical, and radio evolution of the soft X-ray transient GRO J0422+32

NASA Technical Reports Server (NTRS)

Shrader, C. R.; Wagner, R. Mark; Hjellming, R. M.; Han, X. H.; Starrfield, S. G.

1994-01-01

We have monitored the evolution of the transient X-ray source GRO J0422+32 from approximately 2 weeks postdiscovery into its early decline phase at ultraviolet, optical, and radio wavelengths. Optical and ultraviolet spectra exhibit numerous, but relatively weak, high-excitation emission lines such as those arising from He II, N III, N V, and C IV superposed on an intrinsically blue continuum. High-resolution optical spectroscopy reveals line profiles which are double peaked, and in the case of the higher order Balmer lines, superposed on a broad absorption profile. The early outburst optical-ultraviolet continuum energy distribution is well represented by a two power-law fit with a break at approximately equal 4000 A. Radio observations with the Very Large Array (VLA) reveal a flat-spectrum source, slowly increasing in intensity at the earliest epochs observed, followed by an approximate power-law decay light curve with an index of -1. Light curves for each wavelength domain are presented and discussed. Notable are the multiple secondary outbursts seen in the optical more than 1 year postdiscovery, and spectral changes associated with secondary rises seen in the radio and UV. We find that the ultraviolet and optical characteristics of GRO J0422+32 as well as its radio evolution, are similar to other recent well-observed soft X-ray transients (also called X-ray novae) such as Cen X-4, A0620-00 (V616 Mon), and Nova Muscae 1991 (GS 1124-683), suggesting that GRO J0422+32 is also a member of that subclass of low-mass X-ray binaries. We present definitive astrometric determination of the source position, and place an upper limit of R approximately equals 20 from our analysis of the Palomar Observatory Sky Survey (POSS). Additionally, we derive distinct values for color excess from analysis of the optical (E(B-V) = 0.23) and ultraviolet (E(B-V) = 0.4) data, suggesting an intrinsic magnitude of 19-19.5 for the progenitor if it is mid-K dwarf. This leads to a likely range of 2.4-3.0 kpc for the source distance, which is consistent with our separate estimate of 2.4 +/- 0.4 kpc based on measurement of the NaD interstellar line profile. Adopting 2.4 kpc and E(B-V) = 0.23, the outburst absolute magnitude was M approximately equals 0.0, which is a typical value for this class of objects.

Radio Frequency Transistors and Circuits Based on CVD MoS2.

PubMed

Sanne, Atresh; Ghosh, Rudresh; Rai, Amritesh; Yogeesh, Maruthi Nagavalli; Shin, Seung Heon; Sharma, Ankit; Jarvis, Karalee; Mathew, Leo; Rao, Rajesh; Akinwande, Deji; Banerjee, Sanjay

2015-08-12

We report on the gigahertz radio frequency (RF) performance of chemical vapor deposited (CVD) monolayer MoS2 field-effect transistors (FETs). Initial DC characterizations of fabricated MoS2 FETs yielded current densities exceeding 200 μA/μm and maximum transconductance of 38 μS/μm. A contact resistance corrected low-field mobility of 55 cm(2)/(V s) was achieved. Radio frequency FETs were fabricated in the ground-signal-ground (GSG) layout, and standard de-embedding techniques were applied. Operating at the peak transconductance, we obtain short-circuit current-gain intrinsic cutoff frequency, fT, of 6.7 GHz and maximum intrinsic oscillation frequency, fmax, of 5.3 GHz for a device with a gate length of 250 nm. The MoS2 device afforded an extrinsic voltage gain Av of 6 dB at 100 MHz with voltage amplification until 3 GHz. With the as-measured frequency performance of CVD MoS2, we provide the first demonstration of a common-source (CS) amplifier with voltage gain of 14 dB and an active frequency mixer with conversion gain of -15 dB. Our results of gigahertz frequency performance as well as analog circuit operation show that large area CVD MoS2 may be suitable for industrial-scale electronic applications.

Sh2-138: physical environment around a small cluster of massive stars

NASA Astrophysics Data System (ADS)

Baug, T.; Ojha, D. K.; Dewangan, L. K.; Ninan, J. P.; Bhatt, B. C.; Ghosh, S. K.; Mallick, K. K.

2015-12-01

We present a multiwavelength study of the Sh2-138, a Galactic compact H II region. The data comprise of optical and near-infrared (NIR) photometric and spectroscopic observations from the 2-m Himalayan Chandra Telescope, radio observations from the Giant Metrewave Radio Telescope (GMRT), and archival data covering radio through NIR wavelengths. A total of 10 Class I and 54 Class II young stellar objects (YSOs) are identified in a 4.6 arcmin×4.6 arcmin area of the Sh2-138 region. Five compact ionized clumps, with four lacking of any optical or NIR counterparts, are identified using the 1280 MHz radio map, and correspond to sources with spectral type earlier than B0.5. Free-free emission spectral energy distribution fitting of the central compact H II region yields an electron density of ˜2250 ± 400 cm-3. With the aid of a wide range of spectra, from 0.5-15 μm, the central brightest source - previously hypothesized to be the main ionizing source - is characterized as a Herbig Be type star. At large scale (15 arcmin ×15 arcmin), the Herschel images (70-500 μm) and the nearest neighbour analysis of YSOs suggest the formation of an isolated cluster at the junction of filaments. Furthermore, using a greybody fit to the dust spectrum, the cluster is found to be associated with the highest column density (˜3 × 1022 cm-2) and high temperature (˜35 K) regime, as well as with the radio continuum emission. The mass of the central clump seen in the column density map is estimated to be ˜3770 M⊙.

MSX Colors of Radio-Selected HII Regions in the Milky Way

NASA Astrophysics Data System (ADS)

Giveon, U.; Becker, R. H.; Helfand, D. J.; White, R. L.

2004-12-01

Investigation of the color properties of sources in the MSX catalog reveals two populations - a blue population composed of mainly evolved stars, masers and molecular clouds, and a red population composed mainly HII regions, planetary nebulae, and unclassified radio sources. We compare the MSX catalog to 5 GHz VLA maps of the first quadrant of the Galactic plane (350o

Interstellar organic chemistry.

NASA Technical Reports Server (NTRS)

Sagan, C.

1972-01-01

Most of the interstellar organic molecules have been found in the large radio source Sagittarius B2 toward the galactic center, and in such regions as W51 and the IR source in the Orion nebula. Questions of the reliability of molecular identifications are discussed together with aspects of organic synthesis in condensing clouds, degradational origin, synthesis on grains, UV natural selection, interstellar biology, and contributions to planetary biology.

The Gould's Belt Very Large Array Survey. I. The Ophiuchus Complex

NASA Astrophysics Data System (ADS)

Dzib, Sergio A.; Loinard, Laurent; Mioduszewski, Amy J.; Rodríguez, Luis F.; Ortiz-León, Gisela N.; Pech, Gerardo; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Hartmann, Lee; Evans, Neal J., II; Briceño, Cesar; Tobin, John

2013-09-01

We present large-scale (~2000 arcmin2), deep (~20 μJy), high-resolution (~1'') radio observations of the Ophiuchus star-forming complex obtained with the Karl G. Jansky Very Large Array at λ = 4 and 6 cm. In total, 189 sources were detected, 56 of them associated with known young stellar sources, and 4 with known extragalactic objects; the other 129 remain unclassified, but most of them are most probably background quasars. The vast majority of the young stars detected at radio wavelengths have spectral types K or M, although we also detect four objects of A/F/B types and two brown dwarf candidates. At least half of these young stars are non-thermal (gyrosynchrotron) sources, with active coronas characterized by high levels of variability, negative spectral indices, and (in some cases) significant circular polarization. As expected, there is a clear tendency for the fraction of non-thermal sources to increase from the younger (Class 0/I or flat spectrum) to the more evolved (Class III or weak line T Tauri) stars. The young stars detected both in X-rays and at radio wavelengths broadly follow a Güdel-Benz relation, but with a different normalization than the most radioactive types of stars. Finally, we detect a ~70 mJy compact extragalactic source near the center of the Ophiuchus core, which should be used as gain calibrator for any future radio observations of this region.

Interplanetary baseline observations of type 3 solar radio bursts. [by Helios satellites

NASA Technical Reports Server (NTRS)

Weber, R. R.; Fitzenreiter, R. J.; Novaco, J. C.; Fainberg, J.

1977-01-01

Simultaneous observations of type III radio bursts using spacecraft separated by several tenths of an AU were made using the solar orbiters HELIOS-A and -B. The burst beginning at 1922 UT on March 28, 1976, was located from the intersection of the source directions measured at each spacecraft, and from the burst arrival time differences. Wide baseline observations give the radial distance of the source at each observing frequency. Consequently, coronal electron densities and exciter velocity were determined directly, without the need to assume a density model as is done with single spacecraft observations. The separation of HELIOS-A and -B also provided the first measurements of burst directivity at low frequencies. For the March 28 burst, the intensity observed from near the source longitude (HELIOS-B) was significantly greater than from 60 W of the source (HELIOS-A).

Interplanetary baseline observations of type III solar radio bursts

NASA Technical Reports Server (NTRS)

Weber, R. R.; Fitzenreiter, R. J.; Novaco, J. C.; Fainberg, J.

1977-01-01

Simultaneous observations of type III radio bursts from spacecraft separated by 0.43 AU have been made using the solar orbiters Helios-A and Helios-B. The burst beginning at 19:22 UT on March 28, 1976, has been located from the intersection of the source directions measured at each spacecraft and from burst arrival-time differences. The source positions range from 0.03 AU from the sun at 3000 kHz to 0.08 AU at 585 kHz. The electron density along the burst trajectory and the exciter velocity (0.13c) were determined directly without the need to assume a density model, as has been done with single-spacecraft observations. The separation of Helios-A and -B has also provided measurements of burst directivity at low frequencies. For the March 28 burst the intensity observed from near the source longitude (Helios-B) was 3-10dB greater than that from 60 deg west of the source (Helios-A)

Evidence for a Population of High-Redshift Submillimeter Galaxies from Interferometric Imaging

NASA Astrophysics Data System (ADS)

Younger, Joshua D.; Fazio, Giovanni G.; Huang, Jia-Sheng; Yun, Min S.; Wilson, Grant W.; Ashby, Matthew L. N.; Gurwell, Mark A.; Lai, Kamson; Peck, Alison B.; Petitpas, Glen R.; Wilner, David J.; Iono, Daisuke; Kohno, Kotaro; Kawabe, Ryohei; Hughes, David H.; Aretxaga, Itziar; Webb, Tracy; Martínez-Sansigre, Alejo; Kim, Sungeun; Scott, Kimberly S.; Austermann, Jason; Perera, Thushara; Lowenthal, James D.; Schinnerer, Eva; Smolčić, Vernesa

2007-12-01

We have used the Submillimeter Array to image a flux-limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 μm with ~2" resolution. All of the sources-two radio-bright and five radio-dim-are detected as single point sources at high significance (>6 σ), with positions accurate to ~0.2" that enable counterpart identification at other wavelengths observed with similarly high angular resolution. All seven have IRAC counterparts, but only two have secure counterparts in deep HST ACS imaging. As compared to the two radio-bright sources in the sample, and those in previous studies, the five radio-dim sources in the sample (1) have systematically higher submillimeter-to-radio flux ratios, (2) have lower IRAC 3.6-8.0 μm fluxes, and (3) are not detected at 24 μm. These properties, combined with size constraints at 890 μm (θ<~1.2''), suggest that the radio-dim submillimeter galaxies represent a population of very dusty starbursts, with physical scales similar to local ultraluminous infrared galaxies, with an average redshift higher than radio-bright sources.

A Search for EGRET/Radio Pulsars in the ETA Carina Region

NASA Technical Reports Server (NTRS)

2002-01-01

Our analysis of EGRET data for the radio pulsar PSR B1046-58, which lies it the Eta Carina region of the Galaxy, was highly successful, resulting in the discovery of strong evidence for gamma-ray pulsations from this source. This work was published in the Astrophysical Journal. Additional support for the association was published in a companion paper in which an analysis of the X-ray counterpart to PSR B1046-58 was done, and we showed that it was the only possible counterpart to the gamma ray source within the EGRET error box.

Near infrared observations of S 155. Evidence of induced star formation?

NASA Astrophysics Data System (ADS)

Hunt, L. K.; Lisi, F.; Felli, M.; Tofani, G.

In order to investigate the possible existence of embedded objects of recent formation in the area of the Cepheus B - Sh2-155 interface, the authors have observed the region of the compact radio continuum source with the new near infrared camera ARNICA and the TIRGO telescope.

A Multi-Wavelength Search for a Counterpart of the Unidentified Gamma-ray source 3EG J2020+4017 (2CG078+2)

NASA Technical Reports Server (NTRS)

Becker, Werner; Weisskopf, Martin C.; Arzoumanian, Zaven; Lorimer, Duncan; Camilo, Fernando; Elsner, Ronald F.; Kanbach, Gottfried; Reimer, Olaf; Swartz, Douglas A.; Tennant, Allyn F.

2004-01-01

In search of the counterpart to the brightest unidentified gamma-ray source 3EG J2020+4017 (2CG078+2) we report on new X-ray and radio observations of the gamma-Cygni field with the Chandra X-ray Observatory and with the Green Bank Telescope (GBT). We also report on reanalysis of archival ROSAT data. With Chandra it became possible for the first time to measure the position of the putative gamma-ray counterpart RX J2020.2+4026 with sub-arcsec accuracy and to deduce its X-ray spectral characteristics. These observations demonstrate that RX J2020.2+4026 is associated with a K field star and therefore is unlikely to be the counterpart of the bright gamma-ray source 2CG078+2 in the SNR G78.2+2.1 as had been previously suggested. The Chandra observation detected 37 additional X-ray sources which were correlated with catalogs of optical and infrared data. Subsequent GBT radio observations covered the complete 99% EGRET likelihood contour of 3EG J2020+4017 with a sensitivity limit of L(sub 820) approx. 0.1 mJy kpc(exp 2) which is lower than most of the recent deep radio search limits. If there is a pulsar operating in 3EG J2020+4017, this sensitivity limit suggests that the pulsar either does not produce significant amounts of radio emission or that its geometry is such that the radio beam does not intersect with the line of sight. Finally, reanalysis of archival ROSAT data leads to a flux upper limit of f(sub x)(0.1-2.4 keV) < 1.8 x 10(exp -13) erg/s/sq cm for a putative point-like X-ray source located within the 68% confidence contour of 3EG J2020+4017. Adopting the SNR age of 5400 yrs and assuming a spin-down to X-ray energy conversion factor of 10(exp -3) this upper limit constraints the parameters of a putative neutron star as a counterpart for 3EG J2020+4017 to be P > or approx. 160/(d/1.5 kpc) ms, P > or approx. 5 x 10(exp -13)/(d/1.5kpc) s s1 and B > or approx. 9 x 10(exp 12)/(d/1.5 kpc) G.

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

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

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

2011-03-15

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

The clustering and bias of radio-selected AGN and star-forming galaxies in the COSMOS field

NASA Astrophysics Data System (ADS)

Hale, C. L.; Jarvis, M. J.; Delvecchio, I.; Hatfield, P. W.; Novak, M.; Smolčić, V.; Zamorani, G.

2018-03-01

Dark matter haloes in which galaxies reside are likely to have a significant impact on their evolution. We investigate the link between dark matter haloes and their constituent galaxies by measuring the angular two-point correlation function of radio sources, using recently released 3 GHz imaging over ˜2 deg2 of the Cosmological Evolution Survey (COSMOS) field. We split the radio source population into star-forming galaxies (SFGs) and active galactic nuclei (AGN), and further separate the AGN into radiatively efficient and inefficient accreters. Restricting our analysis to z < 1, we find SFGs have a bias, b = 1.5 ^{+0.1}_{-0.2}, at a median redshift of z = 0.62. On the other hand, AGN are significantly more strongly clustered with b = 2.1 ± 0.2 at a median redshift of 0.7. This supports the idea that AGN are hosted by more massive haloes than SFGs. We also find low accretion rate AGN are more clustered (b = 2.9 ± 0.3) than high accretion rate AGN (b = 1.8^{+0.4}_{-0.5}) at the same redshift (z ˜ 0.7), suggesting that low accretion rate AGN reside in higher mass haloes. This supports previous evidence that the relatively hot gas that inhabits the most massive haloes is unable to be easily accreted by the central AGN, causing them to be inefficient. We also find evidence that low accretion rate AGN appear to reside in halo masses of Mh ˜ 3-4 × 1013 h-1 M⊙ at all redshifts. On the other hand, the efficient accreters reside in haloes of Mh ˜ 1-2 × 1013 h-1 M⊙ at low redshift but can reside in relatively lower mass haloes at higher redshifts. This could be due to the increased prevalence of cold gas in lower mass haloes at z ≥ 1 compared to z < 1.

The effect of magnetic topography on high-latitude radio emission at Neptune

NASA Technical Reports Server (NTRS)

Sawyer, C. B.; Warwick, James W.; Romig, J. H.

1992-01-01

Occultation by a local elevation on the surface of constant magnetic field is proposed as a new interpretation for the unusual properties of Neptune high-latitude emission. Abrupt changes in intensity and polarization of this broadband smooth radio emission were observed as the Voyager 2 spacecraft passed near the north magnetic pole before closest approach. The observed sequence of cutoffs with polarization reversal would not occur during descent of the spacecraft through regular surfaces of increasing magnetic field. The sequence can be understood in terms of constant-frequency (constant-field) surfaces that are not only offset from the planet center but are locally highly distorted by an elevation that occults the outgoing extraordinary-mode beam. The required occulter is similar to the field enhancement observed directly by the magnetometer team when Voyager reached lower altitude farther to the west. Evidence is presented that the sources of the high-altitude emission are located near the longitude of the minimum-B anomaly associated with the dipole offset and that the local elevation of constant-B surfaces extends eastward from the longitude where it is directly measured by the magnetometer to the longitude where occultation of the remote radio source is observed. Together, the radio and magnetometer experiments indicate that the constant-frequency surfaces are distorted by an elevation that extends 0.3 rad in the longitudinal direction.

Phenomenological model for the evolution of radio galaxies such as Cygnus A

NASA Astrophysics Data System (ADS)

Artyukh, V. S.

2015-06-01

A phenomenological model for the evolution of classical radio galaxies such as Cygnus A is presented. An activity cycle of the host galaxy in the radio begins with the birth of radio jets, which correspond to shocks on scales ˜1 pc (the radio galaxy B0108+388). In the following stage of the evolution, the radio emission comes predominantly from formations on scales of 10-100 pc, whose physical parameters are close to those of the hot spots of Cygnus A (this corresponds to GHz-peaked spectrum radio sources). Further, the hot spots create radio lobes on scales of 103-104 pc (compact steep-spectrum radio sources). The fully formed radio galaxies have radio jets, hot spots, and giant radio lobes; the direction of the jets can vary in a discrete steps with time, creating new hot spots and inflating the radio lobes (as in Cygnus A). In the final stage of the evolutionary cycle, first the radio jets disappear, then the hot spots, and finally the radio lobes (similar to the giant radio galaxies DA 240 and 3C 236). A large fraction of radio galaxies with repeating activity cycles is observed. The close connection between Cygnus A-type radio galaxies and optical quasars is noted, as well as similarity in the cosmological evolution of powerful radio galaxies and optical quasars.

Statistics of the fractional polarization of extragalactic dusty sources in Planck HFI maps

NASA Astrophysics Data System (ADS)

Bonavera, L.; González-Nuevo, J.; De Marco, B.; Argüeso, F.; Toffolatti, L.

2017-11-01

We estimate the average fractional polarization at 143, 217 and 353 GHz of a sample of 4697 extragalactic dusty sources by applying stacking technique. The sample is selected from the second version of the Planck Catalogue of Compact Sources at 857 GHz, avoiding the region inside the Planck Galactic mask (fsky ∼ 60 per cent). We recover values for the mean fractional polarization at 217 and 353 GHz of (3.10 ± 0.75) per cent and (3.65 ± 0.66) per cent, respectively, whereas at 143 GHz we give a tentative value of (3.52 ± 2.48) per cent. We discuss the possible origin of the measured polarization, comparing our new estimates with those previously obtained from a sample of radio sources. We test different distribution functions and we conclude that the fractional polarization of dusty sources is well described by a log-normal distribution, as determined in the radio band studies. For this distribution we estimate μ217GHz = 0.3 ± 0.5 [that would correspond to a median fractional polarization of Πmed = (1.3 ± 0.7) per cent] and μ353GHz = 0.7 ± 0.4 (Πmed = (2.0 ± 0.8) per cent), σ217GHz = 1.3 ± 0.2 and σ353GHz = 1.1 ± 0.2. With these values we estimate the source number counts in polarization and the contribution given by these sources to the Cosmic Microwave Background B-mode angular power spectrum at 217, 353, 600 and 800 GHz. We conclude that extragalactic dusty sources might be an important contaminant for the primordial B-mode at frequencies >217 GHz.

Radio astronomy Explorer B antenna aspect processor

NASA Technical Reports Server (NTRS)

Miller, W. H.; Novello, J.; Reeves, C. C.

1972-01-01

The antenna aspect system used on the Radio Astronomy Explorer B spacecraft is described. This system consists of two facsimile cameras, a data encoder, and a data processor. Emphasis is placed on the discussion of the data processor, which contains a data compressor and a source encoder. With this compression scheme a compression ratio of 8 is achieved on a typical line of camera data. These compressed data are then convolutionally encoded.

Optical Spectra of Candidate International Celestial Reference Frame (ICRF) Flat-spectrum Radio Sources. III.

NASA Astrophysics Data System (ADS)

Titov, O.; Pursimo, T.; Johnston, Helen M.; Stanford, Laura M.; Hunstead, Richard W.; Jauncey, David L.; Zenere, Katrina A.

2017-04-01

In extending our spectroscopic program, which targets sources drawn from the International Celestial Reference Frame (ICRF) Catalog, we have obtained spectra for ˜160 compact, flat-spectrum radio sources and determined redshifts for 112 quasars and radio galaxies. A further 14 sources with featureless spectra have been classified as BL Lac objects. Spectra were obtained at three telescopes: the 3.58 m European Southern Observatory New Technology Telescope, and the two 8.2 m Gemini telescopes in Hawaii and Chile. While most of the sources are powerful quasars, a significant fraction of radio galaxies is also included from the list of non-defining ICRF radio sources.

Overview of Solar Radio Bursts and their Sources

NASA Astrophysics Data System (ADS)

Golla, Thejappa; MacDowall, Robert J.

2018-06-01

Properties of radio bursts emitted by the Sun at frequencies below tens of MHz are reviewed. In this frequency range, the most prominent radio emissions are those of solar type II, complex type III and solar type IV radio bursts, excited probably by the energetic electron populations accelerated in completely different environments: (1) type II bursts are due to non-relativistic electrons accelerated by the CME driven interplanetary shocks, (2) complex type III bursts are due to near-relativistic electrons accelerated either by the solar flare reconnection process or by the SEP shocks, and (3) type IV bursts are due to relativistic electrons, trapped in the post-eruption arcades behind CMEs; these relativistic electrons probably are accelerated by the continued reconnection processes occurring beneath the CME. These radio bursts, which can serve as the natural plasma probes traversing the heliosphere by providing information about various crucial space plasma parameters, are also an ideal instrument for investigating acceleration mechanisms responsible for the high energy particles. The rich collection of valuable high quality radio and high time resolution in situ wave data from the WAVES experiments of the STEREO A, STEREO B and WIND spacecraft has provided an unique opportunity to study these different radio phenomena and understand the complex physics behind their excitation. We have developed Monte Carlo simulation techniques to estimate the propagation effects on the observed characteristics of these low frequency radio bursts. We will present some of the new results and describe how one can use these radio burst observations for space weather studies. We will also describe some of the non-linear plasma processes detected in the source regions of both solar type III and type II radio bursts. The analysis and simulation techniques used in these studies will be of immense use for future space based radio observations.

The nature of radio emission from distant galaxies

NASA Astrophysics Data System (ADS)

Richards, Eric A.

I describe an observational program aimed at understanding the radio emission from distant, rapidly evolving galaxy populations. These observations were carried out at 1.4 and 8.5 GHz with the VLA centered on the Hubble Deep Field. Further MERLIN observations of the HDF region at 1.4 GHz provided an angular resolution of 0.2'' and when combined with the VLA data produced an image with an unprecedented rms noise of 4 μJy. All radio sources detected in the VLA complete sample are resolved with a median angular size of 1-2''. The differential count of the radio sources is marginally sub-Euclidean (γ = -2.4 +/- 0.1) and fluctuation analysis suggests nearly 60 sources per armin2 are present at the 1 μJy level. A correlation analysis indicates spatial clustering among the 371 radio sources on angular scales of 1-40 arcmin. Optical identifications are made primarily with bright (I = 22) disk systems composed of irregulars, peculiars, interacting/merging galaxies, and a few isolated field spirals. Available redshifts span the range 0.2-3. These clues coupled with the steep spectral index of the 1.4 GHz selected sample are indicative of diffuse synchrotron radiation in distant galactic disks. Thus the evolution in the microjansky radio population is driven principally by star-formation. I have isolated a number of optically faint radio sources (about 25% of the overall sample) which remain unidentified to I = 26-28 in the HDF and flanking optical fields. Several of these objects have extremely red counterparts and constitute a new class of radio sources which are candidate high redshift dusty protogalaxies.

Fermi LAT detection of a GeV flare from the gravitationally lensed blazar S3 0218+35

NASA Astrophysics Data System (ADS)

Ciprini, S.

2012-08-01

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity from a source positionally consistent with the blazar S3 0218+35 (also known as 2FGL J0221.0+3555, Nolan et al. 2012, ApJS, 199, 31, and B2 0218+35, OD 330, lens B0218+357) placed at radio coordinates R.A.: 35.27279 deg, Dec: +35.93715 deg.

Is there a cluster in the massive star forming region IRAS 20126+4104?

NASA Astrophysics Data System (ADS)

Montes, V. A.; Hofner, Peter; Anderson, C.; Rosero, V.

2017-03-01

A Chandra X-ray Observatory ACIS-I observation and a 6 cm continuum radio observation with the Karl G. Jansky Very Large Array (VLA) together with a multiwavelength study in infrared (2MASS and Spitzer) and optical (USNO-B1.0) shows an increasing surface density of X-ray sources toward the massive protostar. There are at least 43 YSOs within 1.2 pc distance from the massive protostar. This number is consistent with typical B-type stars clusters (Lada & Lada 2003).

DSN 70-meter antenna microwave optics design and performance improvements. Part 2: Comparison with measurements

NASA Technical Reports Server (NTRS)

Bathker, D. A.; Slobin, S. D.

1989-01-01

The measured Deep Space Network (DSN) 70-meter antenna performance at S- and X-bands is compared with the design expectations. A discussion of natural radio-source calibration standards is given. New estimates of DSN 64-meter antenna performance are given, based on improved values of calibration source flux and size correction. A comparison of the 64- and 70-meter performances shows that average S-band peak gain improvement is 1.94 dB, compared with a design expectation of 1.77 dB. At X-band, the average peak gain improvement is 2.12 dB, compared with the (coincidentally similar) design expectation of 1.77 dB. The average measured 70-meter S-band peak gain exceeds the nominal design-expected gain by 0.02 dB; the average measured 70-meter X-band peak gain is 0.14 dB below the nominal design-expected gain.

The BL LAC phenomenon: X-ray observations of transition objects and determination of the x-ray spectrum of a complete sample of flat-spectrum radio sources

NASA Technical Reports Server (NTRS)

Worrall, Diana M.

1994-01-01

This report summarizes the activities related to two ROSAT investigations: (1) x-ray properties of radio galaxies thought to contain BL Lac type nuclei; and (2) x-ray spectra of a complete sample of flat-spectrum radio sources. The following papers describing the research are provided as attachments: Multiple X-ray Emission Components in Low Power Radio Galaxies; New X-ray Results on Radio Galaxies; Analysis Techniques for a Multiwavelength Study of Radio Galaxies; Separation of X-ray Emission Components in Radio Galaxies; X-ray Emission in Powerful Radio Galaxies and Quasars; Extended and Compact X-ray Emission in Powerful Radio Galaxies; and X-ray Spectra of a Complete Sample of Extragalactic Core-dominated Radio Sources.

Radio-planetary from tie from Phobos-2 VLBI data

NASA Technical Reports Server (NTRS)

Hildebrand, C. E.; Iijima, B. A.; Kroger, P. M.; Folkner, W. M.; Edwards, C. D.

1994-01-01

In an ongoing effort to improve the knowledge of the relative orientation (the 'frame tie') of the planetary ephemeris reference frame used in deep navigation and a second reference frame that is defined by the coordinates of a set of extragalactic radio sources, VLBI observations of the Soviet Phobos-2 spacecraft and nearby (in angle) radio sources were obtained at two epochs in 1989, shortly after the spacecraft entered orbit about Mars. The frame tie is an important systematic error source affecting both interplanetary navigation and the process of improving the theory of the Earth's orientation. The data from a single Phobos-2 VLBI session measure one component of the direction vector from Earth to Mars in the frame of the extragalactic radio sources (the 'radio frame'). The radio frame has been shown to be stable and internally consistent with an accuracy of 5 nrad. The planetary ephemeris reference frame has an internal consistency of approximately 15 nrad. The planetary and radio source reference frames were aligned prior to 1989 and measurements of occulations of the radio source 3C273 by the Moon. The Phobos-2 VLBI measurements provide improvement in the accuracy of two of the three angles describing a general rotation between the planetary and radio reference frames. A complete set of measurements is not available because data acquisition was terminated prematurely by loss of spacecraft. The analysis of the two Phobos-2 VLBI data sets indicates that, in the directions of the two rotation components determined by these data, the JPL planetary ephemeris DE200 is aligned with the radio frame as adopted by the International Earth Rotation Service within an accuracy of 20-40 nrad, depending on direction. The limiting errors in the solutions for these offsets are spacecraft trajectory (20 nrad), instrumental biases (19 nrad), and dependence of quasar coordinates on observing frequency (24 nrad).

NRL SSD Research Achievements: 19601970. Volume 1

DTIC Science & Technology

2015-10-30

radio sources between declinations +10 and -20,” Mills, B.Y., Slee O.B., Hill, E.R. 1958, Australian J. Phys., 11 , 360-387 12. “SPEAR: Small Payload... 11 . SPONSOR / MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION / AVAILABILITY STATEMENT 13. SUPPLEMENTARY NOTES 14. ABSTRACT 15. SUBJECT TERMS 16...from a tour-de-force lunar occultation rocket experiment; and the First Detection of X-Ray Pulsations from the Crab Pulsar that matched the radio

Simulations of cm-wavelength Sunyaev-Zel'dovich galaxy cluster and point source blind sky surveys and predictions for the RT32/OCRA-f and the Hevelius 100-m radio telescope

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

Lew, Bartosz; Kus, Andrzej; Birkinshaw, Mark

We investigate the effectiveness of blind surveys for radio sources and galaxy cluster thermal Sunyaev-Zel'dovich effects (TSZEs) using the four-pair, beam-switched OCRA-f radiometer on the 32-m radio telescope in Poland. The predictions are based on mock maps that include the cosmic microwave background, TSZEs from hydrodynamical simulations of large scale structure formation, and unresolved radio sources. We validate the mock maps against observational data, and examine the limitations imposed by simplified physics. We estimate the effects of source clustering towards galaxy clusters from NVSS source counts around Planck-selected cluster candidates, and include appropriate correlations in our mock maps. The studymore » allows us to quantify the effects of halo line-of-sight alignments, source confusion, and telescope angular resolution on the detections of TSZEs. We perform a similar analysis for the planned 100-m Hevelius radio telescope (RTH) equipped with a 49-beam radio camera and operating at frequencies up to 22 GHz.We find that RT32/OCRA-f will be suitable for small-field blind radio source surveys, and will detect 33{sup +17}{sub −11} new radio sources brighter than 0.87 mJy at 30 GHz in a 1 deg{sup 2} field at > 5σ CL during a one-year, non-continuous, observing campaign, taking account of Polish weather conditions. It is unlikely that any galaxy cluster will be detected at 3σ CL in such a survey. A 60-deg{sup 2} survey, with field coverage of 2{sup 2} beams per pixel, at 15 GHz with the RTH, would find <1.5 galaxy clusters per year brighter than 60 μJy (at 3σ CL), and would detect about 3.4 × 10{sup 4} point sources brighter than 1 mJy at 5σ CL, with confusion causing flux density errors ∼< 2% (20%) in 68% (95%) of the detected sources.A primary goal of the planned RTH will be a wide-area (π sr) radio source survey at 15 GHz. This survey will detect nearly 3 × 10{sup 5} radio sources at 5σ CL down to 1.3 mJy, and tens of galaxy clusters, in one year of operation with typical weather conditions. Confusion will affect the measured flux densities by ∼< 1.5% (16%) for 68% (95%) of the point sources. We also gauge the impact of the RTH by investigating its performance if equipped with the existing RT32 receivers, and the performance of the RT32 equipped with the RTH radio camera.« less

Fermi-LAT and Suzaku observations of the radio galaxy Centaurus B

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

Katsuta, J.; Tanaka, Y. T.; Stawarz, Ł.

2013-01-28

Centaurus B is a nearby radio galaxy positioned in the southern hemisphere close to the Galactic plane. Here, in this work, we present a detailed analysis of about 43 months of accumulated Fermi-LAT data of the γ-ray counterpart of the source initially reported in the 2nd Fermi-LAT catalog, and of newly acquired Suzaku X-ray data. We confirm its detection at GeV photon energies and analyze the extension and variability of the γ-ray source in the LAT dataset, in which it appears as a steady γ-ray emitter. The X-ray core of Centaurus B is detected as a bright source of amore » continuum radiation. We do not detect, however, any diffuse X-ray emission from the known radio lobes, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. Two scenarios that connect the X-ray and γ-ray properties are considered. In the first one, we assume that the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. In this case, modeling the inverse-Compton emission shows that the observed γ-ray flux of the source may in principle be produced within the lobes. This association would imply that efficient in-situ acceleration of the radiating electrons is occurring and that the lobes are dominated by the pressure from the relativistic particles. In the second scenario, with the diffuse X-ray emission well below the Suzaku upper limits, the lobes in the system are instead dominated by the magnetic pressure. In this case, the observed γ-ray flux is not likely to be produced within the lobes, but instead within the nuclear parts of the jet. In conclusion, by means of synchrotron self-Compton modeling, we show that this possibility could be consistent with the broad-band data collected for the unresolved core of Centaurus B, including the newly derived Suzaku spectrum.« less

X-ray Properties of Deep Radio-Selected Quasars

NASA Technical Reports Server (NTRS)

Becker, Robert

2002-01-01

This report summarizes the research supported by the ADP grant entitled 'X-ray Properties of Deep Radio-Selected Quasars'. The primary effort consisted of correlating the ROSAT All-Sky Survey catalog with the April 1997 release of the FIRST (Faint Images of the Radio Sky at Twenty centimeters) radio catalog. We found that a matching radius of 60 sec excluded most false matches while retaining most of the true radio-X-ray sources. The correlation of the approx. 80,000 source RASS and approx. 268,000 FIRST catalogs matched 2,588 FIRST sources with 1,649 RASS sources out of a possible 5,520 RASS sources residing in the FIRST survey area. This number is much higher than expected from our previous experience of correlating the RASS with radio surveys and indicates we detected new classes of objects not seen in the correlations with less sensitive radio surveys.

Radio astronomy aspects of the NASA SETI Sky Survey

NASA Technical Reports Server (NTRS)

Klein, Michael J.

1986-01-01

The application of SETI data to radio astronomy is studied. The number of continuum radio sources in the 1-10 GHz region to be counted and cataloged is predicted. The radio luminosity functions for steep and flat spectrum sources at 2, 8, and 22 GHz are derived using the model of Peacock and Gull (1981). The relation between source number and flux density is analyzed and the sensitivity of the system is evaluated.

Technique to determine location of radio sources from measurements taken on spinning spacecraft

NASA Technical Reports Server (NTRS)

Fainberg, J.

1979-01-01

The procedure developed to extract average source direction and average source size from spin-modulated radio astronomy data measured on the IMP-6 spacecraft is described. Because all measurements are used, rather than just finding maxima or minima in the data, the method is very sensitive, even in the presence of large amounts of noise. The technique is applicable to all experiments with directivity characteristics. It is suitable for onboard processing on satellites to reduce the data flow to Earth. The application to spin-modulated nonpolarized radio astronomy data is made and includes the effects of noise, background, and second source interference. The analysis was tested with computer simulated data and the results agree with analytic predictions. Applications of this method with IMP-6 radio data have led to: (1) determination of source positions of traveling solar radio bursts at large distances from the Sun; (2) mapping of magnetospheric radio emissions by radio triangulation; and (3) detection of low frequency radio emissions from Jupiter and Saturn.

Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis.

PubMed

Rogers, A E; Cappallo, R J; Hinteregger, H F; Levine, J I; Nesman, E F; Webber, J C; Whitney, A R; Clark, T A; Ma, C; Ryan, J; Corey, B E; Counselman, C C; Herring, T A; Shapiro, I I; Knight, C A; Shaffer, D B; Vandenberg, N R; Lacasse, R; Mauzy, R; Rayhrer, B; Schupler, B R; Pigg, J C

1983-01-07

The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.

A Radio Study of the Ultra-luminous FIR Galaxy NGC 6240

NASA Astrophysics Data System (ADS)

Colbert, E.; Wilson, A. S.; Bland-Hawthorn, J.

1993-05-01

A number of galaxies observed in the IRAS mission are noted to emit ~ 99% of their bolometric flux in the FIR, with FIR luminosities in excess of 10(11) Lsun. The interacting galaxy NGC 6240 has often been referred to as the ``proto-typical'' ultra-luminous (L_FIR >~ 10(12) Lsun) FIR galaxy. The origin of the FIR excess remains a disputed subject in the literature. New observations of NGC 6240 were taken with the VLA at 20cm in the B-configuration, and at 3.6cm in the A-configuration. No significant radio emission was detected from or near the possible ultra-massive ``dark core'' hypothesized by Bland-Hawthorn et. al. (1991); however, approximately 30% of Seyfert galaxies have 20 cm radio luminosities weaker than the upper limit derived from the radio maps. The non-thermal radio emission from luminous FIR galaxies is tightly correlated with the FIR emission. Previous radio observations of NGC 6240 revealed two compact, steep-spectrum nuclear sources, nearly coincident with the two nuclear sources seen in optical images. The 2 images from the new VLA observations and 5 images from previous VLA observations are used to identify the morphological and spectral features of the strong, compact components in the nuclear regions (<~ 1.5 kpc; D=100 Mpc) and of the weaker ``clumps'' of diffuse emission south and west (>~ 3 kpc) from the nucleus. Feasible explanations for the radio emission are discussed. The models that have been proposed in the literature for the FIR excess of NGC 6240 are evaluated for consistency with the observed radio emission.

Observations of compact radio nuclei in Cygnus A, Centaurus A, and other extended radio sources

NASA Technical Reports Server (NTRS)

Kellermann, K. I.; Clark, B. G.; Niell, A. E.; Shaffer, D. B.

1975-01-01

Observations of Cygnus A show a compact radio core 2 milliarcsec in extent oriented in the same direction as the extended components. Other large double- or multiple-component sources, including Centaurus A, have also been found to contain compact radio nuclei with angular sizes in the range 1-10 milliarcsec.

A search for faint high-redshift radio galaxy candidates at 150 MHz

NASA Astrophysics Data System (ADS)

Saxena, A.; Jagannathan, P.; Röttgering, H. J. A.; Best, P. N.; Intema, H. T.; Zhang, M.; Duncan, K. J.; Carilli, C. L.; Miley, G. K.

2018-04-01

Ultrasteep spectrum (USS) radio sources are good tracers of powerful radio galaxies at z > 2. Identification of even a single bright radio galaxy at z > 6 can be used to detect redshifted 21 cm absorption due to neutral hydrogen in the intervening intergalactic medium. Here we describe a new sample of high-redshift radio galaxy (HzRG) candidates constructed from the TIFR GMRT Sky Survey First Alternative Data Release survey at 150 MHz. We employ USS selection (α ≤ -1.3) in ˜10 000 deg2, in combination with strict size selection and non-detections in all-sky optical and infrared surveys. We apply flux density cuts that probe a unique parameter space in flux density (50 mJy < S150 < 200 mJy) to build a sample of 32 HzRG candidates. Follow-up Karl G. Jansky Very Large Array (VLA) observations at 1.4 GHz with an average beam size of 1.3 arcsec revealed ˜ 48 per cent of sources to have a single radio component. P-band (370 MHz) imaging of 17 of these sources revealed a flattening radio SED for 10 sources at low frequencies, which is expected from compact HzRGs. Two of our sources lie in fields where deeper multiwavelength photometry and ancillary radio data are available and for one of these we find a best-fitting photo-z of 4.8 ± 2.0. The other source has zphot = 1.4 ± 0.1 and a small angular size (3.7 arcsec), which could be associated with an obscured star-forming galaxy or with a `dead' elliptical. One USS radio source not part of the HzRG sample but observed with the VLA none the less is revealed to be a candidate giant radio galaxy with a host galaxy photo-z of 1.8 ± 0.5, indicating a size of 875 kpc.

Detailed Investigation of the Gamma-Ray Emission in the Vicinity of SNR W28 with FERMI-LAT

NASA Astrophysics Data System (ADS)

Hanabata, Y.; Katagiri, H.; Hewitt, J. W.; Ballet, J.; Fukazawa, Y.; Fukui, Y.; Hayakawa, T.; Lemoine-Goumard, M.; Pedaletti, G.; Strong, A. W.; Torres, D. F.; Yamazaki, R.

2014-05-01

We present a detailed investigation of the γ-ray emission in the vicinity of the supernova remnant (SNR) W28 (G6.4-0.1) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We detected significant γ-ray emission spatially coincident with TeV sources HESS J1800-240A, B, and C, located outside the radio boundary of the SNR. Their spectra in the 2-100 GeV band are consistent with the extrapolation of the power-law spectra of the TeV sources. We also identified a new source of GeV emission, dubbed Source W, which lies outside the boundary of TeV sources and coincides with radio emission from the western part of W28. All of the GeV γ-ray sources overlap with molecular clouds in the velocity range from 0 to 20 km s-1. Under the assumption that the γ-ray emission toward HESS J1800-240A, B, and C comes from π0 decay due to the interaction between the molecular clouds and cosmic rays (CRs) escaping from W28, they can be naturally explained by a single model in which the CR diffusion coefficient is smaller than the theoretical expectation in the interstellar space. The total energy of the CRs escaping from W28 is constrained through the same modeling to be larger than ~2 × 1049 erg. The emission from Source W can also be explained with the same CR escape scenario.

Detailed Investigation of the Gamma-Ray Emission in the Vicinity of SNR W28 with FERMI-LAT

NASA Technical Reports Server (NTRS)

Hanabata, Y.; Katagiri, H.; Hewitt, John William; Ballet, J.; Fukazawa, Y.; Fukui, Y.; Hayakawa, T.; Lemoine-Goumard, M.; Pedaletti, G.; Strong, A. W.;

A VLA SURVEY FOR FAINT COMPACT RADIO SOURCES IN THE ORION NEBULA CLUSTER

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

Sheehan, Patrick D.; Eisner, Josh A.; Mann, Rita K.

We present Karl G. Jansky Very Large Array 1.3, 3.6, and 6 cm continuum maps of compact radio sources in the Orion Nebular Cluster (ONC). We mosaicked 34 arcmin{sup 2} at 1.3 cm, 70 arcmin{sup 2} at 3.6 cm and 109 arcmin{sup 2} at 6 cm, containing 778 near-infrared detected young stellar objects and 190 Hubble Space Telescope -identified proplyds (with significant overlap between those characterizations). We detected radio emission from 175 compact radio sources in the ONC, including 26 sources that were detected for the first time at these wavelengths. For each detected source, we fitted a simple free–freemore » and dust emission model to characterize the radio emission. We extrapolate the free–free emission spectrum model for each source to ALMA bands to illustrate how these measurements could be used to correctly measure protoplanetary disk dust masses from submillimeter flux measurements. Finally, we compare the fluxes measured in this survey with previously measured fluxes for our targets, as well as four separate epochs of 1.3 cm data, to search for and quantify the variability of our sources.« less

The Position/Structure Stability of Four ICRF2 Sources

NASA Technical Reports Server (NTRS)

Fomalont, Ed; Johnston, Kenneth; Fey, Alan; Boboltz, Dave; Oyama, Tomoaki; Honma, Mareki

2010-01-01

Four compact radio sources in the International Celestial Reference Frame (ICRF2) catalog were observed using phase referencing with the VLBA at 43, 23, and 8.6-GHz, and with VERA at 23-GHz over a one-year period. The goal was to determine the stability of the radio cores and to assess structure effects associated with positions in the ICRF2. Conclusions are: (1) 43-GHz VLBI high-resolution observations are often needed to determine the location of the radio core. (2) Over the observing period, the relative positions among the four radio cores were constant to 0.02 mas, suggesting that once the true radio core is identified, it remains stationary in the sky to this accuracy. (3) The emission in 0556+238, one of the four sources investigated and one of the 295 ICRF2 defining sources, was dominated by a strong component near the core and moved 0.1 mas during the year. (4) Comparison of the VLBA images at 43, 23, and 8.6-GHz with the ICRF2 positions suggests that the 8-GHz structure is often dominated by a bright non-core component. The measured ICRF2 position can be displaced more than 0.5 mas from the radio core and partake in the motion of the bright jet component.

A Kalman filter approach for the determination of celestial reference frames

NASA Astrophysics Data System (ADS)

Soja, Benedikt; Gross, Richard; Jacobs, Christopher; Chin, Toshio; Karbon, Maria; Nilsson, Tobias; Heinkelmann, Robert; Schuh, Harald

2017-04-01

The coordinate model of radio sources in International Celestial Reference Frames (ICRF), such as the ICRF2, has traditionally been a constant offset. While sufficient for a large part of radio sources considering current accuracy requirements, several sources exhibit significant temporal coordinate variations. In particular, the group of the so-called special handling sources is characterized by large fluctuations in the source positions. For these sources and for several from the "others" category of radio sources, a coordinate model that goes beyond a constant offset would be beneficial. However, due to the sheer amount of radio sources in catalogs like the ICRF2, and even more so with the upcoming ICRF3, it is difficult to find the most appropriate coordinate model for every single radio source. For this reason, we have developed a time series approach to the determination of celestial reference frames (CRF). We feed the radio source coordinates derived from single very long baseline interferometry (VLBI) sessions sequentially into a Kalman filter and smoother, retaining their full covariances. The estimation of the source coordinates is carried out with a temporal resolution identical to the input data, i.e. usually 1-4 days. The coordinates are assumed to behave like random walk processes, an assumption which has already successfully been made for the determination of terrestrial reference frames such as the JTRF2014. To be able to apply the most suitable process noise value for every single radio source, their statistical properties are analyzed by computing their Allan standard deviations (ADEV). Additional to the determination of process noise values, the ADEV allows drawing conclusions whether the variations in certain radio source positions significantly deviate from random walk processes. Our investigations also deal with other means of source characterization, such as the structure index, in order to derive a suitable process noise model. The Kalman filter CRFs resulting from the different approaches are compared among each other, to the original radio source position time series, as well as to a traditional CRF solution, in which the constant source positions are estimated in a global least squares adjustment.

Multiwavelength observations of unidentified high energy gamma ray sources

NASA Technical Reports Server (NTRS)

Halpern, Jules P.

1993-01-01

As was the case for COS B, the majority of high-energy (greater than 100 MeV) gamma-ray sources detected by the EGRET instrument on GRO are not immediately identifiable with cataloged objects at other wavelengths. These persistent gamma-ray sources are, next to the gamma-ray bursts, the least understood objects in the universe. Even a rudimentary understanding of their nature awaits identifications and follow-up work at other wavelengths to tell us what they are. The as yet unidentified sources are potentially the most interesting, since they may represent unrecognized new classes of astronomical objects, such as radio-quiet pulsars or new types of active galactic nuclei (AGN's). This two-year investigation is intended to support the analysis, correlation, and theoretical interpretation of data that we are obtaining at x ray, optical, and radio wavelengths in order to render the gamma-ray data interpretable. According to plan, in the first year concentration was on the identification and study of Geminga. The second year will be devoted to studies of similar unidentified gamma-ray sources which will become available in the first EGRET catalogs. The results obtained so far are presented in the two papers which are reproduced in the Appendix. In these papers, we discuss the pulse profiles of Geminga, the geometry and efficiency of the magnetospheric accelerator, the distance to Geminga, the implications for theories of polar cap heating, the effect of the magnetic field on the surface emission and environment of the neutron star, and possible interpretations of a radio-quiet Geminga. The implications of the other gamma-ray pulsars which were discovered to have high gamma-ray efficiency are also discussed, and the remaining unidentified COS B sources are attributed to a population of efficient gamma-ray sources, some of which may be radio quiet.

A New Radio Loudness Diagnostic for Active Galaxies: A Radio-to-Mid-Infrared Parameter

NASA Technical Reports Server (NTRS)

Melendez, Marcio B.; Kraemer, S. B.; Schmitt, H. R.

2010-01-01

We have studied the relationship between the nuclear (high-resolution) radio emission, at 8.4GHz (3.6cm) and 1.4GHz (20cm), the [O IV) (gamma)25.89 micron, [Ne III] (gamma)l5.56 micron and [Ne II] (gamma)l2.81 micron emission lines and the black hole mass accretion rate for a sample of Seyfert galaxies. In order to characterize the radio contribution for the Seyfert nuclei we used the 8.4 GHz/[O IV] ratio, assuming that [0 IV] scales with the luminosity of the active galactic nuclei (AGN). From this we find that Seyfert 1 s (i.e. Seyfert 1.0s, 1.2s and 1.5s) and Seyfert 2s (i.e. Seyfert 1.8s, 1.9s and 2.0s) have similar radio contributions, relative to the AGN. On the other hand, sources in which the [Ne u] emission is dominated either by the AGN or star formation have statistically different radio contributions, with star formation dominated sources more 'radio loud', by a factor of approx.2.8 on average, than AGN dominated sources. We show that star formation dominated sources with relatively larger radio contribution have smaller mass accretion rates. Overall, we suggest that 8.4 GHz/[O IV], or alternatively, 1.4 GHz/[O IV] ratios, can be used to characterize the radio contribution, relative to the AGN, without the limitation of previous methods that rely on optical observables. Key words: Galaxy: stellar content - galaxies: Seyfert - infrared: galaxies

Rotational and X-ray luminosity evolution of high-B radio pulsars

NASA Astrophysics Data System (ADS)

Benli, Onur; Ertan, Ünal

2018-05-01

In continuation of our earlier work on the long-term evolution of the so-called high-B radio pulsars (HBRPs) with measured braking indices, we have investigated the long-term evolution of the remaining five HBRPs for which braking indices have not been measured yet. This completes our source-by-source analyses of HBRPs in the fallback disc model that was also applied earlier to anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs), and dim isolated neutron stars (XDINs). Our results show that the X-ray luminosities and the rotational properties of these rather different neutron star populations can be acquired by neutron stars with fallback discs as a result of differences in their initial conditions, namely the initial disc mass, initial period and the dipole field strength. For the five HBRPs, unlike for AXPs, SGRs and XDINs, our results do not constrain the dipole field strengths of the sources. We obtain evolutionary paths leading to the properties of HBRPs in the propeller phase with dipole fields sufficiently strong to produce pulsed radio emission.

F-GAMMA program: Unification and physical interpretation of the radio spectra variability patterns in Fermi blazars and detection of radio jet emission from NLSY1 galaxies

NASA Astrophysics Data System (ADS)

Angelakis, E.

2012-01-01

The F-GAMMA program aims at understanding the physics at work in AGN via a multi-frequency monitoring approach. A number of roughly 65 Fermi-GST detectable blazars are being monitored monthly since January 2007 at radio wavelengths. The core program relies on the 100-m Effelsberg telescope operating at 8 frequencies between 2.6 and 43 GHz, the 30-m IRAM telescope observing at 86, 145 and 240 GHz and the APEX 12-m telescope at 345 GHz. For the targeted sources the LAT instrument onboard Fermi-GST provides gamma-ray light curves sampled daily. Here we discuss two recent findings: A). On the basis of their variability pattern, the observed quasi-simultaneous broad-band spectra can be classified to merely 5 classes. The variability for the first 4 is clearly dominated by spectral-evolution. Sources of the last class vary self-similarly with almost no apparent shift of the peak frequency. The former classes can be attributed to a two-component principal system made of a quiescent optically thin spectrum and a super-imposed flaring event. The later class must be interpreted in terms of a completely different mechanism. The apparent differences among the classes are explained in terms of a redshift modulus and an intrinsic-source/flare parameters modulus. Numerical simulations have shown that a shock-in-jet model can very well describe the observed behavior. It is concluded therefore that only two mechanisms seem to be producing variability. None of the almost 90 sources used for this study show a switch of class indicating that the variability mechanism is either (a) a finger-print of the source, or (b) remains stable on timescales far longer than the monitoring period of almost 4 years. B). Recently it has been disclosed that Narrow Line Seyfert 1 galaxies show gamma-ray emission. Within the F-GAMMA program radio jet emission has been detected from 3 such sources challenging the belief that jets are associated with elliptical galaxies. The recent findings in this area will be discussed.

Arcsecond positions for milliarcsecond VLBI nuclei of extragalactic radio sources. IV - Seventeen sources

NASA Technical Reports Server (NTRS)

Morabito, D. D.; Preston, R. A.; Linfield, R. P.; Slade, M. A.; Jauncey, D. L.

1986-01-01

VLBI measurements of time delay and delay rate at 2.29 and 8.42 GHz on baselines of 10,000 km have been used to determine the positions of the milliarcsecond nuclei in 17 extragalactic radio sources with estimated accuracies of 0.1 to 0.3 arcsec. The observed sources are part of an all-sky VLBI catalog of milliarcsecond radio sources. In addition, slightly improved positions are presented for 101 sources originally reported by Morabito et al. (1983). Arcsecond positions have now been determined for 836 sources.

Optical Spectra of Candidate International Celestial Reference Frame (ICRF) Flat-spectrum Radio Sources. III

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

Titov, O.; Stanford, Laura M.; Pursimo, T.

In extending our spectroscopic program, which targets sources drawn from the International Celestial Reference Frame (ICRF) Catalog, we have obtained spectra for ∼160 compact, flat-spectrum radio sources and determined redshifts for 112 quasars and radio galaxies. A further 14 sources with featureless spectra have been classified as BL Lac objects. Spectra were obtained at three telescopes: the 3.58 m European Southern Observatory New Technology Telescope, and the two 8.2 m Gemini telescopes in Hawaii and Chile. While most of the sources are powerful quasars, a significant fraction of radio galaxies is also included from the list of non-defining ICRF radiomore » sources.« less

Evolution of Extragalactic Radio Sources and Quasar/Galaxy Unification

NASA Astrophysics Data System (ADS)

Onah, C. I.; Ubachukwu, A. A.; Odo, F. C.; Onuchukwu, C. C.

2018-04-01

We use a large sample of radio sources to investigate the effects of evolution, luminosity selection and radio source orientation in explaining the apparent deviation of observed angular size - redshift (θ - z) relation of extragalactic radio sources (EGRSs) from the standard model. We have fitted the observed θ - z data with standard cosmological models based on a flat universe (Ω0 = 1). The size evolution of EGRSs has been described as luminosity, temporal and orientation-dependent in the form DP,z,Φ ≍ P±q(1 + z)-m sinΦ, with q=0.3, Φ=59°, m=-0.26 for radio galaxies and q=-0.5, Φ=33°, m=3.1 for radio quasars respectively. Critical points of luminosity, logPcrit=26.33 WHz-1 and logDc=2.51 kpc (316.23 kpc) of the present sample of radio sources were also observed. All the results were found to be consistent with the popular quasar/galaxy unification scheme.

The Second International Celestial Reference Frame (ICRF2)

NASA Technical Reports Server (NTRS)

Ma, Chopo

2010-01-01

The ICRF2 catalog was constructed by the IERS/IVS Working Group with oversight by the IAU Working Group. Derived using data from August 1979 through March 2009, it is a great improvement over the original ICRF with 3414 extragalactic radio source positions, a noise floor of 40 microarcsec, and axis stability of 10 microarcsec. Significant refinements were made in the selection of defining sources, modeling, and the integration of CRF, TRF, and EOP. The adoption of the ICRF2 was approved by the IAU in Resolution B3 at the XXVII IAU General Assembly and became effective 1 January 2010.

ULTRA STEEP SPECTRUM RADIO SOURCES IN THE LOCKMAN HOLE: SERVS IDENTIFICATIONS AND REDSHIFT DISTRIBUTION AT THE FAINTEST RADIO FLUXES

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

Afonso, J.; Bizzocchi, L.; Grossi, M.

2011-12-20

Ultra steep spectrum (USS) radio sources have been successfully used to select powerful radio sources at high redshifts (z {approx}> 2). Typically restricted to large-sky surveys and relatively bright radio flux densities, it has gradually become possible to extend the USS search to sub-mJy levels, thanks to the recent appearance of sensitive low-frequency radio facilities. Here a first detailed analysis of the nature of the faintest USS sources is presented. By using Giant Metrewave Radio Telescope and Very Large Array radio observations of the Lockman Hole at 610 MHz and 1.4 GHz, a sample of 58 USS sources, with 610more » MHz integrated fluxes above 100 {mu}Jy, is assembled. Deep infrared data at 3.6 and 4.5 {mu}m from the Spitzer Extragalactic Representative Volume Survey (SERVS) are used to reliably identify counterparts for 48 (83%) of these sources, showing an average total magnitude of [3.6]{sub AB} = 19.8 mag. Spectroscopic redshifts for 14 USS sources, together with photometric redshift estimates, improved by the use of the deep SERVS data, for a further 19 objects, show redshifts ranging from z = 0.1 to z = 2.8, peaking at z {approx} 0.6 and tailing off at high redshifts. The remaining 25 USS sources, with no redshift estimate, include the faintest [3.6] magnitudes, with 10 sources undetected at 3.6 and 4.5 {mu}m (typically [3.6] {approx}> 22-23 mag from local measurements), which suggests the likely existence of higher redshifts among the sub-mJy USS population. The comparison with the Square Kilometre Array Design Studies Simulated Skies models indicates that Fanaroff-Riley type I radio sources and radio-quiet active galactic nuclei may constitute the bulk of the faintest USS population, and raises the possibility that the high efficiency of the USS technique for the selection of high-redshift sources remains even at the sub-mJy level.« less

Fermi Large Area Telescope Observations of Misaligned Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Abdo, A. A.; Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Buehler, R.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Cannon, A.; Caraveo, P. A.; Carrigan, S.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Çelik, Ö.; Celotti, A.; Charles, E.; Chekhtman, A.; Chen, A. W.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Colafrancesco, S.; Conrad, J.; Davis, D. S.; Dermer, C. D.; de Angelis, A.; de Palma, F.; Silva, E. do Couto e.; Drell, P. S.; Dubois, R.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Fortin, P.; Frailis, M.; Fukazawa, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grandi, P.; Grenier, I. A.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hadasch, D.; Hayashida, M.; Hays, E.; Horan, D.; Hughes, R. E.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lee, S.-H.; Lemoine-Goumard, M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Malaguti, G.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Michelson, P. F.; Migliori, G.; Mitthumsiri, W.; Mizuno, T.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Nestoras, I.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Persic, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reyes, L. C.; Roth, M.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Scargle, J. D.; Sgrò, C.; Siskind, E. J.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Stecker, F. W.; Strickman, M. S.; Suson, D. J.; Takahashi, H.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Torresi, E.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vilchez, N.; Villata, M.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Yang, Z.; Ylinen, T.; Ziegler, M.

2010-09-01

Analysis is presented for 15 months of data taken with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope for 11 non-blazar active galactic nuclei (AGNs), including seven FRI radio galaxies and four FRII radio sources consisting of two FRII radio galaxies and two steep spectrum radio quasars. The broad line FRI radio galaxy 3C 120 is reported here as a γ-ray source for the first time. The analysis is based on directional associations of LAT sources with radio sources in the 3CR, 3CRR, and MS4 (collectively referred to as 3C-MS) catalogs. Seven of the eleven LAT sources associated with 3C-MS radio sources have spectral indices larger than 2.3 and, except for the FRI radio galaxy NGC 1275 that shows possible spectral curvature, are well described by a power law. No evidence for time variability is found for any sources other than NGC 1275. The γ-ray luminosities of FRI radio galaxies are significantly smaller than those of the BL Lac objects detected by the LAT, whereas the γ-ray luminosities of the FRII sources are quite similar to those of FSRQs, which could reflect different beaming factors for the γ-ray emission. A core dominance (CD) study of the 3CRR sample indicates that sources closer to the jet axis are preferentially detected with the Fermi LAT, insofar as the γ-ray-detected misaligned AGNs have larger CD at a given average radio flux. The results are discussed in view of the AGN unification scenario.

Radio Galaxy Zoo: cosmological alignment of radio sources

NASA Astrophysics Data System (ADS)

Contigiani, O.; de Gasperin, F.; Miley, G. K.; Rudnick, L.; Andernach, H.; Banfield, J. K.; Kapińska, A. D.; Shabala, S. S.; Wong, O. I.

2017-11-01

We study the mutual alignment of radio sources within two surveys, Faint Images of the Radio Sky at Twenty-centimetres (FIRST) and TIFR GMRT Sky Survey (TGSS). This is done by producing two position angle catalogues containing the preferential directions of respectively 30 059 and 11 674 extended sources distributed over more than 7000 and 17 000 deg2. The identification of the sources in the FIRST sample was performed in advance by volunteers of the Radio Galaxy Zoo (RGZ) project, while for the TGSS sample it is the result of an automated process presented here. After taking into account systematic effects, marginal evidence of a local alignment on scales smaller than 2.5 deg is found in the FIRST sample. The probability of this happening by chance is found to be less than 2 per cent. Further study suggests that on scales up to 1.5 deg the alignment is maximal. For one third of the sources, the RGZ volunteers identified an optical counterpart. Assuming a flat Λ cold dark matter cosmology with Ω _m = 0.31, Ω _Λ = 0.69, we convert the maximum angular scale on which alignment is seen into a physical scale in the range [19, 38] Mpc h_{70}^{-1}. This result supports recent evidence reported by Taylor and Jagannathan of radio jet alignment in the 1.4 deg2 ELAIS N1 field observed with the Giant Metrewave Radio Telescope. The TGSS sample is found to be too sparsely populated to manifest a similar signal.

Radio and optical observations of 0218+357 - The smallest Einstein ring?

NASA Technical Reports Server (NTRS)

O'Dea, Christopher P.; Baum, Stefi A.; Stanghellini, Carlo; Dey, Arjun; Van Breugel, Wil; Deustua, Susana; Smith, Eric P.

1992-01-01

VLA radio observations and optical imaging and spectroscopy of the Einstein radio ring 0218+357 are presented. The ring is detected at 22.4 GHz and shows a basically similar structure at 5, 15, and 22.4 GHz. The B component has varied and was about 15 percent brighter in the 8.4 GHz data than in the data of Patnaik et al. (1992). The ring is highly polarized. A weak jetlike feature extending out roughly 2 arcsec to the southeast of component A is detected at 6 cm. The source has amorphous radio structure extending out to about 11 arcsec from the core. For an adopted redshift of 0.68, the extended radio emission is very powerful. The optical spectrum is rather red and shows no strong features. A redshift of about 0.68 is obtained. The identification is a faint compact m(r) about 20 galaxy which extends to about 4.5 arcsec (about 27 kpc). As much as 50 percent of the total light may be due to a central AGN. The observed double core and ring may be produced by an off-center radio core with extended radio structure.

Infrared-faint radio sources remain undetected at far-infrared wavelengths. Deep photometric observations using the Herschel Space Observatory

NASA Astrophysics Data System (ADS)

Herzog, A.; Norris, R. P.; Middelberg, E.; Spitler, L. R.; Leipski, C.; Parker, Q. A.

2015-08-01

Context. Showing 1.4 GHz flux densities in the range of a few to a few tens of mJy, infrared-faint radio sources (IFRS) are a type of galaxy characterised by faint or absent near-infrared counterparts and consequently extreme radio-to-infrared flux density ratios up to several thousand. Recent studies showed that IFRS are radio-loud active galactic nuclei (AGNs) at redshifts ≳2, potentially linked to high-redshift radio galaxies (HzRGs). Aims: This work explores the far-infrared emission of IFRS, providing crucial information on the star forming and AGN activity of IFRS. Furthermore, the data enable examining the putative relationship between IFRS and HzRGs and testing whether IFRS are more distant or fainter siblings of these massive galaxies. Methods: A sample of six IFRS was observed with the Herschel Space Observatory between 100 μm and 500 μm. Using these results, we constrained the nature of IFRS by modelling their broad-band spectral energy distribution (SED). Furthermore, we set an upper limit on their infrared SED and decomposed their emission into contributions from an AGN and from star forming activity. Results: All six observed IFRS were undetected in all five Herschel far-infrared channels (stacking limits: σ = 0.74 mJy at 100 μm, σ = 3.45 mJy at 500 μm). Based on our SED modelling, we ruled out the following objects to explain the photometric characteristics of IFRS: (a) known radio-loud quasars and compact steep-spectrum sources at any redshift; (b) starburst galaxies with and without an AGN and Seyfert galaxies at any redshift, even if the templates were modified; and (c) known HzRGs at z ≲ 10.5. We find that the IFRS analysed in this work can only be explained by objects that fulfil the selection criteria of HzRGs. More precisely, IFRS could be (a) known HzRGs at very high redshifts (z ≳ 10.5); (b) low-luminosity siblings of HzRGs with additional dust obscuration at lower redshifts; (c) scaled or unscaled versions of Cygnus A at any redshift; and (d) scaled and dust-obscured radio-loud quasars or compact steep spectrum sources. We estimated upper limits on the infrared luminosity, the black hole accretion rate, and the star formation rate of IFRS, which all agreed with corresponding numbers of HzRGs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Radio emission from dusty galaxies observed by AKARI

NASA Astrophysics Data System (ADS)

Pepiak, A.; Pollo, A.; Takeuchi, T. T.; Solarz, A.; Jurusik, W.

2014-10-01

We probe radio-infrared correlation for two samples of extragalactic sources from the local Universe from the AKARI All-Sky Catalogue. The first, smaller sample (1053 objects) was constructed by the cross-correlation of the AKARI/FIS All-Sky Survey Bright Source Catalogue, the AKARI IRC All-Sky Survey Point Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the mid- and far-infrared by AKARI, and at the 1.4 GHz radio frequency by NRAO. The second, larger sample (13,324 objects) was constructed by the cross-correlation of only the AKARI/FIS All-Sky Survey Bright Source Catalogue and the NRAO VLA Sky Survey, i.e. it consists of sources detected in the far-infrared and radio, without a condition to be detected in the mid-infrared. Additionally, all objects in both samples were identified as galaxies in the NED and/or SIMBAD databases, and a part of them is known to host active galactic nuclei (AGNs). For the present analysis, we have restricted our samples only to sources with known redshift z. In this paper, we analyse the far-infrared-radio correlation for both of these samples. We compare the ratio of infrared and radio emission from normal star-forming dusty galaxies and AGNs in both samples. For the smaller sample we obtained =2.14 for AGNs and =2.27 for normal galaxies, while for the larger sample =2.15 for AGNs and =2.22 for normal galaxies. An average value of the slope in both samples is ~2.2, which is consistent with the previous measurements from the literature.

Detection of radio continuum emission from Herbig-Haro objects 1 and 2 and from their central exciting source

NASA Technical Reports Server (NTRS)

Pravdo, S. H.; Rodriguez, L. F.; Curiel, S.; Canto, J.; Torrelles, J. M.; Becker, R. H.; Sellgren, K.

1985-01-01

The region in Orion containing HH 1 and HH 2 was observed with the VLA at 20, 6, and 2 cm on several occasions from 1981 to 1984. At lower resolution, four continuum sources were detected. Two of these sources coincide positionally with HH 1 and HH 2. At 6 cm and higher resolution, HH 1 is resolved into at least two components. The emission is probably bremsstrahlung originating in the same region where the visible line emission is produced. This is the first detection of radio continuum from classic Herbig-Haro objects. At a position closely centered between HH 1 and HH 2, an object that can be interpreted as the energy source of the system was detected. The central source spectrum is S(nu) of about nu to the alpha power, where alpha = 0.4 + or - 0.2, suggesting a stellar wind. Finally, the fourth radio continuum source coincides positionally with an H2O maser and is probably excited by an independent star. There is evidence of time variability in its radio flux. No emission was detected from the Cohen-Schwartz (1979) star at the 0.1 mJy level.

Discovery of a GeV blazar shining through the galactic plane

DOE PAGES

Vandenbroucke, J.; Buehler, R.; Ajello, M.; ...

2010-07-14

The Fermi Large Area Telescope (LAT) discovered a new gamma-ray source near the Galactic plane, Fermi J0109+6134, when it flared brightly in 2010 February. The low Galactic latitude (b = –1more » $$ο\\atop{.}$$2) indicated that the source could be located within the Galaxy, which motivated rapid multi-wavelength follow-up including radio, optical, and X-ray observations. Here, we report the results of analyzing all 19 months of LAT data for the source, and of X-ray observations with both Swift and the Chandra X-ray Observatory. We determined the source redshift, z = 0.783, using a Keck Low-Resolution Imaging Spectrometer observation. Finally, we compiled a broadband spectral energy distribution (SED) from both historical and new observations contemporaneous with the 2010 February flare. The redshift, SED, optical line width, X-ray absorption, and multi-band variability indicate that this new GeV source is a blazar seen through the Galactic plane. Because several of the optical emission lines have equivalent width >5 Å, this blazar belongs in the flat-spectrum radio quasar category.« less

On the Interaction of the PKS B1358-113 Radio Galaxy with the A1836 Cluster

DOE PAGES

Stawarz, L.; Szostek, A.; Cheung, C. C.; ...

2014-10-07

In this study, we present the analysis of multifrequency data gathered for the Fanaroff-Riley type-II (FR II) radio galaxy PKS B1358-113, hosted in the brightest cluster galaxy in the center of A1836. The galaxy harbors one of the most massive black holes known to date, and our analysis of the acquired optical data reveals that this black hole is only weakly active, with a mass accretion ratemore » $$\\dot{M}_{\\rm acc} \\sim 2 \\times 10^{-4} \\, \\dot{M}_{\\rm Edd} \\sim 0.02 \\, M_{\\odot }$$ yr –1. Based on analysis of new Chandra and XMM-Newton X-ray observations and archival radio data, and assuming the well-established model for the evolution of FR II radio galaxies, we derive the preferred range for the jet kinetic luminosity L j ~ (1-6) × 10 –3 L Edd ~ (0.5-3) × 10 45 erg s –1. This is above the values implied by various scaling relations proposed for radio sources in galaxy clusters, being instead very close to the maximum jet power allowed for the given accretion rate. We also constrain the radio source lifetime as τ j ~ 40-70 Myr, meaning the total amount of deposited jet energy E tot ~ (2-8) × 10 60 erg. We argue that approximately half of this energy goes into shock heating of the surrounding thermal gas, and the remaining 50% is deposited into the internal energy of the jet cavity. The detailed analysis of the X-ray data provides indication for the presence of a bow shock driven by the expanding radio lobes into the A1836 cluster environment. We derive the corresponding shock Mach number in the range $$\\mathcal {M}_{\\rm sh} \\sim 2\\hbox{--}4$$, which is one of the highest claimed for clusters or groups of galaxies. This, together with the recently growing evidence that powerful FR II radio galaxies may not be uncommon in the centers of clusters at higher redshifts, supports the idea that jet-induced shock heating may indeed play an important role in shaping the properties of clusters, galaxy groups, and galaxies in formation. In this context, we speculate on a possible bias against detecting stronger jet-driven shocks in poorer environments, resulting from inefficient electron heating at the shock front, combined with a relatively long electron-ion temperature equilibration timescale.« less

Polarimetry of the Fast Radio Burst Source FRB121102

NASA Astrophysics Data System (ADS)

Michilli, Daniele; Seymour, Andrew; Hessels, Jason W. T.; Spitler, Laura; Gajjar, Vishal; Archibald, Anne; Bower, Geoffrey C.; Chatterjee, Shami; Cordes, Jim; Gourdji, Kelly; Heald, George; Kaspi, Victoria; Law, Casey; Sobey, Charlotte

2018-01-01

Fast radio bursts (FRBs) are millisecond-duration radio flashes of presumably extragalactic origin. FRB121102 is the only FRB known to repeat and the only one with a precise localization. It is co-located with a persistent radio source inside a star-forming region in a dwarf galaxy at z=0.2. While the persistent source is compatible with either a low-luminosity accreting black hole or a very energetic nebula and supernova remnant, the source of the bursts is still a mystery. We present new bursts from FRB121102 detected at relatively high radio frequencies of ~5GHz. These observations allow us to investigate the polarization properties of the bursts, placing new constraints on the environment of FRB121102.

Search for very high energy gamma-ray emission from the peculiar radio galaxy IC 310 with TACTIC during 2012 to 2015

NASA Astrophysics Data System (ADS)

Ghosal, B.; Singh, K. K.; Yadav, K. K.; Tickoo, A. K.; Rannot, R. C.; Chandra, P.; Kothari, M.; Gaur, K. K.; Goyal, H. C.; Goyal, A.; Kumar, N.; Marandi, P.; Chanchalani, K.; Agarwal, N. K.; Dhar, V. K.; Koul, M. K.; Koul, R.; Venugopal, K.; Bhat, C. K.; Chouhan, N.; Borwankar, C.; Kaul, S. R.; Bhatt, H.; Agarwal, A.; Gupta, A. C.

2018-04-01

Non-blazar active galactic nuclei like radio galaxies have emerged as a new class of γ-ray sources in the sky. Observations of very high energy (VHE) γ-rays from radio galaxies with misaligned jets offer a unique tool to understand the physical processes involved in these type of objects. In this work, we present the results of our observations of the nearby peculiar radio galaxy IC 310 (z = 0.0189) with TACTIC telescope for nearly 95.5 hours from 03 December, 2012 to 19 January, 2015 (MJD 56265 - 57041). Detailed analysis of the data reveals absence of a statistically significant γ-ray signal from the source direction (both on the overall period and on yearly basis). Our results suggest that the source was possibly in a low-TeV emission state (below the TACTIC sensitivity level) during the above mentioned observation period and the resulting 3σ upper limit on the integral flux above 850 GeV has been estimated to be 4.99 ×10-12phcm-2s-1 (23% of the Crab Nebula flux). Analysis of the contemporaneous data collected by Fermi-LAT in the 30 - 300 GeV energy range, also indicate the absence of a statistically significant γ-ray signal, therefore 2σ upper limit on the integral flux above 30 GeV has been estimated on yearly basis. We also report the results from dedicated optical observations in B, V and R bands from ARIES observatory carried out from December, 2014 to March, 2015.

Fermi Large Area Telescope Observations Of Misaligned Active Galactic Nuclei

DOE PAGES

Abdo, A. A.

2010-08-13

Analysis is presented for 15 months of data taken with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope for 11 non-blazar active galactic nuclei (AGNs), including seven FRI radio galaxies and four FRII radio sources consisting of two FRII radio galaxies and two steep spectrum radio quasars. The broad line FRI radio galaxy 3C 120 is reported here as a γ-ray source for the first time. The analysis is based on directional associations of LAT sources with radio sources in the 3CR, 3CRR, and MS4 (collectively referred to as 3C-MS) catalogs. Seven of the eleven LAT sourcesmore » associated with 3C-MS radio sources have spectral indices larger than 2.3 and, except for the FRI radio galaxy NGC 1275 that shows possible spectral curvature, are well described by a power law. No evidence for time variability is found for any sources other than NGC 1275. The γ-ray luminosities of FRI radio galaxies are significantly smaller than those of the BL Lac objects detected by the LAT, whereas the γ-ray luminosities of the FRII sources are quite similar to those of FSRQs, which could reflect different beaming factors for the γ-ray emission. A core dominance (CD) study of the 3CRR sample indicates that sources closer to the jet axis are preferentially detected with the Fermi LAT, insofar as the γ-ray-detected misaligned AGNs have larger CD at a given average radio flux. The results are discussed in view of the AGN unification scenario.« less

Plasma and radio waves from Neptune: Source mechamisms and propagation

NASA Technical Reports Server (NTRS)

Menietti, J. Douglas

1994-01-01

The purpose of this project was to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as it flew by Neptune. The study has included data analysis, theoretical and numerical calculations, and ray tracing to determine the possible source mechanisms and locations of the radiation, including the narrowband bursty and smooth components of the Neptune radio emission.

Galaxy Evolution in the Reddest Possible Filter

NASA Astrophysics Data System (ADS)

Richards, E. A.

We describe an observational programme aimed at understanding the radio emission from distant, rapidly evolving galaxy populations. These observations were carried out at 1.4 and 8.5 GHz with the VLA, centred on the Hubble Deep Field, obtaining limiting flux densities of 40 and 8 μJy respectively. The differential count of the radio sources is marginally sub-Euclidean to the completeness limits (γ = - 2.4 +/- 0.1) and fluctuation analysis suggests nearly 60 sources per arcmin^2 at the 1 μJy level. Using high-resolution 1.4 GHz observations obtained with MERLIN, we resolve all radio sources detected in the VLA complete sample and measure a median angular size for the microjansky radio population of 1-2``. This clue, coupled with the steep spectral index of the 1.4 GHz selected sample, suggests diffuse synchrotron radiation in z ~ 1 galactic discs. The wide-field HST and ground-based optical exposures show that the radio sources are identified primarily with disc systems composed of irregulars, peculiars, interacting/merging galaxies and a few isolated field spirals. Only 20% of the radio sources can be attributed to AGN - the majority are probably associated with starburst activity. The available redshifts range from 0.1 to 3, with a mean of about 0.8. We are plrobably witnessing a major episode of starburst activity in these luminous (L > L_*) systems, occasionally accompanied by an embedded AGN. About 20% of the radio sources remain unidentified to I = 26-28 in the HDF and flanking fields. Several of these objects have extremely red counterparts. We suggest that these are high-redshift dusty protogalaxies.

Radio weak lensing shear measurement in the visibility domain - II. Source extraction

NASA Astrophysics Data System (ADS)

Rivi, M.; Miller, L.

2018-05-01

This paper extends the method introduced in Rivi et al. (2016b) to measure galaxy ellipticities in the visibility domain for radio weak lensing surveys. In that paper, we focused on the development and testing of the method for the simple case of individual galaxies located at the phase centre, and proposed to extend it to the realistic case of many sources in the field of view by isolating visibilities of each source with a faceting technique. In this second paper, we present a detailed algorithm for source extraction in the visibility domain and show its effectiveness as a function of the source number density by running simulations of SKA1-MID observations in the band 950-1150 MHz and comparing original and measured values of galaxies' ellipticities. Shear measurements from a realistic population of 104 galaxies randomly located in a field of view of 1 \\deg ^2 (i.e. the source density expected for the current radio weak lensing survey proposal with SKA1) are also performed. At SNR ≥ 10, the multiplicative bias is only a factor 1.5 worse than what found when analysing individual sources, and is still comparable to the bias values reported for similar measurement methods at optical wavelengths. The additive bias is unchanged from the case of individual sources, but it is significantly larger than typically found in optical surveys. This bias depends on the shape of the uv coverage and we suggest that a uv-plane weighting scheme to produce a more isotropic shape could reduce and control additive bias.

Evidence of Non-Coincidence between Radio and Optical Positions of ICRF Sources.

NASA Astrophysics Data System (ADS)

Andrei, A. H.; da Silva, D. N.; Assafin, M.; Vieira Martins, R.

2003-11-01

Silva Neto et al. (SNAAVM: 2002) show that comparing the ICRF Ext1 sources standard radio position (Ma et al., 1998) against their optical counterpart position(ZZHJVW: Zacharias et al., 1999; USNO A2.0: Monet et al., 1998), a systematic pattern appears, which depends on the radio structure index (Fey and Charlot, 2000). The optical to radio offsets produce a distribution suggestive of a coincidence of the optical and radio centroids worse for the radio extended than for the radio compact sources. On average, the coincidence between the optical and radio centroids is found 7.9 +/- 1.1 mas smaller for the compact than for the extended sources. Such an effect is reasonably large, and certainly much too large to be due to errors on the VLBI radio position. On the other hand, it is too small to be accounted to the errors on the optical position, which moreover should be independent from the radio structure. Thus, other than a true pattern of centroids non-coincidence, the remaining explanation is of a hazard result. This paper summarizes the several statistical tests used to discard the hazard explanation.

Radio supernovae and super star clusters in the circumnuclear region of NGC 1365

NASA Astrophysics Data System (ADS)

Lindblad, P. O.; Kristen, H.

Groundbased optical and VLA observations have shown that the nucleus of the barred Seyfert 1 galaxy NGC 1365 is surrounded by a number of star forming regions, or "hot spots", as well as a number of resolved and unresolved continuum radio sources. HST/FOC observations reveal that the nucleus is surrounded by a ring of very compact unresolved sources of the kind that have been discovered in a number of other galaxies, and that have been assumed to be very compact young globular star clusters. The hot spots are resolved into groups of such compact sources. VLA observations at lambda = 2 cm, where the resolution approaches that of HST, reveals that the brightest unresolved radio source at 2 cm, which has been assumed to be a radio supernova, coincides with one of the compact HST sources. The implications of this will be discussed.

Detailed investigation of the gamma-ray emission in the vicinity of SNR W28 with Fermi-LAT

DOE PAGES

Hanabata, Y.; Katagiri, H.; Hewitt, J. W.; ...

2014-04-25

Here, we present a detailed investigation of the γ-ray emission in the vicinity of the supernova remnant (SNR) W28 (G6.4–0.1) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We detected significant γ-ray emission spatially coincident with TeV sources HESS J1800–240A, B, and C, located outside the radio boundary of the SNR. Their spectra in the 2-100 GeV band are consistent with the extrapolation of the power-law spectra of the TeV sources. We also identified a new source of GeV emission, dubbed Source W, which lies outside the boundary of TeV sources and coincides withmore » radio emission from the western part of W28. All of the GeV γ-ray sources overlap with molecular clouds in the velocity range from 0 to 20 km s –1. Under the assumption that the γ-ray emission toward HESS J1800–240A, B, and C comes from π 0 decay due to the interaction between the molecular clouds and cosmic rays (CRs) escaping from W28, they can be naturally explained by a single model in which the CR diffusion coefficient is smaller than the theoretical expectation in the interstellar space. Furthermore, we constrain the total energy of the CRs escaping from W28 through the same modeling to be larger than ~2 × 10 49 erg. The emission from Source W can also be explained with the same CR escape scenario.« less

AGN Feedback And Evolution of Radio Sources: Discovery of An X-Ray Cluster Associated With Z=1 Quasar

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

Siemiginowska, Aneta; /Harvard-Smithsonian Ctr. Astrophys.; Cheung, C.C.

2006-01-11

We report the first significant detection of an X-ray cluster associated with a powerful (L{sub bol} {approx} 10{sup 47} erg sec{sup -1}) radio-loud quasar at high redshift (z=1.06). Diffuse X-ray emission is detected out to {approx} 120 kpc from the CSS quasar 3C 186. A strong Fe-line emission at the z{sub rest} = 1.06 confirms its thermal nature. We find that the CSS radio source is highly overpressured with respect to the thermal cluster medium by 2-3 orders of magnitude. This provides direct observational evidence that the radio source is not thermally confined as posited in the ''frustrated'' scenario formore » CSS sources. Instead, the radio source may be young and at an early stage of its evolution. This source provides the first detection of the AGN in outburst in the center of a cooling flow cluster. Powerful radio sources are thought to be triggered by the cooling flows. The evidence for the AGN activity and intermittent outbursts comes from the X-ray morphology of low redshift clusters, which usually do not harbour quasars. 3C186 is a young active radio source which can supply the energy into the cluster and potentially prevent its cooling. We discuss energetics related to the quasar activity and the cluster cooling flow, and possible feedback between the evolving radio source and the cluster.« less

HIghZ: A search for HI absorption in high-redshift radio galaxies

NASA Astrophysics Data System (ADS)

Allison, J.; Callingham, J.; Sadler, E.; Wayth, R.; Curran, S.; Mahoney, E.

2017-01-01

We will use the unique low-frequency spectral capability of the MWA to carry out a pilot survey for neutral gas in the interstellar medium of the most distant (z>5) radio galaxies in the Universe. Through detection of the HI 21-cm line in absorption we aim to place stringent lower limits on the source redshift, confirming its location in the early Universe. Our sample makes use of the excellent wide-band spectral information available from the recently completed MWA GLEAM survey, from which we have selected a sample of ultra-steep peaked-spectrum radio sources that have a spectral turnover below 300 MHz. These sources should be ideal candidates for high-redshift compact radio galaxies since they have (a) spectral peaks that turnover below 1GHz and (b) very steep (alpha < -1.0) spectral indices that are consistent with the high density environments expected for radio galaxies in the early Universe. Using the MWA, we aim to verify this hypothesis through the detection of significant column densities of cold HI. This pathfinder project will provide important technical information that will inform future absorption surveys both with the MWA and, ultimately, the SKA-LOW telescope.

Radio Sources Associated with Intermediate X-ray Luminosity Objects in Merging Galaxy Systems

NASA Technical Reports Server (NTRS)

Neff, S. G.; Ulvestad, J. S.; Oegerle, William R. (Technical Monitor)

2002-01-01

We present new, high-resolution 6, 3.6, and 2 cm radio images of a time-ordered sequence of merging galaxy systems. The new data have a resolution of less than 100pc and a sensitivity comparable to a few x Cas A. We detect compact radio sources in all systems, generally embedded in more diffuse radio emission at the longer wavelengths. Several of the compact radio sources are coincident with compact Intermediate-luminosity X-ray Objects (IXOs) in these systems, and many more are within the 3$/sigma$ Chandra position errors for other IXOs. The fraction of radio identifications and the nature of the radio sources changes as a function of merger stage. These data suggest that the IXOs are associated with complexes of supernova remnants, and therefore with star formation that has occurred within the last $/sim$10$circumflex7$ yr, but are not located in HII regions where copious star formation is occurring currently.

A Search for FRB 121102-like Persistent Radio-luminous Sources—Candidates and Implications for the FRB Rate and Searches

NASA Astrophysics Data System (ADS)

Ofek, Eran O.

2017-09-01

The localization of the repeating fast radio burst (FRB), FRB 121102, suggests that it is associated with a persistent radio-luminous compact source in the FRB host galaxy. Using the FIRST radio catalog, I present a search for luminous persistent sources in nearby galaxies, with radio luminosities > 10 % of the FRB 121102 persistent source luminosity. The galaxy sample contains about 30% of the total galaxy g-band luminosity within < 108 Mpc, in a footprint of 10,600 deg2. After rejecting sources likely due to active galactic nuclei activity or background sources, I am left with 11 candidates that are presumably associated with galactic disks or star-formation regions. At least some of these candidates are likely to be due to chance alignment. In addition, I find 85 sources within 1\\prime\\prime of galactic nuclei. Assuming that the radio persistent sources are not related to galactic nuclei and that they follow the galaxy g-band light, the 11 sources imply a 95% confidence upper limit on the space density of luminous persistent sources of ≲ 5× {10}-5 Mpc-3, and that at any given time only a small fraction of galaxies host a radio-luminous persistent source (≲ {10}-3 {L}* -1). Assuming a persistent source lifetime of 100 years, this implies a birth rate of ≲ 5× {10}-7 yr-1 Mpc-3. Given the FRB volumetric rate, and assuming that all FRBs repeat and are associated with persistent radio sources, this sets a lower limit on the rate of FRB events per persistent source of ≳ 0.8 yr-1. I argue that these 11 candidates are good targets for FRB searches and I estimate the FRB event rate from these candidates.

An AGN Identification for 3EG J2006-2321

NASA Technical Reports Server (NTRS)

Wallace, P. M.; Halpern, J. P.; Magalhaes, A. M.; Thompson, D. J.; White, Nicholas E. (Technical Monitor)

2001-01-01

We present a multiwavelength analysis of the high-energy gamma-ray source 3EG J2006-2321 (l = 18 deg.82, b = -26 deg.26). The flux of this source above 100 MeV is shown to be variable on time scales of days and months. Optical observations and careful examination of archived radio data indicate that its most probable identification is with PMN J2005-2310, a flat-spectrum radio quasar with a 5GHz flux density of 260 mJy. Study of the V = 19.3 optical counterpart indicates a redshift of 0.833 and variable linear polarization. No X-ray source has been detected near the position of PMN J2005-2310, but an X-ray upper limit is derived from ROSAT data. This upper limit provides for a spectral energy distribution with global characteristics similar to those of known gamma-ray blazars. Taken together, these data indicate that 3EG J2006-2321, listed as unidentified in the 3rd EGRET Catalog, is a member of the blazar class of AGN. The 5-GHz radio flux density of this blazar is the lowest of the 68 EGRET-detected AGN. The fact that EGRET has detected such a source has implications for unidentified EGRET sources, particularly those at high latitudes (absolute value of b greater than 30 deg), many of which may be blazars.

Radio Selection of the Most Distant Galaxy Clusters

NASA Astrophysics Data System (ADS)

Daddi, E.; Jin, S.; Strazzullo, V.; Sargent, M. T.; Wang, T.; Ferrari, C.; Schinnerer, E.; Smolčić, V.; Calabró, A.; Coogan, R.; Delhaize, J.; Delvecchio, I.; Elbaz, D.; Gobat, R.; Gu, Q.; Liu, D.; Novak, M.; Valentino, F.

2017-09-01

We show that the most distant X-ray-detected cluster known to date, Cl J1001 at {z}{spec}=2.506, hosts a strong overdensity of radio sources. Six of them are individually detected (within 10\\prime\\prime ) in deep 0\\buildrel{\\prime\\prime}\\over{.} 75 resolution VLA 3 GHz imaging, with {S}3{GHz}> 8 μ {Jy}. Of the six, an active galactic nucleus (AGN) likely affects the radio emission in two galaxies, while star formation is the dominant source powering the remaining four. We searched for cluster candidates over the full COSMOS 2 deg2 field using radio-detected 3 GHz sources and looking for peaks in {{{Σ }}}5 density maps. Cl J1001 is the strongest overdensity by far with > 10σ , with a simple {z}{phot}> 1.5 preselection. A cruder photometric rejection of z< 1 radio foregrounds leaves Cl J1001 as the second strongest overdensity, while even using all radio sources Cl J1001 remains among the four strongest projected overdensities. We conclude that there are great prospects for future deep and wide-area radio surveys to discover large samples of the first generation of forming galaxy clusters. In these remarkable structures, widespread star formation and AGN activity of massive galaxy cluster members, residing within the inner cluster core, will ultimately lead to radio continuum as one of the most effective means for their identification, with detection rates expected in the ballpark of 0.1-1 per square degree at z≳ 2.5. Samples of hundreds such high-redshift clusters could potentially constrain cosmological parameters and test cluster and galaxy formation models.

Einstein observations of the X-ray structure of Centaurus A - Evidence for the radio-lobe energy source

NASA Technical Reports Server (NTRS)

Schreier, E. J.; Feigelson, E.; Delvaille, J.; Giacconi, R.; Grindlay, J.; Schwartz, D. A.; Fabian, A. C.

1979-01-01

The X-ray source at the center of the radio galaxy Centaurus A has been resolved into the following components with the imaging detectors on board the Einstein X-ray Observatory: (1) a point source coincident with the infrared nucleus; (2) diffuse X-ray emission coinciding with the inner radio lobes; (3) a 4-arcmin extended region of emission about the nucleus; and (4) an X-ray jet between the nucleus and the NE inner radio lobe. The 2 x 10 to the 39th ergs/s detected from the radio lobes probably arises from inverse Compton scattering of the microwave background. The average magnetic field in the SW lobe is determined to be not less than 4 microgauss. The extended region may be due to emission by a cloud of hot gas, cosmic-ray scattering, or stellar sources. The jet provides strong evidence for the continuous resupply of energy to the lobes from the nucleus.

75 FR 10439 - Cognitive Radio Technologies and Software Defined Radios

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-08

... Technologies and Software Defined Radios AGENCY: Federal Communications Commission. ACTION: Final rule. SUMMARY... concerning the use of open source software to implement security features in software defined radios (SDRs... ongoing technical developments in cognitive and software defined radio (SDR) technologies. 2. On April 20...

Investigating the unification of LOFAR-detected powerful AGN in the Boötes field

NASA Astrophysics Data System (ADS)

Morabito, Leah K.; Williams, W. L.; Duncan, Kenneth J.; Röttgering, H. J. A.; Miley, George; Saxena, Aayush; Barthel, Peter; Best, P. N.; Bruggen, M.; Brunetti, G.; Chyży, K. T.; Engels, D.; Hardcastle, M. J.; Harwood, J. J.; Jarvis, Matt J.; Mahony, E. K.; Prandoni, I.; Shimwell, T. W.; Shulevski, A.; Tasse, C.

2017-08-01

Low radio frequency surveys are important for testing unified models of radio-loud quasars and radio galaxies. Intrinsically similar sources that are randomly oriented on the sky will have different projected linear sizes. Measuring the projected linear sizes of these sources provides an indication of their orientation. Steep-spectrum isotropic radio emission allows for orientation-free sample selection at low radio frequencies. We use a new radio survey of the Boötes field at 150 MHz made with the Low-Frequency Array (LOFAR) to select a sample of radio sources. We identify 60 radio sources with powers P > 1025.5 W Hz-1 at 150 MHz using cross-matched multiwavelength information from the AGN and Galaxy Evolution Survey, which provides spectroscopic redshifts and photometric identification of 16 quasars and 44 radio galaxies. When considering the radio spectral slope only, we find that radio sources with steep spectra have projected linear sizes that are on average 4.4 ± 1.4 larger than those with flat spectra. The projected linear sizes of radio galaxies are on average 3.1 ± 1.0 larger than those of quasars (2.0 ± 0.3 after correcting for redshift evolution). Combining these results with three previous surveys, we find that the projected linear sizes of radio galaxies and quasars depend on redshift but not on power. The projected linear size ratio does not correlate with either parameter. The LOFAR data are consistent within the uncertainties with theoretical predictions of the correlation between the quasar fraction and linear size ratio, based on an orientation-based unification scheme.

47 CFR 2.815 - External radio frequency power amplifiers.

Code of Federal Regulations, 2014 CFR

2014-10-01

... amplifier is any device which, (1) when used in conjunction with a radio transmitter as a signal source is capable of amplification of that signal, and (2) is not an integral part of a radio transmitter as... following: (1) The external radio frequency power amplifier shall not be capable of amplification in the...

47 CFR 2.815 - External radio frequency power amplifiers.

Code of Federal Regulations, 2013 CFR

2013-10-01

... amplifier is any device which, (1) when used in conjunction with a radio transmitter as a signal source is capable of amplification of that signal, and (2) is not an integral part of a radio transmitter as... following: (1) The external radio frequency power amplifier shall not be capable of amplification in the...

47 CFR 2.815 - External radio frequency power amplifiers.

Code of Federal Regulations, 2012 CFR

2012-10-01

... amplifier is any device which, (1) when used in conjunction with a radio transmitter as a signal source is capable of amplification of that signal, and (2) is not an integral part of a radio transmitter as... following: (1) The external radio frequency power amplifier shall not be capable of amplification in the...

The many facets of extragalactic radio surveys: towards new scientific challenges

NASA Astrophysics Data System (ADS)

2015-10-01

Radio continuum surveys are a powerful tool to detect large number of objects over a wide range of redshifts and obtain information on the intensity, polarization and distribution properties of radio sources across the sky. They are essential to answer to fundamental questions of modern astrophysics. Radio astronomy is in the midst of a transformation. Developments in high-speed digital signal processing and broad-band optical fibre links between antennas have enabled significant upgrades of the existing radio facilities (e-MERLIN, JVLA, ATCA-CABB, eEVN, APERTIF), and are leading to next-generation radio telescopes (LOFAR, MWA, ASKAP, MeerKAT). All these efforts will ultimately lead to the realization of the Square Kilometre Array (SKA), which, owing to advances in sensitivity, field-of-view, frequency range and spectral resolution, will yield transformational science in many astrophysical research fields. The purpose of this meeting is to explore new scientific perspectives offered by modern radio surveys, focusing on synergies allowed by multi-frequency, multi-resolution observations. We will bring together researchers working on wide aspects of the physics and evolution of extra-galactic radio sources, from star-forming galaxies to AGNs and clusters of galaxies, including their role as cosmological probes. The organization of this conference has been inspired by the recent celebration of the 50th anniversary of the Northern Cross Radio Telescope in Medicina (BO), whose pioneering B2 and B3 surveys provided a significant contribution to radio astronomical studies for many decades afterwards. The conference was organized by the Istituto di Radioastronomia (INAF), and was held at the CNR Research Area in Bologna, on 20-23 October 2015. This Conference has received support from the following bodies and funding agencies: National Institute for Astrophysics (INAF), ASTRON, RadioNet3 (through the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 283393) and the Ministry of Foreign Affairs and International Cooperation, Directorate General for the Country Promotion (under the Bilateral Grant Agreement ZA14GR02 - Mapping the Universe on the Pathway to SKA). Scientific Organizing Committee: I. Prandoni (INAF-IRA) co-chair R. Morganti (ASTRON) co-chair P. Best (ROE) A. Bonafede (Hamburg Univ.) R. Braun (SKA Org) L. Feretti (INAF-IRA) M. Jarvis (Western Cape/Oxford Univ.) E. Murphy (Caltech) R. Norris (CSIRO) M. Perez-Torres (IAA) L. Saripalli (Raman) T. Venturi (INAF-IRA) Local Organizing Committee: R. Cassano (co-chair) I. Prandoni (co-chair) A. Casoni D. Guidetti R. Lico R. Ricci M. Stagni

X-ray Counterparts of Infrared Faint Radio Sources

NASA Astrophysics Data System (ADS)

Schartel, Norbert

2011-10-01

Infrared Faint Radio Sources (IFRS) are radio sources with extremely faint or even absent infrared emission in deep Spitzer Surveys. Models of their spectral energy distributions, the ratios of radio to infrared flux densities and their steep radio spectra strongly suggest that IFRS are AGN at high redshifts (2

High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars

DOE PAGES

Giroletti, M.; Massaro, F.; D’Abrusco, R.; ...

2016-04-01

Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. In this paper, we characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. We cross-correlated the 6100 deg 2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detectedmore » by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120–180 MHz) blazar spectral index is (α low) = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Finally, upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population.« less

High-energy sources at low radio frequency: the Murchison Widefield Array view of Fermi blazars

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

Giroletti, M.; Massaro, F.; D’Abrusco, R.

Low-frequency radio arrays are opening a new window for the study of the sky, both to study new phenomena and to better characterize known source classes. Being flat-spectrum sources, blazars are so far poorly studied at low radio frequencies. In this paper, we characterize the spectral properties of the blazar population at low radio frequency, compare the radio and high-energy properties of the gamma-ray blazar population, and search for radio counterparts of unidentified gamma-ray sources. We cross-correlated the 6100 deg 2 Murchison Widefield Array Commissioning Survey catalogue with the Roma blazar catalogue, the third catalogue of active galactic nuclei detectedmore » by Fermi-LAT, and the unidentified members of the entire third catalogue of gamma-ray sources detected by Fermi-LAT. When available, we also added high-frequency radio data from the Australia Telescope 20 GHz catalogue. We find low-frequency counterparts for 186 out of 517 (36%) blazars, 79 out of 174 (45%) gamma-ray blazars, and 8 out of 73 (11%) gamma-ray blazar candidates. The mean low-frequency (120–180 MHz) blazar spectral index is (α low) = 0.57 ± 0.02: blazar spectra are flatter than the rest of the population of low-frequency sources, but are steeper than at ~GHz frequencies. Low-frequency radio flux density and gamma-ray energy flux display a mildly significant and broadly scattered correlation. Ten unidentified gamma-ray sources have a (probably fortuitous) positional match with low radio frequency sources. Low-frequency radio astronomy provides important information about sources with a flat radio spectrum and high energy. However, the relatively low sensitivity of the present surveys still misses a significant fraction of these objects. Finally, upcoming deeper surveys, such as the GaLactic and Extragalactic All-Sky MWA (GLEAM) survey, will provide further insight into this population.« less

OPTICAL SPECTRA OF CANDIDATE INTERNATIONAL CELESTIAL REFERENCE FRAME (ICRF) FLAT-SPECTRUM RADIO SOURCES

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

Titov, O.; Stanford, Laura M.; Johnston, Helen M.

2013-07-01

Continuing our program of spectroscopic observations of International Celestial Reference Frame (ICRF) sources, we present redshifts for 120 quasars and radio galaxies. Data were obtained with five telescopes: the 3.58 m European Southern Observatory New Technology Telescope, the two 8.2 m Gemini telescopes, the 2.5 m Nordic Optical Telescope (NOT), and the 6.0 m Big Azimuthal Telescope of the Special Astrophysical Observatory in Russia. The targets were selected from the International VLBI Service for Geodesy and Astrometry candidate International Celestial Reference Catalog which forms part of an observational very long baseline interferometry (VLBI) program to strengthen the celestial reference frame.more » We obtained spectra of the potential optical counterparts of more than 150 compact flat-spectrum radio sources, and measured redshifts of 120 emission-line objects, together with 19 BL Lac objects. These identifications add significantly to the precise radio-optical frame tie to be undertaken by Gaia, due to be launched in 2013, and to the existing data available for analyzing source proper motions over the celestial sphere. We show that the distribution of redshifts for ICRF sources is consistent with the much larger sample drawn from Faint Images of the Radio Sky at Twenty cm (FIRST) and Sloan Digital Sky Survey, implying that the ultra-compact VLBI sources are not distinguished from the overall radio-loud quasar population. In addition, we obtained NOT spectra for five radio sources from the FIRST and NRAO VLA Sky Survey catalogs, selected on the basis of their red colors, which yielded three quasars with z > 4.« less

A Multi-Frequency Study of the Milky Way-Like Spiral Galaxy NGC 6744

NASA Astrophysics Data System (ADS)

Yew, Miranda; Filipović, Miroslav D.; Roper, Quentin; Collier, Jordan D.; Crawford, Evan J.; Jarrett, Thomas H.; Tothill, Nicholas F. H.; O'Brien, Andrew N.; Pavlović, Marko Z.; Pannuti, Thomas G.; Galvin, Timothy J.; Kapińska, Anna D.; Cluver, Michelle E.; Banfield, Julie K.; Schlegel, Eric M.; Maxted, Nigel; Grieve, Kevin R.

2018-03-01

We present a multi-frequency study of the intermediate spiral SAB(r)bc type galaxy NGC 6744, using available data from the Chandra X-Ray telescope, radio continuum data from the Australia Telescope Compact Array and Murchison Widefield Array, and Wide-field Infrared Survey Explorer infrared observations. We identify 117 X-ray sources and 280 radio sources. Of these, we find nine sources in common between the X-ray and radio catalogues, one of which is a faint central black hole with a bolometric radio luminosity similar to the Milky Way's central black hole. We classify 5 objects as supernova remnant (SNR) candidates, 2 objects as likely SNRs, 17 as H ii regions, 1 source as an AGN; the remaining 255 radio sources are categorised as background objects and one X-ray source is classified as a foreground star. We find the star-formation rate (SFR) of NGC 6744 to be in the range 2.8-4.7 M⊙ yr - 1 signifying the galaxy is still actively forming stars. The specific SFR of NGC 6744 is greater than that of late-type spirals such as the Milky Way, but considerably less that that of a typical starburst galaxy.

Tracing Large-Scale Structure with Radio Sources

NASA Astrophysics Data System (ADS)

Lindsay, S. N.

2015-02-01

In this thesis, I investigate the spatial distribution of radio sources, and quantify their clustering strength over a range of redshifts, up to z _ 2:2, using various forms of the correlation function measured with data from several multi-wavelength surveys. I present the optical spectra of 30 radio AGN (S1:4 > 100 mJy) in the GAMA/H-ATLAS fields, for which emission line redshifts could be deduced, from observations of 79 target sources with the EFOSC2 spectrograph on the NTT. The mean redshift of these sources is z = 1:2; 12 were identified as quasars (40 per cent), and 6 redshifts (out of 24 targets) were found for AGN hosts to multiple radio components. While obtaining spectra for hosts of these multi-component sources is possible, their lower success rate highlights the difficulty in acheiving a redshift-complete radio sample. Taking an existing spectroscopic redshift survey (GAMA) and radio sources from the FIRST survey (S1:4 > 1 mJy), I then present a cross-matched radio sample with 1,635 spectroscopic redshifts with a median value of z = 0:34. The spatial correlation function of this sample is used to find the redshiftspace (s0) and real-space correlation lengths (r0 _ 8:2 h Mpc), and a mass bias of _1.9. Insight into the redshift-dependence of these quantities is gained by using the angular correlation function and Limber inversion to measure the same spatial clustering parameters. Photometric redshifts! from SDSS/UKIDSS are incorporated to produce a larger matched radio sample at z ' 0:48 (and low- and high-redshift subsamples at z ' 0:30 and z ' 0:65), while their redshift distribution is subtracted from that taken from the SKADS radio simulations to estimate the redshift distribution of the remaining unmatched sources (z ' 1:55). The observed bias evolution over this redshift range is compared with model predictions based on the SKADS simulations, with good agreement at low redshift. The bias found at high redshift significantly exceeds these predictions, however, suggesting a more massive population of galaxies than expected, either due to the relative proportions of different radio sources, or a greater typical halo mass for the high-redshift sources. Finally, the reliance on a model redshift distribution to reach to higher redshifts is removed, as the angular cross-correlation function is used with deep VLA data (S1:4 > 90 _Jy) and optical/IR data from VIDEO/CFHTLS (Ks < 23:5) over 1 square degree. With high-quality photometric redshifts up to z _ 4, and a high signal-to-noise clustering measurement (due to the _100,000 Ks-selected galaxies), I am able to find the bias of a matched sample of only 766 radio sources (as well as of v vi the VIDEO sources), divided into 4 redshift bins reaching a median bias at z ' 2:15. Again, at high redshift, the measured bias appears to exceed the prediction made from the SKADS simulations. Applying luminosity cuts to the radio sample at L > 1023 WHz and higher (removing any non-AGN sources), I find a bias of 8-10 at z _ 1:5, considerably higher than for the full sample, and consistent with the more numerous FRI AGN having similar mass to the FRIIs (M _ 10^14 M_), contrary to the assumptions made in the SKADS simulations. Applying this adjustment to the model bias produces a better fit to the observations for the FIRST radio sources cross-matched with GAMA/SDSS/UKIDSS, as well as for the high-redshift radio sources in VIDEO. Therefore, I have shown that we require a more robust model of the evolution of AGN, and their relation to the underlying dark matter distribution. In particular, understanding these quantities for the abundant FRI population is crucial if we are to use such sources to probe the cosmological model as has been suggested by a number of authors (e.g. Raccanelli et al., 2012; Camera et al., 2012; Ferramacho et al., 2014).

General relativistic considerations of the field shedding model of fast radio bursts

NASA Astrophysics Data System (ADS)

Punsly, Brian; Bini, Donato

2016-06-01

Popular models of fast radio bursts (FRBs) involve the gravitational collapse of neutron star progenitors to black holes. It has been proposed that the shedding of the strong neutron star magnetic field (B) during the collapse is the power source for the radio emission. Previously, these models have utilized the simplicity of the Schwarzschild metric which has the restriction that the magnetic flux is magnetic `hair' that must be shed before final collapse. But neutron stars have angular momentum and charge and a fully relativistic Kerr-Newman solution exists in which B has its source inside of the event horizon. In this Letter, we consider the magnetic flux to be shed as a consequence of the electric discharge of a metastable collapsed state of a Kerr-Newman black hole. It has also been argued that the shedding model will not operate due to pair creation. By considering the pulsar death line, we find that for a neutron star with B = 1011-1013 G and a long rotation period, >1s this is not a concern. We also discuss the observational evidence supporting the plausibility of magnetic flux shedding models of FRBs that are spawned from rapidly rotating progenitors.

Time-Frequency and Non-Laplacian Phenomena at Radio Frequencies

DTIC Science & Technology

2017-01-22

Unlimited UU UU UU UU 22-01-2017 30-Sep-2012 30-Sep-2016 Final Report: Time -Frequency and Non-Laplacian Phenomena at Radio Frequencies The views...average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data... Time ‐Frequency and Non‐Laplacian Phenomena at Radio Frequencies  U.S. Army Research Office grant W911NF‐12‐1‐0526  Michael B. Steer  Department of

X-Ray Properties of the Youngest Radio Sources and Their Environments

NASA Astrophysics Data System (ADS)

Siemiginowska, Aneta; Sobolewska, Małgosia; Migliori, Giulia; Guainazzi, Matteo; Hardcastle, Martin; Ostorero, Luisa; Stawarz, Łukasz

2016-05-01

We present the first results from our X-ray study of young radio sources classified as compact symmetric objects (CSOs). Using the Chandra X-ray Observatory we observed six CSOs for the first time in X-rays, and re-observed four CSOs already observed with XMM-Newton or BeppoSAX. We also included six other CSOs with archival data to built a pilot study of a sample of the 16 CSO sources observed in X-rays to date. All the sources are nearby, z\\lt 1, and the age of their radio structures (\\lt 3000 yr) has been derived from the expansion velocity of their hot spots. Our results show the heterogeneous nature of the CSOs’ X-ray emission, indicating a complex environment associated with young radio sources. The sample covers a range in X-ray luminosity, {L}2{--10{keV}}˜ {10}41-1045 erg s-1, and intrinsic absorbing column density of {N}{{H}}≃ {10}21-1022 cm-2. In particular, we detected extended X-ray emission in 1718-649 a hard photon index of {{Γ }}≃ 1 in 2021+614 and 1511+0518 consistent with either a Compton-thick absorber or non-thermal emission from compact radio lobes, and in 0710+439 an ionized iron emission line at {E}{rest}=(6.62+/- 0.04) keV and EW ˜ 0.15-1.4 keV, and a decrease by an order of magnitude in the 2-10 keV flux since the 2008 XMM-Newton observation in 1607+26. We conclude that our pilot study of CSOs provides a variety of exceptional diagnostics and highlights the importance of deep X-ray observations of large samples of young sources. This is necessary in order to constrain theoretical models for the earliest stage of radio source evolution and to study the interactions of young radio sources with the interstellar environment of their host galaxies.

Spectral Index Properties of millijansky Radio Sources in ATLAS

NASA Astrophysics Data System (ADS)

Randall, Kate; Hopkins, A. M.; Norris, R. P.; Zinn, P.; Middelberg, E.; Mao, M. Y.; Sharp, R. G.

2012-01-01

At the faintest radio flux densities (S1.4GHz < 10 milliJansky (mJy)), the spectral index properties of radio sources are not well constrained. The bright radio source population (S1.4GHz > 10 mJy) is well studied and is predominantly comprised of AGN. At fainter flux densities, particularly into the microJansky regime, star-forming galaxies begin to dominate the radio source population. Understanding these faint radio source populations is essential for understanding galaxy evolution, and the link between AGN and star formation. Conflicting results have recently arisen regarding whether there is a flattening of the average spectral index between a low radio frequency (325 or 610 MHz) and 1.4 GHz at these faint flux densities. To explore this issue, we have investigated the spectral index properties of a new catalogue of 843 MHz radio sources in the ELAIS-S1 (the European Large Area ISO Survey - South 1 Region) field. Our results support previous work showing a tendency towards flatter radio spectra at fainter flux densities. This catalogue is cross-matched to the Australia Telescope Large Area Survey (ATLAS), the widest deep radio survey to date at 1.4 GHz, with complementary 2.3 GHz, optical and infrared Spitzer Wide-area Infra-Red Extragalactic data. The variation of spectral index properties have been explored as a function of redshift, luminosity and flux density. [These new measurements have been used to identify a population of faint Compact Steep Spectrum sources, thought to be one of the earliest stages of the AGN life-cycle. Exploring this population will aid us in understanding the evolution of AGN as a whole.

High-resolution radio and X-ray observations of the supernova remnant W28

NASA Technical Reports Server (NTRS)

Andrews, M. D.; Basart, J. P.; Lamb, R. C.; Becker, R. H.

1983-01-01

The present study has the objective to report the first high resolution radio and X-ray observations of the central part of the galactic supernova remnant, W28, taking into account the possible association of the remnant with the unidentified gamma-ray source, 2CG 006-00. This gamma-ray source is approximately two-thirds as bright as the Crab pulsar above 100 MeV, and has a somewhat flatter spectrum. Both the radio and X-ray observations reveal previously unknown aspects of W28 which support the possibility of W28 being a gamma-ray source. The radio data show a flat-spectrum, nonthermal component reminiscent of the Crab Nebula and Vela, both of which are confirmed gamma-ray sources. The X-ray observations reveal a compact source within W28, again suggestive of both the Crab and Vela. If the similarities among W28, the Crab Nebula, and the Vela remnant are valid, the gamma-ray source 2CG 00-00 should be studied for periodicity, the conclusive signature of a compact source of emission.

Radio Observations of Ultra-Luminous X-Ray Sources and their Implication for Models

NASA Astrophysics Data System (ADS)

Koerding, E. G.; Colbert, E. J. M.; Falcke, H.

2004-05-01

We present the results of a radio monitoring campaign to search for radio emission from nearby ultra-luminous X-ray sources (ULXs). These intriguing sources are bright off-nuclear X-ray point sources with luminosities exceeding LX > 1039 erg/sec. Assuming isotropic emission the Eddington Limit suggests that they harbor intermediate mass black holes. Due to the problems of this explanation also other possibilities are currently discussed, among them are anisotropic emission, super-Eddington accretion flows or relativistically beamed emission from microquasars. Detections of compact radio cores at the positions of ULXs would be a direct hint to jet-emission. However, as the ULX phenomenom is connected to star formation we have to assume that they are strongly accreting objects. Thus, similar to their nearest Galactic cousins, the very high state X-ray binaries (see e.g., GRS 1915), ULXs may show radio flares. A well-defined sample of the 9 nearest ULXs has been monitored eight times during 5 months with the Very Large Array in A and B configuration. Our limiting sensitivity is 0.15 mJy (4 σ ) for flares and 68 μ Jy for continuous emission. In M82 some ULXs seem to be connected to radio supernova remnants. Besides that no flare or continuous emission has been detected. As the timescales of radio flares in ULXs are highly uncertain, it could well be that we have undersampled the lightcurve. However, upper bounds for the probability to detect a flare can be given. The upper limits for the continuous emission are compared with the emission found in NGC 5408 X-1 and with quasars and microquasars. We show that these limits are well in agreement with the microblazar model using the Radio/X-ray correlation of XRBs and AGN. Thus, it could well be that ULXs are microblazers which may be radio loud.

An 'X-banded' Tidbinbilla interferometer

NASA Technical Reports Server (NTRS)

Batty, Michael J.; Gardyne, R. G.; Gay, G. J.; Jauncy, David L.; Gulkis, S.; Kirk, A.

1986-01-01

The recent upgrading of the Tidbinbilla two-element interferometer to simultaneous S-band (2.3 GHz) and X-band (8.4 GHz) operation has provided a powerful new astronomical facility for weak radio source measurement in the Southern Hemisphere. The new X-band system has a minimum fringe spacing of 38 arcsec, and about the same positional measurement capability (approximately 2 arcsec) and sensitivity (1 s rms noise of 10 mJy) as the previous S-band system. However, the far lower confusion limit will allow detection and accurate positional measurements for sources as weak as a few millijanskys. This capability will be invaluable for observations of radio stars, X-ray sources and other weak, compact radio sources.

Galactic supernova remnant candidates discovered by THOR

NASA Astrophysics Data System (ADS)

Anderson, L. D.; Wang, Y.; Bihr, S.; Rugel, M.; Beuther, H.; Bigiel, F.; Churchwell, E.; Glover, S. C. O.; Goodman, A. A.; Henning, Th.; Heyer, M.; Klessen, R. S.; Linz, H.; Longmore, S. N.; Menten, K. M.; Ott, J.; Roy, N.; Soler, J. D.; Stil, J. M.; Urquhart, J. S.

2017-09-01

Context. There is a considerable deficiency in the number of known supernova remnants (SNRs) in the Galaxy compared to that expected. This deficiency is thought to be caused by a lack of sensitive radio continuum data. Searches for extended low-surface brightness radio sources may find new Galactic SNRs, but confusion with the much larger population of H II regions makes identifying such features challenging. SNRs can, however, be separated from H II regions using their significantly lower mid-infrared (MIR) to radio continuum intensity ratios. Aims: Our goal is to find missing SNR candidates in the Galactic disk by locating extended radio continuum sources that lack MIR counterparts. Methods: We use the combination of high-resolution 1-2 GHz continuum data from The HI, OH, Recombination line survey of the Milky Way (THOR) and lower-resolution VLA 1.4 GHz Galactic Plane Survey (VGPS) continuum data, together with MIR data from the Spitzer GLIMPSE, Spitzer MIPSGAL, and WISE surveys to identify SNR candidates. To ensure that the candidates are not being confused with H II regions, we exclude radio continuum sources from the WISE Catalog of Galactic H II Regions, which contains all known and candidate H II regions in the Galaxy. Results: We locate 76 new Galactic SNR candidates in the THOR and VGPS combined survey area of 67.4° > ℓ > 17.5°, | b | ≤ 1.25° and measure the radio flux density for 52 previously-known SNRs. The candidate SNRs have a similar spatial distribution to the known SNRs, although we note a large number of new candidates near ℓ ≃ 30°, the tangent point of the Scutum spiral arm. The candidates are on average smaller in angle compared to the known regions, 6.4' ± 4.7' versus 11.0' ± 7.8', and have lower integrated flux densities. Conclusions: The THOR survey shows that sensitive radio continuum data can discover a large number of SNR candidates, and that these candidates can be efficiently identified using the combination of radio and MIR data. If the 76 candidates are confirmed as true SNRs, for example using radio polarization measurements or by deriving radio spectral indices, this would more than double the number of known Galactic SNRs in the survey area. This large increase would still, however, leave a discrepancy between the known and expected SNR populations of about a factor of two.

Radio to gamma-ray variability study of blazar S5 0716+714

DOE PAGES

Rani, B.; Krichbaum, T. P.; Fuhrmann, L.; ...

2013-03-13

In this paper, we present the results of a series of radio, optical, X-ray, and γ-ray observations of the BL Lac object S50716+714 carried out between April 2007 and January 2011. The multifrequency observations were obtained using several ground- and space-based facilities. The intense optical monitoring of the source reveals faster repetitive variations superimposed on a long-term variability trend on a time scale of ~350 days. Episodes of fast variability recur on time scales of ~60-70 days. The intense and simultaneous activity at optical and γ-ray frequencies favors the synchrotron self-Compton mechanism for the production of the high-energy emission. Twomore » major low-peaking radio flares were observed during this high optical/γ-ray activity period. The radio flares are characterized by a rising and a decaying stage and agrees with the formation of a shock and its evolution. We found that the evolution of the radio flares requires a geometrical variation in addition to intrinsic variations of the source. Different estimates yield robust and self-consistent lower limits of δ ≥ 20 and equipartition magnetic field B eq ≥ 0.36 G. Causality arguments constrain the size of emission region θ ≤ 0.004 mas. We found a significant correlation between flux variations at radio frequencies with those at optical and γ-rays. Theoptical/GeV flux variations lead the radio variability by ~65 days. The longer time delays between low-peaking radio outbursts and optical flares imply that optical flares are the precursors of radio ones. An orphan X-ray flare challenges the simple, one-zone emission models, rendering them too simple. Finally, here we also describe the spectral energy distribution modeling of the source from simultaneous data taken through different activity periods.« less

The structure of the inner arcsecond of R Aquarii observed with the Hubble Space Telescope

NASA Technical Reports Server (NTRS)

Burgarella, Denis; Paresce, Francesco

1992-01-01

The inner arcsec of R Aquarii has been observed with the Faint Object Camera on the Hubble Space Telescope. A simple and reliable linear deconvolution method is used to resolve the two features, designated C1 and C2 from radio observations, into several condensations. C1 is composed of four objects, designated C1a, C1b located at 0.099 arcsec from C1a, C3 at 0.162 arcsec from C1a, and C4 at 0.137 arcsec from C1a. The source C3, detected at 2 cm in the radio and in H-alpha, might be the V = 6-11 Mira variable. The nature of feature C4 is still unknown. Features C1a and C1b have not been resolved by another instrument, and it might be possible that the hot star is one of the two or a nearby nondetected object.

Radio emission in peculiar galaxies

NASA Technical Reports Server (NTRS)

Demellorabaca, Dulia F.; Abraham, Zulema

1990-01-01

During the last decades a number of surveys of peculiar galaxies have been carried out and accurate positions become available. Since peculiarities are a possible evidence of radio emission (Wright, 1974; Sulentic, 1976; Stocke et al., 1978), the authors selected a sample of 24 peculiar galaxies with optical jet-like features or extensions in different optical catalogues, mainly the Catalogue of Southern Peculiar Galaxies and Associations (Arp and Madore, 1987) and the ESO/Uppsala Survey of the ESO(B) Atlas (Lauberts, 1982) for observation at the radio continuum frequency of 22 GHz. The sample is listed in a table. Sol (1987) studied this sample and concluded that the majority of the jet-like features seem to admit an explanation in terms of interactive galaxies with bridges and/or tails due to tidal effects. Only in a few cases do the jets seem to be possibly linked to some nuclear activity of the host galaxy. The observations were made with the 13.7m-radome enclosed Itapetinga Radiotelescope (HPBW of 4.3 arcmin), in Brazil. The receiver was a 1 GHz d.s.b. super-heterodine mixer operated in total-power mode, with a system temperature of approximately 800 K. The observational technique consisted in scans in right ascention, centralized in the optical position of the galaxy. The amplitude of one scan was 43 arcmin, and its duration time was 20 seconds. The integration time was at least 2 hours (12 ten-minute observations) and the sensibility limit adopted was an antenna temperature greater than 3 times the r.m.s. error of the baseline determination. Virgo A was used as the calibrator source. Three galaxies were detected for the first time as radio sources and four other known galaxies at low frequencies had their flux densities measured at 22 GHz. The results for these sources are presented.

Radio jet refraction in galactic atmospheres with static pressure gradients

NASA Technical Reports Server (NTRS)

Henriksen, R. N.; Vallee, J. P.; Bridle, A. H.

1981-01-01

A theory based on the refraction of radio jets in the extended atmosphere of an elliptical galaxy, is proposed for double radio sources with a Z or S morphology. The model describes a collimated jet of supersonic material that bends self-consistently under the influence of external static pressure gradients, and may alternatively be seen as a continuous-jet version of the buoyancy model proposed by Gull (1973). Emphasis is placed on (1) S-shaped radio sources identified with isolated galaxies, such as 3C 293, whose radio structures should be free of distortions resulting from motion relative to a cluster medium, and (2) small-scale, galaxy-dominated rather than environment-dominated S-shaped sources such as the inner jet structure of Fornax A.

SETI Searches for Radio Transients from Kepler Field Planets and Astropulse Candidates

NASA Astrophysics Data System (ADS)

Gautam, Abhimat Krishna; Siemion, Andrew; Korpela, Eric J.; Cobb, Jeff; Lebofsky, Matt; Werthimer, Dan

2014-06-01

We present a search for fast radio transients in targeted observations of planet candidates in the Kepler Field and candidate Astropulse sources.Kepler Field observations were conducted in the band 1.1 and 1.9 GHz using the Green Bank Telescope in Green Bank, West Virginia and are centered on 86 stars hosting candidate planets identified by the Kepler spacecraft. These stars were chosen based on the properties of their putative planetary system thought to be conducive to the development of advanced life, including all systems known (as of May 2011) hosting a Kepler Object of Interest (KOI) with a calculated equilibrium temperature between 230 and 380 K, at least 4 KOIs or a KOI with an inferred radius < 3.0 r_earth and a period > 50 d. The Kepler Field is centered at an intermediate galactic latitude, b = 13.5°, which presents an additional opportunity to detect signals from the older population of millisecond and recycled pulsars located above the galactic plane.The Astropulse radio survey searches for brief wide-band pulses in a 2.5 MHz band centered at 1420 MHz using commensal data recorded from the Arecibo ALFA receiver. In early Astropulse analysis, 108 candidate sources were identified that passed a series of tests designed to eliminate potential sources of radio frequency interference (RFI). We have performed targeted re-observations of these sources at Arecibo over the full (1214-1536 MHz) ALFA band.We have developed a software pipeline to locate fast dispersed transients in these observations, leveraging components of the PRESTO software library. This pipeline consists of finding and removing RFI, conducting de-dispersion to remove the effects of dispersion from the interstellar medium (ISM) on the signal and identifying over- threshold events. We also perform de-dispersion at negative dispersion measures, proposed to be a potential technique for intelligent civilizations to distinguish their emission from natural sources. We carry out both a periodicity and single-pulse search on de-dispersed time series. The outputs from these steps are examined to look for both technological and astrophysical sources of impulsive radio emission.

Do Radio Jets Contribute to Driving Ionized Gas Outflows in Moderate Luminosity Type 2 AGN?

NASA Astrophysics Data System (ADS)

Fowler, Julia; Sajina, Anna; Lacy, Mark

2016-01-01

This poster examines the role of AGN-driven feedback in low to intermediate power radio galaxies. We begin with [OIII] measurements of ionized gas outflows in 29 moderate AGN-luminosity z~0.3-0.7 dust-obscured Type 2 AGN. We aim to examine the relative role of the AGN itself, of star-formation and of nascent radio jets in driving these outflows. The strength of the AGN and star formation are based on the [OIII] luminosities, and the far-IR luminosities respectively. For the radio jets, we present multi-frequency radio (X, S, and L-bands) JVLA imaging of our sample, which allows us both to constrain the overall radio power, but also look for signatures of young radio sources, including Giga-hertz Peaked Spectrum (GPS) sources, as well as small-scale jets. While radio jet-driven outflows are well known for powerful radio-loud galaxies, this study allows us to constrain the degree to which this mechanism is significant at more modest radio luminosities of L5GHz~10^22-25 W/Hz.

Discovery of two millisecond pulsars in Fermi sources with the Nancay Radio Telescope

DOE PAGES

Cognard, I.; Guillemot, L.; Johnson, Tyrel J.; ...

2011-04-14

Here, we report the discovery of two millisecond pulsars in a search for radio pulsations at the positions of Fermi-Large Area Telescope sources with no previously known counterparts, using the Nançay Radio Telescope. The two millisecond pulsars, PSRs J2017+0603 and J2302+4442, have rotational periods of 2.896 and 5.192 ms and are both in binary systems with low-eccentricity orbits and orbital periods of 2.2 and 125.9 days, respectively, suggesting long recycling processes. Gamma-ray pulsations were subsequently detected for both objects, indicating that they power the associated Fermi sources in which they were found. The gamma-ray light curves and spectral properties aremore » similar to those of previously detected gamma-ray millisecond pulsars. Detailed modeling of the observed radio and gamma-ray light curves shows that the gamma-ray emission seems to originate at high altitudes in their magnetospheres. Additionally, X-ray observations revealed the presence of an X-ray source at the position of PSR J2302+4442, consistent with thermal emission from a neutron star. These discoveries along with the numerous detections of radio-loud millisecond pulsars in gamma rays suggest that many Fermi sources with no known counterpart could be unknown millisecond pulsars.« less

Radio Transients and their Environments

NASA Astrophysics Data System (ADS)

Rajwade, Kaustubh

The interstellar medium is the principal ingredient for star formation and hence, it is necessary to study the properties of the interstellar medium. Radio sources in our Galaxy and beyond can be used as a probe of the intervening medium. In this dissertation, I present an attempt to use radio transients like pulsars and fast radio bursts and their interactions with the environment around them to study interstellar medium. We show that radio emission from pulsars is absorbed by dense ionized gas in their surroundings, causing a turnover in their flux density spectrum that can be used to reveal information about the absorbing medium. We carried out a multi-wavelength observation campaign of PSR B0611+22. The pulsar shows peculiar emission variability that is broadband in nature. Moreover, we show that the flux density spectrum of B0611+22 is unusual which can be attributed to the environment it lies in. We also present predictions of fast radio burst detections from upcoming low frequency surveys. We show that future surveys with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) will be able to detect 1 radio burst per hour even if the radio burst undergoes significant absorption and scattering. Finally, we present our results of pulsar population synthesis to understand the pulsar population in the Galactic Centre (GC) and place conservative upper limits on the GC pulsar population. We obtain an upper limit of 52 CPs and 10,000 MSPs in the GC. The dense, ionized environment of the GC gives us the opportunity to predict the probability of detection by considering scattering and absorption as the principle sources of flux mitigation. Our results suggest that the optimal frequency range for a pulsar survey in the GC is 9-14 GHz. A larger sample of absorbed spectrum pulsars and fast radio bursts will be beneficial not only for the study of emission processes but also for discerning the properties of the material permeating through space.

Sensitive radio survey of obscured quasar candidates

NASA Astrophysics Data System (ADS)

Alexandroff, Rachael M.; Zakamska, Nadia L.; van Velzen, Sjoert; Greene, Jenny E.; Strauss, Michael A.

2016-12-01

We study the radio properties of moderately obscured quasars in samples at both low (z ˜ 0.5) and high (z ˜ 2.5) redshift to understand the role of radio activity in accretion, using the Karl G. Jansky Very Large Array (VLA) at 6.0 GHz and 1.4 GHz. Our z ˜ 2.5 sample consists of optically selected obscured quasar candidates, all of which are radio-quiet, with typical radio luminosities of νLν[1.4 GHz] ≲ 1040 erg s-1. Only a single source is individually detected in our deep (rms˜10 μJy) exposures. This population would not be identified by radio-based selection methods used for distinguishing dusty star-forming galaxies and obscured active nuclei. In our pilot A-array study of z ˜ 0.5 radio-quiet quasars, we spatially resolve four of five objects on scales ˜5 kpc and find they have steep spectral indices with an average value of α = -0.75. Therefore, radio emission in these sources could be due to jet-driven or radiatively driven bubbles interacting with interstellar material on the scale of the host galaxy. Finally, we also study the additional population of ˜200 faint ( ˜ 40 μJy-40 mJy) field radio sources observed over ˜120 arcmin2 of our data. 60 per cent of these detections (excluding our original targets) are matched in the Sloan Digital Sky Survey (SDSS) and/or Wide-Field Infrared Survey Explorer (WISE) and are, in roughly equal shares, active galactic nuclei (AGN) at a broad range of redshifts, passive galaxies with no other signs of nuclear activity and infrared-bright but optically faint sources. Spectroscopically or photometrically confirmed star-forming galaxies constitute only a small minority of the matches. Such sensitive radio surveys allow us to address important questions of AGN evolution and evaluate the AGN contribution to the radio-quiet sky.

Planck intermediate results: XLV. Radio spectra of northern extragalactic radio sources

DOE PAGES

Ade, P. A. R.; Aghanim, N.; Aller, H. D.; ...

2016-12-12

Continuum spectra covering centimetre to submillimetre wavelengths are presented in this paper for a northern sample of 104 extragalactic radio sources, mainly active galactic nuclei, based on four-epoch Planck data. The nine Planck frequencies, from 30 to 857 GHz, are complemented by a set of simultaneous ground-based radio observations between 1.1 and 37 GHz. The single-survey Planck data confirm that the flattest high-frequency radio spectral indices are close to zero, indicating that the original accelerated electron energy spectrum is much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The radio spectra peak at highmore » frequencies and exhibit a variety of shapes. For a small set of low-z sources, we find a spectral upturn at high frequencies, indicating the presence of intrinsic cold dust. Finally, variability can generally be approximated by achromatic variations, while sources with clear signatures of evolving shocks appear to be limited to the strongest outbursts.« less

Planck intermediate results. XLV. Radio spectra of northern extragalactic radio sources

NASA Astrophysics Data System (ADS)

Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Aller, H. D.; Aller, M. F.; Arnaud, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Burigana, C.; Calabrese, E.; Catalano, A.; Chiang, H. C.; Christensen, P. R.; Clements, D. L.; Colombo, L. P. L.; Couchot, F.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giraud-Héraud, Y.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gruppuso, A.; Gurwell, M. A.; Hansen, F. K.; Harrison, D. L.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Hildebrandt, S. R.; Hobson, M.; Hornstrup, A.; Hovatta, T.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Järvelä, E.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lähteenmäki, A.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Max-Moerbeck, W.; Meinhold, P. R.; Melchiorri, A.; Mennella, A.; Migliaccio, M.; Mingaliev, M.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Nati, F.; Natoli, P.; Nieppola, E.; Noviello, F.; Novikov, D.; Novikov, I.; Pagano, L.; Pajot, F.; Paoletti, D.; Partridge, B.; Pasian, F.; Pearson, T. J.; Perdereau, O.; Perotto, L.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Pratt, G. W.; Ramakrishnan, V.; Rastorgueva-Foi, E. A.; S Readhead, A. C.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Richards, J. L.; Ristorcelli, I.; Rocha, G.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Savelainen, M.; Savini, G.; Scott, D.; Sotnikova, Y.; Stolyarov, V.; Sunyaev, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tammi, J.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tornikoski, M.; Tristram, M.; Tucci, M.; Türler, M.; Valenziano, L.; Valiviita, J.; Valtaoja, E.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wehrle, A. E.; Wehus, I. K.; Yvon, D.; Zacchei, A.; Zonca, A.

2016-12-01

Continuum spectra covering centimetre to submillimetre wavelengths are presented for a northern sample of 104 extragalactic radio sources, mainly active galactic nuclei, based on four-epoch Planck data. The nine Planck frequencies, from 30 to 857 GHz, are complemented by a set of simultaneous ground-based radio observations between 1.1 and 37 GHz. The single-survey Planck data confirm that the flattest high-frequency radio spectral indices are close to zero, indicating that the original accelerated electron energy spectrum is much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The radio spectra peak at high frequencies and exhibit a variety of shapes. For a small set of low-z sources, we find a spectral upturn at high frequencies, indicating the presence of intrinsic cold dust. Variability can generally be approximated by achromatic variations, while sources with clear signatures of evolving shocks appear to be limited to the strongest outbursts.

Planck intermediate results: XLV. Radio spectra of northern extragalactic radio sources

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

Ade, P. A. R.; Aghanim, N.; Aller, H. D.

Continuum spectra covering centimetre to submillimetre wavelengths are presented in this paper for a northern sample of 104 extragalactic radio sources, mainly active galactic nuclei, based on four-epoch Planck data. The nine Planck frequencies, from 30 to 857 GHz, are complemented by a set of simultaneous ground-based radio observations between 1.1 and 37 GHz. The single-survey Planck data confirm that the flattest high-frequency radio spectral indices are close to zero, indicating that the original accelerated electron energy spectrum is much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The radio spectra peak at highmore » frequencies and exhibit a variety of shapes. For a small set of low-z sources, we find a spectral upturn at high frequencies, indicating the presence of intrinsic cold dust. Finally, variability can generally be approximated by achromatic variations, while sources with clear signatures of evolving shocks appear to be limited to the strongest outbursts.« less

VLBA Observations of Strong Anisotripic Radio Scattering Toward the Orion Nebula

NASA Astrophysics Data System (ADS)

Kounkel, Marina; Hartmann, Lee; Loinard, Laurent; Mioduszewski, Amy J.; Rodríguez, Luis F.; Ortiz-León, Gisela N.; Johnson, Michael D.; Torres, Rosa M.; Briceño, Cesar

2018-05-01

We present observations of VLBA 20, a radio source found toward the edge of the Orion Nebula Cluster (ONC). Nonthermal emission dominates the spectral energy distribution of this object from the radio to mid-infrared regime, suggesting that VLBA 20 is extragalactic. This source is heavily scattered in the radio regime. Very Long Baseline Array observations resolve it to ∼34 × 19 mas at 5 GHz, and the wavelength dependence of the scattering disk is consistent with ν ‑2 at other frequencies. The origin of the scattering is most likely the ionized X-ray emitting gas from the winds of the most massive stars of the ONC. The scattering is highly anisotropic, with the axis ratio of 2:1, higher than what is typically observed toward other sources.

X-ray properties of quasars

NASA Technical Reports Server (NTRS)

Ku, W. H.-M.; Helfand, D. J.; Lucy, L. B.

1980-01-01

The X-ray properties of 111 catalogued quasars have been examined with the imaging proportional counter on board the Einstein Observatory. Thirty-five of the objects, of redshift between 0.064 and 3.53, were detected as X-ray sources. The 0.5-4.5-keV X-ray properties of these quasars are correlated with their optical and radio continuum properties and with their redshifts and variability characteristics. The X-ray luminosity of quasars tends to be highest for those objects which are bright in the optical and radio regimes and which exhibit optically violent variability. These observations suggest that quasars should be divided into two classes on the basis of radio luminosities, spectra, evolution and underlying morphology and that quasars can make up a significant portion of the diffuse soft X-ray background only if the slope of the optical quasar log N-log S relation is steeper than 2 to m sub b of about 21.5.

Cosmological origin of anomalous radio background

NASA Astrophysics Data System (ADS)

Cline, James M.; Vincent, Aaron C.

2013-02-01

The ARCADE 2 collaboration has reported a significant excess in the isotropic radio background, whose homogeneity cannot be reconciled with clustered sources. This suggests a cosmological origin prior to structure formation. We investigate several potential mechanisms and show that injection of relativistic electrons through late decays of a metastable particle can give rise to the observed excess radio spectrum through synchrotron emission. However, constraints from the cosmic microwave background (CMB) anisotropy, on injection of charged particles and on the primordial magnetic field, present a challenge. The simplest scenario is with a gtrsim9 GeV particle decaying into e+e- at a redshift of z ~ 5, in a magnetic field of ~ 5μG, which exceeds the CMB B-field constraints, unless the field was generated after decoupling. Decays into exotic millicharged particles can alleviate this tension, if they emit synchroton radiation in conjunction with a sufficiently large background magnetic field of a dark U(1)' gauge field.

VizieR Online Data Catalog: Infrared morphology of HII regions (Topchieva+, 2017)

NASA Astrophysics Data System (ADS)

Topchieva, A. P.; Wiebe, D. S.; Kirsanova, M. S.; Krushinskii, V. V.

2018-03-01

The 20-cm New GPS survey (http://third.ucllnl.org/gps), created using the MAGPIS database of radio images of regions with Galactic coordinates |bGal|<0.8° and 5°

On the evolution of high-B radio pulsars with measured braking indices

NASA Astrophysics Data System (ADS)

Benli, O.; Ertan, Ü.

2017-11-01

We have investigated the long-term evolutions of the high-magnetic field radio pulsars (HBRPs) with measured braking indices in the same model that was applied earlier to individual anomalous X-ray pulsars (AXPs), soft gamma repeaters (SGRs) and dim isolated neutron stars (XDINs). We have shown that the rotational properties (period, period derivative and braking index) and the X-ray luminosity of individual HBRPs can be acquired simultaneously by the neutron stars evolving with fallback discs. The model sources reach the observed properties of HBRPs in the propeller phases, when pulsed radio emission is allowed, at ages consistent with the estimated ages of the supernova remnants of the sources. Our results indicate that the strength of magnetic dipole fields of HBRPs are comparable to and even greater than those of AXP/SGRs and XDINs, but still one or two orders of magnitude smaller than the values inferred from the magnetic dipole torque formula. The possible evolutionary paths of the sources imply that they will lose their seemingly HBRP property after about a few 104 yr, because either their rapidly decreasing period derivatives will lead them into the normal radio pulsar population or they will evolve into the accretion phase switching off the radio pulses.

Optical Characteristics of Astrometric Radio Sources OCARS

NASA Astrophysics Data System (ADS)

Malkin, Z.

2013-04-01

In this paper, the current status of the catalog of Optical Characteristics of Astrometric Radio Sources OCARS is presented. The catalog includes radio sources observed in various astrometric and geodetic VLBI programs in 1979-2012. For these sources the physical object type, redshift and visual or infrared magnitude is given when available. Detailed comments are provided when some problems with published data were encountered. Since the first version created in December 2007, the catalog is continuously developed and expanded in respect to inclusion of new radio sources and addition of new or correction of old astrophysical data. Several sources of information are used for OCARS. The main of them are the NASA/IPAC Extragalactic Database (NED) and SIMBAD astronomical databases. Besides several astronomical journals and arXiv depository are regularly monitored, so that new data is included in OCARS just after publication. The redshift for about 150 sources have been determined from dedicated optical spectroscopic observations. As of October 2012, OCARS catalog includes 7173 radio sources. 3898 sources have known redshift, and 4860 sources have known magnitude. In 2009, it was used as a supplement material to the ICRF2. The list of radio sources with a good observational history but lacking astrophysical information is provide for planning of optical observations of the most important astrometric sources. The OCARS catalog is updated, in average every several weeks and is available at http://www.gao.spb.ru/english/as/ac_vlbi/ocars.txt.

Infrared-faint radio sources in the SERVS deep fields. Pinpointing AGNs at high redshift

NASA Astrophysics Data System (ADS)

Maini, A.; Prandoni, I.; Norris, R. P.; Spitler, L. R.; Mignano, A.; Lacy, M.; Morganti, R.

2016-12-01

Context. Infrared-faint radio sources (IFRS) represent an unexpected class of objects which are relatively bright at radio wavelength, but unusually faint at infrared (IR) and optical wavelengths. A recent and extensive campaign on the radio-brightest IFRSs (S1.4 GHz≳ 10 mJy) has provided evidence that most of them (if not all) contain an active galactic nuclei (AGN). Still uncertain is the nature of the radio-faintest IFRSs (S1.4 GHz≲ 1 mJy). Aims: The scope of this paper is to assess the nature of the radio-faintest IFRSs, testing their classification and improving the knowledge of their IR properties by making use of the most sensitive IR survey available so far: the Spitzer Extragalactic Representative Volume Survey (SERVS). We also explore how the criteria of IFRSs can be fine-tuned to pinpoint radio-loud AGNs at very high redshift (z > 4). Methods: We analysed a number of IFRS samples identified in SERVS fields, including a new sample (21 sources) extracted from the Lockman Hole. 3.6 and 4.5 μm IR counterparts of the 64 sources located in the SERVS fields were searched for and, when detected, their IR properties were studied. Results: We compared the radio/IR properties of the IR-detected IFRSs with those expected for a number of known classes of objects. We found that IR-detected IFRSs are mostly consistent with a mixture of high-redshift (z ≳ 3) radio-loud AGNs. The faintest ones (S1.4 GHz 100 μJy), however, could be also associated with nearer (z 2) dust-enshrouded star-burst galaxies. We also argue that, while IFRSs with radio-to-IR ratios >500 can very efficiently pinpoint radio-loud AGNs at redshift 2 < z < 4, lower radio-to-IR ratios ( 100-200) are expected for higher redshift radio-loud AGNs.

Planetary radio astronomy observations from Voyager-2 near Saturn

NASA Technical Reports Server (NTRS)

Warwick, J. W.; Evans, D. R.; Romig, J. H.; Alexander, J. K.; Desch, M. D.; Kaiser, M. L.; Aubier, M.; Leblanc, Y.; Lecacheux, A.; Pedersen, B. M.

1981-01-01

Voyager-2 planetry radio astronomy measurements obtained near Saturn are discussed. They indicate that Saturnian kilometric radiation is emitted by a strong, dayside source at auroral latitudes in the northern hemisphere and by a weaker (by more than an order of magnitude) source at complementary latitudes in the southern hemisphere. These emissions are variable both due to Saturn's rotation and, on longer time scales, probably due to influences of the solar wind and the satellite Dione. The Saturn electrostatic discharge bursts first discovered by Voyager-1 and attributed to emissions from the B-ring were again observed with the same broadband spectral properties and a 10(h)11(m) + or - 5(m) episodic recurrence period but with an occurrence frequency of only of about 30 percent of that detected with Voyager-1. During the crossing of the ring plane at a distance of 2.88 R sub S, an intense noise event is interpreted to be consequence of the impact/vaporization/ionization of charged micron-size G-ring particles distributed over a total vertical thickness of about 1500 km.

AGILE detects enhanced gamma-ray emission above 100 MeV from the blazar S4 0554+58 region

NASA Astrophysics Data System (ADS)

Lucarelli, F.; Pittori, C.; Verrecchia, F.; Tavani, M.; Piano, G.; Bulgarelli, A.; Fioretti, V.; Striani, E.; Vercellone, S.; Donnarumma, I.; Cardillo, M.; Gianotti, F.; Trifoglio, M.; Giuliani, A.; Mereghetti, S.; Caraveo, P.; Perotti, F.; Chen, A.; Argan, A.; Costa, E.; Del Monte, E.; Evangelista, Y.; Feroci, M.; Lazzarotto, F.; Lapshov, I.; Pacciani, L.; Soffitta, P.; Sabatini, S.; Vittorini, V.; Pucella, G.; Rapisarda, M.; Di Cocco, G.; Fuschino, F.; Galli, M.; Labanti, C.; Marisaldi, M.; Pellizzoni, A.; Trois, A.; Pilia, M.; Barbiellini, G.; Vallazza, E.; Longo, F.; Morselli, A.; Picozza, P.; Prest, M.; Lipari, P.; Zanello, D.; Cattaneo, P. W.; Rappoldi, A.; Colafrancesco, S.; Parmiggiani, N.; Ferrari, A.; Giommi, P.; Salotti, L.; Valentini, G.; D'Amico, F.

2015-02-01

AGILE is detecting increased gamma-ray emission above 100 MeV from a source positionally consistent with the flat spectrum radio quasar S4 0554+58 (also known as BZQ J0559+5804), with radio coordinates R.A.: 89.8058092 deg, Dec.: 58.0676239 deg (J2000, A. J. Beasley et al., 2002ApJS..141...13B).

The Gamma-Ray Properties of Radio-Selected Extragalactic Jets

DTIC Science & Technology

2010-06-01

Interferometry (VLBI) techniques. This information is important to understand the broad-band emission mechanism of these sources. In this work we... relativistic speed, thus the emission is Doppler boosted (Blandford & Rees, 1978; Maraschi et a!., 1992). This model is supported by the apparent... superluminal motion which is typically found in the inner radio-jets of blazars (Lister et al., 2009b, , and therein). Since 2008 August 11: the sky

Forecasting the Contribution of Polarized Extragalactic Radio Sources in CMB Observations

NASA Astrophysics Data System (ADS)

Puglisi, G.; Galluzzi, V.; Bonavera, L.; Gonzalez-Nuevo, J.; Lapi, A.; Massardi, M.; Perrotta, F.; Baccigalupi, C.; Celotti, A.; Danese, L.

2018-05-01

We combine the latest data sets obtained with different surveys to study the frequency dependence of polarized emission coming from extragalactic radio sources (ERS). We consider data over a very wide frequency range starting from 1.4 GHz up to 217 GHz. This range is particularly interesting since it overlaps the frequencies of the current and forthcoming cosmic microwave background (CMB) experiments. Current data suggest that at high radio frequencies (ν ≥ 20 GHz) the fractional polarization of ERS does not depend on the total flux density. Conversely, recent data sets indicate a moderate increase of polarization fraction as a function of frequency, physically motivated by the fact that Faraday depolarization is expected to be less relevant at high radio frequencies. We compute ERS number counts using updated models based on recent data, and we forecast the contribution of unresolved ERS in CMB polarization spectra. Given the expected sensitivities and the observational patch sizes of forthcoming CMB experiments, about ∼200 (up to ∼2000) polarized ERS are expected to be detected. Finally, we assess that polarized ERS can contaminate the cosmological B-mode polarization if the tensor-to-scalar ratio is <0.05 and they have to be robustly controlled to de-lens CMB B-modes at the arcminute angular scales.

Time correlation between the radio and gamma-ray activity in blazars and the production site of the gamma-ray emission

DOE PAGES

Max-Moerbeck, W.; Hovatta, T.; Richards, J. L.; ...

2014-09-22

In order to determine the location of the gamma-ray emission site in blazars, we investigate the time-domain relationship between their radio and gamma-ray emission. Light-curves for the brightest detected blazars from the first 3 years of the mission of the Fermi Gamma-ray Space Telescope are cross-correlated with 4 years of 15GHz observations from the OVRO 40-m monitoring program. The large sample and long light-curve duration enable us to carry out a statistically robust analysis of the significance of the cross-correlations, which is investigated using Monte Carlo simulations including the uneven sampling and noise properties of the light-curves. Modeling the light-curvesmore » as red noise processes with power-law power spectral densities, we find that only one of 41 sources with high quality data in both bands shows correlations with significance larger than 3σ (AO0235+164), with only two more larger than even 2.25σ (PKS 1502+106 and B2 2308+34). Additionally, we find correlated variability in Mrk 421 when including a strong flare that occurred in July-September 2012. These results demonstrate very clearly the difficulty of measuring statistically robust multiwavelength correlations and the care needed when comparing light-curves even when many years of data are used. This should be a caution. In all four sources the radio variations lag the gamma-ray variations, suggesting that the gamma-ray emission originates upstream of the radio emission. Continuous simultaneous monitoring over a longer time period is required to obtain high significance levels in cross-correlations between gamma-ray and radio variability in most blazars.« less

A Reverse Shock and Unusual Radio Properties in GRB 160625B

NASA Astrophysics Data System (ADS)

Alexander, K. D.; Laskar, T.; Berger, E.; Guidorzi, C.; Dichiara, S.; Fong, W.; Gomboc, A.; Kobayashi, S.; Kopac, D.; Mundell, C. G.; Tanvir, N. R.; Williams, P. K. G.

2017-10-01

We present multi-wavelength observations and modeling of the exceptionally bright long γ-ray burst GRB 160625B. The optical and X-ray data are well fit by synchrotron emission from a collimated blastwave with an opening angle of {θ }j≈ 3\\buildrel{\\circ}\\over{.} 6 and kinetic energy of {E}K≈ 2× {10}51 erg, propagating into a low-density (n≈ 5× {10}-5 cm-3) medium with a uniform profile. The forward shock is sub-dominant in the radio band; instead, the radio emission is dominated by two additional components. The first component is consistent with emission from a reverse shock, indicating an initial Lorentz factor of {{{Γ }}}0≳ 100 and an ejecta magnetization of {R}B≈ 1{--}100. The second component exhibits peculiar spectral and temporal evolution and is most likely the result of scattering of the radio emission by the turbulent Milky Way interstellar medium (ISM). Such scattering is expected in any sufficiently compact extragalactic source and has been seen in GRBs before, but the large amplitude and long duration of the variability seen here are qualitatively more similar to extreme scattering events previously observed in quasars, rather than normal interstellar scintillation effects. High-cadence, broadband radio observations of future GRBs are needed to fully characterize such effects, which can sensitively probe the properties of the ISM and must be taken into account before variability intrinsic to the GRB can be interpreted correctly.

PSR B0329+54: substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330 000 km

NASA Astrophysics Data System (ADS)

Popov, Mikhail V.; Bartel, Norbert; Gwinn, Carl R.; Johnson, Michael D.; Andrianov, Andrey; Fadeev, Evgeny; Joshi, Bhal Chandra; Kardashev, Nikolay; Karuppusamy, Ramesh; Kovalev, Yuri Y.; Kramer, Michael; Rudnitskiy, Alexey; Shishov, Vladimir; Smirnova, Tatiana; Soglasnov, Vladimir A.; Zensus, J. Anton

2017-02-01

We have resolved the scatter-broadened image of PSR B0329+54 and detected a substructure within it. These results are not influenced by any extended structure of a source but instead are directly attributed to the interstellar medium. We obtained these results at 324 MHz with the ground-space interferometer RadioAstron, which included the Space Radio Telescope, ground-based Westerbork Synthesis Radio Telescope and 64-m Kalyazin Radio Telescope on baseline projections up to 330 000 km in 2013 November 22 and 2014 January 1 to 2. At short 15 000 to 35 000 km ground-space baseline projections, the visibility amplitude decreases with baseline length, providing a direct measurement of the size of the scattering disc of 4.8 ± 0.8 mas. At longer baselines, no visibility detections from the scattering disc would be expected. However, significant detections were obtained with visibility amplitudes of 3 to 5 per cent of the maximum scattered around a mean and approximately constant up to 330 000 km. These visibilities reflect a substructure from scattering in the interstellar medium and offer a new probe of ionized interstellar material. The size of the diffraction spot near Earth is 17 000 ± 3 000 km. With the assumption of turbulent irregularities in the plasma of the interstellar medium, we estimate that the effective scattering screen is located 0.6 ± 0.1 of the distance from the Earth towards the pulsar.

Earth-based observations of Faraday rotation in radio bursts from Jupiter

NASA Technical Reports Server (NTRS)

Phillips, J. A.; Ferree, Thomas C.; Wang, Joe

1989-01-01

New observations have been made of Faraday rotation in decameter-wavelength radio bursts from the planet Jupiter. Data obtained during six Io-B storms clearly indicate that an appreciable fraction of the observed Faraday rotation occurs in the Jovian magnetosphere. All of the Faraday rotation observed during a single Io-A storm can be accounted for by earth's ionosphere. Measurements of the Faraday effect in Io-B emissions indicate that the source is in Jupiter's northern magnetic hemisphere. Observations of the Faraday effect in Io-C emissions are proposed to determine its location as well.

CO detections and IRAS observations of bright radio spiral galaxies at cz equal or less than 9000 kilometers per second

NASA Technical Reports Server (NTRS)

Sanders, D. B.; Mirabel, I. F.

1985-01-01

CO emission has been detected from 20 of 21 bright radio spirals with strong extended nuclear sources, including the most distant (NGC 7674) and the most luminous (IC 4553 = Arp 220, NGC 6240) galaxies yet detected in CO. All of these galaxies are rich in molecular gas, with M total(H2) = 3 x 10 to the 8th - 2 x 10 to the 10th solar masses. IRAS observations show that they have a strong far-infrared (FIR) excess, with L(FIR)/L(B) approximately equal to 1-35 and L(FIR) (40-400 microns) approximately equal to 10 to the 10th - 10 to the 12th L solar masses. The primary luminosity source for these radio cores appears to be star formation in molecular clouds. A strong correlation is found between the FIR and extended 21 cm continuum flux, implying that the fraction of massive stars formed is independent of the star formation rate. The ratio L(FIR)/M(H2) provides a measure of the current rate of star formation, which is found to be a factor 3-20 larger in these galaxies than for the ensemble of molecular clouds in the Milky Way. At these rates their molecular gas will be depleted in about 10 to the 8th yr.

MiR-20a-5p promotes radio-resistance by targeting Rab27B in nasopharyngeal cancer cells.

PubMed

Huang, Dabing; Bian, Geng; Pan, Yueyin; Han, Xinghua; Sun, Yubei; Wang, Yong; Shen, Guodong; Cheng, Min; Fang, Xiang; Hu, Shilian

2017-01-01

MicroRNAs (miRNAs) was reported to be involved in cancer radio-resistance, which remains a major obstacle for effective cancer therapy. The differently expressed miRNAs were detected by RNA-seq experiment in nasopharyngeal cancer (NPC) cells. MiR-20a-5p was selected as our target, which was subject to finding its target gene Rab27B via bioinformatics analysis. The qRT-PCR, western blot and the luciferase reporter assays were performed to confirm Rab27B as the target of miR-20a-5p. In addition, the roles of miR-20a-5p in NPC radio-resistance were detected by transfection of either miR-20a-5p-mimic or miR-20a-5p-antagomiR. The involvement of Rab27B with NPC radio-resistance was also detected by the experiments with siRNA-mediated repression of Rab27B or over-expression of GFP-Rab27B. Wound healing and invasion assays were performed to detect the roles of both miR-20a-5p and Rab27B. MiR-20a-5p promotes NPC radio-resistance. We identified that its target gene Rab27B negatively correlates with miR-20a-5p-mediated NPC radio-resistance by systematic studies of a radio-sensitive (CNE-2) and resistant (CNE-1) NPC cell lines. Repression of Rab27B by siRNA suppresses cell apoptosis and passivates CNE-2 cells, whereas over-expression of Rab27B triggered cell apoptosis and sensitizes CNE-1 cells. MiR-20a-5p and its target gene Rab27B might be involved in the NPC radio-resistance. Thus the key players and regulators involved in this pathway might be the potential targets for developing effective therapeutic strategies against NPC.

Radio Jet Feedback and Star Formation in Heavily Obscured, Hyperluminous Quasars at Redshifts ˜ 0.5-3. I. ALMA Observations

NASA Astrophysics Data System (ADS)

Lonsdale, Carol J.; Lacy, M.; Kimball, A. E.; Blain, A.; Whittle, M.; Wilkes, B.; Stern, D.; Condon, J.; Kim, M.; Assef, R. J.; Tsai, C.-W.; Efstathiou, A.; Jones, S.; Eisenhardt, P.; Bridge, C.; Wu, J.; Lonsdale, Colin J.; Jones, K.; Jarrett, T.; Smith, R.

2015-11-01

We present Atacama Large Millimeter/submillimeter Array (ALMA) 870 μm (345 GHz) data for 49 high-redshift (0.47 < z < 2.85), luminous (11.7\\lt {log}({L}{{bol}}/{L}⊙ )\\lt 14.2) radio-powerful active galactic nuclei (AGNs), obtained to constrain cool dust emission from starbursts concurrent with highly obscured radiative-mode black hole (BH) accretion in massive galaxies that possess a small radio jet. The sample was selected from the Wide-field Infrared Survey Explorer with extremely steep (red) mid-infrared colors and with compact radio emission from NVSS/FIRST. Twenty-six sources are detected at 870 μm, and we find that the sample has large mid- to far-infrared luminosity ratios, consistent with a dominant and highly obscured quasar. The rest-frame 3 GHz radio powers are 24.7\\lt {log}({P}\\text{3.0 GHz}/{{{W}} {Hz}}-1)\\lt 27.3, and all sources are radio-intermediate or radio-loud. BH mass estimates are 7.7 < log(MBH/M⊙) < 10.2. The rest-frame 1-5 μm spectral energy distributions are very similar to the “Hot DOGs” (hot dust-obscured galaxies), and steeper (redder) than almost any other known extragalactic sources. ISM masses estimated for the ALMA-detected sources are 9.9 < log (MISM/M⊙) < 11.75 assuming a dust temperature of 30 K. The cool dust emission is consistent with star formation rates reaching several thousand M⊙ yr-1, depending on the assumed dust temperature, but we cannot rule out the alternative that the AGN powers all the emission in some cases. Our best constrained source has radiative transfer solutions with approximately equal contributions from an obscured AGN and a young (10-15 Myr) compact starburst.

ATCA observations of the MACS-Planck Radio Halo Cluster Project. II. Radio observations of an intermediate redshift cluster sample

NASA Astrophysics Data System (ADS)

Martinez Aviles, G.; Johnston-Hollitt, M.; Ferrari, C.; Venturi, T.; Democles, J.; Dallacasa, D.; Cassano, R.; Brunetti, G.; Giacintucci, S.; Pratt, G. W.; Arnaud, M.; Aghanim, N.; Brown, S.; Douspis, M.; Hurier, J.; Intema, H. T.; Langer, M.; Macario, G.; Pointecouteau, E.

2018-04-01

Aim. A fraction of galaxy clusters host diffuse radio sources whose origins are investigated through multi-wavelength studies of cluster samples. We investigate the presence of diffuse radio emission in a sample of seven galaxy clusters in the largely unexplored intermediate redshift range (0.3 < z < 0.44). Methods: In search of diffuse emission, deep radio imaging of the clusters are presented from wide band (1.1-3.1 GHz), full resolution ( 5 arcsec) observations with the Australia Telescope Compact Array (ATCA). The visibilities were also imaged at lower resolution after point source modelling and subtraction and after a taper was applied to achieve better sensitivity to low surface brightness diffuse radio emission. In case of non-detection of diffuse sources, we set upper limits for the radio power of injected diffuse radio sources in the field of our observations. Furthermore, we discuss the dynamical state of the observed clusters based on an X-ray morphological analysis with XMM-Newton. Results: We detect a giant radio halo in PSZ2 G284.97-23.69 (z = 0.39) and a possible diffuse source in the nearly relaxed cluster PSZ2 G262.73-40.92 (z = 0.421). Our sample contains three highly disturbed massive clusters without clear traces of diffuse emission at the observed frequencies. We were able to inject modelled radio haloes with low values of total flux density to set upper detection limits; however, with our high-frequency observations we cannot exclude the presence of RH in these systems because of the sensitivity of our observations in combination with the high z of the observed clusters. The reduced images are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/611/A94

The FIRST Survey: Faint Images of the Radio Sky at Twenty Centimeters

NASA Astrophysics Data System (ADS)

Becker, Robert H.; White, Richard L.; Helfand, David J.

1995-09-01

The FIRST survey to produce Faint Images of the Radio Sky at Twenty centimeters is now underway using the NRAO Very Large Array. We describe here the scientific motivation for a large-area sky survey at radio frequencies which has a sensitivity and angular resolution comparable to the Palomar Observatory Sky Survey, and we recount the history that led to the current survey project. The technical design of the survey is covered in detail, including a description and justification of the grid pattern chosen, the rationale behind the integration time and angular resolution selected, and a summary of the other considerations which informed our planning for the project. A comprehensive description of the automated data analysis pipeline we have developed is presented. We also report here the results of the first year of FIRST observations. A total of 144 hr of time in 1993 April and May was used for a variety of tests, as well as to cover an initial strip of the survey extending between 07h 15m and 16h 30m in a 2°.8 wide declination zone passing through the local zenith (28.2 <δ < 31.0). A total of 2153 individual pointings yielded an image database containing 1039 merged images 46'.5 × 34'.5 in extent with 1".8 pixels and a typical rms of 0.13 mJy. A catalog derived from this 300 deg2 region contains 28,000 radio sources. We have performed extensive tests on the images and source list in order to establish the photometric and astrometric accuracy of these data products. We find systematic astrometric errors of < 0".05 individual sources down to the 1 mJy survey flux density threshold have 90% confidence error circles with radii of < 1". CLEAN bias introduces a systematic underestimate of point-source flux densities of ˜0.25 mJy; the bias is more severe for extended sources. Nonetheless, a comparison with a published deep survey field demonstrates that we successfully detect 39/49 sources with integrated flux densities greater than 0.75 mJy, including 19 of 20 sources above 2.0 mJy; the sources not detected are known to be very extended and so have surface brightnesses well below our threshold. With 480 hr of observing time committed for each of the next three B-configuration periods, FIRST will complete nearly one-half of its goal of covering the 10,000 deg2 of the north Galactic cap scheduled for inclusion in the Sloan Digital Sky Survey. All of the FIRST data raw visibilities, self-calibrated UV data sets, individual pointing maps, final merged images, source catalogs, and individual source images are being placed in the public domain as soon as they are verified; all of the 1993 data are now available through the NRAO and/or the STScI archive. We conclude with a brief summary of the scientific significance of FIRST, which represents an improvement by a factor of 50 in both angular resolution and sensitivity over the best available large area radio surveys.

OMC-1 as Revealed by HST NICMOS Polarization Measurements

NASA Astrophysics Data System (ADS)

Simpson, J. P.; Burton, M. G.; Colgan, S. W. J.; Erickson, E. F.; Schultz, A. S. B.; Simpson, E.

2004-12-01

The Orion Molecular Cloud (OMC-1) harbors the nearest and most studied massive star-forming region. Signs of the formation of multiple stars in this optically obscured region include powerful CO outflows, H2O and SiO maser emission, remarkable H2 "bullets", "fingers", and "streamers", and X-rays from pre-main-sequence stars. Highly polarized clouds indicate that the illuminating sources lie in the directions of the Becklin-Neugebauer object (BN), and stars in the vicinity of IRc2, radio source I, NIR source n, and others. Here we present 2 μ m polarization measurements of positions north and south of BN made with NICMOS Camera 2 on the Hubble Space Telescope. Near-infrared starlight can be polarized by scattering from nearby dust grains and by dichroic absorption by non-spherical dust grains aligned by a magnetic field. Within the 19'' field of view of Camera 2, BN appears to be the illuminating source of most of the nebulosity to its north; however, the material to the south is illuminated either by a star near I (IRc4) or by source n (IRc2B). Source n also illuminates material 1'' - 2'' to its northeast and southwest, at the same position angles as the extended radio source at the same location. We discuss possible interpretations of the strong polarization of IRc7, which is not illuminated by source I. We also display several stars (NICMOS point sources) that are the source of their own polarization, which ranges up to 40% and occurs at distinctly different angles from the polarization of the immediately surrounding diffuse emission. This may be caused by dichroic absorption and scattering in edge-on circumstellar disks. At least two faint stars are variable. Support for proposal 9752 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

Development of a Multi-frequency Interferometer Telescope for Radio Astronomy (MITRA)

NASA Astrophysics Data System (ADS)

Ingala, Dominique Guelord Kumamputu

2015-03-01

This dissertation describes the development and construction of the Multi-frequency Interferometer Telescope for Radio Astronomy (MITRA) at the Durban University of Technology. The MITRA station consists of 2 antenna arrays separated by a baseline distance of 8 m. Each array consists of 8 Log-Periodic Dipole Antennas (LPDAs) operating from 200 MHz to 800 MHz. The design and construction of the LPDA antenna and receiver system is described. The receiver topology provides an equivalent noise temperature of 113.1 K and 55.1 dB of gain. The Intermediate Frequency (IF) stage was designed to produce a fixed IF frequency of 800 MHz. The digital Back-End and correlator were implemented using a low cost Software Defined Radio (SDR) platform and Gnu-Radio software. Gnu-Octave was used for data analysis to generate the relevant received signal parameters including total power, real, and imaginary, magnitude and phase components. Measured results show that interference fringes were successfully detected within the bandwidth of the receiver using a Radio Frequency (RF) generator as a simulated source. This research was presented at the IEEE Africon 2013 / URSI Session Mauritius, and published in the proceedings.

The 3CR Chandra Snapshot Survey: Extragalactic Radio Sources with Redshifts between 1 and 1.5

NASA Astrophysics Data System (ADS)

Stuardi, C.; Missaglia, V.; Massaro, F.; Ricci, F.; Liuzzo, E.; Paggi, A.; Kraft, R. P.; Tremblay, G. R.; Baum, S. A.; O’Dea, C. P.; Wilkes, B. J.; Kuraszkiewicz, J.; Forman, W. R.; Harris, D. E.

2018-04-01

The aim of this paper is to present an analysis of newly acquired X-ray observations of 16 extragalactic radio sources listed in the Third Cambridge Revised (3CR) catalog and not previously observed by Chandra. Observations were performed during Chandra Cycle 17, extending X-ray coverage for the 3CR extragalactic catalog up to z = 1.5. Among the 16 targets, two lie at z < 0.5 (3CR 27 at z = 0.184 and 3CR 69 at z = 0.458) all of the remaining 14 have redshifts between 1.0 and 1.5. In the current sample, there are three compact steep spectrum (CSS) sources, three quasars, and an FR I radio galaxy, while the other nine are FR II radio galaxies. All radio sources have an X-ray counterpart. We measured nuclear X-ray fluxes as well as X-ray emission associated with radio jet knots, hotspots, or lobes in three energy bands: soft (0.5–1 keV), medium (1–2 keV), and hard (2–7 keV). We also performed standard X-ray spectral analysis for the four brightest nuclei. We discovered X-ray emission associated with the radio lobe of 3CR 124, a hotspot of the quasar 3CR 220.2, another hotspot of the radio galaxy 3CR 238, and the jet knot of 3CR 297. We also detected extended X-ray emission around the nuclear region of 3CR 124 and 3CR 297 on scales of several tens of kiloparsecs. Finally, we present an update on the X-ray observations performed with Chandra and XMM-Newton on the entire 3CR extragalactic catalog.

Compact radio sources in the starburst galaxy M82 and the Sigma-D relation for supernova remnants

NASA Technical Reports Server (NTRS)

Huang, Z. P.; Thuan, T. X.; Chevalier, R. A.; Condon, J. J.; Yin, Q. F.

1994-01-01

We have obtained an 8.4 GHz Very Large Array (VLA) A-array map of the starburst galaxy M82 with a resolution Full Width at Half Maximum (FWHM) approximately 0.182 sec. About 50 compact radio sources in the central region of M82 were detected with a peak surface brightness approximately greater than 10(exp -17) W/Hz/sq m/sr. Comparison with previous observations shows that most sources are declining in flux. Three previously visible sources have faded into the background of our map (approximately less than 0.2 mJy/beam), while a few sources, including the second and third brightest radio sources in M82, may have increased slightly in flux over the last decade. No new radio supernova was found. The birth rate of the compact radio sources is estimated to be 0.11 + or - 0.05/yr. We attribute the population of such bright, small supernova remnants (SNRs) in M82 to the high pressure in the central region that can truncate the mass loss during a red supergiant phase or allow dense ionized clouds to be present. The compact radio sources obey a Sigma(radio surface brightness) - D(diameter) relation which is remarkably similar to that followed by supernova remnants in the Galaxy and the Magellanic Clouds and by two of the strongest known extragalactic radio supernovae: SN 1986J and SN 1979C. A least-squares fit to the SNR data gives: Sigma(sub 8.4 GHz) (W/Hz/sq m/sr) = 4.4 x 10(exp -16) D(sub pc)(exp -3.5 +/- 0.1) covering seven orders of magnitude in Sigma. Possible selection effects are discussed and a theoretical discussion of the correlation is presented.

Is There a Maximum Star Formation Rate in High-redshift Galaxies?

NASA Astrophysics Data System (ADS)

Barger, A. J.; Cowie, L. L.; Chen, C.-C.; Owen, F. N.; Wang, W.-H.; Casey, C. M.; Lee, N.; Sanders, D. B.; Williams, J. P.

2014-03-01

We use the James Clerk Maxwell Telescope's SCUBA-2 camera to image a 400 arcmin2 area surrounding the GOODS-N field. The 850 μm rms noise ranges from a value of 0.49 mJy in the central region to 3.5 mJy at the outside edge. From these data, we construct an 850 μm source catalog to 2 mJy containing 49 sources detected above the 4σ level. We use an ultradeep (11.5 μJy at 5σ) 1.4 GHz image obtained with the Karl G. Jansky Very Large Array together with observations made with the Submillimeter Array to identify counterparts to the submillimeter galaxies. For most cases of multiple radio counterparts, we can identify the correct counterpart from new and existing Submillimeter Array data. We have spectroscopic redshifts for 62% of the radio sources in the 9' radius highest sensitivity region (556/894) and 67% of the radio sources in the GOODS-N region (367/543). We supplement these with a modest number of additional photometric redshifts in the GOODS-N region (30). We measure millimetric redshifts from the radio to submillimeter flux ratios for the unidentified submillimeter sample, assuming an Arp 220 spectral energy distribution. We find a radio-flux-dependent K - z relation for the radio sources, which we use to estimate redshifts for the remaining radio sources. We determine the star formation rates (SFRs) of the submillimeter sources based on their radio powers and their submillimeter fluxes and find that they agree well. The radio data are deep enough to detect star-forming galaxies with SFRs >2000 M ⊙ yr-1 to z ~ 6. We find galaxies with SFRs up to ~6000 M ⊙ yr-1 over the redshift range z = 1.5-6, but we see evidence for a turn-down in the SFR distribution function above 2000 M ⊙ yr-1. The James Clerk Maxwell Telescope is operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the United Kingdom, the National Research Council of Canada, and (until 2013 March 31) the Netherlands Organisation for Scientific Research. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

X-ray study of a sample of FR0 radio galaxies: unveiling the nature of the central engine

NASA Astrophysics Data System (ADS)

Torresi, E.; Grandi, P.; Capetti, A.; Baldi, R. D.; Giovannini, G.

2018-06-01

Fanaroff-Riley type 0 radio galaxies (FR0s) are compact radio sources that represent the bulk of the radio-loud active galactic nuclei (AGN) population, but they are still poorly understood. Pilot studies on these sources have been already performed at radio and optical wavelengths: here we present the first X-ray study of a sample of 19 FR0 radio galaxies selected from the Sloan Digital Sky Survey/NRAO VLA Sky Survey/Faint Images of the Radio Sky at Twenty-cm sample of Best & Heckman, with redshift ≤0.15, radio size ≤10 kpc, and optically classified as low-excitation galaxies. The X-ray spectra are modelled with a power-law component absorbed by Galactic column density with, in some cases, a contribution from thermal extended gas. The X-ray photons are likely produced by the jet as attested by the observed correlation between X-ray (2-10 keV) and radio (5 GHz) luminosities, similar to Fanaroff-Riley type I radio galaxies (FRIs). The estimated Eddington-scaled luminosities indicate a low accretion rate. Overall, we find that the X-ray properties of FR0s are indistinguishable from those of FRIs, thus adding another similarity between AGN associated with compact and extended radio sources. A comparison between FR0s and low-luminosity BL Lacs rules out important beaming effects in the X-ray emission of the compact radio galaxies. FR0s have different X-ray properties with respect to young radio sources (e.g. gigahertz-peaked spectrum/compact steep spectrum sources), generally characterized by higher X-ray luminosities and more complex spectra. In conclusion, the paucity of extended radio emission in FR0s is probably related to the intrinsic properties of their jets that prevent the formation of extended structures, and/or to intermittent activity of their engines.

ALMA observations of AGN fuelling. The case of PKS B1718-649

NASA Astrophysics Data System (ADS)

Maccagni, F. M.; Morganti, R.; Oosterloo, T. A.; Oonk, J. B. R.; Emonts, B. H. C.

2018-06-01

We present ALMA observations of the 12CO (2-1) line of the newly born (tradio 102 years) active galactic nucleus (AGN), PKS B1718-649. These observations reveal that the carbon monoxide in the innermost 15 kpc of the galaxy is distributed in a complex warped disk. In the outer parts of this disk, the CO gas follows the rotation of the dust lane and of the stellar body of the galaxy hosting the radio source. In the innermost kiloparsec, the gas abruptly changes orientation and forms a circumnuclear disk (r ≲ 700 pc) with its major axis perpendicular to that of the outer disk. Against the compact radio emission of PKS B1718-649 (r 2 pc), we detect an absorption line at red-shifted velocities with respect to the systemic velocity (Δv = +365 ± 22 km s-1). This absorbing CO gas could trace molecular clouds falling onto the central super-massive black hole. A comparison with the near-infrared H2 1-0 S(1) observations shows that the clouds must be close to the black hole (r ≲ 75 pc). The physical conditions of these clouds are different from the gas at larger radii, and are in good agreement with the predictions for the conditions of the gas when cold chaotic accretion triggers an active galactic nucleus. These observations on the centre of PKS B1718-649 provide one of the best indications that a population of cold clouds is falling towards a radio AGN, likely fuelling its activity. The reduced datacube is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/614/A42

The radio and optical counterpart of the new Fermi LAT flaring source J0109+6134

NASA Astrophysics Data System (ADS)

Paredes, J. M.; Martí, J.; Peracaula, M.

2010-02-01

Following the recent ATELs #2414, #2416 and #2420 concerning the Fermi-LAT, AGILE and Swift/XRT consistent detections of the new gamma-ray flaring source J0109+6134, we wish to remind that the proposed radio counterpart (VCS2 J0109+6133/GT 0106+613) was extensively observed nearly two decades ago by different authors in the context of the GT catalogue of Galactic Plane radio sources (Taylor and Gregory 1983, AJ, 88, 1784; Gregory and Taylor 1986, AJ 92, 371).

The Southern Hemisphere VLBI experiment

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

Preston, R.A.; Meier, D.L.; Louie, A.P.

1989-07-01

Six radio telescopes were operated as the first Southern Hemisphere VLBI array in April and May 1982. Observations were made at 2.3 and 8.4 GHz. This array provided VLBI modeling and hybrid imaging of celestial radio sources in the Southern Hemisphere, high-accuracy VLBI geodesy between Southern Hemisphere sites, and subarcsecond radio astrometry of celestial sources south of declination -45 deg. The goals and implementation of the array are discussed, the methods of modeling and hybrid image production are explained, and the VLBI structure of the sources that were observed is summarized. 36 refs.

LOFAR-Boötes: properties of high- and low-excitation radio galaxies at 0.5 < z < 2.0

NASA Astrophysics Data System (ADS)

Williams, W. L.; Calistro Rivera, G.; Best, P. N.; Hardcastle, M. J.; Röttgering, H. J. A.; Duncan, K. J.; de Gasperin, F.; Jarvis, M. J.; Miley, G. K.; Mahony, E. K.; Morabito, L. K.; Nisbet, D. M.; Prandoni, I.; Smith, D. J. B.; Tasse, C.; White, G. J.

2018-04-01

This paper presents a study of the redshift evolution of radio-loud active galactic nuclei (AGN) as a function of the properties of their galaxy hosts in the Boötes field. To achieve this we match low-frequency radio sources from deep 150-MHz LOFAR (LOw Frequency ARray) observations to an I-band-selected catalogue of galaxies, for which we have derived photometric redshifts, stellar masses, and rest-frame colours. We present spectral energy distribution (SED) fitting to determine the mid-infrared AGN contribution for the radio sources and use this information to classify them as high- versus low-excitation radio galaxies (HERGs and LERGs) or star-forming galaxies. Based on these classifications, we construct luminosity functions for the separate redshift ranges going out to z = 2. From the matched radio-optical catalogues, we select a sub-sample of 624 high power (P150 MHz > 1025 W Hz-1) radio sources between 0.5 ≤ z < 2. For this sample, we study the fraction of galaxies hosting HERGs and LERGs as a function of stellar mass and host galaxy colour. The fraction of HERGs increases with redshift, as does the fraction of sources in galaxies with lower stellar masses. We find that the fraction of galaxies that host LERGs is a strong function of stellar mass as it is in the local Universe. This, combined with the strong negative evolution of the LERG luminosity functions over this redshift range, is consistent with LERGs being fuelled by hot gas in quiescent galaxies.

An X-ray investigation of the unusual supernova remnant CTB 80

NASA Technical Reports Server (NTRS)

Wang, Z. R.; Seward, F. D.

1984-01-01

The X-ray properties of SNR CTB 80 (G68.8 + 2.8) are discussed based on both low- and high-resolution images from the Einstein satellite. The X-ray maps show a point source coinciding with the region of maximum radio emission. Diffuse X-ray emission is evident mainly along the radio lobe extending about 8 arcmin east of the point source and aligned with the projected magnetic field lines. The observed X-ray luminosity is 3.2 x 10 to the 34th ergs/s with 1.0 x 10 to the 3th ergs/s from the point source (assuming a distance of 3 kpc). There is also faint, diffuse, X-ray emission south of the point source, where radio emission is absent. The unusual radio and X-ray morphologies are interpreted as a result of relativistic jets energized by the central object, and the possible association of CTB 80 with SN 1408 as recorded by Chinese observers is discussed.

Comparing two lower-dose cisplatin programs for radio-chemotherapy of locally advanced head-and-neck cancers.

PubMed

Rades, Dirk; Seidl, Daniel; Janssen, Stefan; Strojan, Primoz; Karner, Katarina; Bajrovic, Amira; Hakim, Samer G; Wollenberg, Barbara; Schild, Steven E

2017-02-01

Radio-chemotherapy is a common treatment for locally advanced squamous cell head-and-neck cancers (LA-SCCHN). Cisplatin (100 mg/m 2 ) every 3 weeks is very common but associated with considerable toxicity. Therefore, cisplatin programs with lower daily doses were introduced. There is a lack of studies comparing lower-dose programs. In this study, 85 patients receiving radio-chemotherapy with 20 mg/m 2 cisplatin on 5 days every 4 weeks (group A) were retrospectively compared to 85 patients receiving radio-chemotherapy with 30-40 mg/m 2 cisplatin weekly (group B). Groups were matched for nine factors including age, gender, performance score, tumor site, T-/N-category, surgery, hemoglobin before radio-chemotherapy, and radiation technique. One- and 3-year loco-regional control rates were 83 and 69 % in group A versus 74 and 63 % in group B (p = 0.12). One- and 3-year survival rates were 93 % and 73 % in group A versus 91 and 49 % in group B (p = 0.011). On multivariate analysis, survival was significantly better for group A (HR 1.17; p = 0.002). In groups A and B, 12 and 28 % of patients, respectively, did not receive a cumulative cisplatin dose ≥180 mg/m 2 (p = 0.016). Toxicity rates were not significantly different. On subgroup analyses, group A patients had better loco-regional control (p = 0.040) and survival (p = 0.005) than group B patients after definitive radio-chemotherapy. In patients receiving adjuvant radio-chemotherapy, outcomes were not significantly different. Thus, 20 mg/m 2 cisplatin on 5 days every 4 weeks resulted in better loco-regional control and survival in patients receiving definitive radio-chemotherapy and may be preferable for these patients. Confirmation of these results in a randomized trial is warranted.

The Atacama Cosmology Telescope: Extragalactic Sources at 148 GHz in the 2008 Survey

NASA Technical Reports Server (NTRS)

Marriage, T. A.; Juin, J. B.; Lin, Y. T.; Marsden, D.; Nolta, M. R.; Partridge, B.; Ade, P. A. R.; Aguirre, P.; Amiri, M.; Appel, J. W.;

Spectral characteristics of VLF sferics associated with TGFs

NASA Astrophysics Data System (ADS)

Mezentsev, Andrew; Lehtinen, Nikolai; Ostgaard, Nikolai; Perez-Invernon, Javier; Cummer, Steven

2017-04-01

A detailed analysis of RHESSI TGFs is performed in association with WWLLN sources and VLF sferics recorded at Duke University. The analysis of the TGF-WWLLN matches allowed to evaluate RHESSI clock systematic offsets [1], which allows to perform a more precise timing analysis involving TGF data comparisons with the VLF sferics recorded at Duke University. In this work we analyzed the energy spectra of 35 VLF sferics, which were identified as candidates to be emitted by the TGF source, based on the simultaneity and location coincidence between the TGF and radio sources. 20 events have WWLLN detections, which provides a reliable source location of the event. For the other 15 events several selection criteria were used: source location should be consistent with the simultaneity of the TGF and VLF sferic within ±200 μs uncertainty; source location should lay within the azimuthal ±4° cone defined by the ratio of the radial and azimuthal magnetic field components of the VLF sferic; source location should lay within 800 km circle around the RHESSI foot-point; source location should lay within a cluster of a current lightning activity validated by WWLLN (or any other lightning detection network). The energy spectra of 35 VLF sferics related to TGFs were analyzed in the context of the TGF radio emission model developed in [2]. Proposed model represents a TGF at source as a sequence of Np seeding pulses of energetic particles which develop into runaway avalanches in the strong ambient field. These relativistic electrons ionize air along their propagation path which results in secondary currents of low energy electrons and light ions in the ambient electric field. These secondary currents produce radio emissions that can be detected by the ground based sensors. Proposed model allows to express the TGF source current moment energy spectrum using the T50 TGF duration measured by RHESSI. This gives the opportunity to establish and validate empirically the functional link between the satellite measurements and radio recordings of TGFs. Distances from the analyzed TGF sources to the Duke VLF receiver range from 2000 to 4000 km. This involves the consideration of the propagation effects in the Earth-ionosphere wave guide (EIWG). The EIWG transfer function was calculated for each event using the full wave propagation method. Thus, the modeled energy spectrum of the TGF source current moment can be transformed into how it would look like for the Duke VLF receiver. Comparative analysis of the energy spectra of modeled TGF radio emission and associated VLF sferics for 20 events with WWLLN confirmed location and 15 events without WWLLN detection shows that 31 of these 35 events exhibit a good fit between the modeled and observed spectra, with only 4 exceptions, that look inconsistent with the proposed model. The second cutoff frequency fB with the number of avalanches Np define the shape of the observed energy spectrum of the sferic emitted by a TGF. Multiplicity of the TGF serves as another important discriminative factor that shows the consistency between the modeled and observed spectra. The results show that the number of avalanches Np should be relatively small, of the order of 30-300, to make the modeled TGF radio emission consistent with the observed VLF sferics. These small values of Np give an argument in favor of the leader model of the TGF production, and also might refer to streamers in the streamer zone of the leader tip, as candidates, producing initial seeding pulses that develop into RREAs, generating a TGF. [1]. Mezentsev, A., Østgaard, N., Gjesteland, T., Albrechtsen, K., Lehtinen, N., Marisaldi, M., Smith, D., and Cummer, S. (2016), Radio emissions from double RHESSI TGFs, J. Geophys. Res., 121, doi:10.1002/2016JD025111 [2]. Dwyer, J. R., and S. A. Cummer (2013), Radio emissions from terrestrial gamma ray flashes, J. Geophys. Res., 118, doi:10.1002/jgra.50188.

THE POSITION/STRUCTURE STABILITY OF FOUR ICRF2 SOURCES

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

Fomalont, Ed; Johnston, Kenneth; Fey, Alan

2011-03-15

Four close radio sources in the International Celestial Reference Frame (ICRF) catalog were observed using phase referencing with the VLBA at 43, 23, and 8.6 GHz, and with VERA at 23 GHz over a one-year period. The goal was to determine the stability of the radio cores and to assess structure effects associated with positions in the ICRF. Although the four sources were compact at 8.6 GHz, the VLBA images at 43 GHz with 0.3 mas resolution showed that all were composed of several components. A component in each source was identified as the radio core using some or allmore » of the following emission properties: compactness, spectral index, location at the end of the extended emission region, and stationary in the sky. Over the observing period, the relative positions between the four radio cores were constant to 0.02 mas, the phase-referencing positional accuracy obtained at 23 and 43 GHz among the sources, suggesting that once a radio core is identified, it remains stationary in the sky to this accuracy. Other radio components in two of the four sources had detectable motion in the radio jet direction. Comparison of the 23 and 43 GHz VLBA images with the VLBA 8.6 GHz images and the ICRF positions suggests that some ICRF positions are dominated by a moving jet component; hence, they can be displaced up to 0.5 mas from the radio core and may also reflect the motion of the jet component. Future astrometric efforts to determine a more accurate quasar reference frame at 23 and 43 GHz and from the VLBI2010 project are discussed, and supporting VLBA or European VLBI Network observations of ICRF sources at 43 GHz are recommended in order to determine the internal structure of the sources. A future collaboration between the radio (ICRF) and the optical frame of GAIA is discussed.« less

Infrared Faint Radio Sources in the Extended Chandra Deep Field South

NASA Astrophysics Data System (ADS)

Huynh, Minh T.

2009-01-01

Infrared-Faint Radio Sources (IFRSs) are a class of radio objects found in the Australia Telescope Large Area Survey (ATLAS) which have no observable counterpart in the Spitzer Wide-area Infrared Extragalactic Survey (SWIRE). The extended Chandra Deep Field South now has even deeper Spitzer imaging (3.6 to 70 micron) from a number of Legacy surveys. We report the detections of two IFRS sources in IRAC images. The non-detection of two other IFRSs allows us to constrain the source type. Detailed modeling of the SED of these objects shows that they are consistent with high redshift AGN (z > 2).

Planck Early Results. XV. Spectral Energy Distributions and Radio Continuum Spectra of Northern Extragalactic Radio Sources

NASA Technical Reports Server (NTRS)

Aatrokoski, J.; Ade, P. A. R.; Aghanim, N.; Aller, H. D.; Aller, M. F.; Angelakis, E.; Amaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.;

Planck early results. XV. Spectral energy distributions and radio continuum spectra of northern extragalactic radio sources

DOE PAGES

Aatrokoski, J.

2011-12-01

Spectral energy distributions (SEDs) and radio continuum spectra are presented for a northern sample of 104 extragalactic radio sources, based on the Planck Early Release Compact Source Catalogue (ERCSC) and simultaneous multifrequency data. The nine Planck frequencies, from 30 to 857GHz, are complemented by a set of simultaneous observations ranging from radio to gamma-rays. This is the first extensive frequency coverage in the radio and millimetre domains for an essentially complete sample of extragalactic radio sources, and it shows how the individual shocks, each in their own phase of development, shape the radio spectra as they move in the relativisticmore » jet. The SEDs presented in this paper were fitted with second and third degree polynomials to estimate the frequencies of the synchrotron and inverse Compton (IC) peaks, and the spectral indices of low and high frequency radio data, including the Planck ERCSC data, were calculated. SED modelling methods are discussed, with an emphasis on proper, physical modelling of the synchrotron bump using multiple components. Planck ERCSC data also suggest that the original accelerated electron energy spectrum could be much harder than commonly thought, with power-law index around 1.5 instead of the canonical 2.5. The implications of this are discussed for the acceleration mechanisms effective in blazar shock. Furthermore in many cases the Planck data indicate that gamma-ray emission must originate in the same shocks that produce the radio emission.« less

The phylogeny of quasars and the ontogeny of their central black holes

NASA Astrophysics Data System (ADS)

Fraix-Burnet, Didier; Marziani, Paola; D'Onofrio, Mauro; Dultzin, Deborah

2017-02-01

The connection between multifrequency quasar observational and physical parameters related to accretion processes is still open to debate. In the last 20 year, Eigenvector 1-based approaches developed since the early papers by Boroson and Green (1992) and Sulentic et al. (2000b) have been proved to be a remarkably powerful tool to investigate this issue, and have led to the definition of a quasar "main sequence". In this paper we perform a cladistic analysis on two samples of 215 and 85 low-z quasars (z ~ 0.7) which were studied in several previous works and which offer a satisfactory coverage of the Eigenvector 1-derived main sequence. The data encompass accurate measurements of observational parameters which represents key aspects associated with the structural diversity of quasars. Cladistics is able to group sources radiating at higher Eddington ratios, as well as to separate radio-quiet (RQ) and radio-loud (RL) quasars. The analysis suggests a black hole mass threshold for powerful radio emission and also properly distinguishes core-dominated and lobe-dominated quasars, in accordance with the basic tenet of RL unification schemes. Considering that black hole mass provides a sort of "arrow of time" of nuclear activity, a phylogenetic interpretation becomes possible if cladistic trees are rooted on black hole mass: the ontogeny of black holes is represented by their monotonic increase in mass. More massive radio-quiet Population B sources at low-z become a more evolved counterpart of Population A i.e., wind dominated sources to which the "local" Narrow-Line Seyfert 1s belong.

EVN observations of eleven GHz-Peaked-Spectrum radio sources at 2.3/8.4 GHz

NASA Astrophysics Data System (ADS)

Xiang, L.; Dallacasa, D.; Cassaro, P.; Jiang, D.; Reynolds, C.

2005-04-01

We present results of EVN observations of eleven GHz-Peaked-Spectrum (GPS) radio sources at 2.3/8.4 GHz. These sources are from the classical "bright" GPS source samples with peak flux densities > 0.2 Jy and spectral indices α < -0.2 (S ∝ ν-α) in the optically thick regime of their convex spectra. Most of the target sources did not have VLBI images at the time this project started. The aim of the work is to find Compact Symmetric Object (CSO) candidates from the "bright" GPS samples. These CSOs play a key role in understanding the very early stage of the evolution of individual radio galaxies. The reason for investigating GPS source samples is that CSO candidates are more frequently found among this class of radio sources. In fact both classes, GPS and CSO, represent a small fraction of the flux limited and flat-spectrum samples like PR+CJ1 (PR: Pearson-Readhead survey, CJ1: the first Caltech-Jodrell Bank survey) and CJF (the Caltech-Jodrell Bank flat spectrum source survey) with a single digit percentage progressively decreasing with decreasing flux density limit. Our results, with at least 3, but possibly more CSO sources detected among a sample of 11, underline the effectiveness of our approach. The three confirmed CSO sources (1133+432, 1824+271, and 2121-014) are characterized by a symmetric pair of resolved components, each with steep spectral indices. Five further sources (0144+209, 0554-026, 0904+039, 0914+114 and 2322-040) can be considered likely CSO candidates. The remaining three sources (0159+839, 0602+780 and 0802+212) are either of core-jet type or dominated by a single component at both frequencies.

Fast radio burst discovered in the Arecibo pulsar ALFA survey

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

Spitler, L. G.; Freire, P. C. C.; Lazarus, P.

Recent work has exploited pulsar survey data to identify temporally isolated, millisecond-duration radio bursts with large dispersion measures (DMs). These bursts have been interpreted as arising from a population of extragalactic sources, in which case they would provide unprecedented opportunities for probing the intergalactic medium; they may also be linked to new source classes. Until now, however, all so-called fast radio bursts (FRBs) have been detected with the Parkes radio telescope and its 13-beam receiver, casting some concern about the astrophysical nature of these signals. Here we present FRB 121102, the first FRB discovery from a geographic location other thanmore » Parkes. FRB 121102 was found in the Galactic anti-center region in the 1.4 GHz Pulsar Arecibo L-band Feed Array (ALFA) survey with the Arecibo Observatory with a DM = 557.4 ± 2.0 pc cm{sup –3}, pulse width of 3.0 ± 0.5 ms, and no evidence of interstellar scattering. The observed delay of the signal arrival time with frequency agrees precisely with the expectation of dispersion through an ionized medium. Despite its low Galactic latitude (b = –0.°2), the burst has three times the maximum Galactic DM expected along this particular line of sight, suggesting an extragalactic origin. A peculiar aspect of the signal is an inverted spectrum; we interpret this as a consequence of being detected in a sidelobe of the ALFA receiver. FRB 121102's brightness, duration, and the inferred event rate are all consistent with the properties of the previously detected Parkes bursts.« less

The Gould's Belt very large array survey. III. The Orion region

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

Kounkel, Marina; Hartmann, Lee; Loinard, Laurent

2014-07-20

We present results from a high-sensitivity (60 μJy), large-scale (2.26 deg{sup 2}) survey obtained with the Karl G. Jansky Very Large Array as part of the Gould's Belt Survey program. We detected 374 and 354 sources at 4.5 and 7.5 GHz, respectively. Of these, 148 are associated with previously known young stellar objects (YSOs). Another 86 sources previously unclassified at either optical or infrared wavelengths exhibit radio properties that are consistent with those of young stars. The overall properties of our sources at radio wavelengths such as their variability and radio to X-ray luminosity relation are consistent with previous resultsmore » from the Gould's Belt Survey. Our detections provide target lists for follow-up Very Long Baseline Array radio observations to determine their distances as YSOs are located in regions of high nebulosity and extinction, making it difficult to measure optical parallaxes.« less

The Gould's Belt Very Large Array Survey. III. The Orion Region

NASA Astrophysics Data System (ADS)

Kounkel, Marina; Hartmann, Lee; Loinard, Laurent; Mioduszewski, Amy J.; Dzib, Sergio A.; Ortiz-León, Gisela N.; Rodríguez, Luis F.; Pech, Gerardo; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Evans, Neal J., II; Briceño, Cesar; Tobin, John

2014-07-01

We present results from a high-sensitivity (60 μJy), large-scale (2.26 deg2) survey obtained with the Karl G. Jansky Very Large Array as part of the Gould's Belt Survey program. We detected 374 and 354 sources at 4.5 and 7.5 GHz, respectively. Of these, 148 are associated with previously known young stellar objects (YSOs). Another 86 sources previously unclassified at either optical or infrared wavelengths exhibit radio properties that are consistent with those of young stars. The overall properties of our sources at radio wavelengths such as their variability and radio to X-ray luminosity relation are consistent with previous results from the Gould's Belt Survey. Our detections provide target lists for follow-up Very Long Baseline Array radio observations to determine their distances as YSOs are located in regions of high nebulosity and extinction, making it difficult to measure optical parallaxes.

ASCA Observations of W44

NASA Technical Reports Server (NTRS)

Hughes, John P.

1999-01-01

We report the detection, using data from the Advanced Satellite for Cosmology and Astrophysics (ASCA), of a hard X-ray source in the vicinity of the radio pulsar PSR B1853+01, which is located within the supernova remnant (SNR) W44. PSR B1853+01, a 267 ms pulsar, has to date been detected only in the radio band. Previous observations at soft X-ray energies (e.g., with ROSAT HRI) have failed to detect any significant X-ray emission (pulsed or unpulsed) from the pulsar. In addition, no high-energy emission (approx. > 4 keV) has been detected previously from W44. Over the 0.5-4.0 keV band, the ASCA data show soft thermal emission from W44, with a morphology very similar to that observed earlier by Einstein and ROSAT. In the high-energy band (4.0-9.5 keV), the SNR is, for the most part, invisible, although a source coincident with the position of PSR B1853+01 is evident. The observed ASCA spectra are consistent with a power-law origin (photon index approx. 2.3) for the X-ray emission from this source at a flux level (flux density approx. 0.5 micro Jy at I keV) consistent with previous upper limits. The maximum allowed size for the source is determined directiv from the ASCA data (<5 min.), while the minimum size is derived from the nondetection of a point source in the ROSAT HRI data (approx. > 30 sec.). Timing analysis of the hard X-ray source failed to detect pulsations at the pulsar's period. Based on these lines of evidence, we conclude that the new hard source in W44 represents an X-ray synchrotron nebula associated with PSR B1853+01, rather than the beamed output of the pulsar itself. This discoverv adds W44 to the small group of previously known plerionic SNRs This nebula lies at the low end of, but is consistent with, the correlation between X-ray luminosity and pulsar spin-down energy loss found for such objects, lending further support to our interpretation.

A Measurement of the Millimeter Emission and the Sunyaev-zel'dovich Effect Associated with Low-frequency Radio Sources

NASA Technical Reports Server (NTRS)

Gralla, Megan B.; Crichton, Devin; Marriage, Tobias A.; Mo, Wenli; Aguirre, Paula; Addison, Graeme E.; Asboth, V.; Battaglia, Nick; Bock, James; Bond, J. Richard;

Radio outbursts in extragalactic sources

NASA Astrophysics Data System (ADS)

Kinzel, Wayne Morris

Three aspects of the flux density variability of extragalactic radio sources were examined: millimeter wavelength short timescale variability, the spectral evolution of outbursts, and whether the outbursts are periodically spaced. Observations of extragalactic radio sources were conducted using the Five College Radio Astronomy Observatory between January and June 1985 at 88.2 GHz and during June and July 1985 at 40.0 GHz. Many of the sources exhibited significant flux density variations during the observing span. In addition, the most rapid variations observed were comparable with those reported in previous works. Two sources, 0355+50 and OJ287, both exhibited outbursts whose rise and fall timescales were less than a month. An anomalous flux density dropout was observed in 3C446 and was interpreted as an occultation event. Data at five frequencies between 2.7 and 89.6 GHz from the Dent-Balonek monitoring program were used to investigate the spectral evolution of eight outbursts. Outburst profile fitting was used to deconvolve the individual outbursts from one another at each frequency. The fit profiles were used to generate multiple epoch spectra to investigate the evolution of the outbursts. A phase residual minimization method was used to examine four sources for periodic behavior.

Three millisecond pulsars in FERMI LAT unassociated bright sources

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

Ransom, S. M.; Ray, P. S.; Camilo, F.

2010-12-23

We searched for radio pulsars in 25 of the non-variable, unassociated sources in the Fermi LAT Bright Source List with the Green Bank Telescope at 820 MHz. Here, we report the discovery of three radio and γ-ray millisecond pulsars (MSPs) from a high Galactic latitude subset of these sources. All of the pulsars are in binary systems, which would have made them virtually impossible to detect in blind γ-ray pulsation searches. They seem to be relatively normal, nearby (≤2 kpc) MSPs. These observations, in combination with the Fermi detection of γ-rays from other known radio MSPs, imply that most, ifmore » not all, radio MSPs are efficient γ-ray producers. The γ-ray spectra of the pulsars are power law in nature with exponential cutoffs at a few GeV, as has been found with most other pulsars. The MSPs have all been detected as X-ray point sources. Finally, their soft X-ray luminosities of ~10 30-10 31 erg s –1 are typical of the rare radio MSPs seen in X-rays.« less

Three Millisecond Pulsars in Fermi LAT Unassociated Bright Sources

NASA Technical Reports Server (NTRS)

Ransom, S. M.; Ray, P. S.; Camilo, F.; Roberts, M. S. E.; Celik, O.; Wolff, M. T.; Cheung, C. C.; Kerr, M.; Pennucci, T.; DeCesar, M. E.;

Identification and properties of host galaxies of RCR radio sources

NASA Astrophysics Data System (ADS)

Zhelenkova, O. P.; Soboleva, N. S.; Majorova, E. K.; Temirova, A. V.

2013-01-01

FIRST and NVSS radio maps are used to cross identify the radio sources of the RCR catalog, which is based on observational data obtained in several runs of the "Cold" survey, with the SDSS and DPOSS digital optical sky surveys and the 2MASS, LAS UKIDSS, and WISE infrared surveys. Digital images in various filters and the coadded gri-band SDSS images, red and infrared DPOSS images, JHK-band UKIDSS images, and JHK-band 2MASS images are analyzed for the sources with no optical candidates found in the above catalogs. Our choice of optical candidates was based on the data on the structure of the radio source, its photometry, and spectroscopy (where available). We found reliable identifications for 86% of the radio sources; possible counterparts for 8% of the sources, and failed to find any optical counterparts for 6% of the sources because their host objects proved to be fainter than the limiting magnitude of the corresponding surveys. A little over half of all the identifications proved to be galaxies; about one quarter were quasars, and the types of the remaining objects were difficult to determine because of their faintness. A relation between the luminosity and the radioloudness index was derived and used to estimate the 1.4 and 3.94 GHz luminosities for the sources with unknown redshifts. We found 3% and 60% of all the RCR radio sources to be FRI-type objects ( L ≲ 1024 W/Hz at 1.4 GHz) and powerful FRII-type galaxies ( L ≳ 1026.5 W/Hz), respectively, whereas the rest are sources including objects of the FRI, FRII, and mixed FRI-FRII types. Unlike quasars, galaxies show a trend of decreasing luminosity with decreasing flux density. Note that identification would be quite problematic without the software and resources of the virtual observatory.

Molecular basis of 'hypoxic' breast cancer cell radio-sensitization: phytochemicals converge on radiation induced Rel signaling.

PubMed

Aravindan, Sheeja; Natarajan, Mohan; Herman, Terence S; Awasthi, Vibhudutta; Aravindan, Natarajan

2013-03-04

Heterogeneously distributed hypoxic areas are a characteristic property of locally advanced breast cancers (BCa) and generally associated with therapeutic resistance, metastases, and poor patient survival. About 50% of locally advanced BCa, where radiotherapy is less effective are suggested to be due to hypoxic regions. In this study, we investigated the potential of bioactive phytochemicals in radio-sensitizing hypoxic BCa cells. Hypoxic (O2-2.5%; N2-92.5%; CO2-5%) MCF-7 cells were exposed to 4 Gy radiation (IR) alone or after pretreatment with Curcumin (CUR), curcumin analog EF24, neem leaf extract (NLE), Genistein (GEN), Resveratrol (RES) or raspberry extract (RSE). The cells were examined for inhibition of NFκB activity, transcriptional modulation of 88 NFκB signaling pathway genes, activation and cellular localization of radio-responsive NFκB related mediators, eNos, Erk1/2, SOD2, Akt1/2/3, p50, p65, pIκBα, TNFα, Birc-1, -2, -5 and associated induction of cell death. EMSA revealed that cells exposed to phytochemicals showed complete suppression of IR-induced NFκB. Relatively, cells exposed EF24 revealed a robust inhibition of IR-induced NFκB. QPCR profiling showed induced expression of 53 NFκB signaling pathway genes after IR. Conversely, 53, 50, 53, 53, 53 and 53 of IR-induced genes were inhibited with EF24, NLE, CUR, GEN, RES and RSE respectively. In addition, 25, 29, 24, 16, 11 and 21 of 35 IR-suppressed genes were further inhibited with EF24, NLE, CUR, GEN, RES and RSE respectively. Immunoblotting revealed a significant attenuating effect of IR-modulated radio-responsive eNos, Erk1/2, SOD2, Akt1/2/3, p50, p65, pIκBα, TNFα, Birc-1, -2 and -5 with EF24, NLE, CUR, GEN, RES or RSE. Annexin V-FITC staining showed a consistent and significant induction of IR-induced cell death with these phytochemicals. Notably, EF24 robustly conferred IR-induced cell death. Together, these data identifies the potential hypoxic cell radio-sensitizers and further implies that the induced radio-sensitization may be exerted by selectively targeting IR-induced NFκB signaling.

A multiparametric analysis of the Einstein sample of early-type galaxies. 1: Luminosity and ISM parameters

NASA Technical Reports Server (NTRS)

Eskridge, Paul B.; Fabbiano, Giuseppina; Kim, Dong-Woo

1995-01-01

We have conducted bivariate and multivariate statistical analysis of data measuring the luminosity and interstellar medium of the Einstein sample of early-type galaxies (presented by Fabbiano, Kim, & Trinchieri 1992). We find a strong nonlinear correlation between L(sub B) and L(sub X), with a power-law slope of 1.8 +/- 0.1, steepening to 2.0 +/- if we do not consider the Local Group dwarf galaxies M32 and NGC 205. Considering only galaxies with log L(sub X) less than or equal to 40.5, we instead find a slope of 1.0 +/- 0.2 (with or without the Local Group dwarfs). Although E and S0 galaxies have consistent slopes for their L(sub B)-L(sub X) relationships, the mean values of the distribution functions of both L(sub X) and L(sub X)/L(sub B) for the S0 galaxies are lower than those for the E galaxies at the 2.8 sigma and 3.5 sigma levels, respectively. We find clear evidence for a correlation between L(sub X) and the X-ray color C(sub 21), defined by Kim, Fabbiano, & Trinchieri (1992b), which indicates that X-ray luminosity is correlated with the spectral shape below 1 keV in the sense that low-L(sub X) systems have relatively large contributions from a soft component compared with high-L(sub X) systems. We find evidence from our analysis of the 12 micron IRAS data for our sample that our S0 sample has excess 12 micron emission compared with the E sample, scaled by their optical luminosities. This may be due to emission from dust heated in star-forming regions in S0 disks. This interpretation is reinforced by the existence of a strong L(sub 12)-L(sub 100) correlation for our S0 sample that is not found for the E galaxies, and by an analysis of optical-IR colors. We find steep slopes for power-law relationships between radio luminosity and optical, X-ray, and far-IR (FIR) properties. This last point argues that the presence of an FIR-emitting interstellar medium (ISM) in early-type galaxies is coupled to their ability to generate nonthermal radio continuum, as previously argued by, e.g., Walsh et al. (1989). We also find that, for a given L(sub 100), galaxies with larger L(sub X)/L(sub B) tend to be stronger nonthermal radio sources, as originally suggested by Kim & Fabbiano (1990). We note that, while L(sub B) is most strongly correlated with L(sub 6), the total radio luminosity, both L(sub X) and L(sub X)/L(sub B) are more strongly correlated with L(sub 6 CO), the core radio luminosity. These points support the argument (proposed by Fabbiano, Gioia, & Trinchieri 1989) that radio cores in early-type galaxies are fueled by the hot ISM.

Do solar decimetric spikes originate in coronal X-ray sources?

NASA Astrophysics Data System (ADS)

Battaglia, M.; Benz, A. O.

2009-06-01

Context: In the standard solar flare scenario, a large number of particles are accelerated in the corona. Nonthermal electrons emit both X-rays and radio waves. Thus, correlated signatures of the acceleration process are predicted at both wavelengths, coinciding either close to the footpoints of a magnetic loop or near the coronal X-ray source. Aims: We attempt to study the spatial connection between coronal X-ray emission and decimetric radio spikes to determine the site and geometry of the acceleration process. Methods: The positions of radio-spike sources and coronal X-ray sources are determined and analyzed in a well-observed limb event. Radio spikes are identified in observations from the Phoenix-2 spectrometer. Data from the Nançay radioheliograph are used to determine the position of the radio spikes. RHESSI images in soft and hard X-ray wavelengths are used to determine the X-ray flare geometry. Those observations are complemented by images from GOES/SXI. Results: We find that the radio emission originates at altitudes much higher than the coronal X-ray source, having an offset from the coronal X-ray source amounting to 90´´ and to 113´´ and 131´´ from the two footpoints, averaged over time and frequency. Conclusions: Decimetric spikes do not originate from coronal X-ray flare sources contrary to previous expectations. However, the observations suggest a causal link between the coronal X-ray source, related to the major energy release site, and simultaneous activity in the higher corona.

Addressing the changing sources of health information in iran.

PubMed

Alishahi-Tabriz, Amir; Sohrabi, Mohammad-Reza; Kiapour, Nazanin; Faramarzi, Nina

2013-01-01

Following the entrance of new technologies in health information era, this study aimed to assess changes in health information sources of Iranian people during past decade. Totally 3000 people were asked about their main sources of health information. They were selected as two community-based samples of 1500 people of more than 18-years-old in two different periods of time in August 2002 and August 2010 from the same locations in Tehran, the capital of Iran. Data analyzed based on age group, sex, educational level and household income in two different periods of time using Chi-square. Odds ratios associated with each basic characteristic were calculated using logistic regression. Most common sources of health information in 2002 were radio and television (17.7%), caregivers (14.9%) and internet (14.2%) and in 2010 were radio and television (19.3%), internet (19.3%) and caregivers (15.8%) (P < 0.001). In 2010, young adults female used television and radio and male used internet as the main source of health information (P = 0.003). In moderate educational level women got their health information from radio and television and caregivers; while men used radio and television and internet as main source of health information (P = 0.005). Highly educated women and men mainly got their health information from internet and radio and television (P > 0.05). Although during 8 years of study radio and television remained as main source of health information but there is an increasing tendency to use internet especially in men. Policymakers should revise their broadcasting strategies based on people demand.

The Nature of Radio Emission from Distant Galaxies: The 1.4 GHZ Observations

NASA Astrophysics Data System (ADS)

Richards, E. A.

2000-04-01

We have conducted a deep radio survey with the Very Large Array at 1.4 GHz of a region containing the Hubble Deep Field (HDF). This survey overlaps previous observations at 8.5 GHz allowing us to investigate the radio spectral properties of microjansky sources to flux densities greater than 40 μJy at 1.4 GHz and greater than 8 μJy at 8.5 GHz. A total of 371 sources have been cataloged at 1.4 GHz as part of a complete sample within 20' of the HDF. The differential source count for this region is only marginally sub-Euclidean and is given by n(S)=(8.3+/-0.4)S-2.4+/-0.1 sr-1 Jy-1. Above about 100 μJy the radio source count is systematically lower in the HDF as compared to other fields. We conclude that there is clustering in our radio sample on size scales of 1'-40'. The 1.4 GHz-selected sample shows that the radio spectral indices are preferentially steep (α1.4=0.85) and that the sources are moderately extended with average angular size θ=1.8". Optical identification with disk-type systems at z~0.1-1 suggests that synchrotron emission, produced by supernovae remnants, is powering the radio emission in the majority of sources. The 8.5 GHz sample contains primarily moderately flat spectrum sources (α8.5=0.35), with less than 15% inverted. We argue that we may be observing an increased fraction of optically thin bremsstrahlung over synchrotron radiation in these distant star-forming galaxies.

The TexOx-1000 redshift survey of radio sources I: the TOOT00 region

NASA Astrophysics Data System (ADS)

Vardoulaki, Eleni; Rawlings, Steve; Hill, Gary J.; Mauch, Tom; Inskip, Katherine J.; Riley, Julia; Brand, Kate; Croft, Steve; Willott, Chris J.

2010-01-01

We present optical spectroscopy, near-infrared (mostly K-band) and radio (151-MHz and 1.4-GHz) imaging of the first complete region (TOOT00) of the TexOx-1000 (TOOT) redshift survey of radio sources. The 0.0015-sr (~5 deg2) TOOT00 region is selected from pointed observations of the Cambridge Low-Frequency Survey Telescope at 151 MHz at a flux density limit of ~=100 mJy, approximately five times fainter than the 7C Redshift Survey (7CRS), and contains 47 radio sources. We have obtained 40 spectroscopic redshifts (~85 per cent completeness). Adding redshifts estimated for the seven other cases yields a median redshift zmed ~ 1.25. We find a significant population of objects with Fanaroff-Riley type I (FRI) like radio structures at radio luminosities above both the low-redshift FRI/II break and the break in the radio luminosity function. The redshift distribution and subpopulations of TOOT00 are broadly consistent with extrapolations from the 7CRS/6CE/3CRR data sets underlying the SKADS Simulated Skies Semi-Empirical Extragalactic Data base, S3-SEX.

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

PubMed

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

2005-04-28

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

The Southern HII Region Discovery Survey: Preliminary Results

NASA Astrophysics Data System (ADS)

Shea, Jeanine; Wenger, Trey; Balser, Dana S.; Anderson, Loren D.; Armentrout, William P.; Bania, Thomas M.; Dawson, Joanne; Miller Dickey, John; Jordan, Christopher; McClure-Griffiths, Naomi M.

2017-01-01

HII regions are some of the brightest sources at radio frequencies in the Milky Way and are the sites of massive O and B-type star formation. They have relatively short (< 10 Myr) lifetimes compared to other Galactic objects and therefore reveal information about spiral structure and the chemical evolution of the Galaxy. The HII Region Discovery Surveys (HRDS) discovered about 800 new HII regions in the Galactic longitude range -20 degrees to 270 degrees using primarily the Green Bank Telescope. Candidate HII regions were selected from mid-infrared emission coincident with radio continuum emission, and confirmed as HII regions by the detection of radio recombination lines. Here we discuss the Southern HII Region Discovery Survey (SHRDS), a continuation of the HRDS using the Australia Telescope Compact Array over the Galactic longitude range 230 to 360 degrees. We have reduced and analyzed a small sub-set of the SHRDS sources and discuss preliminary results, including kinematic distances and metallicities.

Testing the Triggering Mechanism for Luminous, Radio-Quiet Red Quasars in the Clearing Phase: A Comparison to Radio-Loud Red Quasars

NASA Astrophysics Data System (ADS)

Glikman, Eliat

2016-10-01

We propose to conduct a controlled study of the relationship between radio emission and host galaxy morphology for a new sample of radio-quiet dust-reddened quasars selected by their infrared colors in WISE and 2MASS (W2M). These sources are the radio-quiet analogs to the FIRST-2MASS (F2M) red quasars, which we found to be predominantly driven by major mergers. F2M red quasars are accreting at very high rates and exhibit broad absorption lines associated with outflows and feedback. Their properties are consistent with buried quasars expelling their dusty shrouds in an an evolutionary phase predicted by merger-driven co-evolution models. The quasars in both samples are the most intrinsically luminous objects in the Universe - the regime where we expect mergers to dominate. However, recent lines of evidence suggest that radio emission may be linked to AGN reddening and merging hosts. We will use WFC3/IR and ACS to image the host galaxies of W2M quasars in the two redshift regimes that our previous studies probed, z 0.7 and z 2, testing the merger-driven quasar paradigm across the full radio range with a minimum of selection effects or other biases that plague many studies comparing different samples. The images proposed here will sample the host galaxies in rest-frame visible and UV light to look for merger signatures. Evidence for mergers in these quasar hosts would support a picture in which luminous quasars and galaxies co-evolve through major-mergers, independent of their radio properties. The absence of mergers in our data would link radio emission to mergers and require an alternate explanation for the extreme properties of these radio-quiet sources.

Growth of magnesium diboride films on 2 inch diameter copper discs by hybrid physical–chemical vapor deposition

DOE PAGES

Withanage, Wenura K.; Xi, X. X.; Nassiri, Alireza; ...

2017-02-16

Here, magnesium diboride (MgB 2) coating is a potential candidate to replace bulk niobium (Nb) for superconducting radio frequency cavities due to the appealing superconducting properties of MgB 2. MgB 2 coating on copper may allow cavity operation near 20–25 K as a result of the high transition temperature (T c) of MgB 2 and excellent thermal conductivity of Cu. We have grown MgB 2 films on 2 inch diameter Cu discs by hybrid physical–chemical vapor deposition for radio frequency characterization. Structural and elemental analyses showed a uniform MgB 2 coating on top of a Mg–Cu alloy layer with occasionalmore » intrusion of Mg–Cu alloy regions. High T c values of around 37 K and high critical current density (J c) on the order of 107 A cm –2 at zero field were observed. Radio frequency measurements at 11.4 GHz confirmed a high T c and showed a quality factor (Q 0) much higher than for Cu and close to that of Nb.« less

Growth of magnesium diboride films on 2 inch diameter copper discs by hybrid physical–chemical vapor deposition

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

Withanage, Wenura K.; Xi, X. X.; Nassiri, Alireza

Here, magnesium diboride (MgB 2) coating is a potential candidate to replace bulk niobium (Nb) for superconducting radio frequency cavities due to the appealing superconducting properties of MgB 2. MgB 2 coating on copper may allow cavity operation near 20–25 K as a result of the high transition temperature (T c) of MgB 2 and excellent thermal conductivity of Cu. We have grown MgB 2 films on 2 inch diameter Cu discs by hybrid physical–chemical vapor deposition for radio frequency characterization. Structural and elemental analyses showed a uniform MgB 2 coating on top of a Mg–Cu alloy layer with occasionalmore » intrusion of Mg–Cu alloy regions. High T c values of around 37 K and high critical current density (J c) on the order of 107 A cm –2 at zero field were observed. Radio frequency measurements at 11.4 GHz confirmed a high T c and showed a quality factor (Q 0) much higher than for Cu and close to that of Nb.« less

Growth of magnesium diboride films on 2 inch diameter copper discs by hybrid physical–chemical vapor deposition

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

Withanage, Wenura K.; Xi, X. X.; Nassiri, Alireza

Magnesium diboride (MgB2) coating is a potential candidate to replace bulk niobium (Nb) for superconducting radio frequency cavities due to the appealing superconducting properties of MgB2. MgB2 coating on copper may allow cavity operation near 20–25 K as a result of the high transition temperature (T c) of MgB2 and excellent thermal conductivity of Cu. We have grown MgB2 films on 2 inch diameter Cu discs by hybrid physical–chemical vapor deposition for radio frequency characterization. Structural and elemental analyses showed a uniform MgB2 coating on top of a Mg–Cu alloy layer with occasional intrusion of Mg–Cu alloy regions. High Tmore » c values of around 37 K and high critical current density (J c) on the order of 107 A cm-2 at zero field were observed. Radio frequency measurements at 11.4 GHz confirmed a high T c and showed a quality factor (Q 0) much higher than for Cu and close to that of Nb.« less

The Physics of Cooling Flow Clusters with Central Radio Sources

NASA Technical Reports Server (NTRS)

Sarazin, Craig L.

2005-01-01

Central galaxies in rich clusters are the sites of cluster cooling flows, with large masses of gas cooling through part of the X-ray band. Many of these galaxies host powerful radio sources. These sources can displace and compress the X-ray gas leading to enhanced cooling and star formation. We observed the bright cooling flow Abell 2626 with a strangely distorted central radio source. We wished to understand the interaction of radio and X-ray thermal plasma, and to determine the dynamical nature of this cluster. One aim was to constrain the source of additional pressure in radio "holes" in the X-ray emission needed to support overlying shells of X-ray gas. We also aimed to study the problem of the lack of kT < 1-2 keV gas in cooling flows by searching for abundance inhomogeneities, heating from the radio source, and excess absorption. We also have a Chandra observation of this cluster. There were problems with the pipeline processing of this data due to a telemetry dropout. We are publishing the Chandra and XMM data together. Delays with the Chandra data have slowed up the publication. At the center of the cluster, there is a complex interaction of the odd, Z-shaped radio source, and the X-ray plasma. However, there are no clear radio bubbles. Also, the cluster SO galaxy IC 5337, which is projected 1.5 arcmin west of the cluster center, has unusual tail-like structures in both the radio and X-ray. It appears to be falling into the cluster center. There is a hot, probably shocked region of gas to the southwest, which is apparently due to the merger of a subcluster in this part of the system. There is also a merging subcluster to the northeast. The axes of these two mergers agrees with a supercluster filament structure.

Radio polarization properties of quasars and active galaxies at high redshifts

NASA Astrophysics Data System (ADS)

Vernstrom, T.; Gaensler, B. M.; Vacca, V.; Farnes, J. S.; Haverkorn, M.; O'Sullivan, S. P.

2018-04-01

We present the largest ever sample of radio polarization properties for z > 4 sources, with 14 sources having significant polarization detections. Using wide-band data from the Karl G. Jansky Very Large Array, we obtained the rest-frame total intensity and polarization properties of 37 radio sources, nine of which have spectroscopic redshifts in the range 1 ≤ z ≤ 1.4, with the other 28 having spectroscopic redshifts in the range 3.5 ≤ z ≤ 6.21. Fits are performed for the Stokes I and fractional polarization spectra, and Faraday rotation measures are derived using rotation measure synthesis and QU fitting. Using archival data of 476 polarized sources, we compare high-redshift (z > 3) source properties to a 15 GHz rest-frame luminosity matched sample of low-redshift (z < 3) sources to investigate if the polarization properties of radio sources at high redshifts are intrinsically different than those at low redshift. We find a mean of the rotation measure absolute values, corrected for Galactic rotation, of 50 ± 22 rad m-2 for z > 3 sources and 57 ± 4 rad m-2 for z < 3. Although there is some indication of lower intrinsic rotation measures at high-z possibly due to higher depolarization from the high-density environments, using several statistical tests we detect no significant difference between low- and high-redshift sources. Larger samples are necessary to determine any true physical difference.

Search for the Identification of 3EG J1835+5918: Evidence for a New Type of High-Energy Gamma-Ray Source?

NASA Technical Reports Server (NTRS)

Mirabal, N.; Halpern, Jules P.; Eracleous, M.; Becker, R. H.; Oliversen, Ronald (Technical Monitor)

2001-01-01

Most of the EGRET high-energy gamma-ray sources remain unidentified. It is highly likely that many of these are fainter blazars or pulsars, but there may also be new types of sources to be discovered. We have focussed our search for novel gamma-ray sources on 3EG 1835+5918, which is the brightest and most accurately positioned of the unidentified EGRET sources at high Galactic latitude (l, b = 89 deg, 25 deg). In this talk, we will summarize the results of X-ray, radio, and optical surveys of this location. In particular, we have made complete optical identifications of all of the ROSAT and ASCA sources in this region to a flux limit of approximately 1 x 10(exp -13) ergs/sq cm s. All of the X-ray sources within the EGRET error circle are radio-quiet quasars or coronally emitting stars. Previous radio pulsar searches have been unsuccessful. We set an upper limit of 3.8 mJy (at 1.4 GHz) on any possible radio counterpart to 3EG 1835+5918. We also find several quasars and white dwarfs using optical color selection, and we have monitored the entire field for variable optical objects on short and long time scales. Since no blazar-like or pulsar-like candidate has been found as a result of these searches, we assert that 3EG 1835+5918 must be lacking in one or more of the physically essential attributes of those classes of gamma-ray emitters. In particular, its radio flux is at least two orders of magnitude fainter than any of the securely identified EGRET blazars, and its soft X-ray flux is at least 30 times fainter than that of Geminga and other EGRET pulsars. If it is an AGN it lacks the beamed radio emission of blazars. If it is an isolated neutron star, it lacks both the thermal X-rays from a cooling surface and the magnetospheric non-thermal X-ray emission that is characteristic of all EGRET pulsars. As such, it is more problematic physically than Geminga, which is an ordinary pulsar that only lacks radio emission. As a pulsar, 3EG 1835+5918 would have to be either older or more distant than Geminga, and probably an even more efficient gamma-ray engine.

THE SECOND CATALOG OF ACTIVE GALACTIC NUCLEI DETECTED BY THE FERMI LARGE AREA TELESCOPE

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

Ackermann, M.; Ajello, M.; Allafort, A.

The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The second LAT AGN catalog (2LAC) includes 1017 {gamma}-ray sources located at high Galactic latitudes (|b| > 10 Degree-Sign ) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However, some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently, we define a Clean Sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lac objects), 310 flat-spectrum radio quasars (FSRQs), 157more » candidate blazars of unknown type (i.e., with broadband blazar characteristics but with no optical spectral measurement yet), 8 misaligned AGNs, 4 narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types, and 2 starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency <10{sup 14} Hz, about half of the BL Lac objects have a synchrotron-peak frequency >10{sup 15} Hz. The 2LAC represents a significant improvement relative to the first LAT AGN catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broadband data. Various properties, such as {gamma}-ray fluxes and photon power-law spectral indices, redshifts, {gamma}-ray luminosities, variability, and archival radio luminosities and their correlations are presented and discussed for the different blazar classes. The general trends observed in 1LAC are confirmed.« less

BROADBAND RADIO POLARIMETRY AND FARADAY ROTATION OF 563 EXTRAGALACTIC RADIO SOURCES

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

Anderson, C. S.; Gaensler, B. M.; Feain, I. J.

2015-12-10

We present a broadband spectropolarimetric survey of 563 discrete, mostly unresolved radio sources between 1.3 and 2.0 GHz using data taken with the Australia Telescope Compact Array. We have used rotation-measure synthesis to identify Faraday-complex polarized sources, those objects whose frequency-dependent polarization behavior indicates the presence of material possessing complicated magnetoionic structure along the line of sight (LOS). For sources classified as Faraday-complex, we have analyzed a number of their radio and multiwavelength properties to determine whether they differ from Faraday-simple polarized sources (sources for which LOS magnetoionic structures are comparatively simple) in these properties. We use this information tomore » constrain the physical nature of the magnetoionic structures responsible for generating the observed complexity. We detect Faraday complexity in 12% of polarized sources at ∼1′ resolution, but we demonstrate that underlying signal-to-noise limitations mean the true percentage is likely to be significantly higher in the polarized radio source population. We find that the properties of Faraday-complex objects are diverse, but that complexity is most often associated with depolarization of extended radio sources possessing a relatively steep total intensity spectrum. We find an association between Faraday complexity and LOS structure in the Galactic interstellar medium (ISM) and claim that a significant proportion of the Faraday complexity we observe may be generated at interfaces of the ISM associated with ionization fronts near neutral hydrogen structures. Galaxy cluster environments and internally generated Faraday complexity provide possible alternative explanations in some cases.« less

The Gould’s Belt Very Large Array Survey. V. The Perseus Region

NASA Astrophysics Data System (ADS)

Pech, Gerardo; Loinard, Laurent; Dzib, Sergio A.; Mioduszewski, Amy J.; Rodríguez, Luis F.; Ortiz-León, Gisela N.; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Hartman, Lee; Kounkel, Marina A.; Evans, Neal J., II; Briceño, Cesar; Tobin, John; Zapata, Luis A.

2016-02-01

We present multiepoch, large-scale (˜2000 arcmin2), fairly deep (˜16 μJy), high-resolution (˜1″) radio observations of the Perseus star-forming complex obtained with the Karl G. Jansky Very Large Array at frequencies of 4.5 and 7.5 GHz. These observations were mainly focused on the clouds NGC 1333 and IC 348, although we also observed several fields in other parts of the Perseus complex. We detect a total of 206 sources, 42 of which are associated with young stellar objects (YSOs). The radio properties of about 60% of the YSOs are compatible with a nonthermal radio emission origin. Based on our sample, we find a fairly clear relation between the prevalence of nonthermal radio emission and evolutionary status of the YSOs. By comparing our results with previously reported X-ray observations, we show that YSOs in Perseus follow a Güdel-Benz relation with κ = 0.03, consistent with other regions of star formation. We argue that most of the sources detected in our observations but not associated with known YSOs are extragalactic, but provide a list of 20 unidentified radio sources whose radio properties are consistent with being YSO candidates. Finally, we also detect five sources with extended emission features that can clearly be associated with radio galaxies.

INTERSTELLAR SCINTILLATION AND THE RADIO COUNTERPART OF THE FAST RADIO BURST FRB 150418

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

Akiyama, Kazunori; Johnson, Michael D., E-mail: kazu@haystack.mit.edu

Keane et al. have recently reported the discovery of a new fast radio burst (FRB), FRB 150418, with a promising radio counterpart at 5.5 and 7.5 GHz—a rapidly decaying source, falling from 200–300 μ Jy to 100 μ Jy on timescales of ∼6 days. This transient source may be associated with an elliptical galaxy at redshift z = 0.492, providing the first firm spectroscopic redshift for an FRB and the ability to estimate the density of baryons in the intergalactic medium via the combination of known redshift and radio dispersion of the FRB. An alternative explanation, first suggested by Williamsmore » and Berger, is that the identified counterpart may instead be a compact active galactic nucleus (AGN). The putative counterpart’s variation may then instead be extrinsic, caused by refractive scintillation in the ionized interstellar medium of the Milky Way, which would invalidate the association with FRB 150418. We examine this latter explanation in detail and show that the reported observations are consistent with scintillating radio emission from the core of a radio-loud AGN having a brightness temperature T {sub b} ≳ 10{sup 9} K. Using numerical simulations of the expected scattering for the line of sight to FRB 150418, we provide example images and light curves of such an AGN at 5.5 and 7.5 GHz. These results can be compared with continued radio monitoring to conclusively determine the importance of scintillation for the observed radio variability, and they show that scintillation is a critical consideration for continued searches for FRB counterparts at radio wavelengths.« less

Radio pulsar death lines to SGRs/AXPs and white dwarfs pulsars

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

Lobato, Ronaldo V.; Malheiro, M.; Coelho, J. G.

Recently, an alternative model based on white dwarfs pulsars has been proposed to explain a class of pulsars known as Soft Gamma Repeaters (SGR) and Anomalus X-Ray Pulsars (AXP) [1], usually named as magnetars. In this model, the magnetized white dwarfs can have surface magnetic field B ∼ 10{sup 7} − 10{sup 10} G and rotate very fast with angular frequencies Ω ∼ 1 rad/s, allowing them to produce large electromagnetic (EM) potentials and generate electron-positron pairs. These EM potentials are comparable with the ones of neutron star pulsars with strong magnetic fields and even larger. In this study wemore » consider two possible processes associated with the particle acceleration, both of them are common used to explain radio emission in neutron star pulsars: in the first process the pair production happens near to the star polar caps, i.e. inside of the light cylinder where magnetic field lines are closed; in the second one the creation of pair happens in the outer magnetosphere, i.e. far away of the star surface where magnetic field lines are open [2]. The analysis of the possibility of radio emission were done for 23 SGRs/AXPs of the McGill Online Magnetar Catalog [3] that contains the current information available on these sources. The results of this work show that the model where the particles production occur in the outer magnetosphere emission “o2” is the process compatible with the astronomical observations of absence of radio emission for almost all SGRs/AXPs when these sources are understood as white dwarf pulsars. Our work is a first attempted to find an explanation for the puzzle why for almost all the SGRs/AXPs was expected radio emission, but it was observed in only four of them. These four sources, as it was suggested recently [4], seem to belong to an high magnetic field neutron star pulsar category, different from all the others SGRs/AXPs that our work indicate to belong to a new class of white dwarf pulsars, very fast and magnetized.« less

A High Resolution Survey of the Galactic Plane at 408 MHz

NASA Astrophysics Data System (ADS)

Tung, A. K.; Kothes, R.; Landecker, T. L.; Geisbüsch, J.; Del Rizzo, D.; Taylor, A. R.; Brunt, C. M.; Gray, A. D.; Dougherty, S. M.

2017-10-01

The interstellar medium is a complex “ecosystem” with gas constituents in the atomic, molecular and ionized states, dust, magnetic fields, and relativistic particles. The Canadian Galactic Plane Survey has imaged these constituents at multiple radio and infrared frequencies with angular resolution of the order of arcminutes. This paper presents radio continuum data at 408 MHz over the area of 52^\\circ ≤slant {\\ell }≤slant 193^\\circ , -6\\buildrel{\\circ}\\over{.} 5≤slant b≤slant 8\\buildrel{\\circ}\\over{.} 5, with an extension to b=21^\\circ in the range of 97^\\circ ≤slant {\\ell }≤slant 120^\\circ , with angular resolution 2\\buildrel{ \\prime}\\over{.} 8× 2\\buildrel{ \\prime}\\over{.} 8 cosecδ. Observations were made with the Synthesis Telescope at the Dominion Radio Astrophysical Observatory as part of the Canadian Galactic Plane Survey. The calibration of the survey using existing radio source catalogs is described. The accuracy of 408 MHz flux densities from the data is 6%. Information on large structures has been incorporated into the data using the single-antenna survey of Haslam et al. The paper presents the data, describes how it can be accessed electronically, and gives examples of applications of the data to ISM research.

OPTICAL SPECTRA OF CANDIDATE SOUTHERN HEMISPHERE INTERNATIONAL CELESTIAL REFERENCE FRAME (ICRF) RADIO SOURCES

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

Titov, O.; Jauncey, D. L.; Johnston, H. M.

2011-11-15

We present the results of spectroscopic observations of the optical counterparts of 47 southern radio sources from the candidate International Celestial Reference Catalogue as part of a very long baseline interferometry (VLBI) program to strengthen the celestial reference frame, especially in the south. We made the observations with the 3.58 m European Southern Observatory New Technology Telescope. We obtained redshifts for 30 quasars and one radio galaxy, with a further seven objects being probable BL Lac objects with featureless spectra. Of the remainder, four were clear misidentifications with Galactic stars and five had low signal-to-noise spectra and could not bemore » classified. These results, in combination with new VLBI data of the radio sources with redshifts more than 2, add significantly to the existing data needed to refine the distribution of source proper motions over the celestial sphere.« less

An Analysis of the Effects of RFID Tags on Narrowband Navigation and Communication Receivers

NASA Technical Reports Server (NTRS)

LaBerge, E. F. Charles

2007-01-01

The simulated effects of the Radio Frequency Identification (RFID) tag emissions on ILS Localizer and ILS Glide Slope functions match the analytical models developed in support of DO-294B provided that the measured peak power levels are adjusted for 1) peak-to-average power ratio, 2) effective duty cycle, and 3) spectrum analyzer measurement bandwidth. When these adjustments are made, simulated and theoretical results are in extraordinarily good agreement. The relationships hold over a large range of potential interference-to-desired signal power ratios, provided that the adjusted interference power is significantly higher than the sum of the receiver noise floor and the noise-like contributions of all other interference sources. When the duty-factor adjusted power spectral densities are applied in the evaluation process described in Section 6 of DO-294B, most narrowband guidance and communications radios performance parameters are unaffected by moderate levels of RFID interference. Specific conclusions and recommendations are provided.

The high brightness temperature of B0529+483 revealed by RadioAstron and implications for interstellar scattering

NASA Astrophysics Data System (ADS)

Pilipenko, S. V.; Kovalev, Y. Y.; Andrianov, A. S.; Bach, U.; Buttaccio, S.; Cassaro, P.; Cimò, G.; Edwards, P. G.; Gawroński, M. P.; Gurvits, L. I.; Hovatta, T.; Jauncey, D. L.; Johnson, M. D.; Kovalev, Yu A.; Kutkin, A. M.; Lisakov, M. M.; Melnikov, A. E.; Orlati, A.; Rudnitskiy, A. G.; Sokolovsky, K. V.; Stanghellini, C.; de Vicente, P.; Voitsik, P. A.; Wolak, P.; Zhekanis, G. V.

2018-03-01

The high brightness temperatures, Tb ≳ 1013 K, detected in several active galactic nuclei by RadioAstron space VLBI observations challenge theoretical limits. Refractive scattering by the interstellar medium may affect such measurements. We quantify the scattering properties and the sub-mas scale source parameters for the quasar B0529+483. Using RadioAstron correlated flux density measurements at 1.7, 4.8, and 22 GHz on projected baselines up to 240 000 km we find two characteristic angular scales in the quasar core, about 100 and 10 μas. Some indications of scattering substructure are found. Very high brightness temperatures, Tb ≥ 1013 K, are estimated at 4.8 and 22 GHz even taking into account the refractive scattering. Our findings suggest a clear dominance of the particle energy density over the magnetic field energy density in the core of this quasar.

FR-type radio sources in COSMOS: relation of radio structure to size, accretion modes and large-scale environment

NASA Astrophysics Data System (ADS)

Vardoulaki, Eleni; Faustino Jimenez Andrade, Eric; Delvecchio, Ivan; Karim, Alexander; Smolčić, Vernesa; Magnelli, Benjamin; Bertoldi, Frank; Schinnener, Eva; Sargent, Mark; Finoguenov, Alexis; VLA COSMOS Team

2018-01-01

The radio sources associated with active galactic nuclei (AGN) can exhibit a variety of radio structures, from simple to more complex, giving rise to a variety of classification schemes. The question which still remains open, given deeper surveys revealing new populations of radio sources, is whether this plethora of radio structures can be attributed to the physical properties of the host or to the environment. Here we present an analysis on the radio structure of radio-selected AGN from the VLA-COSMOS Large Project at 3 GHz (JVLA-COSMOS; Smolčić et al.) in relation to: 1) their linear projected size, 2) the Eddington ratio, and 3) the environment their hosts lie within. We classify these as FRI (jet-like) and FRII (lobe-like) based on the FR-type classification scheme, and compare them to a sample of jet-less radio AGN in JVLA-COSMOS. We measure their linear projected sizes using a semi-automatic machine learning technique. Their Eddington ratios are calculated from X-ray data available for COSMOS. As environmental probes we take the X-ray groups (hundreds kpc) and the density fields (~Mpc-scale) in COSMOS. We find that FRII radio sources are on average larger than FRIs, which agrees with literature. But contrary to past studies, we find no dichotomy in FR objects in JVLA-COSMOS given their Eddington ratios, as on average they exhibit similar values. Furthermore our results show that the large-scale environment does not explain the observed dichotomy in lobe- and jet-like FR-type objects as both types are found on similar environments, but it does affect the shape of the radio structure introducing bents for objects closer to the centre of an X-ray group.

Coma cluster ultradiffuse galaxies are not standard radio galaxies

NASA Astrophysics Data System (ADS)

Struble, Mitchell F.

2018-02-01

Matching members in the Coma cluster catalogue of ultradiffuse galaxies (UDGs) from SUBARU imaging with a very deep radio continuum survey source catalogue of the cluster using the Karl G. Jansky Very Large Array (VLA) within a rectangular region of ∼1.19 deg2 centred on the cluster core reveals matches consistent with random. An overlapping set of 470 UDGs and 696 VLA radio sources in this rectangular area finds 33 matches within a separation of 25 arcsec; dividing the sample into bins with separations bounded by 5, 10, 20 and 25 arcsec finds 1, 4, 17 and 11 matches. An analytical model estimate, based on the Poisson probability distribution, of the number of randomly expected matches within these same separation bounds is 1.7, 4.9, 19.4 and 14.2, each, respectively, consistent with the 95 per cent Poisson confidence intervals of the observed values. Dividing the data into five clustercentric annuli of 0.1° and into the four separation bins, finds the same result. This random match of UDGs with VLA sources implies that UDGs are not radio galaxies by the standard definition. Those VLA sources having integrated flux >1 mJy at 1.4 GHz in Miller, Hornschemeier and Mobasher without SDSS galaxy matches are consistent with the known surface density of background radio sources. We briefly explore the possibility that some unresolved VLA sources near UDGs could be young, compact, bright, supernova remnants of Type Ia events, possibly in the intracluster volume.

GNSS Radio Occultation Observations as a data source for Ionospheric Assimilation: COSMIC-1 & COSMIC-2

NASA Astrophysics Data System (ADS)

Yue, X.; Schreiner, W. S.; Kuo, Y. H.

2014-12-01

Since the pioneer GPS/MET mission, low Earth orbit (LEO) based global navigation satellite system (GNSS) Radio Occultation (RO) technique has been a powerful technique in ionosphere monitoring. After that, many LEO satellites were launched with RO payload, include: CHAMP , GRACE, SAC-C/D, COSMIC, C/NOFS, Metop-A/B, TerraSAR-X/TanDEM-X, and etc. COSMIC was the first constellation of satellites dedicated primarily to RO and delivering RO data in near real time. Currently in UCAR CDAAC, we process most of these missions' RO data for the community. Due to the success of COSMIC mission, a follow on mission called COSMIC-2 will be launched in 2016 and 2018, respectively. The COSMIC-2 RO data will be 4-6 times of COSMIC due to the doubled satellite and GNSS signals. In this paper we will describe: (1) Data process and quality in UCAR/CDAAC; (2) Ionospheric data assimilation results based on COSMIC data; (3) OSSE study for COSMIC-2.

FERMI/LAT OBSERVATIONS OF SWIFT/BAT SEYFERT GALAXIES: ON THE CONTRIBUTION OF RADIO-QUIET ACTIVE GALACTIC NUCLEI TO THE EXTRAGALACTIC {gamma}-RAY BACKGROUND

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

Teng, Stacy H.; Mushotzky, Richard F.; Reynolds, Christopher S.

2011-12-01

We present the analysis of 2.1 years of Fermi Large Area Telescope (LAT) data on 491 Seyfert galaxies detected by the Swift Burst Alert Telescope (BAT) survey. Only the two nearest objects, NGC 1068 and NGC 4945, which were identified in the Fermi first year catalog, are detected. Using Swift/BAT and radio 20 cm fluxes, we define a new radio-loudness parameter R{sub X,BAT} where radio-loud objects have log R{sub X,BAT} > -4.7. Based on this parameter, only radio-loud sources are detected by Fermi/LAT. An upper limit to the flux of the undetected sources is derived to be {approx}2 Multiplication-Sign 10{supmore » -11} photons cm{sup -2} s{sup -1}, approximately seven times lower than the observed flux of NGC 1068. Assuming a median redshift of 0.031, this implies an upper limit to the {gamma}-ray (1-100 GeV) luminosity of {approx}< 3 Multiplication-Sign 10{sup 41} erg s{sup -1}. In addition, we identified 120 new Fermi/LAT sources near the Swift/BAT Seyfert galaxies with significant Fermi/LAT detections. A majority of these objects do not have Swift/BAT counterparts, but their possible optical counterparts include blazars, flat-spectrum radio quasars, and quasars.« less

Renewed Radio Activity of Age 370 years in the Extragalactic Source 0108+388

NASA Astrophysics Data System (ADS)

Owsianik, I.; Conway, J. E.; Polatidis, A. G.

1998-08-01

We present the results of multi-epoch global VLBI observations of the Compact Symmetric Object (CSO) 0108+388 at 5 GHz. Analysis of data spread over 12 years shows strong evidence for an increase in the separation of the outer components at a rate of 0.197+/-0.026 h(-1) c. Given an overall size of 22.2 h(-1) pc this implies a kinematic age of only 367+/-48 yrs. This result strongly supports the idea that radio emission in Compact Symmetric Objects arises from recently activated radio sources. The presence of weak radio emission on kpc-scales in 0108+388 suggests recurrent activity in this source, and that we are observing it just as a new period of activity is beginning.

SUZAKU X-RAY IMAGING OF THE EXTENDED LOBE IN THE GIANT RADIO GALAXY NGC 6251 ASSOCIATED WITH THE FERMI-LAT SOURCE 2FGL J1629.4+8236

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

Takeuchi, Y.; Kataoka, J.; Takahashi, Y.

2012-04-10

We report the results of a Suzaku X-ray imaging study of NGC 6251, a nearby giant radio galaxy with intermediate FR I/II radio properties. Our pointing direction was centered on the {gamma}-ray emission peak recently discovered with the Fermi Large Area Telescope (LAT) around the position of the northwest (NW) radio lobe 15 arcmin offset from the nucleus. After subtracting two 'off-source' pointings adjacent to the radio lobe and removing possible contaminants in the X-ray Imaging Spectrometer field of view, we found significant residual X-ray emission most likely diffuse in nature. The spectrum of the excess X-ray emission is wellmore » fitted by a power law with a photon index {Gamma} = 1.90 {+-} 0.15 and a 0.5-8 keV flux of 4 Multiplication-Sign 10{sup -13} erg cm{sup -2} s{sup -1}. We interpret this diffuse X-ray emission component as being due to inverse Compton upscattering of the cosmic microwave background photons by ultrarelativistic electrons within the lobe, with only a minor contribution from the beamed emission of the large-scale jet. Utilizing archival radio data for the source, we demonstrate by means of broadband spectral modeling that the {gamma}-ray flux of the Fermi-LAT source 2FGL J1629.4+8236 may well be accounted for by the high-energy tail of the inverse Compton continuum of the lobe. Thus, this claimed association of {gamma}-rays from the NW lobe of NGC 6251, together with the recent Fermi-LAT imaging of the extended lobes of Centaurus A, indicates that particles may be efficiently (re-)accelerated up to ultrarelativistic energies within extended radio lobes of nearby radio galaxies in general.« less

The Gould's Belt Very Large Array Survey. II. The Serpens Region

NASA Astrophysics Data System (ADS)

Ortiz-León, Gisela N.; Loinard, Laurent; Mioduszewski, Amy J.; Dzib, Sergio A.; Rodríguez, Luis F.; Pech, Gerardo; Rivera, Juana L.; Torres, Rosa M.; Boden, Andrew F.; Hartmann, Lee; Evans, Neal J., II; Briceño, Cesar; Tobin, John; Kounkel, Marina A.; González-Lópezlira, Rosa A.

2015-05-01

We present deep (∼17 μJy) radio continuum observations of the Serpens molecular cloud, the Serpens south cluster, and the W40 region obtained using the Very Large Array in its A configuration. We detect a total of 146 sources, 29 of which are young stellar objects (YSOs), 2 of which are BV stars, and 5 more of which are associated with phenomena related to YSOs. Based on their radio variability and spectral index, we propose that about 16 of the remaining 110 unclassified sources are also YSOs. For approximately 65% of the known YSOs detected here as radio sources, the emission is most likely non-thermal and related to stellar coronal activity. As also recently observed in Ophiuchus, our sample of YSOs with X-ray counterparts lies below the fiducial Güdel & Benz relation. Finally, we analyze the proper motions of nine sources in the W40 region. This allows us to better constrain the membership of the radio sources in the region.

Shocks and Bubbles in a Deep Chandra Observation of the Cooling Flow Cluster Abell 2052

DTIC Science & Technology

2009-01-01

the bubble rims related to radio source outbursts have been found in a few clusters including M87/ Virgo (Forman et al. 2005), Hydra A (Nulsen et al...Printed in the U.S.A. SHOCKS AND BUBBLES IN A DEEP CHANDRA OBSERVATION OF THE COOLING FLOW CLUSTER ABELL 2052 E. L. Blanton1, S. W. Randall2, E. M...Douglass1, C. L. Sarazin3, T. E. Clarke4,5, and B. R. McNamara2,6,7 1 Institute for Astrophysical Research , Boston University, 725 Commonwealth Avenue

Einstein observations of active galaxies and quasars

NASA Technical Reports Server (NTRS)

Schreier, E. J.

1979-01-01

The radio galaxies Centaurus A and Signus B are discussed. In both these sources, a comparison of the radio and imaged X-ray flux is allowed for the measurement of the magnetic fields. Einstein observations of quasars are discussed. The number of known X-ray emitting QSO's was increased from 3 to 22 and the distances where these QSO's were seen to correspond to an age of 15 billion years. It was shown that these quasars contributed significantly to the X-ray background.

VizieR Online Data Catalog: ROSAT detected quasars. I. (Brinkmann+ 1997)

NASA Astrophysics Data System (ADS)

Brinkmann, W.; Yuan, W.

1996-09-01

We have compiled a sample of all quasars with measured radio emission from the Veron-Cetty - Veron catalogue (1993, VV93 ) detected by ROSAT in the ALL-SKY SURVEY (RASS, Voges 1992), as targets of pointed observations, or as serendipitous sources from pointed observations as publicly available from the ROSAT point source catalogue (ROSAT-SRC, Voges et al. 1995). The total number of ROSAT detected radio quasars from the above three sources is 654 objects. 69 of the objects are classified as radio-quiet using the defining line at a radio-loudness of 1.0, and 10 objects have no classification. The 5GHz data are from the 87GB radio survey, the NED database, or from the Veron-Cetty - Veron catalogue. The power law indices and their errors are estimated from the two hardness ratios given by the SASS assuming Galactic absorption. The X-ray flux densities in the ROSAT band (0.1-2.4keV) are calculated from the count rates using the energy to counts conversion factor for power law spectra and Galactic absorption. For the photon index we use the value obtained for a individual source if the estimated 1 sigma error is smaller than 0.5, otherwise we use the mean value 2.14. (1 data file).

SCO X-1: Origin of the radio and hard X-ray emissions

NASA Technical Reports Server (NTRS)

Ramaty, R.; Cheng, C. C.; Tsuruta, S.

1973-01-01

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.

High-resolution observations of low-luminosity gigahertz-peaked spectrum and compact steep-spectrum sources

NASA Astrophysics Data System (ADS)

Collier, J. D.; Tingay, S. J.; Callingham, J. R.; Norris, R. P.; Filipović, M. D.; Galvin, T. J.; Huynh, M. T.; Intema, H. T.; Marvil, J.; O'Brien, A. N.; Roper, Q.; Sirothia, S.; Tothill, N. F. H.; Bell, M. E.; For, B.-Q.; Gaensler, B. M.; Hancock, P. J.; Hindson, L.; Hurley-Walker, N.; Johnston-Hollitt, M.; Kapińska, A. D.; Lenc, E.; Morgan, J.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, C.; Zheng, Q.; Heywood, I.; Popping, A.

2018-06-01

We present very long baseline interferometry observations of a faint and low-luminosity (L1.4 GHz < 1027 W Hz-1) gigahertz-peaked spectrum (GPS) and compact steep-spectrum (CSS) sample. We select eight sources from deep radio observations that have radio spectra characteristic of a GPS or CSS source and an angular size of θ ≲ 2 arcsec, and detect six of them with the Australian Long Baseline Array. We determine their linear sizes, and model their radio spectra using synchrotron self-absorption (SSA) and free-free absorption (FFA) models. We derive statistical model ages, based on a fitted scaling relation, and spectral ages, based on the radio spectrum, which are generally consistent with the hypothesis that GPS and CSS sources are young and evolving. We resolve the morphology of one CSS source with a radio luminosity of 10^{25} W Hz^{-1}, and find what appear to be two hotspots spanning 1.7 kpc. We find that our sources follow the turnover-linear size relation, and that both homogeneous SSA and an inhomogeneous FFA model can account for the spectra with observable turnovers. All but one of the FFA models do not require a spectral break to account for the radio spectrum, while all but one of the alternative SSA and power-law models do require a spectral break to account for the radio spectrum. We conclude that our low-luminosity sample is similar to brighter samples in terms of their spectral shape, turnover frequencies, linear sizes, and ages, but cannot test for a difference in morphology.

SAIP2014, the 59th Annual Conference of the South African Institute of Physics

NASA Astrophysics Data System (ADS)

Engelbrecht, Chris; Karataglidis, Steven

2015-04-01

The International Celestial Reference Frame (ICRF) was adopted by the International Astronomical Union (IAU) in 1997. The current standard, the ICRF-2, is based on Very Long Baseline Interferometric (VLBI) radio observations of positions of 3414 extragalactic radio reference sources. The angular resolution achieved by the VLBI technique is on a scale of milliarcsecond to sub-milliarcseconds and defines the ICRF with the highest accuracy available at present. An ideal reference source used for celestial reference frame work should be unresolved or point-like on these scales. However, extragalactic radio sources, such as those that definevand maintain the ICRF, can exhibit spatially extended structures on sub-milliarsecond scalesvthat may vary both in time and frequency. This variability can introduce a significant error in the VLBI measurements thereby degrading the accuracy of the estimated source position. Reference source density in the Southern celestial hemisphere is also poor compared to the Northern hemisphere, mainly due to the limited number of radio telescopes in the south. In order to dene the ICRF with the highest accuracy, observational efforts are required to find more compact sources and to monitor their structural evolution. In this paper we show that the astrometric VLBI sessions can be used to obtain source structure information and we present preliminary imaging results for the source J1427-4206 at 2.3 and 8.4 GHz frequencies which shows that the source is compact and suitable as a reference source.

Radio Source Contributions to the Microwave Sky

NASA Astrophysics Data System (ADS)

Boughn, S. P.; Partridge, R. B.

2008-03-01

Cross-correlations of the Wilkinson Microwave Anisotropy Probe (WMAP) full sky K-, Ka-, Q-, V-, and W-band maps with the 1.4 GHz NVSS source count map and the HEAO I A2 2-10 keV full sky X-ray flux map are used to constrain rms fluctuations due to unresolved microwave sources in the WMAP frequency range. In the Q band (40.7 GHz), a lower limit, taking account of only those fluctuations correlated with the 1.4 GHz radio source counts and X-ray flux, corresponds to an rms Rayleigh-Jeans temperature of ˜2 μK for a solid angle of 1 deg2 assuming that the cross-correlations are dominated by clustering, and ˜1 μK if dominated by Poisson fluctuations. The correlated fluctuations at the other bands are consistent with a β = -2.1 ± 0.4 frequency spectrum. If microwave sources are distributed similarly in redshift to the radio and X-ray sources and are similarly clustered, then the implied total rms microwave fluctuations correspond to ˜5 μK. While this value should be considered no more than a plausible estimate, it is similar to that implied by the excess, small angular scale fluctuations observed in the Q band by WMAP and is consistent with estimates made by extrapolating low-frequency source counts.

Sequencing the Earliest Stages of Active Galactic Nuclei Development Using The Youngest Radio Sources

NASA Astrophysics Data System (ADS)

Collier, Jordan; Filipovic, Miroslav; Norris, Ray; Chow, Kate; Huynh, Minh; Banfield, Julie; Tothill, Nick; Sirothia, Sandeep Kumar; Shabala, Stanislav

2014-04-01

This proposal is a continuation of an extensive project (the core of Collier's PhD) to explore the earliest stages of AGN formation, using Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources. Both are widely believed to represent the earliest stages of radio-loud AGN evolution, with GPS sources preceding CSS sources. In this project, we plan to (a) test this hypothesis, (b) place GPS and CSS sources into an evolutionary sequence with a number of other young AGN candidates, and (c) search for evidence of the evolving accretion mode. We will do this using high-resolution radio observations, with a number of other multiwavelength age indicators, of a carefully selected complete faint sample of 80 GPS/CSS sources. Analysis of the C2730 ELAIS-S1 data shows that we have so far met our goals, resolving the jets of 10/49 sources, and measuring accurate spectral indices from 0.843-10 GHz. This particular proposal is to almost triple the sample size by observing an additional 80 GPS/CSS sources in the Chandra Deep Field South (arguably the best-studied field) and allow a turnover frequency - linear size relation to be derived at >10-sigma. Sources found to be unresolved in our final sample will subsequently be observed with VLBI. Comparing those sources resolved with ATCA to the more compact sources resolved with VLBI will give a distribution of source sizes, helping to answer the question of whether all GPS/CSS sources grow to larger sizes.

Radio Galaxy Zoo: A Search for Hybrid Morphology Radio Galaxies

NASA Astrophysics Data System (ADS)

Kapińska, A. D.; Terentev, I.; Wong, O. I.; Shabala, S. S.; Andernach, H.; Rudnick, L.; Storer, L.; Banfield, J. K.; Willett, K. W.; de Gasperin, F.; Lintott, C. J.; López-Sánchez, Á. R.; Middelberg, E.; Norris, R. P.; Schawinski, K.; Seymour, N.; Simmons, B.

2017-12-01

Hybrid morphology radio sources (HyMoRS) are a rare type of radio galaxy that display different Fanaroff-Riley classes on opposite sides of their nuclei. To enhance the statistical analysis of HyMoRS, we embarked on a large-scale search of these sources within the international citizen science project, Radio Galaxy Zoo (RGZ). Here, we present 25 new candidate hybrid morphology radio galaxies. Our selected candidates are moderate power radio galaxies ({L}{median}=4.7× {10}24 W Hz-1 sr-1) at redshifts 0.14< z< 1.0. Hosts of nine candidates have spectroscopic observations, of which six are classified as quasars, one as high- and two as low-excitation galaxies. Two candidate HyMoRS are giant (> 1 Mpc) radio galaxies, one resides at the center of a galaxy cluster, and one is hosted by a rare green bean galaxy. Although the origin of the hybrid morphology radio galaxies is still unclear, this type of radio source starts depicting itself as a rather diverse class. We discuss hybrid radio morphology formation in terms of the radio source environment (nurture) and intrinsically occurring phenomena (nature; activity cessation and amplification), showing that these peculiar radio galaxies can be formed by both mechanisms. While high angular resolution follow-up observations are still necessary to confirm our candidates, we demonstrate the efficacy of the RGZ in the pre-selection of these sources from all-sky radio surveys, and report the reliability of citizen scientists in identifying and classifying complex radio sources.

Dense plasma focus (DPF) accelerated non radio isotopic radiological source

DOEpatents

Rusnak, Brian; Tang, Vincent

2017-01-31

A non-radio-isotopic radiological source using a dense plasma focus (DPF) to produce an intense z-pinch plasma from a gas, such as helium, and which accelerates charged particles, such as generated from the gas or injected from an external source, into a target positioned along an acceleration axis and of a type known to emit ionizing radiation when impinged by the type of accelerated charged particles. In a preferred embodiment, helium gas is used to produce a DPF-accelerated He2+ ion beam to a beryllium target, to produce neutron emission having a similar energy spectrum as a radio-isotopic AmBe neutron source. Furthermore, multiple DPFs may be stacked to provide staged acceleration of charged particles for enhancing energy, tunability, and control of the source.

47 CFR 2.106 - Table of Frequency Allocations.

Code of Federal Regulations, 2013 CFR

2013-10-01

... radio astronomy service from harmful interference. Emissions from spaceborne or airborne stations can be particularly serious sources of interference to the radio astronomy service (see Nos. 4.5 and 4.6 and Article...-401 MHz, administrations shall take all practicable steps to protect the radio astronomy service in...

47 CFR 2.106 - Table of Frequency Allocations.

Code of Federal Regulations, 2011 CFR

2011-10-01

... radio astronomy service from harmful interference. Emissions from spaceborne or airborne stations can be particularly serious sources of interference to the radio astronomy service (see Nos. 4.5 and 4.6 and Article...-401 MHz, administrations shall take all practicable steps to protect the radio astronomy service in...

47 CFR 2.106 - Table of Frequency Allocations.

Code of Federal Regulations, 2012 CFR

2012-10-01

... radio astronomy service from harmful interference. Emissions from spaceborne or airborne stations can be particularly serious sources of interference to the radio astronomy service (see Nos. 4.5 and 4.6 and Article...-401 MHz, administrations shall take all practicable steps to protect the radio astronomy service in...

Fermi/LAT Observations of Swift/BAT Seyfert Galaxies: On the Contribution of Radio-Quiet Active Galactic Nuclei to the Extragalactic gamma-Ray Background

NASA Technical Reports Server (NTRS)

Teng, Stacy H.; Mushotzky, Richard F.; Sambruna, Rita M.; Davis, David S.; Reynolds, Christopher S.

2011-01-01

We present the analysis of 2.1 years of Fermi Large Area Telescope (LAT) data on 491 Seyfert galaxies detected by the Swift Burst Alert Telescope (BAT) survey. Only the two nearest objects, NGC 1068 and NGC 4945, which were identified in the Fermi first year catalog, are detected. Using Swift/BAT and radio 20 cm fluxes, we define a new radio-loudness parameter R(sub X,BAT) where radio-loud objects have logR(sub X,BAT) > -4.7. Based on this parameter, only radio-loud sources are detected by Fermi/LAT. An upper limit to the flux of the undetected sources is derived to be approx.2x10(exp -11) photons/sq cm/s, approximately seven times lower than the observed flux of NGC 1068. Assuming a median redshift of 0.031, this implies an upper limit to the gamma-ray (1-100 GeV) luminosity of < approx.3x10(exp 41) erg/s. In addition, we identified 120 new Fermi/LAT sources near the Swift/BAT Seyfert galaxies with significant Fermi/LAT detections. A majority of these objects do not have Swift/BAT counterparts, but their possible optical counterparts include blazars, flat-spectrum radio quasars, and quasars.

Raman dissipative soliton fiber laser pumped by an ASE source.

PubMed

Pan, Weiwei; Zhang, Lei; Zhou, Jiaqi; Yang, Xuezong; Feng, Yan

2017-12-15

The mode locking of a Raman fiber laser with an amplified spontaneous emission (ASE) pump source is investigated for performance improvement. Raman dissipative solitons with a compressed pulse duration of 1.05 ps at a repetition rate of 2.47 MHz are generated by utilizing nonlinear polarization rotation and all-fiber Lyot filter. A signal-to-noise ratio as high as 85 dB is measured in a radio-frequency spectrum, which suggests excellent temporal stability. Multiple-pulse operation with unique random static distribution is observed for the first time, to the best of our knowledge, at higher pump power in mode-locked Raman fiber lasers.

Feeding and feedback in radio galaxies of the local universe

NASA Astrophysics Data System (ADS)

Couto, Guilherme dos Santos

2016-10-01

We present integral field spectroscopic data covering the inner kiloparsecs of four radio galaxies of the local Universe (z<0.07), Arp 102B, Pictor A, 3C 33 and 4C +29.30, obtained with the GMOS-IFU instrument of the Gemini telescopes. We use these data to analyze the gas excitation and kinematics via two-dimensional maps. Using the flux distributions of the emission lines, we identify extended emission in ionized gas up to the edges of the observed field, which corresponds to 1.7 kpc x 2.5 kpc for Arp 102B, 2.5 kpc x 3.4 kpc for Pictor A, 4.0 kpc x 5.8 kpc for 3C 33 and 4.3 kpc x 6.2 kpc for 4C +29.30. The extended line emitting gas displays structures resembling rotating disks, spiral arms and bars. Line ratios indicate that both photons from the nuclear source and shocks originated in the interaction of the radio jet with circumnuclear gas are ionizing mechanisms of the gas. Line ratio values are typical of Seyfert galaxies for 3C 33 and 4C +29.30, while intermediate values between Seyferts and LINERs are observed in Arp 102B. Pictor A galaxy, however, shows low values of [NII]/Ha=0.15-0.25, expected for HII regions. We suggest that these values are observed due to the low gas metallicity (12+log(O/H)=8.39). Centroid velocity maps show that the gas kinematics is dominated by rotation only in Arp 102B and 3C 33. Outflows are observed in the galaxies Arp 102B, 3C 33 and 4C +29.30. We obtain mass outflow rates of 0.32-0.49 Msun per year, but the outflow kinetic power is small, ranging 0.04-0.07% of the AGN bolometric luminosity, indicating that the feedback has little impact in the host galaxies evolution. The high masses of ionized gas, ranging from 7.4E7 to 4.6E8 Msun, and the fact that these galaxies are early-type, suggest an external origin of the gas. Indeed, it is observed evidence of interaction with companion galaxies in Arp 102B, Pictor A and 4C +29.30. We suggest that the capture of mass has triggered the nuclear activity in these galaxies, with the high masses feeding not only the SMBH but also being a possible source of star formation.

The radio emission from the ultraluminous far-infrared galaxy NGC 6240

NASA Technical Reports Server (NTRS)

Colbert, Edward J. M.; Wilson, Andrew S.; Bland-Hawthorn, Jonathan

1994-01-01

We present new radio observations of the 'prototypical' ultraluminous far-infrared galaxy NGC 6240, obtained using the Very Large Array (VLA) at lambda = 20 cm in B-configuration and at lambda = 3.6 cm in A-configuration. These data, along with those from four previous VLA observations, are used to perform a comprehensive study of the radio emission from NGC 6240. Approximately 70% (approximately 3 x 10(exp 23) W/Hz) of the total radio power at 20 cm originates from the nuclear region (approximately less than 1.5 kpc), of which half is emitted by two unresolved (R approximately less than 36 pc) cores and half by a diffuse component. The radio spectrum of the nuclear emission is relatively flat (alpha approximately equals 0.6; S(sub nu) proportional to nu(exp -alpha). The supernova rate required to power the diffuse component is consistent with that predicted by the stellar evolution models of Rieke et al. (1985). If the radio emission from the two compact cores is powered by supernova remnants, then either the remnants overlap and form hot bubbles in the cores, or they are very young (approximately less than 100 yr.) Nearly all of the remaining 30% of the total radio power comes from an 'armlike' region extending westward from the nuclear region. The western arm emission has a steep spectrum (alpha approximately equals 1.0), suggestive of aging effects from synchrotron or inverse-Compton losses, and is not correlated with starlight; we suggest that it is synchrotron emission from a shell of material driven by a galactic superwind. Inverse Compton scattering of far-infrared photons in the radio sources is expected to produce an X-ray flux of approximately 2 - 6 x 10(exp -14) ergs/s/sq cm in the 2 - 10 keV band. No significant radio emission is detected from or near the possible ultramassive 'dark core'.

Source Regions of the Type II Radio Burst Observed During a CME-CME Interaction on 2013 May 22

NASA Technical Reports Server (NTRS)

Makela, P.; Gopalswamy, N.; Reiner, M. J.; Akiyama, S.; Krupar, V.

2016-01-01

We report on our study of radio source regions during the type II radio burst on 2013 May 22 based on direction finding analysis of the Wind/WAVES and STEREO/WAVES (SWAVES) radio observations at decameter-hectometric wavelengths. The type II emission showed an enhancement that coincided with the interaction of two coronal mass ejections (CMEs) launched in sequence along closely spaced trajectories. The triangulation of the SWAVES source directions posited the ecliptic projections of the radio sources near the line connecting the Sun and the STEREO-A spacecraft. The WAVES and SWAVES source directions revealed shifts in the latitude of the radio source, indicating that the spatial location of the dominant source of the type II emission varies during the CME-CME interaction. The WAVES source directions close to 1MHz frequencies matched the location of the leading edge of the primary CME seen in the images of the LASCO/C3 coronagraph. This correspondence of spatial locations at both wavelengths confirms that the CME-CME interaction region is the source of the type II enhancement. Comparison of radio and white-light observations also showed that at lower frequencies scattering significantly affects radio wave propagation.

The black hole candidate MAXI J1659-152 in and towards quiescence in X-ray and radio

NASA Astrophysics Data System (ADS)

Jonker, P. G.; Miller-Jones, J. C. A.; Homan, J.; Tomsick, J.; Fender, R. P.; Kaaret, P.; Markoff, S.; Gallo, E.

2012-07-01

In this paper we report on Expanded Very Large Array radio and Chandra and Swift X-ray observations of the outburst decay of the transient black hole candidate MAXI J1659-152 in 2011. We discuss the distance to the source taking the high inclination into account and conclude that the source distance is probably 6 ± 2 kpc. The lowest observed flux corresponds to a luminosity of ? erg s-1. This, together with the orbital period of 2.4 h reported in the literature, suggests that the quiescent X-ray luminosity is higher than predicted on the basis of the orbital period-quiescent X-ray luminosity relationship. It is more in line with that expected for a neutron star, although the outburst spectral and timing properties reported in the literature strongly suggest that MAXI J1659-152 harbours a black hole. This conclusion is subject to confirmation of the lowest observed flux as the quiescent flux. The relation between the accretion and ejection mechanisms can be studied using the observed correlation between the radio and X-ray luminosities as these evolve over an outburst. We determine the behaviour of MAXI J1659-152 in the radio-X-ray diagram at low X-ray luminosities using the observations reported in this paper and at high X-ray luminosities using values reported in the literature. At high X-ray luminosities, the source lies closer to the sources that follow a correlation index steeper than 0.6-0.7. However, when compared to other sources that follow a steeper correlation index, the X-ray luminosity in MAXI J1659-152 is also lower. The latter can potentially be explained by the high inclination of MAXI J1659-152 if the X-ray emission comes from close to the source and the radio emission is originating in a more extended region. However, it is probable that the source was not in the canonical low-hard state during these radio observations and this may affect the behaviour of the source as well. At intermediate X-ray luminosities, the source makes the transition from the radio underluminous sources in the direction of the relation traced by the 'standard' correlation similar to what has been reported for H 1743-322 in the literature. However, MAXI J1659-152 remains underluminous with respect to this 'standard' correlation.

Far Outer Galaxy H II Regions

NASA Technical Reports Server (NTRS)

Rudolph, A. L.; deGues, E. J.; Brand, J.; Wouterloot, J. G. A.; Gross, Anthony R. (Technical Monitor)

1994-01-01

We have made a multifrequency (6, 3.6, and 2 cm), high-resolution (3"-6"), radio continuum survey of IRAS selected sources from the catalogue of Wouterloot & Brand (1989) to search for and study H II regions in the far outer Galaxy. We identified 31 sources in this catalog with well determined galactocentric distances, and with R approx.. greater than 15 kpc and L(sub FIR) approx.greater than 10(exp 4) solar luminosity, indicating the presence of high-mass star-formation. We have observed 11 of these sources with the Very Large Array (VLA). We observed the sources at 6 and 2 cm using "scaled arrays", making possible a direct and reliable comparison of the data at these two wavelengths for the determination of spectral indices. We detected a total of 12 radio sources, of which 10 have spectral indices consistent with optically-thin free-free emission from H II regions. Combined with previous VLA observations by other investigators, we have data on a total of 15 H II regions at galactocentric distances of 15 to 18.2kpc, among the most remote H II regions found in our Galaxy. The sizes of the H II regions range from approx. less than 0.10 to 2.3 pc. Using the measured fluxes and sizes, we determine the electron densities, emission measures, and excitation parameters of the H II regions, as well as the fluxes of Lyman continuum photons needed to keep the nebulae ionized. The sizes and electron densities are consistent with most of the sources detected in this survey being compact or ultracompact H II regions. Seven of the fifteen H II regions have sizes approx. less than 0.20 pc. Assuming simple pressure-driven expansion of the H II regions, these sizes indicate ages approx. less than 5 x 10(exp 4) yr, or only 1% of the lifetime of an O star, which implies an unlikely overabundance of O stars in the outer Galaxy. Thus, the large number of compact H II regions suggests that the time these regions spend in a compact phase must be much longer than their dynamical expansion times. Five of the fifteen H II regions have cometary shapes; the remainder are spherical or unresolved. Comparison of the radio continuum data with molecular line maps suggests that the cometary shape of the two H II regions in S 127 may be due to pressure confinement of the expanding ionized gas, as in the "blister" or "champagne flow" models of H II regions. Comparison of the radio continuum data with the IRAS far-infrared data indicates that the five most luminous H II regions are consistent with a single 0 or B star exciting a dust-free H II region. Subject headings: stars: formation - ISM: H II regions - ISM: individual objects: S 127 radio continuum: interstellar

46 CFR 129.395 - Radio installations.

Code of Federal Regulations, 2014 CFR

2014-10-01

... INSTALLATIONS Power Sources and Distribution Systems § 129.395 Radio installations. A separate circuit, with... radios, if installed, may be powered from a local lighting power source, such as the pilothouse lighting panel, provided each radio power source has a separate overcurrent protection device. ...

46 CFR 129.395 - Radio installations.

Code of Federal Regulations, 2011 CFR

2011-10-01

... INSTALLATIONS Power Sources and Distribution Systems § 129.395 Radio installations. A separate circuit, with... radios, if installed, may be powered from a local lighting power source, such as the pilothouse lighting panel, provided each radio power source has a separate overcurrent protection device. ...

46 CFR 129.395 - Radio installations.

Code of Federal Regulations, 2012 CFR

2012-10-01

... INSTALLATIONS Power Sources and Distribution Systems § 129.395 Radio installations. A separate circuit, with... radios, if installed, may be powered from a local lighting power source, such as the pilothouse lighting panel, provided each radio power source has a separate overcurrent protection device. ...

46 CFR 129.395 - Radio installations.

Code of Federal Regulations, 2013 CFR

2013-10-01

... INSTALLATIONS Power Sources and Distribution Systems § 129.395 Radio installations. A separate circuit, with... radios, if installed, may be powered from a local lighting power source, such as the pilothouse lighting panel, provided each radio power source has a separate overcurrent protection device. ...

VLBI observations at 2.3 GHz of the compact galaxy 1934-638

NASA Technical Reports Server (NTRS)

Tzioumis, Anastasios K.; Jauncey, David L.; Preston, Robert A.; Meier, David L.; Morabito, David D.; Skjerve, Lyle; Slade, Martin A.; Nicolson, George D.; Niell, Arthur E.; Wehrle, Ann E.

1989-01-01

VLBI observations of the strong radio source 1934-638 show it to be a binary with a component separation of 42.0 + or - 0.2 mas, a position angle of 90.5 + or - 1 deg, and component sizes of about 2.5 mas. The results imply the presence of an additional elongated component aligned with, and between, the compact double components. The sources's almost equal compact double structure, peaked spectrum, low variability, small polarization, and particle-dominated radio lobes suggests that it belongs to the class of symmetric compact double sources identified by Phillips and Mutel (1980, 1981, 1982).

Decameter Type IV Burst Associated with a Behind-the-limb CME Observed on 7 November 2013

NASA Astrophysics Data System (ADS)

Melnik, V. N.; Brazhenko, A. I.; Konovalenko, A. A.; Dorovskyy, V. V.; Rucker, H. O.; Panchenko, M.; Frantsuzenko, A. V.; Shevchuk, M. V.

2018-03-01

We report on the results of observations of a type IV burst made by the Ukrainian Radio interferometer of the Academy of Sciences (URAN-2) in the frequency range 22 - 33 MHz. The burst is associated with a coronal mass ejection (CME) initiated by a behind-the-limb active region (N05E151) and was also observed by the Nançay Decameter Array (NDA) radio telescope in the frequency band 30 - 60 MHz. The purpose of the article is the determination of the source of this type IV burst. After analysis of the observational data obtained with the URAN-2, the NDA, the Solar-Terrestrial Relations Observatory (STEREO) A and B spacecraft, and the Solar and Heliospheric Observatory (SOHO) spacecraft, we come to the conclusion that the source of the burst is the core of a behind-the-limb CME. We conclude that the radio emission can escape the center of the CME core at a frequency of 60 MHz and originates from the periphery of the core at a frequency of 30 MHz that is due to occultation by the solar corona at the corresponding frequencies. We find plasma densities in these regions assuming the plasma mechanism of radio emission. We show that the frequency drift of the start of the type IV burst is governed by an expansion of the CME core. The type III bursts that were observed against this type IV burst are shown to be generated by fast electrons propagating through the CME core plasma. A type II burst was registered at frequencies of 44 - 64 MHz and 3 - 16 MHz and was radiated by a shock with velocities of about 1000 km s^{-1} and 800 km s^{-1}, respectively.

JVLA Observations of Young Brown Dwarfs

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

Rodríguez, Luis F.; Zapata, Luis A.; Palau, Aina, E-mail: l.rodriguez@crya.unam.mx, E-mail: l.zapata@crya.unam.mx, E-mail: a.palau@crya.unam.mx

We present sensitive 3.0 cm JVLA radio continuum observations of six regions of low-mass star formation that include twelve young brown dwarfs (BDs) and four young BD candidates. We detect a total of 49 compact radio sources in the fields observed, of which 24 have no reported counterparts and are considered new detections. Twelve of the radio sources show variability in timescales of weeks to months, suggesting gyrosynchrotron emission produced in active magnetospheres. Only one of the target BDs, FU Tau A, was detected. However, we detected radio emission associated with two of the BD candidates, WL 20S and CHLTmore » 2. The radio flux densities of the sources associated with these BD candidates are more than an order of magnitude larger than expected for a BD and suggest a revision of their classification. In contrast, FU Tau A falls on the well-known correlation between radio luminosity and bolometric luminosity, suggesting that the emission comes from a thermal jet and that this BD seems to be forming as a scaled-down version of low-mass stars.« less

A radio telescope for the calibration of radio sources at 32 gigahertz

NASA Technical Reports Server (NTRS)

Gatti, M. S.; Stewart, S. R.; Bowen, J. G.; Paulsen, E. B.

1994-01-01

A 1.5-m-diameter radio telescope has been designed, developed, and assembled to directly measure the flux density of radio sources in the 32-GHz (Ka-band) frequency band. The main goal of the design and development was to provide a system that could yield the greatest absolute accuracy yet possible with such a system. The accuracy of the measurements have a heritage that is traceable to the National Institute of Standards and Technology. At the present time, the absolute accuracy of flux density measurements provided by this telescope system, during Venus observations at nearly closest approach to Earth, is plus or minus 5 percent, with an associated precision of plus or minus 2 percent. Combining a cooled high-electron mobility transistor low-noise amplifier, twin-beam Dicke switching antenna, and accurate positioning system resulted in a state-of-the-art system at 32 GHz. This article describes the design and performance of the system as it was delivered to the Owens Valley Radio Observatory to support direct calibrations of the strongest radio sources at Ka-band.

Molecular basis of ‘hypoxic’ breast cancer cell radio-sensitization: phytochemicals converge on radiation induced Rel signaling

PubMed Central

2013-01-01

Background Heterogeneously distributed hypoxic areas are a characteristic property of locally advanced breast cancers (BCa) and generally associated with therapeutic resistance, metastases, and poor patient survival. About 50% of locally advanced BCa, where radiotherapy is less effective are suggested to be due to hypoxic regions. In this study, we investigated the potential of bioactive phytochemicals in radio-sensitizing hypoxic BCa cells. Methods Hypoxic (O2-2.5%; N2-92.5%; CO2-5%) MCF-7 cells were exposed to 4 Gy radiation (IR) alone or after pretreatment with Curcumin (CUR), curcumin analog EF24, neem leaf extract (NLE), Genistein (GEN), Resveratrol (RES) or raspberry extract (RSE). The cells were examined for inhibition of NFκB activity, transcriptional modulation of 88 NFκB signaling pathway genes, activation and cellular localization of radio-responsive NFκB related mediators, eNos, Erk1/2, SOD2, Akt1/2/3, p50, p65, pIκBα, TNFα, Birc-1, -2, -5 and associated induction of cell death. Results EMSA revealed that cells exposed to phytochemicals showed complete suppression of IR-induced NFκB. Relatively, cells exposed EF24 revealed a robust inhibition of IR-induced NFκB. QPCR profiling showed induced expression of 53 NFκB signaling pathway genes after IR. Conversely, 53, 50, 53, 53, 53 and 53 of IR-induced genes were inhibited with EF24, NLE, CUR, GEN, RES and RSE respectively. In addition, 25, 29, 24, 16, 11 and 21 of 35 IR-suppressed genes were further inhibited with EF24, NLE, CUR, GEN, RES and RSE respectively. Immunoblotting revealed a significant attenuating effect of IR-modulated radio-responsive eNos, Erk1/2, SOD2, Akt1/2/3, p50, p65, pIκBα, TNFα, Birc-1, -2 and −5 with EF24, NLE, CUR, GEN, RES or RSE. Annexin V-FITC staining showed a consistent and significant induction of IR-induced cell death with these phytochemicals. Notably, EF24 robustly conferred IR-induced cell death. Conclusions Together, these data identifies the potential hypoxic cell radio-sensitizers and further implies that the induced radio-sensitization may be exerted by selectively targeting IR-induced NFκB signaling. PMID:23452621

Radio Follow-up on All Unassociated Gamma-Ray Sources from the Third Fermi Large Area Telescope Source Catalog

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

Schinzel, Frank K.; Petrov, Leonid; Taylor, Gregory B.

The third Fermi Large Area Telescope γ -ray source catalog (3FGL) contains over 1000 objects for which there is no known counterpart at other wavelengths. The physical origin of the γ -ray emission from those objects is unknown. Such objects are commonly referred to as unassociated and mostly do not exhibit significant γ -ray flux variability. We performed a survey of all unassociated γ -ray sources found in 3FGL using the Australia Telescope Compact Array and Very Large Array in the range 4.0–10.0 GHz. We found 2097 radio candidates for association with γ -ray sources. The follow-up with very longmore » baseline interferometry for a subset of those candidates yielded 142 new associations with active galactic nuclei that are γ -ray sources, provided alternative associations for seven objects, and improved positions for another 144 known associations to the milliarcsecond level of accuracy. In addition, for 245 unassociated γ -ray sources we did not find a single compact radio source above 2 mJy within 3 σ of their γ -ray localization. A significant fraction of these empty fields, 39%, are located away from the Galactic plane. We also found 36 extended radio sources that are candidates for association with a corresponding γ -ray object, 19 of which are most likely supernova remnants or H ii regions, whereas 17 could be radio galaxies.« less

X-ray Properties and the Environment of Compact Radio Sources.

NASA Astrophysics Data System (ADS)

Siemiginowska, Aneta; Sobolewska, Malgorzata; Guainazzi, Matteo; Hardcastle, Martin; Migliori, Giulia; Ostorero, Luisa; Stawarz, Lukasz

2018-01-01

Compact extragalactic radio sources provide important insights into the initial stages of radio source evolution and probe states of a black hole activity at the time of the formation of the relativistic outflow. Such outflows propagate out to hundreds kpc distances from the origin and impact environment on many scales, and thus influence evolution of structures in the universe. These compact sources show radio features typically observed in large-scale radio galaxies (jets, lobes, hot spots), but contained within the central 1 kpc region of the host galaxy. Compact Symmetric Objects (CSOs, a subclass of GigaHertz Peaked spectrum radio sources) are symmetric and not affected by beaming. Their linear radio size can be translated into a source age if one measures the expansion velocity of the radio structures. Such ages has been measured for a small sample of CSOs. Using the Chandra X-ray Observatory and XMM-Newton we observed a pilot samples of 16 CSOs in X-rays (6 for the first time). Our results show heterogeneous nature of the CSOs X-ray emission indicating a range of AGN luminosities and a complex environment. In particular, we identified four Compton Thick sources with a dense medium (equivalent column > 1e24 cm^-2) capable of disturbing/slowing down the jet and confining the jet to a small region. Thus for the first time we gain the observational evidence in X-ray domain in favor of the hypothesis that in a sub-population of CSOs the radio jets may be confined by the dense X-ray obscuring medium. As a consequence, the kinematic ages of these CSOs may be underestimated.. We discuss the implications of our results on the emission models of CSOs, the earliest stages of the radio source evolution, jet interactions with the ISM, diversity of the environments in which the jets expand, and jet-galaxy co-evolution.Partial support for this work was provided by the NASA grants GO1-12145X, GO4-15099X, NNX10AO60G, NNX17AC23G and XMM AO15 project 78461. This work supported in part by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center.

Revisiting the Gamma-Ray Source 2FGL J1823.8+4312

NASA Astrophysics Data System (ADS)

Stern, Daniel; Assef, Roberto J.

2013-02-01

One of the great challenges of gamma-ray astronomy is identifying the lower energy counterparts to these high-energy sources. Recently, in this journal, Massaro et al. attempted to find the counterpart of 2FGL J1823.8+4312, a gamma-ray active galactic nucleus (AGN) of uncertain type from the Second Fermi Large Area Telescope catalog. After considering mid-infrared data in the field from the Wide-field Infrared Survey Explorer (WISE), those authors conclude that the preferred identification of 2FGL J1823.8+4312 is WISE J182352.33+431452.5, despite the fact that the mid-infrared source is undetected at radio energies. They claim that WISE J182352.33+431452.5 constitutes the discovery of a new class of extragalactic X-ray source, either a radio-faint blazar or the prototype of a new class of active galaxy with an enigmatic spectral energy distribution. This conclusion is claimed to be independent of whether or not the WISE source is the actual counterpart to 2FGL J1823.8+4312. Based on a re-analysis of public data in this field and new spectroscopy from Palomar, we conclude that WISE J182352.33+431452.5 is a dust-reddened quasar at z = 0.560, a representative example of a very common extragalactic AGN class. Were WISE J182352.33+431452.5 to be associated with the gamma-ray emission, this would be an unusual and exciting discovery. However, we argue that 2FGL J1823.8+4312 is more likely associated with either WISE J182409.25+431404.7 or, more likely, WISE J182419.04+430949.6, two radio-loud sources in the field. The former is a radio-loud quasar and the latter is an optically variable source with a featureless blue spectrum.

High-mass Star Formation Toward Southern Infrared Bubble S10

NASA Astrophysics Data System (ADS)

Ranjan Das, Swagat; Tej, Anandmayee; Vig, Sarita; Ghosh, Swarna K.; Ishwara Chandra, C. H.

2016-11-01

An investigation in radio and infrared wavelengths of two high-mass star-forming regions toward the southern Galactic bubble S10 is presented here. The two regions under study are associated with the broken bubble S10 and Extended Green Object, G345.99-0.02, respectively. Radio continuum emission mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India, is detected toward both of the regions. These regions are estimated to be ionized by early-B- to late-O-type stars. Spitzer GLIMPSE mid-infrared data is used to identify young stellar objects (YSOs) associated with these regions. A Class-I/II-type source, with an estimated mass of 6.2 M ⊙, lies ˜7″ from the radio peak. Pixel-wise, modified blackbody fits to the thermal dust emission using Herschel far-infrared data is performed to construct dust temperature and column density maps. Eight clumps are detected in the two regions using the 250 μm image. The masses and linear diameter of these range between ˜300-1600 M ⊙ and 0.2-1.1 pc, respectively, which qualifies them as high-mass star-forming clumps. Modeling of the spectral energy distribution of these clumps indicates the presence of high luminosity, high accretion rate, massive YSOs possibly in the accelerating accretion phase. Furthermore, based on the radio and MIR morphology, the occurrence of a possible bow wave toward the likely ionizing star is explored.

Giant Metrewave Radio Telescope Observations of Head–Tail Radio Galaxies

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

Sebastian, Biny; Lal, Dharam V.; Rao, A. Pramesh, E-mail: biny@ncra.tifr.res.in

We present results from a study of seven large known head–tail radio galaxies based on observations using the Giant Metrewave Radio Telescope at 240 and 610 MHz. These observations are used to study the radio morphologies and distribution of the spectral indices across the sources. The overall morphology of the radio tails of these sources is suggestive of random motions of the optical host around the cluster potential. The presence of multiple bends and wiggles in several head–tail sources is possibly due to the precessing radio jets. We find steepening of the spectral index along the radio tails. The prevailingmore » equipartition magnetic field also decreases along the radio tails of these sources. These steepening trends are attributed to the synchrotron aging of plasma toward the ends of the tails. The dynamical ages of these sample sources have been estimated to be ∼10{sup 8} yr, which is a factor of six more than the age estimates from the radiative losses due to synchrotron cooling.« less

The X-Ray Core of the Low-Luminosity Radio Galaxy 3C346 and ASCA Spectroscopy to Test BL LAC/Radio Galaxy Unification

NASA Technical Reports Server (NTRS)

Worrall, Diana

2000-01-01

Radio galaxies are relatively faint sources for Advanced Spacecraft for Cosmology Astrophysics (ASCA), and so in order to get the best possible results from the observations two things have been necessary, both of which delayed the fast preparation of papers. Firstly, the best possible data screening and background subtraction were necessary to improve the signal-to-noise, and all our several initial analysis trials were discarded in favor of using FTOOLS versions 4.1 and above. Secondly, we found that the ASCA spectra were statistically too poor to discriminate well between non-thermal and thermal models, never mind the mixture of the two which we expected on the basis of our ROSAT spatial separation of components in radio galaxies. This means that in each case we have needed to combine the ASCA spectroscopy with analysis of data from other X-ray or radio observations in order to exploit the ASCA data to the full. Our analysis for 3C 346 has yielded the cleanest final result. This powerful radio galaxy at a redshift of 0.161, lies in a poor cluster, which we have separated well from the dominant X-ray component of unresolved emission using a spatial analysis of archival ROSAT data. We were then able to fix the thermal component in our ASCA spectral analysis, and have found evidence that the unresolved emission varied by 32 +/- 13% over the 18 months between the ROSAT and ASCA observations. The unresolved X-ray emission does not suffer from intrinsic absorption, and we have related it to radio structures on both milliarcsecond scales and the arcsecond scales which Chandra can resolve. The source is a target of a Chandra AO2 proposal which we have recently submitted to follow up on our ASCA (and ROSAT) work. 3C 346's orientation to the line of sight is uncertain. However, the absence of X-ray absorption, and the radio/optical/X-ray colors, when combined with with previous radio evidence that the source is a foreshortened radio galaxy of the FRII class, suggest that the radio jets are seen at an angle to the line of sight of about 30 deg, intermediate between the radio-galaxy and quasar classes. The relatively hard ASCA response has allowed us to place an upper limit of 5.6 x 10(exp 43) ergs/ s on the 2-10 keV luminosity of any central X-ray component absorbed bN, gas which might be obscuring the broad-line emission region. Attached to this report is an almost final draft of a paper which we have prepared for submission to the Astrophysical Journal. Our combined ASCA and ROSAT results for NGC 6251 rule out our previously preferred flat-spectrum model and inverse-Compton interpretation for the source based on ROSAT data alone, but a softer X-ray spectrum and moderate absorption bring all the available data (including our early VLA HI measurements) into consistency, and we are reasonably confident that we understand the processes responsible for the X-ray emission. We have made some more sensitive HI absorption measurements which are currently being analyzed, and our plans are to publish our ASCA analysis in conjunction with the new HI results. The ASCA data for NGC 4261 have been difficult to interpret. A re-analysis of our ROSAT data with a wider range of physical parameters brings the ROSAT and ASCA results into reasonable agreement only if the emission from hot gas dominates more than suggested by our earlier work, which is itself unexpected since the radio core is bright and a large jet-related X-ray component would bring the source into agreement with results for others of its type. However, we have recently received our Chandra A01 data for this source, with the spatial resolution which allows us to separate thermal and non-thermal emission components. Our ASCA results will be re-interpreted once the analysis of our Chandra data is complete. The interpretation of the ASCA data for BL Lac object 3C 371 is ongoing, in conjunction with analysis of archival multifrequency data. Radio galaxies are complex in their X-ray properties, and hindsight has shown that the spatial resolution of ASCA is too poor for a reliable interpretation of the data without drawing on other observations. However, the ASCA spectra have made a useful contribution to the interpretation of these sources, and the groundwork is now there for more sensitive work using Chandra and XMM-Newton.

VizieR Online Data Catalog: VLBI ICRF2 (Fey+, 2015)

NASA Astrophysics Data System (ADS)

Fey, A. L.; Gordon, D.; Jacobs, C. S.; Ma, C.; Gaume, R. A.; Arias, E. F.; Bianco, G.; Boboltz, D. A.; Bockmann, S.; Bolotin, S.; Charlot, P.; Collioud, A.; Engelhardt, G.; Gipson, J.; Gontier, A.-M.; Heinkelmann, R.; Kurdubov, S.; Lambert, S.; Lytvyn, S.; MacMillan, D. S.; Malkin, Z.; Nothnagel, A.; Ojha, R.; Skurikhina, E.; Sokolova, J.; Souchay, J.; Sovers, O. J.; Tesmer, V.; Titov, O.; Wang, G.; Zharov, V.

2016-01-01

We present the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths using nearly 30 years of Very Long Baseline Interferometry observations. The earliest observations used are from 1979 August and the latest are from 2009 March. ICRF2 consists of accurate positions of 295 new "defining" sources and positions of 3119 additional compact radio sources to densify the frame. ICRF2 has more than 5 times as many sources as ICRF1 (Ma et al. 1997, cat. I/251), is roughly 5-6 times more accurate, and is nearly twice as stable in the orientation of its axes. (3 data files).

Distribution of inhomogeneities in the interstellar plasma in the directions of three distant pulsars from observations with the RadioAstron ground-space interferometer

NASA Astrophysics Data System (ADS)

Popov, M. V.; Andrianov, A. S.; Bartel, N.; Gwinn, C.; Joshi, B. C.; Jauncey, D.; Kardashev, N. S.; Rudnitskii, A. G.; Smirnova, T. V.; Soglasnov, V. A.; Fadeev, E. N.; Shishov, V. I.

2016-09-01

The RadioAstron ground-space interferometer has been used to measure the angular sizes of the scattering disks of the three distant pulsars B1641-45, B1749-28, and B1933+16. The observations were carried out with the participation of the Westerbork Synthesis Radio Telescope; two 32-m telescopes at Torun, Poland and Svetloe, Russia (the latter being one antenna of the KVAZAR network); the Saint Croix VLBA antenna; the Arecibo radio telescope; the Parkes, Narrabri (ATCA), Mopra, Hobart, and Ceduna Australian radio telescopes; and the Hartebeesthoek radio telescope in South Africa. The full widths at half maximum of the scattering disks were 27 mas at 1668 MHz for B1641-45, 0.5 mas at 1668 MHz for B1749-28, and 12.3 at 316 MHz and 0.84 mas at 1668 MHz for B1933+16. The characteristic time scales for scatter-broadening of the pulses on inhomogeneities in the interstellar plasma τsc were also measured for these pulsars using various methods. Joint knowledge of the size of the scattering disk and the scatter-broadening time scale enables estimation of the distance to the effective scattering screen d. For B1641-45, d = 3.0 kpc for a distance to the pulsar D = 4.9 kpc, and for B1749-28, d = 0.95 kpc for D = 1.3 kpc. Observations of B1933+16 were carried out simultaneously at 316 and 1668 MHz. The positions of the screen derived using the measurements at the two frequencies agree: d 1 = 2.6 and d 2 = 2.7 kpc, for a distance to the pulsar of 3.7 kpc. Two screens were detected for this pulsar from an analysis of parabolic arcs in the secondary dynamic spectrum at 1668 MHz, at 1.3 and 3.1 kpc. The scattering screens for two of the pulsars are identified with real physical objects located along the lines of sight toward the pulsars: G339.1-04 (B1641-45) and G0.55-0.85 (B1749-28).

Flat-Spectrum Radio Sources as Likely Counterparts of Unidentified INTEGRAL Sources (Research Note)

NASA Technical Reports Server (NTRS)

Molina, M.; Landi, R.; Bassani, L.; Malizia, A.; Stephen, J. B.; Bazzano, A.; Bird, A. J.; Gehrels, N.

2012-01-01

Many sources in the fourth INTEGRAL/IBIS catalogue are still unidentified since they lack an optical counterpart. An important tool that can help in identifying and classifying these sources is the cross-correlation with radio catalogues, which are very sensitive and positionally accurate. Moreover, the radio properties of a source, such as the spectrum or morphology, could provide further insight into its nature. In particular, flat-spectrum radio sources at high Galactic latitudes are likely to be AGN, possibly associated to a blazar or to the compact core of a radio galaxy. Here we present a small sample of 6 sources extracted from the fourth INTEGRAL/IBIS catalogue that are still unidentified or unclassified, but which are very likely associated with a bright, flat-spectrum radio object. To confirm the association and to study the source X-ray spectral parameters, we performed X-ray follow-up observations with Swift/XRT of all objects. We report in this note the overall results obtained from this search and discuss the nature of each individual INTEGRAL source. We find that 5 of the 6 radio associations are also detected in X-rays; furthermore, in 3 cases they are the only counterpart found. More specifically, IGR J06073-0024 is a flat-spectrum radio quasar at z = 1.08, IGR J14488-4008 is a newly discovered radio galaxy, while IGR J18129-0649 is an AGN of a still unknown type. The nature of two sources (IGR J07225-3810 and IGR J19386-4653) is less well defined, since in both cases we find another X-ray source in the INTEGRAL error circle; nevertheless, the flat-spectrum radio source, likely to be a radio loud AGN, remains a viable and, in fact, a more convincing association in both cases. Only for the last object (IGR J11544-7618) could we not find any convincing counterpart since the radio association is not an X-ray emitter, while the only X-ray source seen in the field is a G star and therefore unlikely to produce the persistent emission seen by INTEGRAL.

A Spitzer Spectroscopic Survey of Low-Ionization Nuclear Emission-Line Regions: Characterization of the Central Source

DTIC Science & Technology

2009-02-01

All Sky Survey ( 2MASS ) coordinates of the nucleus were used to verify the coordinates of each observation. The SH and LH staring observations include...isolate the nuclear region in the mapping obser- vations, fluxes were extracted from a single slit coinciding with the radio or 2MASS nuclear...presence of a hard X-ray point source coin- cident with either the radio or 2MASS nucleus and log(LX) 38 erg s−1. The resulting subsample consists of

A Multi-wavelength Study of the Turbulent Central Engine of the Low-mass AGN Hosted by NGC 404

NASA Astrophysics Data System (ADS)

Nyland, Kristina; Davis, Timothy A.; Nguyen, Dieu D.; Seth, Anil; Wrobel, Joan M.; Kamble, Atish; Lacy, Mark; Alatalo, Katherine; Karovska, Margarita; Maksym, W. Peter; Mukherjee, Dipanjan; Young, Lisa M.

2017-08-01

The nearby dwarf galaxy NGC 404 harbors a low-luminosity active galactic nucleus powered by the lowest-mass (<150,000 M ⊙) central massive black hole (MBH), with a dynamical mass constraint, currently known, thus providing a rare low-redshift analog to the MBH “seeds” that formed in the early universe. Here, we present new imaging of the nucleus of NGC 404 at 12-18 GHz with the Karl G. Jansky Very Large Array (VLA) and observations of the CO(2-1) line with the Atacama Large Millimeter/Submillimeter Array (ALMA). For the first time, we have successfully resolved the nuclear radio emission, revealing a centrally peaked, extended source spanning 17 pc. Combined with previous VLA observations, our new data place a tight constraint on the radio spectral index and indicate an optically thin synchrotron origin for the emission. The peak of the resolved radio source coincides with the dynamical center of NGC 404, the center of a rotating disk of molecular gas, and the position of a compact, hard X-ray source. We also present evidence for shocks in the NGC 404 nucleus from archival narrowband HST imaging, Chandra X-ray data, and Spitzer mid-infrared spectroscopy, and discuss possible origins for the shock excitation. Given the morphology, location, and steep spectral index of the resolved radio source, as well as constraints on nuclear star formation from the ALMA CO(2-1) data, we find the most likely scenario for the origin of the radio source in the center of NGC 404 to be a radio outflow associated with a confined jet driven by the active nucleus.

A Multi-wavelength Study of the Turbulent Central Engine of the Low-mass AGN Hosted by NGC 404

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

Nyland, Kristina; Lacy, Mark; Davis, Timothy A.

The nearby dwarf galaxy NGC 404 harbors a low-luminosity active galactic nucleus powered by the lowest-mass (<150,000 M {sub ⊙}) central massive black hole (MBH), with a dynamical mass constraint, currently known, thus providing a rare low-redshift analog to the MBH “seeds” that formed in the early universe. Here, we present new imaging of the nucleus of NGC 404 at 12–18 GHz with the Karl G. Jansky Very Large Array (VLA) and observations of the CO(2–1) line with the Atacama Large Millimeter/Submillimeter Array (ALMA). For the first time, we have successfully resolved the nuclear radio emission, revealing a centrally peaked,more » extended source spanning 17 pc. Combined with previous VLA observations, our new data place a tight constraint on the radio spectral index and indicate an optically thin synchrotron origin for the emission. The peak of the resolved radio source coincides with the dynamical center of NGC 404, the center of a rotating disk of molecular gas, and the position of a compact, hard X-ray source. We also present evidence for shocks in the NGC 404 nucleus from archival narrowband HST imaging, Chandra X-ray data, and Spitzer mid-infrared spectroscopy, and discuss possible origins for the shock excitation. Given the morphology, location, and steep spectral index of the resolved radio source, as well as constraints on nuclear star formation from the ALMA CO(2–1) data, we find the most likely scenario for the origin of the radio source in the center of NGC 404 to be a radio outflow associated with a confined jet driven by the active nucleus.« less

VizieR Online Data Catalog: Radio fluxes of 195 ICRF2-Gaia transfer sources (Le Bail+, 2016)

NASA Astrophysics Data System (ADS)

Le Bail, K.; Gipson, J. M.; Gordon, D.; MacMillan, D. S.; Behrend, D.; Thomas, C. C.; Bolotin, S.; Himwich, W. E.; Baver, K. D.; Corey, B. E.; Titus, M.; Bourda, G.; Charlot, P.; Collioud, A.

2016-07-01

The second realization of the International Celestial Reference Frame (ICRF2) is based on Very Long Baseline Interferometry (VLBI) data at radio frequencies in X band and S band. The European Space Agency's Gaia mission, launched on 2013 December 19, started routine scientific operations in 2014 July. By scanning the whole sky, it is expected to observe ~500000 Quasi Stellar Objects in the optical domain. This means that, in the future, two extragalactic celestial reference frames, at two different frequency domains, will coexist. It will thus be important to align them very accurately. In 2012, the Laboratoire d'Astrophysique de Bordeaux (LAB) selected 195 sources from ICRF2 that will be observed by Gaia and should be suitable for aligning the radio and optical frames: they are called ICRF2-Gaia transfer sources. The LAB submitted a proposal to the International VLBI Service (IVS) to regularly observe these ICRF2-Gaia transfer sources at the same rate as Gaia observes them in the optical realm, e.g., roughly once a month. Of the 195 sources, all but one have been successfully observed in the 12 months prior to 2015 September 01. Table1 lists the 195 ICRF2-Gaia transfer sources. Beginning in 2003 June, the Goddard VLBI group developed a program to purposefully monitor when sources were observed and to increase the observations of "under-observed" sources. In 2013 March, we added all 195 ICRF2-Gaia transfer sources to the IVS source monitoring program with an observation target of 12 successful sessions per year. (1 data file).

Emission Patterns of Solar Type III Radio Bursts: Stereoscopic Observations

NASA Technical Reports Server (NTRS)

Thejappa, G.; MacDowall, R.; Bergamo, M.

2012-01-01

Simultaneous observations of solar type III radio bursts obtained by the STEREO A, B, and WIND spacecraft at low frequencies from different vantage points in the ecliptic plane are used to determine their directivity. The heliolongitudes of the sources of these bursts, estimated at different frequencies by assuming that they are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere, and the heliolongitudes of the spacecraft are used to estimate the viewing angle, which is the angle between the direction of the magnetic field at the source and the line connecting the source to the spacecraft. The normalized peak intensities at each spacecraft Rj = Ij /[Sigma]Ij (the subscript j corresponds to the spacecraft STEREO A, B, and WIND), which are defined as the directivity factors are determined using the time profiles of the type III bursts. It is shown that the distribution of the viewing angles divides the type III bursts into: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field with angular width of approximately 2 deg and (2) bursts emitting into a wider cone with angular width spanning from [approx] -100 deg to approximately 100 deg. The plots of the directivity factors versus the viewing angles of the sources from all three spacecraft indicate that the type III emissions are very intense along the tangent to the spiral magnetic field lines at the source, and steadily fall as the viewing angles increase to higher values. The comparison of these emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relatively weaker bursts visible to a wide range of angles are probably emitted in the harmonic mode.

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

NASA Technical Reports Server (NTRS)

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

1999-01-01

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

X-RAY AND RADIO OBSERVATIONS OF THE MASSIVE STAR-FORMING REGION IRAS 20126+4104

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

Montes, V. A.; Hofner, P.; Anderson, C.

2015-08-15

We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6 cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17′ × 17′ ACIS-I field, and a total of 13 radio sources within the 9.′2 primary beam at 4.9 GHz. Among these observtions are the first 6 cm detections of the central sources reported by Hofner et al., namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-raymore » sources had 6 cm counterparts. Based on an NIR color–color analysis and on the Besançon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2 pc from the massive protostar.« less

A physical classification scheme for blazars

NASA Astrophysics Data System (ADS)

Landt, Hermine; Padovani, Paolo; Perlman, Eric S.; Giommi, Paolo

2004-06-01

Blazars are currently separated into BL Lacertae objects (BL Lacs) and flat spectrum radio quasars based on the strength of their emission lines. This is performed rather arbitrarily by defining a diagonal line in the Ca H&K break value-equivalent width plane, following Marchã et al. We readdress this problem and put the classification scheme for blazars on firm physical grounds. We study ~100 blazars and radio galaxies from the Deep X-ray Radio Blazar Survey (DXRBS) and 2-Jy radio survey and find a significant bimodality for the narrow emission line [OIII]λ5007. This suggests the presence of two physically distinct classes of radio-loud active galactic nuclei (AGN). We show that all radio-loud AGN, blazars and radio galaxies, can be effectively separated into weak- and strong-lined sources using the [OIII]λ5007-[OII]λ3727 equivalent width plane. This plane allows one to disentangle orientation effects from intrinsic variations in radio-loud AGN. Based on DXRBS, the strongly beamed sources of the new class of weak-lined radio-loud AGN are made up of BL Lacs at the ~75 per cent level, whereas those of the strong-lined radio-loud AGN include mostly (~97 per cent) quasars.

The Second Catalog Of Active Galactic Nuclei Detected By The Fermi Large Area Telescope

DOE PAGES

Ackermann, M.

2011-12-02

The second catalog of active galactic nuclei (AGNs) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation is presented. The Second LAT AGN Catalog (2LAC) includes 1017 γ-ray sources located at high Galactic latitudes (|b| > 10°) that are detected with a test statistic (TS) greater than 25 and associated statistically with AGNs. However some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently we define a clean sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lacs), 310 flat-spectrum radio quasars (FSRQs), 157 candidate blazars ofmore » unknown type (i.e., with broad-band blazar characteristics but with no optical spectral measurement yet), eight misaligned AGNs, four narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types and two starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. While almost all FSRQs have a synchrotron-peak frequency < 10 14 Hz, about half of the BL Lacs have a synchrotron-peak frequency > 10 15 Hz. The 2LAC represents a significant improvement relative to the First LAT AGN Catalog (1LAC), with 52% more associated sources. The full characterization of the newly detected sources will require more broad-band data. Various properties, such as γ-ray fluxes and photon power law spectral indices, redshifts, γ-ray luminosities, variability, and archival radio luminosities—and their correlations are presented and discussed for the different blazar classes. The general trends observed in 1LAC are confirmed.« less

Radio and X-ray variability of the nucleus of Centaurus A (NGC 5128)

NASA Technical Reports Server (NTRS)

Beall, J. H.; Rose, W. K.; Graf, W.; Price, K. M.; Dent, W. A.; Hobbs, R. W.; Conklin, E. K.; Ulich, B. L.; Dennis, B. R.; Crannell, C. J.

1977-01-01

Centaurus A was observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons.

A Submillimeter Perspective on the Goods Fields. II. The High Radio Power Population in the Goods-N

NASA Astrophysics Data System (ADS)

Barger, A. J.; Cowie, L. L.; Owen, F. N.; Hsu, L.-Y.; Wang, W.-H.

2017-01-01

We use ultradeep 20 cm data from the Karl G. Jansky Very Large Array and 850 μm data from SCUBA-2 and the Submillimeter Array of an 124 arcmin2 region of the Chandra Deep Field-north to analyze the high radio power ({P}20{cm}> {10}31 erg s-1 Hz-1) population. We find that 20 (42 ± 9%) of the spectroscopically identified z> 0.8 sources have consistent star formation rates (SFRs) inferred from both submillimeter and radio observations, while the remaining sources have lower (mostly undetected) submillimeter fluxes, suggesting that active galactic nucleus (AGN) activity dominates the radio power in these sources. We develop a classification scheme based on the ratio of submillimeter flux to radio power versus radio power and find that it agrees with AGN and star-forming galaxy classifications from Very Long Baseline Interferometry. Our results provide support for an extremely rapid drop in the number of high SFR galaxies above about a thousand solar masses per year (Kroupa initial mass function) and for the locally determined relation between X-ray luminosity and radio power for star-forming galaxies applying at high redshifts and high radio powers. We measure far-infrared (FIR) luminosities and find that some AGNs lie on the FIR-radio correlation, while others scatter below. The AGNs that lie on the correlation appear to do so based on their emission from the AGN torus. We measure a median radio size of 1.″0 ± 0.3 for the star-forming galaxies. The radio sizes of the star-forming galaxies are generally larger than those of the AGNs. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

Investigation of Ionospheric Turbulence and Whistler Wave Interactions with Space Plasmas

DTIC Science & Technology

2012-11-21

an oscillating LOS velocity with the same periodicity as the heating modulation pattern. A set of Fourier periodogram from the MUIR LOS velocity...scale ionospheric turbulence are discussed separately, viz., (a) anomalous heat source-induced acoustic gravity waves (AGW), and (b) HF radio wave...ionospheric ducts, acoustic gravity waves (AGWs), anomalous heat sources, inner and outer radiation belts, L parameter, whistler wave interactions

A direct localization of a fast radio burst and its host.

PubMed

Chatterjee, S; Law, C J; Wharton, R S; Burke-Spolaor, S; Hessels, J W T; Bower, G C; Cordes, J M; Tendulkar, S P; Bassa, C G; Demorest, P; Butler, B J; Seymour, A; Scholz, P; Abruzzo, M W; Bogdanov, S; Kaspi, V M; Keimpema, A; Lazio, T J W; Marcote, B; McLaughlin, M A; Paragi, Z; Ransom, S M; Rupen, M; Spitler, L G; van Langevelde, H J

2017-01-04

Fast radio bursts are astronomical radio flashes of unknown physical nature with durations of milliseconds. Their dispersive arrival times suggest an extragalactic origin and imply radio luminosities that are orders of magnitude larger than those of all known short-duration radio transients. So far all fast radio bursts have been detected with large single-dish telescopes with arcminute localizations, and attempts to identify their counterparts (source or host galaxy) have relied on the contemporaneous variability of field sources or the presence of peculiar field stars or galaxies. These attempts have not resulted in an unambiguous association with a host or multi-wavelength counterpart. Here we report the subarcsecond localization of the fast radio burst FRB 121102, the only known repeating burst source, using high-time-resolution radio interferometric observations that directly image the bursts. Our precise localization reveals that FRB 121102 originates within 100 milliarcseconds of a faint 180-microJansky persistent radio source with a continuum spectrum that is consistent with non-thermal emission, and a faint (twenty-fifth magnitude) optical counterpart. The flux density of the persistent radio source varies by around ten per cent on day timescales, and very long baseline radio interferometry yields an angular size of less than 1.7 milliarcseconds. Our observations are inconsistent with the fast radio burst having a Galactic origin or its source being located within a prominent star-forming galaxy. Instead, the source appears to be co-located with a low-luminosity active galactic nucleus or a previously unknown type of extragalactic source. Localization and identification of a host or counterpart has been essential to understanding the origins and physics of other kinds of transient events, including gamma-ray bursts and tidal disruption events. However, if other fast radio bursts have similarly faint radio and optical counterparts, our findings imply that direct subarcsecond localizations may be the only way to provide reliable associations.

Galactic Supernova Remnant Candidates Discovered by THOR

NASA Astrophysics Data System (ADS)

Anderson, Loren; Wang, Yuan; Bihr, Simon; Rugel, Michael; Beuther, Henrik; THOR Team

2018-01-01

There is a considerable deficiency in the number of known supernova remnants (SNRs) in the Galaxy compared to that expected. Searches for extended low-surface brightness radio sources may find new Galactic SNRs, but confusion with the much larger population of HII regions makes identifying such features challenging. SNRs can, however, be separated from HII regions using their significantly lower mid-infrared (MIR) to radio continuum intensity ratios. We use the combination of high-resolution 1-2 GHz continuum data from The HI, OH, Recombination line survey of the Milky Way (THOR) and lower-resolution VLA 1.4 GHz Galactic Plane Survey (VGPS) continuum data, together with MIR data from the Spitzer GLIMPSE, Spitzer MIPSGAL, and WISE surveys to identify SNR candidates. To ensure that the candidates are not being confused with HII regions, we exclude radio continuum sources from the WISE Catalog of Galactic HII Regions, which contains all known and candidate H II regions in the Galaxy. We locate 76 new Galactic SNR candidates in the THOR and VGPS combined survey area of 67.4deg>l>17.5deg, |b|<1.25deg and measure the radio flux density for 52 previously-known SNRs. The candidate SNRs have a similar spatial distribution to the known SNRs, although we note a large number of new candidates near l=30deg, the tangent point of the Scutum spiral arm. The candidates are on average smaller in angle compared to the known regions, 6.4'+/-4.7' versus 11.0'+/-7.8', and have lower integrated flux densities. If the 76 candidates are confirmed as true SNRs, for example using radio polarization measurements or by deriving radio spectral indices, this would more than double the number of known Galactic SNRs in the survey area. This large increase would still, however, leave a discrepancy between the known and expected SNR populations of about a factor of two.

A young source of optical emission from distant radio galaxies.

PubMed

Hammer, F; Fèvre, O Le; Angonin, M C

1993-03-25

DISTANT radio galaxies provide valuable insights into the properties of the young Universe-they are the only known extended optical sources at high redshift and might represent an early stage in the formation and evolution of galaxies in general. This extended optical emission often has very complex morphologies, but the origin of the light is still unclear. Here we report spectroscopic observations for several distant radio galaxies (0.75≤ z ≤ 1.1) in which the rest-frame spectra exhibit featureless continua between 2,500 Å and 5,000 Å. We see no evidence for the break in the spectrum at 4,000 Å expected for an old stellar population 1-3 , and suggest that young stars or scattered emissions from the active nuclei are responsible for most of the observed light. In either case, this implies that the source of the optical emission is com-parable in age to the associated radio source, namely 10 7 years or less.

The History and Evolution of Young and Distant Radio Sources

NASA Astrophysics Data System (ADS)

Collier, Jordan

We study two classes of object to gain a better understanding of the evolution of Active Galactic Nuclei (AGN): Infrared-Faint Radio Sources (IFRSs) and Gigahertz Peaked Spectrum (GPS) / Compact Steep Spectrum (CSS) sources. IFRSs are a recently discovered rare class of object, which were found to be strong in the radio but undetectable in extremely sensitive infrared observations from the Spitzer Space Telescope, even in stacked images with sigma < 1muJy. IFRSs were found to exhibit a relatively high sky density, and were thought to represent AGN at z > 3. Therefore, IFRSs may significantly increase the number of known high-redshift galaxies. However, their non-detections in the optical and infrared prevented confirmation of their nature. Previous studies of IFRSs focused on very sensitive observations of a few small regions of the sky, and the largest sample consisted of 55 IFRSs. However, we follow the strategy of combining radio data with IR and optical data for a large region of the sky. Using these data, we discover a population of >1300 brighter IFRSs which are, for the first time, reliably detected in the infrared and optical. We present the first spectroscopic redshifts of IFRSs and show that the brightest IFRSs are at z > 2. Furthermore, we rule out that IFRSs are Star Forming Galaxies, hotspots, lobes or misidentifications. We find the first X-ray counterparts of IFRSs, and increase the number of known polarised IFRSs five-fold. We present an analysis of their radio spectra and show that IFRSs consist of GPS, CSS and ultra-steep-spectrum sources. We follow up >50 of these using VLBI observations, and confirm the AGN status of IFRSs. GPS and CSS sources are compact radio sources with a convex radio spectrum. They are widely thought to represent young and evolving radio galaxies that have recently launched their jets. However, good evidence exists in individual cases that GPS and CSS sources are one of the following: 1) frustrated by interactions with dense gas and dust in their environment; 2) prematurely dying radio sources; 3) recurrent radio galaxies. Their convex spectrum is generally thought to be caused by Synchrotron Self Absorption (SSA), an internal process in which the same population of electrons is responsible for the synchrotron emission and self-absorption. However, recent studies have shown that the convex spectrum may be caused by Free-Free Absorption (FFA), an external process in which an inhomogeneous screen absorbs the synchrotron emission. The majority of GPS and CSS samples consist of Jy-level and therefore, high-luminosity sources. VLBI images show that GPS and CSS sources typically have double-lobed, edge-brightened morphologies on mas scales, appearing as scaled down versions of Fanaroff-Riley Class II (FR II) galaxies. Recently, two low-luminosity GPS sources were found to have jet-brightened morphologies, which appeared as scaled down versions of Fanaroff-Riley Class I (FR I) galaxies. From this, it was proposed that there exists a morphology-luminosity break analogous to the FR I/II break and that low-luminosity GPS and CSS sources are the compact counterparts of FR I galaxies. However, this hypothesis remains unconfirmed, since very few samples of low-luminosity GPS and CSS sources exist. We conclude that, despite being historically favoured, single inhomogeneous SSA is not the dominant form of absorption amongst a large fraction of GPS and CSS sources. We find that FFA provides a good model for the majority of the spectra with observable turnovers, suggesting an inhomogeneous and clumpy ambient medium. Furthermore, we conclude that the majority of our GPS and CSS sources are young and evolving and may undergo recurrent activity over small time scales. We conclude that a very small fraction of GPS and CSS sources consists of frustrated, dying or restarted radio galaxies. (Abstract shortened by ProQuest.).

47 CFR 95.1125 - RF safety.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PERSONAL RADIO SERVICES Wireless Medical Telemetry Service (WMTS) General Provisions § 95.1125 RF safety. Portable devices as defined in § 2.1093(b) of this chapter operating in the WMTS are subject to radio frequency...

J1649+2635: A Grand-Design Spiral with a Large Double-Lobed Radio Source

NASA Technical Reports Server (NTRS)

Mao, Minnie Y.; Owen, Frazer; Duffin, Ryan; Keel, Bill; Lacy, Mark; Momjian, Emmanuel; Morrison, Glenn; Mroczkowski, Tony; Neff, Susan; Norris, Ray P.;

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

Migliori, G.; Loh, A.; Corbel, S.

We report the γ -ray detection of a young radio galaxy, PKS 1718−649, belonging to the class of compact symmetric objects (CSOs), with the Large Area Telescope (LAT) on board the Fermi satellite. The third Fermi Gamma-ray LAT catalog (3FGL) includes an unassociated γ -ray source, 3FGL J1728.0−6446, located close to PKS 1718−649. Using the latest Pass 8 calibration, we confirm that the best-fit 1 σ position of the γ -ray source is compatible with the radio location of PKS 1718−649. Cross-matching of the γ -ray source position with the positions of blazar sources from several catalogs yields negative results.more » Thus, we conclude that PKS 1718−649 is the most likely counterpart to the unassociated LAT source. We obtain a detection test statistics TS ∼ 36 (>5 σ ) with a best-fit photon spectral index Γ = 2.9 ± 0.3 and a 0.1–100 GeV photon flux density F {sub 0.1−100} {sub GeV} = (11.5 ± 0.3) × 10{sup −9} ph cm{sup −2} s{sup −1}. We argue that the linear size (∼2 pc), the kinematic age (∼100 years), and the source distance ( z = 0.014) make PKS 1718−649 an ideal candidate for γ -ray detection in the framework of the model proposing that the most compact and the youngest CSOs can efficiently produce GeV radiation via inverse-Compton scattering of the ambient photon fields by the radio lobe non-thermal electrons. Thus, our detection of the source in γ -rays establishes young radio galaxies as a distinct class of extragalactic high-energy emitters and yields a unique insight on the physical conditions in compact radio lobes interacting with the interstellar medium of the host galaxy.« less

The Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS): survey design, data catalogue and GAMA/WiggleZ spectroscopy

NASA Astrophysics Data System (ADS)

Ching, John H. Y.; Sadler, Elaine M.; Croom, Scott M.; Johnston, Helen M.; Pracy, Michael B.; Couch, Warrick J.; Hopkins, A. M.; Jurek, Russell J.; Pimbblet, K. A.

2017-01-01

We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ˜ 0.8. The catalogue covers ˜800 deg2 of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of Imod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radio-loud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc.

VizieR Online Data Catalog: GB6 catalog of radio sources (Gregory+ 1996)

NASA Astrophysics Data System (ADS)

Gregory, P. C.; Scott, W. K.; Douglas, K.; Condon, J. J.

1997-01-01

The final set of sky maps from the Green Bank 4.85 GHz survey (Condon J.J., Broderick J.J., Seielstad G.A., Douglas K., & Gregory P.C. in 1994AJ....107.1829C) was used to construct the GB6 Catalog of sources stronger than S ~ 18 mJy in the declination range 0deg < Dec. < +75deg (Gregory P.C., Scott W.K., Douglas K., & Condon J.J. in 1996ApJS..103..427G). There are two machine-readable versions of the GB6 catalog, with coordinates precessed to B1950 (file b1950.dat) and J2000 (file j2000.dat). Each catalog file contains one line per source (75,162 lines each), and the sources are sorted by increasing B1950 or J2000 right ascension. (3 data files).

Multi-messenger astronomy of gravitational-wave sources with flexible wide-area radio transient surveys

NASA Astrophysics Data System (ADS)

Kavic, Michael; Cregg C. Yancey, Brandon E. Bear, Bernadine Akukwe, Kevin Chen, Jayce Dowell, Jonathan D. Gough, Jonah Kanner, Kenneth Obenberger, Peter Shawhan, John H. Simonetti , Gregory B. Taylor , Jr-Wei Tsai

2016-01-01

We explore opportunities for multi-messenger astronomy using gravitational waves (GWs) and prompt, transient low-frequency radio emission to study highly energetic astrophysical events. We review the literature on possible sources of correlated emission of GWs and radio transients, highlighting proposed mechanisms that lead to a short-duration, high-flux radio pulse originating from the merger of two neutron stars or from a superconducting cosmic string cusp. We discuss the detection prospects for each of these mechanisms by low-frequency dipole array instruments such as LWA1, the Low Frequency Array and the Murchison Widefield Array. We find that a broad range of models may be tested by searching for radio pulses that, when de-dispersed, are temporally and spatially coincident with a LIGO/Virgo GW trigger within a ˜30 s time window and ˜200-500 deg(2) sky region. We consider various possible observing strategies and discuss their advantages and disadvantages. Uniquely, for low-frequency radio arrays, dispersion can delay the radio pulse until after low-latency GW data analysis has identified and reported an event candidate, enabling a prompt radio signal to be captured by a deliberately targeted beam. If neutron star mergers do have detectable prompt radio emissions, a coincident search with the GW detector network and low-frequency radio arrays could increase the LIGO/Virgo effective search volume by up to a factor of ˜2. For some models, we also map the parameter space that may be constrained by non-detections.

Multi-messenger Astronomy of Gravitational-wave Sources with Flexible Wide-area Radio Transient Surveys

NASA Astrophysics Data System (ADS)

Yancey, Cregg C.; Bear, Brandon E.; Akukwe, Bernadine; Chen, Kevin; Dowell, Jayce; Gough, Jonathan D.; Kanner, Jonah; Kavic, Michael; Obenberger, Kenneth; Shawhan, Peter; Simonetti, John H.; -Wei Tsai, Gregory B. Taylor, Jr.

2015-10-01

We explore opportunities for multi-messenger astronomy using gravitational waves (GWs) and prompt, transient low-frequency radio emission to study highly energetic astrophysical events. We review the literature on possible sources of correlated emission of GWs and radio transients, highlighting proposed mechanisms that lead to a short-duration, high-flux radio pulse originating from the merger of two neutron stars or from a superconducting cosmic string cusp. We discuss the detection prospects for each of these mechanisms by low-frequency dipole array instruments such as LWA1, the Low Frequency Array and the Murchison Widefield Array. We find that a broad range of models may be tested by searching for radio pulses that, when de-dispersed, are temporally and spatially coincident with a LIGO/Virgo GW trigger within a ˜30 s time window and ˜200-500 deg2 sky region. We consider various possible observing strategies and discuss their advantages and disadvantages. Uniquely, for low-frequency radio arrays, dispersion can delay the radio pulse until after low-latency GW data analysis has identified and reported an event candidate, enabling a prompt radio signal to be captured by a deliberately targeted beam. If neutron star mergers do have detectable prompt radio emissions, a coincident search with the GW detector network and low-frequency radio arrays could increase the LIGO/Virgo effective search volume by up to a factor of ˜2. For some models, we also map the parameter space that may be constrained by non-detections.

VizieR Online Data Catalog: Blazars equivalent widths and radio luminosity (Landt+, 2004)

NASA Astrophysics Data System (ADS)

Landt, H.; Padovani, P.; Perlman, E. S.; Giommi, P.

2004-07-01

Blazars are currently separated into BL Lacertae objects (BL Lacs) and flat spectrum radio quasars based on the strength of their emission lines. This is performed rather arbitrarily by defining a diagonal line in the Ca H&K break value-equivalent width plane, following Marcha et al. (1996MNRAS.281..425M). We readdress this problem and put the classification scheme for blazars on firm physical grounds. We study ~100 blazars and radio galaxies from the Deep X-ray Radio Blazar Survey (DXRBS, Cat. and ) and 2-Jy radio survey and find a significant bimodality for the narrow emission line [OIII]{lambda}5007. This suggests the presence of two physically distinct classes of radio-loud active galactic nuclei (AGN). We show that all radio-loud AGN, blazars and radio galaxies, can be effectively separated into weak- and strong-lined sources using the [OIII]{lambda}5007-[OII]{lambda}3727 equivalent width plane. This plane allows one to disentangle orientation effects from intrinsic variations in radio-loud AGN. Based on DXRBS, the strongly beamed sources of the new class of weak-lined radio-loud AGN are made up of BL Lacs at the ~75 per cent level, whereas those of the strong-lined radio-loud AGN include mostly (~97 per cent) quasars. (4 data files).

HIGH-RESOLUTION IMAGING OF THE ATLBS REGIONS: THE RADIO SOURCE COUNTS

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

Thorat, K.; Subrahmanyan, R.; Saripalli, L.

2013-01-01

The Australia Telescope Low-brightness Survey (ATLBS) regions have been mosaic imaged at a radio frequency of 1.4 GHz with 6'' angular resolution and 72 {mu}Jy beam{sup -1} rms noise. The images (centered at R.A. 00{sup h}35{sup m}00{sup s}, decl. -67 Degree-Sign 00'00'' and R.A. 00{sup h}59{sup m}17{sup s}, decl. -67 Degree-Sign 00'00'', J2000 epoch) cover 8.42 deg{sup 2} sky area and have no artifacts or imaging errors above the image thermal noise. Multi-resolution radio and optical r-band images (made using the 4 m CTIO Blanco telescope) were used to recognize multi-component sources and prepare a source list; the detection thresholdmore » was 0.38 mJy in a low-resolution radio image made with beam FWHM of 50''. Radio source counts in the flux density range 0.4-8.7 mJy are estimated, with corrections applied for noise bias, effective area correction, and resolution bias. The resolution bias is mitigated using low-resolution radio images, while effects of source confusion are removed by using high-resolution images for identifying blended sources. Below 1 mJy the ATLBS counts are systematically lower than the previous estimates. Showing no evidence for an upturn down to 0.4 mJy, they do not require any changes in the radio source population down to the limit of the survey. The work suggests that automated image analysis for counts may be dependent on the ability of the imaging to reproduce connecting emission with low surface brightness and on the ability of the algorithm to recognize sources, which may require that source finding algorithms effectively work with multi-resolution and multi-wavelength data. The work underscores the importance of using source lists-as opposed to component lists-and correcting for the noise bias in order to precisely estimate counts close to the image noise and determine the upturn at sub-mJy flux density.« less

Plasma and radio waves from Neptune: Source mechanisms and propagation

NASA Astrophysics Data System (ADS)

Wong, H. K.

1994-03-01

This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

Plasma and radio waves from Neptune: Source mechanisms and propagation

NASA Technical Reports Server (NTRS)

Wong, H. K.

1994-01-01

This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

Improved operation of the nonambipolar electron source.

PubMed

Longmier, Ben; Hershkowitz, Noah

2008-09-01

Significant improvements have been made to the nonambipolar electron source (NES), a radio frequency (rf) plasma-based electron source that does not rely on electron emission at a cathode surface [B. Longmier, S. Baalrud, and N. Hershkowitz, Rev. Sci. Instrum. 77, 113504 (2006)]. A prototype NES has produced 30 A of continuous electron current, using 2 SCCM (SCCM denotes cubic centimeter per minute at STP) Xe, 1300 W rf power at 13.56 MHz, yielding a 180 times gas utilization factor. A helicon mode transition has also been identified during NES operation with an argon propellant, using 15 SCCM Ar, 1000 W rf, and 100 G magnetic field. This NES technology has the ability to replace hollow cathode electron sources and to enable high power electric propulsion missions, eliminating one of the lifetime restrictions that many ion thrusters have previously been faced with.

THE ABUNDANCE OF X-SHAPED RADIO SOURCES. I. VLA SURVEY OF 52 SOURCES WITH OFF-AXIS DISTORTIONS

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

Roberts, David H.; Cohen, Jake P.; Lu, Jing

Cheung identified a sample of 100 candidate X-shaped radio galaxies using the NRAO FIRST survey; these are small-axial-ratio extended radio sources with off-axis emission. Here, we present radio images of 52 of these sources that have been made from archival Very Large Array data with resolution of about 1″. Fifty-one of the 52 were observed at 1.4 GHz, 7 were observed at 1.4 and 5 GHz, and 1 was observed only at 5 GHz. We also present overlays of the Sloan Digital Sky Survey red images for 48 of the sources, and DSS II overlays for the remainder. Optical counterpartsmore » have been identified for most sources, but there remain a few empty fields. Our higher resolution VLA images along with FIRST survey images of the sources in the sample reveal that extended extragalactic radio sources with small axial ratios are largely (60%) cases of double radio sources with twin lobes that have off-axis extensions, usually with inversion-symmetric structure. The available radio images indicate that at most 20% of sources might be genuine X-shaped radio sources that could have formed by a restarting of beams in a new direction following an interruption and axis flip. The remaining 20% are in neither of these categories. The implications of this result for the gravitational wave background are discussed in Roberts et al.« less

A statistical study of radio-source structure effects on astrometric very long baseline interferometry observations

NASA Technical Reports Server (NTRS)

Ulvestad, J. S.

1989-01-01

Errors from a number of sources in astrometric very long baseline interferometry (VLBI) have been reduced in recent years through a variety of methods of calibration and modeling. Such reductions have led to a situation in which the extended structure of the natural radio sources used in VLBI is a significant error source in the effort to improve the accuracy of the radio reference frame. In the past, work has been done on individual radio sources to establish the magnitude of the errors caused by their particular structures. The results of calculations on 26 radio sources are reported in which an effort is made to determine the typical delay and delay-rate errors for a number of sources having different types of structure. It is found that for single observations of the types of radio sources present in astrometric catalogs, group-delay and phase-delay scatter in the 50 to 100 psec range due to source structure can be expected at 8.4 GHz on the intercontinental baselines available in the Deep Space Network (DSN). Delay-rate scatter of approx. 5 x 10(exp -15) sec sec(exp -1) (or approx. 0.002 mm sec (exp -1) is also expected. If such errors mapped directly into source position errors, they would correspond to position uncertainties of approx. 2 to 5 nrad, similar to the best position determinations in the current JPL VLBI catalog. With the advent of wider bandwidth VLBI systems on the large DSN antennas, the system noise will be low enough so that the structure-induced errors will be a significant part of the error budget. Several possibilities for reducing the structure errors are discussed briefly, although it is likely that considerable effort will have to be devoted to the structure problem in order to reduce the typical error by a factor of two or more.

Are Fast Radio Bursts the Birthmark of Magnetars?

NASA Astrophysics Data System (ADS)

Lieu, Richard

2017-01-01

A model of fast radio bursts, which enlists young, short period extragalactic magnetars satisfying B/P > 2 × 1016 G s-1 (1 G = 1 statvolt cm-1) as the source, is proposed. When the parallel component {{\\boldsymbol{E}}}\\parallel of the surface electric field (under the scenario of a vacuum magnetosphere) of such pulsars approaches 5% of the critical field {E}c={m}e2{c}3/(e{\\hslash }), in strength, the field can readily decay via the Schwinger mechanism into electron-positron pairs, the back reaction of which causes {{\\boldsymbol{E}}}\\parallel to oscillate on a characteristic timescale smaller than the development of a spark gap. Thus, under this scenario, the open field line region of the pulsar magnetosphere is controlled by Schwinger pairs, and their large creation and acceleration rates enable the escaping pairs to coherently emit radio waves directly from the polar cap. The majority of the energy is emitted at frequencies ≲ 1 {GHz} where the coherent radiation has the highest yield, at a rate large enough to cause the magnetar to lose spin significantly over a timescale ≈ a few × {10}-3 s, the duration of a fast radio burst. Owing to the circumstellar environment of a young magnetar, however, the ≲1 GHz radiation is likely to be absorbed or reflected by the overlying matter. It is shown that the brightness of the remaining (observable) frequencies of ≈ 1 {GHz} and above are on a par with a typical fast radio burst. Unless some spin-up mechanism is available to recover the original high rotation rate that triggered the Schwinger mechanism, the fast radio burst will not be repeated again in the same magnetar.

The Pearson-Readhead Survey of Compact Extragalactic Radio Sources from Space. II. Analysis of Source Properties

NASA Astrophysics Data System (ADS)

Lister, M. L.; Tingay, S. J.; Preston, R. A.

2001-06-01

We have performed a multidimensional correlation analysis on the observed properties of a statistically complete core-selected sample of compact radio-loud active galactic nuclei based on data from the VLBI Space Observing Programme (Paper I) and previously published studies. Our sample is drawn from the well-studied Pearson-Readhead (PR) survey and is ideally suited for investigating the general effects of relativistic beaming in compact radio sources. In addition to confirming many previously known correlations, we have discovered several new trends that lend additional support to the beaming model. These trends suggest that the most highly beamed sources in core-selected samples tend to have (1) high optical polarizations; (2) large parsec- kiloparsec-scale jet misalignments; (3) prominent VLBI core components; (4) one-sided, core, or halo radio morphology on kiloparsec scales; (5) narrow emission line equivalent widths; and (6) a strong tendency for intraday variability at radio wavelengths. We have used higher resolution space and ground-based VLBI maps to confirm the bimodality of the jet misalignment distribution for the PR survey and find that the sources with aligned parsec- and kiloparsec-scale jets generally have arcsecond-scale radio emission on both sides of the core. The aligned sources also have broader emission line widths. We find evidence that the BL Lacertae objects in the PR survey are all highly beamed and have very similar properties to the high optically polarized quasars, with the exception of smaller redshifts. A cluster analysis on our data shows that after partialing out the effects of redshift, the luminosities of our sample objects in various wave bands are generally well correlated with each other but not with other source properties.

MEqTrees Telescope and Radio-sky Simulations and CPU Benchmarking

NASA Astrophysics Data System (ADS)

Shanmugha Sundaram, G. A.

2009-09-01

MEqTrees is a Python-based implementation of the classical Measurement Equation, wherein the various 2×2 Jones matrices are parametrized representations in the spatial and sky domains for any generic radio telescope. Customized simulations of radio-source sky models and corrupt Jones terms are demonstrated based on a policy framework, with performance estimates derived for array configurations, ``dirty''-map residuals and processing power requirements for such computations on conventional platforms.

Deep Wideband Single Pointings and Mosaics in Radio Interferometry: How Accurately Do We Reconstruct Intensities and Spectral Indices of Faint Sources?

NASA Astrophysics Data System (ADS)

Rau, U.; Bhatnagar, S.; Owen, F. N.

2016-11-01

Many deep wideband wide-field radio interferometric surveys are being designed to accurately measure intensities, spectral indices, and polarization properties of faint source populations. In this paper, we compare various wideband imaging methods to evaluate the accuracy to which intensities and spectral indices of sources close to the confusion limit can be reconstructed. We simulated a wideband single-pointing (C-array, L-Band (1-2 GHz)) and 46-pointing mosaic (D-array, C-Band (4-8 GHz)) JVLA observation using a realistic brightness distribution ranging from 1 μJy to 100 mJy and time-, frequency-, polarization-, and direction-dependent instrumental effects. The main results from these comparisons are (a) errors in the reconstructed intensities and spectral indices are larger for weaker sources even in the absence of simulated noise, (b) errors are systematically lower for joint reconstruction methods (such as Multi-Term Multi-Frequency-Synthesis (MT-MFS)) along with A-Projection for accurate primary beam correction, and (c) use of MT-MFS for image reconstruction eliminates Clean-bias (which is present otherwise). Auxiliary tests include solutions for deficiencies of data partitioning methods (e.g., the use of masks to remove clean bias and hybrid methods to remove sidelobes from sources left un-deconvolved), the effect of sources not at pixel centers, and the consequences of various other numerical approximations within software implementations. This paper also demonstrates the level of detail at which such simulations must be done in order to reflect reality, enable one to systematically identify specific reasons for every trend that is observed, and to estimate scientifically defensible imaging performance metrics and the associated computational complexity of the algorithms/analysis procedures. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Quasi-periodic Reversals of Radio Polarization at 17 GHz Observed in the 2002 April 21 Solar Event

NASA Astrophysics Data System (ADS)

Huang, Guangli; Lin, Jun

2006-03-01

We investigate high spatial resolution radio polarization data obtained by the Nobeyama Radioheliograph (NoRH) and high time resolution data observed with the Nobeyama Radio Polarimeters (NoRP) during the well-studied flare/CME event of 2002 April 21. A 17 GHz radio source at the loop top was seen by NoRH to move upward together with the expanding flare loops at a speed of around 10 km s-1. In the 5 minutes before the source began its upward motion, the Stokes V of the radio signals at 17 GHz showed quasi-periodic reversals between left-circular polarization (LCP) and right-circular polarization (RCP). Following this interval, the polarizations gradually turned to LCP. During this period, the polarization of the corresponding footpoint source maintained the RCP sense. The reversal of Stokes V between RCP and LCP was also detected at lower frequencies (1-2 GHz) by NoRP, without spatial resolution. The observed reversals between RCP and LCP of the radio signals from the top of the flare loop system can be taken as evidence that magnetic energy is released or energetic particles are produced at the magnetic reconnection site in a quasi-periodic fashion.

Discovery of millisecond pulsars in radio searches of southern Fermi Large Area Telescope sources

DOE PAGES

Keith, M. J.; Johnston, S.; Ray, P. S.; ...

2011-06-08

Using the Parkes Radio Telescope, we have carried out deep observations of 11 unassociated gamma-ray sources. Periodicity searches of these data have discovered two millisecond pulsars, PSR J1103–5403 (1FGL J1103.9–5355) and PSR J2241–5236 (1FGL J2241.9–5236), and a long-period pulsar, PSR J1604–44 (1FGL J1604.7–4443). In addition, we searched for but did not detect any radio pulsations from six gamma-ray pulsars discovered by the Fermi satellite to a level of ~0.04 mJy (for pulsars with a 10 per cent duty cycle). The timing of the millisecond pulsar PSR J1103–5403 has shown that its position is 9 arcmin from the centroid of themore » gamma-ray source. Since these observations were carried out, independent evidence has shown that 1FGL J1103.9–5355 is associated with the flat spectrum radio source PKS 1101–536. It appears certain that the pulsar is not associated with the gamma-ray source, despite the seemingly low probability of a chance detection of a radio millisecond pulsar. We consider that PSR J1604–44 is a chance discovery of a weak, long-period pulsar and is unlikely to be associated with 1FGL J1604.7–4443. PSR J2241–5236 has a spin period of 2.2 ms and orbits a very low mass companion with a 3.5-h orbital period. The relatively high flux density and low dispersion measure of PSR J2241–5236 make it an excellent candidate for high precision timing experiments. The gamma rays of 1FGL J2241.9–5236 have a spectrum that is well modelled by a power law with an exponential cut-off, and phase binning with the radio ephemeris results in a multipeaked gamma-ray pulse profile. Furthermore, observations with Chandra have identified a coincident X-ray source within 0.1 arcsec of the position of the pulsar obtained by radio timing.« less

Unveiling the nature of two unidentified EGRET blazar candidates through spectroscopic observations

NASA Astrophysics Data System (ADS)

Nkundabakura, P.; Meintjes, P. J.

2012-11-01

Studies using the Energetic Gamma-Ray Experiment Telescope (EGRET) revealed that blazars [flat-spectrum radio quasars (FSRQs) and BL Lac objects] emit most of their luminosity in the high-energy gamma-ray (E > 100 MeV) range. From the 271 sources observed by EGRET, 131 are still unidentified. A systematic search is conducted to identify possible high-energy gamma-ray blazars among the unidentified EGRET population. Based upon multiwavelength emission properties, 13 extragalactic radio sources were selected in the EGRET error boxes for further investigation. From the above-mentioned sample, results of a multiwavelength follow-up of two EGRET sources, 3EG J0821-5814 and 3EG J0706-3837, are presented. These sources are associated with their radio counterparts PKS J0820-5705 and PMN J0710-3850, respectively. Spectroscopic observations utilizing the SOAR/Goodman spectrograph at the Cerro Tololo Inter-American Observatory in Chile reveal a spectrum of PKS J0820-5705 that corresponds to that of a radio-loud active galactic nucleus (FSRQ) with redshift z = 0.06 ± 0.01, while the visibility of wide and narrow emission lines in the spectrum of PMN J0710-3850 resembles that of a low-ionization nuclear emission-line region (LINER) or type 1 Seyfert galaxy at z = 0.129 ± 0.001. The observed Ca II K&H lines depression ratio at 4000 Å showed a shallow depression of 8.8 ± 2.5 per cent for PKS J0820-5705 and 80 ± 1 per cent for PMN J0710-3850, suggesting the presence of a strong non-thermal optical contribution in PKS J0820-5705, which clearly distinguishes its spectrum from that of a radio galaxy. The weaker optical non-thermal contribution for PMN J0710-3850 is in accordance with that expected of a LINER. For PMN J0710-3850 the line flux ratios [O III] λ5007/Hβ < 3 and [N II] λ6583/Hα > 0.6 which are in agreement with the expected ratios of LINERs. However, the absence of [O II] λ3727 implies an anomalously low [O II]/[O III] < 0.5 ratio for a LINER, and agrees more with the ratio observed in type 1 Seyfert galaxies. The average velocities inferred from the Balmer lines range between 2300 and 4300 km s-1, while [O I] and [O III] velocities range between 420 and 490 km s-1, consistent with both LINERs and type 1 Seyfert galaxies. The X-ray luminosities of these two sources are LX ˜ 9 × 1043 erg s-1 (PKS J0820-5705) and LX ˜ 9 × 1042 erg s-1 (PMN J0710-3850), respectively. The X-ray luminosity of PMN J0710-3850 is an order of magnitude higher than the upper limit detected from LINERs, and correlates well with the typical X-ray luminosities observed in type 1 Seyfert galaxies. The X-ray luminosity of PKS J0820-5705 is consistent with the observed luminosity of FSRQs. Optical photometry carried out with the South African Astronomical Observatory 1.0-m telescope displayed 1-2 mag variability in the B and R bands for PKS J0821-5705, on time-scales of hours, while a 5σ variability of the average R-band magnitude could be discerned over a 3 d time span. A smaller 0.5 mag variability is visible in the B band for PMN J0710-3850 on time-scales of hours. No variability was detected in the R band for this source.

NGC 2024: Far-infrared and radio molecular observations

NASA Technical Reports Server (NTRS)

Thronson, H. A., Jr.; Lada, C. J.; Schwartz, P. R.; Smith, H. A.; Smith, J.; Glaccum, W.; Harper, D. A.; Loewenstein, R. F.

1984-01-01

Far infrared continuum and millimeter wave molecular observations are presented for the infrared and radio source NGC 2024. The measurements are obtained at relatively high angular resolution, enabling a description of the source energetics and mass distribution in greater detail than previously reported. The object appears to be dominated by a dense ridge of material, extended in the north/south direction and centered on the dark lane that is seen in visual photographs. Maps of the source using the high density molecules CS and HCN confirm this picture and allow a description of the core structure and molecular abundances. The radio molecular and infrared observations support the idea that an important exciting star in NGC 2024 has yet to be identified and is centered on the dense ridge about 1' south of the bright mid infrared source IRS 2. The data presented here allows a presentation of a model for the source.

Radio and infrared emission from Markarian starburst galaxies

NASA Technical Reports Server (NTRS)

Stine, Peter C.

1992-01-01

Radio and infrared emission were compared for a sample of 58 Markarian starburst galaxies, chosen to cover a wide range of 60-micron luminosity density. New radio observations were from the VLA at 6 and 20 cm in the B and A configurations. IRAS data were reanalyzed for 25 of the starbursts that were previously undetected at either 25 or 100 microns. The correlation between the global radio and IR emission for the starbursts in the sample is strongest at 25 and 60 microns, wavelengths in which the warm dust dominates. The radio spectral index steepens away from the center. This indicates that nonthermal emission leaks out of the starburst region. The change in the spectral index implies that while nonthermal sources dominate in the entire region, the bulk of the interior emission at 6 cm is thermal. The radio spectral index does not appear to vary as a function of the infrared luminosity or the infrared colors, which indicates that the slope of the initial mass function does not appear to be a function of either the mass or temperature of the starburst.

The discovery of nonthermal radio emission from magnetic Bp-Ap stars

NASA Technical Reports Server (NTRS)

Drake, Stephen A.; Abbott, David C.; Bastian, T. S.; Bieging, J. H.; Churchwell, E.

1987-01-01

In a VLA survey of chemically peculiar B- and A-type stars with strong magnetic fields, five of the 34 stars observed have been identified as 6 cm continuum sources. Three of the detections are helium-strong early Bp stars (Sigma Ori E, HR 1890, and Delta Ori C), and two are helium weak, silicon-strong stars with spectral types near A0p (IQ Aur = HD 34452, Babcock's star = HD 215441). The 6 cm luminosities L6 (ergs/s Hz) range from log L6 = 16.2 to 17.9, somewhat less than the OB supergiants and W-R stars. Three-frequency observations indicate that the helium-strong Bp stars are variable nonthermal sources.

Discovery of an Energetic Pulsar Associated with SNR G76.9+1.0

NASA Technical Reports Server (NTRS)

Arzoumanian, Zaven; Gotthelf, E. V.; Ransom, S. M.; Safi-Harb, S.; Kothes, R.; Landecker, T. L.

2012-01-01

We report the discovery of PSR J2022-<-3842, a 24 ms radio and X-ray pulsar in the supernova remnant G76.9+i.0, in observations with the Chandra X-ray telescope, the Robert C. Byrd Green Bank Radio Telescope, and the Rossi X-ray Timing Explorer (RXTE). The pulsar's spin-down rate implies a rotation-powered luminosity E = 1.2 X 10(exp 38) erg/s, a surface dipole magnetic field strength B(sub S), = 1.0 X 10(exp 12) G, and a characteristic age of 8.9 kyr. PSR J2022+3842 is thus the second-most energetic Galactic pulsar known, after the Crab, as well as the most rapidly-rotating young, radio-bright pulsar known. The radio pulsations are highly dispersed and broadened by interstellar scattering, and we find that a large (delta f/f approximates 1.9 x 10(exp -6)) spin glitch must have occurred between our discovery and confirmation observations. The X-ray pulses are narrow (0.06 cycles FWHM) and visible up to 20 keV, consistent with magnetospheric emission from a rotation-powered pulsar. The Chandra X-ray image identifies the pulsar with a hard, unresolved source at the midpoint of the double-lobed radio morphology of G76.9+ 1.0 and embedded within faint, compact X-ray nebulosity. The spatial relationship of the X-ray and radio emissions is remarkably similar to extended structure seen around the Vela pulsar. The combined Chandra and RXTE pulsar spectrum is well-fitted by an absorbed power-law model with column density N(sub H) = (1.7 +/- 0.3) x 10(exp 22) / sq cm and photon index Gamma = 1.0 +/- 0.2; it implies that the Chandra point-source flux is virtually 100% pulsed. For a distance of 10 kpc, the X-ray luminosity of PSR J2022+3842 is L(sub x){2-1O keV) = 7.0 x 10(exp 33) erg/s. Despite being extraordinarily energetic, PSR J2022+3842 lacks a bright X-ray wind nebula and has an unusually low conversion efficiency of spin-down power to X-ray luminosity, Lx/E = 5.9 X 10(exp-5).

VizieR Online Data Catalog: Optically Bright extragalactic Radio Sources II (Petrov, 2013)

NASA Astrophysics Data System (ADS)

Petrov, L.

2014-06-01

The first VLBI (Very Long Baseline Interferometry) observing campaign in 2007 resulted in the detection of 398 targets with the European VLBI Network (EVN; Bourda et al., 2010, cat. J/A+A/520/A113). During the second observing campaign, a subset of 105 sources detected in the previous campaign was observed (Bourda et al., 2011, cat. J/A+A/526/A102). Their positions were derived by Petrov (2011, cat. J/AJ/142/105) and formed the OBRS-1 (Optically Bright extragalactic Radio Sources) catalog. The remaining sources were observed in the third campaign, called OBRS-2. During the OBRS-2 campaign, there were three observing sessions with 10 VLBA (Very Long Baseline Array) stations and 5-6 EVN stations from this list: EFLSBERG, MEDICINA, ONSALA60, YEBES40M, DSS63, HARTRAO, and NOTO. Observations were made on 2010 Mar 23 (session ID gc034a), on 2011 Nov 8 (gc034bcd), and on 2011 Mar 15 (gc034ef). The OBRS-2 catalog presents precise positions of the 295 extragalactic radio sources as well as median correlated flux densities at 8.4 and 2.2GHz at baseline lengths shorter than 900km and at baseline lengths longer than 5000km. (1 data file).

Associating Fast Radio Bursts with Extragalactic Radio Sources: General Methodology and a Search for a Counterpart to FRB 170107

NASA Astrophysics Data System (ADS)

Eftekhari, T.; Berger, E.; Williams, P. K. G.; Blanchard, P. K.

2018-06-01

The discovery of a repeating fast radio burst (FRB) has led to the first precise localization, an association with a dwarf galaxy, and the identification of a coincident persistent radio source. However, further localizations are required to determine the nature of FRBs, the sources powering them, and the possibility of multiple populations. Here we investigate the use of associated persistent radio sources to establish FRB counterparts, taking into account the localization area and the source flux density. Due to the lower areal number density of radio sources compared to faint optical sources, robust associations can be achieved for less precise localizations as compared to direct optical host galaxy associations. For generally larger localizations that preclude robust associations, the number of candidate hosts can be reduced based on the ratio of radio-to-optical brightness. We find that confident associations with sources having a flux density of ∼0.01–1 mJy, comparable to the luminosity of the persistent source associated with FRB 121102 over the redshift range z ≈ 0.1–1, require FRB localizations of ≲20″. We demonstrate that even in the absence of a robust association, constraints can be placed on the luminosity of an associated radio source as a function of localization and dispersion measure (DM). For DM ≈1000 pc cm‑3, an upper limit comparable to the luminosity of the FRB 121102 persistent source can be placed if the localization is ≲10″. We apply our analysis to the case of the ASKAP FRB 170107, using optical and radio observations of the localization region. We identify two candidate hosts based on a radio-to-optical brightness ratio of ≳100. We find that if one of these is indeed associated with FRB 170107, the resulting radio luminosity (1029‑ 4 × 1030 erg s‑1 Hz‑1, as constrained from the DM value) is comparable to the luminosity of the FRB 121102 persistent source.

New methods to constrain the radio transient rate: results from a survey of four fields with LOFAR.

PubMed

Carbone, D; van der Horst, A J; Wijers, R A M J; Swinbank, J D; Rowlinson, A; Broderick, J W; Cendes, Y N; Stewart, A J; Bell, M E; Breton, R P; Corbel, S; Eislöffel, J; Fender, R P; Grießmeier, J-M; Hessels, J W T; Jonker, P; Kramer, M; Law, C J; Miller-Jones, J C A; Pietka, M; Scheers, L H A; Stappers, B W; van Leeuwen, J; Wijnands, R; Wise, M; Zarka, P

2016-07-01

We report on the results of a search for radio transients between 115 and 190 MHz with the LOw-Frequency ARray (LOFAR). Four fields have been monitored with cadences between 15 min and several months. A total of 151 images were obtained, giving a total survey area of 2275 deg 2 . We analysed our data using standard LOFAR tools and searched for radio transients using the LOFAR Transients Pipeline. No credible radio transient candidate has been detected; however, we are able to set upper limits on the surface density of radio transient sources at low radio frequencies. We also show that low-frequency radio surveys are more sensitive to steep-spectrum coherent transient sources than GHz radio surveys. We used two new statistical methods to determine the upper limits on the transient surface density. One is free of assumptions on the flux distribution of the sources, while the other assumes a power-law distribution in flux and sets more stringent constraints on the transient surface density. Both of these methods provide better constraints than the approach used in previous works. The best value for the upper limit we can set for the transient surface density, using the method assuming a power-law flux distribution, is 1.3 × 10 -3  deg -2 for transients brighter than 0.3 Jy with a time-scale of 15 min, at a frequency of 150 MHz. We also calculated for the first time upper limits for the transient surface density for transients of different time-scales. We find that the results can differ by orders of magnitude from previously reported, simplified estimates.

Are the infrared-faint radio sources pulsars?

NASA Astrophysics Data System (ADS)

Cameron, A. D.; Keith, M.; Hobbs, G.; Norris, R. P.; Mao, M. Y.; Middelberg, E.

2011-07-01

Infrared-faint radio sources (IFRS) are objects which are strong at radio wavelengths but undetected in sensitive Spitzer observations at infrared wavelengths. Their nature is uncertain and most have not yet been associated with any known astrophysical object. One possibility is that they are radio pulsars. To test this hypothesis we undertook observations of 16 of these sources with the Parkes Radio Telescope. Our results limit the radio emission to a pulsed flux density of less than 0.21 mJy (assuming a 50 per cent duty cycle). This is well below the flux density of the IFRS. We therefore conclude that these IFRS are not radio pulsars.

FAST's Discovery of a New Millisecond Pulsar (MSP) toward the Fermi-LAT unassociated source 3FGL J0318.1+0252

NASA Astrophysics Data System (ADS)

Wang, Pei; Li, Di; Zhu, Weiwei; Zhang, Chengmin; Yan, Jun; Hou, Xian; Clark, Colin J.; Saz Parkinson, Pablo M.; Michelson, Peter F.; Ferrara, Elizabeth C.; Thompson, David J.; Smith, David A.; Ray, Paul S.; Kerr, Matthew; Shen, Zhiqiang; Wang, Na; Fermi-LAT Collaboration

2018-04-01

The Five hundred-meter Aperture Spherical radio Telescope (FAST), operated by the National Astronomical Observatories, Chinese Academy of Sciences, has discovered a radio millisecond pulsar (MSP) coincident with the unassociated gamma-ray source 3FGL J0318.1+0252 (Acero et al. 2015 ApJS, 218, 23), also known as FL8Y J0318.2+0254 in the recently released Fermi Large Area Telescope (LAT) 8-year Point Source List (FL8Y).

High-resolution Observations of the Massive Protostar in IRAS 18566+0408

NASA Astrophysics Data System (ADS)

Hofner, P.; Cesaroni, R.; Kurtz, S.; Rosero, V.; Anderson, C.; Furuya, R. S.; Araya, E. D.; Molinari, S.

2017-07-01

We report 3 mm continuum, CH3CN(5-4) and 13CS(2-1) line observations with CARMA (Combined Array for Research in Millimeter-wave Astronomy), in conjunction with 6 and 1.3 cm continuum VLA data, and 12 and 25 μm broadband data from the Subaru Telescope toward the massive proto-star IRAS 18566+0408. The VLA data resolve the ionized jet into four components aligned in the E-W direction. Radio components A, C, and D have flat centimeter SEDs indicative of optically thin emission from ionized gas, and component B has a spectral index α = 1.0, and a decreasing size with frequency \\propto {ν }-0.5. Emission from the CARMA 3 mm continuum and from the 13CS(2-1) and CH3CN(5-4) spectral lines is compact (I.e., < 6700 {au}) and peaks near the position of the VLA centimeter source, component B. Analysis of these lines indicates hot and dense molecular gas, which is typical for HMCs. Our Subaru telescope observations detect a single compact source, coincident with radio component B, demonstrating that most of the energy in IRAS 18566+0408 originates from a region of size < 2400 {au}. We also present UKIRT near-infrared archival data for IRAS 18566+0408, which show extended K-band emission along the jet direction. We detect an E-W velocity shift of about 10 km s-1 over the HMC in the CH3CN lines possibly tracing the interface of the ionized jet with the surrounding core gas. Our data demonstrate the presence of an ionized jet at the base of the molecular outflow and support the hypothesis that massive protostars with O-type luminosity form with a mechanism similar to lower mass stars.

DEEP CHANDRA X-RAY IMAGING OF A NEARBY RADIO GALAXY 4C+29.30: X-RAY/RADIO CONNECTION

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

Siemiginowska, Aneta; Aldcroft, Thomas L.; Burke, D. J.

2012-05-10

We report results from our deep Chandra X-ray observations of a nearby radio galaxy, 4C+29.30 (z = 0.0647). The Chandra image resolves structures on sub-arcsec to arcsec scales, revealing complex X-ray morphology and detecting the main radio features: the nucleus, a jet, hotspots, and lobes. The nucleus is absorbed (N{sub H} {approx_equal} 3.95{sup +0.27}{sub -0.33} Multiplication-Sign 10{sup 23} cm{sup -2}) with an unabsorbed luminosity of L{sub 2-10keV} {approx_equal} (5.08 {+-} 0.52) Multiplication-Sign 10{sup 43} erg s{sup -1} characteristic of Type 2 active galactic nuclei. Regions of soft (<2 keV) X-ray emission that trace the hot interstellar medium (ISM) are correlatedmore » with radio structures along the main radio axis, indicating a strong relation between the two. The X-ray emission extends beyond the radio source and correlates with the morphology of optical-line-emitting regions. We measured the ISM temperature in several regions across the galaxy to be kT {approx_equal} 0.5 keV, with slightly higher temperatures (of a few keV) in the center and in the vicinity of the radio hotspots. Assuming that these regions were heated by weak shocks driven by the expanding radio source, we estimated the corresponding Mach number of 1.6 in the southern regions. The thermal pressure of the X-ray-emitting gas in the outermost regions suggests that the hot ISM is slightly underpressured with respect to the cold optical-line-emitting gas and radio-emitting plasma, which both seem to be in a rough pressure equilibrium. We conclude that 4C+29.30 displays a complex view of interactions between the jet-driven radio outflow and host galaxy environment, signaling feedback processes closely associated with the central active nucleus.« less

Thermal behavior of the Medicina 32-meter radio telescope

NASA Astrophysics Data System (ADS)

Pisanu, Tonino; Buffa, Franco; Morsiani, Marco; Pernechele, Claudio; Poppi, Sergio

2010-07-01

We studied the thermal effects on the 32 m diameter radio-telescope managed by the Institute of Radio Astronomy (IRA), Medicina, Bologna, Italy. The preliminary results show that thermal gradients deteriorate the pointing performance of the antenna. Data has been collected by using: a) two inclinometers mounted near the elevation bearing and on the central part of the alidade structure; b) a non contact laser alignment optical system capable of measuring the secondary mirror position; c) twenty thermal sensors mounted on the alidade trusses. Two series of measurements were made, the first series was performed by placing the antenna in stow position, the second series was performed while tracking a circumpolar astronomical source. When the antenna was in stow position we observed a strong correlation between the inclinometer measurements and the differential temperature. The latter was measured with the sensors located on the South and North sides of the alidade, thus indicating that the inclinometers track well the thermal deformation of the alidade. When the antenna pointed at the source we measured: pointing errors, the inclination of the alidade, the temperature of the alidade components and the subreflector position. The pointing errors measured on-source were 15-20 arcsec greater than those measured with the inclinometer.

Radio frequency power load and associated method

NASA Technical Reports Server (NTRS)

Sims, III, William Herbert (Inventor); Chavers, Donald Gregory (Inventor); Richeson, James J. (Inventor)

2010-01-01

A radio frequency power load and associated method. A radio frequency power load apparatus includes a container and a fluid having an ion source therein, the fluid being contained in the container. Two conductors are immersed in the fluid. A radio frequency transmission system includes a radio frequency transmitter, a radio frequency amplifier connected to the transmitter and a radio frequency power load apparatus connected to the amplifier. The apparatus includes a fluid having an ion source therein, and two conductors immersed in the fluid. A method of dissipating power generated by a radio frequency transmission system includes the steps of: immersing two conductors of a radio frequency power load apparatus in a fluid having an ion source therein; and connecting the apparatus to an amplifier of the transmission system.

VizieR Online Data Catalog: Broadband polarisation of radio AGN (O'Sullivan+, 2017)

NASA Astrophysics Data System (ADS)

O'Sullivan, S. P.; Purcell, C. R.; Anderson, C. S.; Farnes, J. S.; Sun, X. H.; Gaensler, B. M.

2017-08-01

Linear polarisation data as a function of wavelength-squared for 100 extragalactic radio sources, selected to be highly polarised at 1.4GHz. The data presented here were obtained using the Australia Telescope Compact Array (ATCA) over 1.1-3.1GHz (16cm) with 1MHz spectral resolution between 2014 April 19-28. The integrated emission from each source, imaged at 10 MHz intervals, is presented below. See Section 2 for details. (2 data files).

Gamma-ray burster counterparts - Radio

NASA Technical Reports Server (NTRS)

Schaefer, Bradley E.; Cline, Thomas L.; Desai, U. D.; Teegarden, B. J.; Atteia, J.-L.; Barat, C.; Estulin, I. V.; Evans, W. D.; Fenimore, E. E.; Hurley, K.

1989-01-01

Many observers and theorists have suggested that gamma-ray bursters (GRBs) are related to highly magnetized rotating, neutron stars, in which case an analogy with pulsars implies that GRBs would be prodigious emitters of polarized radio emission during quiescence. The paper reports on a survey conducted with the Very Large Array radio telescope of 10 small GRB error regions for quiescent radio emission at wavelengths of 2, 6, and 20 cm. The sensitivity of the survey varied from 0.1 to 0.8 mJy. The observations did indeed reveal four radio sources inside the GRB error regions.

GMRT discovery of PSR J1544+4937: An eclipsing black-widow pulsar identified with a Fermi-LAT source

DOE PAGES

Bhattacharyya, B.; Roy, J.; Ray, P. S.; ...

2013-07-29

Using the Giant Metrewave Radio Telescope, we performed deep observations to search for radio pulsations in the directions of unidentified Fermi-Large Area Telescope γ-ray sources. We report the discovery of an eclipsing black-widow millisecond pulsar, PSR J1544+4937, identified with the uncataloged γ-ray source FERMI J1544.2+4941. This 2.16 ms pulsar is in a 2.9 hr compact circular orbit with a very low mass companion (Mc > 0.017M ⊙). At 322 MHz this pulsar is found to be eclipsing for 13% of its orbit, whereas at 607 MHz the pulsar is detected throughout the low-frequency eclipse phase. Variations in the eclipse ingressmore » phase are observed, indicating a clumpy and variable eclipsing medium. Moreover, additional short-duration absorption events are observed around the eclipse boundaries. Finally, using the radio timing ephemeris we were able to detect γ-ray pulsations from this pulsar, confirming it as the source powering the γ-ray emission.« less

GMRT DISCOVERY OF PSR J1544+4937: AN ECLIPSING BLACK-WIDOW PULSAR IDENTIFIED WITH A FERMI-LAT SOURCE

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

Bhattacharyya, B.; Roy, J.; Gupta, Y.

2013-08-10

Using the Giant Metrewave Radio Telescope, we performed deep observations to search for radio pulsations in the directions of unidentified Fermi-Large Area Telescope {gamma}-ray sources. We report the discovery of an eclipsing black-widow millisecond pulsar, PSR J1544+4937, identified with the uncataloged {gamma}-ray source FERMI J1544.2+4941. This 2.16 ms pulsar is in a 2.9 hr compact circular orbit with a very low mass companion (M{sub c} > 0.017M{sub Sun }). At 322 MHz this pulsar is found to be eclipsing for 13% of its orbit, whereas at 607 MHz the pulsar is detected throughout the low-frequency eclipse phase. Variations in themore » eclipse ingress phase are observed, indicating a clumpy and variable eclipsing medium. Moreover, additional short-duration absorption events are observed around the eclipse boundaries. Using the radio timing ephemeris we were able to detect {gamma}-ray pulsations from this pulsar, confirming it as the source powering the {gamma}-ray emission.« less

Pulsar B0329+54: scattering disk resolved by RadioAstron interferometer at 324 MHz

NASA Astrophysics Data System (ADS)

Popov, M.

Propagation of pulsar radio emission through the interstellar plasma is accompanied with scattering by inhomogeneities of the plasma. The scattering produces a range of effects: angular broadening, pulse broadening, intensity modulation (scintillations), and distortion of radio spectra (diffraction pattern). In this presentation, we will primarily deal with scattering effects affecting interferometric measurements. Pulsars are point like radio sources at angular resolution provided by space VLBI even at largest baseline projections. Therefore, any structure, observed by the space-ground interferometer, is due to scattering effects. The objective of our study was to measure parameters of a scattering disk for the PSR B0329+54 at a frequency of 324 MHz with the space-ground interferometer RadioAstron. Observations were conducted on November 26-29 2012 in four sessions, one hour duration each, with progressively increasing baseline projections of 70, 90,175, and 235 thousand kilometers correspondingly. Only one ground radio telescope observed the pulsar together with the space radio telescope (SRT); it was 100-m telescope in Green Bank (GBT). Notable visibility amplitudes were detected at all baseline projections at a maximum level of 0.05 with the SNR of about 20. It was found that visibility function in delay consists of many isolated unresolved spikes. The overall spread of such spikes in delay corresponds to the scattering disk of about 4 mas at a half wide. Fine structure of the visibility amplitude in delay domain corresponds to a model of amplitude modulated noise (AMN). Fringe rate behavior with time indicates on dominant influence of refraction on traveling ionospheric disturbances (TID).

The Red Radio Ring: a gravitationally lensed hyperluminous infrared radio galaxy at z = 2.553 discovered through the citizen science project SPACE WARPS

NASA Astrophysics Data System (ADS)

Geach, J. E.; More, A.; Verma, A.; Marshall, P. J.; Jackson, N.; Belles, P.-E.; Beswick, R.; Baeten, E.; Chavez, M.; Cornen, C.; Cox, B. E.; Erben, T.; Erickson, N. J.; Garrington, S.; Harrison, P. A.; Harrington, K.; Hughes, D. H.; Ivison, R. J.; Jordan, C.; Lin, Y.-T.; Leauthaud, A.; Lintott, C.; Lynn, S.; Kapadia, A.; Kneib, J.-P.; Macmillan, C.; Makler, M.; Miller, G.; Montaña, A.; Mujica, R.; Muxlow, T.; Narayanan, G.; O'Briain, D.; O'Brien, T.; Oguri, M.; Paget, E.; Parrish, M.; Ross, N. P.; Rozo, E.; Rusu, Cristian E.; Rykoff, E. S.; Sanchez-Argüelles, D.; Simpson, R.; Snyder, C.; Schloerb, F. P.; Tecza, M.; Wang, W.-H.; Van Waerbeke, L.; Wilcox, J.; Viero, M.; Wilson, G. W.; Yun, M. S.; Zeballos, M.

2015-09-01

We report the discovery of a gravitationally lensed hyperluminous infrared galaxy (intrinsic LIR ≈ 1013 L⊙) with strong radio emission (intrinsic L1.4 GHz ≈ 1025 W Hz-1) at z = 2.553. The source was identified in the citizen science project SPACE WARPS through the visual inspection of tens of thousands of iJKs colour composite images of luminous red galaxies (LRGs), groups and clusters of galaxies and quasars. Appearing as a partial Einstein ring (re ≈ 3 arcsec) around an LRG at z = 0.2, the galaxy is extremely bright in the sub-millimetre for a cosmological source, with the thermal dust emission approaching 1 Jy at peak. The redshift of the lensed galaxy is determined through the detection of the CO(3→2) molecular emission line with the Large Millimetre Telescope's Redshift Search Receiver and through [O III] and Hα line detections in the near-infrared from Subaru/Infrared Camera and Spectrograph. We have resolved the radio emission with high-resolution (300-400 mas) eMERLIN L-band and Very Large Array C-band imaging. These observations are used in combination with the near-infrared imaging to construct a lens model, which indicates a lensing magnification of μ ≈ 10. The source reconstruction appears to support a radio morphology comprised of a compact (<250 pc) core and more extended component, perhaps indicative of an active nucleus and jet or lobe.

Pulsar searches of Fermi unassociated sources with the Effelsberg telescope

NASA Astrophysics Data System (ADS)

Barr, E. D.; Guillemot, L.; Champion, D. J.; Kramer, M.; Eatough, R. P.; Lee, K. J.; Verbiest, J. P. W.; Bassa, C. G.; Camilo, F.; Çelik, Ö.; Cognard, I.; Ferrara, E. C.; Freire, P. C. C.; Janssen, G. H.; Johnston, S.; Keith, M.; Lyne, A. G.; Michelson, P. F.; Parkinson, P. M. Saz; Ransom, S. M.; Ray, P. S.; Stappers, B. W.; Wood, K. S.

2013-02-01

Using the 100-m Effelsberg radio telescope operating at 1.36 GHz, we have performed a targeted radio pulsar survey of 289 unassociated γ-ray sources discovered by the Large Area Telescope (LAT) aboard the Fermi satellite and published in the 1FGL catalogue (Abdo et al. 2010a). This survey resulted in the discovery of millisecond pulsar J1745+1017, which resides in a short-period binary system with a low-mass companion, M_{c,{min}} ˜ 0.0137 M_{⊙}, indicative of `black widow' type systems. A 2-yr timing campaign has produced a refined radio ephemeris, accurate enough to allow for phase-folding of the LAT photons, resulting in the detection of a dual-peaked γ-ray light curve, proving that PSR J1745+1017 is the source responsible for the γ-ray emission seen in 1FGL J1745.5+1018 (2FGL J1745.6+1015; Nolan et al. 2012). We find the γ-ray spectrum of PSR J1745+1017 to be well modelled by an exponentially cut-off power law with cut-off energy 3.2 GeV and photon index 1.6. The observed sources are known to contain a further 10 newly discovered pulsars which were undetected in this survey. Our radio observations of these sources are discussed and in all cases limiting flux densities are calculated. The reasons behind the seemingly low yield of discoveries are also discussed.

Pulsar searches of Fermi unassociated sources with the Effelsberg telescope

DOE PAGES

Barr, E. D.; Guillemot, L.; Champion, D. J.; ...

2012-12-21

Using the 100-m Effelsberg radio telescope operating at 1.36 GHz, we have performed a targeted radio pulsar survey of 289 unassociated γ-ray sources discovered by the Large Area Telescope (LAT) aboard the Fermi satellite and published in the 1FGL catalogue (Abdo et al. 2010a). In addition, this survey resulted in the discovery of millisecond pulsar J1745+1017, which resides in a short-period binary system with a low-mass companion, M c,min~0.0137M⊙, indicative of ‘black widow’ type systems. A 2-yr timing campaign has produced a refined radio ephemeris, accurate enough to allow for phase-folding of the LAT photons, resulting in the detection ofmore » a dual-peaked γ-ray light curve, proving that PSR J1745+1017 is the source responsible for the γ-ray emission seen in 1FGL J1745.5+1018 (2FGL J1745.6+1015; Nolan et al. 2012). We find the γ-ray spectrum of PSR J1745+1017 to be well modelled by an exponentially cut-off power law with cut-off energy 3.2 GeV and photon index 1.6. The observed sources are known to contain a further 10 newly discovered pulsars which were undetected in this survey. Our radio observations of these sources are discussed and in all cases limiting flux densities are calculated. Lastly, the reasons behind the seemingly low yield of discoveries are also discussed.« less

Prospects for the Detection of Fast Radio Bursts with the Murchison Widefield Array

NASA Astrophysics Data System (ADS)

Trott, Cathryn M.; Tingay, Steven J.; Wayth, Randall B.

2013-10-01

Fast radio bursts (FRBs) are short timescale (Lt1 s) astrophysical radio signals, presumed to be a signature of cataclysmic events of extragalactic origin. The discovery of six high-redshift events at ~1400 MHz from the Parkes radio telescope suggests that FRBs may occur at a high rate across the sky. The Murchison Widefield Array (MWA) operates at low radio frequencies (80-300 MHz) and is expected to detect FRBs due to its large collecting area (~2500 m2) and wide field-of-view (FOV, ~ 1000 deg2 at ν = 200 MHz). We compute the expected number of FRB detections for the MWA assuming a source population consistent with the reported detections. Our formalism properly accounts for the frequency-dependence of the antenna primary beam, the MWA system temperature, and unknown spectral index of the source population, for three modes of FRB detection: coherent; incoherent; and fast imaging. We find that the MWA's sensitivity and large FOV combine to provide the expectation of multiple detectable events per week in all modes, potentially making it an excellent high time resolution science instrument. Deviations of the expected number of detections from actual results will provide a strong constraint on the assumptions made for the underlying source population and intervening plasma distribution.

Radio variability in the Phoenix Deep Survey at 1.4 GHz

NASA Astrophysics Data System (ADS)

Hancock, P. J.; Drury, J. A.; Bell, M. E.; Murphy, T.; Gaensler, B. M.

2016-09-01

We use archival data from the Phoenix Deep Survey to investigate the variable radio source population above 1 mJy beam-1 at 1.4 GHz. Given the similarity of this survey to other such surveys we take the opportunity to investigate the conflicting results which have appeared in the literature. Two previous surveys for variability conducted with the Very Large Array (VLA) achieved a sensitivity of 1 mJy beam-1. However, one survey found an areal density of radio variables on time-scales of decades that is a factor of ˜4 times greater than a second survey which was conducted on time-scales of less than a few years. In the Phoenix deep field we measure the density of variable radio sources to be ρ = 0.98 deg-2 on time-scales of 6 months to 8 yr. We make use of Wide-field Infrared Survey Explorer infrared cross-ids, and identify all variable sources as an active galactic nucleus of some description. We suggest that the discrepancy between previous VLA results is due to the different time-scales probed by each of the surveys, and that radio variability at 1.4 GHz is greatest on time-scales of 2-5 yr.

A DECAMETER STATIONARY TYPE IV BURST IN IMAGING OBSERVATIONS ON 2014 SEPTEMBER 6

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

Koval, Artem; Chen, Yao; Feng, Shiwei

2016-08-01

First-of-its-kind radio imaging of a decameter solar stationary type IV radio burst has been presented in this paper. On 2014 September 6 the observations of type IV burst radio emission were carried out with the two-dimensional heliograph based on the Ukrainian T-shaped radio telescope (UTR-2), together with other telescope arrays. Starting at ∼09:55 UT and for ∼3 hr, the radio emission was kept within the observational session of UTR-2. The interesting observation covered the full evolution of this burst, “from birth to death.” During the event lifetime, two C-class solar X-ray flares with peak times 11:29 UT and 12:24 UTmore » took place. The time profile of this burst in radio has a double-humped shape that can be explained by injection of energetic electrons, accelerated by the two flares, into the burst source. According to the heliographic observations, we suggest that the burst source was confined within a high coronal loop, which was part of a relatively slow coronal mass ejection. The latter has been developed for several hours before the onset of the event. Through analysis of about 1.5 × 10{sup 6} heliograms (3700 temporal frames with 4096 images in each frame that correspond to the number of frequency channels), the radio burst source imaging shows a fascinating dynamical evolution. Both space-based ( GOES , SDO , SOHO , STEREO ) data and various ground-based instrumentation (ORFEES, NDA, RSTO, NRH) records have been used for this study.« less

Proper Motion of Components in 4C 39.25

NASA Technical Reports Server (NTRS)

Guirado, J. C.; Marcaide, J. M.; Alberdi, A.; Elosegui, P.; Ratner, M. I.; Shapiro, I. I.; Kilger, R.; Mantovani, F.; Venturi, T.; Rius, A.;

SOURCE REGIONS OF THE TYPE II RADIO BURST OBSERVED DURING A CME–CME INTERACTION ON 2013 MAY 22

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

Mäkelä, P.; Reiner, M. J.; Akiyama, S.

2016-08-20

We report on our study of radio source regions during the type II radio burst on 2013 May 22 based on direction-finding analysis of the Wind /WAVES and STEREO /WAVES (SWAVES) radio observations at decameter–hectometric wavelengths. The type II emission showed an enhancement that coincided with the interaction of two coronal mass ejections (CMEs) launched in sequence along closely spaced trajectories. The triangulation of the SWAVES source directions posited the ecliptic projections of the radio sources near the line connecting the Sun and the STEREO-A spacecraft. The WAVES and SWAVES source directions revealed shifts in the latitude of the radiomore » source, indicating that the spatial location of the dominant source of the type II emission varies during the CME–CME interaction. The WAVES source directions close to 1 MHz frequencies matched the location of the leading edge of the primary CME seen in the images of the LASCO/C3 coronagraph. This correspondence of spatial locations at both wavelengths confirms that the CME–CME interaction region is the source of the type II enhancement. Comparison of radio and white-light observations also showed that at lower frequencies scattering significantly affects radio wave propagation.« less

The isotropic radio background revisited

NASA Astrophysics Data System (ADS)

Fornengo, Nicolao; Lineros, Roberto A.; Regis, Marco; Taoso, Marco

2014-04-01

We present an extensive analysis on the determination of the isotropic radio background. We consider six different radio maps, ranging from 22 MHz to 2.3 GHz and covering a large fraction of the sky. The large scale emission is modeled as a linear combination of an isotropic component plus the Galactic synchrotron radiation and thermal bremsstrahlung. Point-like and extended sources are either masked or accounted for by means of a template. We find a robust estimate of the isotropic radio background, with limited scatter among different Galactic models. The level of the isotropic background lies significantly above the contribution obtained by integrating the number counts of observed extragalactic sources. Since the isotropic component dominates at high latitudes, thus making the profile of the total emission flat, a Galactic origin for such excess appears unlikely. We conclude that, unless a systematic offset is present in the maps, and provided that our current understanding of the Galactic synchrotron emission is reasonable, extragalactic sources well below the current experimental threshold seem to account for the majority of the brightness of the extragalactic radio sky.

The detectability of radio emission from exoplanets

NASA Astrophysics Data System (ADS)

Lynch, C. R.; Murphy, Tara; Lenc, E.; Kaplan, D. L.

2018-05-01

Like the magnetised planets in our Solar System, magnetised exoplanets should emit strongly at radio wavelengths. Radio emission directly traces the planetary magnetic fields and radio detections can place constraints on the physical parameters of these features. Large comparative studies of predicted radio emission characteristics for the known population of exoplanets help to identify what physical parameters could be key for producing bright, observable radio emission. Since the last comparative study, many thousands of exoplanets have been discovered. We report new estimates for the radio flux densities and maximum emission frequencies for the current population of known exoplanets orbiting pre-main sequence and main-sequence stars with spectral types F-M. The set of exoplanets predicted to produce observable radio emission are Hot Jupiters orbiting young stars. The youth of these system predicts strong stellar magnetic fields and/or dense winds, which are key for producing bright, observable radio emission. We use a new all-sky circular polarisation Murchison Widefield Array survey to place sensitive limits on 200 MHz emission from exoplanets, with 3σ values ranging from 4.0 - 45.0 mJy. Using a targeted Giant Metre Wave Radio Telescope observing campaign, we also report a 3σ upper limit of 4.5 mJy on the radio emission from V830 Tau b, the first Hot Jupiter to be discovered orbiting a pre-main sequence star. Our limit is the first to be reported for the low-frequency radio emission from this source.

HIGH-MASS STAR FORMATION TOWARD SOUTHERN INFRARED BUBBLE S10

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

Das, Swagat Ranjan; Tej, Anandmayee; Vig, Sarita

2016-11-01

An investigation in radio and infrared wavelengths of two high-mass star-forming regions toward the southern Galactic bubble S10 is presented here. The two regions under study are associated with the broken bubble S10 and Extended Green Object, G345.99-0.02, respectively. Radio continuum emission mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India, is detected toward both of the regions. These regions are estimated to be ionized by early-B- to late-O-type stars. Spitzer GLIMPSE mid-infrared data is used to identify young stellar objects (YSOs) associated with these regions. A Class-I/II-type source, with an estimated mass of 6.2  M {submore » ⊙}, lies ∼7″ from the radio peak. Pixel-wise, modified blackbody fits to the thermal dust emission using Herschel far-infrared data is performed to construct dust temperature and column density maps. Eight clumps are detected in the two regions using the 250 μ m image. The masses and linear diameter of these range between ∼300–1600  M {sub ⊙} and 0.2–1.1 pc, respectively, which qualifies them as high-mass star-forming clumps. Modeling of the spectral energy distribution of these clumps indicates the presence of high luminosity, high accretion rate, massive YSOs possibly in the accelerating accretion phase. Furthermore, based on the radio and MIR morphology, the occurrence of a possible bow wave toward the likely ionizing star is explored.« less

A radio spectral index map and catalogue at 147-1400 MHz covering 80 per cent of the sky

NASA Astrophysics Data System (ADS)

de Gasperin, F.; Intema, H. T.; Frail, D. A.

2018-03-01

The radio spectral index is a powerful probe for classifying cosmic radio sources and understanding the origin of the radio emission. Combining data at 147 MHz and 1.4 GHz from the TIFR GMRT Sky Survey (TGSS) and the NRAO VLA Sky Survey (NVSS), we produced a large-area radio spectral index map of ˜80 per cent of the sky (Dec. > - 40 deg), as well as a radio spectral index catalogue containing 1396 515 sources, of which 503 647 are not upper or lower limits. Almost every TGSS source has a detected counterpart, while this is true only for 36 per cent of NVSS sources. We released both the map and the catalogue to the astronomical community. The catalogue is analysed to discover systematic behaviours in the cosmic radio population. We find a differential spectral behaviour between faint and bright sources as well as between compact and extended sources. These trends are explained in terms of radio galaxy evolution. We also confirm earlier reports of an excess of steep-spectrum sources along the galactic plane. This corresponds to 86 compact and steep-spectrum source in excess compared to expectations. The properties of this excess are consistent with normal non-recycled pulsars, which may have been missed by pulsation searches due to larger than average scattering along the line of sight.

The 2017 Periastron Passage of PSR B1259-63 in Gamma-rays and X-rays

NASA Astrophysics Data System (ADS)

Wood, Kent S.; Johnson, Tyrel; Ray, Paul S.; Kerr, Matthew T.; Chernyakova, Masha; Fermi LAT Collaboration

2018-01-01

PSR B1259‑ 63 is a 48-ms radio pulsar in a highly eccentric 3.4-yr orbit with a Be star LS 2883. While the pulsed emission has been detected only in radio, un-pulsed radio, X-ray and gamma-ray emission are regularly observed from the binary system around the periastron. It is likely that the collision of the pulsar wind with the anisotropic wind of the Be star plays a crucial role in the generation of the observed non-thermal emission. The spectral energy distribution observed near periastron peaks in GeV gamma-rays, reaching maximum flux several weeks past periastron. In September 2017 it is being observed for a third periastron passage by the Fermi satellite. Here we present first results of the 2017 multi-wavelength campaign. The 2017 observations are compared to the two previous cycles, and used to test current models. Until recently there was no similar source known in the Galaxy but now a near-twin to it, PSR J2032+4127 , (Pspin=143 ms, Porbit ~50 yr, detectable radio to gamma rays) has been found, and is also undergoing periastron passage in Nov 2017. Gamma-ray and X-ray phenomena in the two sources are compared and discussed. These objects may represent a transitional phase, with possible later phases being accreting pulsars, and eventually perhaps NS-BH or NS-NS binary systems. Portions of this research performed at the US Naval Research Laboratory are sponsored by NASA DPR S-15633-Y.

Emission and propagation of Saturn kilometric radiation: Magnetoionic modes, beaming pattern, and polarization state

NASA Astrophysics Data System (ADS)

Lamy, L.; Cecconi, B.; Zarka, P.; Canu, P.; Schippers, P.; Kurth, W. S.; Mutel, R. L.; Gurnett, D. A.; Menietti, D.; Louarn, P.

2011-04-01

The Cassini mission crossed the source region of the Saturn kilometric radiation (SKR) on 17 October 2008. On this occasion, the Radio and Plasma Wave Science (RPWS) experiment detected both local and distant radio sources, while plasma parameters were measured in situ by the magnetometer and the Cassini Plasma Spectrometer. A goniopolarimetric inversion was applied to RPWS three-antenna electric measurements to determine the wave vector k and the complete state of polarization of detected waves. We identify broadband extraordinary (X) mode as well as narrowband ordinary (O) mode SKR at low frequencies. Within the source region, SKR is emitted just above the X mode cutoff frequency in a hot plasma, with a typical electron-to-wave energy conversion efficiency of ˜1% (2% peak). The knowledge of the k vector is then used to derive the locus of SKR sources in the kronian magnetosphere, which shows X and O components emanating from the same regions. We also compute the associated beaming angle at the source θ‧ = (k, -B) either from (1) in situ measurements or a model of the magnetic field vector (for local to distant sources) or (2) polarization measurements (for local sources). Obtained results, similar for both modes, suggest quasi-perpendicular emission for local sources, whereas the beaming pattern of distant sources appears as a hollow cone with a frequency-dependent constant aperture angle: θ‧ = 75° ± 15° below 300 kHz, decreasing at higher frequencies to reach θ‧ (1000 kHz) = 50° ± 25°. Finally, we investigate quantitatively the SKR polarization state, observed to be strongly elliptical at the source, and quasi-purely circular for sources located beyond approximately two kronian radii. We show that conditions of weak mode coupling are achieved along the raypath, under which the magnetoionic theory satisfactorily describes the evolution of the observed polarization. These results are analyzed comparatively with the auroral kilometric radiation at Earth.

A high-sensitivity survey of radio continuum emission from Herbig Ae/Be stars

NASA Technical Reports Server (NTRS)

Skinner, Stephen L.; Brown, Alexander; Stewart, Ron T.

1993-01-01

Results of a high-sensitivity VLA/Australia Telescope survey of radio continuum emission from the 57 Herbig Ae/Be stars and candidates in the 1984 catalog of Finkenzeller and Mundt are presented. Twelve stars were detected at the primary observing wavelength of 3.6 cm, on the basis that not less than 4 sigma radio sources lie within 1 arcsec of the optical positions. It is suggested that the radio emission is predominantly thermal and in many cases wind-related. The unusual eclipsing binary TY CrA is an exception and is classified as a nonthermal radio source on the basis of its decidedly negative spectral index (alpha = -1.2). A simple spherically symmetric free-fall accretion model is used to show that the predicted radio fluxes due to accretion at rates, estimated in the literature, of about 10 exp -6 to 10 exp -5 solar mass/yr are one to four orders of magnitude larger than observed.

The Extragalactic Lens VLBI Imaging Survey (ELVIS): Investigating galaxy cores and black holes with gravitational lens central images

NASA Astrophysics Data System (ADS)

Boyce, Edward R.

This thesis describes the Extragalactic Lens VLBI Imaging Survey (ELVIS), a search for central images in gravitational lenses. We present the first four ELVIS targets, for which we have radio VLBI observations with resolutions of a few milli-arcseconds and sensitivities of 15 - 38mJy. For PMN J1838-3427, CLASS B0739+366 and CLASS B0445+123 we have not detected any central images, but have set stringent upper limits on their flux densities. For CLASS B2319+051 we have made a tentative detection of a third radio source, which may be either a central image or radio emission from the lens galaxy. Using the upper limits on the central image flux densities, we gain new information about the matter distributions in the lens galaxies of these systems. We fit a broken power law model for the matter profile, and constrain the allowed break radii and inner index of this model. To demagnify the central images to the observed level the matter profiles must be slightly shallower than or steeper than isothermal, which is consistent with previous studies of early type galaxy profiles. The presence of a super-massive black hole weakens the constraints somewhat, but the profiles are still close to isothermal. Relative to previous work, we reduce the maximum sizes of shallow cores by factors of 2 to 3, and raise the indices of r 0( r -g central cusps by g = 0.05 - 0.35. If we take the source in B2319+051 to be a central image, then we select a narrow band of allowed break radii and inner indices, finding that a constant density core has size 150--380 pc, and a pure power law has index g = 1.5 - 1.67. Our constraints still allow sufficiently shallow profiles that some super-massive black holes may form central image pairs rather than eliminating the central image, and these image pairs may be detected with future instruments. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

Sco X-1 - A galactic radio source with an extragalactic radio morphology

NASA Technical Reports Server (NTRS)

Geldzahler, B. J.; Corey, B. E.; Fomalont, E. B.; Hilldrup, K.

1981-01-01

VLA observations of radio emissions at 1465 and 4885 MHz, of Sco X-1 confirm the existence of a colinear triple structure. Evidence that the three components of Sco X-1 are physically associated is presented, including the morphology, spectrum, variability, volume emissivity and magnetic field strength. The possibility of a physical phenomenon occurring in Sco X-1 similar to that occurring in extragalactic radio sources is discussed, and two galactic sources are found having extended emission similar to that in extragalactic objects. The extended structure of Sco X-1 is also observed to be similar to that of the hot spots in luminous extragalactic sources, and a radio source 20 arcmin from Sco X-1 is found to lie nearly along the radio axis formed by the components of Sco X-1.

Selection of radio sources for Venus balloon-Pathfinder Delta-DOR navigation at 1.7 GHz

NASA Technical Reports Server (NTRS)

Liewer, K. M

1986-01-01

In order to increase the success rate of the Delta-DOR (Delta-Differential One-way Range) VLBI navigational support for the French-Soviet Venus Balloon and Halley Pathfinder projects, forty-four extragalactic radio sources were observed in advance of these projects to determine which were suitable for use as reference sources. Of these forty-four radio sources taken from the existing JPL radio source catalogue, thirty-six were determined to be of sufficient strength for use in Delta-DOR VLBI navigation.

The Tidbinbilla-U.K. Schmidt radio quasar identification program

NASA Technical Reports Server (NTRS)

Jauncey, D. L.; Batty, M. J.; Savage, A.; Gulkis, S.

1983-01-01

A program is under way at Tidbinbilla to measure accurate (up to 2 arcsec r.m.s) radio positions for compact sources in the Parkes 2.7 GHz survey south of declination -30 deg. Optical identifications are being made on the basis of radio-optical position coincidence alone, without regard to colour or morphology, using the U.K. Schmidt IIIa-J sky survey to a limiting magnitude of 22.5. This program is aimed at producing an evaluation of the radio quasar redshift distribution with particular emphasis on those objects with redshifts greater than 3.0.

How Expanded Ionospheres of Hot Jupiters Can Prevent Escape of Radio Emission Generated by the Cyclotron Maser Instability

NASA Astrophysics Data System (ADS)

Weber, Christof; Lammer, Helmut; Shaikhislamov, Ildar F.; Erkaev, Nikolai; Chadney, Joshua M.; Khodachenko, Maxim L.; Grießmeier, Jean-Mathias; Rucker, Helmut O.; Vocks, Christian; Macher, Wolfgang; Odert, Petra; Kislyakova, Kristina G.

2017-04-01

We present a study of the plasma conditions in the atmospheres of the Hot Jupiters HD 209458b and HD 189733b and for an HD 209458b-like planet at orbit locations between 0.2-1 AU around a Sun-like star. We discuss how these conditions influence the radio emission we expect from their planetary magnetospheres. We find that the environmental conditions for the cyclotron maser instability (CMI), the process which is responsible for the generation of radio waves at magnetic planets in the solar system, most likely will not operate at Hot Jupiters. The reason for that is that hydrodynamically expanding atmospheres possess extended ionospheres whose plasma densities within the magnetosphere are so large that the plasma frequency is much higher than the cyclotron frequency, which contradicts the necessary condition for the production of radio emission and prevents the escape of radio waves from close-in extrasolar planets at distances <0.05 AU from a Sun-like host star. The upper atmosphere structure of Hot Jupiters around stars similar to the Sun changes between 0.2 and 0.5 AU from the hydrodynamic to a hydrostatic regime and this results in conditions similar to solar system planets with a region of depleted plasma between the exobase and the magnetopause where the plasma frequency can be lower than the cyclotron frequency. In such an environment a beam of highly energetic electrons accelerated along the field lines towards the planet can produce radio emission. However, even if the CMI could operate the extended ionospheres of Hot Jupiters are too dense to let the radio emission escape from the planets. We also investigate the possible radio emission of the Hot Jupiter Tau Bootis b by placing it at different orbital distances from the host star, i.e. 0.1 and 0.2 AU. In particular we check if the atmosphere of Tau Bootis b at 0.046 AU is in the hydrostatic or in the hydrodynamic regime. If it is in the hydrodynamic regime it's ionosphere is extended and will constitute an obstacle for possibly generated radio waves or the generation via the Cyclotron Maser Instability (CMI) might even be prevented completely. Furthermore we investigate at which orbital location the atmosphere undergoes the transformation from hydrodynamic to hydrostatic, i.e. the transformation to more favourable conditions for the CMI.

Richness of compact radio sources in NGC 6334D to F

NASA Astrophysics Data System (ADS)

Medina, S.-N. X.; Dzib, S. A.; Tapia, M.; Rodríguez, L. F.; Loinard, L.

2018-02-01

Context. The presence and properties of compact radio sources embedded in massive star forming regions can reveal important physical properties about these regions and the processes occurring within them. The NGC 6334 complex, a massive star forming region, has been studied extensively. Nevertheless, none of these studies has focused in its content in compact radio sources. Aims: Our goal here is to report on a systematic census of the compact radio sources toward NGC 6334, and their characteristics. This will be used to attempt to define their very nature. Methods: We used the VLA C band (4-8 GHz) archive data with 0.̋36 (500 AU) of spatial resolution and noise level of 50 μJy bm‑1 to carry out a systematic search for compact radio sources within NGC 6334. We also searched for infrared counterparts to provide some constraints on the nature of the detected radio sources. Results: A total of 83 compact sources and three slightly resolved sources were detected. Most of them are here reported for the first time. We found that 29 of these 86 sources have infrared counterparts and three are highly variable. Region D contains 18 of these sources. The compact source toward the center, in projection, of region E is also detected. Conclusions: From statistical analyses, we suggest that the 83 reported compact sources are real and most of them are related to NGC 6334 itself. A stellar nature for 27 of them is confirmed by their IR emission. Compared with Orion, region D suffers a deficit of compact radio sources. The infrared nebulosities around two of the slightly resolved sources are suggested to be warm dust, and we argue that the associated radio sources trace free-free emission from ionized material. We confirm the thermal radio emission of the compact source in region E. However, its detection at infrared wavelengths implies that it is located in the foreground of the molecular cloud. Finally, three strongly variable sources are suggested to be magnetically active young stars.

Extreme Radio Flares and Associated X-Ray Variability from Young Stellar Objects in the Orion Nebula Cluster

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

Forbrich, Jan; Reid, Mark J.; Wolk, Scott J.

Young stellar objects are known to exhibit strong radio variability on timescales of weeks to months, and a few reports have documented extreme radio flares with at least an order of magnitude change in flux density on timescales of hours to days. However, there have been few constraints on the occurrence rate of such radio flares or on the correlation with pre-main sequence X-ray flares, although such correlations are known for the Sun and nearby active stars. Here we report simultaneous deep VLA radio and Chandra X-ray observations of the Orion Nebula Cluster, targeting hundreds of sources to look formore » the occurrence rate of extreme radio variability and potential correlation with the most extreme X-ray variability. We identify 13 radio sources with extreme radio variability, with some showing an order of magnitude change in flux density in less than 30 minutes. All of these sources show X-ray emission and variability, but we find clear correlations with extreme radio flaring only on timescales <1 hr. Strong X-ray variability does not predict the extreme radio sources and vice versa. Radio flares thus provide us with a new perspective on high-energy processes in YSOs and the irradiation of their protoplanetary disks. Finally, our results highlight implications for interferometric imaging of sources violating the constant-sky assumption.« less

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

NASA Technical Reports Server (NTRS)

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

1993-01-01

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

Precision Geodesy via Radio Interferometry.

PubMed

Hinteregger, H F; Shapiro, I I; Robertson, D S; Knight, C A; Ergas, R A; Whitney, A R; Rogers, A E; Moran, J M; Clark, T A; Burke, B F

1972-10-27

Very-long-baseline interferometry experiments, involving observations of extragalactic radio sources, were performed in 1969 to determine the vector separations between antenna sites in Massachusetts and West Virginia. The 845.130-kilometer baseline was estimated from two separate experiments. The results agreed with each other to within 2 meters in all three components and with a special geodetic survey to within 2 meters in length; the differences in baseline direction as determined by the survey and by interferometry corresponded to discrepancies of about 5 meters. The experiments also yielded positions for nine extragalactic radio sources, most to within 1 arc second, and allowed the hydrogen maser clocks at the two sites to be synchronized a posteriori with an uncertainty of only a few nanoseconds.

THE RADIO JET ASSOCIATED WITH THE MULTIPLE V380 ORI SYSTEM

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

Rodríguez, Luis F.; Yam, J. Omar; Carrasco-González, Carlos

The giant Herbig–Haro object 222 extends over ∼6′ in the plane of the sky, with a bow shock morphology. The identification of its exciting source has remained uncertain over the years. A non-thermal radio source located at the core of the shock structure was proposed to be the exciting source. However, Very Large Array studies showed that the radio source has a clear morphology of radio galaxy and a lack of flux variations or proper motions, favoring an extragalactic origin. Recently, an optical–IR study proposed that this giant HH object is driven by the multiple stellar system V380 Ori, locatedmore » about 23′ to the SE of HH 222. The exciting sources of HH systems are usually detected as weak free–free emitters at centimeter wavelengths. Here, we report the detection of an elongated radio source associated with the Herbig Be star or with its close infrared companion in the multiple V380 Ori system. This radio source has the characteristics of a thermal radio jet and is aligned with the direction of the giant outflow defined by HH 222 and its suggested counterpart to the SE, HH 1041. We propose that this radio jet traces the origin of the large scale HH outflow. Assuming that the jet arises from the Herbig Be star, the radio luminosity is a few times smaller than the value expected from the radio–bolometric correlation for radio jets, confirming that this is a more evolved object than those used to establish the correlation.« less

Fermi-LAT and Suzaku Observations of the Radio Galaxy Centaurus B

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

Katsuta, Junichiro; /Stanford U., HEPL /KIPAC, Menlo Park; Tanaka, Y.T.

2012-08-17

CentaurusB is a nearby radio galaxy positioned in the Southern hemisphere close to the Galactic plane. Here we present a detailed analysis of about 43 months accumulation of Fermi-LAT data and of newly acquired Suzaku X-ray data for Centaurus B. The source is detected at GeV photon energies, although we cannot completely exclude the possibility that it is an artifact due to incorrect modeling of the bright Galactic diffuse emission in the region. The LAT image provides a weak hint of a spatial extension of the {gamma} rays along the radio lobes, which is consistent with the lack of sourcemore » variability in the GeV range. We note that the extension cannot be established statistically due to the low number of the photons. Surprisingly, we do not detect any diffuse emission of the lobes at X-ray frequencies, with the provided upper limit only marginally consistent with the previously claimed ASCA flux. The broad-band modeling shows that the observed {gamma}-ray flux of the source may be produced within the lobes, if the diffuse non-thermal X-ray emission component is not significantly below the derived Suzaku upper limit. This association would imply that efficient in-situ acceleration of the ultrarelativistic particles is occurring and that the lobes are dominated by the pressure from the relativistic particles. However, if the diffuse X-ray emission is much below the Suzaku upper limits, the observed {gamma}-ray flux is not likely to be produced within the lobes, but instead within the unresolved core of Centaurus B. In this case, the extended lobes could be dominated by the pressure of the magnetic field.« less

An Overdensity of Massive, Dusty Starbursts Associated with the High-Redshift Radio Galaxy MRC1138-262 at z = 2.16

NASA Astrophysics Data System (ADS)

Altieri, Bruno; Dannerbauer, Helmut

We present Herschel and APEX LABOCA 870 μm imaging of the field of the high-redshift radio galaxy MRC1138 at z = 2.16. We detect 16 submillimeter galaxies in this ˜140 arcmin2 large bolometer map, with flux densities in the range 3-11 mJy. The pure number counts indicate an overdensity of SMGs by a factor of five compared to blank field surveys. Based on an exquisite multi-wavelength database including VLA 1.4 GHz radio and infrared observations, we verifiy whether these sources are members of the proto-cluster structure at z = 2.2 or not. Based on Herschel PACS+ SPIRE and Spitzer MIPS photometry, we derived reliable far-infrared photometric redshifts for all of our sources. VLT-ISAAC near-infrared spectroscopic observations confirmed redshifts of z ≈ 2.2 for four of these SMGs. We conclude that in total at least seven sources are part of this proto-cluster at z = 2.16. We measure a star formation rate density S FRD ˜ 1500 M⊙ yr-1 Mpc-3, four magntiudes higher compared to the global SFRD at this redshift. Striklingly, these seven sources are concentrated within a region of 2 Mpc (the typical size of clusters in the local universe) and are not distributed in the filaments as predicted by theories and traced by the Hα emitters at z ≈ 2.2. This concentration of massive, dusty starbursts is not centered on the radio galaxy which is submm bright. A significant fraction, six out of 11 SMGs with z ≈ 2.2 Hα imaging coverage are associated with Hα emitters, demonstrating the potential of tracing SMG counterparts with this source population. Our results demonstrate that indeed submm observations enable us to reveal clusters of massive, dusty starbursts and will pave the road for systematic and detailed investigations with this technique in the future.

Bent-tailed radio sources in the australia telescope large area survey of the Chandra deep field south

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

Dehghan, S.; Johnston-Hollitt, M.; Franzen, T. M. O.

2014-11-01

Using the 1.4 GHz Australia Telescope Large Area Survey, supplemented by the 1.4 GHz Very Large Array images, we undertook a search for bent-tailed (BT) radio galaxies in the Chandra Deep Field South. Here we present a catalog of 56 detections, which include 45 BT sources, 4 diffuse low-surface-brightness objects (1 relic, 2 halos, and 1 unclassified object), and a further 7 complex, multi-component sources. We report BT sources with rest-frame powers in the range 10{sup 22} ≤ P {sub 1.4} {sub GHz} ≤ 10{sup 26} W Hz{sup –1}, with redshifts up to 2 and linear extents from tens ofmore » kiloparsecs up to about 1 Mpc. This is the first systematic study of such sources down to such low powers and high redshifts and demonstrates the complementary nature of searches in deep, limited area surveys as compared to shallower, large surveys. Of the sources presented here, one is the most distant BT source yet detected at a redshift of 2.1688. Two of the sources are found to be associated with known clusters: a wide-angle tail source in A3141 and a putative radio relic which appears at the infall region between the galaxy group MZ 00108 and the galaxy cluster AMPCC 40. Further observations are required to confirm the relic detection, which, if successful, would demonstrate this to be the least powerful relic yet seen with P {sub 1.4} {sub GHz} = 9 × 10{sup 22} W Hz{sup –1}. Using these data, we predict future 1.4 GHz all-sky surveys with a resolution of ∼10 arcsec and a sensitivity of 10 μJy will detect of the order of 560,000 extended low-surface-brightness radio sources of which 440,000 will have a BT morphology.« less

MULTI-MESSENGER ASTRONOMY OF GRAVITATIONAL-WAVE SOURCES WITH FLEXIBLE WIDE-AREA RADIO TRANSIENT SURVEYS

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

Yancey, Cregg C.; Shawhan, Peter; Bear, Brandon E.

We explore opportunities for multi-messenger astronomy using gravitational waves (GWs) and prompt, transient low-frequency radio emission to study highly energetic astrophysical events. We review the literature on possible sources of correlated emission of GWs and radio transients, highlighting proposed mechanisms that lead to a short-duration, high-flux radio pulse originating from the merger of two neutron stars or from a superconducting cosmic string cusp. We discuss the detection prospects for each of these mechanisms by low-frequency dipole array instruments such as LWA1, the Low Frequency Array and the Murchison Widefield Array. We find that a broad range of models may bemore » tested by searching for radio pulses that, when de-dispersed, are temporally and spatially coincident with a LIGO/Virgo GW trigger within a ∼30 s time window and ∼200–500 deg{sup 2} sky region. We consider various possible observing strategies and discuss their advantages and disadvantages. Uniquely, for low-frequency radio arrays, dispersion can delay the radio pulse until after low-latency GW data analysis has identified and reported an event candidate, enabling a prompt radio signal to be captured by a deliberately targeted beam. If neutron star mergers do have detectable prompt radio emissions, a coincident search with the GW detector network and low-frequency radio arrays could increase the LIGO/Virgo effective search volume by up to a factor of ∼2. For some models, we also map the parameter space that may be constrained by non-detections.« less

Interferometric imaging of the high-redshift radio galaxy, 4C60.07: an SMA, Spitzer and VLA study reveals a binary AGN/starburst

NASA Astrophysics Data System (ADS)

Ivison, R. J.; Morrison, G. E.; Biggs, A. D.; Smail, Ian; Willner, S. P.; Gurwell, M. A.; Greve, T. R.; Stevens, J. A.; Ashby, M. L. N.

2008-11-01

High-resolution submillimetre (submm) imaging of the high-redshift radio galaxy (HzRG), 4C60.07, at z = 3.8, has revealed two dusty components of roughly equal integrated flux. Spitzer imaging shows that one of these components (`B') is coincident with an extremely red active galactic nucleus (AGN), offset by ~4arcsec (~30kpc) from the HzRG core. The other submm component (`A') - resolved by our synthesized beam and devoid of emission at 3.6-8.0μm - lies between `B' and the HzRG core. Since the radio galaxy was discovered via its extremely young, steep-spectrum radio lobes and the creation of these lobes was likely triggered by the interaction, we argue that we are witnessing an early-stage merger, prior to its eventual equilibrium state. The interaction is between the host galaxy of an actively fuelled black hole (BH) and a gas-rich starburst/AGN (`B') marked by the compact submm component and coincident with broad CO(4-3) emission. The second submm component (`A') is a plume of cold, dusty gas, associated with a narrow (~150kms-1) CO feature, and may represent a short-lived tidal structure. It has been claimed that HzRGs and submillimetre-selected galaxies (SMGs) differ only in the activity of their AGNs, but such complex submm morphologies are seen only rarely amongst SMGs, which are usually older, more relaxed systems. Our study has important implications: where a galaxy's gas reservoir is not aligned with its central BH, CO may be an unreliable probe of dynamical mass, affecting work on the co-assembly of BHs and host spheroids. Our data support the picture wherein close binary AGN are induced by mergers. They also raise the possibility that some supposedly jet-induced starbursts may have formed co-evally (yet independently of) the radio jets, both triggered by the same interaction. Finally, we note that the HzRG host would have gone unnoticed without its jets and its companion, so there may be many other unseen BHs at high redshift, lost in the sea of ~5 × 108 similarly bright Infrared Array Camera (IRAC) sources - sufficiently massive to drive a >1027-W radio source, yet practically invisible unless actively fuelled.

On the Nature of Orion Source I

NASA Astrophysics Data System (ADS)

Báez-Rubio, A.; Jiménez-Serra, I.; Martín-Pintado, J.; Zhang, Q.; Curiel, S.

2018-01-01

The Kleinmann–Low nebula in Orion, the closest region of massive star formation, harbors Source I, whose nature is under debate. Knowledge of this source may have profound implications for our understanding of the energetics of the hot core in Orion KL since it might be the main heating source in the region. The spectral energy distribution of this source in the radio is characterized by a positive spectral index close to 2, which is consistent with (i) thermal bremsstrahlung emission of ionized hydrogen gas produced by a central massive protostar, or (ii) photospheric bremsstrahlung emission produced by electrons when deflected by the interaction with neutral and molecular hydrogen like Mira-like variable stars. If ionized hydrogen gas were responsible for the observed continuum emission, its modeling would predict detectable emission from hydrogen radio recombination lines (RRLs). However, our SMA observations were obtained with a high enough sensitivity to rule out that the radio continuum emission arises from a dense hypercompact H II region because the H26α line would have been detected, in contrast with our observations. To explain the observational constraints, we investigate further the nature of the radio continuum emission from source I. We have compared available radio continuum data with the predictions from our upgraded non-LTE 3D radiative transfer model, MOdel for REcombination LInes, to show that radio continuum fluxes and sizes can only be reproduced by assuming both dust and bremsstrahlung emission from neutral gas. The dust emission contribution is significant at ν ≥ 43 GHz. In addition, our RRL peak intensity predictions for the ionized metals case are consistent with the nondetection of Na and K RRLs at millimeter and submillimeter wavelengths.

Zebra pattern in decametric radio emission of Jupiter

NASA Astrophysics Data System (ADS)

Panchenko, M.; Rošker, S.; Rucker, H. O.; Brazhenko, A.; Zarka, P.; Litvinenko, G.; Shaposhnikov, V. E.; Konovalenko, A. A.; Melnik, V.; Franzuzenko, A. V.; Schiemel, J.

2018-03-01

We report the systematic analysis of zebra-like fine spectral structures in decametric frequency range of Jovian radio emission. Observations were performed by the large ground-based radio telescope URAN-2 during three observation campaigns between, Sep., 2012, and May, 2015. In total, 51 zebra pattern (ZP) events were detected. These rare fine radio features are observed in frequency range from 12.5 to 29.7 MHz as quasi-harmonically related bands of enhanced brightness. ZPs are strongly polarized radio emission with a duration from 20 s to 290 s and flux densities 105-106 Jy (normalized to 1 AU), that is, 1-2 orders lower than for Io-decametric radio emission (DAM). Occurrence of the events does not depend on the position of Io satellite but is strongly controlled by the Jovian central meridian longitude (CML). ZPs are mainly detected in two active sectors of Jovian CMLs: 100∘ to 160∘ for Northern sources (right-handed polarized) and 300∘ and 60∘ (via 360∘) for the Southern sources (left-handed). The frequency interval between neighboring stripes is from 0.26 to 1.5 MHz and in most cases this interval increases with frequency. We discussed the double plasma resonance with electrons or ions as a possible source of the ZPs. The performed analysis of the observations allows us to conclude that the observed ZPs are a new type of narrow band spectral structures in the Jovian DAM.

Search for Pulsations from a Nearby Millisecond Pulsar and Wasilewski 49: Mirror for a Hidden Seyfert 1 Nucleus

NASA Technical Reports Server (NTRS)

Halpern, Jules P.

1999-01-01

Five studies are reported in this final report. The recently discovered 5.3 ms pulsar J1012+5307 at a distance of 520 pc is in an area of the sky which is particularly deficient in absorbing gas. The column density along the line of sight is less than 7.5 x 10(exp 19) CM(exp -2) which facilitates soft X-ray observations. Halpern reported a possible ROSAT Position Sensitive Proportional Counter (PSPC) detection of the pulsar in a serendipitous, off-axis observation. We have now confirmed the X-ray emission of PSR J1012+,5307 in a 23 ksec observation with the ROSAT High Resolution Imager (HRI). A point source is detected within 3" of the radio position. Its count rate of 1.6 +/- 0.3 x 10(exp -3) s(exp -1) corresponds to an unabsorbed 0. 1-2.4 keV flux of 6.4 x 10(exp -14) ergs cm(exp -2) s(exp -1), similar to that reported previously. This counts-to-flux conversion is valid for N(sub H) = 5 x 10(exp 19) cm(exp -2), and either a power-law spectrum of photon index 2.5 or a blackbody of kT = 0.1 keV. The implied X-ray luminosity of 2.0 x 10(exp 30) ergs s(exp -1) is 5 X 10(exp -4) of the pulsar's spin-down power dot-E, and similar to that of the nearest millisecond pulsar J0437-4715, which is nearly a twin of J1012+5307 in P dot-E. We subjected the 37 photons (and 13 background counts) within the source region to a pulsar search, but no evidence for pulsation was found. The pulsar apparently emits over a large fraction of its rotation cycle, and the absence of sharp modulation can be taken as evidence for surface thermal emission, as is favored for PSR J0437-4715, rather than magnetospheric X-ray emission which is apparent in the sharp pulses of the much more energetic millisecond pulsar B1821-24. A further test of this interpretation will be made with a longer ROSAT observation, which will increase the number of photons collected by a factor of 5, and permit a more sensitive examination of the light curve for modulation due to emission from heated polar caps. If found, such modulation will be further evidence that surface reheating by the impact of particles accelerated along open fiel;d lines operates in these approximately 10(exp -9) year old pulsars. In a second study, a new AM Her star serendipitously in a 25 day observation was detected with the EUVE satellite. A coherent period of 85.82 min is present in the EUVE Deep Survey imager light curve of this source. A spectroscopic optical identification is made with a 19th magnitude blue star that has H and He emission lines, and broad cyclotron humps typical of a magnetic cataclysmic variable. A lower limit to the polar magnetic field of 50 MG is estimated from the spacing of the cyclotron harmonics. EUVE J0425.6-5714 is also detected in archival ROSAT HRI observations spanning two months, and its stable and highly structured light curve permits us to fit a coherent ephemeris linking the ROSAT and EUVE data over a 1.3 yr gap. The derived period is 85.82107 +/- 0.00020 min, and the ephemeris should be accurate to 0.1 cycles until the year 2005. A narrow but partial X-ray eclipse suggests that this object belongs to the group of AM Her stars whose viewing geometry is such that the accretion stream periodically occults the soft X-ray emitting accretion spot on the surface of the white dwarf. A non-detection of hard X-rays from ASCA observations that are contemporaneous with the ROSAT HRI shows that the soft X-rays must dominate by at least an order of magnitude, which is consistent with a known trend among AM Her stars with large magnetic field. This object should not be confused with the Seyfert galaxy IH 0419-577 (= LB 1727), another X-ray/EUV source which lies only 3'95 away, and was the principal target of these monitoring observations. In a third report; the identity of the persistent high-energy (> 100 MeV) gamma-ray sources in the Galaxy, still largely a mystery is investigated. The second installment of the EGRET (2EG) lists a total of 128 sources, of which 51 are likely or possibly identified with AGNs, five with rotation-powered pulsars, and one is the LMC. There are 71 unidentified sources, of which 33, or almost half, lie in the narrow band of absolute value of b < 10 degrees along the Galactic plane. This excess of low-latitude sources must, therefore, constitute a Galactic population that is either similar to the already identified gamma-ray pulsars, or an entirely new class of gamma-ray emitters associated with the disk population. We are continuing our program, begun in A06, that is aimed at intermediate-latitude sources, arguing that X-ray detection of them is the most plausible method of identifying the Galactic population. The sources at high latitude must statistically be mostly AGNS, and are more straightforwardly identified through radio and optical means. For the fourth report, identification of the EGRET Source the identity of the persistent, high-energy gamma-ray sources in the Galactic plane is a mystery. The most likely scenario is a population of middle-aged pulsars, many of which could be radio quiet like Geminga. We have an ongoing program of ROSAT, VLA, and optical observations of selected EGRET error circles at intermediate Galactic latitude. For one of these fields, at (l, b) = (106 degrees, +3), our complete census of X-ray and radio sources, reveals a remarkable association between a radio shell with unique properties, and a complete census of X-ray and radio sources reveals a remarkable association between a radio shell with unique properties, and a compact X-ray source. Further observations are needed to determine whether or not this source has a hard X-ray spectrum like that of other gamma ray pulsars and, ideally, to find its pulsations. A fifth report reviews, Wasilewski 49, an interacting pair of Seyfert galaxies at z = 0.063, one of which contains a hidden Seyfert I nucleus as evidenced by broad wings on its Balmer lines.

ROSAT observations of clusters with wide-angle tailed radio sources

NASA Technical Reports Server (NTRS)

Burns, Jack O.

1993-01-01

The goal of these ROSAT PSPC pointed observations was to understand the nature of X-ray emission associated clusters that contain luminous wide-angle tailed (WAT) radio sources identified with the centrally dominant cluster galaxies. These 500 kpc diameter radio sources are strongly affected by confinement and interaction with the intracluster medium. So, a complete picture of the origin and evolution of these radio sources is not possible without detailed X-ray observations which sample the distribution and temperature of the surrounding hot gas. Two WAT clusters have been observed with the ROSAT PSPC to date. The first is Abell 2634 which contains the WAT 3C 465 and was approved for observations in AO-1. Unfortunately, these observations were broken into two widely separated pieces in time. The first data set containing about 9000 sec of integration arrived in mid-March, 1992. The second data set containing about 10,500 sec arrived just recently in early April (after a first tape was destroyed in the mail). The second cluster is 1919+479 which was approved for observations in AO-2. These ROSAT data arrived in October 1992.

QUEST FOR COSMOS SUBMILLIMETER GALAXY COUNTERPARTS USING CARMA AND VLA: IDENTIFYING THREE HIGH-REDSHIFT STARBURST GALAXIES

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

Smolcic, V.; Navarrete, F.; Bertoldi, F.

2012-05-01

We report on interferometric observations at 1.3 mm at 2''-3'' resolution using the Combined Array for Research in Millimeter-wave Astronomy. We identify multi-wavelength counterparts of three submillimeter galaxies (SMGs; F{sub 1m} > 5.5 mJy) in the COSMOS field, initially detected with MAMBO and AzTEC bolometers at low, {approx}10''-30'', resolution. All three sources-AzTEC/C1, Cosbo-3, and Cosbo-8-are identified to coincide with positions of 20 cm radio sources. Cosbo-3, however, is not associated with the most likely radio counterpart, closest to the MAMBO source position, but with that farther away from it. This illustrates the need for intermediate-resolution ({approx}2'') mm-observations to identify themore » correct counterparts of single-dish-detected SMGs. All of our three sources become prominent only at NIR wavelengths, and their mm-to-radio flux based redshifts suggest that they lie at redshifts z {approx}> 2. As a proof of concept, we show that photometric redshifts can be well determined for SMGs, and we find photometric redshifts of 5.6 {+-} 1.2, 1.9{sup +0.9}{sub -0.5}, and {approx}4 for AzTEC/C1, Cosbo-3, and Cosbo-8, respectively. Using these we infer that these galaxies have radio-based star formation rates of {approx}> 1000 M{sub Sun} yr{sup -1}and IR luminosities of {approx}10{sup 13} L{sub Sun} consistent with properties of high-redshift SMGs. In summary, our sources reflect a variety of SMG properties in terms of redshift and clustering, consistent with the framework that SMGs are progenitors of z {approx} 2 and today's passive galaxies.« less

Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A

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

Perley, D. A.; Perley, R. A.; Dhawan, V.

2017-06-01

We report the appearance of a new radio source at a projected offset of 460 pc from the nucleus of Cygnus A. The flux density of the source (which we designate Cygnus A-2) rose from an upper limit of <0.5 mJy in 1989 to 4 mJy in 2016 ( ν = 8.5 GHz), but is currently not varying by more than a few percent per year. The radio luminosity of the source is comparable to the most luminous known supernovae, it is compact in Very Long Baseline Array observations down to a scale of 4 pc, and it is coincidentmore » with a near-infrared point source seen in pre-existing adaptive optics and HST observations. The most likely interpretation of this source is that it represents a secondary supermassive black hole in a close orbit around the Cygnus A primary, though an exotic supernova model cannot be ruled out. The gravitational influence of a secondary SMBH at this location may have played an important role in triggering the rapid accretion that has powered the Cygnus A radio jet over the past 10{sup 7} years.« less

A search for radio emission from Galactic supersoft X-ray sources

NASA Astrophysics Data System (ADS)

Ogley, R. N.; Chaty, S.; Crocker, M.; Eyres, S. P. S.; Kenworthy, M. A.; Richards, A. M. S.; Rodríguez, L. F.; Stirling, A. M.

2002-03-01

We have made a deep search for radio emission from all the northern hemisphere supersoft X-ray sources using the Very Large Array (VLA) and multi-element radio-linked interferometer network (MERLIN) telescopes, at 5 and 8.4GHz. Three previously undetected sources, T Pyx, V1974 Cygni and RX J0019.8+2156, were imaged in quiescence using the VLA in order to search for any persistent emission. No radio emission was detected in any of the VLA fields down to a typical 1σ rms noise of 20μJybeam-1, however, 17 new point sources were detected in the fields with 5-GHz fluxes between 100 and 1500μJy, giving an average 100-μJy source density of ~200deg-2, comparable to what was found in the MERLIN Hubble Deep Field survey. The persistent source AG Draconis was observed by MERLIN to provide a confirmation of previous VLA observations and to investigate the source at a higher resolution. The core is resolved at the milliarcsec scale into two components that have a combined flux of ~1mJy. It is possible that we are detecting nebulosity, which is becoming resolved out by the higher MERLIN resolution. We have investigated possible causes of radio emission from a wind environment, both directly from the secondary star, and also consequently, of the high X-ray luminosity from the white dwarf. There is an order of magnitude discrepancy between observed and modelled values that can be explained by the uncertainty in fundamental quantities within these systems.

Deep 3 GHz number counts from a P(D) fluctuation analysis

NASA Astrophysics Data System (ADS)

Vernstrom, T.; Scott, Douglas; Wall, J. V.; Condon, J. J.; Cotton, W. D.; Fomalont, E. B.; Kellermann, K. I.; Miller, N.; Perley, R. A.

2014-05-01

Radio source counts constrain galaxy populations and evolution, as well as the global star formation history. However, there is considerable disagreement among the published 1.4-GHz source counts below 100 μJy. Here, we present a statistical method for estimating the μJy and even sub-μJy source count using new deep wide-band 3-GHz data in the Lockman Hole from the Karl G. Jansky Very Large Array. We analysed the confusion amplitude distribution P(D), which provides a fresh approach in the form of a more robust model, with a comprehensive error analysis. We tested this method on a large-scale simulation, incorporating clustering and finite source sizes. We discuss in detail our statistical methods for fitting using Markov chain Monte Carlo, handling correlations, and systematic errors from the use of wide-band radio interferometric data. We demonstrated that the source count can be constrained down to 50 nJy, a factor of 20 below the rms confusion. We found the differential source count near 10 μJy to have a slope of -1.7, decreasing to about -1.4 at fainter flux densities. At 3 GHz, the rms confusion in an 8-arcsec full width at half-maximum beam is ˜ 1.2 μJy beam-1, and a radio background temperature ˜14 mK. Our counts are broadly consistent with published evolutionary models. With these results, we were also able to constrain the peak of the Euclidean normalized differential source count of any possible new radio populations that would contribute to the cosmic radio background down to 50 nJy.

Measuring cosmic shear and birefringence using resolved radio sources

NASA Astrophysics Data System (ADS)

Whittaker, Lee; Battye, Richard A.; Brown, Michael L.

2018-02-01

We develop a new method of extracting simultaneous measurements of weak lensing shear and a local rotation of the plane of polarization using observations of resolved radio sources. The basis of the method is an assumption that the direction of the polarization is statistically linked with that of the gradient of the total intensity field. Using a number of sources spread over the sky, this method will allow constraints to be placed on cosmic shear and birefringence, and it can be applied to any resolved radio sources for which such a correlation exists. Assuming that the rotation and shear are constant across the source, we use this relationship to construct a quadratic estimator and investigate its properties using simulated observations. We develop a calibration scheme using simulations based on the observed images to mitigate a bias which occurs in the presence of measurement errors and an astrophysical scatter on the polarization. The method is applied directly to archival data of radio galaxies where we measure a mean rotation signal of $\\omega=-2.02^{\\circ}\\pm0.75^{\\circ}$ and an average shear compatible with zero using 30 reliable sources. This level of constraint on an overall rotation is comparable with current leading constraints from CMB experiments and is expected to increase by at least an order of magnitude with future high precision radio surveys, such as those performed by the SKA. We also measure the shear and rotation two-point correlation functions and estimate the number of sources required to detect shear and rotation correlations in future surveys.

Radio spectra of bright compact sources at z > 4.5

NASA Astrophysics Data System (ADS)

Coppejans, Rocco; van Velzen, Sjoert; Intema, Huib T.; Müller, Cornelia; Frey, Sándor; Coppejans, Deanne L.; Cseh, Dávid; Williams, Wendy L.; Falcke, Heino; Körding, Elmar G.; Orrú, Emanuela; Paragi, Zsolt; Gabányi, Krisztina É.

2017-05-01

High-redshift quasars are important to study galaxy and active galactic nuclei evolution, test cosmological models and study supermassive black hole growth. Optical searches for high-redshift sources have been very successful, but radio searches are not hampered by dust obscuration and should be more effective at finding sources at even higher redshifts. Identifying high-redshift sources based on radio data is, however, not trivial. Here we report on new multifrequency Giant Metrewave Radio Telescope observations of eight z > 4.5 sources previously studied at high angular resolution with very long baseline interferometry (VLBI). Combining these observations with those from the literature, we construct broad-band radio spectra of all 30 z > 4.5 sources that have been observed with VLBI. In the sample we found flat, steep and peaked spectra in approximately equal proportions. Despite several selection effects, we conclude that the z > 4.5 VLBI (and likely also non-VLBI) sources have diverse spectra and that only about a quarter of the sources in the sample have flat spectra. Previously, the majority of high-redshift radio sources were identified based on their ultrasteep spectra. Recently, a new method has been proposed to identify these objects based on their megahertz-peaked spectra. No method would have identified more than 18 per cent of the high-redshift sources in this sample. More effective methods are necessary to reliably identify complete samples of high-redshift sources based on radio data.

Flat spectrum multicomponent radio sources - Cosmic conspiracy or geometry

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

Pacholczyk, A.G.

1981-01-01

Compact radio sources which do not exhibit currently large flux density variations, are often characterized by spectra nearly flat over a wide range of wavelengths. Cotton et al. (1980) recently reported the results of the VLBI multifrequency interferometric and total flux density observations of a typical representative of the flat spectrum class of sources, a BL Lacertae object PKS 0735+178. If 0735+178 is indeed representative of flat spectrum sources, then some mechanism causing the component production and energy loss to be balanced must be operative among this type of radio source to maintain a flat spectrum over at least certainmore » periods of time. This effect is referred to as 'cosmic conspiracy'. It is suggested that the flatness of spectra of this class of radio sources may be related to a specific symmetry in the radio structure, namely, to a predominantly linear, one-dimensional evolution of radio radiating material, rather than spherical, three-dimensional evolution.« less

Two-Component Structure of the Radio Source 0014+813 from VLBI Observations within the CONT14 Program

NASA Astrophysics Data System (ADS)

Titov, O. A.; Lopez, Yu. R.

2018-03-01

We consider a method of reconstructing the structure delay of extended radio sources without constructing their radio images. The residuals derived after the adjustment of geodetic VLBI observations are used for this purpose. We show that the simplest model of a radio source consisting of two point components can be represented by four parameters (the angular separation of the components, the mutual orientation relative to the poleward direction, the flux-density ratio, and the spectral index difference) that are determined for each baseline of a multi-baseline VLBI network. The efficiency of this approach is demonstrated by estimating the coordinates of the radio source 0014+813 observed during the two-week CONT14 program organized by the International VLBI Service (IVS) in May 2014. Large systematic deviations have been detected in the residuals of the observations for the radio source 0014+813. The averaged characteristics of the radio structure of 0014+813 at a frequency of 8.4 GHz can be calculated from these deviations. Our modeling using four parameters has confirmed that the source consists of two components at an angular separation of 0.5 mas in the north-south direction. Using the structure delay when adjusting the CONT14 observations leads to a correction of the average declination estimate for the radio source 0014+813 by 0.070 mas.

Identification of a Likely Radio Counterpart to the Rapid Burster

NASA Astrophysics Data System (ADS)

Moore, Christopher B.; Rutledge, Robert E.; Fox, Derek W.; Guerriero, Robert A.; Lewin, Walter H. G.; Fender, Robert; van Paradijs, Jan

2000-04-01

We have identified a likely radio counterpart to the low-mass X-ray binary MXB 1730-335 (the Rapid Burster). The counterpart has shown 8.4 GHz radio on/off behavior correlated with the X-ray on/off behavior as observed by the RXTE/ASM during six VLA observations. The probability of an unrelated, randomly varying background source duplicating this behavior is 1%-3% depending on the correlation timescale. The location of the radio source is R.A. 17h33m24.61s, decl. -33 deg23'19.8" (J2000), +/-0.1". We do not detect 8.4 GHz radio emission coincident with type II (accretion-driven) X-ray bursts. The ratio of radio to X-ray emission during such bursts is constrained to be below the ratio observed during X-ray-persistent emission at the 2.9 σ level. Synchrotron bubble models of the radio emission can provide a reasonable fit to the full data set, collected over several outbursts, assuming that the radio evolution is the same from outburst to outburst but given the physical constraints the emission is more likely to be due to ~1 hr radio flares such as have been observed from the X-ray binary GRS 1915+105.

THE VLA-COSMOS PERSPECTIVE ON THE INFRARED-RADIO RELATION. I. NEW CONSTRAINTS ON SELECTION BIASES AND THE NON-EVOLUTION OF THE INFRARED/RADIO PROPERTIES OF STAR-FORMING AND ACTIVE GALACTIC NUCLEUS GALAXIES AT INTERMEDIATE AND HIGH REDSHIFT

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

Sargent, M. T.; Schinnerer, E.; MartInez-Sansigre, A.

2010-02-01

VLA 1.4 GHz ({sigma}{approx} 0.012 mJy) and MIPS 24 and 70 {mu}m ({sigma}{approx} 0.02 and 1.7 mJy, respectively) observations covering the 2 deg{sup 2} COSMOS field are combined with an extensive multiwavelength data set to study the evolution of the infrared (IR)-radio relation at intermediate and high redshift. With {approx}4500 sources-of which {approx}30% have spectroscopic redshifts-the current sample is significantly larger than previous ones used for the same purpose. Both monochromatic IR/radio flux ratios (q {sub 24} and q {sub 70}), as well as the ratio of the total IR and the 1.4 GHz luminosity (q {sub TIR}), are usedmore » as indicators for the IR/radio properties of star-forming galaxies and active galactic nuclei (AGNs). Using a sample jointly selected at IR and radio wavelengths in order to reduce selection biases, we provide firm support for previous findings that the IR-radio relation remains unchanged out to at least z{approx} 1.4. Moreover, based on data from {approx}150 objects we also find that the local relation likely still holds at zin [2.5, 5]. At redshift z< 1.4, we observe that radio-quiet AGNs populate the locus of the IR-radio relation in similar numbers as star-forming sources. In our analysis, we employ the methods of survival analysis in order to ensure a statistically sound treatment of flux limits arising from non-detections. We determine the observed shift in average IR/radio properties of IR- and radio-selected populations and show that it can reconcile apparently discrepant measurements presented in the literature. Finally, we also investigate variations of the IR/radio ratio with IR and radio luminosity and find that it hardly varies with IR luminosity but is a decreasing function of radio luminosity.« less

Infrared imaging of WENSS radio sources

NASA Astrophysics Data System (ADS)

Villani, D.; di Serego Alighieri, S.

1999-03-01

We have performed deep imaging in the IR J- and K- bands for three sub-samples of radio sources extracted from the Westerbork Northern Sky Survey, a large low-frequency radio survey containing Ultra Steep Spectrum (USS), Gigahertz Peaked Spectrum (GPS) and Flat Spectrum (FS) sources. We present the results of these IR observations, carried out with the ARcetri Near Infrared CAmera (ARNICA) at the Nordic Optical Telescope (NOT), providing photometric and morphologic information on high redshift radio galaxies and quasars. We find that the radio galaxies contained in our sample do not show the pronounced radio/IR alignment claimed for 3CR sources. IR photometric measurements of the gravitational lens system 1600+434 are also presented. % This paper is based on data obtained at the Nordic Optical Telescope on La Palma (Canary Islands).

Internet Resources for Radio Astronomy

NASA Astrophysics Data System (ADS)

Andernach, H.

A subjective overview of Internet resources for radio-astronomical information is presented. Basic observing techniques and their implications for the interpretation of publicly available radio data are described, followed by a discussion of existing radio surveys, their level of optical identification, and nomenclature of radio sources. Various collections of source catalogues and databases for integrated radio source parameters are reviewed and compared, as well as the web interfaces to interrogate the current and ongoing large-area surveys. Links to radio observatories with archives of raw (uv-) data are presented, as well as services providing images, both of individual objects or extracts (``cutouts'') from large-scale surveys. While the emphasis is on radio continuum data, a brief list of sites providing spectral line data, and atomic or molecular information is included. The major radio telescopes and surveys under construction or planning are outlined. A summary is given of a search for previously unknown optically bright radio sources, as performed by the students as an exercise, using Internet resources only. Over 200 different links are mentioned and were verified, but despite the attempt to make this report up-to-date, it can only provide a snapshot of the situation as of mid-1998.

Tuning Into Brown Dwarfs: Long-Term Radio Monitoring of Two Very Low Mass Dwarfs

NASA Astrophysics Data System (ADS)

Van Linge, Russell; Burgasser, Adam J.; Melis, Carl; Williams, Peter K. G.

2017-01-01

The very lowest-mass (VLM) stars and brown dwarfs, with effective temperatures T < 3000 K, exhibit mixed magnetic activity trends, with H-alpha and X-ray emission that declines rapidly beyond type M7/M8, but persistent radio emission in roughly 10-20% of sources. The dozen or so VLM radio emitters known show a broad range of emission characteristics and time-dependent behavior, including steady persistent emission, periodic oscillations, periodic polarized bursts, and aperiodic flares. Understanding the evolution of these variability patterns, and in particular whether they undergo solar-like cycles, requires long-term monitoring. We report the results of a long-term JVLA monitoring program of two magnetically-active VLM dwarf binaries, the young M7 2MASS 1314+1320AB and older L5 2MASS 1315-2649AB. On the bi-weekly cadence, 2MASS 1314 continues to show variability by revealing regular flaring while 2MASS 1315 continues to be a quiescent emitter. On the daily time scale, both sources show a mean flux density that can vary significantly just over a few days. These results suggest long-term radio behavior in radio-emitting VLM dwarfs is just as diverse and complex as short-term behavior.

Is 4C+29.48 a γ-ray source?

NASA Astrophysics Data System (ADS)

Gabányi, K. É.; Frey, S.; An, T.

2018-05-01

Context. The Fermi Large Area Telescope revealed that the extragalactic γ-ray sky is dominated by blazars, active galactic nuclei (AGN) whose jet is seen at very small angle to the line of sight. To associate and then classify the γ-ray sources, data have been collected from lower frequency surveys and observations. Since those have superior angular resolution and positional accuracy compared to the γ-ray observations, some associations are not straightforward. Aims: The γ-ray source 3FGL J1323.0+2942 is associated with the radio source 4C+29.48 and classified as a blazar of unknown type, lacking optical spectrum and redshift. The higher-resolution radio data showed that 4C+29.48 comprises three bright radio-emitting features located within a 1'-diameter area. We aim to reveal their nature and pinpoint the origin of the γ-ray emission. Methods: We (re-)analyzed archival Very Large Array (VLA) and unpublished very long baseline interferometry (VLBI) observations conducted by the Very Long Baseline Array (VLBA) and the European VLBI Network of 4C+29.48. We also collected data form optical, infrared and X-ray surveys. Results: According to the VLBI data, the northernmost complex of 4C+29.48 contains a blazar with a high brightness temperature compact core and a steep-spectrum jet feature. The blazar is positionally coincident with an optical source at a redshift of 1.142. Its mid-infrared colors also support its association with a γ-ray emitting blazar. The two other radio complexes have steep radio spectra similar to AGN-related lobes and do not have optical or infrared counterparts in currently available surveys. Based on the radio morphology, they are unlikely to be related to the blazar. There is an optical source between the two radio features, also detected in infrared wavebands. We discuss the possibilities whether the two radio features are lobes of a radio galaxy, or gravitationally lensed images of a background source. Conclusions: We propose to associate the γ-ray source 3FGL J1323.0+2942 in subsequent versions of the Fermi catalog with the blazar residing in northernmost complex. We suggest naming this radio source J1323+2941A to avoid misinterpretation arising from the fact that the coordinates of the currently listed radio counterpart 4C+29.48 is closer to a most probably unrelated radio source.

VizieR Online Data Catalog: z<1 3CR radio galaxies and quasars star formation (Westhues+, 2016)

NASA Astrophysics Data System (ADS)

Westhues, C.; Haas, M.; Barthel, P.; Wilkes, B. J.; Willner, S. P.; Kuraszkiewicz, J.; Podigachoski, P.; Leipski, C.; Meisenheimer, K.; Siebenmorgen, R.; Chini, R.

2018-03-01

This work studies a sample of 87 sources from the 3CR catalog (Edge et al. 1959, Cat. VIII/1; Bennett 1962MNRAS.125...75B; Laing et al. 1983, J/MNRAS/204/151; Spinrad et al. 1985, J/PASP/97/932). With the Herschel Space Observatory (Pilbratt et al. 2010A&A...518L...1P) we measured the FIR/submm spectral energy distributions (SEDs) of the 3CR sources in two complementary proposals: one at redshift 1

X-ray emission associated with radio galaxies in the Perseus cluster

NASA Technical Reports Server (NTRS)

Rhee, George; Burns, Jack O.; Kowalski, Michael P.

1994-01-01

In this paper, we report on new x-ray observations of the Perseus cluster made using four separate pointings of the Roentgen Satellite (ROSAT) Positron Sensitive Proportional Counter (PSPC). We searched for x-ray emission associated with 16 radio galaxies and detected six above 3 sigma. We made use of the PSPC spectra to determine if the x-ray emission associated with radio galaxies in Perseus is thermal or nonthermal in origin (i.e., hot gas or an active galactic nuclei (AGN)). For the head-tail radio galaxy IC 310, we find that the data are best fit by a power law model with an unusually large spectral index alpha = 2.7. This is consistent with its unresolved spatial structure. On the other hand, a second resolved x-ray source associated with another radio galaxy 2.3 Mpc from the Perseus center (V Zw 331) is best fit by a thermal model. For three sources with insufficient flux for a full spectral analysis, we calculated hardness ratios. On this basis, the x-ray emission associated with the well known head-tail source NGC 1265 is consistent with thermal radiation. The x-ray spectra of UGC 2608 and UGC 2654 probably arise from hot gas, although very steep power-law spectra (alpha greater than 3.2) are also possible. The spectrum of NGC 1275 is quite complex due to the presence of an AGN and the galaxy's location at the center of a cluster cooling flow.

Cosmological evolution of supermassive black holes in the centres of galaxies

NASA Astrophysics Data System (ADS)

Kapinska, Anna D.

2012-06-01

Radio galaxies and quasars are among the largest and most powerful single objects known and are believed to have had a significant impact on the evolving Universe and its large scale structure. Their jets inject a significant amount of energy into the surrounding medium, hence they can provide useful information in the study of the density and evolution of the intergalactic and intracluster medium. The jet activity is also believed to regulate the growth of massive galaxies via the AGN feedback. In this thesis I explore the intrinsic and extrinsic physical properties of the population of Fanaroff-Riley II (FR II) objects, i.e. their kinetic luminosities, lifetimes, and central densities of their environments. In particular, the radio and kinetic luminosity functions of these powerful radio sources are investigated using the complete, flux limited radio catalogues of 3CRR and BRL. I construct multidimensional Monte Carlo simulations using semi-analytical models of FR II source time evolution to create artificial samples of radio galaxies. Unlike previous studies, I compare radio luminosity functions found with both the observed and simulated data to explore the best-fitting fundamental source parameters. The Monte Carlo method presented here allows one to: (i) set better limits on the predicted fundamental parameters of which confidence intervals estimated over broad ranges are presented, and (ii) generate the most plausible underlying parent populations of these radio sources. Moreover, I allow the source physical properties to co-evolve with redshift, and I find that all the investigated parameters most likely undergo cosmological evolution; however these parameters are strongly degenerate, and independent constraints are necessary to draw more precise conclusions. Furthermore, since it has been suggested that low luminosity FR IIs may be distinct from their powerful equivalents, I attempt to investigate fundamental properties of a sample of low redshift, low radio luminosity density radio galaxies. Based on SDSS-FIRST-NVSS radio sample I construct a low frequency (325 MHz) sample of radio galaxies and attempt to explore the fundamental properties of these low luminosity radio sources. The results are discussed through comparison with the results from the powerful radio sources of the 3CRR and BRL samples. Finally, I investigate the total power injected by populations of these powerful radio sources at various cosmological epochs and discuss the significance of the impact of these sources on the evolving Universe. Remarkably, sets of two degenerate fundamental parameters, the kinetic luminosity and maximum lifetimes of radio sources, despite the degeneracy provide particularly robust estimates of the total power produced by FR IIs during their lifetimes. This can be also used for robust estimations of the quenching of the cooling flows in cluster of galaxies.

Star Formation Under the Outflow: The Discovery of a Non-thermal Jet from OMC-2 FIR 3 and Its Relationship to the Deeply Embedded FIR 4 Protostar

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

Osorio, Mayra; Díaz-Rodríguez, Ana K.; Anglada, Guillem

We carried out multiwavelength (0.7–5 cm), multi-epoch (1994–2015) Very Large Array (VLA) observations toward the region enclosing the bright far-IR sources FIR 3 (HOPS 370) and FIR 4 (HOPS 108) in OMC-2. We report the detection of 10 radio sources, 7 of them identified as young stellar objects. We image a well-collimated radio jet with a thermal free–free core (VLA 11) associated with the Class I intermediate-mass protostar HOPS 370. The jet features several knots (VLA 12N, 12C, 12S) of non-thermal radio emission (likely synchrotron from shock-accelerated relativistic electrons) at distances of ∼7500–12,500 au from the protostar, in a regionmore » where other shock tracers have been previously identified. These knots are moving away from the HOPS 370 protostar at ∼100 km s{sup −1}. The Class 0 protostar HOPS 108, which itself is detected as an independent, kinematically decoupled radio source, falls in the path of these non-thermal radio knots. These results favor the previously proposed scenario in which the formation of HOPS 108 is triggered by the impact of the HOPS 370 outflow with a dense clump. However, HOPS 108 has a large proper motion velocity of ∼30 km s{sup −1}, similar to that of other runaway stars in Orion, whose origin would be puzzling within this scenario. Alternatively, an apparent proper motion could result because of changes in the position of the centroid of the source due to blending with nearby extended emission, variations in the source shape, and/or opacity effects.« less

The Cosmological Evolution of Radio Sources with CENSORS

NASA Technical Reports Server (NTRS)

Brookes, Mairi; Best, Philip; Peacock, John; Dunlop, James; Rottgering, Huub

2006-01-01

The CENSORS survey, selected from the NVSS, has been followed up using EIS, K-band imaging and spectroscopic observations to produce a radio sample capable of probing the source density in the regime: z greater than 2.5. With a current spectroscopic completeness of 62%, CENSORS has been used in direct modeling of RLF evolution and in V/V(sub max) tests. There is evidence for a shallow decline in number density of source in the luminosity range 10(sup 26) - 10(sup 27)WHz(sup -1) at 1.4GHz.

VizieR Online Data Catalog: Radio sources in the NCP region with the 21CMA (Zheng+, 2016)

NASA Astrophysics Data System (ADS)

Zheng, Q.; Wu, X.-P.; Johnston-Hollitt, M.; Gu, J.-H.; Xu, H.

2017-03-01

In the current work, we present the point radio sources observed with the 40 pods of the 21 Centimeter Array (21CMA) E-W baselines for an integration of 12hr made on 2013 April 13; centered on the North Celestial Pole (NCP). An extra deep sample with a higher sensitivity from a longer integration time of up to years will be published later. We have detected a total of 624 radio sources over the central field within 3° in a frequency range of 75-175MHz and the outer annulus of 3°-5° in the 75-125MHz bands. By performing a Monte-Carlo simulation, we have estimated a completeness of 50% at S~0.2Jy. (1 data file).

Light curves of flat-spectrum radio sources (Jenness+, 2010)

NASA Astrophysics Data System (ADS)

Jenness, T.; Robson, E. I.; Stevens, J. A.

2010-05-01

Calibrated data for 143 flat-spectrum extragalactic radio sources are presented at a wavelength of 850um covering a 5-yr period from 2000 April. The data, obtained at the James Clerk Maxwell Telescope using the Submillimetre Common-User Bolometer Array (SCUBA) camera in pointing mode, were analysed using an automated pipeline process based on the Observatory Reduction and Acquisition Control - Data Reduction (ORAC-DR) system. This paper describes the techniques used to analyse and calibrate the data, and presents the data base of results along with a representative sample of the better-sampled light curves. A re-analysis of previously published data from 1997 to 2000 is also presented. The combined catalogue, comprising 10493 flux density measurements, provides a unique and valuable resource for studies of extragalactic radio sources. (2 data files).

The LBA Calibrator Survey of Southern Compact Extragalactic Radio Sources - LCS1

NASA Technical Reports Server (NTRS)

Petrov, Leonid; Phillips, Chris; Bertarini, Alessandra; Murphy, Tara; Sadler, Elaine M.

2011-01-01

We present a catalogue of accurate positions and correlated flux densities for 410 flat-spectrum, compact extragalactic radio sources previously detected in the Australia Telescope 20 GHz (AT20G) survey. The catalogue spans the declination range [-90deg, -40deg] and was constructed from four 24-h very long baseline interferometry (VLBI) observing sessions with the Australian Long Baseline Array at 8.3 GHz. The VLBI detection rate in these experiments is 97 per cent, the median uncertainty of the source positions is 2.6 mas and the median correlated flux density on projected baselines longer than 1000 km is 0.14 Jy. The goals of this work are (1) to provide a pool of southern sources with positions accurate to a few milliarcsec, which can be used for phase-referencing observations, geodetic VLBI and space navigation; (2) to extend the complete flux-limited sample of compact extragalactic sources to the Southern hemisphere; and (3) to investigate the parsec-scale properties of high-frequency selected sources from the AT20G survey. As a result of this VLBI campaign, the number of compact radio sources south of declination -40deg which have measured VLBI correlated flux densities and positions known to milliarcsec accuracy has increased by a factor of 3.5.

Testing the Young Neutron Star Scenario with Persistent Radio Emission Associated with FRB 121102

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

Kashiyama, Kazumi; Murase, Kohta

Recently a repeating fast radio burst (FRB) 121102 has been confirmed to be an extragalactic event and a persistent radio counterpart has been identified. While other possibilities are not ruled out, the emission properties are broadly consistent with Murase et al. that theoretically proposed quasi-steady radio emission as a counterpart of both FRBs and pulsar-driven supernovae. Here, we constrain the model parameters of such a young neutron star scenario for FRB 121102. If the associated supernova has a conventional ejecta mass of M {sub ej} ≳ a few M {sub ⊙}, a neutron star with an age of t {submore » age} ∼ 10–100 years, an initial spin period of P{sub i} ≲ a few ms, and a dipole magnetic field of B {sub dip} ≲ a few × 10{sup 13} G can be compatible with the observations. However, in this case, the magnetically powered scenario may be favored as an FRB energy source because of the efficiency problem in the rotation-powered scenario. On the other hand, if the associated supernova is an ultra-stripped one or the neutron star is born by the accretion-induced collapse with M {sub ej} ∼ 0.1 M {sub ⊙}, a younger neutron star with t {sub age} ∼ 1–10 years can be the persistent radio source and might produce FRBs with the spin-down power. These possibilities can be distinguished by the decline rate of the quasi-steady radio counterpart.« less

Psr J2030+3641: Radio Discovery And Gamma-Ray Study Of A Middle-Aged Pulsar In The Now Identified Fermi -Lat Source 1FGL J2030.0+3641

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

Camilo, F.; Kerr, M.; Ray, P. S.

2012-01-23

In a radio search with the Green Bank Telescope of three unidentified low Galactic latitude Fermi-LAT sources, we have discovered the middle-aged pulsar J2030+3641, associated with 1FGL J2030.0+3641 (2FGL J2030.0+3640). Following the detection of gamma-ray pulsations using a radio ephemeris, we have obtained a phase-coherent timing solution based on gamma-ray and radio pulse arrival times that spans the entire Fermi mission. With a rotation period of 0.2 s, spin-down luminosity of 3X10 34 erg s -1, and characteristic age of 0.5 Myr, PSR J2030+3641 is a middle-aged neutron star with spin parameters similar to those of the exceedingly gamma-ray-bright andmore » radio-undetected Geminga. Its gamma-ray flux is 1% that of Geminga, primarily because of its much larger distance, as suggested by the large integrated column density of free electrons, DM = 246 pc cm-3. We fit the gamma-ray light curve, along with limited radio polarimetric constraints, to four geometrical models of magnetospheric emission, and while none of the fits have high significance some are encouraging and suggest that further refinements of these models may be worthwhile. We argue that not many more non-millisecond radio pulsars may be detected along the Galactic plane that are responsible for LAT sources, but that modified methods to search for gamma-ray pulsations should be productive — PSR J2030+3641 would have been found blindly in gamma rays if only & 0:8 GeV photons had been considered, owing to its relatively flat spectrum and location in a region of high soft background.« less

Chapter 27: Deja vu All Over Again: Using NVO Tools to Re-Investigate a Complete Sample of Texas Radio Survey Sources

NASA Astrophysics Data System (ADS)

Lucas, Ray A.; Rohde, David; Tamura, Takayuki; van Dyne, Jeffrey

At the first NVO Summer School in September 2004, a complete sample of Texas Radio Survey sources, first derived in 1989 and subsequently observed with the VLA in A-array snapshot mode in 1990, was revisited. The original investigators had never had the occasion to reduce the A-array 5-minute snapshot data, nor to do any other significant follow-up, though the sample still seemed a possibly useful but relatively small study of radio galaxies, AGN, quasars, extragalactic sources, and galaxy clusters, etc. At the time of the original sample definition in late 1989, the best optical material available for the region was the SRC-J plate from the UK Schmidt Telescope in Australia. In much more recent times, the Sloan Digital Sky Survey has included the region in its DR2 data release, so good multicolor optical imaging in a number of standard bandpasses has finally become available. These data, along with other material in the radio, infrared, and (where available) were used to get a better preliminary idea of the nature of the objects in the 1989 sample. We also investigated one of the original questions: whether these radio sources with steeper (or at least non-flat) radio spectra were associated with galaxy clusters, and in some cases higher-redshift galaxy clusters and AGN. A rudimentary web service was created which allowed the user to perform simple cone searches and SIAP image extractions of specified field sizes for multiwavelength data across the electromagnetic spectrum, and a prototype web page was set up which would display the resulting images in wavelength order across the page for sources in the sample. Finally, as an additional investigation, using radio and X-ray IDs as a proxy for AGN which might be associated with large, central cluster galaxies, positional matches of radio and X-ray sources from two much larger catalogs were done using the tool TOPCAT in order to search for the degree of correlation between ID positions, radio luminosity, and cluster ID positions. It was hoped that cross-correlated matches could possibly give some clue to the relationship of these radio sources to galaxy clusters. These preliminary results need more in-depth investigation and are currently being pursued via a NVO grant to the first author. The original VLA 5-minute A-array snapshots have also now been reduced and are complementary in nature to the VLA FIRST data. It is planned to eventually make these reduced VLA A-array data publicas part of a web service via the NVO facilities along with a table of multiwavelength properties for the sources in VOTable format.

149 Sources and 15 Years Later: The Navy-NRAO Green Bank Interferometer Monitoring Program

NASA Astrophysics Data System (ADS)

Lazio, T. J. W.; Waltman, E. B.; Ghigo, F.; Johnston, K. J.

2000-12-01

Flux densities for 149 sources were monitored with the Green Bank Interferometer for durations ranging from 3 to 15 yrs, covering the interval 1979--1996, with most sources observed for 6 yrs. Observations were at two radio frequencies (approximately 2.5 and 8.2 GHz) and have a typical sampling of one flux density measurement every 2 days. We have used these light curves to conduct various variability analysis of the sources. We find suggestive, though not unambiguous evidence, that these sources have a common, broadband mechanism for intrinsic variations. We also find that the extrinsic variation is more consistent with radio-wave scattering in an extended medium rather than in a thin screen. The primary motivation for this monitoring program was the identification of extreme scattering events. In an effort to identify ESEs in a systematic manner, we have taken the wavelet transform of the light curves. We find 15 events in the light curves of 12 sources that we classify as probable ESEs. However, we also find that five ESEs previously identified from these data do not survive our wavelet selection criteria. Future identification of ESEs will probably continue to rely on both visual and systematic methods. We present examples of the light curves and variability analyses. Instructions for obtaining the data are also given. The GBI is a facility of the National Science Foundation and was operated by the National Radio Astronomy Observatory under contract to the USNO and NRL during these observations. A portion of this work was performed while TJWL held a National Research Council-NRL Research Associateship. Basic research in radio astronomy at the NRL is supported by the Office of Naval Research.

Enormous disc of cool gas surrounding the nearby powerful radio galaxy NGC612 (PKS0131-36)

NASA Astrophysics Data System (ADS)

Emonts, B. H. C.; Morganti, R.; Oosterloo, T. A.; Holt, J.; Tadhunter, C. N.; van der Hulst, J. M.; Ojha, R.; Sadler, E. M.

2008-06-01

We present the detection of an enormous disc of cool neutral hydrogen (HI) gas surrounding the S0 galaxy NGC612, which hosts one of the nearest powerful radio sources (PKS0131-36). Using the Australia Telescope Compact Array, we detect MHI = 1.8 × 109Msolar of HI emission-line gas that is distributed in a 140-kpc wide disc-like structure along the optical disc and dust lane of NGC612. The bulk of the gas in the disc appears to be settled in regular rotation with a total velocity range of 850kms-1, although asymmetries in this disc indicate that perturbations are being exerted on part of the gas, possibly by a number of nearby companions. The HI disc in NGC612 suggests that the total mass enclosed by the system is Menc ~ 2.9 × 1012 sin-2 iMsolar, implying that this early-type galaxy contains a massive dark matter halo. We also discuss an earlier study by Holt et al. that revealed the presence of a prominent young stellar population at various locations throughout the disc of NGC612, indicating that this is a rare example of an extended radio source that is hosted by a galaxy with a large-scale star-forming disc. In addition, we map a faint HI bridge along a distance of 400kpc in between NGC612 and the gas-rich (MHI = 8.9 × 109Msolar) barred galaxy NGC619, indicating that likely an interaction between both systems occurred. From the unusual amounts of HI gas and young stars in this early-type galaxy, in combination with the detection of a faint optical shell and the system's high infrared luminosity, we argue that either ongoing or past galaxy interactions or a major merger event are a likely mechanism for the triggering of the radio source in NGC612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies and it presents the first example of large-scale HI detected around a powerful Fanaroff-Riley type II (FR-II) radio galaxy. The HI properties of the FR-II radio galaxy NGC612 are very similar to those found for low-power compact radio sources, but different from those of extended Fanaroff-Riley type I (FR-I) sources.

Automated cross-identifying radio to infrared surveys using the LRPY algorithm: a case study

NASA Astrophysics Data System (ADS)

Weston, S. D.; Seymour, N.; Gulyaev, S.; Norris, R. P.; Banfield, J.; Vaccari, M.; Hopkins, A. M.; Franzen, T. M. O.

2018-02-01

Cross-identifying complex radio sources with optical or infra red (IR) counterparts in surveys such as the Australia Telescope Large Area Survey (ATLAS) has traditionally been performed manually. However, with new surveys from the Australian Square Kilometre Array Pathfinder detecting many tens of millions of radio sources, such an approach is no longer feasible. This paper presents new software (LRPY - Likelihood Ratio in PYTHON) to automate the process of cross-identifying radio sources with catalogues at other wavelengths. LRPY implements the likelihood ratio (LR) technique with a modification to account for two galaxies contributing to a sole measured radio component. We demonstrate LRPY by applying it to ATLAS DR3 and a Spitzer-based multiwavelength fusion catalogue, identifying 3848 matched sources via our LR-based selection criteria. A subset of 1987 sources have flux density values for all IRAC bands which allow us to use criteria to distinguish between active galactic nuclei (AGNs) and star-forming galaxies (SFG). We find that 936 radio sources ( ≈ 47 per cent) meet both of the Lacy and Stern AGN selection criteria. Of the matched sources, 295 have spectroscopic redshifts and we examine the radio to IR flux ratio versus redshift, proposing an AGN selection criterion below the Elvis radio-loud AGN limit for this dataset. Taking the union of all three AGNs selection criteria we identify 956 as AGNs ( ≈ 48 per cent). From this dataset, we find a decreasing fraction of AGNs with lower radio flux densities consistent with other results in the literature.

Nonequilibrium atmospheric pressure plasma jet using a combination of 50 kHz/2 MHz dual-frequency power sources

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

Zhou, Yong-Jie; Yuan, Qiang-Hua; Li, Fei

2013-11-15

An atmospheric pressure plasma jet is generated by dual sinusoidal wave (50 kHz and 2 MHz). The dual-frequency plasma jet exhibits the advantages of both low frequency and radio frequency plasmas, namely, the long plasma plume and the high electron density. The radio frequency ignition voltage can be reduced significantly by using dual-frequency excitation compared to the conventional radio frequency without the aid of the low frequency excitation source. A larger operating range of α mode discharge can be obtained using dual-frequency excitation which is important to obtain homogeneous and low-temperature plasma. A larger controllable range of the gas temperaturemore » of atmospheric pressure plasma could also be obtained using dual-frequency excitation.« less

36 CFR Appendix B to Part 1191 - Americans With Disabilities Act: Scoping

Code of Federal Regulations, 2014 CFR

2014-07-01

... of Sport Activity. That portion of a room or space where the play or practice of a sport occurs..., receivers, and coupling devices to bypass the acoustical space between a sound source and a listener by means of induction loop, radio frequency, infrared, or direct-wired equipment. Boarding Pier. A portion...

Star formation towards the southern cometary H II region IRAS 17256-3631

NASA Astrophysics Data System (ADS)

Veena, V. S.; Vig, S.; Tej, A.; Varricatt, W. P.; Ghosh, S. K.; Chandrasekhar, T.; Ashok, N. M.

2016-03-01

IRAS 17256-3631 is a southern Galactic massive star-forming region located at a distance of 2 kpc. In this paper, we present a multiwavelength investigation of the embedded cluster, the H II region, as well as the parent cloud. Radio images at 325, 610 and 1372 MHz were obtained using Giant Metrewave Radio Telescope, India while the near-infrared imaging and spectroscopy were carried out using United Kingdom Infrared Telescope and Mt. Abu Infrared Telescope, India. The near-infrared K-band image reveals the presence of a partially embedded infrared cluster. The spectral features of the brightest star in the cluster, IRS-1, spectroscopically agree with a late O or early B star and could be the driving source of this region. Filamentary H2 emission detected towards the outer envelope indicates the presence of highly excited gas. The parent cloud is investigated at far-infrared to millimetre wavelengths and 18 dust clumps have been identified. The spectral energy distributions of these clumps have been fitted as modified blackbodies and the best-fitting peak temperatures are found to range from 14 to 33 K, while the column densities vary from 0.7 to 8.5 × 1022 cm-2. The radio maps show a cometary morphology for the distribution of ionized gas that is density bounded towards the north-west and ionization bounded towards the south-east. This morphology is better explained with the champagne flow model as compared to the bow-shock model. Using observations at near-, mid- and far-infrared, submillimetre and radio wavelengths, we examine the evolutionary stages of various clumps.

Type II Radio Bursts Observed by STEREO/Waves and Wind/Waves instruments

NASA Astrophysics Data System (ADS)

Krupar, V.; Magdalenic, J.; Zhukov, A.; Rodriguez, L.; Mierla, M.; Maksimovic, M.; Cecconi, B.; Santolik, O.

2013-12-01

Type II radio bursts are slow-drift emissions triggered by suprathermal electrons accelerated on shock fronts of propagating CMEs. We present several events at kilometric wavelengths observed by radio instruments onboard the STEREO and Wind spacecraft. The STEREO/Waves and Wind/Waves have goniopolarimetric (GP, also referred to as direction finding) capabilities that allow us to triangulate radio sources when an emission is observed by two or more spacecraft. As the GP inversion has high requirements on the signal-to-noise ratio we only have a few type II radio bursts with sufficient intensity for this analysis. We have compared obtained radio sources with white-light observations of STEREO/COR and STEREO/HI instruments. Our preliminary results indicate that radio sources are located at flanks of propagating CMEs.

ACCELERATION OF COMPACT RADIO JETS ON SUB-PARSEC SCALES

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

Lee, Sang-Sung; Lobanov, Andrei P.; Krichbaum, Thomas P.

2016-08-01

Jets of compact radio sources are highly relativistic and Doppler boosted, making studies of their intrinsic properties difficult. Observed brightness temperatures can be used to study the intrinsic physical properties of relativistic jets, and constrain models of jet formation in the inner jet region. We aim to observationally test such inner jet models. The very long baseline interferometry (VLBI) cores of compact radio sources are optically thick at a given frequency. The distance of the core from the central engine is inversely proportional to the frequency. Under the equipartition condition between the magnetic field energy and particle energy densities, themore » absolute distance of the VLBI core can be predicted. We compiled the brightness temperatures of VLBI cores at various radio frequencies of 2, 8, 15, and 86 GHz. We derive the brightness temperature on sub-parsec scales in the rest frame of the compact radio sources. We find that the brightness temperature increases with increasing distance from the central engine, indicating that the intrinsic jet speed (the Lorentz factor) increases along the jet. This implies that the jets are accelerated in the (sub-)parsec regions from the central engine.« less

Computationally Efficient Radio Frequency Source Localization for Radio Interferometric Arrays

NASA Astrophysics Data System (ADS)

Steeb, J.-W.; Davidson, David B.; Wijnholds, Stefan J.

2018-03-01

Radio frequency interference (RFI) is an ever-increasing problem for remote sensing and radio astronomy, with radio telescope arrays especially vulnerable to RFI. Localizing the RFI source is the first step to dealing with the culprit system. In this paper, a new localization algorithm for interferometric arrays with low array beam sidelobes is presented. The algorithm has been adapted to work both in the near field and far field (only the direction of arrival can be recovered when the source is in the far field). In the near field the computational complexity of the algorithm is linear with search grid size compared to cubic scaling of the state-of-the-art 3-D MUltiple SIgnal Classification (MUSIC) method. The new method is as accurate as 3-D MUSIC. The trade-off is that the proposed algorithm requires a once-off a priori calculation and storing of weighting matrices. The accuracy of the algorithm is validated using data generated by low-frequency array while a hexacopter was flying around it and broadcasting a continuous-wave signal. For the flight, the mean distance between the differential GPS positions and the corresponding estimated positions of the hexacopter is 2 m at a wavelength of 6.7 m.

Radio structure effects on the optical and radio representations of the ICRF

NASA Astrophysics Data System (ADS)

Andrei, A. H.; da Silva Neto, D. N.; Assafin, M.; Vieira Martins, R.

Silva Neto et al. (2002) show that comparing the ICRF Ext.1 sources standard radio position (Ma et al. 1998) against their optical counterpart position (Zacharias et al. 1999, Monet et al., 1998), a systematic pattern appears, which depends on the radio structure index (Fey and Charlot, 2000). The optical to radio offsets produce a distribution suggestive of a coincidence of the optical and radio centroids worse for the radio extended than for the radio compact sources. On average, the coincidence between the optical and radio centroids is found 7.9±1.1 mas smaller for the compact than for the extended sources. Such an effect is reasonably large, and certainly much too large to be due to errors on the VLBI radio position. On the other hand, it is too small to be accounted to the errors on the optical position, which moreover should be independent from the radio stucture. Thus, other than a true pattern of centroids non-coincidence, the remaining explanation is of a hazard result. This paper summarizes the several statistical tests used to discard the hazard explanation.

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

NASA Astrophysics Data System (ADS)

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

2016-02-01

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

The Most Compact Bright Radio-loud AGNs. II. VLBA Observations of 10 Sources at 43 and 86 GHz

NASA Astrophysics Data System (ADS)

Cheng, X.-P.; An, T.; Hong, X.-Y.; Yang, J.; Mohan, P.; Kellermann, K. I.; Lister, M. L.; Frey, S.; Zhao, W.; Zhang, Z.-L.; Wu, X.-C.; Li, X.-F.; Zhang, Y.-K.

2018-01-01

Radio-loud active galactic nuclei (AGNs), hosting powerful relativistic jet outflows, provide an excellent laboratory for studying jet physics. Very long baseline interferometry (VLBI) enables high-resolution imaging on milli-arcsecond (mas) and sub-mas scales, making it a powerful tool to explore the inner jet structure, shedding light on the formation, acceleration, and collimation of AGN jets. In this paper, we present Very Long Baseline Array observations of 10 radio-loud AGNs at 43 and 86 GHz that were selected from the Planck catalog of compact sources and are among the brightest in published VLBI images at and below 15 GHz. The image noise levels in our observations are typically 0.3 and 1.5 mJy beam‑1 at 43 and 86 GHz, respectively. Compared with the VLBI data observed at lower frequencies from the literature, our observations with higher resolutions (with the highest resolution being up to 0.07 mas at 86 GHz and 0.18 mas at 43 GHz) and at higher frequencies detected new jet components at sub-parsec scales, offering valuable data for studies of the physical properties of the innermost jets. These include the compactness factor of the radio structure (the ratio of core flux density to total flux density), and core brightness temperature ({T}{{b}}). In all these sources, the compact core accounts for a significant fraction (> 60 % ) of the total flux density. Their correlated flux density at the longest baselines is higher than 0.16 Jy. The compactness of these sources make them good phase calibrators of millimeter-wavelength ground-based and space VLBI.

Radio and X-ray variability of the nucleus of Centaurus A /NGC 5128/

NASA Technical Reports Server (NTRS)

Beall, J. H.; Rose, W. K.; Graf, W.; Price, K. M.; Dent, W. A.; Hobbs, R. W.; Dennis, B. R.; Crannell, C. J.; Conklin, E. K.; Ulich, B. L.

1978-01-01

Centaurus A (NGC 5128) has been observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. These observations, together with results reported by other workers, are interpreted in terms of models of the nucleus of this radio galaxy. The radio observations cover the period from 1973 through early 1977. The X-ray observations cover two 10-day intervals, one in July and August (1975) and the other in July and August 1976. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are shown to be consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons. Upper limits obtained with the model indicate that there may be sufficient energy available in the nucleus to form radio lobes with the same total energy as those already present.

Fermi Large Area Telescope Detection of Extended Gamma-Ray Emission from the Radio Galaxy Fornax A

NASA Astrophysics Data System (ADS)

Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caragiulo, M.; Caraveo, P. A.; Cavazzuti, E.; Cecchi, C.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiaro, G.; Ciprini, S.; Cohen, J. M.; Cohen-Tanugi, J.; Costanza, F.; Cutini, S.; D'Ammando, F.; Davis, D. S.; de Angelis, A.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Lalla, N.; Di Mauro, M.; Di Venere, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Georganopoulos, M.; Giglietto, N.; Giordano, F.; Giroletti, M.; Godfrey, G.; Green, D.; Grenier, I. A.; Guiriec, S.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Jogler, T.; Jóhannesson, G.; Kensei, S.; Kuss, M.; Larsson, S.; Latronico, L.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lubrano, P.; Magill, J. D.; Maldera, S.; Manfreda, A.; Mayer, M.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Negro, M.; Nuss, E.; Ohno, M.; Ohsugi, T.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Schmid, J.; Sgrò, C.; Simone, D.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Stawarz, Ł.; Takahashi, H.; Thayer, J. B.; Thompson, D. J.; Torres, D. F.; Tosti, G.; Troja, E.; Vianello, G.; Wood, K. S.; Wood, M.; Zimmer, S.; Fermi LAT Collaboration

2016-07-01

We report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to be < 14% of the total γ-ray flux. A preferred alignment of the γ-ray elongation with the radio lobes was demonstrated by rotating the radio lobes template. We found no significant evidence for variability on ˜0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. With the extended nature of the > 100 MeV γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ˜2-3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton-proton collisions of cosmic rays with thermal plasma within the radio lobes.

Fermi large area telescope detection of extended gamma-ray emission from the radio galaxy fornax A

DOE PAGES

Ackermann, M.; Ajello, M.; Baldini, L.; ...

2016-07-14

Here, we report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to bemore » $$\\lt 14$$% of the total γ-ray flux. We also demonstrated a preferred alignment of the γ-ray elongation with the radio lobes by rotating the radio lobes template. We found no significant evidence for variability on ~0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. Furthermore, with the extended nature of the $$\\gt 100\\;{\\rm{MeV}}$$ γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ~2–3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton–proton collisions of cosmic rays with thermal plasma within the radio lobes.« less

Occultations of Astrophysical Radio Sources as Probes of Planetary Environments: A Case Study of Jupiter and Possible Applications to Exoplanets

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

Withers, Paul; Vogt, Marissa F.

Properties of planetary atmospheres, ionospheres, and magnetospheres are difficult to measure from Earth. Radio occultations are a common method for measuring these properties, but they traditionally rely on radio transmissions from a spacecraft near the planet. Here, we explore whether occultations of radio emissions from a distant astrophysical radio source can be used to measure magnetic field strength, plasma density, and neutral density around planets. In a theoretical case study of Jupiter, we find that significant changes in polarization angle due to Faraday rotation occur for radio signals that pass within 10 Jupiter radii of the planet and that significantmore » changes in frequency and power occur from radio signals that pass through the neutral atmosphere. There are sufficient candidate radio sources, such as pulsars, active galactic nuclei, and masers, that occultations are likely to occur at least once per year. For pulsars, time delays in the arrival of their emitted pulses can be used to measure plasma density. Exoplanets, whose physical properties are very challenging to observe, may also occult distant astrophysical radio sources, such as their parent stars.« less

Imaging spectroscopy of solar radio burst fine structures.

PubMed

Kontar, E P; Yu, S; Kuznetsov, A A; Emslie, A G; Alcock, B; Jeffrey, N L S; Melnik, V N; Bian, N H; Subramanian, P

2017-11-15

Solar radio observations provide a unique diagnostic of the outer solar atmosphere. However, the inhomogeneous turbulent corona strongly affects the propagation of the emitted radio waves, so decoupling the intrinsic properties of the emitting source from the effects of radio wave propagation has long been a major challenge in solar physics. Here we report quantitative spatial and frequency characterization of solar radio burst fine structures observed with the Low Frequency Array, an instrument with high-time resolution that also permits imaging at scales much shorter than those corresponding to radio wave propagation in the corona. The observations demonstrate that radio wave propagation effects, and not the properties of the intrinsic emission source, dominate the observed spatial characteristics of radio burst images. These results permit more accurate estimates of source brightness temperatures, and open opportunities for quantitative study of the mechanisms that create the turbulent coronal medium through which the emitted radiation propagates.

Characterizing radio continuum sources in a sample of Hi-GAL massive cores

NASA Astrophysics Data System (ADS)

Armstrong, Jason

In 2012 and 2013, Olmi and collaborators conducted a survey for 6.7GHz methanol masers with the Arecibo Telescope toward far infrared sources selected from the Hi-GAL catalog of massive cores. They reported a number of sources with weak 6.7GHz methanol masers, possibly indicating regions in early stages of star formation. Follow-up observations were conducted with the Karl G. Jansky Very Large Array (VLA) in New Mexico to characterize the sources. This thesis presents the results of radio continuum observations of nine of the Arecibo regions. A total of 33 radio continuum sources were detected. The nature of the radio continuum sources was analyzed based on their spectral indices. Most of the sources have negative spectral indices, which is indicative of synchrotron radiation. Many of the synchrotron sources are associated with a supernova remnant in our Galaxy, while the rest are likely background radio galaxies and quasars. Evidence for thermal bremsstrahlung radiation was found toward six sources associated with the Arecibo regions, which is consistent with the interpretation of gas ionized by young high-mass stellar objects.

78 FR 71557 - Radio Broadcasting Services; Tohatchi, New Mexico

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-29

...] Radio Broadcasting Services; Tohatchi, New Mexico AGENCY: Federal Communications Commission. ACTION... Channel 268C2, Tohatchi, New Mexico, as a first local service under the Tribal Priority. A staff... [Amended] 0 2. Section 73.202(b), the Table of FM Allotments under New Mexico, is amended by adding...

Studying the highly bent spectra of FR II-type radio galaxies with the KDA EXT model

NASA Astrophysics Data System (ADS)

Kuligowska, Elżbieta

2018-04-01

Context. The Kaiser, Dennett-Thorpe & Alexander (KDA, 1997, MNRAS, 292, 723) EXT model, that is, the extension of the KDA model of Fanaroff & Riley (FR) II-type source evolution, is applied and confronted with the observational data for selected FR II-type radio sources with significantly aged radio spectra. Aim. A sample of FR II-type radio galaxies with radio spectra strongly bent at their highest frequencies is used for testing the usefulness of the KDA EXT model. Methods: The dynamical evolution of FR II-type sources predicted with the KDA EXT model is briefly presented and discussed. The results are then compared to the ones obtained with the classical KDA approach, assuming the source's continuous injection and self-similarity. Results: The results and corresponding diagrams obtained for the eight sample sources indicate that the KDA EXT model predicts the observed radio spectra significantly better than the best spectral fit provided by the original KDA model.

Radio Source Morphology: 'nature or nuture'?

NASA Astrophysics Data System (ADS)

Banfield, Julie; Emonts, Bjorn; O'Sullivan, Shane

2012-10-01

Radio sources, emanating from supermassive black-holes in the centres of active galaxies, display a large variety of morphological properties. It is a long-standing debate to what extent the differences between various types of radio sources are due to intrinsic properties of the central engine (`nature') or due to the properties of the interstellar medium that surrounds the central engine and host galaxy (`nurture'). Settling this `nature vs. nurture' debate for nearby radio galaxies, which can be studied in great detail, is vital for understanding the properties and evolution of radio galaxies throughout the Universe. We propose to observe the radio galaxy NGC 612 where previous observations have detected the presence of a large-scale HI bridge between the host galaxy and a nearby galaxy NGC 619. We request a total of 13 hrs in the 750m array-configuration to determine whether or not the 100 kpc-scale radio source morphology is directly related to the intergalactic distribution of neutral hydrogen gas.

A Complete VLA Census of the ~7000 Milky Way HII Regions

NASA Astrophysics Data System (ADS)

Armentrout, William Paul; Anderson, Loren; Wenger, Trey V.; Balser, Dana; Bania, Thomas

2018-01-01

How many HII regions are in the Milky Way? Even with the success of recent surveys, we still do not have an adequate answer to this fundamental question. HII regions are the archetypical tracers of Galactic high-mass star formation, but population synthesis modeling indicates that their detection throughout the Galaxy is incomplete, biased toward the most luminous and nearby complexes. Using mid-infrared (MIR) data from the WISE satellite, we identified over 8000 HII regions and candidates, all of which share the characteristic morphology of 12 micron emission enveloping a core of 22 micron emission. Of these, nearly 4000 candidates have no detectable radio continuum emission from Galactic plane surveys and therefore their classification is unknown. These “radio quiet” candidates could represent a significant population of faint HII regions which are ionized by B-stars and/or are especially distant, or they might not be HII regions at all.We present here a survey of radio quiet HII regions in the second and third Galactic quadrants with the Very Large Array. This was the first systematic study of radio quiet HII region candidates. Nearly 60% of the 145 sources observed were detected by the VLA at X-band (10 GHz) to sub-mJy sensitivities. Coupled with their MIR morphologies, detection of continuum strongly indicate they are HII regions. If 60% of radio quiet candidates throughout the Galaxy prove to be HII regions, the number of expected HII regions in the Milky Way would more than double. Constraining the total number of HII regions within the Milky Way will feed back into stellar population synthesis modeling, informing both the high-mass tail of the Galactic star formation rate and the role of high-mass stars in the evolution of the ISM. We estimate there are between 6500 and 7000 HII regions in Milky Way created by a star of type B2 or earlier.

CONSTRAINING RELATIVISTIC BOW SHOCK PROPERTIES IN ROTATION-POWERED MILLISECOND PULSAR BINARIES.

PubMed

Wadiasingh, Zorawar; Harding, Alice K; Venter, Christo; Böttcher, Markus; Baring, Matthew G

2017-04-20

Multiwavelength followup of unidentified Fermi sources has vastly expanded the number of known galactic-field "black widow" and "redback" millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology in a consistent framework. We advocate the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase-centering of the double-peaked X-ray orbital modulation originating from mildly-relativistic Doppler boosting. By constructing a geometric model for radio eclipses, we constrain the shock geometry as functions of binary inclination and shock stand-off R 0 . We develop synthetic X-ray synchrotron orbital light curves and explore the model parameter space allowed by radio eclipse constraints applied on archetypal systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the stand-off is R 0 ~ 0.15-0.3 fraction of binary separation from the companion center, depending on the orbit inclination. Constructed X-ray light curves for B1957+20 using these values are qualitatively consistent with those observed, and we find occultation of the shock by the companion as a minor influence, demanding significant Doppler factors to yield double peaks. For J1023+0038, radio eclipses imply R 0 ≲ 0.4 while X-ray light curves suggest 0.1 ≲ R 0 ≲ 0.3 (from the pulsar). Degeneracies in the model parameter space encourage further development to include transport considerations. Generically, the spatial variation along the shock of the underlying electron power-law index should yield energy-dependence in the shape of light curves motivating future X-ray phase-resolved spectroscopic studies to probe the unknown physics of pulsar winds and relativistic shock acceleration therein.

CONSTRAINING RELATIVISTIC BOW SHOCK PROPERTIES IN ROTATION-POWERED MILLISECOND PULSAR BINARIES

PubMed Central

Wadiasingh, Zorawar; Harding, Alice K.; Venter, Christo; Böttcher, Markus; Baring, Matthew G.

2018-01-01

Multiwavelength followup of unidentified Fermi sources has vastly expanded the number of known galactic-field “black widow” and “redback” millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology in a consistent framework. We advocate the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase-centering of the double-peaked X-ray orbital modulation originating from mildly-relativistic Doppler boosting. By constructing a geometric model for radio eclipses, we constrain the shock geometry as functions of binary inclination and shock stand-off R0. We develop synthetic X-ray synchrotron orbital light curves and explore the model parameter space allowed by radio eclipse constraints applied on archetypal systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the stand-off is R0 ~ 0.15–0.3 fraction of binary separation from the companion center, depending on the orbit inclination. Constructed X-ray light curves for B1957+20 using these values are qualitatively consistent with those observed, and we find occultation of the shock by the companion as a minor influence, demanding significant Doppler factors to yield double peaks. For J1023+0038, radio eclipses imply R0 ≲ 0.4 while X-ray light curves suggest 0.1 ≲ R0 ≲ 0.3 (from the pulsar). Degeneracies in the model parameter space encourage further development to include transport considerations. Generically, the spatial variation along the shock of the underlying electron power-law index should yield energy-dependence in the shape of light curves motivating future X-ray phase-resolved spectroscopic studies to probe the unknown physics of pulsar winds and relativistic shock acceleration therein. PMID:29651167

Constraining Relativistic Bow Shock Properties in Rotation-Powered Millisecond Pulsar Binaries

NASA Technical Reports Server (NTRS)

Wadiasingh, Zorawar; Harding, Alice K.; Venter, Christo; Bottcher, Markus; Baring, Matthew G.

2017-01-01

Multiwavelength follow-up of unidentified Fermi sources has vastly expanded the number of known galactic-field "black widow" and "redback" millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology in a consistent framework. We advocate the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase-centering of the double-peaked X-ray orbital modulation originating from mildly-relativistic Doppler boosting. By constructing a geometric model for radio eclipses, we constrain the shock geometry as functions of binary inclination and shock stand-off R(sub 0). We develop synthetic X-ray synchrotron orbital light curves and explore the model parameter space allowed by radio eclipse constraints applied on archetypal systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the stand-off is R(sub 0) approximately 0:15 - 0:3 fraction of binary separation from the companion center, depending on the orbit inclination. Constructed X-ray light curves for B1957+20 using these values are qualitatively consistent with those observed, and we find occultation of the shock by the companion as a minor influence, demanding significant Doppler factors to yield double peaks. For J1023+0038, radio eclipses imply R(sub 0) is approximately less than 0:4 while X-ray light curves suggest 0:1 is approximately less than R(sub 0) is approximately less than 0:3 (from the pulsar). Degeneracies in the model parameter space encourage further development to include transport considerations. Generically, the spatial variation along the shock of the underlying electron power-law index should yield energy-dependence in the shape of light curves motivating future X-ray phase-resolved spectroscopic studies to probe the unknown physics of pulsar winds and relativistic shock acceleration therein.

Constraining Relativistic Bow Shock Properties in Rotation-powered Millisecond Pulsar Binaries

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

Wadiasingh, Zorawar; Venter, Christo; Böttcher, Markus

2017-04-20

Multiwavelength follow-up of unidentified Fermi sources has vastly expanded the number of known galactic-field “black widow” and “redback” millisecond pulsar binaries. Focusing on their rotation-powered state, we interpret the radio to X-ray phenomenology in a consistent framework. We advocate the existence of two distinct modes differing in their intrabinary shock orientation, distinguished by the phase centering of the double-peaked X-ray orbital modulation originating from mildly relativistic Doppler boosting. By constructing a geometric model for radio eclipses, we constrain the shock geometry as functions of binary inclination and shock standoff R {sub 0}. We develop synthetic X-ray synchrotron orbital light curvesmore » and explore the model parameter space allowed by radio eclipse constraints applied on archetypal systems B1957+20 and J1023+0038. For B1957+20, from radio eclipses the standoff is R {sub 0} ∼ 0.15–0.3 fraction of binary separation from the companion center, depending on the orbit inclination. Constructed X-ray light curves for B1957+20 using these values are qualitatively consistent with those observed, and we find occultation of the shock by the companion as a minor influence, demanding significant Doppler factors to yield double peaks. For J1023+0038, radio eclipses imply R {sub 0} ≲ 0.4, while X-ray light curves suggest 0.1 ≲ R {sub 0} ≲ 0.3 (from the pulsar). Degeneracies in the model parameter space encourage further development to include transport considerations. Generically, the spatial variation along the shock of the underlying electron power-law index should yield energy dependence in the shape of light curves, motivating future X-ray phase-resolved spectroscopic studies to probe the unknown physics of pulsar winds and relativistic shock acceleration therein.« less

Interstellar scintillations of PSR B1919+21: space-ground interferometry

NASA Astrophysics Data System (ADS)

Shishov, V. I.; Smirnova, T. V.; Gwinn, C. R.; Andrianov, A. S.; Popov, M. V.; Rudnitskiy, A. G.; Soglasnov, V. A.

2017-07-01

We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radio telescope, together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60 000 km. We show that interstellar scintillation of this pulsar consists of two components: diffractive scintillations from inhomogeneities in a layer of turbulent plasma at a distance z1 = 440 pc from the observer or homogeneously distributed scattering material to the pulsar; and weak scintillations from a screen located near the observer at z2 = 0.14 ± 0.05 pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift in observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded a scattering angle in the observer plane of θscat = 0.7 mas. An analysis of the time-frequency correlation function for weak scintillations yielded an angle of refraction in the direction to the pulsar θref, 0 = 110 ms and a distance to the prism zprism ≤ 2 pc.

Dense magnetized plasma associated with a fast radio burst.

PubMed

Masui, Kiyoshi; Lin, Hsiu-Hsien; Sievers, Jonathan; Anderson, Christopher J; Chang, Tzu-Ching; Chen, Xuelei; Ganguly, Apratim; Jarvis, Miranda; Kuo, Cheng-Yu; Li, Yi-Chao; Liao, Yu-Wei; McLaughlin, Maura; Pen, Ue-Li; Peterson, Jeffrey B; Roman, Alexander; Timbie, Peter T; Voytek, Tabitha; Yadav, Jaswant K

2015-12-24

Fast radio bursts are bright, unresolved, non-repeating, broadband, millisecond flashes, found primarily at high Galactic latitudes, with dispersion measures much larger than expected for a Galactic source. The inferred all-sky burst rate is comparable to the core-collapse supernova rate out to redshift 0.5. If the observed dispersion measures are assumed to be dominated by the intergalactic medium, the sources are at cosmological distances with redshifts of 0.2 to 1 (refs 10 and 11). These parameters are consistent with a wide range of source models. One fast burst revealed circular polarization of the radio emission, but no linear polarization was detected, and hence no Faraday rotation measure could be determined. Here we report the examination of archival data revealing Faraday rotation in the fast radio burst FRB 110523. Its radio flux and dispersion measure are consistent with values from previously reported bursts and, accounting for a Galactic contribution to the dispersion and using a model of intergalactic electron density, we place the source at a maximum redshift of 0.5. The burst has a much higher rotation measure than expected for this line of sight through the Milky Way and the intergalactic medium, indicating magnetization in the vicinity of the source itself or within a host galaxy. The pulse was scattered by two distinct plasma screens during propagation, which requires either a dense nebula associated with the source or a location within the central region of its host galaxy. The detection in this instance of magnetization and scattering that are both local to the source favours models involving young stellar populations such as magnetars over models involving the mergers of older neutron stars, which are more likely to be located in low-density regions of the host galaxy.

Radio variability in complete samples of extragalactic radio sources at 1.4 GHz

NASA Astrophysics Data System (ADS)

Rys, S.; Machalski, J.

1990-09-01

Complete samples of extragalactic radio sources obtained in 1970-1975 and the sky survey of Condon and Broderick (1983) were used to select sources variable at 1.4 GHz, and to investigate the characteristics of variability in the whole population of sources at this frequency. The radio structures, radio spectral types, and optical identifications of the selected variables are discussed. Only compact flat-spectrum sources vary at 1.4 GHz, and all but four are identified with QSOs, BL Lacs, or other (unconfirmed spectroscopically) stellar objects. No correlation of degree of variability at 1.4 GHz with Galactic latitude or variability at 408 MHz has been found, suggesting that most of the 1.4-GHz variability is intrinsic and not caused by refractive scintillations. Numerical models of the variability have been computed.

About the Modeling of Radio Source Time Series as Linear Splines

NASA Astrophysics Data System (ADS)

Karbon, Maria; Heinkelmann, Robert; Mora-Diaz, Julian; Xu, Minghui; Nilsson, Tobias; Schuh, Harald

2016-12-01

Many of the time series of radio sources observed in geodetic VLBI show variations, caused mainly by changes in source structure. However, until now it has been common practice to consider source positions as invariant, or to exclude known misbehaving sources from the datum conditions. This may lead to a degradation of the estimated parameters, as unmodeled apparent source position variations can propagate to the other parameters through the least squares adjustment. In this paper we will introduce an automated algorithm capable of parameterizing the radio source coordinates as linear splines.

Exploring the multiband emission of TXS 0536+145: the most distant -γray flaring blazar

DOE PAGES

Orienti, M.; D'Ammando, F.; Giroletti, M.; ...

2014-09-15

We report results of a multi-band monitoring campaign of the flat spectrum radio quasar TXS 0536+145 at redshift 2.69. This source was detected during a very high γ-ray activity state in 2012 March by the Large Area Telescope on board Fermi, becoming the γ-ray flaring blazar at the highest redshift detected so far. At the peak of the flare the source reached an apparent isotropic γ-ray luminosity of 6.6×1049 erg s-1 which is comparable to the values achieved by the most luminous blazars. This activity triggered radio-to-X-rays monitoring observations by Swift, Very Long Baseline Array, European VLBI Network, and Medicinamore » single-dish telescope. Significant variability was observed from radio to X-rays supporting the identification of the γ-ray source with TXS 0536+145. Both the radio and γ-ray light curves show a similar behaviour, with the γ-rays leading the radio variability with a time lag of about 4-6 months. The luminosity increase is associated with a flattening of the radio spectrum. No new superluminal component associated with the flare was detected in high resolution parsec-scale radio images. During the flare the γ-ray spectrum seems to deviate from a power law, showing a curvature that was not present during the average activity state. The γ-ray properties of TXS 0536+145 are consistent with those shown by the high-redshift γ-ray blazar population.« less

Investigating Possible Outliers in the Fermi Blazar AGN Sample

NASA Astrophysics Data System (ADS)

Shrader, Chris

2018-01-01

The Fermi Gamma-Ray Space Telescope (Fermi) has cataloged over 3000 gamma-ray (>100 MeV) point sources of which more than 1100 are likely AGN. These AGN are predominantly among the radio-loud “blazar” subclass. Recently however, a significant sample of bright (F_15GHz >1.5 Jy), radio selected AGN was found to overlap with Fermi at only the ~80% level (Lister et. al., 2015). This could be a result of some selection bias or it could be due to deficient Doppler boosting among that ~20%. Additionally, a recent survey of high-latitude gamma-ray sources by Schinzel et al. (2017) reveals a sample of ~100 objects which are not detected in the 4-10 GHz radio band to a limiting flux of about 2mJy. This apparent lack of radio flux is puzzling, and may indicate either an extreme Compton-dominated sample, or copious gamma-ray emission from a heretofore unknown population such as a subclass of radio-quiet AGN. Speculatively, these radio-loud/gamma-quiet and gamma-loud/radio quiet samples could be odd cases of the blazar phenomena which reside outside of the well-known blazar sequence. To explore this problem further we have undertaken a study to construct or constrain individual source SEDs as a first step towards their classification. In this contribution we present results from our search for emission in the Swift-BAT 15-100-keV hard X-ray band for each of these samples.

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

Ackermann, M.; Ajello, M.; Baldini, L.

Here, we report the Fermi Large Area Telescope detection of extended γ-ray emission from the lobes of the radio galaxy Fornax A using 6.1 years of Pass 8 data. After Centaurus A, this is now the second example of an extended γ-ray source attributed to a radio galaxy. Both an extended flat disk morphology and a morphology following the extended radio lobes were preferred over a point-source description, and the core contribution was constrained to bemore » $$\\lt 14$$% of the total γ-ray flux. We also demonstrated a preferred alignment of the γ-ray elongation with the radio lobes by rotating the radio lobes template. We found no significant evidence for variability on ~0.5 year timescales. Taken together, these results strongly suggest a lobe origin for the γ-rays. Furthermore, with the extended nature of the $$\\gt 100\\;{\\rm{MeV}}$$ γ-ray emission established, we model the source broadband emission considering currently available total lobe radio and millimeter flux measurements, as well as X-ray detections attributed to inverse Compton (IC) emission off the cosmic microwave background (CMB). Unlike the Centaurus A case, we find that a leptonic model involving IC scattering of CMB and extragalactic background light (EBL) photons underpredicts the γ-ray fluxes by factors of about ~2–3, depending on the EBL model adopted. An additional γ-ray spectral component is thus required, and could be due to hadronic emission arising from proton–proton collisions of cosmic rays with thermal plasma within the radio lobes.« less

Exploring the multiband emission of TXS 0536+145: the most distant γ-ray flaring blazar

NASA Astrophysics Data System (ADS)

Orienti, M.; D'Ammando, F.; Giroletti, M.; Finke, J.; Ajello, M.; Dallacasa, D.; Venturi, T.

2014-11-01

We report results of a multiband monitoring campaign of the flat spectrum radio quasar TXS 0536+145 at redshift 2.69. This source was detected during a very high γ-ray activity state in 2012 March by the Large Area Telescope on board Fermi, becoming the γ-ray flaring blazar at the highest redshift detected so far. At the peak of the flare the source reached an apparent isotropic γ-ray luminosity of 6.6 × 1049 erg s-1 which is comparable to the values achieved by the most luminous blazars. This activity triggered radio-to-X-rays monitoring observations by Swift, Very Long Baseline Array, European VLBI Network, and Medicina single-dish telescope. Significant variability was observed from radio to X-rays supporting the identification of the γ-ray source with TXS 0536+145. Both the radio and γ-ray light curves show a similar behaviour, with the γ-rays leading the radio variability with a time lag of about 4-6 months. The luminosity increase is associated with a flattening of the radio spectrum. No new superluminal component associated with the flare was detected in high-resolution parsec-scale radio images. During the flare the γ-ray spectrum seems to deviate from a power law, showing a curvature that was not present during the average activity state. The γ-ray properties of TXS 0536+145 are consistent with those shown by the high-redshift γ-ray blazar population.

High–frequency cluster radio galaxies: Luminosity functions and implications for SZE–selected cluster samples

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

Gupta, Nikhel; Saro, A.; Mohr, J. J.

We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the meta-catalogue of X-ray-detected clusters of galaxies (MCXC; < z > = 0.14) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg 2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multifrequency catalogue of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev–Zel’dovich Effect (SZE) signal, whichmore » is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogues. We find that the high-frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass–observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 per cent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. As a result, allowing for redshift evolution of the form (1 + z) 2.5 increases the incompleteness to 5.6 ± 1.0 per cent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.« less

High–frequency cluster radio galaxies: Luminosity functions and implications for SZE–selected cluster samples

DOE PAGES

Gupta, Nikhel; Saro, A.; Mohr, J. J.; ...

2017-01-15

We study the overdensity of point sources in the direction of X-ray-selected galaxy clusters from the meta-catalogue of X-ray-detected clusters of galaxies (MCXC; < z > = 0.14) at South Pole Telescope (SPT) and Sydney University Molonglo Sky Survey (SUMSS) frequencies. Flux densities at 95, 150 and 220 GHz are extracted from the 2500 deg 2 SPT-SZ survey maps at the locations of SUMSS sources, producing a multifrequency catalogue of radio galaxies. In the direction of massive galaxy clusters, the radio galaxy flux densities at 95 and 150 GHz are biased low by the cluster Sunyaev–Zel’dovich Effect (SZE) signal, whichmore » is negative at these frequencies. We employ a cluster SZE model to remove the expected flux bias and then study these corrected source catalogues. We find that the high-frequency radio galaxies are centrally concentrated within the clusters and that their luminosity functions (LFs) exhibit amplitudes that are characteristically an order of magnitude lower than the cluster LF at 843 MHz. We use the 150 GHz LF to estimate the impact of cluster radio galaxies on an SPT-SZ like survey. The radio galaxy flux typically produces a small bias on the SZE signal and has negligible impact on the observed scatter in the SZE mass–observable relation. If we assume there is no redshift evolution in the radio galaxy LF then 1.8 ± 0.7 per cent of the clusters with detection significance ξ ≥ 4.5 would be lost from the sample. As a result, allowing for redshift evolution of the form (1 + z) 2.5 increases the incompleteness to 5.6 ± 1.0 per cent. Improved constraints on the evolution of the cluster radio galaxy LF require a larger cluster sample extending to higher redshift.« less

Broadband radio spectro-polarimetric observations of high-Faraday-rotation-measure AGN

NASA Astrophysics Data System (ADS)

Pasetto, Alice; Carrasco-González, Carlos; O'Sullivan, Shane; Basu, Aritra; Bruni, Gabriele; Kraus, Alex; Curiel, Salvador; Mack, Karl-Heinz

2018-06-01

We present broadband polarimetric observations of a sample of high-Faraday-rotation-measure (high-RM) active galactic nuclei (AGN) using the Karl. G. Jansky Very Large Array (JVLA) telescope from 1 to 2 GHz, and 4 to 12 GHz. The sample (14 sources) consists of very compact sources (linear resolution smaller than ≈5 kpc) that are unpolarized at 1.4 GHz in the NRAO VLA Sky Survey (NVSS). Total intensity data have been modeled using a combination of synchrotron components, revealing complex structure in their radio spectra. Depolarization modeling, through the so-called qu-fitting (the modeling of the fractional quantities of the Stokes Q and U parameters), has been performed on the polarized data using an equation that attempts to simplify the process of fitting many different depolarization models. These models can be divided into two major categories: external depolarization (ED) and internal depolarization (ID) models. Understanding which of the two mechanisms is the most representative would help the qualitative understanding of the AGN jet environment and whether it is embedded in a dense external magneto-ionic medium or if it is the jet-wind that causes the high RM and strong depolarization. This could help to probe the jet magnetic field geometry (e.g., helical or otherwise). This new high-sensitivity data shows a complicated behavior in the total intensity and polarization radio spectrum of individual sources. We observed the presence of several synchrotron components and Faraday components in their total intensity and polarized spectra. For the majority of our targets (12 sources), the depolarization seems to be caused by a turbulent magnetic field. Thus, our main selection criteria (lack of polarization at 1.4 GHz in the NVSS) result in a sample of sources with very large RMs and depolarization due to turbulent magnetic fields local to the source. These broadband JVLA data reveal the complexity of the polarization properties of this class of radio sources. We show how the new qu-fitting technique can be used to probe the magnetized radio source environment and to spectrally resolve the polarized components of unresolved radio sources.

A radiometric Bode's Law: Predictions for Uranus

NASA Technical Reports Server (NTRS)

Desch, M. D.; Kaiser, M. L.

1984-01-01

The magnetospheres of three planets, Earth, Jupiter, and Saturn, are known to be sources of intense, nonthermal radio bursts. The emissions from these sources undergo pronounced long term intensity fluctuations that are caused by the solar wind interaction with the magnetosphere of each planet. Determinations by spacecraft of the low frequency radio spectra and radiation beam geometry now permit a reliable assessment of the overall efficiency of the solar wind in stimulating these emissions. Earlier estimates of how magnetospheric radio output scales with the solar wind energy input must be revised greatly, with the result that, while the efficiency is much lower than previously thought, it is remarkably uniform from planet to planet. The formulation of a radiometric Bode's Law from which a planet's magnetic moment is estimated from its radio emission output is presented. Applying the radiometric scaling law to Uranus, the low-frequency radio power is likely to be measured by the Voyager 2 spacecraft as it approaches this planet.

Nonthermal processes around collapsed objects: High energy gamma ray sources in the radio sky

NASA Technical Reports Server (NTRS)

Helfand, David J.; Ruderman, Malvin; Applegate, James H.; Becker, Robert H.

1993-01-01

In our proposal responding to the initial Guest Observer NRA for the Compton Gamma Ray Observatory, 'Nonthermal Processes Around Collapsed Objects: High Energy Gamma Ray Sources in the Radio Sky', we stated that 'At high energies - the identity of the principal Galactic source population remains unknown' although the 'one certain source of high energy emission is young radio pulsars'. These two statements remain true, although at this writing, eighteen months after the beginning of the Compton allsky survey, much of the gamma-ray data required to greatly extend our knowledge of the Galaxy's high energy emission has been collected. The thrust of the program supported by our grant was to collect and analyze a complementary set of data on the Milky Way at radio wavelengths in order to help identify the dominant Pop 1 component of the Galaxy's gamma ray sources, and to pursue theoretical investigations on the origins and emission mechanisms of young pulsars, the one component of this population identified to date. We summarize here our accomplishments under the grant. In Section 2, we describe our VLA surveys of the Galactic Plane along with the current status of the radio source catalogs derived therefrom; unfortunately, owing to the TDRSS antenna problem and subsequent extension of the Sky Survey, we were not able to carry out a comparison with the EGRET data directly, although everything is now in place to do so as soon as it becomes available. In Section 2, we summarize our progress on the theoretical side, including the substantial completion of a dissertation on pulsar origins and work on the high energy emission mechanisms of isolated pulsars. We list the personnel supported by the grant in section 4 and provide a complete bibliography of publications supported in whole or in part by the grant in the final section.

Global VLBI Observations of Weak Extragalactic Radio Sources: Imaging Candidates to Align the VLBI and Gaia Frames

NASA Technical Reports Server (NTRS)

Bourda, Geraldine; Collioud, Arnaud; Charlot, Patrick; Porcas, Richard; Garrington, Simon

2010-01-01

The space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames (International Celestial Reference Frame) with the highest accuracy. In this respect, it is found that only 10% of the ICRF sources are suitable to establish this link (70 sources), either because most of the ICRF sources are not bright enough at optical wavelengths or because they show extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we initiated a multi-step VLBI observational project, dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of about 450 optically-bright radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating optical and radio catalogs. The initial observations, aimed at checking whether these sources are detectable with VLBI, and conducted with the European VLBI Network (EVN) in 2007, showed an excellent 90% detection rate. This paper reports on global VLBI observations carried out in March 2008 to image 105 from the 398 previously detected sources. All sources were successfully imaged, revealing compact VLBI structure for about half of them, which is very promising for the future.

Electron cyclotron resonance sources: Historical review and future prospects (invited)

NASA Astrophysics Data System (ADS)

Geller, R.

1998-03-01

Low charge state electron cyclotron resonance ion source (ECRIS) work since 1965 and high charge state ECRIS since 1974. These ECR sources are categorized into three main sections: (1) Low charged ion (ECRIS) inside simple magnetic mirror or Bucket configurations. (2) High charged ion ECRIS inside min-B mirror configurations. (3) Short pulsed ECRIS with highly charged ions where the ion confinement is disturbed for a short while, which allows the extraction of intense ion pulses. Future prospects are based on rational scaling of the magnetic confinement including high B modes, by increasing the radio frequency (rf) frequency and ECR magnetic field. In this case, charge exchange has to be minimized and plasma instabilities have to be avoided. However, clever empirical tricks lead also to outstanding not always predicted improvements. Let us cite: optimized rf plasma coupling, electron guns, gas mixing, wall coating, biased electrodes, and more recently multiple ECR frequency heating. ECRIS have not yet achieved their optimal possibilities. Let us wait for the next generation of superconducting ECRIS and the possible use of subcentimeter waves.

Electron cyclotron resonance sources: Historical review and future prospects (invited)

NASA Astrophysics Data System (ADS)

Geller, R.

1998-02-01

Low charge state electron cyclotron resonance ion source (ECRIS) work since 1965 and high charge state ECRIS since 1974. These ECR sources are categorized into three main sections: (1) Low charged ion (ECRIS) inside simple magnetic mirror or Bucket configurations. (2) High charged ion ECRIS inside min-B mirror configurations. (3) Short pulsed ECRIS with highly charged ions where the ion confinement is disturbed for a short while, which allows the extraction of intense ion pulses. Future prospects are based on rational scaling of the magnetic confinement including high B modes, by increasing the radio frequency (rf) frequency and ECR magnetic field. In this case, charge exchange has to be minimized and plasma instabilities have to be avoided. However, clever empirical tricks lead also to outstanding not always predicted improvements. Let us cite: optimized rf plasma coupling, electron guns, gas mixing, wall coating, biased electrodes, and more recently multiple ECR frequency heating. ECRIS have not yet achieved their optimal possibilities. Let us wait for the next generation of superconducting ECRIS and the possible use of subcentimeter waves.

The black hole candidate XTE J1752-223 towards and in quiescence: optical and simultaneous X-ray-radio observations

NASA Astrophysics Data System (ADS)

Ratti, E. M.; Jonker, P. G.; Miller-Jones, J. C. A.; Torres, M. A. P.; Homan, J.; Markoff, S.; Tomsick, J. A.; Kaaret, P.; Wijnands, R.; Gallo, E.; Özel, F.; Steeghs, D. T. H.; Fender, R. P.

2012-07-01

We present optical, X-ray and radio observations of the black hole transient (BHT) XTE J1752-223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752-223 is fainter than 24.4 mag in the i' band. A comparison with measurements of the source during its 2009-2010 outburst shows that the outburst amplitude is more than 8 mag in the i' band. Known X-ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital-period system (Porb≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲d≲ 8 kpc. Simultaneous X-ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X-ray and radio flux of XTE J1752-223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low-luminosity end of the X-ray-radio correlation for this source and compared it with other BHTs. We found that XTE J1752-223 adds to the number of outliers with respect to the 'standard' X-ray-radio luminosity relation. Furthermore, XTE J1752-223 is the second source, after the BHT H1743-322, that shows a transition from the region of the outliers towards the 'standard' correlation at low luminosity. Finally, we report on a faint, variable X-ray source we discovered with Chandra at an angular distance of ˜2.9 arcsec to XTE J1752-223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X-ray emission associated with a jet from XTE J1752-223.

Exploratory X-ray Monitoring of z>4 Radio-Quiet Quasars

NASA Astrophysics Data System (ADS)

Shemmer, Ohad

2017-09-01

We propose to extend our exploratory X-ray monitoring project of some of the most distant radio-quiet quasars by obtaining one snapshot observation per Cycle for each of four sources at z>4. Combining these observations with six available X-ray epochs per source will provide basic temporal information over rest-frame timescales of 3-5 yr. We are supporting this project with Swift monitoring of luminous radio-quiet quasars at z=1.3-2.7 to break the L-z degeneracy and test evolutionary scenarios of the central engine in active galactic nuclei. Our ultimate goal is to provide a basic assessment of the X-ray variability properties of luminous quasars at the highest accessible redshifts that will serve as the benchmark for X-ray variability studies of such sources with future X-ray missions.

A VLA Study of High-redshift GRBs. II. The Complex Radio Afterglow of GRB 140304A: Shell Collisions and Two Reverse Shocks

NASA Astrophysics Data System (ADS)

Laskar, Tanmoy; Berger, Edo; Margutti, Raffaella; Zauderer, B. Ashley; Williams, Peter K. G.; Fong, Wen-fai; Sari, Re’em; Alexander, Kate D.; Kamble, Atish

2018-06-01

We present detailed multifrequency, multiepoch radio observations of GRB 140304A at z = 5.283 from 1 to 86 GHz and from 0.45 to 89 days. The radio and millimeter data exhibit unusual multiple spectral components, which cannot be simply explained by standard forward and reverse shock scenarios. Through detailed multiwavelength analysis spanning radio to X-rays, we constrain the forward shock parameters to E k,iso ≈ 4.9 × 1054 erg, {A}* ≈ 2.6 × 10‑2, {ε }{{e}} ≈ 2.5 × 10‑2, {ε }{{B}} ≈ 5.9 × 10‑2, p ≈ 2.6, and {θ }jet} ≈ 1.°1, yielding a beaming-corrected γ-ray and kinetic energy, {E}γ ≈ 2.3 × 1049 erg and {E}{{K}} ≈ 9.5 × 1050 erg, respectively. We model the excess radio emission as due to a combination of a late-time reverse shock (RS) launched by a shell collision, which also produces a rebrightening in the X-rays at ≈0.26 days, and either a standard RS or diffractive interstellar scintillation (ISS). Under the standard RS interpretation, we invoke consistency arguments between the forward and reverse shocks to derive a deceleration time, t dec ≈ 100 s, the ejecta Lorentz factor, Γ(t dec) ≈ 300, and a low RS magnetization, R B ≈ 0.6. Our observations highlight both the power of radio observations in capturing RS emission and thus constraining the properties of GRB ejecta and central engines and the challenge presented by ISS in conclusively identifying RS emission in GRB radio afterglows.

The Third EGRET Catalog of High-Energy Gamma-Ray Sources

NASA Technical Reports Server (NTRS)

Hartman, R. C.; Bertsch, D. L.; Bloom, S. D.; Chen, A. W.; Deines-Jones, P.; Esposito, J. A.; Fichtel, C. E.; Friedlander, D. P.; Hunter, S. D.; McDonald, L. M.;

An Unlikely Radio Halo in the Low X-Ray Luminosity Galaxy Cluster RXCJ1514.9-1523

NASA Technical Reports Server (NTRS)

Marketvitch, M.; ZuHone, J. A.; Lee, D.; Giacintucci, S.; Dallacasa, D.; Venturi, T.; Brunetti, G.; Cassano, R.; Markevitch, M.; Athreya, R. M.

2011-01-01

Aims: We report the discovery of a giant radio halo in the galaxy cluster RXCJ1514,9-1523 at z=0.22 with a relatively low X-ray luminosity, L(sub X) (0.1-2.4kev) approx. 7 x 10(exp 44) ergs/s. Methods: This faint, diffuse radio source is detected with the Giant Meterwave Radio Telescope at 327 MHz. The source is barely detected at 1.4 GHz in a NVSS pointing that we have reanalyzed. Results: The integrated radio spectrum of the halo is quite steep, with a slope alpha = 1.6 between 327 MHz and 1.4 GHz. While giant radio halos are common in more X-ray luminous cluster mergers, there is a less than 10% probability to detect a halo in systems with L(sub X) < 8 x 10(exp 44) ergs/s. The detection of a new giant halo in this borderline luminosity regime can be particularly useful for discriminating between the competing theories for the origin of ultrarelativistic electrons in clusters. Furthermore, if our steep radio spectral index is confirmed by future deeper radio observations, this cluster would provide another example of the very rare, new class of ultra-steep spectrum radio halos, predicted by the model in which the cluster cosmic ray electrons are produced by turbulent reacceleration.

The environmental properties of radio-emitting AGN

NASA Astrophysics Data System (ADS)

Magliocchetti, M.; Popesso, P.; Brusa, M.; Salvato, M.

2018-05-01

We study the environmental properties of z≲ 1.2 radio-selected AGN belonging to the ˜2 deg2 of the COSMOS field, finding that about 20% of them appear within overdense structures. AGN with P_{1.4 GHz}>10^{23.5} W Hz^{-1} sr^{-1} are twice more likely to be found in clusters with respect to fainter sources (˜38% vs ˜15%), just as radio-selected AGN with stellar masses M* > 1011M⊙ are twice more likely to be found in overdense environments with respect to objects of lower mass (˜24% vs ˜11%). Comparisons with galaxy samples further suggest that radio-selected AGN of large stellar mass tend to avoid underdense environments more than normal galaxies with the same stellar content. Stellar masses also seem to determine the location of radio-active AGN within clusters: ˜100% of the sources found as satellite galaxies have M* < 1011.3M⊙, while ˜100% of the AGN coinciding with a cluster central galaxy have M* > 1011M⊙. No different location within the cluster is instead observed for AGN of various radio luminosities. Radio AGN which also emit in the MIR show a marked preference to be found as isolated galaxies (˜70%) at variance with those also active in the X-ray which all seem to reside within overdensities. What emerges from our work is a scenario whereby physical processes on sub-pc and kpc scales (e.g. emission respectively related to the AGN and to star formation) are strongly interconnected with the large-scale environment of the AGN itself.

Radio observations of a few selected blazars

NASA Technical Reports Server (NTRS)

Saikia, D. J.; Salter, C. J.; Neff, S. G.; Gower, A. C.; Sinha, R. P.

1987-01-01

The paper presents total-intensity and linear-polarization observations of four selected blazars, 0716+714, 0752+258, 1156+295 and 1400+162, with the VLA A-array, and MERLIN and EVN observations of 1400+162. The sources 0752+258 and 1400+162 which have nearly constant optical polarization, have well-defined double-lobed radio structure, with relatively weak radio cores, and are likely to be at large viewing angles. In addition, 0752+258 appears to be a twin-jet blazar. The position angle (PA) of the VLBI jet in 1400+162 is close to that of the arcsec-scale jet near the nucleus, as well as the optical and 2-cm core polarization PAs. The blazars 0716+714 and 1156+295, which exhibit strongly variable optical polarization, have a core-dominated radio structure and perhaps have their jet axes close to the line-of-sight. From polarization observations at 20, 18, 6, and 2 cm, it is found that the rotation measure of the radio core in 0716+714 is about -20 rad/sq m. It is suggested that low values of core rotation measure in core-dominated sources could be consistent with the relativistic beaming models.

Radio Observations of Type Ia SN2006X

NASA Astrophysics Data System (ADS)

Soderberg, Alicia

2006-02-01

Alicia Soderberg (Caltech) reports: I observed the Type Ia supernova 2006X in NGC 4321 (IAUC 8667, CBET 393) with the Very Large Array on 2006 February 9.34 UT (approximately 2 days after optical discovery). The 2.5 hour observation at 8.46 GHz reveals no radio source coincident with the optical SN position. I place a limit on the radio flux density of 45 microJy (3 sigma). At a distance of 16 Mpc this limit corresponds to a luminosity of 1.4 x 10^25 erg/s/Hz.

Detection of the Intrinsic Size of Sagittarius A* Through Closure Amplitude Imaging

NASA Astrophysics Data System (ADS)

Bower, Geoffrey C.; Falcke, Heino; Herrnstein, Robeson M.; Zhao, Jun-Hui; Goss, W. M.; Backer, Donald C.

2004-04-01

We have detected the intrinsic size of Sagittarius A*, the Galactic center radio source associated with a supermassive black hole, showing that the short-wavelength radio emission arises from very near the event horizon of the black hole. Radio observations with the Very Long Baseline Array show that the source has a size of 24 +/- 2 Schwarzschild radii at 7-millimeter wavelength. In one of eight 7-millimeter epochs, we also detected an increase in the intrinsic size of 60+25-17%. These observations place a lower limit to the mass density of Sagittarius A* of 1.4 × 104 solar masses per cubic astronomical unit.

Do the enigmatic ``Infrared-Faint Radio Sources'' include pulsars?

NASA Astrophysics Data System (ADS)

Hobbs, George; Middelberg, Enno; Norris, Ray; Keith, Michael; Mao, Minnie; Champion, David

2009-04-01

The Australia Telescope Large Area Survey (ATLAS) team have surveyed seven square degrees of sky at 1.4GHz. During processing some unexpected infrared-faint radio sources (IFRS sources) were discovered. The nature of these sources is not understood, but it is possible that some of these sources may be pulsars within our own galaxy. We propose to observe the IFRS sources with steep spectral indices using standard search techniques to determine whether or not they are pulsars. A pulsar detection would 1) remove a subset of the IFRS sources from the ATLAS sample so they would not need to be observed with large optical/IR telescopes to find their hosts and 2) be intrinsically interesting as the pulsar would be a millisecond pulsar and/or have an extreme spatial velocity.

Rapid Changes in the Structure of the BN Object

NASA Technical Reports Server (NTRS)

Danchi, William C.; Gezari, D. Y.; Greenhill, L. J.; Najita, J.; Monnier, J. D.; Tuthill, P. G.; Wishnow, E. H.; Townes, C. H.; Fisher, Richard R. (Technical Monitor)

2001-01-01

The BN/KL region in Orion is the archetypal region of high-mass star formation, radiating approx. 10(sup)5 Lsun and displaying promininent bulk outflows. In particular, there is no certain identification of the sources responsible for the high luminosity and outflows, and is the origin of a major explosive event (Shultz et al. 1999, ApJ, 511, 282). Using 18.7 and 12.5 micron data from observations in December 1999 and October 2000 made at the Keck I telescope, we discovered that the BN Object has a companion previously seen only at radio wavelengths (Menten & Reid 1995, ApJ, 445, L157). We call this companion B2 and it is about 1.5 arcsec West of the bright component. We also see changes in the shape of BN and the emission of "blobs" or "bullets" of material. While B2 remains unchanged and in the same place between the two epochs, there is an additional structure in BN to the South-South-East and the North-East, as well as a finger of material pointing North from B2 itself. Such a change has not been seen before in the infrared. We have looked very carefully at these images, calibrator images taken within a few minutes of the source images, as well as our previous images and cannot find any technical faults with the data. We explore the implications of these results, in particular, can these features be connected with previously observed "bullets" or "fingers" (see Allen & Burton 1993, for example), making BN a source for the bullets, implying they are not from IRc2 as previously thought? Or could they be produced by an interaction between material from BN and other sources such as IRc2?

RAiSE II: resolved spectral evolution in radio AGN

NASA Astrophysics Data System (ADS)

Turner, Ross J.; Rogers, Jonathan G.; Shabala, Stanislav S.; Krause, Martin G. H.

2018-01-01

The active galactic nuclei (AGN) lobe radio luminosities modelled in hydrodynamical simulations and most analytical models do not address the redistribution of the electron energies due to adiabatic expansion, synchrotron radiation and inverse-Compton scattering of cosmic microwave background photons. We present a synchrotron emissivity model for resolved sources that includes a full treatment of the loss mechanisms spatially across the lobe, and apply it to a dynamical radio source model with known pressure and volume expansion rates. The bulk flow and dispersion of discrete electron packets is represented by tracer fields in hydrodynamical simulations; we show that the mixing of different aged electrons strongly affects the spectrum at each point of the radio map in high-powered Fanaroff & Riley type II (FR-II) sources. The inclusion of this mixing leads to a factor of a few discrepancy between the spectral age measured using impulsive injection models (e.g. JP model) and the dynamical age. The observable properties of radio sources are predicted to be strongly frequency dependent: FR-II lobes are expected to appear more elongated at higher frequencies, while jetted FR-I sources appear less extended. The emerging FR0 class of radio sources, comprising gigahertz peaked and compact steep spectrum sources, can potentially be explained by a population of low-powered FR-Is. The extended emission from such sources is shown to be undetectable for objects within a few orders of magnitude of the survey detection limit and to not contribute to the curvature of the radio spectral energy distribution.

Fabrication and radio frequency test of large-area MgB 2 films on niobium substrates

DOE PAGES

Ni, Zhimao; Guo, Xin; Welander, Paul B.; ...

2017-01-19

Magnesium diboride (MgB 2) is a promising candidate material for superconducting radio frequency (RF) cavities because of its higher transition temperature and critical field compared with niobium. To meet the demand of RF test devices, the fabrication of large-area MgB 2 films on metal substrates is needed. Here, in this work, high quality MgB 2 films with 50 mm diameter were fabricated on niobium by using an improved HPCVD system at Peking University, and RF tests were carried out at SLAC National Accelerator Laboratory. The transition temperature is approximately 39.6 K and the RF surface resistance is about 120 μΩmore » at 4 K and 11.4 GHz. Finally, the fabrication processes, surface morphology, DC superconducting properties and RF tests of these large-area MgB 2 films are presented.« less

Fabrication and radio frequency test of large-area MgB 2 films on niobium substrates

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

Ni, Zhimao; Guo, Xin; Welander, Paul B.

Magnesium diboride (MgB 2) is a promising candidate material for superconducting radio frequency (RF) cavities because of its higher transition temperature and critical field compared with niobium. To meet the demand of RF test devices, the fabrication of large-area MgB 2 films on metal substrates is needed. Here, in this work, high quality MgB 2 films with 50 mm diameter were fabricated on niobium by using an improved HPCVD system at Peking University, and RF tests were carried out at SLAC National Accelerator Laboratory. The transition temperature is approximately 39.6 K and the RF surface resistance is about 120 μΩmore » at 4 K and 11.4 GHz. Finally, the fabrication processes, surface morphology, DC superconducting properties and RF tests of these large-area MgB 2 films are presented.« less

Poynting-vector based method for determining the bearing and location of electromagnetic sources

DOEpatents

Simons, David J.; Carrigan, Charles R.; Harben, Philip E.; Kirkendall, Barry A.; Schultz, Craig A.

2008-10-21

A method and apparatus is utilized to determine the bearing and/or location of sources, such as, alternating current (A.C.) generators and loads, power lines, transformers and/or radio-frequency (RF) transmitters, emitting electromagnetic-wave energy for which a Poynting-Vector can be defined. When both a source and field sensors (electric and magnetic) are static, a bearing to the electromagnetic source can be obtained. If a single set of electric (E) and magnetic (B) sensors are in motion, multiple measurements permit location of the source. The method can be extended to networks of sensors allowing determination of the location of both stationary and moving sources.

An optical imaging study of 0.4 ≤ z ≤ 0.8 quasar host galaxies . II. Analysis and interpretation

NASA Astrophysics Data System (ADS)

Örndahl, E.; Rönnback, J.

2005-11-01

We performed optical imaging of 102 radio-loud and radio-quiet quasars at z=0.4{-}0.8, of which 91 fields were found suitable for host galaxy analysis after the deselection of saturated and otherwise flawed images. The data sets were obtained mainly in the R band, but also in the V and I or Gunn i band, and were presented in Rönnback et al.(1996, MNRAS, 283, 282) and Örndahl et al. (2003, A&A, 404, 883). In this paper we combine the two above-mentioned samples and also separately discuss additional hosts, extracted from data taken by Wold et al. (2000, MNRAS, 316, 267; 2001, MNRAS, 323, 231). The joint sample forms a sizeable fraction of the to-date total number of observed sources at intermediate redshifts and increases the number of resolved radio-quiet hosts at z>0.4 considerably. Equal numbers of radio-loud and radio-quiet objects were observed, resulting in a detection rate of 79% for the radio-loud hosts and 66% for the radio-quiet hosts. Profile fitting could only be carried out for a minority of the sample, but it results in predominantly elliptical morphologies. This is consistent with the mean values of the axial ratios, for which we find b/a⪆0.8 for both radio-quiet and radio-loud hosts, just as in the case of normal elliptical galaxies. The mean absolute magnitudes of the radio-loud and radio-quiet hosts is M_R=-23.5 in both cases. This similarity between the mean magnitudes of the two types of host galaxy is also seen in the other imaged bands. While the radio-loud host absolute R magnitudes are correlated with redshift, only a weak trend of the same sort is seen for the radio-quiet host magnitudes. Note, however, that the sample is not fully resolved and that the detection limit, in combination with the relationship between host and nuclear luminosity, may conspire in creating the illusion of an upturn in magnitude. The average nucleus-to-host galaxy luminosity ratios of the radio-loud and radio-quiet objects do not differ significantly in any band, nor is the difference between the average luminosity ratios of flat spectrum and steep spectrum radio-loud quasars larger than 1.5σ. Thus, no effect of beaming (as expected in the unifying scheme) is seen. The colours of both radio-loud and radio-quiet host galaxies are found to be as blue as present-day late-type spirals and starburst galaxies. These blue colours are most likely due neither to galaxy evolution over the range, which only gives rise to a colour shift of 0.2 mag, nor to scattered nuclear light, since colours determined from annular apertures yield very similar results. Since close companions in projection are not uncommon (and a few sources even exhibit tidal tail-like features and other signs of interaction), ongoing star formation is a reasonable explanation of the blue host colours. As multiple-band imaging primarily was carried out for quasars showing indications of the presence of a host galaxy, the colour analysis results are valid for host galaxies which are large, bright, have low nucleus-to-host luminosity ratios, and/or display large scale disturbances, but cannot however safely be generalised to hold for the quasar host galaxy population at intermediate redshift as a whole.

The GOODS-N Jansky VLA 10 GHz Pilot Survey: Sizes of Star-forming μJY Radio Sources

NASA Astrophysics Data System (ADS)

Murphy, Eric J.; Momjian, Emmanuel; Condon, James J.; Chary, Ranga-Ram; Dickinson, Mark; Inami, Hanae; Taylor, Andrew R.; Weiner, Benjamin J.

2017-04-01

Our sensitive ({σ }{{n}}≈ 572 {nJy} {{beam}}-1), high-resolution (FWHM {θ }1/2=0\\buildrel{\\prime\\prime}\\over{.} 22≈ 2 {kpc} {at} z≳ 1), 10 GHz image covering a single Karl G. Jansky Very Large Array (VLA) primary beam (FWHM {{{\\Theta }}}1/2≈ 4\\buildrel{ \\prime}\\over{.} 25) in the GOODS-N field contains 32 sources with {S}{{p}}≳ 2 μ {Jy} {{beam}}-1 and optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is < {θ }{{M}}> =167+/- 32 {mas}≈ 1.2+/- 0.28 {kpc}, with rms scatter ≈ 91 {mas}≈ 0.79 {kpc}. In units of the effective radius {r}{{e}} that encloses half their flux, these radio sizes are < {r}{{e}}> ≈ 69+/- 13 {mas}≈ 509+/- 114 {pc}, with rms scatter ≈ 38 {mas}≈ 324 {pc}. These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected Hα sizes. We made a low-resolution ({θ }1/2=1\\buildrel{\\prime\\prime}\\over{.} 0) image with ≈ 10× better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices {α }1.4 {GHz}10 {GHz}. It contains six new sources with {S}{{p}}≳ 3.9 μ {Jy} {{beam}}-1 and OIR counterparts. The median redshift of all 38 sources is < z> =1.24+/- 0.15. The 19 sources with 1.4 GHz counterparts have a median spectral index of < {α }1.4 {GHz}10 {GHz}> =-0.74+/- 0.10, with rms scatter ≈ 0.35. Including upper limits on α for sources not detected at 1.4 GHz flattens the median to < {α }1.4 {GHz}10 {GHz}> ≳ -0.61, suggesting that the μJy radio sources at higher redshifts—and hence those selected at higher rest-frame frequencies—may have flatter spectra. If the non-thermal spectral index is {α }{NT}≈ -0.85, the median thermal fraction of sources selected at median rest-frame frequency ≈ 20 {GHz} is ≳48%.

Interplanetary radio storms. 2: Emission levels and solar wind speed in the range 0.05-0.8 AU

NASA Technical Reports Server (NTRS)

Bougeret, J. L.; Fainberg, J.; Stone, R. G.

1982-01-01

Storms of interplanetary type III radio bursts (IP storms) are commonly observed in the interplanetry medium by the ISEE-3 radio instrument. This instrument has the capability of accurately determining the arrival direction of the radio emission. At each observing frequency, the storm radio sources are tracked as they cross the line-of-sight to the Sun. Usng a simple model, the emission levels are determined at a number of radio frequencies for four separate storms. The IP storm radiation is found to occur in regions of enhanced density at levels of 0.05 to 0.8 AU. The density in these enhancements falls off faster than R(-2). The solar wind speed in the storm region is also measured. The analysis is consistent with steady conditions in the storm region during a few days around the central meridian passage of the storm. The comparison with average in situ density measurements compiled from the HELIOS 1-2 observations favors type III storm burst radio emission at the harmonic of the local plasma frequency.

A 20 GHz bright sample for δ > 72° - II. Multifrequency follow-up

NASA Astrophysics Data System (ADS)

Ricci, R.; Righini, S.; Verma, R.; Prandoni, I.; Carretti, E.; Mack, K.-H.; Massardi, M.; Procopio, P.; Zanichelli, A.; Gregorini, L.; Mantovani, F.; Gawroński, M. P.; Peel, M. W.

2013-11-01

We present follow-up observations at 5, 8 and 30 GHz of the K-band Northern Wide Survey (KNoWS) 20 GHz Bright Sample, performed with the 32-m Medicina radio telescope and the 32-m Toruń radio telescope. The KNoWS sources were selected in the Northern Polar Cap (δ > 72°) and have a flux density limit S20 GHz = 115 mJy. We include NRAO-VLA Sky Survey 1.4 GHz measurements to derive the source radio spectra between 1.4 and 30 GHz. Based on optical identifications, 68 per cent of the sources are quasars and 27 per cent are radio galaxies. A redshift measurement is available for 58 per cent of the sources. The radio spectral properties of the different source populations are found to be in agreement with those of other high-frequency-selected samples.

The distribution of radio plasma in time and space.

PubMed

Blundell, Katherine M

2005-03-15

The influence of jet-ejected plasma has been an important theme of this meeting; I draw attention to the prevalence of jet-ejected plasma, in particular that which has not been properly accounted for in the past. There are three strands to this paper: important emission which is prominent only at the lowest radio frequencies; relic radio plasma which must exist if even the most basic aspects of radio source evolutionary models are correct; and evidence that some 'radio-quiet' quasars could be FR-I radio sources.

The Extraordinary Outburst in the Massive Protostellar System NGC 6334I-MM1: Emergence of Strong 6.7 GHz Methanol Masers

NASA Astrophysics Data System (ADS)

Hunter, T. R.; Brogan, C. L.; MacLeod, G. C.; Cyganowski, C. J.; Chibueze, J. O.; Friesen, R.; Hirota, T.; Smits, D. P.; Chandler, C. J.; Indebetouw, R.

2018-02-01

We report the first sub-arcsecond VLA imaging of 6 GHz continuum, methanol maser, and excited-state hydroxyl maser emission toward the massive protostellar cluster NGC 6334I following the recent 2015 outburst in (sub)millimeter continuum toward MM1, the strongest (sub)millimeter source in the protocluster. In addition to detections toward the previously known 6.7 GHz Class II methanol maser sites in the hot core MM2 and the UCHII region MM3 (NGC 6334F), we find new maser features toward several components of MM1, along with weaker features ∼1″ north, west, and southwest of MM1, and toward the nonthermal radio continuum source CM2. None of these areas have heretofore exhibited Class II methanol maser emission in three decades of observations. The strongest MM1 masers trace a dust cavity, while no masers are seen toward the strongest dust sources MM1A, 1B, and 1D. The locations of the masers are consistent with a combination of increased radiative pumping due to elevated dust grain temperature following the outburst, the presence of infrared photon propagation cavities, and the presence of high methanol column densities as indicated by ALMA images of thermal transitions. The nonthermal radio emission source CM2 (2″ north of MM1) also exhibits new maser emission from the excited 6.035 and 6.030 GHz OH lines. Using the Zeeman effect, we measure a line-of-sight magnetic field of +0.5 to +3.7 mG toward CM2. In agreement with previous studies, we also detect numerous methanol and excited OH maser spots toward the UCHII region MM3, with predominantly negative line-of-sight magnetic field strengths of ‑2 to ‑5 mG and an intriguing south–north field reversal.

RAiSE III: 3C radio AGN energetics and composition

NASA Astrophysics Data System (ADS)

Turner, Ross J.; Shabala, Stanislav S.; Krause, Martin G. H.

2018-03-01

Kinetic jet power estimates based exclusively on observed monochromatic radio luminosities are highly uncertain due to confounding variables and a lack of knowledge about some aspects of the physics of active galactic nuclei (AGNs). We propose a new methodology to calculate the jet powers of the largest, most powerful radio sources based on combinations of their size, lobe luminosity, and shape of their radio spectrum; this approach avoids the uncertainties encountered by previous relationships. The outputs of our model are calibrated using hydrodynamical simulations and tested against independent X-ray inverse-Compton measurements. The jet powers and lobe magnetic field strengths of radio sources are found to be recovered using solely the lobe luminosity and spectral curvature, enabling the intrinsic properties of unresolved high-redshift sources to be inferred. By contrast, the radio source ages cannot be estimated without knowledge of the lobe volumes. The monochromatic lobe luminosity alone is incapable of accurately estimating the jet power or source age without knowledge of the lobe magnetic field strength and size, respectively. We find that, on average, the lobes of the Third Cambridge Catalogue of Radio Sources (3C) have magnetic field strengths approximately a factor three lower than the equipartition value, inconsistent with equal energy in the particles and the fields at the 5σ level. The particle content of 3C radio lobes is discussed in the context of complementary observations; we do not find evidence favouring an energetically dominant proton population.

How Fred Hoyle Reconciled Radio Source Counts and the Steady State Cosmology

NASA Astrophysics Data System (ADS)

Ekers, Ron

2012-09-01

In 1969 Fred Hoyle invited me to his Institute of Theoretical Astronomy (IOTA) in Cambridge to work with him on the interpretation of the radio source counts. This was a period of extreme tension with Ryle just across the road using the steep slope of the radio source counts to argue that the radio source population was evolving and Hoyle maintaining that the counts were consistent with the steady state cosmology. Both of these great men had made some correct deductions but they had also both made mistakes. The universe was evolving, but the source counts alone could tell us very little about cosmology. I will try to give some indication of the atmosphere and the issues at the time and look at what we can learn from this saga. I will conclude by briefly summarising the exponential growth of the size of the radio source counts since the early days and ask whether our understanding has grown at the same rate.

Simultaneous X-Ray, Gamma-Ray, and Radio Observations of the Repeating Fast Radio Burst FRB 121102

NASA Astrophysics Data System (ADS)

Scholz, P.; Bogdanov, S.; Hessels, J. W. T.; Lynch, R. S.; Spitler, L. G.; Bassa, C. G.; Bower, G. C.; Burke-Spolaor, S.; Butler, B. J.; Chatterjee, S.; Cordes, J. M.; Gourdji, K.; Kaspi, V. M.; Law, C. J.; Marcote, B.; McLaughlin, M. A.; Michilli, D.; Paragi, Z.; Ransom, S. M.; Seymour, A.; Tendulkar, S. P.; Wharton, R. S.

2017-09-01

We undertook coordinated campaigns with the Green Bank, Effelsberg, and Arecibo radio telescopes during Chandra X-ray Observatory and XMM-Newton observations of the repeating fast radio burst FRB 121102 to search for simultaneous radio and X-ray bursts. We find 12 radio bursts from FRB 121102 during 70 ks total of X-ray observations. We detect no X-ray photons at the times of radio bursts from FRB 121102 and further detect no X-ray bursts above the measured background at any time. We place a 5σ upper limit of 3 × 10‑11 erg cm‑2 on the 0.5–10 keV fluence for X-ray bursts at the time of radio bursts for durations < 700 ms, which corresponds to a burst energy of 4 × 1045 erg at the measured distance of FRB 121102. We also place limits on the 0.5–10 keV fluence of 5 × 10‑10 and 1 × 10‑9 erg cm‑2 for bursts emitted at any time during the XMM-Newton and Chandra observations, respectively, assuming a typical X-ray burst duration of 5 ms. We analyze data from the Fermi Gamma-ray Space Telescope Gamma-ray Burst Monitor and place a 5σ upper limit on the 10–100 keV fluence of 4 × 10‑9 erg cm‑2 (5 × 1047 erg at the distance of FRB 121102) for gamma-ray bursts at the time of radio bursts. We also present a deep search for a persistent X-ray source using all of the X-ray observations taken to date and place a 5σ upper limit on the 0.5–10 keV flux of 4 × 10‑15 erg s‑1 cm‑2 (3 × 1041 erg s‑1 at the distance of FRB 121102). We discuss these non-detections in the context of the host environment of FRB 121102 and of possible sources of fast radio bursts in general.

Report on GMI Special Study #15: Radio Frequency Interference

NASA Technical Reports Server (NTRS)

Draper, David W.

2015-01-01

This report contains the results of GMI special study #15. An analysis is conducted to identify sources of radio frequency interference (RFI) to the Global Precipitation Measurement (GPM) Microwave Imager (GMI). The RFI impacts the 10 GHz and 18 GHz channels at both polarities. The sources of RFI are identified for the following conditions: over the water (including major inland water bodies) in the earth view, and over land in the earth view, and in the cold sky view. A best effort is made to identify RFI sources in coastal regions, with noted degradation of flagging performance due to the highly variable earth scene over coastal regions. A database is developed of such sources, including latitude, longitude, country and city of earth emitters, and position in geosynchronous orbit for space emitters. A description of the recommended approach for identifying the sources and locations of RFI in the GMI channels is given in this paper. An algorithm to flag RFI contaminated pixels which can be incorporated into the GMI Level 1Base/1B algorithms is defined, which includes Matlab code to perform the necessary flagging of RFI. A Matlab version of the code is delivered with this distribution.

H{sub 2}O Megamasers toward Radio-bright Seyfert 2 Nuclei

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

Zhang, J. S.; Liu, Z. W.; Henkel, C.

2017-02-20

Using the Effelsberg-100 m telescope, we perform a successful pilot survey on H{sub 2}O maser emission toward a small sample of radio-bright Seyfert 2 galaxies with a redshift larger than 0.04. The targets were selected from a large Seyfert 2 sample derived from the spectroscopic Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). One source, SDSS J102802.9+104630.4 ( z ∼ 0.0448), was detected four times during our observations, with a typical maser flux density of ∼30 mJy and a corresponding (very large) luminosity of ∼1135 L {sub ⊙}. The successful detection of this radio-bright Seyfert 2 and an additional tentativemore » detection support our previous statistical results that H{sub 2}O megamasers tend to arise from Seyfert 2 galaxies with large radio luminosity. The finding provides further motivation for an upcoming larger H{sub 2}O megamaser survey toward Seyfert 2s with particularly radio-bright nuclei with the basic goal to improve our understanding of the nuclear environment of active megamaser host galaxies.« less

Hubble Space Telescope NICMOS Polarization Measurements of OMC-1

NASA Technical Reports Server (NTRS)

Simpson, Janet P.; Colgan, Sean W. J.; Erickson, Edwin F.; Burton, Michael G.; Schultz, A. S. B.

2006-01-01

We present 2 micrometer polarization measurements of positions in the BN region of the Orion Molecular Cloud (OMC-1) made with NICMOS Camera 2 (0.2" resolution) on Hubble Space Telescope. Our goals are to seek the sources of heating for IRc2, 3, 4, and 7, identify possible young stellar objects (YSOs), and characterize the grain alignment in the dust clouds along the lines-of-sight to the stars. Our results are as follows: BN is approximately 29% polarized by dichroic absorption and appears to be the illuminating source for most of the nebulosity to its north and up to approximately 5" to its south. Although the stars are probably all polarized by dichroic absorption, there are a number of compact, but non-point-source, objects that could be polarized by a combination of both dichroic absorption and local scattering of star light. We identify several candidate YSOs, including an approximately edge-on bipolar YSO 8.7" east of BN, and a deeply-embedded IRc7, all of which are obviously self-luminous at mid-infrared wavelengths and may be YSOs. None of these is a reflection nebula illuminated by a star located near radio source I, as was previously suggested. Other IRc sources are clearly reflection nebulae: IRc3 appears to be illuminated by IRc2-B or a combination of the IRc2 sources, and IRc4 and IRc5 appear to be illuminated by an unseen star in the vicinity of radio source I, or by Star n or IRc2-A. Trends in the magnetic field direction are inferred from the polarization of the 26 stars that are bright enough to be seen as NICMOS point sources. Their polarization ranges from N less than or equal to 1% (all stars with this low polarization are optically visible) to greater than 40%. The most polarized star has a polarization position angle different from its neighbors by approximately 40 degrees, but in agreement with the grain alignment inferred from millimeter polarization measurements of the cold dust cloud in the southern part of OMC-1. The polarization position angle of another highly-polarized, probable star also requires a grain alignment and magnetic field orientation substantially different from the general magnetic field orientation of OMC-1.

Pulsar emission amplified and resolved by plasma lensing in an eclipsing binary.

PubMed

Main, Robert; Yang, I-Sheng; Chan, Victor; Li, Dongzi; Lin, Fang Xi; Mahajan, Nikhil; Pen, Ue-Li; Vanderlinde, Keith; van Kerkwijk, Marten H

2018-05-01

Radio pulsars scintillate because their emission travels through the ionized interstellar medium along multiple paths, which interfere with each other. It has long been realized that, independent of their nature, the regions responsible for the scintillation could be used as 'interstellar lenses' to localize pulsar emission regions 1,2 . Most such lenses, however, resolve emission components only marginally, limiting results to statistical inferences and detections of small positional shifts 3-5 . As lenses situated close to their source offer better resolution, it should be easier to resolve emission regions of pulsars located in high-density environments such as supernova remnants 6 or binaries in which the pulsar's companion has an ionized outflow. Here we report observations of extreme plasma lensing in the 'black widow' pulsar, B1957+20, near the phase in its 9.2-hour orbit at which its emission is eclipsed by its companion's outflow 7-9 . During the lensing events, the observed radio flux is enhanced by factors of up to 70-80 at specific frequencies. The strongest events clearly resolve the emission regions: they affect the narrow main pulse and parts of the wider interpulse differently. We show that the events arise naturally from density fluctuations in the outer regions of the outflow, and we infer a resolution of our lenses that is comparable to the pulsar's radius, about 10 kilometres. Furthermore, the distinct frequency structures imparted by the lensing are reminiscent of what is observed for the repeating fast radio burst FRB 121102, providing observational support for the idea that this source is observed through, and thus at times strongly magnified by, plasma lenses 10 .

Pulsar emission amplified and resolved by plasma lensing in an eclipsing binary

NASA Astrophysics Data System (ADS)

Main, Robert; Yang, I.-Sheng; Chan, Victor; Li, Dongzi; Lin, Fang Xi; Mahajan, Nikhil; Pen, Ue-Li; Vanderlinde, Keith; van Kerkwijk, Marten H.

2018-05-01

Radio pulsars scintillate because their emission travels through the ionized interstellar medium along multiple paths, which interfere with each other. It has long been realized that, independent of their nature, the regions responsible for the scintillation could be used as `interstellar lenses' to localize pulsar emission regions1,2. Most such lenses, however, resolve emission components only marginally, limiting results to statistical inferences and detections of small positional shifts3-5. As lenses situated close to their source offer better resolution, it should be easier to resolve emission regions of pulsars located in high-density environments such as supernova remnants6 or binaries in which the pulsar's companion has an ionized outflow. Here we report observations of extreme plasma lensing in the `black widow' pulsar, B1957+20, near the phase in its 9.2-hour orbit at which its emission is eclipsed by its companion's outflow7-9. During the lensing events, the observed radio flux is enhanced by factors of up to 70-80 at specific frequencies. The strongest events clearly resolve the emission regions: they affect the narrow main pulse and parts of the wider interpulse differently. We show that the events arise naturally from density fluctuations in the outer regions of the outflow, and we infer a resolution of our lenses that is comparable to the pulsar's radius, about 10 kilometres. Furthermore, the distinct frequency structures imparted by the lensing are reminiscent of what is observed for the repeating fast radio burst FRB 121102, providing observational support for the idea that this source is observed through, and thus at times strongly magnified by, plasma lenses10.

`Zwicky's Nonet': a compact merging ensemble of nine galaxies and 4C 35.06, a peculiar radio galaxy with dancing radio jets

NASA Astrophysics Data System (ADS)

Biju, K. G.; Bagchi, Joydeep; Ishwara-Chandra, C. H.; Pandey-Pommier, M.; Jacob, Joe; Patil, M. K.; Kumar, P. Sunil; Pandge, Mahadev; Dabhade, Pratik; Gaikwad, Madhuri; Dhurde, Samir; Abraham, Sheelu; Vivek, M.; Mahabal, Ashish A.; Djorgovski, S. G.

2017-10-01

We report the results of our radio, optical and infrared studies of a peculiar radio source 4C 35.06, an extended radio-loud active galactic nucleus (AGN) at the centre of galaxy cluster Abell 407 (z = 0.047). The central region of this cluster hosts a remarkably tight ensemble of nine galaxies, the spectra of which resemble those of passive red ellipticals, embedded within a diffuse stellar halo of ˜1 arcmin size. This system (named 'Zwicky's Nonet') provides unique and compelling evidence for a multiple-nucleus cD galaxy precursor. Multifrequency radio observations of 4C 35.06 with the Giant Meterwave Radio Telescope (GMRT) at 610, 235 and 150 MHz reveal a system of 400-kpc scale helically twisted and kinked radio jets and outer diffuse lobes. The outer extremities of jets contain extremely steep-spectrum (spectral index -1.7 to -2.5) relic/fossil radio plasma with a spectral age of a few ×(107-108) yr. Such ultra-steep spectrum relic radio lobes without definitive hotspots are rare and they provide an opportunity to understand the life cycle of relativistic jets and physics of black hole mergers in dense environments. We interpret our observations of this radio source in the context of growth of its central black hole, triggering of its AGN activity and jet precession, all possibly caused by galaxy mergers in this dense galactic system. A slow conical precession of the jet axis due to gravitational perturbation between interacting black holes is invoked to explain the unusual jet morphology.

A catalog of selected compact radio sources for the construction of an extragalactic radio/optical reference frame (Argue et al. 1984): Documentation for the machine-readable version

NASA Technical Reports Server (NTRS)

1990-01-01

This document describes the machine readable version of the Selected Compact Radio Source Catalog as it is currently being distributed from the international network of astronomical data centers. It is intended to enable users to read and process the computerized catalog. The catalog contains 233 strong, compact extragalactic radio sources having identified optical counterparts. The machine version contains the same data as the published catalog and includes source identifications, equatorial positions at J2000.0 and their mean errors, object classifications, visual magnitudes, redshift, 5-GHz flux densities, and comments.

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

Hu, B.; Menten, K. M.; Wu, Y.

We conducted Very Large Array C-configuration observations to measure positions and luminosities of Galactic Class II 6.7 GHz methanol masers and their associated ultra-compact H ii regions. The spectral resolution was 3.90625 kHz and the continuum sensitivity reached 45 μ Jy beam{sup −1}. We mapped 372 methanol masers with peak flux densities of more than 2 Jy selected from the literature. Absolute positions have nominal uncertainties of 0.″3. In this first paper on the data analysis, we present three catalogs; the first gives information on the strongest feature of 367 methanol maser sources, and the second provides information on allmore » detected maser spots. The third catalog presents derived data of the 127 radio continuum counterparts associated with maser sources. Our detection rate of radio continuum counterparts toward methanol masers is approximately one-third. Our catalogs list properties including distance, flux density, luminosity, and the distribution in the Galactic plane. We found no significant relationship between luminosities of masers and their associated radio continuum counterparts, however, the detection rate of radio continuum emission toward maser sources increases statistically with the maser luminosities.« less

Model interpretation of type III radio burst characteristics. I - Spatial aspects

NASA Technical Reports Server (NTRS)

Reiner, M. J.; Stone, R. G.

1988-01-01

The ways that the finite size of the source region and directivity of the emitted radiation modify the observed characteristics of type III radio bursts as they propagate through the interplanetary medium are investigated. A simple model that simulates the radio source region is developed to provide insight into the spatial behavior of the parameters that characterize radio bursts. The model is used to demonstrate that observed radio azimuths are systematically displaced from the geometric centroid of the exciter electron beam in such a way as to cause trajectories of the radio bursts to track back to the observer at low frequencies, rather than to follow expected Archimedean spiral-like paths. The source region model is used to investigate the spatial behavior of the peak intensities of radio bursts, and it is found that the model can qualitatively account for both the frequency dependence and the east-west asymmetry of the observed peak flux densities.

A generalized measurement equation and van Cittert-Zernike theorem for wide-field radio astronomical interferometry

NASA Astrophysics Data System (ADS)

Carozzi, T. D.; Woan, G.

2009-05-01

We derive a generalized van Cittert-Zernike (vC-Z) theorem for radio astronomy that is valid for partially polarized sources over an arbitrarily wide field of view (FoV). The classical vC-Z theorem is the theoretical foundation of radio astronomical interferometry, and its application is the basis of interferometric imaging. Existing generalized vC-Z theorems in radio astronomy assume, however, either paraxiality (narrow FoV) or scalar (unpolarized) sources. Our theorem uses neither of these assumptions, which are seldom fulfiled in practice in radio astronomy, and treats the full electromagnetic field. To handle wide, partially polarized fields, we extend the two-dimensional (2D) electric field (Jones vector) formalism of the standard `Measurement Equation' (ME) of radio astronomical interferometry to the full three-dimensional (3D) formalism developed in optical coherence theory. The resulting vC-Z theorem enables full-sky imaging in a single telescope pointing, and imaging based not only on standard dual-polarized interferometers (that measure 2D electric fields) but also electric tripoles and electromagnetic vector-sensor interferometers. We show that the standard 2D ME is easily obtained from our formalism in the case of dual-polarized antenna element interferometers. We also exploit an extended 2D ME to determine that dual-polarized interferometers can have polarimetric aberrations at the edges of a wide FoV. Our vC-Z theorem is particularly relevant to proposed, and recently developed, wide FoV interferometers such as Low Frequency Array (LOFAR) and Square Kilometer Array (SKA), for which direction-dependent effects will be important.

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

NASA Technical Reports Server (NTRS)

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

1992-01-01

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

Source structure errors in radio-interferometric clock synchronization for ten measured distributions

NASA Technical Reports Server (NTRS)

Thomas, J. B.

1981-01-01

The effects of source structure on radio interferometry measurements were investigated. The brightness distribution measurements for ten extragalactic sources were analyzed. Significant results are reported.

Cold gas and the disruptive effect of a young radio jet

NASA Astrophysics Data System (ADS)

Morganti, R.; Oosterloo, T.; Maccagni, F. M.; Geréb, K.; Oonk, J. B. R.; Tadhunter, C. N.

2016-02-01

Newly born and young radio sources are in a delicate phase of their life. Their jets are fighting their way through the surrounding gaseous medium, strongly experiencing this interaction while, at the same time, impacting and affecting the interstellar medium (ISM). Quantifying this interplay has far reaching implications: the rate of occurrence and the magnitude of the interaction between radio jets and ISM can have consequences for the evolution of the host galaxy. Despite the hostile conditions, cold gas - neutral atomic hydrogen and molecular - has been often found in these objects and can be also associated to fast outflows. Here we present the results from two studies of H I and molecular gas illustrating what can be learned from these phases of the gas. We first describe a statistical study of the occurrence and kinematics of H I observed in absorption with the Westerbork Synthesis Radio telescope. This allows a comparison between the properties of the gas in extended and in compact/young radio sources. The study shows that the young radio sources not only have an higher detection rate of H I, but also systematically broader and more asymmetric H I profiles, most of them blueshifted. This supports the idea that we are looking at young radio jets making their way through the surrounding ISM, which also appears to be, on average, richer in gas than in evolved radio sources. Signatures of the impact of the jet are seen in the kinematics of the gas, but the resulting outflows may be characteristic of only the initial phase of the radio source evolution. However, even among the young sources, we identify a population that remains undetected in H I even after stacking their profiles. Orientation effects can only partly explain the result. These objects either are genuinely gas-poor or have different conditions of the medium, e.g. higher spin temperature. The upcoming blind H I surveys which are about to start with large-field-of-view radio facilities (i.e. Apertif at the WSRT and ASKAP) will allow us to expand the statistics and reach even higher sensitivity with stacking techniques. We further present the case of the radio source IC 5063 where we have used the molecular gas observed with ALMA to trace in detail the jet impacting the ISM. The kinematics of the cold, molecular gas co-spatial with the radio plasma shows this process in action. The ALMA data reveal a fast outflow of molecular gas extending along the entire radio jet (˜1 kpc), with the highest outflow velocities at the location of the brighter hot-spot. The results can be described by a scenario of a radio plasma jet expanding into a clumpy medium, interacting directly with the clouds and inflating a cocoon that drives a lateral outflow into the ISM. This is consistent with the scenario proposed by numerical simulations for the expansion of a young radio jet, confirming the disruptive effect the radio plasma jet can have. Following this case, more ALMA observations of nearby young radio sources will be able to confirm if this process is common, as expected, in the initial phase of the evolution of the radio source.

The changing source of X-ray reflection in the radio-intermediate Seyfert 1 galaxy III Zw 2

NASA Astrophysics Data System (ADS)

Gonzalez, A. G.; Waddell, S. G. H.; Gallo, L. C.

2018-03-01

We report on X-ray observations of the radio-intermediate, X-ray bright Seyfert 1 galaxy, III Zw 2, obtained with XMM-Newton, Suzaku, and Swift over the past 17 yr. The source brightness varies significantly over yearly time-scales, but more modestly over periods of days. Pointed observations with XMM-Newton in 2000 and Suzaku in 2011 show spectral differences despite comparable X-ray fluxes. The Suzaku spectra are consistent with a power-law continuum and a narrow Gaussian emission feature at ˜6.4 keV, whereas the earlier XMM-Newton spectrum requires a broader Gaussian profile and soft-excess below ˜2 keV. A potential interpretation is that the primary power-law emission, perhaps from a jet base, preferentially illuminates the inner accretion disc in 2000, but the distant torus in 2011. The interpretation could be consistent with the hypothesized precessing radio jet in III Zw 2 that may have originated from disc instabilities due to an ongoing merging event.

Superconducting magnets for the RAON electron cyclotron resonance ion source.

PubMed

Choi, S; Kim, Y; Hong, I S; Jeon, D

2014-02-01

The RAON linear accelerator of Rare Isotope Science Project has been developed since 2011, and the superconducting magnet for ECRIS was designed. The RAON ECR ion source was considered as a 3rd generation source. The fully superconducting magnet has been designed for operating using 28 GHz radio frequency. The RAON ECRIS operates in a minimum B field configuration which means that a magnetic sextupole field for radial confinement is superimposed with a magnetic mirror field for axial confinement. The highest field strength reaches 3.5 T on axis and 2 T at the plasma chamber wall for operating frequency up to 28 GHz. In this paper, the design results are presented of optimized superconducting magnet consisting of four solenoids and sextupole. The prototype magnet for ECRIS was fabricated and tested to verify the feasibility of the design. On the basis of test results, a fully superconducting magnet will be fabricated and tested.

Average Heating Rate of Hot Atmospheres in Distant Galaxy Clusters by Radio AGN: Evidence for Continuous AGN Heating

NASA Astrophysics Data System (ADS)

Ma, Cheng-Jiun; McNamara, B.; Nulsen, P.; Schaffer, R.

2011-09-01

X-ray observations of nearby clusters and galaxies have shown that energetic feedback from AGN is heating hot atmospheres and is probably the principal agent that is offsetting cooling flows. Here we examine AGN heating in distant X-ray clusters by cross correlating clusters selected from the 400 Square Degree X-ray Cluster survey with radio sources in the NRAO VLA Sky Survey. The jet power for each radio source was determined using scaling relations between radio power and cavity power determined for nearby clusters, groups, and galaxies with atmospheres containing X-ray cavities. Roughly 30% of the clusters show radio emission above a flux threshold of 3 mJy within the central 250 kpc that is presumably associated with the brightest cluster galaxy. We find no significant correlation between radio power, hence jet power, and the X-ray luminosities of clusters in redshift range 0.1 -- 0.6. The detection frequency of radio AGN is inconsistent with the presence of strong cooling flows in 400SD, but cannot rule out the presence of weak cooling flows. The average jet power of central radio AGN is approximately 2 10^{44} erg/s. The jet power corresponds to an average heating of approximately 0.2 keV/particle for gas within R_500. Assuming the current AGN heating rate remained constant out to redshifts of about 2, these figures would rise by a factor of two. Our results show that the integrated energy injected from radio AGN outbursts in clusters is statistically significant compared to the excess entropy in hot atmospheres that is required for the breaking of self-similarity in cluster scaling relations. It is not clear that central AGN in 400SD clusters are maintained by a self-regulated feedback loop at the base of a cooling flow. However, they may play a significant role in preventing the development of strong cooling flows at early epochs.

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

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

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

2016-02-01

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

Well-defined EUV wave associated with a CME-driven shock

NASA Astrophysics Data System (ADS)

Cunha-Silva, R. D.; Selhorst, C. L.; Fernandes, F. C. R.; Oliveira e Silva, A. J.

2018-05-01

Aims: We report on a well-defined EUV wave observed by the Extreme Ultraviolet Imager (EUVI) on board the Solar Terrestrial Relations Observatory (STEREO) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The event was accompanied by a shock wave driven by a halo CME observed by the Large Angle and Spectrometric Coronagraph (LASCO-C2/C3) on board the Solar and Heliospheric Observatory (SOHO), as evidenced by the occurrence of type II bursts in the metric and dekameter-hectometric wavelength ranges. We investigated the kinematics of the EUV wave front and the radio source with the purpose of verifying the association between the EUV wave and the shock wave. Methods: The EUV wave fronts were determined from the SDO/AIA images by means of two appropriate directions (slices). The heights (radial propagation) of the EUV wave observed by STEREO/EUVI and of the radio source associated with the shock wave were compared considering the whole bandwidth of the harmonic lane of the radio emission, whereas the speed of the shock was estimated using the lowest frequencies of the harmonic lane associated with the undisturbed corona, using an appropriate multiple of the Newkirk (1961, ApJ, 133, 983) density model and taking into account the H/F frequency ratio fH/fF = 2. The speed of the radio source associated with the interplanetary shock was determined using the Mann et al. (1999, A&A, 348, 614) density model. Results: The EUV wave fronts determined from the SDO/AIA images revealed the coexistence of two types of EUV waves, a fast one with a speed of 560 km s-1, and a slower one with a speed of 250 km s-1, which corresponds approximately to one-third of the average speed of the radio source ( 680 km s-1). The radio signature of the interplanetary shock revealed an almost constant speed of 930 km s-1, consistent with the linear speed of the halo CME (950 km s-1) and with the values found for the accelerating coronal shock ( 535-823 km s-1), taking into account the gap between the radio emissions.

An image-based search for pulsars among Fermi unassociated LAT sources

NASA Astrophysics Data System (ADS)

Frail, D. A.; Ray, P. S.; Mooley, K. P.; Hancock, P.; Burnett, T. H.; Jagannathan, P.; Ferrara, E. C.; Intema, H. T.; de Gasperin, F.; Demorest, P. B.; Stovall, K.; McKinnon, M. M.

2018-03-01

We describe an image-based method that uses two radio criteria, compactness, and spectral index, to identify promising pulsar candidates among Fermi Large Area Telescope (LAT) unassociated sources. These criteria are applied to those radio sources from the Giant Metrewave Radio Telescope all-sky survey at 150 MHz (TGSS ADR1) found within the error ellipses of unassociated sources from the 3FGL catalogue and a preliminary source list based on 7 yr of LAT data. After follow-up interferometric observations to identify extended or variable sources, a list of 16 compact, steep-spectrum candidates is generated. An ongoing search for pulsations in these candidates, in gamma rays and radio, has found 6 ms pulsars and one normal pulsar. A comparison of this method with existing selection criteria based on gamma-ray spectral and variability properties suggests that the pulsar discovery space using Fermi may be larger than previously thought. Radio imaging is a hitherto underutilized source selection method that can be used, as with other multiwavelength techniques, in the search for Fermi pulsars.

The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry

NASA Astrophysics Data System (ADS)

Fey, A. L.; Gordon, D.; Jacobs, C. S.; Ma, C.; Gaume, R. A.; Arias, E. F.; Bianco, G.; Boboltz, D. A.; Böckmann, S.; Bolotin, S.; Charlot, P.; Collioud, A.; Engelhardt, G.; Gipson, J.; Gontier, A.-M.; Heinkelmann, R.; Kurdubov, S.; Lambert, S.; Lytvyn, S.; MacMillan, D. S.; Malkin, Z.; Nothnagel, A.; Ojha, R.; Skurikhina, E.; Sokolova, J.; Souchay, J.; Sovers, O. J.; Tesmer, V.; Titov, O.; Wang, G.; Zharov, V.

2015-08-01

We present the second realization of the International Celestial Reference Frame (ICRF2) at radio wavelengths using nearly 30 years of Very Long Baseline Interferometry observations. ICRF2 contains precise positions of 3414 compact radio astronomical objects and has a positional noise floor of ∼40 μas and a directional stability of the frame axes of ∼10 μas. A set of 295 new “defining” sources was selected on the basis of positional stability and the lack of extensive intrinsic source structure. The positional stability of these 295 defining sources and their more uniform sky distribution eliminates the two greatest weaknesses of the first realization of the International Celestial Reference Frame (ICRF1). Alignment of ICRF2 with the International Celestial Reference System was made using 138 positionally stable sources common to both ICRF2 and ICRF1. The resulting ICRF2 was adopted by the International Astronomical Union as the new fundamental celestial reference frame, replacing ICRF1 as of 2010 January 1.

Forthcoming Occultations of Astrometric Radio Sources by Planets

NASA Technical Reports Server (NTRS)

L'vov, Victor; Malkin, Zinovy; Tsekmeister, Svetlana

2010-01-01

Astrometric observations of radio source occultations by solar system bodies may be of large interest for testing gravity theories, dynamical astronomy, and planetary physics. In this paper, we present an updated list of the occultations of astrometric radio sources by planets expected in the coming years. Such events, like solar eclipses, generally speaking can only be observed in a limited region. A map of the shadow path is provided for the events that will occurr in regions with several VLBI stations and hence will be the most interesting for radio astronomy experiments.

Radio and gamma-ray properties of extragalactic jets from the TANAMI sample

DOE PAGES

Böck, M.; Kadler, M.; Müller, C.; ...

2016-05-04

The TANAMI program has been observing parsec-scale radio jets of southern (declination south of - 30°) γ-ray bright AGN, simultaneously with Fermi/LAT monitoring of their γ-ray emission, via high-resolution radio imaging with Very Long Baseline Interferometry techniques. In this paper, we present the radio and γ-rayproperties of the TANAMI sources based on one year of contemporaneous TANAMI and Fermi/LAT data. A large fraction (72%) of the TANAMI sample can be associated with bright γ-ray sources for this time range. Association rates differ for different optical classes with all BL Lacs, 76% of quasars, and just 17% of galaxies detected bymore » the LAT. Upper limits were established on the γ-ray flux from TANAMI sources not detected by LAT. This analysis led to the identification of three new Fermi sources whose detection was later confirmed. The γ-ray and radio luminosities are related by L γ ∝ L r 0.89±0.04. The brightness temperatures of the radio cores increase with the average γ-ray luminosity and the presence of brightness temperatures above the inverse Compton limit implies strong Doppler boosting in those sources. The undetected sources have lower γ/radio luminosity ratios and lower contemporaneous brightness temperatures. Finally, unless the Fermi/LAT-undetected blazars are much γ-ray-fainter than the Fermi/LAT-detected sources, their γ-ray luminosity should not be significantly lower than the upper limits calculated here.« less

Direction-dependent Corrections in Polarimetric Radio Imaging. I. Characterizing the Effects of the Primary Beam on Full-Stokes Imaging

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

Jagannathan, P.; Bhatnagar, S.; Rau, U.

Next generation radio telescope arrays are being designed and commissioned to accurately measure polarized intensity and rotation measures (RMs) across the entire sky through deep, wide-field radio interferometric surveys. Radio interferometer dish antenna arrays are affected by direction-dependent (DD) gains due to both instrumental and atmospheric effects. In this paper, we demonstrate the effect of DD errors of the parabolic dish antenna array on the measured polarized intensities of radio sources in interferometric images. We characterize the extent of polarimetric image degradation due to the DD gains through wide-band VLA simulations of representative point-source simulations of the radio sky atmore » L band (1–2 GHz). We show that at the 0.5 gain level of the primary beam there is significant flux leakage from Stokes I to Q , U amounting to 10% of the total intensity. We further demonstrate that while the instrumental response averages down for observations over large parallactic angle intervals, full-polarization DD correction is required to remove the effects of DD leakage. We also explore the effect of the DD beam on the RM signals and show that while the instrumental effect is primarily centered around 0 rad-m{sup −2}, the effect is significant over a broad range of RM requiring full polarization DD correction to accurately reconstruct the RM synthesis signal.« less

Investigation of broadband digital predistortion for broadband radio over fiber transmission systems

NASA Astrophysics Data System (ADS)

Zhang, Xiupu; Liu, Taijun; Shen, Dongya

2016-12-01

In future broadband cloud radio access networks (C-RAN), front-haul transmission systems play a significant role in performance and cost of C-RAN. Broadband and high linearity radio over fiber (RoF) transmission systems are considered a promising solution for the front-haul. Digital linearization is one possible solution for RoF front-haul. In this paper, we investigate RF domain digital predistortion (DPD) linearization for broadband RoF front-haul. The implemented DPD is first investigated in 2.4 GHz WiFi over fiber transmission systems at 36 Mb/s, and more than 8-dB and 5.6-dB improvements of error vector magnitude (EVM) are achieved in back to back (BTB) and after 10 km single mode fiber (SMF) transmission. Further, both WiFi and ultra wide band (UWB) wireless signals are transmitted together, in which the DPD has linearization bandwidth of 2.4 GHz. It is shown that the implemented DPD leads to EVM improvements of 4.5-dB (BTB) and 3.1-dB (10 km SMF) for the WiFi signal, and 4.6-dB (BTB) and 4-dB (10 km SMF) for the broadband UWB signal.

VizieR Online Data Catalog: X-ray+Radio sources in XBootes (El Bouchefry, 2009)

NASA Astrophysics Data System (ADS)

El Bouchefry, K.

2010-08-01

The radio data are from the 2002 version of the FIRST VLA catalogue (Becker et al., 1995, See Cat. VIII/71), and it is derived from 1993 through 2002 observations. The X-ray data (Kenter et al. 2005, Cat. J/ApJS/161/9; Murray et al. 2005ApJS..161....1M) used in this paper are from the Chandra XBootes surveys. The XBootes catalogue contains ~3213 X-ray point sources and is publicly available through the National Optical Astronomy Observatory (NOAO) Deep Wide Field Survey (NDWFS) homepage (http://www.noao.edu/noao/noaodeep/XBootesPublic/index.html) The NDWFS is a deep multiband imaging (Bw, R, I, J, H, K) designed to study the formation and evolution of large-scale structures (Jannuzi et al., 1999, BAAS, 31, 1392; Brown et al., 2003ApJ...597..225B). (1 data file).

The first catalog of active galactic nuclei detected by the FERMI large area telescope

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2010-04-29

Here, we present the first catalog of active galactic nuclei (AGNs) detected by the Large Area Telescope (LAT), corresponding to 11 months of data collected in scientific operation mode. The First LAT AGN Catalog (1LAC) includes 671 γ-ray sources located at high Galactic latitudes (|b|>10°) that are detected with a test statistic greater than 25 and associated statistically with AGNs. Some LAT sources are associated with multiple AGNs, and consequently, the catalog includes 709 AGNs, comprising 300 BL Lacertae objects, 296 flat-spectrum radio quasars, 41 AGNs of other types, and 72 AGNs of unknown type. We also classify the blazarsmore » based on their spectral energy distributions as archival radio, optical, and X-ray data permit. In addition to the formal 1LAC sample, we provide AGN associations for 51 low-latitude LAT sources and AGN "affiliations" (unquantified counterpart candidates) for 104 high-latitude LAT sources without AGN associations. The overlap of the 1LAC with existing γ-ray AGN catalogs (LBAS, EGRET, AGILE, Swift, INTEGRAL, TeVCat) is briefly discussed. Various properties—such as γ-ray fluxes and photon power-law spectral indices, redshifts, γ-ray luminosities, variability, and archival radio luminosities—and their correlations are presented and discussed for the different blazar classes. Lastly, we compare the 1LAC results with predictions regarding the γ-ray AGN populations, and we comment on the power of the sample to address the question of the blazar sequence.« less

Population Studies of Radio and Gamma-Ray Pulsars

NASA Technical Reports Server (NTRS)

Harding, Alice K; Gonthier, Peter; Coltisor, Stefan

2004-01-01

Rotation-powered pulsars are one of the most promising candidates for at least some of the 40-50 EGRET unidentified gamma-ray sources that lie near the Galactic plane. Since the end of the EGRO mission, the more sensitive Parkes Multibeam radio survey has detected mere than two dozen new radio pulsars in or near unidentified EGRET sources, many of which are young and energetic. These results raise an important question about the nature of radio quiescence in gamma-ray pulsars: is the non-detection of radio emission a matter of beaming or of sensitivity? The answer is very dependent on the geometry of the radio and gamma-ray beams. We present results of a population synthesis of pulsars in the Galaxy, including for the first time the full geometry of the radio and gamma-ray beams. We use a recent empirically derived model of the radio emission and luminosity, and a gamma-ray emission geometry and luminosity derived theoretically from pair cascades in the polar slot gap. The simulation includes characteristics of eight radio surveys of the Princeton catalog plus the Parkes MB survey. Our results indicate that EGRET was capable of detecting several dozen pulsars as point sources, with the ratio of radio-loud to radio-quiet gamma-ray pulsars increasing significantly to about ten to one when the Parkes Survey is included. Polar cap models thus predict that many of the unidentified EGRET sources could be radio-loud gamma- ray pulsars, previously undetected as radio pulsars due to distance, large dispersion and lack of sensitivity. If true, this would make gamma-ray telescopes a potentially more sensitive tool for detecting distant young neutron stars in the Galactic plane.

A symbiotic approach to SETI observations: use of maps from the Westerbork Synthesis Radio Telescope

NASA Technical Reports Server (NTRS)

Tarter, J. C.; Israel, F. P.

1982-01-01

High spatial resolution continuum radio maps produced by the Westerbork Synthesis Radio Telescope (WSRT) of The Netherlands at frequencies near the 21 cm HI line have been examined for anomalous sources of emmission coincident with the locations of nearby bright stars. From a total of 542 stellar positions investigated, no candidates for radio stars or ETI signals were discovered to formal limits on the minimum detectable signal ranging from 7.7 x 10(-22) W/m2 to 6.4 x 10(-24) W/m2. This preliminary study has verified that data collected by radio astronomers at large synthesis arrays can profitably be analysed for SETI signals (in a non-interfering manner) provided only that the data are available in the form of a more or less standard two dimensional map format.

A symbiotic approach to SETI observations: use of maps from the Westerbork Synthesis Radio Telescope.

PubMed

Tarter, J C; Israel, F P

1982-01-01

High spatial resolution continuum radio maps produced by the Westerbork Synthesis Radio Telescope (WSRT) of The Netherlands at frequencies near the 21 cm HI line have been examined for anomalous sources of emmission coincident with the locations of nearby bright stars. From a total of 542 stellar positions investigated, no candidates for radio stars or ETI signals were discovered to formal limits on the minimum detectable signal ranging from 7.7 x 10(-22) W/m2 to 6.4 x 10(-24) W/m2. This preliminary study has verified that data collected by radio astronomers at large synthesis arrays can profitably be analysed for SETI signals (in a non-interfering manner) provided only that the data are available in the form of a more or less standard two dimensional map format.

A decade of Rossi X-ray Timing Explorer Seyfert observations: An RXTE Seyfert spectral database

NASA Astrophysics Data System (ADS)

Mattson, Barbara Jo

2008-10-01

With over forty years of X-ray observations, we should have a grasp on the X- ray nature of active galactic nuclei (AGN). The unification model of Antonucci and Miller (1985) offered a context for understanding observations by defining a "typical" AGN geometry, with observed spectral differences explained by line- of-sight effects. However, the emerging picture is that the central AGN is more complex than unification alone can describe. We explore the unified model with a systematic X-ray spectral study of bright Seyfert galaxies observed by the Rossi X-Ray Timing Explorer (RXTE) over its first 10 years. We develop a spectral-fit database of 821 time-resolved spectra from 39 Seyfert galaxies fitted to a model describing the effects of an X-ray power-law spectrum reprocessed and absorbed by material in the central AGN region. We observe a relationship between radio and X-ray properties for Seyfert 1s, with the spectral parameters differing between radio-loud and radio-quiet Seyfert 1s. We also find a complex relationship between the Fe K equivalent width ( EW ) and the power-law photon index (Gamma) for the Seyfert 1s, with a correlation for the radio-loud sources and an anti-correlation for the radio- quiet sources. These results can be explained if X-rays from the relativistic jet in radio-loud sources contribute significantly to the observed spectrum. We observe scatter in the EW-Gamma relationship for the Seyfert 2s, suggesting complex environments that unification alone cannot explain. We see a strong correlation between Gamma and the reflection fraction ( R ) in the Seyfert 1 and 2 samples, but modeling degeneracies are present, so this relationship cannot be trusted as instructive of the AGN physics. For the Seyfert 1 sample, we find an anticorrelation between EW and the 2 to 10 keV luminosity ( L x ), also known as the X-ray Baldwin effect. This may suggest that higher luminosity sources contain less material or may be due to a time-lag effect. We do not observe the previously reported relationship between Gamma and the ratio of L x to the Eddington luminosity.

Four hot DOGs in the microwave

NASA Astrophysics Data System (ADS)

Frey, Sándor; Paragi, Zsolt; Gabányi, Krisztina Éva; An, Tao

2016-01-01

Hot dust-obscured galaxies (hot DOGs) are a rare class of hyperluminous infrared galaxies identified with the Wide-field Infrared Survey Explorer (WISE) satellite. The majority of them are at high redshifts (z ˜ 2-3), at the peak epoch of star formation in the Universe. Infrared, optical, radio, and X-ray data suggest that hot DOGs contain heavily obscured, extremely luminous active galactic nuclei (AGN). This class may represent a short phase in the life of the galaxies, signifying the transition from starburst- to AGN-dominated phases. Hot DOGs are typically radio-quiet, but some of them show mJy-level emission in the radio (microwave) band. We observed four hot DOGs using the technique of very long baseline interferometry (VLBI). The 1.7 GHz observations with the European VLBI Network (EVN) revealed weak radio features in all sources. The radio is free from dust obscuration and, at such high redshifts, VLBI is sensitive only to compact structures that are characteristic of AGN activity. In two cases (WISE J0757+5113, WISE J1603+2745), the flux density of the VLBI-detected components is much smaller than the total flux density, suggesting that ˜70-90 per cent of the radio emission, while still dominated by AGN, originates from angular scales larger than that probed by the EVN. The source WISE J1146+4129 appears a candidate compact symmetric object, and WISE J1814+3412 shows a 5.1 kpc double structure, reminiscent of hotspots in a medium-sized symmetric object. Our observations support that AGN residing in hot DOGs may be genuine young radio sources where starburst and AGN activities coexist.

The multiple infrared source GL 437

NASA Technical Reports Server (NTRS)

Wynn-Williams, C. G.; Becklin, E. E.; Beichman, C. A.; Capps, R.; Shakeshaft, J. R.

1981-01-01

Infrared and radio continuum observations of the multiple infrared source GL 437 show that it consists of a compact H II region plus two objects which are probably early B stars undergoing rapid mass loss. The group of sources appears to be a multiple system of young stars that have recently emerged from the near side of a molecular cloud. Emission in the unidentified 3.3 micron feature is associated with, but more extended than, the emission from the compact H II region; it probably arises from hot dust grains at the interface between the H II region and the molecular cloud.

THE FIRST BENT DOUBLE LOBE RADIO SOURCE IN A KNOWN CLUSTER FILAMENT: CONSTRAINTS ON THE INTRAFILAMENT MEDIUM

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

Edwards, Louise O. V.; Fadda, Dario; Frayer, David T., E-mail: louise@ipac.caltech.ed

2010-12-01

We announce the first discovery of a bent double lobe radio source (DLRS) in a known cluster filament. The bent DLRS is found at a distance of 3.4 Mpc from the center of the rich galaxy cluster, A1763. We derive a bend angle {alpha} = 25{sup 0}, and infer that the source is most likely seen at a viewing angle of {Phi} = 10{sup 0}. From measuring the flux in the jet between the core and further lobe and assuming a spectral index of 1, we calculate the minimum pressure in the jet, (8.0 {+-} 3.2) x 10{sup -13} dynmore » cm{sup -2}, and derive constraints on the intrafilament medium (IFM) assuming the bend of the jet is due to ram pressure. We constrain the IFM to be between (1-20) x 10{sup -29} gm cm{sup -3}. This is consistent with recent direct probes of the IFM and theoretical models. These observations justify future searches for bent double lobe radio sources located several megaparsecs from cluster cores, as they may be good markers of super cluster filaments.« less

Search for X-ray jets from high redshift radio sources.

NASA Astrophysics Data System (ADS)

Schwartz, Daniel A.; Cheung, Teddy; Gobeille, Doug; Marshall, Herman L.; Migliori, Giulia; Siemiginowska, Aneta; Wardle, John F. C.; Worrall, Diana M.; Birkinshaw, Mark

2018-06-01

We are conducting a Chandra "snapshot" survey of 14 radio quasars at redshifts z>3. These are selected to have one sided, arc-sec scale structure, either a jet or lobe, and come from a complete, objectively-defined sample of sources with radio flux density > 70 mJy, and with a spectroscopic redshift from the SDSS. Our objectives are to find X-ray emitting jets, compare the X-ray and radio morphology, and detect X-ray emission arising from inverse Compton scattering of the cosmic microwave background even for those cases where the radio emission is no longer detectable. For this meeting, we expect 5 of the 14 sources to have been observed.

Galactic Starburst NGC 3603 from X-Rays to Radio

NASA Technical Reports Server (NTRS)

Moffat, A. F. J.; Corcoran, M. F.; Stevens, I. R.; Skalkowski, G.; Marchenko, S. V.; Muecke, A.; Ptak, A.; Koribalski, B. S.; Brenneman, L.; Mushotzky, R.;

FR0CAT: a FIRST catalog of FR 0 radio galaxies

NASA Astrophysics Data System (ADS)

Baldi, R. D.; Capetti, A.; Massaro, F.

2018-01-01

With the aim of exploring the properties of the class of FR 0 radio galaxies, we selected a sample of 108 compact radio sources, called FR0CAT, by combining observations from the NVSS, FIRST, and SDSS surveys. We included in the catalog sources with redshift ≤0.05, with a radio size ≲5 kpc, and with an optical spectrum characteristic of low-excitation galaxies. Their radio luminosities at 1.4 GHz are in the range 1038 ≲ νL1.4 ≲ 1040 erg s-1. The FR0CAT hosts are mostly (86%) luminous (-21 ≳ Mr ≳ -23) red early-type galaxies with black hole masses 108 ≲ MBH ≲ 109M⊙. These properties are similar to those seen for the hosts of FR I radio galaxies, but they are on average a factor 1.6 less massive. The number density of FR0CAT sources is 5 times higher than that of FR Is, and thus they represent the dominant population of radio sources in the local Universe. Different scenarios are considered to account for the smaller sizes and larger abundance of FR 0s with respect to FR Is. An age-size scenario that considers FR 0s as young radio galaxies that will all eventually evolve into extended radio sources cannot be reconciled with the large space density of FR 0s. However, the radio activity recurrence, with the duration of the active phase covering a wide range of values and with short active periods strongly favored with respect to longer ones, might account for their large density number. Alternatively, the jet properties of FR 0s might be intrinsically different from those of the FR Is, the former class having lower bulk Lorentz factors, possibly due to lower black hole spins. Our study indicates that FR 0s and FR I/IIs can be interpreted as two extremes of a continuous population of radio sources that is characterized by a broad distribution of sizes and luminosities of their extended radio emission, but shares a single class of host galaxies.

Improvement in the transport critical current density and microstructure of isotopic Mg11B2 monofilament wires by optimizing the sintering temperature

PubMed Central

Qiu, Wenbin; Jie, Hyunseock; Patel, Dipak; Lu, Yao; Luzin, Vladimir; Devred, Arnaud; Somer, Mehmet; Shahabuddin, Mohammed; Kim, Jung Ho; Ma, Zongqing; Dou, Shi Xue; Hossain, Md. Shahriar Al

2016-01-01

Superconducting wires are widely used in fabricating magnetic coils in fusion reactors. In consideration of the stability of 11B against neutron irradiation and lower induced radio-activation properties, MgB2 superconductor with 11B serving as boron source is an alternative candidate to be used in fusion reactor with severe irradiation environment. In present work, a batch of monofilament isotopic Mg11B2 wires with amorphous 11B powder as precursor were fabricated using powder-in-tube (PIT) process at different sintering temperature, and the evolution of their microstructure and corresponding superconducting properties was systemically investigated. Accordingly, the best transport critical current density (Jc) = 2 × 104 A/cm2 was obtained at 4.2 K and 5 T, which is even comparable to multi-filament Mg11B2 isotope wires reported in other work. Surprisingly, transport Jc vanished in our wire which was heat-treated at excessively high temperature (800 °C). Combined with microstructure observation, it was found that lots of big interconnected microcracks and voids that can isolate the MgB2 grains formed in this whole sample, resulting in significant deterioration in inter-grain connectivity. The results can be a constructive guide in fabricating Mg11B2 wires to be used as magnet coils in fusion reactor systems such as ITER-type tokamak magnet. PMID:27824144

The February 15 2011 CME-CME interaction and possibly associated radio emission

NASA Astrophysics Data System (ADS)

Magdalenic, Jasmina; Temmer, Manuela; Krupar, Vratislav; Marque, Christophe; Veronig, Astrid; Eastwood, Jonathan

2017-04-01

On February 15, 2011 a particular, continuum-like radio emission was observed by STEREO WAVES and WIND WAVES spacecraft. The radio event appeared to be associated with the complex interaction of two coronal mass ejections (CMEs) successively launched (February 14 and February 15) from the same active region. Although the CME-CME interaction was widely studied (e.g. Temmer et al., 2014, Maricic et al., 2014, Mishra & Srivastava, 2014) none of the analyses confirmed an association with the continuum-like radio emission. The usual method of establishing temporal coincidence of radio continuum and a CME-CME interaction is not applicable in this event due to a complex and long-lasting interaction of the CMEs. Therefore, we performed radio triangulation studies (see also Magdalenic et al., 2014) which provided us with the 3D source positions of the radio emission. Comparison of the positions of radio sources and the reconstructed positions of the interacting CMEs, shows that the source position of the continuum-like radio emission is about 0.5 AU away from the interacting CMEs. We can therefore concluded that, in this event, the continuum-like emission is not the radio signature of the CME-CME interaction.

Theoretical scaling law of coronal magnetic field and electron power-law index in solar microwave burst sources

NASA Astrophysics Data System (ADS)

Huang, Y.; Song, Q. W.; Tan, B. L.

2018-04-01

It is first proposed a theoretical scaling law respectively for the coronal magnetic field strength B and electron power-law index δ versus frequency and coronal height in solar microwave burst sources. Based on the non-thermal gyro-synchrotron radiation model (Ramaty in Astrophys. J. 158:753, 1969), B and δ are uniquely solved by the observable optically-thin spectral index and turnover (peak) frequency, the other parameters (plasma density, temperature, view angle, low and high energy cutoffs, etc.) are relatively insensitive to the calculations, thus taken as some typical values. Both of B and δ increase with increasing of radio frequency but with decreasing of coronal height above photosphere, and well satisfy a square or cubic logarithmic fitting.

Chandra Observation of the WAT Radio Source/ICM Interaction in Abell 623

NASA Astrophysics Data System (ADS)

Anand, Gagandeep; Blanton, Elizabeth L.; Randall, Scott W.; Paterno-Mahler, Rachel; Douglass, Edmund

2017-01-01

Galaxy clusters are important objects for studying the physics of the intracluster medium (ICM), galaxy formation and evolution, and cosmological parameters. Clusters containing wide-angle tail (WAT) radio sources are particularly valuable for studies of the interaction between these sources and the surrounding ICM. These sources are thought to form when the ram pressure from the ICM caused by the relative motion between the host radio galaxy and the cluster bends the radio lobes into a distinct wide-angle morphology. We present our results from the analysis of a Chandra observation of the nearby WAT hosting galaxy cluster Abell 623. A clear decrement in X-ray emission is coincident with the southern radio lobe, consistent with being a cavity carved out by the radio source. We present profiles of surface brightness, temperature, density, and pressure and find evidence for a possible shock. Based on the X-ray pressure in the vicinity of the radio lobes and assumptions about the content of the lobes, we estimate the relative ICM velocity required to bend the lobes into the observed angle. We also present spectral model fits to the overall diffuse cluster emission and see no strong signature for a cool core. The sum of the evidence indicates that Abell 623 may be undergoing a large scale cluster-cluster merger.

A search for long-time-scale, low-frequency radio transients

NASA Astrophysics Data System (ADS)

Murphy, Tara; Kaplan, David L.; Croft, Steve; Lynch, Christene; Callingham, J. R.; Bannister, Keith; Bell, Martin E.; Hurley-Walker, Natasha; Hancock, Paul; Line, Jack; Rowlinson, Antonia; Lenc, Emil; Intema, H. T.; Jagannathan, P.; Ekers, Ronald D.; Tingay, Steven; Yuan, Fang; Wolf, Christian; Onken, Christopher A.; Dwarakanath, K. S.; For, B.-Q.; Gaensler, B. M.; Hindson, L.; Johnston-Hollitt, M.; Kapińska, A. D.; McKinley, B.; Morgan, J.; Offringa, A. R.; Procopio, P.; Staveley-Smith, L.; Wayth, R.; Wu, C.; Zheng, Q.

2017-04-01

We present a search for transient and highly variable sources at low radio frequencies (150-200 MHz) that explores long time-scales of 1-3 yr. We conducted this search by comparing the TIFR GMRT Sky Survey Alternative Data Release 1 (TGSS ADR1) and the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey catalogues. To account for the different completeness thresholds in the individual surveys, we searched for compact GLEAM sources above a flux density limit of 100 mJy that were not present in the TGSS ADR1; and also for compact TGSS ADR1 sources above a flux density limit of 200 mJy that had no counterpart in GLEAM. From a total sample of 234 333 GLEAM sources and 275 612 TGSS ADR1 sources in the overlap region between the two surveys, there were 99 658 GLEAM sources and 38 978 TGSS ADR sources that passed our flux density cut-off and compactness criteria. Analysis of these sources resulted in three candidate transient sources. Further analysis ruled out two candidates as imaging artefacts. We analyse the third candidate and show it is likely to be real, with a flux density of 182 ± 26 mJy at 147.5 MHz. This gives a transient surface density of ρ = (6.2 ± 6) × 10-5 deg-2. We present initial follow-up observations and discuss possible causes for this candidate. The small number of spurious sources from this search demonstrates the high reliability of these two new low-frequency radio catalogues.

A census of radio-selected AGNs on the COSMOS field and of their FIR properties

NASA Astrophysics Data System (ADS)

Magliocchetti, M.; Popesso, P.; Brusa, M.; Salvato, M.

2018-01-01

We use the new catalogue by Laigle et al. to provide a full census of VLA-COSMOS radio sources. We identify 90 per cent of such sources and sub-divide them into active galactic nuclei (AGNs) and star-forming galaxies on the basis of their radio luminosity. The AGN sample is complete with respect to radio selection at all z ≲ 3.5. Out of 704 AGNs, 272 have a counterpart in the Herschel maps. By exploiting the better statistics of the new sample, we confirm the results of Magliocchetti et al.: the probability for a radio-selected AGN to be detected at far-infrared (FIR) wavelengths is both a function of radio luminosity and redshift, whereby powerful sources are more likely FIR emitters at earlier epochs. Such an emission is due to star-forming processes within the host galaxy. FIR emitters and non-FIR emitters only differentiate in the z ≲ 1 universe. At higher redshifts, they are indistinguishable from each other, as there is no difference between FIR-emitting AGNs and star-forming galaxies. Lastly, we focus on radio AGNs which show AGN emission at other wavelengths. We find that mid-infrared (MIR) emission is mainly associated with ongoing star formation and with sources which are smaller, younger and more radio luminous than the average parent population. X-ray emitters instead preferentially appear in more massive and older galaxies. We can therefore envisage an evolutionary track whereby the first phase of a radio-active AGN and of its host galaxy is associated with MIR emission, while at later stages the source becomes only active at radio wavelengths and possibly also in the X-ray.