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.).

The integrated radio continuum spectrum of M33 - Evidence for free-free absorption by cool ionized gas

NASA Technical Reports Server (NTRS)

Israel, F. P.; Mahoney, M. J.; Howarth, N.

1992-01-01

We present measurements of the integrated radio continuum flux density of M33 at frequencies between 22 and 610 MHz and discuss the radio continuum spectrum of M33 between 22 MHz and 10 GHz. This spectrum has a turnover between 500 and 900 MHz, depending on the steepness of the high frequency radio spectrum of M33. Below 500 MHz the spectrum is relatively flat. We discuss possible mechanisms to explain this spectral shape and consider efficient free-free absorption of nonthermal emission by a cool (not greater than 1000 K) ionized gas to be a very likely possibility. The surface filling factor of both the nonthermal and the thermal material appears to be small (of order 0.001), which could be explained by magnetic field/density fluctuations in the M 33 interstellar medium. We briefly speculate on the possible presence of a nuclear radio source with a steep spectrum.

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.

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.

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

de Gasperin, F.; Ogrean, G. A.; van Weeren, R. J.

We report that extended steep-spectrum radio emission in a galaxy cluster is usually associated with a recent merger. However, given the complex scenario of galaxy cluster mergers, many of the discovered sources hardly fit into the strict boundaries of a precise taxonomy. This is especially true for radio phoenixes that do not have very well defined observational criteria. Radio phoenixes are aged radio galaxy lobes whose emission is reactivated by compression or other mechanisms. Here in this paper, we present the detection of a radio phoenix close to the moment of its formation. The source is located in Abell 1033,more » a peculiar galaxy cluster which underwent a recent merger. To support our claim, we present unpublished Westerbork Synthesis Radio Telescope and Chandra observations together with archival data from the Very Large Array and the Sloan Digital Sky Survey. We discover the presence of two subclusters displaced along the N–S direction. The two subclusters probably underwent a recent merger which is the cause of a moderately perturbed X-ray brightness distribution. A steep-spectrum extended radio source very close to an active galactic nucleus (AGN) is proposed to be a newly born radio phoenix: the AGN lobes have been displaced/compressed by shocks formed during the merger event. This scenario explains the source location, morphology, spectral index, and brightness. Finally, we show evidence of a density discontinuity close to the radio phoenix and discuss the consequences of its presence.« less

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

Abell 1033: birth of a radio phoenix

DOE PAGES

de Gasperin, F.; Ogrean, G. A.; van Weeren, R. J.; ...

2015-02-26

We report that extended steep-spectrum radio emission in a galaxy cluster is usually associated with a recent merger. However, given the complex scenario of galaxy cluster mergers, many of the discovered sources hardly fit into the strict boundaries of a precise taxonomy. This is especially true for radio phoenixes that do not have very well defined observational criteria. Radio phoenixes are aged radio galaxy lobes whose emission is reactivated by compression or other mechanisms. Here in this paper, we present the detection of a radio phoenix close to the moment of its formation. The source is located in Abell 1033,more » a peculiar galaxy cluster which underwent a recent merger. To support our claim, we present unpublished Westerbork Synthesis Radio Telescope and Chandra observations together with archival data from the Very Large Array and the Sloan Digital Sky Survey. We discover the presence of two subclusters displaced along the N–S direction. The two subclusters probably underwent a recent merger which is the cause of a moderately perturbed X-ray brightness distribution. A steep-spectrum extended radio source very close to an active galactic nucleus (AGN) is proposed to be a newly born radio phoenix: the AGN lobes have been displaced/compressed by shocks formed during the merger event. This scenario explains the source location, morphology, spectral index, and brightness. Finally, we show evidence of a density discontinuity close to the radio phoenix and discuss the consequences of its presence.« less

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

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.

Airborne system for detection and location of radio interference sources

NASA Astrophysics Data System (ADS)

Audone, Bruno; Pastore, Alberto

1992-11-01

The rapid expansion of telecommunication has practically saturated every band of Radio Frequency Spectrum; a similar expansion of electrical and electronic devices has affected all radio communications which are, in some way, influenced by a large amount of interferences, either intentionally or unintentionally produced. Operational consequences of these interferences, particularly in the frequency channels used for aeronautical services, can be extremely dangerous, making mandatory a tight control of Electromagnetic Spectrum. The present paper analyzes the requirements and the problems related to the surveillance, for civil application, of the Electromagnetic Spectrum between 20 and 1000 MHz, with particular attention to the detection and location of radio interference sources; after a brief introduction and the indication of the advantages of an airborne versus ground installation, the airborne system designed by Alenia in cooperation with Italian Ministry of Post and Telecommunication, its practical implementation and the prototype installation on board of a small twin turboprop aircraft for experimentation purposes is presented. The results of the flight tests are also analyzed and discussed.

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.

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).

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.

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

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.

H i Absorption in the Steep-Spectrum Superluminal Quasar 3C 216.

PubMed

Pihlström; Vermeulen; Taylor; Conway

1999-11-01

The search for H i absorption in strong compact steep-spectrum sources is a natural way to probe the neutral gas contents in young radio sources. In turn, this may provide information about the evolution of powerful radio sources. The recently improved capabilities of the Westerbork Synthesis Radio Telescope have made it possible to detect a 0.31% (19 mJy) deep neutral atomic hydrogen absorption line associated with the steep-spectrum superluminal quasar 3C 216. The redshift (z=0.67) of the source shifts the frequency of the 21 cm line down to the ultra-high-frequency (UHF) band (850 MHz). The exact location of the H i-absorbing gas remains to be determined by spectral line VLBI observations at 850 MHz. We cannot exclude that the gas might be extended on galactic scales, but we think it is more likely to be located in the central kiloparsec. Constraints from the lack of X-ray absorption probably rule out obscuration of the core region, and we argue that the most plausible site for the H i absorption is in the jet-cloud interaction observed in this source.

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

Gamma-Ray Emission from the Broad-Line Radio Galaxy 3C 111

NASA Technical Reports Server (NTRS)

Hartman, Robert C.; Kadler, M.; Tueller, Jack

2008-01-01

The broad-line radio galaxy 3C 111 has been suggested as the counterpart of the y-ray source 3EG J0416+3650. While 3C 111 meets most of the criteria for a high-probability identification, like a bright flat-spectrum radio core and a blazar-like broadband SED, in the Third EGRET Catalog, the large positional offset of about 1.5' put 3C 111 outside the 99% probability region for 3EG J0416+3650, making this association questionable. We present a re-analysis of all available archival data for 3C 111 from the EGRET archives, resulting in detection of variable hard-spectrum high-energy gamma-ray emission above 1000 MeV from a position close to the nominal position of 3C 111, in three separate viewing periods (VPs), at a 3sigma level in each. A second variable hard-spectrum source is present nearby. At >100 MeV, one variable soft-spectrum source seems to account for most of the EGRET-detected emission of 3EG J0416+3650. A follow-up Swift UVOT/XRT observation reveals one moderately bright X-ray source in the error box of 3EG J0416+3650, but because of the large EGRET position uncertainty, it is not certain that the X-ray and gamma-ray sources are associated. Another Swift observation near the second (unidentified) hard gamma-ray source detected no X-ray source nearby.

First evidence of diffuse ultra-steep-spectrum radio emission surrounding the cool core of a cluster

NASA Astrophysics Data System (ADS)

Savini, F.; Bonafede, A.; Brüggen, M.; van Weeren, R.; Brunetti, G.; Intema, H.; Botteon, A.; Shimwell, T.; Wilber, A.; Rafferty, D.; Giacintucci, S.; Cassano, R.; Cuciti, V.; de Gasperin, F.; Röttgering, H.; Hoeft, M.; White, G.

2018-05-01

Diffuse synchrotron radio emission from cosmic-ray electrons is observed at the center of a number of galaxy clusters. These sources can be classified either as giant radio halos, which occur in merging clusters, or as mini halos, which are found only in cool-core clusters. In this paper, we present the first discovery of a cool-core cluster with an associated mini halo that also shows ultra-steep-spectrum emission extending well beyond the core that resembles radio halo emission. The large-scale component is discovered thanks to LOFAR observations at 144 MHz. We also analyse GMRT observations at 610 MHz to characterise the spectrum of the radio emission. An X-ray analysis reveals that the cluster is slightly disturbed, and we suggest that the steep-spectrum radio emission outside the core could be produced by a minor merger that powers electron re-acceleration without disrupting the cool core. This discovery suggests that, under particular circumstances, both a mini and giant halo could co-exist in a single cluster, opening new perspectives for particle acceleration mechanisms in galaxy clusters.

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

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.

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.

Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications

DOE PAGES

McConville, W.; Ostorero, L.; Moderski, R.; ...

2011-08-19

Here, we report Fermi Large Area Telescope (LAT) observations and broadband spectral modeling of the radio-loud active galaxy 4C +55.17 (z = 0.896), formally classified as a flat-spectrum radio quasar. Using 19 months of all-sky survey Fermi-LAT data, we detect a γ-ray continuum extending up to an observed energy of 145 GeV, and furthermore we find no evidence of γ-ray variability in the source over its observed history. We illustrate the implications of these results in two different domains. First, we investigate the origin of the steady γ-ray emission, where we re-examine the common classification of 4C +55.17 as amore » quasar-hosted blazar and consider instead its possible nature as a young radio source. We analyze and compare constraints on the source physical parameters in both blazar and young radio source scenarios by means of a detailed multiwavelength analysis and theoretical modeling of its broadband spectrum. Second, we show that the γ-ray spectrum may be formally extrapolated into the very high energy (VHE, ≥100 GeV) range at a flux level detectable by the current generation of ground-based Cherenkov telescopes. This enables us to place constraints on models of extragalactic background light within LAT energies and features the source as a promising candidate for VHE studies of the universe at an unprecedented redshift of z = 0.896.« less

Relativistic jet feedback - II. Relationship to gigahertz peak spectrum and compact steep spectrum radio galaxies

NASA Astrophysics Data System (ADS)

Bicknell, Geoffrey V.; Mukherjee, Dipanjan; Wagner, Alexander Y.; Sutherland, Ralph S.; Nesvadba, Nicole P. H.

2018-04-01

We propose that Gigahertz Peak Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources are the signposts of relativistic jet feedback in evolving galaxies. Our simulations of relativistic jets interacting with a warm, inhomogeneous medium, utilizing cloud densities and velocity dispersions in the range derived from optical observations, show that free-free absorption can account for the ˜ GHz peak frequencies and low-frequency power laws inferred from the radio observations. These new computational models replace a power-law model for the free-free optical depth a more fundamental model involving disrupted log-normal distributions of warm gas. One feature of our new models is that at early stages, the low-frequency spectrum is steep but progressively flattens as a result of a broader distribution of optical depths, suggesting that the steep low-frequency spectra discovered by Callingham et al. may possibly be attributed to young sources. We also investigate the inverse correlation between peak frequency and size and find that the initial location on this correlation is determined by the average density of the warm ISM. The simulated sources track this correlation initially but eventually fall below it, indicating the need for a more extended ISM than presently modelled. GPS and CSS sources can potentially provide new insights into the phenomenon of AGN feedback since their peak frequencies and spectra are indicative of the density, turbulent structure, and distribution of gas in the host galaxy.

Homogeneous spectral spanning of terahertz semiconductor lasers with radio frequency modulation.

PubMed

Wan, W J; Li, H; Zhou, T; Cao, J C

2017-03-08

Homogeneous broadband and electrically pumped semiconductor radiation sources emitting in the terahertz regime are highly desirable for various applications, including spectroscopy, chemical sensing, and gas identification. In the frequency range between 1 and 5 THz, unipolar quantum cascade lasers employing electron inter-subband transitions in multiple-quantum-well structures are the most powerful semiconductor light sources. However, these devices are normally characterized by either a narrow emission spectrum due to the narrow gain bandwidth of the inter-subband optical transitions or an inhomogeneous broad terahertz spectrum from lasers with heterogeneous stacks of active regions. Here, we report the demonstration of homogeneous spectral spanning of long-cavity terahertz semiconductor quantum cascade lasers based on a bound-to-continuum and resonant phonon design under radio frequency modulation. At a single drive current, the terahertz spectrum under radio frequency modulation continuously spans 330 GHz (~8% of the central frequency), which is the record for single plasmon waveguide terahertz lasers with a bound-to-continuum design. The homogeneous broadband terahertz sources can be used for spectroscopic applications, i.e., GaAs etalon transmission measurement and ammonia gas identification.

Homogeneous spectral spanning of terahertz semiconductor lasers with radio frequency modulation

PubMed Central

Wan, W. J.; Li, H.; Zhou, T.; Cao, J. C.

2017-01-01

Homogeneous broadband and electrically pumped semiconductor radiation sources emitting in the terahertz regime are highly desirable for various applications, including spectroscopy, chemical sensing, and gas identification. In the frequency range between 1 and 5 THz, unipolar quantum cascade lasers employing electron inter-subband transitions in multiple-quantum-well structures are the most powerful semiconductor light sources. However, these devices are normally characterized by either a narrow emission spectrum due to the narrow gain bandwidth of the inter-subband optical transitions or an inhomogeneous broad terahertz spectrum from lasers with heterogeneous stacks of active regions. Here, we report the demonstration of homogeneous spectral spanning of long-cavity terahertz semiconductor quantum cascade lasers based on a bound-to-continuum and resonant phonon design under radio frequency modulation. At a single drive current, the terahertz spectrum under radio frequency modulation continuously spans 330 GHz (~8% of the central frequency), which is the record for single plasmon waveguide terahertz lasers with a bound-to-continuum design. The homogeneous broadband terahertz sources can be used for spectroscopic applications, i.e., GaAs etalon transmission measurement and ammonia gas identification. PMID:28272492

The B3-VLA CSS sample. VIII. New optical identifications from the Sloan Digital Sky Survey The ultraviolet-optical spectral energy distribution of the young radio sources

NASA Astrophysics Data System (ADS)

Fanti, C.; Fanti, R.; Zanichelli, A.; Dallacasa, D.; Stanghellini, C.

2011-04-01

Context. Compact steep-spectrum radio sources and giga-hertz peaked spectrum radio sources (CSS/GPS) are generally considered to be mostly young radio sources. In recent years we studied at many wavelengths a sample of these objects selected from the B3-VLA catalog: the B3-VLA CSS sample. Only ≈60% of the sources were optically identified. Aims: We aim to increase the number of optical identifications and study the properties of the host galaxies of young radio sources. Methods: We cross-correlated the CSS B3-VLA sample with the Sloan Digital Sky Survey (SDSS), DR7, and complemented the SDSS photometry with available GALEX (DR 4/5 and 6) and near-IR data from UKIRT and 2MASS. Results: We obtained new identifications and photometric redshifts for eight faint galaxies and for one quasar and two quasar candidates. Overall we have 27 galaxies with SDSS photometry in five bands, for which we derived the ultraviolet-optical spectral energy distribution (UV-O-SED). We extended our investigation to additional CSS/GPS selected from the literature. Most of the galaxies show an excess of ultra-violet (UV) radiation compared with the UV-O-SED of local radio-quiet ellipticals. We found a strong dependence of the UV excess on redshift and analyzed it assuming that it is generated either from the nucleus (hidden quasar) or from a young stellar population (YSP). We also compare the UV-O-SEDs of our CSS/GPS sources with those of a selection of large size (LSO) powerful radio sources from the literature. Conclusions: If the major process of the UV excess is caused by a YSP, our conclusion is that it is the result of the merger process that also triggered the onset of the radio source with some time delay. We do not see evidence for a major contribution from a YSP triggered by the radio sources itself. Appendices A-G are only available in electronic form at http://www.aanda.org

VLA observations of unidentified Leiden-Berkeley Deep-Survey sources - Luminosity and redshift dependence of spectral properties

NASA Technical Reports Server (NTRS)

Kapahi, Vijay K.; Kulkarni, Vasant K.

1990-01-01

VLA observations of a complete subset of the Leiden-Berkeley Deep Survey sources that have S(1.4 GHz) greater than 10 mJy and are not optically identified down to F=22 mag are reported. By comparing the spectral and structural properties of the sources with samples from the literature, an attempt was made to disentangle the luminosity and redshift dependence of the spectral indices of extended emission in radio galaxies and of the incidence of compact steep-spectrum sources. It is found that the fraction of compact sources among those with a steep spectrum is related primarily to redshift, being much larger at high redshifts for sources of similar radio luminosity. Only a weak and marginally significant dependence of spectral indices of the extended sources on luminosity and redshift is found in samples selected at 1.4 and 2.7 GHz. It is pointed out that the much stronger correlation of spectral indices with luminosity may be arising partly from spectral curvature, and partly due to the preferential inclusion of very steep-spectrum sources from high redshift in low-frequency surveys.

Observations of flat-spectrum radio sources at λ850μm from the James Clerk Maxwell Telescope II. April 2000 to June 2005

NASA Astrophysics Data System (ADS)

Jenness, T.; Robson, E. I.; Stevens, J. A.

2010-01-01

Calibrated data for 143 flat-spectrum extragalactic radio sources are presented at a wavelength of 850μm 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.

Ultra-high-energy cosmic rays from radio galaxies

NASA Astrophysics Data System (ADS)

Eichmann, B.; Rachen, J. P.; Merten, L.; van Vliet, A.; Becker Tjus, J.

2018-02-01

Radio galaxies are intensively discussed as the sources of cosmic rays observed above about 3 × 1018 eV, called ultra-high energy cosmic rays (UHECRs). We present a first, systematic approach that takes the individual characteristics of these sources into account, as well as the impact of the extragalactic magnetic-field structures up to a distance of 120 Mpc. We use a mixed simulation setup, based on 3D simulations of UHECRs ejected by observed, individual radio galaxies taken out to a distance of 120 Mpc, and on 1D simulations over a continuous source distribution contributing from beyond 120 Mpc. Additionally, we include the ultra-luminous radio galaxy Cygnus A at a distance of about 250 Mpc, as its contribution is so strong that it must be considered as an individual point source. The implementation of the UHECR ejection in our simulation setup, both that of individual radio galaxies and the continuous source function, is based on a detailed consideration of the physics of radio jets and standard first-order Fermi acceleration. This allows to derive the spectrum of ejected UHECR as a function of radio luminosity, and at the same time provides an absolute normalization of the problem involving only a small set of parameters adjustable within narrow constraints. We show that the average contribution of radio galaxies taken over a very large volume cannot explain the observed features of UHECRs measured at Earth. However, we obtain excellent agreement with the spectrum, composition, and arrival-direction distribution of UHECRs measured by the Pierre Auger Observatory, if we assume that most UHECRs observed arise from only two sources: the ultra-luminous radio galaxy Cygnus A, providing a mostly light composition of nuclear species dominating up to about 6 × 1019 eV, and the nearest radio galaxy Centaurus A, providing a heavy composition dominating above 6 × 1019 eV . Here we have to assume that extragalactic magnetic fields out to 250 Mpc, which we did not include in the simulation, are able to isotropize the UHECR events {at about 8 EeV} arriving from Cygnus A. Even in this case, significant anisotropy correlated with Cygnus A and Centaurus A could be present at higher energies, and thus allow for differences in UHECR spectrum and composition between the northern and southern hemispheres. If this scenario can be confirmed, it would also imply that the UHECR flux in our local cosmic environment is significantly above the average throughout the universe.

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.;

The dependence of the soft X ray spectral slope with radio property, luminosity, and redshift, for a large sample of AGN from the Einstein IPC data base

NASA Technical Reports Server (NTRS)

Brunner, H.; Worrall, D. M.; Wilkes, Belinda J.; Elvis, Martin

1989-01-01

The dependence of the soft X-ray spectral slope on radio, optical and X-ray properties, and on redshift are reported for a large sample of Active Galactic Nuclei (AGN). The sample includes 317 optically and radio-selected AGN from a preliminary version of the Einstein Imaging Proportional Counter (IPC) quasar and AGN data base. The main results are: the difference in X-ray slope between radio-loud and radio-quiet AGN were confirmed for an independent and much larger sample of sources; a difference in X-ray slope between flat and steep radio spectrum AGN is observed only in high luminosity sub-sample; in flat radio spectrum AGNs there is an indication for a dependence of the X-ray spectral index on X-ray luminosity redshift and alpha sub 0x.

The Telecommunications and Data Acquisition

NASA Technical Reports Server (NTRS)

Renzetti, N. A. (Editor)

1981-01-01

Progress in the development and operations of the Deep Space Network is reported including developments in Earth based radio technology as applied to other research programs. These programs include application of radio interferometry at microwave frequencies to geodetic measurements and geodynamics, use of deep space stations individually and in pairs as an interferometer by radio astronomers for astrophysics research by direct observations of radio sources, and radio search for extraterrestrial intelligence in the microwave region of the electromagnetic spectrum.

Optical Spectra of Four Objects Identified with Variable Radio Sources

NASA Astrophysics Data System (ADS)

Chavushyan, V.; Mujica, R.; Gorshkov, A. G.; Konnikova, V. K.; Mingaliev, M. G.

2000-06-01

We obtained optical spectra of four objects identified with variable radio sources. Three objects (0029+0554, 0400+0550, 2245+0500) were found to be quasars with redshifts of 1.314, 0.761, and 1.091. One object (2349+0534) has a continuum spectrum characteristic of BL Lac objects. We analyze spectra of the radio sources in the range 0.97-21.7 GHz for the epoch 1997 and in the range 3.9-11.1 GHz for the epoch 1990, as well as the pattern of variability of their flux densities on time scales of 1.5 and 7 years.

Machine learning based Intelligent cognitive network using fog computing

NASA Astrophysics Data System (ADS)

Lu, Jingyang; Li, Lun; Chen, Genshe; Shen, Dan; Pham, Khanh; Blasch, Erik

2017-05-01

In this paper, a Cognitive Radio Network (CRN) based on artificial intelligence is proposed to distribute the limited radio spectrum resources more efficiently. The CRN framework can analyze the time-sensitive signal data close to the signal source using fog computing with different types of machine learning techniques. Depending on the computational capabilities of the fog nodes, different features and machine learning techniques are chosen to optimize spectrum allocation. Also, the computing nodes send the periodic signal summary which is much smaller than the original signal to the cloud so that the overall system spectrum source allocation strategies are dynamically updated. Applying fog computing, the system is more adaptive to the local environment and robust to spectrum changes. As most of the signal data is processed at the fog level, it further strengthens the system security by reducing the communication burden of the communications network.

VizieR Online Data Catalog: Extragalactic peaked-spectrum radio sources (Callingham+, 2017)

NASA Astrophysics Data System (ADS)

Callingham, J. R.; Ekers, R. D.; Gaensler, B. M.; Line, J. L. B.; Hurley-Walker, N.; Sadler, E. M.; Tingay, S. J.; Hancock, P. J.; Bell, M. E.; Dwarakanath, K. S.; For, B.-Q.; Franzen, T. M. O.; Hindson, L.; Johnston-Hollitt, M.; Kapinska, A. D.; Lenc, E.; McKinley, B.; Morgan, J.; Offringa, A. R.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, C.; Zheng, Q.

2017-09-01

The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) extragalactic catalog represents a significant advance in selecting peaked-spectrum sources, since it is constituted of sources that were contemporaneously surveyed with the widest fractional radio bandwidth to date, with 20 flux density measurements between 72 and 231MHz. We also use the NRAO VLA Sky Survey (NVSS; Condon+ 1998, VIII/65) and the Sydney University Molonglo Sky Survey (SUMSS; See Mauch+ 2008, VIII/81). Since the combination of NVSS and SUMSS cover the entire GLEAM survey and are an order of magnitude more sensitive, this study is sensitive to peaked-spectrum sources that peak anywhere between 72MHz and 843MHz/1.4GHz. The GLEAM survey was formed from observations conducted by the Murchison Widefield Array (MWA), which surveyed the sky between 72 and 231MHz from 2013 August to 2014 July (Wayth+ 2015PASA...32...25W - see also VIII/100). (5 data files).

A transient, flat spectrum radio pulsar near the Galactic Centre

NASA Astrophysics Data System (ADS)

Dexter, J.; Degenaar, N.; Kerr, M.; Deller, A.; Deneva, J.; Lazarus, P.; Kramer, M.; Champion, D.; Karuppusamy, R.

2017-06-01

Recent studies have shown possible connections between highly magnetized neutron stars ('magnetars'), whose X-ray emission is too bright to be powered by rotational energy, and ordinary radio pulsars. In addition to the magnetar SGR J1745-2900, one of the radio pulsars in the Galactic Centre (GC) region, PSR J1746-2850, had timing properties implying a large magnetic field strength and young age, as well as a flat spectrum. All characteristics are similar to those of rare, transient, radio-loud magnetars. Using several deep non-detections from the literature and two new detections, we show that this pulsar is also transient in the radio. Both the flat spectrum and large amplitude variability are inconsistent with the light curves and spectral indices of three radio pulsars with high magnetic field strengths. We further use frequent, deep archival imaging observations of the GC in the past 15 yr to rule out a possible X-ray outburst with a luminosity exceeding the rotational spin-down rate. This source, either a transient magnetar without any detected X-ray counterpart or a young, strongly magnetized radio pulsar producing magnetar-like radio emission, further blurs the line between the two categories. We discuss the implications of this object for the radio emission mechanism in magnetars and for star and compact object formation in the GC.

Duty-cycle and energetics of remnant radio-loud AGN

NASA Astrophysics Data System (ADS)

Turner, Ross J.

2018-05-01

Deriving the energetics of remnant and restarted active galactic nuclei (AGNs) is much more challenging than for active sources due to the complexity in accurately determining the time since the nucleus switched-off. I resolve this problem using a new approach that combines spectral ageing and dynamical models to tightly constrain the energetics and duty-cycles of dying sources. Fitting the shape of the integrated radio spectrum yields the fraction of the source age the nucleus is active; this, in addition to the flux density, source size, axis ratio, and properties of the host environment, provides a constraint on dynamical models describing the remnant radio source. This technique is used to derive the intrinsic properties of the well-studied remnant radio source B2 0924+30. This object is found to spend 50_{-12}^{+14} Myr in the active phase and a further 28_{-5}^{+6} Myr in the quiescent phase, have a jet kinetic power of 3.6_{-1.7}^{+3.0}× 10^{37} W, and a lobe magnetic field strength below equipartition at the 8σ level. The integrated spectra of restarted and intermittent radio sources are found to yield a `steep-shallow' shape when the previous outburst occurred within 100 Myr. The duty-cycle of B2 0924+30 is hence constrained to be δ < 0.15 by fitting the shortest time to the previous comparable outburst that does not appreciably modify the remnant spectrum. The time-averaged feedback energy imparted by AGNs into their host galaxy environments can in this manner be quantified.

Observations of flat-spectrum radio sources at λ850 μm from the James Clerk Maxwell Telescope - I. 1997 April to 2000 April

NASA Astrophysics Data System (ADS)

Robson, E. I.; Stevens, J. A.; Jenness, T.

2001-11-01

Calibrated data for 65 flat-spectrum extragalactic radio sources are presented at a wavelength of 850μm, covering a three-year period from 1997 April. The data, obtained from the James Clerk Maxwell Telescope using the 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.

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.

VLA observations of unidentified Leiden-Berkeley Deep-Survey sources - Luminosity and redshift dependence of spectral properties

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

Kapahi, V.K.; Kulkarni, V.K.

1990-05-01

VLA observations of a complete subset of the Leiden-Berkeley Deep Survey sources that have S(1.4 GHz) greater than 10 mJy and are not optically identified down to F=22 mag are reported. By comparing the spectral and structural properties of the sources with samples from the literature, an attempt was made to disentangle the luminosity and redshift dependence of the spectral indices of extended emission in radio galaxies and of the incidence of compact steep-spectrum sources. It is found that the fraction of compact sources among those with a steep spectrum is related primarily to redshift, being much larger at highmore » redshifts for sources of similar radio luminosity. Only a weak and marginally significant dependence of spectral indices of the extended sources on luminosity and redshift is found in samples selected at 1.4 and 2.7 GHz. It is pointed out that the much stronger correlation of spectral indices with luminosity may be arising partly from spectral curvature, and partly due to the preferential inclusion of very steep-spectrum sources from high redshift in low-frequency surveys. 54 refs.« less

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

Investigation of a complete sample of flat spectrum radio sources from the S5 survey

NASA Astrophysics Data System (ADS)

Eckart, A.; Witzel, A.; Biermann, P.; Johnston, K. J.; Simon, R.; Schalinski, C.; Kuhr, H.

1986-11-01

An analysis of 13 extragalactic sources of the S5 survey with flux densities greater than or equal to 1 Jy at 4990 MHz, mapped with milliarcsecond resolution at 1.6 and 5 GHz by means of VLBI, is presented. All sources appear to display multiple components dominated in flux density at 6 cm by a core component which is self-absorbed at 18 cm. Comparison of the measured to predicted X-ray flux density of the core radio components suggests that all sources should display bulk relativistic motion with small angles to the line of sight, and four sources show rapid changes in their radio structures which can be interpreted as apparent superliminal motion.

The Mpc-scale radio source associated with the GPS galaxy B1144+352

NASA Astrophysics Data System (ADS)

Schoenmakers, A. P.; de Bruyn, A. G.; Röttgering, H. J. A.; van der Laan, H.

1999-01-01

We present the results of new observations of the enigmatic radio source B1144+352 with the WSRT at 1.4 GHz. This source is hosted by an m_r = 14.3 +/- 0.1 galaxy at a redshift of z=0.063 +/- 0.002 and is one of the lowest redshift Gigahertz Peaked Spectrum (GPS) sources known. It has been known to show radio structure on pc-scale in the radio core and on 20-60 kpc-scale in two jet-like radio structures. The WENSS and NVSS surveys have now revealed faint extended radio structures on an even much larger scale. We have investiga ted these large-scale radio components with new 1.4-GHz WSRT observations. Our radio data indicate that the eastern radio structure has a leading hotspot and we conclude that this structure is a radio lobe originating in the galaxy hosting the GPS source. The western radio structure contains two separate radio sources which are superposed on the sky. The first is a low-power radio source, hosted by a m_R = 15.3 +/- 0.5 galaxy at a similar redshift (z=0.065+/-0.001) to the GPS host galaxy; the second is an extended radio lobe, which we believe is associated with the GPS host galaxy and which contains an elongated tail. The total projected linear size of the extended radio structure associated with B1144+352 is ~ 1.2 Mpc. The core of B1144+353 is a known variable radio source: its flux density at 1.4 GHz has increased continuously between 1974 and 1994. We have measured the flux density of the core in our WSRT observations (epoch 1997.7) and find a value of 541+/-10 mJy This implies that its flux density has decreased by ~ 70 mJy between 1994 and 1997. Further, we have retrieved unpublished archival ROSAT HRI data of B1144+352. The source has been detected and appears to be slightly extended in X-rays. We find a luminosity of (1.26 +/- 0.15)*E(43) erg s(-1) between 0.1 and 2.4 keV, assumin that the X-ray emission is due to an AGN with a powerlaw spectrum with photon index 1.8, or (0.95 +/- 0.11) *E(43) erg s(-1) if it is due to thermal bremsstrahlung at T=10(7) K. The detection of the X-ray source suggests that the intrinsic Hi column density cannot be much larger than a few times 10(21) cm(-2) . The non-detection of an extended X-ray halo in a radius of 250 kpc around the host galaxy limits the X-ray luminosity of an intra-cluster gas component within this radius to <~2.3 x 10(42) erg s(-1) (1sigma upper limit). This is below the luminosity of an X-ray luminous cluster and is more comparable to that of poor groups of galaxies. Also the optical data show no evidence for a rich cluster around the host galaxy. B1144+352 is the second GPS galaxy known to be associated with a Mpc-sized radio source, the other being B1245+676. We argue that the observed structure in both these GPS radio sources must be the result of an interrupted central jet-activity, and that a such they may well be the progenitors of sources belonging to the class of double-double radio galaxy.

Interplanetary Scintillation studies with the Murchison Wide-field Array III: Comparison of source counts and densities for radio sources and their sub-arcsecond components at 162 MHz

NASA Astrophysics Data System (ADS)

Chhetri, R.; Ekers, R. D.; Morgan, J.; Macquart, J.-P.; Franzen, T. M. O.

2018-06-01

We use Murchison Widefield Array observations of interplanetary scintillation (IPS) to determine the source counts of point (<0.3 arcsecond extent) sources and of all sources with some subarcsecond structure, at 162 MHz. We have developed the methodology to derive these counts directly from the IPS observables, while taking into account changes in sensitivity across the survey area. The counts of sources with compact structure follow the behaviour of the dominant source population above ˜3 Jy but below this they show Euclidean behaviour. We compare our counts to those predicted by simulations and find a good agreement for our counts of sources with compact structure, but significant disagreement for point source counts. Using low radio frequency SEDs from the GLEAM survey, we classify point sources as Compact Steep-Spectrum (CSS), flat spectrum, or peaked. If we consider the CSS sources to be the more evolved counterparts of the peaked sources, the two categories combined comprise approximately 80% of the point source population. We calculate densities of potential calibrators brighter than 0.4 Jy at low frequencies and find 0.2 sources per square degrees for point sources, rising to 0.7 sources per square degree if sources with more complex arcsecond structure are included. We extrapolate to estimate 4.6 sources per square degrees at 0.04 Jy. We find that a peaked spectrum is an excellent predictor for compactness at low frequencies, increasing the number of good calibrators by a factor of three compared to the usual flat spectrum criterion.

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 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.;

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.

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.

The Gamma-Ray Emitting Radio-Loud Narrow-Line Seyfert 1 Galaxy PKS 2004-447 II. The Radio View

NASA Technical Reports Server (NTRS)

Schulz, R.; Kreikenbohm, A.; Kadler, M.; Ojha, R.; Ros, E.; Stevens, J.; Edwards, P. G.; Carpenter, B.; Elsaesser, D.; Gehrels, N.;

Influence of synchrotron self-absorption on 21-cm experiments

NASA Astrophysics Data System (ADS)

Zheng, Qian; Wu, Xiang-Ping; Gu, Jun-Hua; Wang, Jingying; Xu, Haiguang

2012-08-01

The presence of spectral curvature resulting from the synchrotron self-absorption of extragalactic radio sources could break down the spectral smoothness feature. This leads to the premise that the bright radio foreground can be successfully removed in 21-cm experiments that search for the epoch of reionization (EoR). We present a quantitative estimate of the effect of the spectral curvature resulting from the synchrotron self-absorption of extragalactic radio sources on the measurement of the angular power spectrum of the low-frequency sky. We incorporate a phenomenological model, which is characterized by the fraction (f) of radio sources with turnover frequencies in the range of 100-1000 MHz and by a broken power law for the spectral transition around the turnover frequencies νm, into simulated radio sources over a small sky area of 10° × 10°. We compare statistically the changes in their residual maps with and without the inclusion of the synchrotron self-absorption of extragalactic radio sources after the bright sources of S150 MHz ≥100 mJy are excised. Furthermore, the best-fitting polynomials in the frequency domain on each pixel are subtracted. It has been shown that the effect of synchrotron self-absorption on the detection of the EoR depends sensitively on the spectral profiles of the radio sources around the turnover frequencies νm. A hard transition model, described by the broken power law with the turnover of spectral index at νm, would leave pronounced imprints on the residual background and would therefore cause serious confusion with the cosmic EoR signal. However, the spectral signatures on the angular power spectrum of the extragalactic foreground, generated by a soft transition model in which the rising and falling power laws of the spectral distribution around νm are connected through a smooth transition spanning ≥200 MHz in a characteristic width, can be fitted and consequently subtracted by the use of polynomials to an acceptable degree (δT < 1 mK). As this latter scenario seems to be favoured in both theoretical expectations and radio spectral observations, we conclude that the contamination of extragalactic radio sources by synchrotron self-absorption in 21-cm experiments is probably very minor.

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

`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.

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.

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.

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

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.

Spectral ageing in the era of big data: integrated versus resolved models

NASA Astrophysics Data System (ADS)

Harwood, Jeremy J.

2017-04-01

Continuous injection models of spectral ageing have long been used to determine the age of radio galaxies from their integrated spectrum; however, many questions about their reliability remain unanswered. With various large area surveys imminent (e.g. LOw Frequency ARray, MeerKAT, Murchison Widefield Array) and planning for the next generation of radio interferometers are well underway (e.g. next generation VLA, Square Kilometre Array), investigations of radio galaxy physics are set to shift away from studies of individual sources to the population as a whole. Determining if and how integrated models of spectral ageing can be applied in the era of big data is therefore crucial. In this paper, I compare classical integrated models of spectral ageing to recent well-resolved studies that use modern analysis techniques on small spatial scales to determine their robustness and validity as a source selection method. I find that integrated models are unable to recover key parameters and, even when known a priori, provide a poor, frequency-dependent description of a source's spectrum. I show a disparity of up to a factor of 6 in age between the integrated and resolved methods but suggest, even with these inconsistencies, such models still provide a potential method of candidate selection in the search for remnant radio galaxies and in providing a cleaner selection of high redshift radio galaxies in z - α selected samples.

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

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.

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.

The VLA-COSMOS Survey - V. 324 MHz continuum observations

NASA Astrophysics Data System (ADS)

Smolčić, Vernesa; Ciliegi, Paolo; Jelić, Vibor; Bondi, Marco; Schinnerer, Eva; Carilli, Chris L.; Riechers, Dominik A.; Salvato, Mara; Brković, Alen; Capak, Peter; Ilbert, Olivier; Karim, Alexander; McCracken, Henry; Scoville, Nick Z.

2014-09-01

We present 90 cm Very Large Array imaging of the COSMOS field, comprising a circular area of 3.14 square degrees at 8.0arcsec × 6.0arcsec angular resolution with an average rms of 0.5 mJy beam-1. The extracted catalogue contains 182 sources (down to 5.5σ), 30 of which are multicomponent sources. Using Monte Carlo artificial source simulations, we derive the completeness of the catalogue, and we show that our 90 cm source counts agree very well with those from previous studies. Using X-ray, NUV-NIR and radio COSMOS data to investigate the population mix of our 90 cm radio sample, we find that our sample is dominated by active galactic nuclei. The average 90-20 cm spectral index (Sν ∝ να, where Sν is the flux density at frequency ν and α the spectral index) of our 90 cm selected sources is -0.70, with an interquartile range from -0.90 to -0.53. Only a few ultra-steep-spectrum sources are present in our sample, consistent with results in the literature for similar fields. Our data do not show clear steepening of the spectral index with redshift. Nevertheless, our sample suggests that sources with spectral indices steeper than -1 all lie at z ≳ 1, in agreement with the idea that ultra-steep-spectrum radio sources may trace intermediate-redshift galaxies (z ≳ 1).

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 radio spectral energy distribution of infrared-faint radio sources

NASA Astrophysics Data System (ADS)

Herzog, A.; Norris, R. P.; Middelberg, E.; Seymour, N.; Spitler, L. R.; Emonts, B. H. C.; Franzen, T. M. O.; Hunstead, R.; Intema, H. T.; Marvil, J.; Parker, Q. A.; Sirothia, S. K.; Hurley-Walker, N.; Bell, M.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Callingham, J. R.; Deshpande, A. A.; Dwarakanath, K. S.; For, B.-Q.; Greenhill, L. J.; Hancock, P.; Hazelton, B. J.; Hindson, L.; Johnston-Hollitt, M.; Kapińska, A. D.; Kaplan, D. L.; Lenc, E.; Lonsdale, C. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Morgan, J.; Oberoi, D.; Offringa, A.; Ord, S. M.; Prabu, T.; Procopio, P.; Udaya Shankar, N.; Srivani, K. S.; Staveley-Smith, L.; Subrahmanyan, R.; Tingay, S. J.; Wayth, R. B.; Webster, R. L.; Williams, A.; Williams, C. L.; Wu, C.; Zheng, Q.; Bannister, K. W.; Chippendale, A. P.; Harvey-Smith, L.; Heywood, I.; Indermuehle, B.; Popping, A.; Sault, R. J.; Whiting, M. T.

2016-10-01

Context. Infrared-faint radio sources (IFRS) are a class of radio-loud (RL) active galactic nuclei (AGN) at high redshifts (z ≥ 1.7) that are characterised by their relative infrared faintness, resulting in enormous radio-to-infrared flux density ratios of up to several thousand. Aims: Because of their optical and infrared faintness, it is very challenging to study IFRS at these wavelengths. However, IFRS are relatively bright in the radio regime with 1.4 GHz flux densities of a few to a few tens of mJy. Therefore, the radio regime is the most promising wavelength regime in which to constrain their nature. We aim to test the hypothesis that IFRS are young AGN, particularly GHz peaked-spectrum (GPS) and compact steep-spectrum (CSS) sources that have a low frequency turnover. Methods: We use the rich radio data set available for the Australia Telescope Large Area Survey fields, covering the frequency range between 150 MHz and 34 GHz with up to 19 wavebands from different telescopes, and build radio spectral energy distributions (SEDs) for 34 IFRS. We then study the radio properties of this class of object with respect to turnover, spectral index, and behaviour towards higher frequencies. We also present the highest-frequency radio observations of an IFRS, observed with the Plateau de Bure Interferometer at 105 GHz, and model the multi-wavelength and radio-far-infrared SED of this source. Results: We find IFRS usually follow single power laws down to observed frequencies of around 150 MHz. Mostly, the radio SEDs are steep (α < -0.8; %), but we also find ultra-steep SEDs (α < -1.3; %). In particular, IFRS show statistically significantly steeper radio SEDs than the broader RL AGN population. Our analysis reveals that the fractions of GPS and CSS sources in the population of IFRS are consistent with the fractions in the broader RL AGN population. We find that at least % of IFRS contain young AGN, although the fraction might be significantly higher as suggested by the steep SEDs and the compact morphology of IFRS. The detailed multi-wavelength SED modelling of one IFRS shows that it is different from ordinary AGN, although it is consistent with a composite starburst-AGN model with a star formation rate of 170 M⊙ yr-1. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

`Fingerprint' Fine Structure in the Solar Decametric Radio Spectrum Solar Physics

NASA Astrophysics Data System (ADS)

Zlotnik, E. Y.; Zaitsev, V. V.; Melnik, V. N.; Konovalenko, A. A.; Dorovskyy, V. V.

2015-07-01

We study a unique fine structure in the dynamic spectrum of the solar radio emission discovered by the UTR-2 radio telescope (Kharkiv, Ukraine) in the frequency band of 20 - 30 MHz. The structure was observed against the background of a broadband type IV radio burst and consisted of parallel drifting narrow bands of enhanced emission and absorption on the background emission. The observed structure differs from the widely known zebra pattern at meter and decimeter wavelengths by the opposite directions of the frequency drift within a single stripe at a given time. We show that the observed properties can be understood in the framework of the radiation mechanism by virtue of the double plasma resonance effect in a nonuniform coronal magnetic trap. We propose a source model providing the observed frequency drift of the stripes.

VLBI observations of galactic nuclei at 18 centimeters - NGC 1052, NGC 4278, M82, and M104

NASA Technical Reports Server (NTRS)

Shaffer, D. B.; Marscher, A. P.

1979-01-01

Compact radio sources about a light year in size have been detected in the nuclei of the galaxies NGC 1052, NGC 3034 (M82), NGC 4278, and NGC 4594 (M104) at a wavelength of 18 cm. The compact nucleus detected in M81 at 6 cm was not seen at 18 cm. The compact source in M82 is unique among extragalactic sources in its size-spectrum relationship. It is either broadened by scattering within M82 or it lies behind, and is absorbed by, an H II region. In these galaxies, the size of the nuclear radio source at 18 cm is larger than it is at higher frequencies. The nucleus of the giant radio galaxy DA 240 was not detected.

A Multi-Wavelength Study of the X-Ray Sources in the NGC 5018

NASA Technical Reports Server (NTRS)

Ghosh, Kajal K.; Swartz, Douglas A.; Tennant, Allyn F.; Wu, Kinwah; Saripalli, Lakshmi

2004-01-01

The E3 giant elliptical galaxy NGC-5018 was observed with the cxo X-ray Observatory's Advanced CCD Imaging Spectrometer for 30-h on 14 April 2001. Results of analysis of these X-ray data as well as of complementary optical, infrared, and radio data are reported. Seven X-ray point sources, including the nucleus, were detected. If they are intrinsic to NGC-5018, then all six non-nuclear sources have luminosities exceeding 10(exp 39)-ergl in the 0.5-8.0-keV energy band; placing them in the class of Ultra- luminous X-ray sources. Comparison of X-ray source positions to archival Hubble Space Telescope/Wide Field Planetary Camera 2 (hst/WFPC2) images reveal four of the six non-nuclear sources are spatially--coincident with bright, M$(sub V)LA -8.6 mag, objects. These four objects have optical magnitudes and (V-I) colors consistent with globular clusters in NGC-5018. However, one of these objects was observed to vary by siml mag in both V and I between observations taken 28 July 1997 and 04 Feb 1999 indicating this source is a background active galactic nucleus (AGN). The nature of the other three optically-bright objects cannot be determined from the available optical data but all have X-ray-to-optical flux ratios consistent with background AGNs. Strong, unpolarized, radio emission has been detected from another of the optically-bright counterparts. It displays an inverted radio spectrum and is the most absorbed of the seven sources in the X-ray band. It, too, is most readily explained as a background AGN, though alternative explanations cannot be ruled out. Extended X-ray emission is detected within a siml5 arcsec radius of the galaxy center at a luminosity of sim lO(exp 40)-ergl in the X-ray band. Its thermal X-ray spectrum (kT sim0.4-keV) and its spatial coincidence with strong H(alpha) emission are consistent with a hot gas origin. The nucleus itself is a weak X-ray source, LA-5 times 10(exp 39)-ergl, but displays a radio spectrum typical of AGN.

Intermediate BL Lac objects

NASA Astrophysics Data System (ADS)

Bondi, M.; Marchã, M. J. M.; Dallacasa, D.; Stanghellini, C.

2001-08-01

The 200-mJy sample, defined by Marchã et al., contains about 60 nearby, northern, flat-spectrum radio sources. In particular, the sample has proved effective at finding nearby radio-selected BL Lac objects with radio luminosities comparable to those of X-ray-selected objects, and low-luminosity flat-spectrum weak emission-line radio galaxies (WLRGs). The 200-mJy sample contains 23 BL Lac objects (including 6 BL Lac candidates) and 19 WLRGs. We will refer to these subsamples as the 200-mJy BL Lac sample and the 200-mJy WLRG sample, respectively. We have started a systematic analysis of the morphological pc-scale properties of the 200-mJy radio sources using VLBI observations. This paper presents VLBI observations at 5 and 1.6GHz of 14 BL Lac objects and WLRGs selected from the 200-mJy sample. The pc-scale morphology of these objects is briefly discussed. We derive the radio beaming parameters of the 200-mJy BL Lac objects and WLRGs and compare them with those of other BL Lac samples and with a sample of FR I radio galaxies. The overall broad-band radio, optical and X-ray properties of the 200-mJy BL Lac sample are discussed and compared with those of other BL Lac samples, radio- and X-ray-selected. We find that the 200-mJy BL Lac objects fill the gap between HBL and LBL objects in the colour-colour plot, and have intermediate αXOX as expected in the spectral energy distribution unification scenario. Finally, we briefly discuss the role of the WLRGs.

Taking the Radio Blinders Off of M83: A Wide Spectrum Analysis of the Historical Point Source Population

NASA Astrophysics Data System (ADS)

Stockdale, Christopher; Keefe, Clayton; Nichols, Michael; Rujevcan, Colton; Blair, William P.; Cowan, John J.; Godfrey, Leith; Miller-Jones, James; Kuntz, K. D.; Long, Knox S.; Maddox, Larry A.; Plucinsky, Paul P.; Pritchard, Tyler A.; Soria, Roberto; Whitmore, Bradley C.; Winkler, P. Frank

2015-01-01

We present low frequency observations of the grand design spiral galaxy, M83, using the C and L bands of the Karl G. Jansky Very Large Array (VLA). With recent optical (HST) and X-ray (Chandra) observations and utilizing the newly expanded bandwidth of the VLA, we are exploring the radio spectral properties of the historical radio point sources in M83. These observations allow us to probe the evolution of supernova remnants (SNRs) and to find previously undiscovered SNRs. These observations represent the fourth epoch of deep VLA observations of M83. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities.

Radio Spectral Imaging of Reflective MHD Waves during the Impulsive Phase of a Solar Flare

NASA Astrophysics Data System (ADS)

Yu, S.; Chen, B.; Reeves, K.

2017-12-01

We report a new type of coherent radio bursts observed by the Karl G. Jansky Very Large Array (VLA) in 1-2 GHz during the impulsive phase of a two-ribbon flare on 2014 November 1, which we interpret as MHD waves reflected near the footpoint of flaring loops. In the dynamic spectrum, this burst starts with a positive frequency drift toward higher frequencies until it slows down near its highest-frequency boundary. Then it turns over and drifts toward lower frequencies. The frequency drift rate in its descending and ascending branch is between 50-150 MHz/s, which is much slower than type III radio bursts associated with fast electron beams but close to the well-known intermediate drift bursts, or fiber bursts, which are usually attributed to propagating whistler or Alfvenic waves. Thanks to VLA's unique capability of imaging with spectrometer-like temporal and spectral resolution (50 ms and 2 MHz), we are able to obtain an image of the radio source at every time and frequency in the dynamic spectrum where the burst is present and trace its spatial evolution. From the imaging results, we find that the radio source firstly moves downward toward one of the flaring ribbons before it "bounces off" at the lowest height (corresponding to the turnover frequency in the dynamic spectrum) and moves upward again. The measured speed in projection is at the order of 1-2 Mm/s, which is characteristic of Alfvenic or fast-mode MHD waves in the low corona. We conclude that the radio burst is emitted by trapped nonthermal electrons in the flaring loop carried along by a large-scale MHD wave. The waves are probably launched during the eruption of a magnetic flux rope in the flare impulsive phase.

Millisecond Pulsars and the Galactic Center Excess

NASA Astrophysics Data System (ADS)

Gonthier, Peter L.; Koh, Yew-Meng; Kust Harding, Alice; Ferrara, Elizabeth C.

2017-08-01

Various groups including the Fermi team have confirmed the spectrum of the gamma- ray excess in the Galactic Center (GCE). While some authors interpret the GCE as evidence for the annihilation of dark matter (DM), others have pointed out that the GCE spectrum is nearly identical to the average spectrum of Fermi millisecond pul- sars (MSP). Assuming the Galactic Center (GC) is populated by a yet unobserved source of MSPs that has similar properties to that of MSPs in the Galactic Disk (GD), we present results of a population synthesis of MSPs from the GC. We establish parameters of various models implemented in the simulation code by matching characteristics of 54 detected Fermi MSPs in the first point source catalog and 92 detected radio MSPs in a select group of thirteen radio surveys and targeting a birth rate of 45 MSPs per mega-year. As a check of our simulation, we find excellent agreement with the estimated numbers of MSPs in eight globular clusters. In order to reproduce the gamma-ray spectrum of the GCE, we need to populate the GC with 10,000 MSPs having a Navarro-Frenk-White distribution suggested by the halo density of DM. It may be possible for Fermi to detect some of these MSPs in the near future; the simulation also predicts that many GC MSPs have radio fluxes S1400above 10 �μJy observable by future pointed radio observations. We express our gratitude for the generous support of the National Science Foundation (RUI: AST-1009731), Fermi Guest Investigator Program and the NASA Astrophysics Theory and Fundamental Program (NNX09AQ71G).

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.

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.

Nature of radio feature formed by re-started jet activity in 3C 84 and its relation with γ-ray emissions

NASA Astrophysics Data System (ADS)

Nagai, H.; Chida, H.; Kino, M.; Orienti, M.; D'Ammando, F.; Giovannini, G.; Hiura, K.

2016-02-01

Re-started jet activity occurred in the bright nearby radio source 3C 84 in about 2005. The re-started jet is forming a prominent component (namely C3) at the tip of jet. The component has showed an increase in radio flux density for more than 7 years while the radio spectrum remains optically thin. This suggests that the component is the head of a radio lobe including a hotspot where the particle acceleration occurs. Thus, 3C 84 is a unique laboratory to study the physical properties at the very early stage of radio source evolution. Another important aspect is that high energy and very high energy γ-ray emissions are detected from this source. The quest for the site of γ-ray emission is quite important to obtain a better understanding of γ-ray emission mechanisms in radio galaxies. In this paper, we review the observational results from very long baseline interferometry (VLBI) monitoring of 3C 84 reported in series of our previous papers. We argue the nature of re-started jet/radio lobe and its relation with high-energy emission.

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

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.

Spectral state transitions of the Ultraluminous X-ray Source IC 342 X-1

NASA Astrophysics Data System (ADS)

Marlowe, H.; Kaaret, P.; Lang, C.; Feng, H.; Grisé, F.; Miller, N.; Cseh, D.; Corbel, S.; Mushotzky, R. F.

2014-10-01

We observed the Ultraluminous X-ray Source (ULX) IC 342 X-1 simultaneously in X-ray and radio with Chandra and the JVLA to investigate previously reported unresolved radio emission coincident with the ULX. The Chandra data reveal a spectrum that is much softer than observed previously and is well modelled by a thermal accretion disc spectrum. No significant radio emission above the rms noise level was observed within the region of the ULX, consistent with the interpretation as a thermal state though other states cannot be entirely ruled out with the current data. We estimate the mass of the black hole using the modelled inner disc temperature to be 30 M_{⊙} ≲ M√{cosi}≲ 200 M_{⊙} based on a Shakura-Sunyaev disc model. Through a study of the hardness and high-energy curvature of available X-ray observations, we find that the accretion state of X-1 is not determined by luminosity alone.

Tapering the sky response for angular power spectrum estimation from low-frequency radio-interferometric data.

PubMed

Choudhuri, Samir; Bharadwaj, Somnath; Roy, Nirupam; Ghosh, Abhik; Ali, Sk Saiyad

2016-06-11

It is important to correctly subtract point sources from radio-interferometric data in order to measure the power spectrum of diffuse radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm signal. It is computationally very expensive and challenging to image a very large area and accurately subtract all the point sources from the image. The problem is particularly severe at the sidelobes and the outer parts of the main lobe where the antenna response is highly frequency dependent and the calibration also differs from that of the phase centre. Here, we show that it is possible to overcome this problem by tapering the sky response. Using simulated 150 MHz observations, we demonstrate that it is possible to suppress the contribution due to point sources from the outer parts by using the Tapered Gridded Estimator to measure the angular power spectrum C ℓ of the sky signal. We also show from the simulation that this method can self-consistently compute the noise bias and accurately subtract it to provide an unbiased estimation of C ℓ .

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.

Faraday rotation from magnesium II absorbers toward polarized background radio sources

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

Farnes, J. S.; O'Sullivan, S. P.; Corrigan, M. E.

2014-11-01

Strong singly ionized magnesium (Mg II) absorption lines in quasar spectra typically serve as a proxy for intervening galaxies along the line of sight. Previous studies have found a correlation between the number of these Mg II absorbers and the Faraday rotation measure (RM) at ≈5 GHz. We cross-match a sample of 35,752 optically identified non-intrinsic Mg II absorption systems with 25,649 polarized background radio sources for which we have measurements of both the spectral index and RM at 1.4 GHz. We use the spectral index to split the resulting sample of 599 sources into flat-spectrum and steep-spectrum subsamples. Wemore » find that our flat-spectrum sample shows significant (∼3.5σ) evidence for a correlation between Mg II absorption and RM at 1.4 GHz, while our steep-spectrum sample shows no such correlation. We argue that such an effect cannot be explained by either luminosity or other observational effects, by evolution in another confounding variable, by wavelength-dependent polarization structure in an active galactic nucleus, by the Galactic foreground, by cosmological expansion, or by partial coverage models. We conclude that our data are most consistent with intervenors directly contributing to the Faraday rotation along the line of sight, and that the intervening systems must therefore have coherent magnetic fields of substantial strength ( B-bar =1.8±0.4 μG). Nevertheless, the weak nature of the correlation will require future high-resolution and broadband radio observations in order to place it on a much firmer statistical footing.« less

On the Evolution of the Cores of Radio Sources and Their Extended Radio Emission

NASA Astrophysics Data System (ADS)

Yuan, Zunli; Wang, Jiancheng

2012-01-01

The work in this paper aims at determining the evolution and possible co-evolution of radio-loud active galactic nuclei (AGNs) and their cores via their radio luminosity functions (i.e., total and core RLFs, respectively). Using a large combined sample of 1063 radio-loud AGNs selected at low radio frequency, we investigate the RLF at 408 MHz of steep-spectrum radio sources. Our results support a luminosity-dependent evolution. Using core flux density data of the complete sample 3CRR, we investigate the core RLF at 5.0 GHz. Based on the combined sample with incomplete core flux data, we also estimate the core RLF using a modified factor of completeness. Both results are consistent and show that the comoving number density of radio cores displays a persistent decline with redshift, implying a negative density evolution. We find that the core RLF is obviously different from the total RLF at the 408 MHz band which is mainly contributed by extended lobes, implying that the cores and extended lobes could not be co-evolving at radio emission.

VizieR Online Data Catalog: MRCR-SUMSS Ultra-steep-spectrum (USS) sample (Broderick+, 2007)

NASA Astrophysics Data System (ADS)

Broderick, J. W.; Bryant, J. J.; Hunstead, R. W.; Sadler, E. M.; Murphy, T.

2008-09-01

This paper introduces a new program to find high-redshift radio galaxies in the Southern hemisphere through ultra-steep spectrum (USS) selection. We define a sample of 234 USS radio sources with spectral indices {alpha}843408<=-1.0 (S{nu}{prop.to}{nu}alpha) and flux densities S408>=200mJy in a region of 0.35sr, chosen by cross-correlating the revised 408MHz Molonglo Reference Catalogue, the 843MHz Sydney University Molonglo Sky Survey and the 1400MHz NRAO VLA Sky Survey in the overlap region -40{deg}

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.

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).

The nuclear region of low luminosity flat radio spectrum sources. II. Emission-line spectra

NASA Astrophysics Data System (ADS)

Gonçalves, A. C.; Serote Roos, M.

2004-01-01

We report on the spectroscopic study of 19 low luminosity Flat Radio Spectrum (LL FRS) sources selected from Marchã's et al. (\\cite{March96}) 200 mJy sample. In the optical, these objects are mainly dominated by the host galaxy starlight. After correcting the data for this effect, we obtain a new set of spectra clearly displaying weak emission lines; such features carry valuable information concerning the excitation mechanisms at work in the nuclear regions of LL FRS sources. We have used a special routine to model the spectra and assess the intensities and velocities of the emission lines; we have analyzed the results in terms of diagnostic diagrams. Our analysis shows that 79% of the studied objects harbour a Low Ionization Nuclear Emission-line Region (or LINER) whose contribution was swamped by the host galaxy starlight. The remaining objects display a higher ionization spectrum, more typical of Seyferts; due to the poor quality of the spectra, it was not possible to identify any possible large Balmer components. The fact that we observe a LINER-type spectrum in LL FRS sources supports the idea that some of these objects could be undergoing an ADAF phase; in addition, such a low ionization emission-line spectrum is in agreement with the black hole mass values and sub-Eddington accretion rates published for some FRS sources. Based on observations collected at the Multiple Mirror Telescope on Mt. Hopkins. Full Fig. 1 is only available in electronic form at http://www.edpsciences.org

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.

2003-12-01

Investigation of the color-space properties of mid-infrared sources in the MSX Galactic plane catalog reveals two distinct populations - a blue population composed mainly of evolved stars, masers and molecular clouds, and a red population comprising sources of a nebular nature - 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. A catalog extracted from these maps was published first by Becker et al., but we have re-reduced the data with significantly improved calibration and mosaicing procedures, resulting in an increase of ˜ 60% in the number of detected sources. Comparison of the radio and infrared catalogs resulted in a sample of 491 matches, out of which we estimate 38 to be false counterparts, all of them from the MSX red population. The radio sources with infrared counterparts are found to have extremely small scale height (FWHM of 14' or ˜ 35 pc), and have thermal radio spectrum. These properties suggest that the sample is dominated by HII regions, most of them are previously uncataloged. This research is supported be the National Science Foundation.

Exploring the Variability of the Flat-spectrum Radio Source 1633+382. II. Physical Properties

NASA Astrophysics Data System (ADS)

Algaba, Juan-Carlos; Lee, Sang-Sung; Rani, Bindu; Kim, Dae-Won; Kino, Motoki; Hodgson, Jeffrey; Zhao, Guang-Yao; Byun, Do-Young; Gurwell, Mark; Kang, Sin-Cheol; Kim, Jae-Young; Kim, Jeong-Sook; Kim, Soon-Wook; Park, Jong-Ho; Trippe, Sascha; Wajima, Kiyoaki

2018-06-01

The flat-spectrum radio quasar 1633+382 (4C 38.41) showed a significant increase of its radio flux density during the period 2012 March–2015 August, which correlates with γ-ray flaring activity. Multi-frequency simultaneous very long baseline interferometry (VLBI) observations were conducted as part of the interferometric monitoring of gamma-ray bright active galactic nuclei (iMOGABA) program and supplemented with additional radio monitoring observations with the OVRO 40 m telescope, the Boston University VLBI program, and the Submillimeter Array. The epochs of the maxima for the two largest γ-ray flares coincide with the ejection of two respective new VLBI components. Analysis of the spectral energy distribution indicates a higher turnover frequency after the flaring events. The evolution of the flare in the turnover frequency-turnover flux density plane probes the adiabatic losses in agreement with the shock-in-jet model. The derived synchrotron self-absorption magnetic fields, of the order of 0.1 mG, do not seem to change dramatically during the flares, and are much weaker, by a factor 104, than the estimated equipartition magnetic fields, indicating that the source of the flare may be associated with a particle-dominated emitting region.

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

On the population of remnant Fanaroff-Riley type II radio galaxies and implications for radio source dynamics

NASA Astrophysics Data System (ADS)

Godfrey, L. E. H.; Morganti, R.; Brienza, M.

2017-10-01

The purpose of this work is two-fold: (1) to quantify the occurrence of ultrasteep spectrum remnant Fanaroff-Riley type II (FRII) radio galaxies in a 74 MHz flux-limited sample, and (2) perform Monte Carlo simulations of the population of active and remnant FRII radio galaxies to confront models of remnant lobe evolution, and to provide guidance for further investigation of remnant radio galaxies. We find that fewer than 2 per cent of FRII radio galaxies with S74 MHz > 1.5 Jy are candidate ultrasteep spectrum remnants, where we define ultrasteep spectrum as α _74 MHz^1400 MHz > 1.2. Our Monte Carlo simulations demonstrate that models involving Sedov-like expansion in the remnant phase, resulting in rapid adiabatic energy losses, are consistent with this upper limit, and predict the existence of nearly twice as many remnants with normal (not ultrasteep) spectra in the observed frequency range as there are ultrasteep spectrum remnants. This model also predicts an ultrasteep remnant fraction approaching 10 per cent at redshifts z < 0.5. Importantly, this model implies the lobes remain overpressured with respect to the ambient medium well after their active lifetime, in contrast with existing observational evidence that many FRII radio galaxy lobes reach pressure equilibrium with the external medium whilst still in the active phase. The predicted age distribution of remnants is a steeply decreasing function of age. In other words, young remnants are expected to be much more common than old remnants in flux-limited samples. For this reason, incorporating higher frequency data ≳5 GHz will be of great benefit to future studies of the remnant population.

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.

The first VLBI image of an infrared-faint radio source

NASA Astrophysics Data System (ADS)

Middelberg, E.; Norris, R. P.; Tingay, S.; Mao, M. Y.; Phillips, C. J.; Hotan, A. W.

2008-11-01

Context: We investigate the joint evolution of active galactic nuclei and star formation in the Universe. Aims: In the 1.4 GHz survey with the Australia Telescope Compact Array of the Chandra Deep Field South and the European Large Area ISO Survey - S1 we have identified a class of objects which are strong in the radio but have no detectable infrared and optical counterparts. This class has been called Infrared-Faint Radio Sources, or IFRS. 53 sources out of 2002 have been classified as IFRS. It is not known what these objects are. Methods: To address the many possible explanations as to what the nature of these objects is we have observed four sources with the Australian Long Baseline Array. Results: We have detected and imaged one of the four sources observed. Assuming that the source is at a high redshift, we find its properties in agreement with properties of Compact Steep Spectrum sources. However, due to the lack of optical and infrared data the constraints are not particularly strong.

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.

Unveiling the AGN in IC 883: discovery of a parsec-scale radio jet

NASA Astrophysics Data System (ADS)

Romero-Cañizales, C.; Alberdi, A.; Ricci, C.; Arévalo, P.; Pérez-Torres, M. Á.; Conway, J. E.; Beswick, R. J.; Bondi, M.; Muxlow, T. W. B.; Argo, M. K.; Bauer, F. E.; Efstathiou, A.; Herrero-Illana, R.; Mattila, S.; Ryder, S. D.

2017-05-01

IC 883 is a luminous infrared galaxy (LIRG) classified as a starburst-active galactic nucleus (AGN) composite. In a previous study, we detected a low-luminosity AGN (LLAGN) radio candidate. Here, we report on our radio follow-up at three frequencies that provides direct and unequivocal evidence of the AGN activity in IC 883. Our analysis of archival X-ray data, together with the detection of a transient radio source with luminosity typical of bright supernovae, gives further evidence of the ongoing star formation activity, which dominates the energetics of the system. At sub-parsec scales, the radio nucleus has a core-jet morphology with the jet being a newly ejected component showing a subluminal proper motion of 0.6-1 c. The AGN contributes less than 2 per cent of the total IR luminosity of the system. The corresponding Eddington factor is ˜10-3, suggesting this is a low-accretion rate engine, as often found in LLAGNs. However, its high bolometric luminosity (˜1044 erg s-1) agrees better with a normal AGN. This apparent discrepancy may just be an indication of the transition nature of the nucleus from a system dominated by star formation, to an AGN-dominated system. The nucleus has a strongly inverted spectrum and a turnover at ˜4.4 GHz, thus qualifying as a candidate for the least luminous (L5.0 GHz ˜ 6.3 × 1028 erg s-1 Hz-1) and one of the youngest (˜3 × 103 yr) gigahertz-peaked spectrum (GPS) sources. If the GPS origin for the IC 883 nucleus is confirmed, then advanced mergers in the LIRG category are potentially key environments to unveil the evolution of GPS sources into more powerful radio galaxies.

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.

VizieR Online Data Catalog: The CLASS blazar survey. I. (Marcha+, 2001)

NASA Astrophysics Data System (ADS)

Marcha, M. J.; Caccianiga, A.; Browne, I. W. A.; Jackson, N.

2002-04-01

This paper presents a new complete and well-defined sample of flat-spectrum radio sources (FSRS) selected from the Cosmic Lens All-Sky Survey (CLASS), with the further constraint of a bright (mag<=17.5) optical counterpart. The sample has been designed to produce a large number of low-luminosity blazars in order to test the current unifying models in the low-luminosity regime. In this first paper the new sample is presented and the radio properties of the 325 sources contained therein are discussed. (1 data file).

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.

Announcment: Conference on Obscured AGN Across Cosmic Time

NASA Astrophysics Data System (ADS)

2006-12-01

Current deep surveys, notably in X-rays and the mid-IR, are making it possible to carry out a census of essentially all the luminous AGN in the Universe. By pene-trating the obscuration that, in Type 2 sources, hides the nuclear regions in the UV to the near-IR spectrum, these new surveys are finding the radio quiet coun-terparts of the powerful radio galaxies.

The Scale Invariant Synchrotron Jet of Flat Spectrum Radio Quasars

NASA Astrophysics Data System (ADS)

Du, L. M.; Bai, J. M.; Xie, Z. H.; Yi, T. F.; Xu, Y. B.; Xue, R.; Wang, X. H.

2015-06-01

In this paper, the scale invariance of the synchrotron jet of Flat Spectrum Radio Quasars has been studied using a sample of combined sources from FKM04 and from SDSS DR3 catalogue. Since the research of scale invariance has been focused on sub-Eddington cases that can be fitted onto the fundamental plane, while near-Eddington sources such as FSRQs have not been explicitly studied. The extracted physical properties of synchrotron jet of FSRQs have been shown to be scale invariant using our sample. The results are in good agreement with theoretical expectations of Heinz & Sunyaev (2003). Therefore, the jet synchrotron is shown to be scale independent, regardless of the accretion modes. Results in this article thus lend support to the scale invariant model of the jet synchrotron throughout the mass scale of black hole systems.

Ultra-high-energy cosmic rays from low-luminosity active galactic nuclei

NASA Astrophysics Data System (ADS)

Duţan, Ioana; Caramete, Laurenţiu I.

2015-03-01

We investigate the production of ultra-high-energy cosmic ray (UHECR) in relativistic jets from low-luminosity active galactic nuclei (LLAGN). We start by proposing a model for the UHECR contribution from the black holes (BHs) in LLAGN, which present a jet power Pj ⩽1046 erg s-1. This is in contrast to the opinion that only high-luminosity AGN can accelerate particles to energies ⩾ 50 EeV. We rewrite the equations which describe the synchrotron self-absorbed emission of a non-thermal particle distribution to obtain the observed radio flux density from sources with a flat-spectrum core and its relationship to the jet power. We found that the UHECR flux is dependent on the observed radio flux density, the distance to the AGN, and the BH mass, where the particle acceleration regions can be sustained by the magnetic energy extraction from the BH at the center of the AGN. We use a complete sample of 29 radio sources with a total flux density at 5 GHz greater than 0.5 Jy to make predictions for the maximum particle energy, luminosity, and flux of the UHECRs from nearby AGN. These predictions are then used in a semi-analytical code developed in Mathematica (SAM code) as inputs for the Monte-Carlo simulations to obtain the distribution of the arrival direction at the Earth and the energy spectrum of the UHECRs, taking into account their deflection in the intergalactic magnetic fields. For comparison, we also use the CRPropa code with the same initial conditions as for the SAM code. Importantly, to calculate the energy spectrum we also include the weighting of the UHECR flux per each UHECR source. Next, we compare the energy spectrum of the UHECRs with that obtained by the Pierre Auger Observatory.

Fermi monitoring of radio-loud narrow-line Seyfert 1 galaxies

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

Paliya, Vaidehi S.; Stalin, C. S.; Ravikumar, C. D., E-mail: vaidehi@iiap.res.in

2015-02-01

We present detailed analysis of the γ-ray flux variability and spectral properties of the five radio-loud narrow line Seyfert 1 (RL-NLSy1) galaxies, detected by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope, namely 1H 0323+342, SBS 0846+513, PMN J0948+0022, PKS 1502+036, and PKS 2004−447. The first three sources show significant flux variations, including the rapid variability of a few hours by 1H 0323+342. The average γ-ray spectrum of 1H 0323+342 and PMN J0948+0022 shows deviation from a simple power-law (PL) behavior, whereas the PL model gives a better fit for the other three sources. The spectra ofmore » 1H 0323+342, SBS 0846+513, and PMN J0948+0022, which are in low, flaring, and moderately active states, respectively, show significant curvature. Such curvature in the γ-ray spectrum of 1H 0323+342 and PMN J0948+0022 could be due to the emission region located inside the broad line region (BLR) where the primary mechanism of the γ-ray emission is inverse-Compton (IC) scattering of BLR photons occurring in the Klein–Nishina regime. The γ-ray emission of SBS 0846+513 is explained by IC scattering of dusty torus photons, which puts the emission region outside the BLR and thus under the Thomson regime. Therefore, the observed curvature of SBS 0846+513 could be intrinsic to the particle energy distribution. The presence of curvature in the γ-ray spectrum and flux variability amplitudes of some of the RL-NLSy1 galaxies suggests that these sources could be akin to low/moderate jet power flat spectrum radio quasars.« 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

AMI-LA observations of the SuperCLASS supercluster

NASA Astrophysics Data System (ADS)

Riseley, C. J.; Grainge, K. J. B.; Perrott, Y. C.; Scaife, A. M. M.; Battye, R. A.; Beswick, R. J.; Birkinshaw, M.; Brown, M. L.; Casey, C. M.; Demetroullas, C.; Hales, C. A.; Harrison, I.; Hung, C.-L.; Jackson, N. J.; Muxlow, T.; Watson, B.; Cantwell, T. M.; Carey, S. H.; Elwood, P. J.; Hickish, J.; Jin, T. Z.; Razavi-Ghods, N.; Scott, P. F.; Titterington, D. J.

2018-03-01

We present a deep survey of the Super-Cluster Assisted Shear Survey (SuperCLASS) supercluster - a region of sky known to contain five Abell clusters at redshift z ˜ 0.2 - performed using the Arcminute Microkelvin Imager (AMI) Large Array (LA) at 15.5 GHz. Our survey covers an area of approximately 0.9 deg2. We achieve a nominal sensitivity of 32.0 μJy beam-1 towards the field centre, finding 80 sources above a 5σ threshold. We derive the radio colour-colour distribution for sources common to three surveys that cover the field and identify three sources with strongly curved spectra - a high-frequency-peaked source and two GHz-peaked-spectrum sources. The differential source count (i) agrees well with previous deep radio source counts, (ii) exhibits no evidence of an emerging population of star-forming galaxies, down to a limit of 0.24 mJy, and (iii) disagrees with some models of the 15 GHz source population. However, our source count is in agreement with recent work that provides an analytical correction to the source count from the Square Kilometre Array Design Study (SKADS) Simulated Sky, supporting the suggestion that this discrepancy is caused by an abundance of flat-spectrum galaxy cores as yet not included in source population models.

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.

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.

An XMM-Newton view of the radio galaxy 3C 411

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

Bostrom, Allison; Reynolds, Christopher S.; Tombesi, Francesco

We present the first high signal-to-noise XMM-Newton observations of the broad-line radio galaxy 3C 411. After fitting various spectral models, an absorbed double power-law (PL) continuum and a blurred relativistic disk reflection model (kdblur) are found to be equally plausible descriptions of the data. While the softer PL component (Γ = 2.11) of the double PL model is entirely consistent with that found in Seyfert galaxies (and hence likely originates from a disk corona), the additional PL component is very hard (Γ = 1.05); amongst the active galactic nucleus zoo, only flat-spectrum radio quasars (FSRQ) have such hard spectra. Togethermore » with the flat radio-spectrum displayed by this source, we suggest that it should instead be classified as an FSRQ. This leads to potential discrepancies regarding the jet inclination angle, with the radio morphology suggesting a large jet inclination but the FSRQ classification suggesting small inclinations. The kdblur model predicts an inner disk radius of at most 20 r {sub g} and relativistic reflection.« less

Low-frequency radio observations of poor clusters of galaxies

NASA Technical Reports Server (NTRS)

Hanisch, R. J.; White, R. A.

1981-01-01

Observations have been made at the Clark Lake Radio Observatory of 16 poor clusters of galaxies at 34.3 MHz. Four of the poor clusters were detected at flux densities greater than 20 Jy. The spectra of the four detected clusters are all rather steep. Two of the detected clusters, AWM 4 and AWM 5, are also known to be X-ray sources. The possibility that the X-ray-emitting gas is heated by Coulomb interactions with the relativistic electrons responsible for the radio emission is investigated, and it is found that the observed X-ray luminosities can be accounted for if the electron energy spectrum extends to very low energies (gamma approximately 1-10). Collective plasma effects may increase the heating efficiency and eliminate the need to extrapolate the electron energy spectrum to such low values.

Extragalactic radio surveys in the pre-Square Kilometre Array era

PubMed Central

2017-01-01

The era of the Square Kilometre Array is almost upon us, and pathfinder telescopes are already in operation. This brief review summarizes our current knowledge of extragalactic radio sources, accumulated through six decades of continuum surveys at the low-frequency end of the electromagnetic spectrum and the extensive complementary observations at other wavelengths necessary to gain this understanding. The relationships between radio survey data and surveys at other wavelengths are discussed. Some of the outstanding questions are identified and prospects over the next few years are outlined. PMID:28791175

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).

Theory of Parabolic Arcs in Interstellar Scintillation Spectra

NASA Astrophysics Data System (ADS)

Cordes, James M.; Rickett, Barney J.; Stinebring, Daniel R.; Coles, William A.

2006-01-01

Interstellar scintillation (ISS), observed as time variation in the intensity of a compact radio source, is caused by small-scale structure in the electron density of the interstellar plasma. Dynamic spectra of ISS show modulation in radio frequency and time. Here we relate the (two-dimensional) power spectrum of the dynamic spectrum-the secondary spectrum-to the scattered image of the source. Recent work has identified remarkable parabolic arcs in secondary spectra. Each point in a secondary spectrum corresponds to interference between points in the scattered image with a certain Doppler shift and a certain delay. The parabolic arc corresponds to the quadratic relation between differential Doppler shift and delay through their common dependence on scattering angle. We show that arcs will occur in all media that scatter significant power at angles larger than the rms angle. Thus, effects such as source diameter, steep spectra, and dissipation scales, which truncate high angle scattering, also truncate arcs. Arcs are equally visible in simulations of nondispersive scattering. They are enhanced by anisotropic scattering when the spatial structure is elongated perpendicular to the velocity. In weak scattering the secondary spectrum is directly mapped from the scattered image, and this mapping can be inverted. We discuss additional observed phenomena including multiple arcs and reverse arclets oriented oppositely to the main arc. These phenomena persist for many refractive scattering times, suggesting that they are due to large-scale density structures, rather than low-frequency components of Kolmogorov turbulence.

State of the Art and Challenges of Radio Spectrum Monitoring in China

NASA Astrophysics Data System (ADS)

Lu, Q. N.; Yang, J. J.; Jin, Z. Y.; Chen, D. Z.; Huang, M.

2017-10-01

This paper provides an overview of radio spectrum monitoring in China. First, research background, the motivation is described and then train of thought, the prototype system, and the accomplishments are presented. Current radio spectrum monitoring systems are man-machine communication systems, which are unable to detect and process the radio interference automatically. In order to realize intelligent radio monitoring and spectrum management, we proposed an Internet of Things-based spectrum sensing approach using information system architecture and implemented a pilot program; then some very interesting results were obtained.

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 Spectrum Landscape: Prospects for Terrestrial Radio Astronomy

NASA Astrophysics Data System (ADS)

Liszt, Harvey Steven

2018-01-01

Radio astronomers work within broad constraints imposed by commercial and other non-astronomical uses of the radio spectrum, somewhat modified to accommodate astronomy’s particular needs through the provision of radio quiet zones, radio frequency allocations, coordination agreements and other devices of spectrum management. As radio astronomers increase the instantaneous bandwidth, frequency coverage and sensitivity of their instruments, these external constraints, and not the limitations of their own instruments, will increasingly be the greatest obstacles to radio astronomy’s ability to observe the cosmos from the surface of the Earth. Therefore, prospects for future radio astronomy operations are contingent on situational awareness and planning for the impact of non-astronomical uses of the radio frequency spectrum. New radio astronomy instruments will have to incorporate adaptive reactions to external developments, and radio astronomers should be encouraged to think in untraditional ways. Increased attention to spectrum management is one of these. In this talk I’ll recap some recent developments such as the proliferation of 76 – 81 GHz car radar and orbiting earth-mapping radars, either of which can burn out a radio astronomy receiver. I’ll summarize present trends for non-astronomical radio spectrum use that will be coming to fruition in the next decade or so, categorized into terrestrial fixed and mobile, airborne and space-borne uses, sub-divided by waveband from the cm to the sub-mm. I’ll discuss how they will impact terrestrial radio astronomy and the various ways in which radio astronomy should be prepared to react. Protective developments must occur both within radio astronomy’s own domain – designing, siting and constructing its instruments and mitigating unavoidable RFI – and facing outward toward the community of other spectrum users. Engagement with spectrum management is no panacea but it is an important means, and perhaps the only means, by which radio astronomy can take an active role in shaping its terrestrial environment.

European VLBI network observations of fourteen GHz-peaked-spectrum radio sources at 5 GHz

NASA Astrophysics Data System (ADS)

Xiang, L.; Reynolds, C.; Strom, R. G.; Dallacasa, D.

2006-08-01

We present the results of EVN polarization observations of fourteen GHz-Peaked-Spectrum (GPS) radio sources at 5 GHz. These sources were selected from bright GPS source samples and we aimed at finding Compact Symmetric Objects (CSOs). We have obtained full polarization 5 GHz VLBI observations of 14 sources providing information on their source structure and spectral indices. The results show that two core-jet sources 1433-040 and DA193, out of 14 GPS sources, exhibit integrated fractional polarizations of 3.6% and 1.0% respectively. The other 12 sources have no clear detection of pc-scale polarization. The results confirm that the GPS sources generally have very low polarization at 5 GHz. The sources 1133+432, 1824+271 and 2121-014 are confirmed as CSOs. Three new CSOs 0914+114, 1518+046 and 2322-040 (tentative) have been classified on the basis of 5 GHz images and spectral indices. The sources 1333+589, 1751+278 and 2323+790 can be classified either as compact doubles, and then they are likely CSO candidates or core-jet sources; further observations are needed for an appropriate classification; 0554-026, 1433-040 and 1509+054 are core-jet sources. In addition, we estimate that a component in the jet of quasar DA193 has superluminal motion of 3.3±0.6 h-1 c in 5.5 years.

Continuum radiation from active galactic nuclei: A statistical study

NASA Technical Reports Server (NTRS)

Isobe, T.; Feigelson, E. D.; Singh, K. P.; Kembhavi, A.

1986-01-01

The physics of the continuum spectrum of active galactic nuclei (AGNs) was examined using a large data set and rigorous statistical methods. A data base was constructed for 469 objects which include radio selected quasars, optically selected quasars, X-ray selected AGNs, BL Lac objects, and optically unidentified compact radio sources. Each object has measurements of its radio, optical, X-ray core continuum luminosity, though many of them are upper limits. Since many radio sources have extended components, the core component were carefully selected out from the total radio luminosity. With survival analysis statistical methods, which can treat upper limits correctly, these data can yield better statistical results than those previously obtained. A variety of statistical tests are performed, such as the comparison of the luminosity functions in different subsamples, and linear regressions of luminosities in different bands. Interpretation of the results leads to the following tentative conclusions: the main emission mechanism of optically selected quasars and X-ray selected AGNs is thermal, while that of BL Lac objects is synchrotron; radio selected quasars may have two different emission mechanisms in the X-ray band; BL Lac objects appear to be special cases of the radio selected quasars; some compact radio sources show the possibility of synchrotron self-Compton (SSC) in the optical band; and the spectral index between the optical and the X-ray bands depends on the optical luminosity.

Testing for EMC (electromagnetic compatibility) in the clinical environment.

PubMed

Paperman, D; David, Y; Martinez, M

1996-01-01

Testing for electromagnetic compatibility (EMC) in the clinical environment introduces a host of complex conditions not normally encountered under laboratory conditions. In the clinical environment, various radio-frequency (RF) sources of electromagnetic interference (EMI) may be present throughout the entire spectrum of interest. Isolating and analyzing the impact from the sources of interference to medical devices involves a multidisciplinary approach based on training in, and knowledge of, the following: operation of medical devices and their susceptibility to EMI; RF propagation modalities and interaction theory; spectrum analysis systems and techniques (preferably with signature analysis capabilities) and calibrated antennas; the investigation methodology of suspected EMC problems, and testing protocols and standards. Using combinations of standard test procedures adapted for the clinical environment with personnel that have an understanding of radio-frequency behavior increases the probability of controlling, proactively, EMI in the clinical environment, thus providing for a safe and more effective patient care environment.

Radio Disappearance of the Magnetar XTE J1810-197 and Continued X-ray Timing

NASA Astrophysics Data System (ADS)

Camilo, F.; Ransom, S. M.; Halpern, J. P.; Alford, J. A. J.; Cognard, I.; Reynolds, J. E.; Johnston, S.; Sarkissian, J.; van Straten, W.

2016-04-01

We report on timing, flux density, and polarimetric observations of the transient magnetar and 5.54 s radio pulsar XTE J1810-197 using the Green Bank, Nançay, and Parkes radio telescopes beginning in early 2006, until its sudden disappearance as a radio source in late 2008. Repeated observations through 2016 have not detected radio pulsations again. The torque on the neutron star, as inferred from its rotation frequency derivative \\dot{ν }, decreased in an unsteady manner by a factor of three in the first year of radio monitoring, until approximately mid-2007. By contrast, during its final year as a detectable radio source, the torque decreased steadily by only 9%. The period-averaged flux density, after decreasing by a factor of 20 during the first 10 months of radio monitoring, remained relatively steady in the next 22 months, at an average of 0.7 ± 0.3 mJy at 1.4 GHz, while still showing day-to-day fluctuations by factors of a few. There is evidence that during this last phase of radio activity the magnetar had a steep radio spectrum, in contrast to earlier flat-spectrum behavior. No secular decrease presaged its radio demise. During this time, the pulse profile continued to display large variations; polarimetry, including of a new profile component, indicates that the magnetic geometry remained consistent with that of earlier times. We supplement these results with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the first 4 years, XTE J1810-197 experienced non-monotonic excursions in frequency derivative by at least a factor of eight. But since 2007, its \\dot{ν } has remained relatively stable near its minimum observed value. The only apparent event in the X-ray record that is possibly contemporaneous with the radio shutdown is a decrease of ≈20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However, the permanence of the high-amplitude, thermal X-ray pulse, even after the (unexplained) radio demise, implies continuing magnetar activity.

A Possible X-Ray and Radio Counterpart of the High-Energy Gamma-Ray Source 3EG J2227+6122

NASA Technical Reports Server (NTRS)

Halpern, Jules P.; Gotthelf, E. V.; Helfand, D. J.; Leighly, K. M.; Oliversen, Ronald (Technical Monitor)

2001-01-01

The identity of the persistent EGRET sources in the Galactic plane is largely a mystery. For one of these, 3EG J2227+6122, our complete census of X-ray and radio sources in its error circle reveals a remarkable superposition of an incomplete radio shell with a flat radio spectrum, and a compact, power-law X-ray source with photon index Gamma = 1.5 and with no obvious optical counterpart. The radio shell is polarized at a level of approx. = 25%. The anomalous properties of the radio source prevent us from deriving a completely satisfactory theory as to its nature. Nevertheless, using data from ROSAT, ASCA, the VLA, and optical imaging and spectroscopy, we argue that the X-ray source may be a young pulsar with an associated wind-blown bubble or bow shock nebula, and an example of the class of radio-quiet pulsars which are hypothesized to comprise the majority of EGRET sources in the Galaxy. The distance to this source can be estimated from its X-ray absorption as 3 kpc. At this distance, the X-ray and gamma-ray luminosities would be approx. = 1.7 x 10(exp 33) and approx. = 3.7 x 10(exp 35) erg/s, respectively, which would require an energetic pulsar to power them. If, on the contrary, this X-ray source is not the counterpart of 3EG J2227+6122, then by process of elimination the X-ray luminosity of the latter must be less than 10(exp -4) of its gamma-ray luminosity, a condition not satisfied by any established class of gamma-ray source counterpart. This would require the existence of at least a quantitatively new type of EGRET source, as has been suggested in studies of other EGRET fields.

A Solar Stationary Type IV Radio Burst and Its Radiation Mechanism

NASA Astrophysics Data System (ADS)

Liu, Hongyu; Chen, Yao; Cho, Kyungsuk; Feng, Shiwei; Vasanth, Veluchamy; Koval, Artem; Du, Guohui; Wu, Zhao; Li, Chuanyang

2018-04-01

A stationary Type IV (IVs) radio burst was observed on September 24, 2011. Observations from the Nançay RadioHeliograph (NRH) show that the brightness temperature (TB) of this burst is extremely high, over 10^{11} K at 150 MHz and over 108 K in general. The degree of circular polarization (q) is between -60% ˜ -100%, which means that it is highly left-handed circularly polarized. The flux-frequency spectrum follows a power-law distribution, and the spectral index is considered to be roughly -3 ˜ -4 throughout the IVs. Radio sources of this event are located in the wake of the coronal mass ejection and are spatially dispersed. They line up to present a formation in which lower-frequency sources are higher. Based on these observations, it is suggested that the IVs was generated through electron cyclotron maser emission.

ADDING CONTEXT TO JAMES WEBB SPACE TELESCOPE SURVEYS WITH CURRENT AND FUTURE 21 cm RADIO OBSERVATIONS

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

Beardsley, A. P.; Morales, M. F.; Lidz, A.

Infrared and radio observations of the Epoch of Reionization promise to revolutionize our understanding of the cosmic dawn, and major efforts with the JWST, MWA, and HERA are underway. While measurements of the ionizing sources with infrared telescopes and the effect of these sources on the intergalactic medium with radio telescopes should be complementary, to date the wildly disparate angular resolutions and survey speeds have made connecting proposed observations difficult. In this paper we develop a method to bridge the gap between radio and infrared studies. While the radio images may not have the sensitivity and resolution to identify individualmore » bubbles with high fidelity, by leveraging knowledge of the measured power spectrum we are able to separate regions that are likely ionized from largely neutral, providing context for the JWST observations of galaxy counts and properties in each. By providing the ionization context for infrared galaxy observations, this method can significantly enhance the science returns of JWST and other infrared observations.« less

A design study of a signal detection system. [for search of extraterrestrial radio sources

NASA Technical Reports Server (NTRS)

Healy, T. J.

1980-01-01

A system is described which can aid in the search for radio signals from extraterrestrial sources, or in other applications characterized by low signal-to-noise ratios and very high data rates. The system follows a multichannel (16 million bin) spectrum analyzer, and has critical processing, system control, and memory fuctions. The design includes a moderately rich set of algorithms to be used in parallel to detect signals of unknown form. A multi-threshold approach is used to obtain high and low signal sensitivities. Relatively compact and transportable memory systems are specified.

Fermi/Large Area Telescope Discovery of Gamma-Ray Emission from a Relativistic Jet in the Narrow-Line Quasar PMN J0948+0022

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2009-06-17

In this paper, we report the discovery by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope of high-energy γ-ray emission from the peculiar quasar PMN J0948+0022 (z = 0.5846). The optical spectrum of this object exhibits rather narrow Hβ (FWHM(Hβ) ~1500 km s –1), weak forbidden lines, and is therefore classified as a narrow-line type I quasar. This class of objects is thought to have relatively small black hole mass and to accrete at a high Eddington ratio. The radio loudness and variability of the compact radio core indicate the presence of a relativistic jet. Quasi-simultaneous radio/optical/X-raymore » and γ-ray observations are presented. Both radio and γ-ray emissions (observed over five months) are strongly variable. The simultaneous optical and X-ray data from Swift show a blue continuum attributed to the accretion disk and a hard X-ray spectrum attributed to the jet. The resulting broadband spectral energy distribution (SED) and, in particular, the γ-ray spectrum measured by Fermi are similar to those of more powerful Flat-Spectrum Radio Quasars (FSRQs). A comparison of the radio and γ-ray characteristics of PMN J0948+0022 with the other blazars detected by LAT shows that this source has a relatively low radio and γ-ray power with respect to other FSRQs. The physical parameters obtained from modeling the SED also fall at the low power end of the FSRQ parameter region discussed in Celotti & Ghisellini. Finally, we suggest that the similarity of the SED of PMN J0948+0022 to that of more massive and more powerful quasars can be understood in a scenario in which the SED properties depend on the Eddington ratio rather than on the absolute power.« less

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.

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.

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.

HESS J1943+213: A Non-classical High-frequency-peaked BL Lac Object

NASA Astrophysics Data System (ADS)

Straal, S. M.; Gabányi, K. É.; van Leeuwen, J.; Clarke, T. E.; Dubner, G.; Frey, S.; Giacani, E.; Paragi, Z.

2016-05-01

HESS J1943+213 is an unidentified TeV source that is likely a high-frequency-peaked BL Lac (HBL) object, but that is also compatible with a pulsar wind nebula (PWN) nature. Each of these enormously different astronomical interpretations is supported by some of the observed unusual characteristics. In order to finally classify and understand this object, we took a three-pronged approach, through time-domain, high angular resolution, and multi-frequency radio studies. First, our deep time-domain observations with the Arecibo telescope failed to uncover the putative pulsar powering the proposed PWN. We conclude with ˜70% certainty that HESS J1943+213 does not host a pulsar. Second, long-baseline interferometry of the source with e-MERLIN at 1.5 and 5 GHz shows only a core, that is, a point source at ˜ 1-100 mas resolution. Its 2013 flux density is about one-third lower than that detected in the 2011 observations with similar resolution. This radio variability of the core strengthens the HBL object hypothesis. Third, additional evidence against the PWN scenario comes from the radio spectrum we compiled. The extended structure follows a power-law behavior with spectral index α \\=\\-0.54+/- 0.04 while the core component displays a flat spectrum (α \\=\\-0.03+/- 0.03). In contrast, the radio synchrotron emission of PWNe predicts a single power-law distribution. Overall, we rule out the PWN hypothesis and conclude that the source is a BL Lac object. The consistently high fraction (70%) of the flux density from the extended structure then leads us to conclude that HESS J1943+213 must be a non-classical HBL object.

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.

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

DOE PAGES

van Weeren, R. J.; Ogrean, G. A.; Jones, C.; ...

2017-01-31

To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. Northwest of the cluster, ~0.7 Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the intracluster medium (ICM) from the direction of a galaxy filament to the southeast. Here, we detect a density discontinuity north-northeast of this core, which we speculatemore » is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100–300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this active galactic nucleus lead into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot ≳20 keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.« less

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

NASA Astrophysics Data System (ADS)

van Weeren, R. J.; Ogrean, G. A.; Jones, C.; Forman, W. R.; Andrade-Santos, F.; Pearce, Connor J. J.; Bonafede, A.; Brüggen, M.; Bulbul, E.; Clarke, T. E.; Churazov, E.; David, L.; Dawson, W. A.; Donahue, M.; Goulding, A.; Kraft, R. P.; Mason, B.; Merten, J.; Mroczkowski, T.; Nulsen, P. E. J.; Rosati, P.; Roediger, E.; Randall, S. W.; Sayers, J.; Umetsu, K.; Vikhlinin, A.; Zitrin, A.

2017-02-01

To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. Northwest of the cluster, ˜0.7 Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the intracluster medium (ICM) from the direction of a galaxy filament to the southeast. We detect a density discontinuity north-northeast of this core, which we speculate is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100-300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this active galactic nucleus lead into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot ≳20 keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

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

Van Weeren, R. J.; Jones, C.; Forman, W. R.

To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. Northwest of the cluster, ∼0.7 Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the intracluster medium (ICM) from the direction of a galaxy filament to the southeast. We detect a density discontinuity north-northeast of this core, which we speculate ismore » associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100–300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this active galactic nucleus lead into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot ≳20 keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.« less

Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745

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

van Weeren, R. J.; Ogrean, G. A.; Jones, C.

To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. Northwest of the cluster, ~0.7 Mpc from the center, there is a ram-pressure-stripped core that appears to have traversed the densest parts of the cluster after entering the intracluster medium (ICM) from the direction of a galaxy filament to the southeast. Here, we detect a density discontinuity north-northeast of this core, which we speculatemore » is associated with a cold front. Our radio images reveal new details for the complex radio relic and radio halo in this cluster. In addition, we discover several new filamentary radio sources with sizes of 100–300 kpc. A few of these seem to be connected to the main radio relic, while others are either embedded within the radio halo or projected onto it. A narrow-angled-tailed (NAT) radio galaxy, a cluster member, is located at the center of the radio relic. The steep spectrum tails of this active galactic nucleus lead into the large radio relic where the radio spectrum flattens again. This morphological connection between the NAT radio galaxy and relic provides evidence for re-acceleration (revival) of fossil electrons. The presence of hot ≳20 keV ICM gas detected by Chandra near the relic location provides additional support for this re-acceleration scenario.« less

The bright unidentified γ-ray source 1FGL J1227.9–4852: Can it be associated with a low-mass X-ray binary? [The bright unidentified γ-ray source 1FGL J1227.9–4852: Can it be associated with an LMXB?

DOE PAGES

Hill, A. B.; Szostek, A.; Corbel, S.; ...

2011-07-08

We present an analysis of high energy (HE; 0.1–300 GeV) γ-ray observations of 1FGL J1227.9–4852 with the Fermi Gamma-ray Space Telescope, follow-up radio observations with the Australia Telescope Compact Array, Giant Metrewave Radio Telescope and Parkes radio telescopes of the same field and follow-up optical observations with the ESO VLT. We also examine archival XMM– Newton and INTEGRAL X-ray observations of the region around this source. The γ-ray spectrum of 1FGL J1227.9–4852 is best fitted with an exponentially cut-off power law, reminiscent of the population of pulsars observed by Fermi. A previously unknown, compact radio source within the 99.7 permore » cent error circle of 1FGL J1227.9–4852 is discovered and has a morphology consistent either with an AGN core/jet structure or with two roughly symmetric lobes of a distant radio galaxy. A single bright X-ray source XSS J12270–4859, a low-mass X-ray binary, also lies within the 1FGL J1227.9–4852 error circle and we report the first detection of radio emission from this source. The potential association of 1FGL J1227.9–4852 with each of these counterparts is discussed. Based upon the available data we find the association of the γ-ray source to the compact double radio source unlikely and suggest that XSS J12270–4859 is a more likely counterpart to the new HE source. As a result, we propose that XSS J12270–4859 may be a millisecond binary pulsar and draw comparisons with PSR J1023+0038.« 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.; 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.

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.;

Discovery of Misaligned Radio Emission in Galaxy Cluster Zw CL 2971

NASA Astrophysics Data System (ADS)

Wallack, Nicole; Migliore, C.; Resnick, A.; White, T.; Liu, C.

2014-01-01

In a search for green valley galaxies with radio loud active galactic nuclei (AGN), we found one such object that may be associated with the cluster of galaxies Zw CL 2971 (z = 0.098). Serendipitously, we found in this cluster a strong bent-jet radio source associated with the cluster's central dominant (cD) elliptical galaxy. The center of the cD galaxy is coincident (0.35 arcsecond) with the second brightest spot of radio continuum emission (34.3 mJy as measured by FIRST), but the brightest radio hotspot (66.8 mJy) is offset by 4.6 arcseconds 9 kpc at the redshift of the cluster) and has no visible counterpart. Furthermore, the optical spectrum of the cD galaxy has only weak emission lines, suggesting the absence of a currently active nucleus. It is possible that the counterpart is optically faint (possibly due to a recently completed duty cycle) or is not visible due to movement or position. If the radio source is a distant background object, then the brighter jet is most likely magnified by gravitational lensing. If the radio source is located at the redshift of the cluster, then the brighter radio jet trails backward toward and past the cD galaxy to a distance of ~120 kpc, while the fainter jet is bent at a nearly orthogonal angle, ~40 kpc away from the brightest radio hotspot, in the opposite direction. These geometric offsets could be used to constrain the duty cycle history of the AGN creating the radio emission, as well as the dynamical properties of the intracluster medium.

An Evolving Compact Jet in the Black Hole X-Ray Binary Maxi J1836-194

NASA Technical Reports Server (NTRS)

Russell, D. M.; Russell, T. D.; Miller-Jones, J. C. A.; O'Brien, K.; Soria, R.; Sivakoff, G. R.; Slaven-Blair, T.; Lewis, F.; Markoff, S.; Homan, J.;

Time-dependent Models for Blazar Emission with the Second-order Fermi Acceleration

NASA Astrophysics Data System (ADS)

Asano, Katsuaki; Takahara, Fumio; Kusunose, Masaaki; Toma, Kenji; Kakuwa, Jun

2014-01-01

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101-232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range of Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 1038 erg s-1, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.

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.

Radio Frequency Interference: Radio Astronomy's Biggest Enemy

NASA Astrophysics Data System (ADS)

Acevedo, F.; Ghosh, Tapasi

1997-12-01

As technology progresses, the demand for the usage of the electromagnetic spectrum increases with it. The development is so fast and prolific that clean band space for passive users such as Radio Astronomy is becoming ever so scarce. Even though, several spectral bands have been protected for Radio Astronomy by Federal Communication Commission (in the USA) under the recommendations of the International Telecommunication Union (ITU), pressure for making more spectral space commercially usable is extreme. Although these commercial usages make our modern living at all possible, often the extreme vulnerability of passive users are are not fully appreciated, resulting in unwanted emissions (RFI) in the Radio Astronomy Bands. Another source of RFI is the fact that many of the electronic devices used in the observatories themselves generate radio waves. If proper precautions are not taken, these can be received back through the Radio Telescope itself. This problem is referred to as internal RFI. The focus of this paper is the search and diminution of internal RFI in the Arecibo Observatory in Arecibo, Puerto Rico. Using a simple setup of a log-periodic antenna and a Spectrum Analyzer, spectra spanning a frequency range of 100 - 1800 MHZ were recorded in some areas of the Observatory and the new Visitor Center (AOVEF). The measurements disclosed sources of radio emission among some of the digital electronic equipment in the Equipment room and a few displays in the AOVEF. Most prominent of these was a 2.5 MHz comb spanning the entire range of the measurements emitted from the SRENDIP and AOFTM machines. The respective groups were informed and corrective shielding & isolations were implemented immediately. In AOVEF, three displays, some audio-visual equipment, and video/digital cameras used by the visitors were found to be "leaky". In future, the use of such cameras will be prohibited and the exhibits will be screened appropriately.

Modal noise impact in radio over fiber multimode fiber links.

PubMed

Gasulla, I; Capmany, J

2008-01-07

A novel analysis is given on the statistics of modal noise for a graded-index multimode fiber (MMF) link excited by an analog intensity modulated laser diode. We present the speckle contrast as a function of the power spectrum of the modulated source and the transfer function of the MMF which behaves as an imperfect transversal microwave photonic filter. The theoretical results confirm that the modal noise is directly connected with the coherence properties of the optical source and show that the performance of high-frequency Radio Over Fiber (ROF) transmission through MMF links for short and middle reach distances is not substantially degraded by modal noise.

Localization and cooperative communication methods for cognitive radio

NASA Astrophysics Data System (ADS)

Duval, Olivier

We study localization of nearby nodes and cooperative communication for cognitive radios. Cognitive radios sensing their environment to estimate the channel gain between nodes can cooperate and adapt their transmission power to maximize the capacity of the communication between two nodes. We study the end-to-end capacity of a cooperative relaying scheme using orthogonal frequency-division modulation (OFDM) modulation, under power constraints for both the base station and the relay station. The relay uses amplify-and-forward and decode-and-forward cooperative relaying techniques to retransmit messages on a subset of the available subcarriers. The power used in the base station and the relay station transmitters is allocated to maximize the overall system capacity. The subcarrier selection and power allocation are obtained based on convex optimization formulations and an iterative algorithm. Additionally, decode-and-forward relaying schemes are allowed to pair source and relayed subcarriers to increase further the capacity of the system. The proposed techniques outperforms non-selective relaying schemes over a range of relay power budgets. Cognitive radios can be used for opportunistic access of the radio spectrum by detecting spectrum holes left unused by licensed primary users. We introduce a spectrum holes detection approach, which combines blind modulation classification, angle of arrival estimation and number of sources detection. We perform eigenspace analysis to determine the number of sources, and estimate their angles of arrival (AOA). In addition, we classify detected sources as primary or secondary users with their distinct second-orde one-conjugate cyclostationarity features. Extensive simulations carried out indicate that the proposed system identifies and locates individual sources correctly, even at -4 dB signal-to-noise ratios (SNR). In environments with a high density of scatterers, several wireless channels experience nonline-of-sight (NLOS) condition, increasing the localization error, even when the AOA estimate is accurate. We present a real-time localization solver (RTLS) for time-of-arrival (TOA) estimates using ray-tracing methods on the map of the geometry of walls and compare its performance with classical TOA trilateration localization methods. Extensive simulations and field trials for indoor environments show that our method increases the coverage area from 1.9% of the floor to 82.3 % and the accuracy by a 10-fold factor when compared with trilateration. We implemented our ray tracing model in C++ using the CGAL computational geometry algorithm library. We illustrate the real-time property of our RTLS that performs most ray tracing tasks in a preprocessing phase with time and space complexity analyses and profiling of our software.

The Frequency Spectrum Radio.

ERIC Educational Resources Information Center

Howkins, John, Ed.

1979-01-01

This journal issue focuses on the frequency spectrum used in radio communication and on the World Administrative Radio Conference, sponsored by the International Telecommunication Union, held in Geneva, Switzerland, in the fall of 1979. Articles describe the World Administrative Radio Conference as the most important radio communication conference…

NuSTAR observations of the powerful radio-galaxy Cygnus A

DOE PAGES

Reynolds, Christopher S.; Lohfink, Anne M.; Ogle, Patrick M.; ...

2015-07-29

Here, we present NuSTAR observations of the powerful radio galaxy Cygnus A, focusing on the central absorbed active galactic nucleus (AGN). Cygnus A is embedded in a cool-core galaxy cluster, and hence we also examine archival XMM-Newton data to facilitate the decomposition of the spectrum into the AGN and intracluster medium components. NuSTAR gives a source-dominated spectrum of the AGN out tomore » $$\\gt 70$$ keV. In gross terms, the NuSTAR spectrum of the AGN has the form of a power law ($${\\rm{\\Gamma }}\\sim 1.6-1.7$$) absorbed by a neutral column density of $${N}_{{\\rm{H}}}\\sim 1.6\\times {10}^{23}\\;\\;{\\mathrm{cm}}^{-2}$$. However, we also detect curvature in the hard ($$\\gt 10$$ keV) spectrum resulting from reflection by Compton-thick matter out of our line of sight to the X-ray source. Compton reflection, possibly from the outer accretion disk or obscuring torus, is required even permitting a high-energy cut off in the continuum source; the limit on the cut-off energy is $${E}_{\\mathrm{cut}}\\gt 111$$ keV(90% confidence). Interestingly, the absorbed power law plus reflection model leaves residuals suggesting the absorption/emission from a fast ($$15,000-26,000\\;\\;\\mathrm{km}\\;\\;{{\\rm{s}}}^{-1}\\;$$), high column-density ($${N}_{W}\\gt 3\\times {10}^{23}\\;\\;{\\mathrm{cm}}^{-2}$$), highly ionized ($$\\xi \\sim 2500\\;\\mathrm{erg}\\;\\mathrm{cm}\\;{{\\rm{s}}}^{-1}$$) wind. A second, even faster ionized wind component is also suggested by these data. We show that the ionized wind likely carries a significant mass and momentum flux, and may carry sufficient kinetic energy to exercise feedback on the host galaxy. If confirmed, the simultaneous presence of a strong wind and powerful jets in Cygnus A demonstrates that feedback from radio-jets and sub-relativistic winds are not mutually exclusive phases of AGN activity but can occur simultaneously.« less

BVR Photometry Of An Inverted-spectrum, Flat-spectrum Radio Source With The Rowan 0.4-meter Telescope

NASA Astrophysics Data System (ADS)

Guerra, Erick; Diekewicz, A.

2012-01-01

Several galaxies have been selected for an exploratory campaign with 0.4-meter telescope atop Science Hall at Rowan University. These galaxies exhibit inverted radio spectra on the basis of fluxes in the GB6 and VLA FIRST catalogs and have SDSS magnitudes in g-band less than 15.5. The results of BVR photometry of one of these galaxies, CGCG 215-024, are presented. These are the first results from an ongoing campaign to expand the function of the observatory atop Science Hall. Efforts to mitigate bulding vibration and light pollution in future work will be presented. The authors would like to acknowledge Ric and Jean Edelman for their gift that funded the 0.4-meter telescope.

Components of the Extragalactic Gamma-Ray Background

NASA Technical Reports Server (NTRS)

Stecker, Floyd W.; Venters, Tonia M.

2011-01-01

We present new theoretical estimates of the relative contributions of unresolved blazars and star-forming galaxies to the extragalactic gamma-ray background (EGB) and discuss constraints on the contributions from alternative mechanisms such as dark matter annihilation and truly diffuse gamma-ray production. We find that the Fermi source count data do not rule out a scenario in which the EGB is dominated by emission from unresolved blazars, though unresolved star-forming galaxies may also contribute significantly to the background, within order-of-magnitude uncertainties. In addition, we find that the spectrum of the unresolved star-forming galaxy contribution cannot explain the EGB spectrum found by EGRET at energies between 50 and 200 MeV, whereas the spectrum of unresolved flat spectrum radio quasars, when accounting for the energy-dependent effects of source confusion, could be consistent with the combined spectrum of the low-energy EGRET EGB measurements and the Fermi-Large Area Telescope EGB measurements.

High-frequency predictions for number counts and spectral properties of extragalactic radio sources. New evidence of a break at mm wavelengths in spectra of bright blazar sources

NASA Astrophysics Data System (ADS)

Tucci, M.; Toffolatti, L.; de Zotti, G.; Martínez-González, E.

2011-09-01

We present models to predict high-frequency counts of extragalactic radio sources using physically grounded recipes to describe the complex spectral behaviour of blazars that dominate the mm-wave counts at bright flux densities. We show that simple power-law spectra are ruled out by high-frequency (ν ≥ 100 GHz) data. These data also strongly constrain models featuring the spectral breaks predicted by classical physical models for the synchrotron emission produced in jets of blazars. A model dealing with blazars as a single population is, at best, only marginally consistent with data coming from current surveys at high radio frequencies. Our most successful model assumes different distributions of break frequencies, νM, for BL Lacs and flat-spectrum radio quasars (FSRQs). The former objects have substantially higher values of νM, implying that the synchrotron emission comes from more compact regions; therefore, a substantial increase of the BL Lac fraction at high radio frequencies and at bright flux densities is predicted. Remarkably, our best model is able to give a very good fit to all the observed data on number counts and on distributions of spectral indices of extragalactic radio sources at frequencies above 5 and up to 220 GHz. Predictions for the forthcoming sub-mm blazar counts from Planck, at the highest HFI frequencies, and from Herschel surveys are also presented. Appendices are available in electronic form at http://www.aanda.org

SDSS J211852.96-073227.5: a new γ-ray flaring narrow-line Seyfert 1 galaxy

NASA Astrophysics Data System (ADS)

Yang, Hui; Yuan, Weimin; Yao, Su; Li, Ye; Zhang, Jin; Zhou, Hongyan; Komossa, S.; Liu, He-Yang; Jin, Chichuan

2018-07-01

We report on the identification of a new γ-ray-emitting narrow-line Seyfert 1 (NLS1) galaxy, SDSS J211852.96-073227.5 (hereinafter J2118-0732). The galaxy, at a redshift of 0.26, is associated with a radio source of flat/inverted spectrum at high radio frequencies. The analysis of its optical spectrum obtained in the Sloan Digital Sky Survey (SDSS) revealed a small linewidth of the broad component of the Hβ line (full width at half-maximum = 1585 km s-1), making it a radio-loud NLS1 galaxy - an intriguing class of active galactic nuclei with exceptional multiwavelength properties. A new γ-ray source centred at J2118-0732 was sporadically detected during 2009-2013 in form of flares by the Fermi-LAT. Our XMM-Newton observations revealed a flat X-ray spectrum described by a simple power law, and a flux variation by a factor of ˜2.5 in five months. The source also shows intraday variability in the infrared band. Its broad-band spectral energy distribution can be modelled by emission from a simple one-zone leptonic jet model, and the flux drop from infrared to X-rays in five months can be explained by changes of the jet parameters, though the exact values may be subject to relatively large uncertainties. With the NLS1-blazar composite nucleus, the clear detection of the host galaxy, and the synchronous variations in the multiwavelength fluxes, J2118-0732 provides a new perspective on the formation and evolution of relativistic jets under the regime of relatively small black hole masses and high accretion rates.

SDSS J211852.96-073227.5: a new γ-ray flaring narrow-line Seyfert 1 galaxy

NASA Astrophysics Data System (ADS)

Yang, Hui; Yuan, Weimin; Yao, Su; Li, Ye; Zhang, Jin; Zhou, Hongyan; Komossa, S.; Liu, He-Yang; Jin, Chichuan

2018-04-01

We report on the identification of a new γ-ray-emitting narrow-line Seyfert 1 (NLS1) galaxy, SDSS J211852.96-073227.5 (hereafter J2118-0732). The galaxy, at a redshift of 0.26, is associated with a radio source of flat/inverted spectrum at high radio frequencies. The analysis of its optical spectrum obtained in the Sloan Digital Sky Survey revealed a small linewidth of the broad component of the Hβ line (FWHM = 1585 km s-1), making it a radio-loud NLS1 galaxy - an intriguing class of active galactic nuclei with exceptional multi-wavelength properties. A new γ-ray source centred at J2118-0732 was sporadically detected during 2009-2013 in form of flares by the Fermi-LAT. Our XMM-Newton observations revealed a flat X-ray spectrum described by a simple power law, and a flux variation by a factor of ˜2.5 in 5 months. The source also shows intraday variability in the infrared band. Its broad-band spectral energy distribution can be modelled by emission from a simple one-zone leptonic jet model, and the flux drop from infrared to X-rays in five months can be explained by changes of the jet parameters, though the exact values may be subject to relatively large uncertainties. With the NLS1-blazar composite nucleus, the clear detection of the host galaxy and the synchronous variations in the multi-wavelength fluxes, J2118-0732 provides a new perspective on the formation and evolution of relativistic jets under the regime of relatively small black hole masses and high accretion rates.

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.

The Radio-optical Spectra of BL Lacs and Possible Relatives

NASA Astrophysics Data System (ADS)

Dennett-Thorpe, J.

I consider the suggestion that, in a complete sample of flat-spectrum radio sources with available optical spectra (Marcha et al 1996), the strong emission line objects, or those with passive elliptical spectra are close relatives of the BL Lacs. New observations at four frequencies from 8 to 43GHz are presented, together with evidence for radio variability. Combined with other radio and optical data from the literature, we are able to construct the non-thermal SEDs and use these to address the questions: are the optically passive objects potentially `unrecognised' BL Lacs (either intrinsically weak and/or hidden by starlight)? What is the relationship between the surprising number of strong emission-line objects and the BL Lacs?

Fermi LAT detection of increase gamma-ray emission from OJ 248

NASA Astrophysics Data System (ADS)

Orienti, M.; D'Ammando, F.

2012-09-01

The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity from a source positionally consistent with the flat spectrum radio quasar OJ 248 (also known as 2FGL J0830.5+2407, Nolan et al. 2012, ApJS, 199, 31) with radio coordinates R.A.: 127.7170254 deg, Dec: 24.1832836 deg (J2000, Johnston et al. 1995, AJ, 110, 880) at redshift z=0.94 (Hewitt & Burbidge 1993, ApJS, 87, 451).

Fermi LAT detection of an increase of gamma-ray activity of S5 1044+71

NASA Astrophysics Data System (ADS)

D'Ammando, F.; Orienti, M.

2014-01-01

The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity from a source positionally consistent with the flat spectrum radio quasar S5 1044+71 (also known as 2FGL J1048.3+7144, Nolan et al. 2012, ApJS, 199, 31) with radio coordinates R.A.: 162.1150829 deg, Dec: 71.7266494 deg (J2000; Johnston et al. 1995, AJ, 110, 880) at redshift z=1.15 (Polatidis et al.

Fermi LAT detection of a continuing increase of gamma-ray activity of CTA 102

NASA Astrophysics Data System (ADS)

Orienti, M.; D'Ammando, F.

2012-09-01

The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed gamma-ray flaring activity from a source positionally consistent with the flat spectrum radio quasar CTA 102 (also known as 2FGL J2232.4+1143, Nolan et al. 2012, ApJS, 199, 31) with radio coordinates R.A.: 338.1517038 deg, Dec: 11.7308067 deg (J2000, Johnston et al. 1995, AJ, 110, 880) at redshift z=1.037 (Schmidt 1965, ApJ, 141, 1295).

High energy spectrum of spherically accreting black holes

NASA Technical Reports Server (NTRS)

Meszaros, P.; Ostriker, J. P.

1983-01-01

Spherically accreting black holes may sustain strong collisionless shocks, downstream of which the fluid approximation is not valid. The proton-electron Coulomb exchange provides for the downstream matter diffusion into the hole. Energy conversion efficiencies upward of 10-30 percent are obtained, with most of the luminosity in hard X-rays and gamma-rays. The whole spectrum and its application for radio-quiet QSO's and galactic X- and gamma-ray sources are discussed.

Multiband Observations of the Quasar PKS 2326–502 during Active and Quiescent Gamma-Ray States in 2010–2012

DOE PAGES

Dutka, Michael S.; Carpenter, Bryce D.; Ojha, Roopesh; ...

2017-01-30

We present that quasi-simultaneous observations of the Flat Spectrum Radio Quasar PKS 2326-502 were carried out in the γ-ray, X-ray, UV, optical, near-infrared, and radio bands. Using these observations, we are able to characterize the spectral energy distribution (SED) of the source during two flaring and one quiescent γ-ray states. These data were used to constrain one-zone leptonic models of the SEDs of each flare and investigate the physical conditions giving rise to them. While modeling one flare required only changes in the electron spectrum compared to the quiescent state, modeling the other flare required changes in both the electronmore » spectrum and the size of the emitting region. These results are consistent with an emerging pattern of two broad classes of flaring states seen in blazars. Type 1 flares are explained by changes solely in the electron distribution, whereas type 2 flares require a change in an additional parameter. Finally, this suggests that different flares, even in the same source, may result from different physical conditions or different regions in the jet.« less

The IRAS galaxy 0421+040P06: An active spiral (?) galaxy with extended radio lobes

NASA Technical Reports Server (NTRS)

Beichman, C. A.; Wynn-Williams, C. G.; Lonsdale, C. J.; Persson, S. E.; Heasley, J. N.; Miley, G. K.; Soifer, B. T.; Neugebauer, G.; Becklin, E. E.; Houck, J. R.

1984-01-01

The infrared bright galaxy 0421+040P06 detected by IRAS at 25 and 60 microns was studied at optical, infrared, and radio wavelength. It is a luminous galaxy with apparent spiral structure emitting 4 x 10 to the 37th power from far-infrared to optical wavelengths. Optical spectroscopy reveals a Seyfert 2 emission line spectrum, making 0421+040P06 the first active galaxy selected from an unbiased infrared survey of galaxies. The fact that this galaxy shows a flatter energy distribution with more 25 micron emission than other galaxies in the infrared sample may be related to the presence of an intense active nucleus. The radio observations reveal the presence of a non-thermal source that, at 6 cm, shows a prominent double lobed structure 20 to 30 kpc in size extending beyond the optical confines of the galaxy. The radio source is three to ten times larger than structures previously seen in spiral galaxies.

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.

A general method for radio spectrum efficiency defining

NASA Astrophysics Data System (ADS)

Ramadanovic, Ljubomir M.

1986-08-01

A general method for radio spectrum efficiency defining is proposed. Although simple it can be applied to various radio services. The concept of spectral elements, as information carriers, is introduced to enable the organization of larger spectral spaces - radio network models - characteristic for a particular radio network. The method is applied to some radio network models, concerning cellular radio telephone systems and digital radio relay systems, to verify its unified approach capability. All discussed radio services operate continuously.

Noise and interference study for satellite lightning sensor

NASA Technical Reports Server (NTRS)

Herman, J. R.

1981-01-01

The use of radio frequency techniques for the detection and monitoring of terrestrial thunderstorms from space are discussed. Three major points are assessed: (1) lightning and noise source characteristics; (2) propagation effects imposed by the atmosphere and ionosphere; and (3) the electromagnetic environment in near space within which lightning RF signatures must be detected. A composite frequency spectrum of the peak of amplitude from lightning flashes is developed. Propagation effects (ionospheric cutoff, refraction, absorption, dispersion and scintillation) are considered to modify the lightning spectrum to the geosynchronous case. It is suggested that in comparing the modified spectrum with interfering noise source spectra RF lightning pulses on frequencies up to a few GHz are detectable above the natural noise environment in near space.

Mpc-scale diffuse radio emission in two massive cool-core clusters of galaxies

NASA Astrophysics Data System (ADS)

Sommer, Martin W.; Basu, Kaustuv; Intema, Huib; Pacaud, Florian; Bonafede, Annalisa; Babul, Arif; Bertoldi, Frank

2017-04-01

Radio haloes are diffuse synchrotron sources on scales of ˜1 Mpc that are found in merging clusters of galaxies, and are believed to be powered by electrons re-accelerated by merger-driven turbulence. We present measurements of extended radio emission on similarly large scales in two clusters of galaxies hosting cool cores: Abell 2390 and Abell 2261. The analysis is based on interferometric imaging with the Karl G. Jansky Very Large Array, Very Large Array and Giant Metrewave Radio Telescope. We present detailed radio images of the targets, subtract the compact emission components and measure the spectral indices for the diffuse components. The radio emission in A2390 extends beyond a known sloshing-like brightness discontinuity, and has a very steep in-band spectral slope at 1.5 GHz that is similar to some known ultrasteep spectrum radio haloes. The diffuse signal in A2261 is more extended than in A2390 but has lower luminosity. X-ray morphological indicators, derived from XMM-Newton X-ray data, place these clusters in the category of relaxed or regular systems, although some asymmetric features that can indicate past minor mergers are seen in the X-ray brightness images. If these two Mpc-scale radio sources are categorized as giant radio haloes, they question the common assumption of radio haloes occurring exclusively in clusters undergoing violent merging activity, in addition to commonly used criteria for distinguishing between radio haloes and minihaloes.

47 CFR 1.9030 - Long-term de facto transfer leasing arrangements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... additional qualifications are met: (A) The license does not involve spectrum licensed in a Wireless Radio... facilitate international or Interdepartment Radio Advisory Committee (IRAC) coordination). (4) The spectrum... spectrum leasing arrangement involving a licensee in the Public Safety Radio Services (see part 90, subpart...

47 CFR 1.9020 - Spectrum manager leasing arrangements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... geographic overlap with spectrum in any licensed Wireless Radio Service (including the same service), or in... into a spectrum leasing arrangement involving a licensee in the Public Safety Radio Services (see part... Radio Service (PMRS), private, or non-commercial basis. (7) Regulatory fees. The licensee remains...

47 CFR 1.9020 - Spectrum manager leasing arrangements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... geographic overlap with spectrum in any licensed Wireless Radio Service (including the same service), or in... into a spectrum leasing arrangement involving a licensee in the Public Safety Radio Services (see part... Radio Service (PMRS), private, or non-commercial basis. (7) Regulatory fees. The licensee remains...

47 CFR 1.9020 - Spectrum manager leasing arrangements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... geographic overlap with spectrum in any licensed Wireless Radio Service (including the same service), or in... into a spectrum leasing arrangement involving a licensee in the Public Safety Radio Services (see part... Radio Service (PMRS), private, or non-commercial basis. (7) Regulatory fees. The licensee remains...

47 CFR 1.9030 - Long-term de facto transfer leasing arrangements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... additional qualifications are met: (A) The license does not involve spectrum licensed in a Wireless Radio... facilitate international or Interdepartment Radio Advisory Committee (IRAC) coordination). (4) The spectrum... spectrum leasing arrangement involving a licensee in the Public Safety Radio Services (see part 90, subpart...

47 CFR 1.9030 - Long-term de facto transfer leasing arrangements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... additional qualifications are met: (A) The license does not involve spectrum licensed in a Wireless Radio... facilitate international or Interdepartment Radio Advisory Committee (IRAC) coordination). (4) The spectrum... spectrum leasing arrangement involving a licensee in the Public Safety Radio Services (see part 90, subpart...

The diffuse neutrino flux from FR-II radio galaxies and blazars: A source property based estimate

NASA Astrophysics Data System (ADS)

Becker, Julia K.; Biermann, Peter L.; Rhode, Wolfgang

2005-05-01

Water and ice Cherenkov telescopes of the present and future aim for the detection of a neutrino signal from extraterrestrial sources at energies Eν > PeV [Woschnagg and AMANDA Collaboration, Astro-ph/0409423, talk at Neutrino 2004; Montaruli, in: Peter W. Gorham, Particle Astrophysics Instrumentation, Proceedings of the SPIE, vol. 4858, 2003, p. 92; IceCube Collaboration, Astropart. Phys. 20 (2004) 507]. Some of the most promising extragalactic sources are active galactic nuclei (AGN). In this paper, the neutrino flux from two kinds of AGN sources will be estimated assuming pγ interactions in the jets of the AGN. The first analyzed sample contains FR-II radio galaxies while the second AGN type examined are blazars. The result is highly dependent on the proton's index of the energy spectrum. To normalize the spectrum, the connection between neutrino and disk luminosity will be used by applying the jet-disk symbiosis model from Falcke and Biermann [Astron. Astrophys. 293 (1995) 665]. The maximum proton energy and thus, also the maximum neutrino energy of the source is connected to its disk luminosity, which was shown by Lovelace [Nature 262 (1976) 649] and was confirmed by Falcke et al. [Astron. Astrophys. 298 (1995) 375].

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

Fast radio burst search: cross spectrum vs. auto spectrum method

NASA Astrophysics Data System (ADS)

Liu, Lei; Zheng, Weimin; Yan, Zhen; Zhang, Juan

2018-06-01

The search for fast radio bursts (FRBs) is a hot topic in current radio astronomy studies. In this work, we carry out a single pulse search with a very long baseline interferometry (VLBI) pulsar observation data set using both auto spectrum and cross spectrum search methods. The cross spectrum method, first proposed in Liu et al., maximizes the signal power by fully utilizing the fringe phase information of the baseline cross spectrum. The auto spectrum search method is based on the popular pulsar software package PRESTO, which extracts single pulses from the auto spectrum of each station. According to our comparison, the cross spectrum method is able to enhance the signal power and therefore extract single pulses from data contaminated by high levels of radio frequency interference (RFI), which makes it possible to carry out a search for FRBs in regular VLBI observations when RFI is present.

Astronomers Win Protection for Key Part of Radio Spectrum

NASA Astrophysics Data System (ADS)

2000-06-01

Astronomers using the millimeter-wave region of the radio spectrum have won crucial protection for their science. Dedicated allocations for radio astronomy have been given final approval by the 2,500 delegates to the World Radiocommunication Conference (WRC-00), which recently concluded a month of deliberations in Istanbul, Turkey. Radio services can transmit in these parts of the spectrum as long as they don't hinder astronomers' attempts to catch faint signals from the cosmos. The new allocations represent the culmination of more than three years of cooperative planning by radio astronomers in many countries. Millimeter waves -- high-frequency radio waves -- have come of age as an astronomical tool in the last ten years. They are one of the last technological frontiers for astronomers. WRC-00 has protected for science all the frequencies between 71 and 275 Gigahertz (GHz) that radio astronomers currently use, adding more than 90 GHz of spectrum to the 44 GHz already set aside in this frequency range. As a result, radio astronomy is now allocated most of the frequencies between 71 and 275 GHz that can get through the Earth's atmosphere. "We have formal access to all three atmospheric 'windows', apart from their very edges," said Dr. Tom Gergely of the National Science Foundation, one of the U.S. delegates to WRC-00. The WRC also changed most of the frequencies allocated to satellite downlinks within the 71-275 GHz range to frequencies not used for science. Since no satellites yet operate at these high frequencies, no equipment needs to be altered. "Commercial technologies are just starting to develop above 50 GHz," said Dr. Klaus Ruf, Chairman of the Inter-Union Commission for the Allocation of Frequencies. "The WRC's actions mean that, when they are, radio astronomers should be able to share this part of the spectrum with most terrestrial services." The World Radiocommunication Conference is held every two or three years. Here member countries of the International Telecommunication Union meet to painstakingly parcel out the radio frequency spectrum between radio-based applications such as personal communications, satellite broadcasting, GPS and amateur radio, and the sciences of radio astronomy, earth exploration and deep space research. The WRC also coordinates sharing between services in the same radio bands. WRC decisions are incorporated into the Radio Regulations that govern radio services worldwide. The new spectrum allocations for radio astronomy are the first since 1979. Millimeter-wave astronomy was then in its infancy and many of its needs were not yet known. As astronomers began to explore this region of the spectrum they found spectral lines from many interesting molecules in space. Many of those lines had not fallen into the areas originally set aside for astronomy, but most will be under the new allocations. "It's a win for millimeter-wave science," said Dr. John Whiteoak of the Australia Telescope National Facility, Australian delegate to WRC-00. "This secures its future." The protection is a significant step for both existing millimeter-wave telescopes and new ones such as the Atacama Large Millimeter Array (ALMA) now being planned by a U.S.-European consortium. Even at its isolated site in Chile's Atacama desert, ALMA would be vulnerable to interference from satellite emissions. Sensitive radio astronomy receivers are blinded by these emissions, just as an optical telescope would be by a searchlight. "There is more energy at millimeter and sub-millimeter wavelengths washing through the Universe than there is of light or any other kind of radiation," said ALMA Project Scientist, Dr. Al Wootten of the National Radio Astronomy Observatory. "Imaging the sources of this energy can tell us a great deal about the formation of stars and galaxies, and even planets." "But the Earth's atmosphere isn't very kind to us - it has only a few windows at these frequencies, and not very transparent ones at that. They are easily clogged up. It's very important that we keep them as free as possible from interference." The new spectrum allocations were welcomed by Dr Johannes Andersen, General Secretary of the International Astronomical Union, which represents astronomers worldwide. "Protecting our ability to observe the Universe is the top priority for the International Astronomical Union," he said. "This action shows that international bodies accept the need for environmental emission standards in space as well as on Earth, for the benefit of all."

Five New Millisecond Pulsars from a Radio Survey of 14 Unidentified Fermi-LAT Gamma-Ray Sources

NASA Technical Reports Server (NTRS)

Kerr, M.; Camilo, F.; Johnson, T. J.; Ferrara, E. C.; Guillemot, L.; Harding, A. K.; Hessels, J.; Johnson, S.; Keith, M.; Kramer, M.;

47 CFR 214.5 - Responsibilities.

Code of Federal Regulations, 2013 CFR

2013-10-01

... COORDINATION OF THE RADIO SPECTRUM DURING A WARTIME EMERGENCY § 214.5 Responsibilities. (a) The Director, OSTP... of the Radio Spectrum as may be necessary to ensure the effective use of those portions of the radio spectrum shared by Government and non-governments users. (c) The FCC shall assist the Director in the...

47 CFR 90.901 - 800 MHz SMR spectrum subject to competitive bidding.

Code of Federal Regulations, 2010 CFR

2010-10-01

... SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Competitive Bidding Procedures for 800 MHz Specialized Mobile Radio Service § 90.901 800 MHz SMR spectrum subject to competitive bidding. Mutually exclusive initial applications for 800 MHz band licenses in Spectrum Blocks A through V are subject to...

A terrain based simulation system to predict the interference caused by networks of spread spectrum systems

NASA Astrophysics Data System (ADS)

Hagen, William E.; Holtzman, Julian C.

The Army Terrain Integrated Interference Prediction System (ATIIPS), a CAD terrain based simulation tool for determining the degradation effects on a network on nonspread spectrum radios caused by a network of spread spectrum radios is presented. A brief overview of the program is given, with typical graphics displays shown. Typical results for both a link simulation of interference and for a network simulation, using a slow hopped FM/FSK spread spectrum interfering radio network on a narrow band FM/FSK fixed frequency digital radio are presented.

Coding for spread spectrum packet radios

NASA Technical Reports Server (NTRS)

Omura, J. K.

1980-01-01

Packet radios are often expected to operate in a radio communication network environment where there tends to be man made interference signals. To combat such interference, spread spectrum waveforms are being considered for some applications. The use of convolutional coding with Viterbi decoding to further improve the performance of spread spectrum packet radios is examined. At 0.00001 bit error rates, improvements in performance of 4 db to 5 db can easily be achieved with such coding without any change in data rate nor spread spectrum bandwidth. This coding gain is more dramatic in an interference environment.

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; Mo, Wenli; Aguirre, Paula; Addison, Graeme E.; Asboth, V.; Battaglia, Nick; Bock, James; Bond, J. Richard;

Cygnus X-1

NASA Astrophysics Data System (ADS)

Bolton, C.; Murdin, P.

2000-11-01

Cygnus X-1 is one of the strongest x-ray sources. It is the first celestial object for which we had reasonably convincing evidence that it is a BLACK HOLE. Its x-ray properties include an ultra-soft spectrum, compared to massive x-ray binaries containing a neutron star, rapid (˜1 s) flickering, and high/low flux states with different spectral characteristics. In 1971, a RADIO SOURCE appeared at...

The Compact Radio Sources in the Nucleus of NGC 1068

NASA Astrophysics Data System (ADS)

Roy, A. L.; Colbert, E. J. M.; Wilson, A. S.; Ulvestad, J. S.

1998-09-01

We report VLBA images of the nucleus of the Seyfert galaxy NGC 1068 at 1.7, 5, and 15 GHz, with resolutions between 3 and 10 mas (0.2-0.7 pc) and a sensitivity of ~106 K at all three frequencies. Our goals are to study the morphology of the radio emission at subparsec resolution and to investigate thermal gas in the putative obscuring disk or torus and in the narrow-line region clouds through free-free absorption of the radio emission. All four known radio components in the central arcsecond (S2, S1, C, and NE, from south to north) have been detected at either 1.7 or 5 GHz, or both. No radio emission was detected at 15 GHz. Component S1 is probably associated with the active nucleus, with radio emission originating from the inner edge of the obscuring torus according to Gallimore et al. Our observed flux densities at 1.7 and 5 GHz are in agreement with their thermal bremsstrahlung emission model, and we find that the nuclear radiation may be strong enough to heat the gas in S1 to the required temperature of ~4 × 106 K. The bremsstrahlung power would be 0.15(frefl/0.01) times the bolometric luminosity of the nucleus between 1014.6 and 1018.4 Hz (where frefl is the fraction of radiation reflected into our line of sight by the electron-scattering mirror) and so the model is energetically reasonable. We also discuss two other models for S1 that also match the observed radio spectrum: electron scattering by the torus of radio emission from a compact synchrotron self-absorbed source and synchrotron radiation from the torus itself. Components NE and S2 have spectra consistent with optically thin synchrotron emission, without significant absorption. Both of these components are elongated roughly perpendicular to the larger scale radio jet, suggesting that their synchrotron emission is related to transverse shocks in the jet or to bow shocks in the external medium. Component C has a nonthermal spectrum absorbed at low frequency. This absorption is consistent with free-free absorption by plasma with conditions typical of narrow-line region clouds.

The origin of the X-ray, radio and H I structures in the NGC 5903 galaxy group

NASA Astrophysics Data System (ADS)

O'Sullivan, Ewan; Kolokythas, Konstantinos; Kantharia, Nimisha G.; Raychaudhury, Somak; David, Laurence P.; Vrtilek, Jan M.

2018-02-01

The NGC 5903 galaxy group is a nearby (∼30 Mpc) system of ∼30 members, dominated by the giant ellipticals NGC 5903 and NGC 5898. The group contains two unusual structures: a ∼110 kpc long H I filament crossing NGC 5903 and a ∼75 kpc wide diffuse, steep-spectrum radio source of unknown origin that overlaps NGC 5903 and appears to be partly enclosed by the H I filament. Using a combination of Chandra, XMM-Newton, Giant Meterwave Radio Telescope (GMRT) and Very Large Array (VLA) observations, we detect a previously unknown ∼0.65 keV intra-group medium filling the volume within 145 kpc of NGC 5903 and find a loop of enhanced X-ray emission extending ∼35 kpc south-west from the galaxy, enclosing the brightest part of the radio source. The northern and eastern parts of this X-ray structure are also strongly correlated with the southern parts of the H I filament. We determine the spectral index of the bright radio emission to be α _{150}^{612} = 1.03 ± 0.08, indicating a radiative age >360 Myr. We discuss the origin of the correlated radio, X-ray and H I structures, either through an interaction-triggered active galactic nucleus (AGN) outburst with enthalpy 1.8 × 1057 erg, or via a high-velocity collision between a galaxy and the H I filament. While neither scenario provides a complete explanation, we find that an AGN outburst is the most likely source of the principal X-ray and radio structures. However, it is clear that galaxy interactions continue to play an important role in the development of this relatively highly evolved galaxy group. We also resolve the question of whether the group member galaxy ESO 514-3 hosts a double-lobed radio source, confirming that the source is a superposed background AGN.

Unveiling the nature of the  $$\\gamma$$-ray emitting active galactic nucleus PKS 0521-36

DOE PAGES

D'Ammando, F.; Orienti, M.; Tavecchio, F.; ...

2015-05-19

PKS 0521-36 is an active galactic nucleus (AGN) with uncertain classification. Here, we investigate the properties of this source from radio to γ-rays. The broad emission lines in the optical and ultraviolet bands and steep radio spectrum indicate a possible classification as an intermediate object between broad-line radio galaxies (BLRG) and steep spectrum radio quasars (SSRQ). On pc-scales PKS 0521-36 shows a knotty structure similar to misaligned AGN. The core dominance and the γ-ray properties are similar to those estimated for other SSRQ and BLRG detected in γ-rays, suggesting an intermediate viewing angle with respect to the observer. In thismore » context the flaring activity detected from this source by Fermi-Large Area Telescope between 2010 June and 2012 February is very intriguing. We discuss the γ-ray emission of this source in the framework of the structured jet scenario, comparing the spectral energy distribution (SED) of the flaring state in 2010 June with that of a low state. We present three alternative models corresponding to three different choices of the viewing angles θv = 6°, 15°, and 20°. We obtain a good fit for the first two cases, but the SED obtained with θv = 15° if observed at a small angle does not resemble that of a typical blazar since the synchrotron emission should dominate by a large factor (~100) the inverse Compton component. This suggests that a viewing angle between 6° and 15° is preferred, with the rapid variability observed during γ-ray flares favouring a smaller angle. However, we cannot rule out that PKS 0521-36 is the misaligned counterpart of a synchrotron-dominated blazar.« less

Blind Signal Classification via Spare Coding

DTIC Science & Technology

2016-04-10

recall and 14.1% false alarm. I. INTRODUCTION Cognitive radios have emerged over the last decade as a new means to share radio spectrum, the most...utility of radio spectrum resources. Much of contemporary research has viewed cognitive radios as the secondary user of a licensed channel and...the applica- bility of cognitive radios for tactical networking seems even more adequate. The primary advocate for tactical cognitive radio systems

REVIEWS OF TOPICAL PROBLEMS: Cygnus X-3: a powerful galactic source of hard radiation

NASA Astrophysics Data System (ADS)

Vladimirskiĭ, B. M.; Gal'per, A. M.; Luchkov, B. I.; Stepanyan, A. A.

1985-02-01

A review is given of experimental and theoretical research on the galactic source Cyg X-3, whose electromagnetic spectrum extends from radio frequencies to ultrahigh-energy (Eγ ~ 1016 eV) γ-rays. Cyg X-3 also has a high x-ray luminosity (1038 erg/sec) and exhibits diversified sporadic and periodic variations, most notably occasional radio outbursts and a 4h.8 infrared, x-ray, and γ-ray cycle. Analysis of the observations indicates that Cyg X-3 is a close binary system comprising a compact relativistic object (neutron star, black hole) and a dwarf companion losing mass. Particles are accelerated to 1016 eV within the system.

Multiwavength Observations of the Black Hole X-Ray Binary A0620-00 in Quiescence

NASA Astrophysics Data System (ADS)

Dinçer, Tolga; Bailyn, Charles D.; Miller-Jones, James C. A.; Buxton, Michelle; MacDonald, Rachel K. D.

2018-01-01

We present results from simultaneous multiwavelength X-ray, radio, and optical/near-infrared observations of the quiescent black hole X-ray binary A0620-00 performed in 2013 December. We find that the Chandra flux has brightened by a factor of 2 since 2005, and by a factor of 7 since 2000. The spectrum has not changed significantly over this time, being consistent with a power law of {{Γ }}=2.07+/- 0.13 and a hydrogen column of {N}H=(3.0+/- 0.5)× {10}21 {{cm}}-2. Very Large Array observations of A0620-00 at three frequencies, over the interval of 5.25–22.0 GHz, have provided us with the first broadband radio spectrum of a quiescent stellar mass black hole system at X-ray luminosities as low as 10‑8 times the Eddington luminosity. Compared to previous observations, the source has moved to lower radio and higher X-ray luminosity, shifting it perpendicular to the standard track of the radio/X-ray correlation for X-ray binaries. The radio spectrum is inverted with a spectral index α =0.74+/- 0.19 ({S}ν \\propto {ν }α ). This suggests that the peak of the spectral energy distribution is likely to be between 1012 and 1014 Hz, and that the near-IR and optical flux contain significant contributions from the star, the accretion flow, and from the outflow. Decomposing these components may be difficult, but holds the promise of revealing the interplay between accretion and jet in low luminosity systems.

Frequency Allocation; The Radio Spectrum.

ERIC Educational Resources Information Center

Federal Communications Commission, Washington, DC.

The Federal Communications Commission (FCC) assigns segments of the radio spectrum to categories of users, and specific frequencies within each segment to individual users. Since demand for channel space exceeds supply, the process is complex. The radio spectrum can be compared to a long ruler: the portion from 10-540 kiloHertz has been set aside…

LOFAR discovery of a double radio halo system in Abell 1758 and radio/X-ray study of the cluster pair

NASA Astrophysics Data System (ADS)

Botteon, A.; Shimwell, T. W.; Bonafede, A.; Dallacasa, D.; Brunetti, G.; Mandal, S.; van Weeren, R. J.; Brüggen, M.; Cassano, R.; de Gasperin, F.; Hoang, D. N.; Hoeft, M.; Röttgering, H. J. A.; Savini, F.; White, G. J.; Wilber, A.; Venturi, T.

2018-05-01

Radio halos and radio relics are diffuse synchrotron sources that extend over Mpc-scales and are found in a number of merger galaxy clusters. They are believed to form as a consequence of the energy that is dissipated by turbulence and shocks in the intra-cluster medium (ICM). However, the precise physical processes that generate these steep synchrotron spectrum sources are still poorly constrained. We present a new LOFAR observation of the double galaxy cluster Abell 1758. This system is composed of A1758N, a massive cluster hosting a known giant radio halo, and A1758S, which is a less massive cluster whose diffuse radio emission is confirmed here for the first time. Our observations have revealed a radio halo and a candidate radio relic in A1758S, and a suggestion of emission along the bridge connecting the two systems which deserves confirmation. We combined the LOFAR data with archival VLA and GMRT observations to constrain the spectral properties of the diffuse emission. We also analyzed a deep archival Chandra observation and used this to provide evidence that A1758N and A1758S are in a pre-merger phase. The ICM temperature across the bridge that connects the two systems shows a jump which might indicate the presence of a transversal shock generated in the initial stage of the merger.

3C 57 as an atypical radio-loud quasar: implications for the radio-loud/radio-quiet dichotomy

NASA Astrophysics Data System (ADS)

Sulentic, J. W.; Martínez-Carballo, M. A.; Marziani, P.; del Olmo, A.; Stirpe, G. M.; Zamfir, S.; Plauchu-Frayn, I.

2015-06-01

Lobe-dominated radio-loud (LD RL) quasars occupy a restricted domain in the 4D Eigenvector 1 (4DE1) parameter space which implies restricted geometry/physics/kinematics for this subclass compared to the radio-quiet (RQ) majority of quasars. We discuss how this restricted domain for the LD RL parent population supports the notion for a RQ-RL dichotomy among type 1 sources. 3C 57 is an atypical RL quasar that shows both uncertain radio morphology and falls in a region of 4DE1 space where RL quasars are rare. We present new radio flux and optical spectroscopic measures designed to verify its atypical optical/UV spectroscopic behaviour and clarify its radio structure. The former data confirms that 3C 57 falls off the 4DE1 quasar `main sequence' with both extreme optical Fe II emission (R_{Fe II} ˜ 1) and a large C IV λ1549 profile blueshift (˜-1500 km s-1). These parameter values are typical of extreme Population A sources which are almost always RQ. New radio measures show no evidence for flux change over a 50+ year time-scale consistent with compact steep-spectrum (or young LD) over core-dominated morphology. In the 4DE1 context where LD RL are usually low L/LEdd quasars, we suggest that 3C 57 is an evolved RL quasar (i.e. large blackhole mass) undergoing a major accretion event leading to a rejuvenation reflected by strong Fe II emission, perhaps indicating significant heavy metal enrichment, high bolometric luminosity for a low-redshift source and resultant unusually high Eddington ratio giving rise to the atypical C IV λ1549.

The Longterm Centimeter-band Total Flux and Linear Polarization Properties of the Pearson-Readhead Survey Sources

NASA Astrophysics Data System (ADS)

Aller, M. F.; Aller, H. D.; Hughes, P. A.

2001-12-01

Using centimeter-band total flux and linear polarization observations of the Pearson-Readhead sample sources systematically obtained with the UMRAO 26-m radio telescope during the past 16 years, we identify the range of variability properties and their temporal changes as functions of both optical and radio morphological classification. We find that our earlier statistical analysis, based on a time window of 6.4 years, did not delineate the full amplitude range of the total flux variability; further, several galaxies exhibit longterm, systematic changes or rather infrequent outbursts requiring long term observations for detection. Using radio classification as a delineator, we confirm, and find additional evidence, that significant changes in flux density can occur in steep spectrum and lobe-dominated objects as well as in compact, flat-spectrum objects. We find that statistically the time-averaged total flux density spectra steepen when longer time windows are included, which we attribute to a selection effect in the source sample. We have identified preferred orientations of the electric vector of the polarized emission (EVPA) in an unbiased manner in several sources, including several QSOs which have exhibited large variations in total flux while maintaining stable EVPAs, and compared these with orientations of the flow direction indicated by VLB morphology. We have looked for systematic, monotonic changes in EVPA which might be expected in the emission from a precessing jet, but none were identified. A Scargle periodogram analysis found no strong evidence for periodicity in any of the sample sources. We thank the NSF for grants AST-8815678, AST-9120224, AST-9421979, and AST-9900723 which provided partial support for this research. The operation of the 26-meter telescope is supported by the University of Michigan Department of Astronomy.

A variable ULX and possible IMBH candidate in M51a

NASA Astrophysics Data System (ADS)

Earnshaw, Hannah M.; Roberts, Timothy P.; Heil, Lucy M.; Mezcua, Mar; Walton, Dominic J.; Done, Chris; Harrison, Fiona A.; Lansbury, George B.; Middleton, Matthew J.; Sutton, Andrew D.

2016-03-01

Ultraluminous X-ray source (ULX)-7, in the northern spiral arm of M51, demonstrates unusual behaviour for an ULX, with a hard X-ray spectrum but very high short-term variability. This suggests that it is not in a typical ultraluminous state. We analyse the source using archival data from XMM-Newton, Chandra and NuSTAR, and by examining optical and radio data from HST and Very Large Array. Our X-ray spectral analysis shows that the source has a hard power-law spectral shape with a photon index Γ ˜ 1.5, which persists despite the source's X-ray luminosity varying by over an order of magnitude. The power spectrum of the source features a break at 6.5^{+0.5}_{-1.1} × 10-3 Hz, from a low-frequency spectral index of α _1={-}0.1^{+0.5}_{-0.2} to a high-frequency spectral index of α _2=6.5^{+0.05}_{-0.14}, making it analogous to the low-frequency break found in the power spectra of low/hard state black holes (BHs). We can take a lower frequency limit for a corresponding high-frequency break to calculate a BH mass upper limit of 1.6 × 103 M⊙. Using the X-ray/radio Fundamental Plane, we calculate another upper limit to the BH mass of 3.5 × 104 M⊙ for a BH in the low/hard state. The hard spectrum, high rms variability and mass limits are consistent with ULX-7 being an intermediate-mass BH; however we cannot exclude other interpretations of this source's interesting behaviour, most notably a neutron star with an extreme accretion rate.

Time-dependent models for blazar emission with the second-order Fermi acceleration

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

Asano, Katsuaki; Takahara, Fumio; Toma, Kenji

The second-order Fermi acceleration (Fermi-II) driven by turbulence may be responsible for the electron acceleration in blazar jets. We test this model with time-dependent simulations. The hard electron spectrum predicted by the Fermi-II process agrees with the hard photon spectrum of 1ES 1101–232. For other blazars that show softer spectra, the Fermi-II model requires radial evolution of the electron injection rate and/or diffusion coefficient in the outflow. Such evolutions can yield a curved electron spectrum, which can reproduce the synchrotron spectrum of Mrk 421 from the radio to the X-ray regime. The photon spectrum in the GeV energy range ofmore » Mrk 421 is hard to fit with a synchrotron self-Compton model. However, if we introduce an external radio photon field with a luminosity of 4.9 × 10{sup 38} erg s{sup –1}, GeV photons are successfully produced via inverse Compton scattering. The temporal variability of the diffusion coefficient or injection rate causes flare emission. The observed synchronicity of X-ray and TeV flares implies a decrease of the magnetic field in the flaring source region.« less

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.

Studies of LSO:Tb radio-luminescence properties using white beam hard X-ray synchrotron irradiation

NASA Astrophysics Data System (ADS)

Cecilia, A.; Rack, A.; Pelliccia, D.; Douissard, P.-A.; Martin, T.; Couchaud, M.; Dupré, K.; Baumbach, T.

A radio-luminescence set-up was installed at the synchrotron light source ANKA to characterise scintillators under the high X-ray photon flux density of white beam synchrotron radiation. The system allows for investigating the radio-luminescence spectrum of the material under study as well as analysing in situ changes of its scintillation behaviour (e.g. under heat load and/or intensive ionising radiation). In this work we applied the radio-luminescence set-up for investigating the radiation damage effects on the luminescence properties of a new kind of thin single crystal scintillator for high resolution X-ray imaging based on a layer of modified Lu2SiO5 grown by liquid phase epitaxy on a dedicated substrate within the framework of an EC project (SCINTAX).

Optical identification of radio-loud active galactic nuclei in the ROSAT-Green-Bank sample with SDSS spectroscopy

NASA Astrophysics Data System (ADS)

Wang, De-Liang; Wang, Jian-Guo; Dong, Xiao-Bo

2009-10-01

Results of extended and refined optical identification of 181 radio/X-ray sources in the RASS-Green Bank (RGB) catalog are presented (Brinkmann et al. 1997) which have been spectroscopically observed in the Sloan Digital Sky Survey (SDSS) DR5. The SDSS spectra of the optical counterparts are modeled in a careful and self-consistent way by incorporating the host galaxy's starlight. Optical emission line parameters are presented, which are derived accurately and reliably, along with the radio 1.4-5 GHz spectral indices estimated using (non-simultaneous) archival data. For 72 sources, the identifications are presented for the first time. It is confirmed that the majority of strong radio/X-ray emitters are radio-loud active galactic nuclei (AGNs), particularly blazars. Taking advantage of the high spectral quality and resolution and our refined spectral modeling, we are able to disentangle narrow line radio galaxies (NLRGs), as vaguely termed in most previous identification work, into Seyfert II galaxies and LINERs (low-ionization nuclear emission regions), based on the standard emission line diagnostics. The NLRGs in the RGB sample, mostly belonging to 'weak line radio galaxies', are found to have optical spectra consistent predominantly with LINERs, and only a small fraction with Seyfert II galaxies. A small number of LINERs have radio power as high as 1023 - 1026 W Hz-1 at 5 GHz, being among the strongest radio emitting LINERs known so far. Two sources are identified with radio-loud narrow line Seyfert 1 galaxies (NLS1s), a class of rare objects. The presence is also confirmed of flat-spectrum radio quasars whose radio-optical-X-ray effective spectral indices are similar to those of High-energy peaked BL Lacs (HBLs), as suggested by Padovani et al., although it is still a debate as to whether this is the case for their actual spectral energy distributions.

LOFAR discovery of radio emission in MACS J0717.5+3745

NASA Astrophysics Data System (ADS)

Bonafede, A.; Brüggen, M.; Rafferty, D.; Zhuravleva, I.; Riseley, C. J.; van Weeren, R. J.; Farnes, J. S.; Vazza, F.; Savini, F.; Wilber, A.; Botteon, A.; Brunetti, G.; Cassano, R.; Ferrari, C.; de Gasperin, F.; Orrú, E.; Pizzo, R. F.; Röttgering, H. J. A.; Shimwell, T. W.

2018-05-01

We present results from LOFAR and GMRT observations of the galaxy cluster MACS J0717.5+3745. The cluster is undergoing a violent merger involving at least four sub-clusters, and it is known to host a radio halo. LOFAR observations reveal new sources of radio emission in the Intra-Cluster Medium: (i) a radio bridge that connects the cluster to a head-tail radio galaxy located along a filament of galaxies falling into the main cluster, (ii) a 1.9 Mpc radio arc, that is located North West of the main mass component, (iii) radio emission along the X-ray bar, that traces the gas in the X-rays South West of the cluster centre. We use deep GMRT observations at 608 MHz to constrain the spectral indices of these new radio sources, and of the emission that was already studied in the literature at higher frequency. We find that the spectrum of the radio halo and of the relic at LOFAR frequency follows the same power law as observed at higher frequencies. The radio bridge, the radio arc, and the radio bar all have steep spectra, which can be used to constrain the particle acceleration mechanisms. We argue that the radio bridge could be caused by the re-acceleration of electrons by shock waves that are injected along the filament during the cluster mass assembly. Despite the sensitivity reached by our observations, the emission from the radio halo does not trace the emission of the gas revealed by X-ray observations. We argue that this could be due to the difference in the ratio of kinetic over thermal energy of the intra-cluster gas, suggested by X-ray observations.

The X-Ray Reflection Spectrum of the Radio-Loud Quasar 4C 74.26

NASA Technical Reports Server (NTRS)

Lohfink, Ann M.; Fabian, Andrew C.; Ballantyne, David R.; Boggs, S. E.; Boorman, Peter; Christensen, F. E.; Craig, W. W.; Farrah, Duncan; Garcia, Javier; Hailey, C. J.;

The X-Ray Reflection Spectrum of the Radio-loud Quasar 4C 74.26

NASA Astrophysics Data System (ADS)

Lohfink, Anne M.; Fabian, Andrew C.; Ballantyne, David R.; Boggs, S. E.; Boorman, Peter; Christensen, F. E.; Craig, W. W.; Farrah, Duncan; García, Javier; Hailey, C. J.; Harrison, F. A.; Ricci, Claudio; Stern, Daniel; Zhang, W. W.

2017-06-01

The relativistic jets created by some active galactic nuclei are important agents of AGN feedback. In spite of this, our understanding of what produces these jets is still incomplete. X-ray observations, which can probe the processes operating in the central regions in the immediate vicinity of the supermassive black hole, the presumed jet launching point, are potentially particularly valuable in illuminating the jet formation process. Here, we present the hard X-ray NuSTAR observations of the radio-loud quasar 4C 74.26 in a joint analysis with quasi-simultaneous, soft X-ray Swift observations. Our spectral analysis reveals a high-energy cutoff of {183}-35+51 keV and confirms the presence of ionized reflection in the source. From the average spectrum we detect that the accretion disk is mildly recessed, with an inner radius of R in = 4-180 R g. However, no significant evolution of the inner radius is seen during the three months covered by our NuSTAR campaign. This lack of variation could mean that the jet formation in this radio-loud quasar differs from what is observed in broad-line radio galaxies.

The solar spectral irradiances from x ray to radio wavelengths

NASA Technical Reports Server (NTRS)

White, O. R.

1993-01-01

Sources of new measurements of the solar EUV, UV, and visible spectrum are presented together with discussion of formation of the solar spectrum as a problem in stellar atmospheres. Agreement between the data and a modern synthetic spectrum shows that observed radiative variability is a minor perturbation on a photosphere in radiative equilibrium and local thermodynamic equilibrium (LTE). Newly observed solar variability in 1992 defines a magnetic episode on the Sun closely associated with changes in both spectral irradiances and the total irradiance. This episode offers the opportunity to track the relationship between radiation and magnetic flux evolution.

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.

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.

FERMI Large Area Telescope Gamma-Ray Detection of the Radio Galaxy M87

DOE PAGES

Abdo, A. A.; Ackermann, M.; Ajello, M.; ...

2009-11-17

Here, we report the Fermi Large Area Telescope (LAT) discovery of high-energy (MeV/GeV) γ-ray emission positionally consistent with the center of the radio galaxy M87, at a source significance of over 10σ in 10 months of all-sky survey data. Following the detections of Cen A and Per A, this makes M87 the third radio galaxy seen with the LAT. The faint point-like γ-ray source has a >100 MeV flux of 2.45 (±0.63) × 10 –8 photons cm –2 s –1 (photon index = 2.26 ± 0.13) with no significant variability detected within the LAT observation. This flux is comparable withmore » the previous EGRET upper limit (<2.18 × 10 –8 photons cm –2 s –1, 2σ), thus there is no evidence for a significant MeV/GeV flare on decade timescales. Contemporaneous Chandra and Very Long Baseline Array data indicate low activity in the unresolved X-ray and radio core relative to previous observations, suggesting M87 is in a quiescent overall level over the first year of Fermi-LAT observations. The LAT γ-ray spectrum is modeled as synchrotron self-Compton (SSC) emission from the electron population producing the radio-to-X-ray emission in the core. The resultant SSC spectrum extrapolates smoothly from the LAT band to the historical-minimum TeV emission. Lastly, alternative models for the core and possible contributions from the kiloparsec-scale jet in M87 are considered, and cannot be excluded.« less

High-resolution radio study of SNR IC 443 at low radio frequencies

NASA Astrophysics Data System (ADS)

Castelletti, G.; Dubner, G.; Clarke, T.; Kassim, N. E.

2011-10-01

Aims: We investigate the morphology at low radio frequencies of the supernova remnant (SNR) IC 443 in detail and accurately establish its radio continuum spectral properties. Methods: We used the VLA in multiple configurations to produce high-resolution radio images of IC 443 at 74 and 330 MHz. From these data we produced the first sensitive, spatially resolved spectral analysis of the radio emission at long wavelengths. The changes with position in the radio spectral index were correlated with data in near infrared (NIR) from 2MASS, in gamma-rays from VERITAS, and with the molecular 12CO (J = 1 - 0) line emission. Results: The new image at 74 MHz has HPBW = 35'' and rms = 30 mJy beam-1 and at 330 MHz HPBW = 17'' and rms = 1.7 mJy beam-1. The integrated flux densities for the whole SNR are S74 MHzSNR=470±51 Jy and S330 MHzSNR=248±15 Jy. Improved estimates of the integrated spectrum were derived taking a turnover into account to fit the lowest frequency measurements in the literature. Combining our measurements with existing data, we derive an integrated spectral index α10 MHz10700 MHz=-0.39±0.01 with a free-free continuum optical depth at 330 MHz τ330 ~ 7 × 10-4 (τ10 = 1.07); all measurements above ~ 10 MHz are equally consistent with a power law spectrum. For the pulsar wind nebula associated with the compact source CXOU J061705.3+222127, we calculated S330 MHzPWN=0.23±0.05 Jy, S1420 MHzPWN=0.20±0.04 Jy, and α330 MHz8460 MHz˜ 0.0. Substantial variations are observed in spectral index between 74 and 330 MHz across IC 443. The flattest spectral components ( - 0.25 ≤ α ≤ - 0.05) coincide with the brightest parts of the SNR along the eastern border, with an impressive agreement with ionic lines as observed in the 2MASS J and H bands. The diffuse interior of IC 443 has a spectrum steeper than found anywhere in the SNR ( - 0.85 ≤ α ≤ - 0.6), while the southern ridge again has a flatter spectrum (α ~ -0.4). With the available statistics the VERITAS γ-ray emission strikingly matches the CO distribution, but no clear evidence is found for a morphological correlation between the TeV distribution and radio emission. Conclusions: The excellent correspondence between the eastern radio flattest spectrum region and NIR ionic lines strongly suggests that the passage of a fast, dissociating J-type shock across the interacting molecular cloud dissociated the molecules and ionized the gas. We therefore conclude that thermal absorption at 74 MHz (τ74 up to ~0.3) is responsible for the localized spectral index flattening observed along the eastern border of IC 443. Towards the interior of IC 443, the spectrum is consistent with those expected from linear diffusive shock acceleration, while the flatter spectrum in the southern ridge is a consequence of the strong shock/molecular cloud interaction.

Chandra reveals a black hole X-ray binary within the ultraluminous supernova remnant MF 16

NASA Astrophysics Data System (ADS)

Roberts, T. P.; Colbert, E. J. M.

2003-06-01

We present evidence, based on Chandra ACIS-S observations of the nearby spiral galaxy NGC 6946, that the extraordinary X-ray luminosity of the MF 16 supernova remnant actually arises in a black hole X-ray binary. This conclusion is drawn from the point-like nature of the X-ray source, its X-ray spectrum closely resembling the spectrum of other ultraluminous X-ray sources thought to be black hole X-ray binary systems, and the detection of rapid hard X-ray variability from the source. We briefly discuss the nature of the hard X-ray variability, and the origin of the extreme radio and optical luminosity of MF 16 in light of this identification.

Chandra observations of dying radio sources in galaxy clusters

NASA Astrophysics Data System (ADS)

Murgia, M.; Markevitch, M.; Govoni, F.; Parma, P.; Fanti, R.; de Ruiter, H. R.; Mack, K.-H.

2012-12-01

Context. The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. Aims: We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. Methods: We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. Results: The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters. Conclusions: We calculated the non-thermal pressure of the radio lobes assuming that the radio sources are in the minimum energy condition. For all dying sources we found that this is on average about one to two orders of magnitude lower than that of the external gas, as found for many other radio sources at the center of galaxy groups and clusters. We found marginal evidence for the presence of X-ray surface brightness depressions coincident with the fossil radio lobes of the dying sources in A2276 and ZwCl 1829.3+691. We estimated the outburst age and energy output for these two dying sources. The energy power from the AGN outburst is significantly higher than the X-ray luminosity in both clusters. Indeed, it is sufficient that a small fraction of this power is dissipated in the intra-cluster medium to reheat the cool cores. Appendix is available in electronic form at http://www.aanda.org

Chandra Observations of Dying Radio Sources in Galaxy Clusters

NASA Technical Reports Server (NTRS)

Murgia, M.; Markevitch, M.; Govoni, F.; Parma, P.; Fanti, R.; de Ruiter, H. R.; Mack, K.-H.

2012-01-01

Context. The dying radio sources represent a very interesting and largely unexplored stage of the active galactic nucleus (AGN) evolution. They are considered to be very rare, and almost all of the few known ones were found in galaxy clusters. However, considering the small number detected so far, it has not been possible to draw any firm conclusions about their X-ray environment. Aims. We present X-ray observations performed with the Chandra satellite of the three galaxy clusters Abell 2276, ZwCl 1829.3+6912, and RX J1852.1+5711, which harbor at their center a dying radio source with an ultra-steep spectrum that we recently discovered. Methods. We analyzed the physical properties of the X-ray emitting gas surrounding these elusive radio sources. We determined the global X-ray properties of the clusters, derived the azimuthally averaged profiles of metal abundance, gas temperature, density, and pressure. Furthermore, we estimated the total mass profiles. Results. The large-scale X-ray emission is regular and spherical, suggesting a relaxed state for these systems. Indeed, we found that the three clusters are also characterized by significant enhancements in the metal abundance and declining temperature profiles toward the central region. For all these reasons, we classified RX J1852.1+5711, Abell 2276, and ZwCl 1829.3+6912 as cool-core galaxy clusters. Conclusions. We calculated the non-thermal pressure of the radio lobes assuming that the radio sources are in the minimum energy condition. For all dying sources we found that this is on average about one to two orders of magnitude lower than that of the external gas, as found for many other radio sources at the center of galaxy groups and clusters. We found marginal evidence for the presence of X-ray surface brightness depressions coincident with the fossil radio lobes of the dying sources in A2276 and ZwCl 1829.3+691. We estimated the outburst age and energy output for these two dying sources. The energy power from the AGN outburst is significantly higher than the X-ray luminosity in both clusters. Indeed, it is sufficient that a small fraction of this power is dissipated in the intra-cluster medium to reheat the cool cores.

Possibility of testing the light dark matter hypothesis with the alpha magnetic spectrometer.

PubMed

Hooper, Dan; Xue, Wei

2013-01-25

The spectrum and morphology of gamma rays from the Galactic center and the spectrum of synchrotron emission observed from the Milky Way's radio filaments have each been interpreted as possible signals of ∼ 7-10 GeV dark matter particles annihilating in the inner Galaxy. In dark matter models capable of producing these signals, the annihilations should also generate significant fluxes of ∼ 7-10 GeV positrons which can lead to a distinctive bumplike feature in a local cosmic ray positron spectrum. In this Letter, we show that while such a feature would be difficult to detect with PAMELA, it would likely be identifiable by the currently operating Alpha Magnetic Spectrometer experiment. As no known astrophysical (i.e., nondark matter) sources or mechanisms are likely to produce such a sharp feature, the observation of a positron bump at around 7-10 GeV would significantly strengthen the case for a dark matter interpretation of the reported gamma-ray and radio anomalies.

Multi-wavelength observations of PKS 2142-75 during active and quiescent gamma-ray states

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

Dutka, Michael S.; Ojha, Roopesh; Pottschmidt, Katja

2013-12-04

Here, PKS 2142–75 (a.k.a. 2FGL J2147.4–7534) is a flat-spectrum radio quasar that was observed quasi-simultaneously by a suite of instruments across the electromagnetic spectrum during two flaring states in 2010 April and 2011 August as well as a quiescent state from 2011 December through 2012 January. The results of these campaigns and model spectral energy distributions (SEDs) from the active and quiescent states are presented. The SED model parameters of PKS 2142–75 indicate that the two flares of the source are created by unique physical conditions. SED studies of flat-spectrum radio quasars are beginning to indicate that there might bemore » two types of flares, those that can be described purely by changes in the electron distribution and those that require changes in other parameters, such as the magnetic field strength or the size of the emitting region.« less

Fermi LAT detection of renewed strong GeV activity from the FSRQ 3C 279

NASA Astrophysics Data System (ADS)

Ojha, Roopesh; van Zyl, Pfesesani; Fermi Large Area Telescope Collaboration

2018-04-01

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed an intense and hard gamma-ray flare from a source positionally consistent with the flat spectrum radio quasar 3C 279, also known as 3FGL J1256.1-0547 (Acero et al. 2015, ApJS, 218, 23), with radio coordinates R.A.: 12h56m11.1665s, Dec: -05d47m21.523s (J2000.0; Johnston et al. 1995, AJ, 110, 880).

The gamma-ray emitting radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447. I. The X-ray View

NASA Astrophysics Data System (ADS)

Kreikenbohm, A.; Schulz, R.; Kadler, M.; Wilms, J.; Markowitz, A.; Chang, C. S.; Carpenter, B.; Elsässer, D.; Gehrels, N.; Mannheim, K.; Müller, C.; Ojha, R.; Ros, E.; Trüstedt, J.

2016-01-01

As part of the TANAMI multiwavelength progam, we discuss new X-ray observations of the γ-ray and radio-loud narrow line Seyfert 1 galaxy (γ-NLS1) PKS 2004-447. The active galaxy is a member of a small sample of radio-loud NLS1s detected in γ-rays by the Fermi Large Area Telescope. It stands out for being the radio-loudest and the only southern-hemisphere source in this sample. We present results from our X-ray monitoring program comprised of Swift snapshot observations from 2012 through 2014 and two new X-ray observations with XMM-Newton in 2012. Supplemented by archival data from 2004 and 2011, our data set allows for a careful analysis of the X-ray spectrum and variability of this peculiar source. The (0.5-10) keV spectrum is described well by a power law (Γ ~ 1.6), which can be interpreted as non-thermal emission from a relativistic jet. The source exhibits moderate flux variability on timescales of both months and years. Correlated brightness variations in the (0.5-2) keV and (2-10) keV bands are explained by a single variable spectral component, such as the one from the jet. A possible soft excess seen in the data from 2004 cannot be confirmed by the new XMM-Newton observations taken during low-flux states. Any contribution to the total flux in 2004 is less than 20% of the power-law component. The (0.5-10) keV luminosities of PKS 2004-447 are in the range of (0.5-2.7) × 1044 erg s-1. A comparison of the X-ray properties among the known γ-NLS1 galaxies shows that in four out of five cases the X-ray spectrum is dominated by a flat power law without intrinsic absorption. These objects are moderately variable in their brightness, while spectral variability is observed in at least two sources. The major difference across the X-ray spectra of γ-NLS1s is the luminosity, which spans a range of almost two orders of magnitude from 1044 erg s-1 to 1046 erg s-1 in the (0.5-10) keV band.

Kiloparsec Jet Properties of Hybrid, Low-, and High-Synchrotron-Peaked Blazars

NASA Astrophysics Data System (ADS)

Stanley, Ethan C.

Blazars are a rare class of active galactic nucleus (AGN) with relativistic jets closely aligned with the line of sight. Many aspects of the environments and kiloparsec-scale jet structure are not fully understood. Hybrid and high synchrotron peaked (HSP) blazars are two types of blazar that provide unique opportunities to study these jets. Hybrid blazars appear to have jets of differing morphology on each side of their core, suggesting that external factors shape their jet morphology. Three hybrid sources were investigated in radio, optical, and X-ray wavelengths: 8C 1849+670, PKS 2216-038, and PKS 1045-188. For all three, X-ray emission was detected only from the approaching jet. All three had jet radio flux densities and emission mechanisms similar to higher-power FR II sources, but two had approaching jets similar to lower-power FR I sources. None of the three showed definitive signs of asymmetry in their external environments. These results agree with previous multiwavelength studies of hybrid sources that show a dominance of FR I approaching jets and FR II emission mechanisms. With the addition of these three hybrid sources, 13 have been studied in total. Eleven have FR I approaching jets, and eight of those have FR II emission mechanisms. These trends may be due to small number statistics, or they may indicate other factors are creating hybrid-like appearances. High synchrotron peaked blazars are defined by the frequency of the peak of their jet synchrotron emission. Some have shown extreme variability which would imply incredibly-powerful and well-aligned jets, but VLBA observations have measured only modest jet speeds. A radio survey was performed to measure the extended radio luminosity of a large sample of HSP sources. These sources were compared to the complete radio flux density limited MOJAVE 1.5 Jy sample. Flat spectrum radio quasars (FSRQs) showed significant overlap with low synchrotron peaked (LSP) BL Lacs in multiple parameters, which may suggest that many FSRQs are "masquerading'' as LSP BL Lacs. HSP BL Lacs showed slightly lower extended radio luminosities and significantly lower maximum apparent jet speeds, suggesting that they are intrinsically weaker sources. There was a good correlation between maximum apparent jet speed and extended radio luminosity, which supports using the extended radio luminosity as a measure of intrinsic jet power. There was a lack of TeV-detected sources with higher extended radio luminosities, which suggests TeV emission may favor low power jets or high synchrotron peak frequencies. The apparent low power of HSP sources and TeV-detected sources questions any model of TeV emission and variability that depends on the jet (or a part of it) being intrinsically powerful.

The second Caltech-Jodrell Bank VLBI survey. 1: Observations of 91 of 193 sources

NASA Technical Reports Server (NTRS)

Taylor, G. B.; Vermeulen, R. C.; Pearson, T. J.; Readhead, A. C. S.; Henstock, D. R.; Browne, I. W. A.; Wilkinson, P. N.

1994-01-01

We define the sample for the second Caltech-Jodrell Bank very long base interferometry (VLBI) survey. This is a sample of 193 flat- or gigahertz-peaked-spectrum sources selected at 4850 MHz. This paper presents images of 91 sources with a resolution of approximately 1 mas, obtained using VLBI observations at 4992 MHz with a global array. The remaining images and the integrated radio spectra will be presented in a forthcoming paper by Henstock et al.

Broadband spectrum survey at San Diego, California

DOT National Transportation Integrated Search

The National Telecommunications and Information Administration (NTIA) is responsible for managing the Federal Government's use of the radio spectrum. In discharging this responsibility, NTIA uses the Radio Spectrum Measurement System to collect data ...

LOFAR discovery of a 700-kpc remnant radio galaxy at low redshift

NASA Astrophysics Data System (ADS)

Brienza, M.; Godfrey, L.; Morganti, R.; Vilchez, N.; Maddox, N.; Murgia, M.; Orru, E.; Shulevski, A.; Best, P. N.; Brüggen, M.; Harwood, J. J.; Jamrozy, M.; Jarvis, M. J.; Mahony, E. K.; McKean, J.; Röttgering, H. J. A.

2016-01-01

Context. Remnant radio galaxies represent the final dying phase of radio galaxy evolution in which the jets are no longer active. Remnants are rare in flux-limited samples, comprising at most a few percent. As a result of their rarity and because they are difficult to identify, this dying phase remains poorly understood and the luminosity evolution is largely unconstrained. Aims: Here we present the discovery and detailed analysis of a large (700 kpc) remnant radio galaxy with a low surface brightness that has been identified in LOFAR images at 150 MHz. Methods: By combining LOFAR data with new follow-up Westerbork observations and archival data at higher frequencies, we investigated the source morphology and spectral properties from 116 to 4850 MHz. By modelling the radio spectrum, we probed characteristic timescales of the radio activity. Results: The source has a relatively smooth, diffuse, amorphous appearance together with a very weak central compact core that is associated with the host galaxy located at z = 0.051. From our ageing and morphological analysis it is clear that the nuclear engine is currently switched off or, at most, active at a very low power state. We find that the source has remained visible in the remnant phase for about 60 Myr, significantly longer than its active phase of 15 Myr, despite being located outside a cluster. The host galaxy is currently interacting with another galaxy located at a projected separation of 15 kpc and a radial velocity offset of ~ 300 km s-1. This interaction may have played a role in the triggering and/or shut-down of the radio jets. Conclusions: The spectral shape of this remnant radio galaxy differs from most of the previously identified remnant sources, which show steep or curved spectra at low to intermediate frequencies. Our results demonstrate that remnant radio galaxies can show a wide range of evolutionary paths and spectral properties. In light of this finding and in preparation for new-generation deep low-frequency surveys, we discuss the selection criteria to be used to select representative samples of these sources.

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.

Detection of GeV Gamma-Rays from HESS J1534-571 and Multiwavelength Implications for the Origin of the Nonthermal Emission

NASA Astrophysics Data System (ADS)

Araya, Miguel

2017-07-01

HESS J1534-571 is a very high-energy gamma-ray source that was discovered by the H.E.S.S. observatory and reported as one of several new sources with a shell-like morphology at TeV energies, matching in size and location with the supernova remnant (SNR) G323.7-1.0 discovered in radio observations by the Molonglo Galactic Plane Survey. Many known TeV shells also show X-ray emission however, no X-ray counterpart has been seen for HESS J1534-571. The detection of a new GeV source using data from the Fermi satellite that is compatible in extension with the radio SNR and shows a very hard power-law spectrum ≤ft(\\tfrac{{dN}}{{dE}}\\propto {E}-1.35\\right) is presented here, together with the first broadband modeling of the nonthermal emission from this source. It is shown that leptonic emission is compatible with the known multiwavelength data and a corresponding set of physical source parameters is given. The required total energy budget in leptons is reasonable, ˜1.5 × 1048 erg for a distance to the object of 5 kpc. The new GeV observations imply that a hadronic scenario, on the other hand, requires a cosmic-ray spectrum that deviates considerably from theoretical expectations of particle acceleration.

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.

Accretion processes of radio galaxies at high energies

NASA Astrophysics Data System (ADS)

de Jong, Sandra

2013-10-01

AGN are the luminous (L>10^42 erg/s) cores of active galaxies, powered by accretion onto the central super massive black hole, either via an accretion disk or via a radiatively inefficient accretion flow. There are still several open questions, for example on the launching of jets, which are present in about 10% of the AGN. Another question appeared with the Fermi/LAT gamma-ray survey, which detected many blazars but also a small group of radio galaxies. Radio galaxies are postulated to be blazars where the observer sees the jet at an angle θ>10 degrees allowing a view of both jet and core, rather than only the jet as is the case with blazars. Radio galaxies are divided into two classes, depending on the radio luminosity of the jets. The Fanaroff-Riley I (FR-I) sources have jets that are bright near the core, where the FR-IIs display extended edge-brightened jets. The FR-I sources are connected to the BL Lacs, which are low-luminosity blazars. FR-II types are thought to be the parent population of the luminous FSRQ, which are also blazars. This thesis presents a study of gamma-ray bright radio galaxies. By analysing X-ray and gamma-ray data in addition to creating broad-band spectral energy distributions (SEDs), we studied two examples of this new class of sources. For the FR-II source 3C 111 we analysed Suzaku/XIS and PIN and INTEGRAL IBIS/ISGRI observations to create a X-ray spectrum. We also used a Swift/BAT spectrum from the 58-month survey. The 0.4-200 keV spectrum of the source shows both thermal, Seyfert-like signatures such as an iron K-α line, and non-thermal jet features. We also analysed gamma-ray data from Fermi/LAT. The gamma-ray and X-ray data are combined with historical radio, infrared and optical observations to build the SED, which can be well represented with a non-thermal jet model. The bolometric luminosity of 3C111 is rather low, and the SED model shows rather a BL Lac type than the expected FSRQ. The next source we studied is the nearby FR-I M87. This source has been detected ! in gamma-rays and in the TeV band, but so far not in the hard X-rays (>10 keV). The first part of our analysis was focused on setting an upper limit to the hard X-ray emission of this source, using INTEGRAL IBIS/ISGRI observations. In addition to the standard method we applied several techniques in the analysis process, such as pointing selection and shadowgram treatment, in order to decrease the noise level of the result. Using 5.1 Ms of ISGRI data we determined a 3σ upper limit to the average 20-60 keV flux of f < 3x10^-12 erg/cm^2/s. We have also analysed Suzaku/PIN observations, where we detected M87 for the first time in the hard X-ray band, with a flux of f=1.3x 10^-11 erg/cm^2/s. between 20 and 60 keV. This detection indicates a flare, since the flux is significantly higher than the derived average upper limit. We also analysed Fermi/LAT data and combined this with the X-ray upper limits and historical radio, infrared and optical observations to build a SED. The SED can be modelled as a BL Lac source, which is expected since M87 is a FR-I type. We then also examined the general aspects of gamma-ray bright radio galaxies. Most of these objects are of the FR-I type, and the core of at least one FR-II, 3C 111, is rather BL Lac-like than the expected FSRQ. For the other FR-II sources this might also be the case. The gamma-ray emission originates from the jet, similar as in the case of blazars. Due to the large jet angle, the emission is not observed to be boosted. However, since the gamma-ray emission originates near the black hole, either reflection or a large opening angle can explain the observations. In addition, I contributed to the study of a possible dark matter halo observed with Fermi/LAT in the vicinity of the Virgo cluster. Our work has shown that a population of point sources contributes to this emission. In this thesis, the result of an extended emission analysis and the search for possible counter parts of new sources are presented. ! Finally, the detection of two new X-ray sources using Swift is reported here for the first time. These sources, the BL Lac object BZB J1552+0850 and the Seyfert galaxy LSBC F727-V01, are both located within the 95% error circle of the Fermi/LAT source 2FGL J1551.9+0855. We analysed the X-ray data from the XRT and UV data from the UVOT. The likely counterpart of the Fermi source is rather the blazer BZB J1552+0850, since Seyfert galaxies are rarely gamma-ray emitters. To understand the gamma-ray bright radio galaxies, X-ray observations can be used to can characterise these sources. Using for example the new generation of instruments, such as NuSTAR and ASTRO-H, will help with their superior resolution to distinguish between thermal and non-thermal emission in the X-ray spectrum. Additionally, building SEDs from simultaneous multi-wavelength observations will help constrain the broad-band emission. This will also help to pinpoint the counter part of Fermi/LAT detected sources, which is not trivial due to the large uncertainty in position

FPGA-based RF spectrum merging and adaptive hopset selection

NASA Astrophysics Data System (ADS)

McLean, R. K.; Flatley, B. N.; Silvius, M. D.; Hopkinson, K. M.

The radio frequency (RF) spectrum is a limited resource. Spectrum allotment disputes stem from this scarcity as many radio devices are confined to a fixed frequency or frequency sequence. One alternative is to incorporate cognition within a reconfigurable radio platform, therefore enabling the radio to adapt to dynamic RF spectrum environments. In this way, the radio is able to actively sense the RF spectrum, decide, and act accordingly, thereby sharing the spectrum and operating in more flexible manner. In this paper, we present a novel solution for merging many distributed RF spectrum maps into one map and for subsequently creating an adaptive hopset. We also provide an example of our system in operation, the result of which is a pseudorandom adaptive hopset. The paper then presents a novel hardware design for the frequency merger and adaptive hopset selector, both of which are written in VHDL and implemented as a custom IP core on an FPGA-based embedded system using the Xilinx Embedded Development Kit (EDK) software tool. The design of the custom IP core is optimized for area, and it can process a high-volume digital input via a low-latency circuit architecture. The complete embedded system includes the Xilinx PowerPC microprocessor, UART serial connection, and compact flash memory card IP cores, and our custom map merging/hopset selection IP core, all of which are targeted to the Virtex IV FPGA. This system is then incorporated into a cognitive radio prototype on a Rice University Wireless Open Access Research Platform (WARP) reconfigurable radio.

B And V Photometry Of A Inverted-spectrum And Flat-spectrum Radio Sources With The Rowan 0.4-meter Telescope

NASA Astrophysics Data System (ADS)

Guerra, Erick; Pultar, R.

2010-05-01

Several galaxies have been selected for an exploratory campaign with 0.4-meter telescope atop Science Hall at Rowan University. These galaxies exhibit inverted radio spectra on the basis of fluxes in the GB6 and VLA FIRST catalogs and have SDSS magnitudes in g-band less than 15.5. The results of V and R band photometry of theses galaxies are presented. Photometry from multiple nights will be examined to explore variability on the timescales of days or weeks. Targets in the sample include Markarian 668 and NGC 5635. These are the first results from an ongoing campaign to expand the function of the observatory atop Science Hall. The authors would like to acknowledge Ric and Jean Edelman for their gift that funded the 0.4-meter telescope.

Two Active States of the Narrow-Line Gamma-Ray-Loud AGN GB 1310 + 487

NASA Technical Reports Server (NTRS)

Sokolovsky, K. V.; Schinzel, F. K.; Tanaka, Y. T.; Abolmasov, P. K.; Angelakis, E.; Bulgarelli, A.; Carrasco, L.; Cenko, S. B.; Cheung, C. C.; Clubb, K. I.;

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

47 CFR 90.365 - Partitioned licenses and disaggregated spectrum.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 5 2010-10-01 2010-10-01 false Partitioned licenses and disaggregated spectrum. 90.365 Section 90.365 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Intelligent Transportation Systems Radio Service...

Five New Millisecond Pulsars From A Radio Survey Of 14 Unidentified Fermi -Lat Gamma-Ray Sources

DOE PAGES

Kerr, M.; Camilo, F.; Johnson, T. J.; ...

2012-02-27

We have discovered five millisecond pulsars (MSPs) in a survey of 14 unidentified Fermi-LAT sources in the southern sky using the Parkes radio telescope. PSRs J0101–6422, J1514–4946, and J1902–5105 reside in binaries, while PSRs J1658–5324 and J1747–4036 are isolated. Using an ephemeris derived from timing observations of PSR J0101–6422 (P=2.57ms, DM=12 pc cm -3), we have detected γ-ray pulsations and measured its proper motion. Its γ-ray spectrum (a power law of Γ = 0.9 with a cutoff at 1.6GeV) and efficiency are typical of other MSPs, but its radio and γ-ray light curves challenge simple geometric models of emission. Themore » high success rate of this survey—enabled by selecting γ- ray sources based on their detailed spectral characteristics—and other similarly successful searches indicate that a substantial fraction of the local population of MSPs may soon be known.« less

FIVE NEW MILLISECOND PULSARS FROM A RADIO SURVEY OF 14 UNIDENTIFIED FERMI-LAT GAMMA-RAY SOURCES

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

Kerr, M.; Camilo, F.; Johnson, T. J.

2012-03-20

We have discovered five millisecond pulsars (MSPs) in a survey of 14 unidentified Fermi Large Area Telescope sources in the southern sky using the Parkes radio telescope. PSRs J0101-6422, J1514-4946, and J1902-5105 reside in binaries, while PSRs J1658-5324 and J1747-4036 are isolated. Using an ephemeris derived from timing observations of PSR J0101-6422 (P = 2.57 ms, DM = 12 pc cm{sup -3}), we have detected {gamma}-ray pulsations and measured its proper motion. Its {gamma}-ray spectrum (a power law of {Gamma} = 0.9 with a cutoff at 1.6 GeV) and efficiency are typical of other MSPs, but its radio and {gamma}-raymore » light curves challenge simple geometric models of emission. The high success rate of this survey-enabled by selecting {gamma}-ray sources based on their detailed spectral characteristics-and other similarly successful searches indicate that a substantial fraction of the local population of MSPs may soon be known.« 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.

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.

The X-Ray Counterpart to LAT PSR J2021+4026 and Its Interesting Spectrum

NASA Technical Reports Server (NTRS)

Weisskopf, Martin C.; Becker, W.; Carraminana, A.; De Luca, A.; Dormandy, M.; Harding, A.; Kanbach, G.; O'Dell, S. L.; Parkinson, P. Saz; Ray, P.;

Joint subchannel pairing and power control for cognitive radio networks with amplify-and-forward relaying.

PubMed

Shen, Yanyan; Wang, Shuqiang; Wei, Zhiming

2014-01-01

Dynamic spectrum sharing has drawn intensive attention in cognitive radio networks. The secondary users are allowed to use the available spectrum to transmit data if the interference to the primary users is maintained at a low level. Cooperative transmission for secondary users can reduce the transmission power and thus improve the performance further. We study the joint subchannel pairing and power allocation problem in relay-based cognitive radio networks. The objective is to maximize the sum rate of the secondary user that is helped by an amplify-and-forward relay. The individual power constraints at the source and the relay, the subchannel pairing constraints, and the interference power constraints are considered. The problem under consideration is formulated as a mixed integer programming problem. By the dual decomposition method, a joint optimal subchannel pairing and power allocation algorithm is proposed. To reduce the computational complexity, two suboptimal algorithms are developed. Simulations have been conducted to verify the performance of the proposed algorithms in terms of sum rate and average running time under different conditions.

Conceptual Background to Radio

NASA Astrophysics Data System (ADS)

Ponsonby, J. E. B.

2004-06-01

The International Telecommunications Union (ITU) conceives the radio spectrum as primarily a resource for telecommunications. Indeed most applications of radio are for communications and other radio services, particularly the Radio Astronomy Service, are deemed to be `pretend'communication serviceas for spectrum amnagement purposes. The language of Radio Spectrum Management is permeated by the terminology ofcommunications, some derived from the physics of radio and some from aspects of information theory. This contribution touches on all the essential concepts of radiocommunications which the author thinks should be the common mental equipment of the Spectrum Manager. The fundamental capacity of a communication channel is discussed in terms of the degrees of freedom and bandwidth of a signal, and the signal to noise ratio. It is emphasized that an information bearing signal is inherently unpredictable, and must, at some level, be discontinuous. This has important consequences for the form of its power spectrum. The effect of inserting filters is discussed particularly with regard to constant amplitude signals and, in the context of non-linear power amplifiers, the phenomenon of`sideband recovery'. All the common generic forms of modulation are discussed including the very different case of `no-modulation' which applies in all forms of passive remote sensing. Whilst all are agreed that the radio spectrum should be used `efficiently', there is no quantitative measure of spectral efficiency which embraces all relevant aspects of spectral usage. These various aspects are dicussed. Finally a brief outline of some aspects of antennae are reviewed. It is pointed out that the recent introduction of so-called `active antennnae', which have properties unlike traditional passive antennae, has confused the interpretation of those ITU Radio Regulations which refer to antennae.

Extended X-ray emission in PKS 1718-649

NASA Astrophysics Data System (ADS)

Beuchert, T.; Rodríguez-Ardila, A.; Moss, V. A.; Schulz, R.; Kadler, M.; Wilms, J.; Angioni, R.; Callingham, J. R.; Gräfe, C.; Krauß, F.; Kreikenbohm, A.; Langejahn, M.; Leiter, K.; Maccagni, F. M.; Müller, C.; Ojha, R.; Ros, E.; Tingay, S. J.

2018-04-01

PKS 1718-649 is one of the closest and most comprehensively studied candidates of a young active galactic nucleus (AGN) that is still embedded in its optical host galaxy. The compact radio structure, with a maximal extent of a few parsecs, makes it a member of the group of compact symmetric objects (CSO). Its environment imposes a turnover of the radio synchrotron spectrum towards lower frequencies, also classifying PKS 1718-649 as gigahertz-peaked radio spectrum (GPS) source. Its close proximity has allowed the first detection of extended X-ray emission in a GPS/CSO source with Chandra that is for the most part unrelated to nuclear feedback. However, not much is known about the nature of this emission. By co-adding all archival Chandra data and complementing these datasets with the large effective area of XMM-Newton, we are able to study the detailed physics of the environment of PKS 1718-649. Not only can we confirm that the bulk of the ≲kiloparsec-scale environment emits in the soft X-rays, but we also identify the emitting gas to form a hot, collisionally ionized medium. While the feedback of the central AGN still seems to be constrained to the inner few parsecs, we argue that supernovae are capable of producing the observed large-scale X-ray emission at a rate inferred from its estimated star formation rate.

Simultaneous Chandra X-ray, HST Ultraviolet, and Ulysses Radio Observations of Jupiter's Aurora

NASA Technical Reports Server (NTRS)

Elsner, R. F.; Lugaz, N.; Waite, J. H., Jr.; Cravens, T. E.; Gladstone, G. R.; Ford, P.; Grodent, D.; Bhardwaj, A.; MacDowall, R. J.

2004-01-01

Observations of Jupiter carried out by the Chandra ACIS-S instrument over 24-26 February, 2003, show that the auroral X-ray spectrum consists of line emission consistent with high-charge states of precipitating ions, and not a continuum as might be expected from bremsstrahlung. The part of the spectrum due to oxygen peaks around 650 eV, which indicates a high fraction of fully-stripped oxygen in the precipitating ion flux. A combination of the OVIII emission lines at 653 eV and 774 eV, as well as the OVII emission lines at 561 eV and 666 eV, are evident in the measure auroral spectrum. There is also line emission at lower energies in the spectral region extending from 250 to 350 eV, which could be from sulfur and/or carbon. The Jovian auroral X- ray spectra are significantly different from the X-ray spectra of comets. The charge state distribution of the oxygen ions implied by the measured auroral X-ray spectra strongly suggests that, independent of the source of the energetic ions - magnetospheric or solar wind - the ions have undergone additional acceleration. This spectral evidence for ion acceleration is also consistent with the relatively high intensities of the X-rays compared to the available phase space density of the (unaccelerated) source populations of solar wind or magnetospheric ions at Jupiter, which are orders of magnitude too small to explain the observed emissions. The Chandra X-ray observations were executed simultaneously with observations at ultraviolet wavelengths by the Hubble Space Telescope and at radio wavelengths by the Ulysses spacecraft. These additional data sets suggest that the source of the X-rays is magnetospheric in origin, and that the precipitating particles are accelerated by strong field-aligned electric fields, which simultaneously create both the several-MeV energetic ion population and the relativistic electrons observed in situ by Ulysses that are correlated with approximately 40 minute quasi-periodic radio outbursts.

Radio Detection of the Fermi-LAT Blind Search Millisecond Pulsar J1311-3430

NASA Astrophysics Data System (ADS)

Ray, P. S.; Ransom, S. M.; Cheung, C. C.; Giroletti, M.; Cognard, I.; Camilo, F.; Bhattacharyya, B.; Roy, J.; Romani, R. W.; Ferrara, E. C.; Guillemot, L.; Johnston, S.; Keith, M.; Kerr, M.; Kramer, M.; Pletsch, H. J.; Saz Parkinson, P. M.; Wood, K. S.

2013-01-01

We report the detection of radio emission from PSR J1311-3430, the first millisecond pulsar (MSP) discovered in a blind search of Fermi Large Area Telescope (LAT) gamma-ray data. We detected radio pulsations at 2 GHz, visible for <10% of ~4.5 hr of observations using the Green Bank Telescope (GBT). Observations at 5 GHz with the GBT and at several lower frequencies with Parkes, Nançay, and the Giant Metrewave Radio Telescope resulted in non-detections. We also report the faint detection of a steep spectrum continuum radio source (0.1 mJy at 5 GHz) in interferometric imaging observations with the Jansky Very Large Array. These detections demonstrate that PSR J1311-3430 is not radio quiet and provide additional evidence that radio-quiet MSPs are rare. The radio dispersion measure of 37.8 pc cm-3 provides a distance estimate of 1.4 kpc for the system, yielding a gamma-ray efficiency of 30%, typical of LAT-detected MSPs. We see apparent excess delay in the radio pulses as the pulsar appears from eclipse and we speculate on possible mechanisms for the non-detections of the pulse at other orbital phases and observing frequencies.

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

Radio Frequency Interference Site Survey for Thai Radio Telescopes

NASA Astrophysics Data System (ADS)

Jaroenjittichai, P.; Punyawarin, S.; Singwong, D.; Somboonpon, P.; Prasert, N.; Bandudej, K.; Kempet, P.; Leckngam, A.; Poshyachinda, S.; Soonthornthum, B.; Kramer, B.

2017-09-01

Radio astronomical observations have increasingly been threaten by the march of today telecommunication and wireless technology. Performance of radio telescopes lies within the fact that astronomical sources are extremely weak. National Astronomy Research Institute of Thailand (NARIT) has initiated a 5-year project, known as the Radio Astronomy Network and Geodesy for Development (RANGD), which includes the establishment of 40-meter and 13-meter radio telescopes. Possible locations have been narrowed down to three candidates, situated in the Northern part of Thailand, where the atmosphere is sufficiently dry and suitable for 22 and 43 GHz observations. The Radio Frequency Interference (RFI) measurements were carried out with a DC spectrum analyzer and directional antennas at 1.5 meter above ground, from 20 MHz to 6 GHz with full azimuth coverage. The data from a 3-minute pointing were recorded for both horizontal and vertical polarizations, in maxhold and average modes. The results, for which we used to make preliminary site selection, show signals from typical broadcast and telecommunication services and aeronautics applications. The signal intensity varies accordingly to the presence of nearby population and topography of the region.

Performance Analysis on the Coexistence of Multiple Cognitive Radio Networks

DTIC Science & Technology

2015-05-28

the scarce spectrum resources. Cognitive radio is a key in minimizing the spectral congestion through its adaptability, where the radio parameters...static allocation of spectrum results in congestion in some parts of the spectrum and non use in some others, therefore, spectra utilization is...well as the secondary user (SU) activities in multiple CR networks. It is shown that the scheduler provided much needed gain during congestions . However

On the Physical Environment in the Galactic Nuclei. Ph.D. Thesis - Maryland Univ.

NASA Technical Reports Server (NTRS)

Beall, J. H.

1979-01-01

Galactic nuclei and quasars emit radiation over the entire electromagnetic spectrum. This suggests that concurrent observations over a wide frequency range may provide useful information in determining appropriate models for the physical environment in which the radiation is produced. In conjunction with observations by the high energy spectrometer on OSO-8, four sources have been studied in this manner; the nucleus of the elliptical galaxy, Centaurus A (NGG 5128); the quasar, 30273; the Seyfert galaxy, NGC 4151 and the nucleus of the Milky Way (GCX). Concurrent observations are used to construct the composite spectra (from radio to X-ray) for Cen A and NGC 4151 while the composite spectra of 30273 and GCX are derived from the OSO-8 data and from other observers. A skymap technique used to analyze observations of the galactic center region yielded data consistent with a significant, hard X-ray source at the radio and infrared position of the nucleus of the Milky Way. A theoretical analysis of the temporal variability of the Cen A data is undertaken and its implications discussed. Similarities between the composite spectra of the observed sources suggest that radio-bright and radio-quiet quasars may represent the emission from galactic nuclei with elliptical and Seyfert-like morphologies, respectively.

Hybrid spread spectrum radio system

DOEpatents

Smith, Stephen F [London, TN; Dress, William B [Camas, WA

2010-02-09

Systems and methods are described for hybrid spread spectrum radio systems. A method, includes receiving a hybrid spread spectrum signal including: fast frequency hopping demodulating and direct sequence demodulating a direct sequence spread spectrum signal, wherein multiple frequency hops occur within a single data-bit time and each bit is represented by chip transmissions at multiple frequencies.

Comparison of Three Plasma Sources for Ambient Desorption/Ionization Mass Spectrometry

NASA Astrophysics Data System (ADS)

McKay, Kirsty; Salter, Tara L.; Bowfield, Andrew; Walsh, James L.; Gilmore, Ian S.; Bradley, James W.

2014-09-01

Plasma-based desorption/ionization sources are an important ionization technique for ambient surface analysis mass spectrometry. In this paper, we compare and contrast three competing plasma based desorption/ionization sources: a radio-frequency (rf) plasma needle, a dielectric barrier plasma jet, and a low-temperature plasma probe. The ambient composition of the three sources and their effectiveness at analyzing a range of pharmaceuticals and polymers were assessed. Results show that the background mass spectrum of each source was dominated by air species, with the rf needle producing a richer ion spectrum consisting mainly of ionized water clusters. It was also seen that each source produced different ion fragments of the analytes under investigation: this is thought to be due to different substrate heating, different ion transport mechanisms, and different electric field orientations. The rf needle was found to fragment the analytes least and as a result it was able to detect larger polymer ions than the other sources.

Comparison of three plasma sources for ambient desorption/ionization mass spectrometry.

PubMed

McKay, Kirsty; Salter, Tara L; Bowfield, Andrew; Walsh, James L; Gilmore, Ian S; Bradley, James W

2014-09-01

Plasma-based desorption/ionization sources are an important ionization technique for ambient surface analysis mass spectrometry. In this paper, we compare and contrast three competing plasma based desorption/ionization sources: a radio-frequency (rf) plasma needle, a dielectric barrier plasma jet, and a low-temperature plasma probe. The ambient composition of the three sources and their effectiveness at analyzing a range of pharmaceuticals and polymers were assessed. Results show that the background mass spectrum of each source was dominated by air species, with the rf needle producing a richer ion spectrum consisting mainly of ionized water clusters. It was also seen that each source produced different ion fragments of the analytes under investigation: this is thought to be due to different substrate heating, different ion transport mechanisms, and different electric field orientations. The rf needle was found to fragment the analytes least and as a result it was able to detect larger polymer ions than the other sources.

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

PSR J2030+364I: Radio Discovery and Gamma-ray Study of a Middle-aged Pulsar in the Now Identified Fermi-LAT Source 1FGL J2030.0+3641

NASA Technical Reports Server (NTRS)

Camilo, F.; Kerr, M.; Ray, P. S.; Ransom, S. M.; Johnston, S.; Romani, R. W.; Parent, D.; Decesar, M. E.; Harding, A. K.; Donato, D.;

Fermi-LAT detection of a GeV gamma-ray flare from the blazar PKS 1313-333

NASA Astrophysics Data System (ADS)

Ciprini, Stefano

2016-01-01

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 1313-333 (also known as TXS 1313-333, OP -322, 2EG J1314-3430 and 3FGL J1316.0-3338), with radio counterpart position R.A.: 199.033275 deg, Dec.: -33.64977 deg, (J2000.0, Johnston et al. 1995, AJ, 110, 880) and with redshift z=1.210 (Jauncey et al. 1982, AJ, 87, 763).

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.

Low frequency spectra of type III solar radio bursts

NASA Technical Reports Server (NTRS)

Weber, R. R.

1978-01-01

Flux density spectra have been determined for 91 simple type III solar bursts observed by the Goddard Space Flight Center radio astronomy experiment on the IMP-6 spacecraft during 1971 and 1972. Spectral peaks were found to occur at frequencies ranging from 44 kHz up to 2500 kHz. Half of the bursts peaked between 250 kHz and 900 kHz, corresponding to emission at solar distances of about 0.3 to 0.1 AU. Maximum burst flux density sometimes exceeds 10 to the -14th W/sq m/Hz. The primary factor controlling the spectral peak frequency of these bursts appears to be a variation in intrinsic power radiated by the source as the exciter moves outward from the sun, rather than radio propagation effects between the source and IMP-6. Thus, a burst spectrum strongly reflects the evolution of the properties of the exciting electron beam, and according to current theory, beam deceleration could help account for the observations.

Prospects and limitations for use of frequency spectrum from 40 to 300 GHz

NASA Technical Reports Server (NTRS)

Catoe, C. E.

1979-01-01

The existing and future use of the electromagnetic spectrum from 40 to 300 gigahertz is discussed. The activities envisioned for this segment of the electromagnetic spectrum fall generically into two basic categories: communications and remote sensing. The communications services considered for this region are focused on the existing and future frequency allocations that are required for terrestrial radio services, space to ground radio services, space to space radio services, and space to deep space radio services. The remote sensing services considered for this region are divided into two groups of activities: earth viewing and space viewing.

CENTAURUS A: THE EXTRAGALACTIC SOURCE OF COSMIC RAYS WITH ENERGIES ABOVE THE KNEE

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

Biermann, Peter L.; De Souza, Vitor, E-mail: plbiermann@mpifr-bonn.mpg.de, E-mail: vitor@ifsc.usp.br

2012-02-10

The origin of cosmic rays at all energies is still uncertain. In this paper, we present and explore an astrophysical scenario to produce cosmic rays with energy ranging from below 10{sup 15} to 3 Multiplication-Sign 10{sup 20} eV. We show here that just our Galaxy and the radio galaxy Cen A, each with their own galactic cosmic-ray particles but with those from the radio galaxy pushed up in energy by a relativistic shock in the jet emanating from the active black hole, are sufficient to describe the most recent data in the PeV to near ZeV energy range. Data aremore » available over this entire energy range from the KASCADE, KASCADE-Grande, and Pierre Auger Observatory experiments. The energy spectrum calculated here correctly reproduces the measured spectrum beyond the knee and, contrary to widely held expectations, no other extragalactic source population is required to explain the data even at energies far below the general cutoff expected at 6 Multiplication-Sign 10{sup 19} eV, the Greisen-Zatsepin-Kuz'min turnoff due to interaction with the cosmological microwave background. We present several predictions for the source population, the cosmic-ray composition, and the propagation to Earth which can be tested in the near future.« less

An experiment protocol for a search for radio signals of extraterrestrial intelligent origin in the presence of man-made radio frequency sources

NASA Technical Reports Server (NTRS)

Edelson, R. E.

1977-01-01

Some aspects of signal extraction in a microwave search for evidence of extraterrestrial intelligence are examined. Parametric relations are summarized which are applicable to a microwave search of constrained duration that employs FFT spectrum-analyzer receivers, with sensitivity enhancement by spectrum accumulation and detection by a threshold criterion. Three types of natural and man-made false alarms are identified, the probability of false alarm in a single data channel is computed, and the implications of false alarms for a constant-beamwidth sky survey are considered. It is shown that the key to an efficient search is the prompt and unambiguous elimination of false alarms. An experimental protocol is suggested which eliminates spurious signals primarily through procedural techniques involving antenna repointing, delayed repeated observations, and storage of particular historical parameters for suspect signals.

Comparison of the observed and calculated coherent forward scattering spectra of the 842.5 nm Ar I and 844.6 nm O I lines in a radio frequency glow discharge

NASA Astrophysics Data System (ADS)

Matsuta, Hideyuki

2017-06-01

The coherent forward scattering (CFS) spectra of O I 844.6 nm and Ar I 842.5 nm lines in a radio frequency (RF) glow discharge were measured using a CFS spectrometer that functions in the Faraday configuration with permanent double-ring magnets and a diode-laser source. A significant change in the CFS spectrum of the Ar I 842.5 nm line was observed when the partial pressures of argon in a Hesbnd Ar RF glow discharge were changed . Based on the theoretical calculations of the CFS spectra performed using Faraday functions, a comparison between the observed and calculated spectra was performed. The CFS line profile of O I 844.6 nm and changes in the Ar I 842.5 nm CFS spectrum are explained by theoretical calculations.

47 CFR 90.801 - 900 MHz SMR spectrum subject to competitive bidding.

Code of Federal Regulations, 2010 CFR

2010-10-01

... SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Competitive Bidding Procedures for 900 MHz Specialized Mobile Radio Service § 90.801 900 MHz SMR spectrum subject to competitive bidding. Mutually exclusive initial applications for 900 MHz SMR service licenses are subject to competitive bidding. The...

Particle acceleration areas in two radio galaxies.

NASA Astrophysics Data System (ADS)

Andernach, H.

1989-04-01

Two edge-darkened, tailed radio galaxies (PKS 0123-01 and PKS 2247+11) were mapped with the VLA at 1.4 and 5 GHz at sub-arcmin resolution as well as with the Effelsberg 100-m telescope at 2.7, 5 and 10.7 GHz at arcmin resolution. With additional use of existing low-frequency maps the shape of the radio spectrum is analyzed point by point across the source extent. The shape is found to be concave (i.e. having high-frequency excess) over major parts of the source extent, in the case of 2247+11 even for a region in the far radio tail. Possible mechanisms causing this feature are proposed. Using a subset of maps at higher angular resolution most of the regions with spectral flattening turn out to coincide with bends and wiggles of the radio jets and/or tails. Polarization data are available at four frequencies and some problems in their interpretation are discussed. The following one consists of a 1-page "extended abstract" including two small figures. I attach to this message the processed postscript file which I would be happy to offer in ADS as a "scanned" paper. I include here the full extended abstract text which you could also offer as HTML code. I converted the four references to bibcodes.

Hard X-ray and high-frequency decimetric radio observations of the 4 April 2002 solar flare

NASA Astrophysics Data System (ADS)

Kane, S. R.; Sawant, H. S.; Cecatto, J. R.; Andrade, M. C.; Fernandes, F. C. R.; Karlicky, M.; Meszarosova, H.

Hard X-ray and high frequency decimetric type III radio bursts have been observed in association with the soft X-raysolar flare (GOES class M 6.1) on 4 April 2002 (˜1532 UT). The flare apparently occurred ˜ 6 degrees behind the east limb of the Sun in the active region NOAA 9898. Hard X-ray spectra and images were obtained by the X-ray imager on RHESSI during the impulsive phase of the flare. The Brazilian Solar Spectroscope and Ondrejov Radio Telescopes recorded type III bursts in 800-1400 MHz range in association with the flare. The images of the 3-6, 6-12, 12-25, and 25-50 keV X-ray sources, obtained simultaneously by RHESSI during the early impulsive phase of the flare, show that all the four X-ray sources were essentially at the same location well above the limb of the Sun. During the early impulsive phase, the X-ray spectrum over 8-30 keV range was consistent with a power law with a negative exponent of ˜ 6. The radio spectra show drifting radio structures with emission in a relatively narrow (Δf ≤ 200 MHz) frequency range indicating injection of energetic electrons into a plasmoid which is slowly drifting upwards in the corona.

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.

Discovery of a Fanaroff-Riley type 0 radio galaxy emitting at γ-ray energies

NASA Astrophysics Data System (ADS)

Grandi, Paola; Capetti, Alessandro; Baldi, Ranieri D.

2016-03-01

We present supporting evidence for the first association of a Fermi source, 3FGLJ1330.0-3818, Acero et al. (2015) with the Fanaroff-Riley type 0 (FR 0) radio galaxy Tol1326-379. FR 0s represent the majority of the local population of radio-loud active galactic nuclei but their nature is still unclear. They share the same nuclear and host properties as FR Is, but they show a large deficit of extended radio emission. Here we show that FR 0s can emit photons at very high energies. Tol1326-379 has a GeV luminosity of L>1 GeV ˜ 2 × 1042 erg s-1, typical of FR Is, but with a steeper γ-ray spectrum (Γ = 2.78 ± 0.14). This could be related to the intrinsic jet properties but also to a different viewing angle.

The importance of Radio Quiet Zone (RQZ) for radio astronomy

NASA Astrophysics Data System (ADS)

Umar, Roslan; Abidin, Zamri Zainal; Ibrahim, Zainol Abidin

2013-05-01

Most of radio observatories are located in isolated areas. Since radio sources from the universe is very weak, astronomer need to avoid radio frequency interference (RFI) from active spectrum users and radio noise produced by human made (telecommunication, mobile phone, microwave user and many more. There are many observatories around the world are surrounded by a Radio Quiet Zone (RQZ), which is it was set up using public or state laws. A Radio Quiet Zone normally consists of two areas: an exclusive area in which totally radio emissions are forbidden, with restrictions for residents and business developments, and a larger (radius up to 100 km above) coordination area where the power of radio transmission limits to threshold levels. Geographical Information System (GIS) can be used as a powerful tool in mapping large areas with varying RQZ profiles. In this paper, we report the initial testing of the usage of this system in order to identify the areas were suitable for Radio Quiet Zone. Among the important parameters used to develop the database for our GIS are population density, information on TV and telecommunication (mobile phones) transmitters, road networks (highway), and contour shielding. We will also use other information gathered from on-site RFI level measurements on selected 'best' areas generated by the GIS. The intention is to find the best site for the purpose of establishing first radio quiet zones for radio telescope in Malaysia.

Dynamic spectrum management: an impact on EW systems

NASA Astrophysics Data System (ADS)

Gajewski, P.; Łopatka, J.; Suchanski, M.

2017-04-01

Rapid evolution of wireless systems caused an enormous growth of data streams transmitted through the networks and, as a consequence, an accompanying demand concerning spectrum resources (SR). An avoidance of advisable disturbances is one of the main demands in military communications. To solve the interference problems, dynamic spectrum management (DSM) techniques can be used. Two main techniques are possible: centralized Coordinated Dynamic Spectrum Access (CDSA) and distributed Opportunistic Spectrum Access (OSA). CDSA enables the wireless networks planning automation, and systems dynamic reaction to random changes of Radio Environment (RE). For OSA, cognitive radio (CR) is the most promising technology that enables avoidance of interference with the other spectrum users due to CR's transmission parameters adaptation to the current radio situation, according to predefined Radio Policies rules. If DSM techniques are used, the inherent changes in EW systems are also needed. On one hand, new techniques of jamming should be elaborated, on the other hand, the rules and protocols of cooperation between communication network and EW systems should be developed.

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.

Smart radio: spectrum access for first responders

NASA Astrophysics Data System (ADS)

Silvius, Mark D.; Ge, Feng; Young, Alex; MacKenzie, Allen B.; Bostian, Charles W.

2008-04-01

This paper details the Wireless at Virginia Tech Center for Wireless Telecommunications' (CWT) design and implementation of its Smart Radio (SR) communication platform. The CWT SR can identify available spectrum within a pre-defined band, rendezvous with an intended receiver, and transmit voice and data using a selected quality of service (QoS). This system builds upon previous cognitive technologies developed by CWT for the public safety community, with the goal of providing a prototype mobile communications package for military and public safety First Responders. A master control (MC) enables spectrum awareness by characterizing the radio environment with a power spectrum sensor and an innovative signal detection and classification module. The MC also enables spectrum and signal memory by storing sensor results in a knowledge database. By utilizing a family radio service (FRS) waveform database, the CWT SR can create a new communication link on any designated FRS channel frequency using FM, BPSK, QPSK, or 8PSK modulations. With FM, it supports analog voice communications with legacy hand-held FRS radios. With digital modulations, it supports IP data services, including a CWT developed CVSD-based VoIP protocol. The CWT SR coordinates spectrum sharing between analog primary users and digital secondary users by applying a simple but effective channel-change protocol. It also demonstrates a novel rendezvous protocol to facilitate the detection and initialization of communications links with neighboring SR nodes through the transmission of frequency-hopped rendezvous beacons. By leveraging the GNU Radio toolkit, writing key modules entirely in Python, and utilizing the USRP hardware front-end, the CWT SR provides a dynamic spectrum test bed for future smart and cognitive radio research.

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.

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.

75 FR 38959 - Uniform License Renewal, Discontinuance of Operations, and Geographic Partitioning and Spectrum...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-07

... Spectrum Disaggregation Rules and Policies for Certain Wireless Radio Services AGENCY: Federal..., geographic partitioning, and spectrum disaggregation for certain Wireless Radio Services in an effort to... Counsel, Mobility Division, Wireless Telecommunications Bureau, at (202) 418- 0920, or e-mail at Richard...

47 CFR 1.9020 - Spectrum manager leasing arrangements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... geographic overlap with spectrum in any licensed Wireless Radio Service (including the same service), or in... Safety Radio Services (see part 90, subpart B and § 90.311(a)(1)(i) of this chapter) is not required to... Radio Service (PMRS), private, or non-commercial basis. (7) Regulatory fees. The licensee remains...

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'.

The Peculiar Radio-loud Narrow Line Seyfert 1 Galaxy 1H 0323+342

NASA Astrophysics Data System (ADS)

Paliya, Vaidehi S.; Sahayanathan, S.; Parker, M. L.; Fabian, A. C.; Stalin, C. S.; Anjum, Ayesha; Pandey, S. B.

2014-07-01

We present a multiwavelength study of the radio-loud narrow-line Seyfert 1 galaxy (NLSy1) 1H 0323+342, detected by the Fermi Gamma-Ray Space Telescope. Multiband light curves show many orphan X-ray and optical flares having no corresponding γ-ray counterparts. Such anomalous variability behavior can be due to different locations of the emission region from the central source. During a large flare, a γ-ray flux doubling timescale as small as ~3 hr is noticed. We built spectral energy distributions (SEDs) during different activity states and modeled them using a one-zone leptonic model. The shape of the optical/UV component of the SEDs is dominated by accretion disk emission in all the activity states. In the X-ray band, significant thermal emission from the hot corona is inferred during quiescent and first flaring states; however, during subsequent flares, the nonthermal jet component dominates. The γ-ray emission in all the states can be well explained by inverse-Compton scattering of accretion disk photons reprocessed by the broad-line region. The source showed violent intra-night optical variability, coinciding with one of the high γ-ray activity states. An analysis of the overall X-ray spectrum fitted with an absorbed power-law plus relativistic reflection component hints at the presence of an Fe Kα line and returns a high black hole spin value of a = 0.96 ± 0.14. We argue that 1H 0323+342 possesses dual characteristics, akin to both flat-spectrum radio quasars (FSRQs) and radio-quiet NLSy1 galaxies, though at a low jet power regime compared to powerful FSRQs.

Collective Evidence for Inverse Compton Emission from External Photons in High-Power Blazars

NASA Technical Reports Server (NTRS)

Meyer, Eileen T.; Fossati, Giovanni; Georganopoulos, Markos; Lister, Matthew L.

2012-01-01

We present the first collective evidence that Fermi-detected jets of high kinetic power (L(sub kin)) are dominated by inverse Compton emission from upscattered external photons. Using a sample with a broad range in orientation angle, including radio galaxies and blazars, we find that very high power sources (L(sub kin) > 10(exp 45.5) erg/s) show a significant increase in the ratio of inverse Compton to synchrotron power (Compton dominance) with decreasing orientation angle, as measured by the radio core dominance and confirmed by the distribution of superluminal speeds. This increase is consistent with beaming expectations for external Compton (EC) emission, but not for synchrotron self Compton (SSC) emission. For the lowest power jets (L(sub kin) < 10(exp 43.5) erg /s), no trend between Compton and radio core dominance is found, consistent with SSC. Importantly, the EC trend is not seen for moderately high power flat spectrum radio quasars with strong external photon fields. Coupled with the evidence that jet power is linked to the jet speed, this finding suggests that external photon fields become the dominant source of seed photons in the jet comoving frame only for the faster and therefore more powerful jets.

The characterization of the distant blazar GB6 J1239+0443 from flaring and low activity periods

DOE PAGES

Pacciani, L.; Donnarumma, I.; Denney, K. D.; ...

2012-08-27

In 2008, AGILE and Fermi detected gamma-ray flaring activity from the unidentified EGRET source 3EG J1236+0457, recently associated with a flat spectrum radio quasar (GB6 J1239+0443) at z = 1.762. The optical counterpart of the gamma-ray source underwent a flux enhancement of a factor of 15–30 in six years, and of ~10 in six months. Here, we interpret this flare-up in terms of a transition from an accretion-disc-dominated emission to a synchrotron-jet-dominated one. We analysed a Sloan Digital Sky Survey (SDSS) archival optical spectrum taken during a period of low radio and optical activity of the source. We estimated themore » mass of the central black hole using the width of the C iv emission line. In our work, we have also investigated SDSS archival optical photometric data and ultraviolet GALEX observations to estimate the thermal disc emission contribution of GB6 J1239+0443. This analysis of the gamma-ray data taken during the flaring episodes indicates a flat gamma-ray spectrum, with an extension of up to 15 GeV, with no statistically relevant sign of absorption from the broad-line region, suggesting that the blazar zone is located beyond the broad-line region. Our result is confirmed by the modelling of the broad-band spectral energy distribution (well constrained by the available multiwavelength data) of the flaring activity periods and by the accretion disc luminosity and black hole mass estimated by us using archival data.« less

G25.5 + 0.2 - A very young galactic supernova remnant

NASA Technical Reports Server (NTRS)

Cowan, John J.; Ekers, R. D.; Goss, W. M.; Sramek, R. A.; Roberts, Douglas A.

1989-01-01

Radio emission has been detected from a compact source which satisfies the criteria for a very young galactic supernova remnant. The source, G25.5 + 0.2 has a partially-filled shell structure, a total integrated flux density at 20 cm of 315 mJy, and a flat spectrum between 2 and 20 cm. Observations at 843 and 327 MHz indicate thermal absorption at low frequencies with a turnover in the spectrum near 1 GHz. It is suggested that the lower limit for the age of the supernova remnant is 25 yr, while the upper limit is about 100 yr. It is concluded that G25.5 + 0.2 could be the youngest known supernova remnant in the Galaxy.

Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012

DOE PAGES

Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; ...

2016-06-02

1ES 1011+496 (z = 0.212) was discovered in very high-energy (VHE, E> 100 GeV) γ rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED). In this paper, we study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and Metsähovi in addition to optical polarimetry data andmore » radio maps from the Liverpool Telescope and MOJAVE. The VHE spectrum was fit with a simple power law with a photon index of 3.69 ± 0.22 and a flux above 150 GeV of (1.46 ± 0.16) x 10 -11 ph cm -2s -1. The source 1ES 1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 ± 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1 GeV to 1 TeV, which permitted a more reliable interpretation within the one-zone SSC scenario. Finally, the polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission.« less

Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012

NASA Astrophysics Data System (ADS)

Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Arcaro, C.; Babic, A.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; de Oña Wilhelmi, E.; Delgado Mendez, C.; Di Pierro, F.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Godinović, N.; González Muñoz, A.; Gozzini, S. R.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Knoetig, M. L.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Persic, M.; Poutanen, J.; Prada Moroni, P. G.; Prandini, E.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Saito, T.; Saito, K.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Stamerra, A.; Steinbring, T.; Strzys, M.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Torres, D. F.; Toyama, T.; Treves, A.; Vogler, P.; Will, M.; Zanin, R.; Buson, S.; D'Ammando, F.; Lähteenmäki, A.; Hovatta, T.; Kovalev, Y. Y.; Lister, M. L.; Max-Moerbeck, W.; Mundell, C.; Pushkarev, A. B.; Rastorgueva-Foi, E.; Readhead, A. C. S.; Richards, J. L.; Tammi, J.; Sanchez, D. A.; Tornikoski, M.; Savolainen, T.; Steele, I.

2016-06-01

Context. 1ES 1011+496 (z = 0.212) was discovered in very high-energy (VHE, E> 100 GeV) γ rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED). Aims: We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum. Methods: We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and Metsähovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE. Results: The VHE spectrum was fit with a simple power law with a photon index of 3.69 ± 0.22 and a flux above 150 GeV of (1.46 ± 0.16) × 10-11 ph cm-2 s-1. The source 1ES 1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 ± 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac. Conclusions: For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1 GeV to 1 TeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission.

Radio Detection of the Fermi-LAT Blind Search Millisecond Pulsar J1311-3430

NASA Technical Reports Server (NTRS)

Ray, P. S.; Ransom, S. M.; Cheung, C. C.; Giroletti, M.; Cognard, I.; Camilo, F.; Bhattacharyya, B.; Roy, J.; Romani, R. W.; Ferrara, E. C.;

Radio Detection of the FERMI-LAT Blind Search Millisecond Pulsar J1311–3430

DOE PAGES

Ray, P. S.; Ransom, S. M.; Cheung, C. C.; ...

2013-01-02

In this article, we report the detection of radio emission from PSR J1311–3430, the first millisecond pulsar (MSP) discovered in a blind search of Fermi Large Area Telescope (LAT) gamma-ray data. We detected radio pulsations at 2 GHz, visible for <10% of ~4.5 hr of observations using the Green Bank Telescope (GBT). Observations at 5 GHz with the GBT and at several lower frequencies with Parkes, Nançay, and the Giant Metrewave Radio Telescope resulted in non-detections. We also report the faint detection of a steep spectrum continuum radio source (0.1 mJy at 5 GHz) in interferometric imaging observations with themore » Jansky Very Large Array. These detections demonstrate that PSR J1311–3430 is not radio quiet and provide additional evidence that radio-quiet MSPs are rare. The radio dispersion measure of 37.8 pc cm –3 provides a distance estimate of 1.4 kpc for the system, yielding a gamma-ray efficiency of 30%, typical of LAT-detected MSPs. Lastly, we see apparent excess delay in the radio pulses as the pulsar appears from eclipse and we speculate on possible mechanisms for the non-detections of the pulse at other orbital phases and observing frequencies.« less

RADIO DETECTION OF THE FERMI-LAT BLIND SEARCH MILLISECOND PULSAR J1311-3430

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

Ray, P. S.; Wood, K. S.; Ransom, S. M.

2013-01-20

We report the detection of radio emission from PSR J1311-3430, the first millisecond pulsar (MSP) discovered in a blind search of Fermi Large Area Telescope (LAT) gamma-ray data. We detected radio pulsations at 2 GHz, visible for <10% of {approx}4.5 hr of observations using the Green Bank Telescope (GBT). Observations at 5 GHz with the GBT and at several lower frequencies with Parkes, Nancay, and the Giant Metrewave Radio Telescope resulted in non-detections. We also report the faint detection of a steep spectrum continuum radio source (0.1 mJy at 5 GHz) in interferometric imaging observations with the Jansky Very Largemore » Array. These detections demonstrate that PSR J1311-3430 is not radio quiet and provide additional evidence that radio-quiet MSPs are rare. The radio dispersion measure of 37.8 pc cm{sup -3} provides a distance estimate of 1.4 kpc for the system, yielding a gamma-ray efficiency of 30%, typical of LAT-detected MSPs. We see apparent excess delay in the radio pulses as the pulsar appears from eclipse and we speculate on possible mechanisms for the non-detections of the pulse at other orbital phases and observing frequencies.« less

Investigating powerful jets in radio-loud narrow-line Seyfert 1s

DOE PAGES

Orienti, M.; D'Ammando, F.; Larsson, J.; ...

2015-09-14

Here, we report results on multiband observations from radio to γ-rays of the two radio-loud narrow-line Seyfert 1 (NLSy1) galaxies PKS 2004-447 and J1548+3511. Furthermore, both sources show a core–jet structure on parsec scale, while they are unresolved at the arcsecond scale. The high core dominance and the high variability brightness temperature make these NLSy1 galaxies good γ-ray source candidates. Fermi-Large Area Telescope detected γ-ray emission only from PKS 2004-447, with a γ-ray luminosity comparable to that observed in blazars. There was no γ-ray emission observed for J1548+3511. Both sources are variable in X-rays. J1548+3511 shows a hardening of themore » spectrum during high activity states, while PKS 2004-447 has no spectral variability. A spectral steepening likely related to the soft excess is hinted below 2 keV for J1548+3511, while the X-ray spectra of PKS 2004-447 collected by XMM–Newton in 2012 are described by a single power law without significant soft excess. No additional absorption above the Galactic column density or the presence of an Fe line is detected in the X-ray spectra of both sources.« less

Prospects for Pulsar Studies with the GLAST Large Area Telescope

NASA Technical Reports Server (NTRS)

Harding, Alice K.

2006-01-01

The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST) will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered pulsars. As the only presently known galactic GeV source class, pulsars will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma ray pulsars, including millisecond pulsars, giving much better statistics for elucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric particle acceleration and radiation mechanisms, by comparing data with theoretical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all unidentified EGRET sources, to possibly uncover more radio-quiet Geminga-like pulsars.

Multiband Observations of the Quasar PKS 2326–502 during Active and Quiescent Gamma-Ray States in 2010–2012

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

Dutka, Michael S.; Carpenter, Bryce D.; Gehrels, Neil

2017-02-01

Quasi-simultaneous observations of the Flat Spectrum Radio Quasar PKS 2326−502 were carried out in the γ -ray, X-ray, UV, optical, near-infrared, and radio bands. Using these observations, we are able to characterize the spectral energy distribution (SED) of the source during two flaring and one quiescent γ -ray states. These data were used to constrain one-zone leptonic models of the SEDs of each flare and investigate the physical conditions giving rise to them. While modeling one flare required only changes in the electron spectrum compared to the quiescent state, modeling the other flare required changes in both the electron spectrummore » and the size of the emitting region. These results are consistent with an emerging pattern of two broad classes of flaring states seen in blazars. Type 1 flares are explained by changes solely in the electron distribution, whereas type 2 flares require a change in an additional parameter. This suggests that different flares, even in the same source, may result from different physical conditions or different regions in the jet.« less

Effelsberg Monitoring of a Sample of RadioAstron Blazars: Analysis of Intra-Day Variability

NASA Astrophysics Data System (ADS)

Liu, Jun; Bignall, Hayley; Krichbaum, Thomas; Liu, Xiang; Kraus, Alex; Kovalev, Yuri; Sokolovsky, Kirill; Angelakis, Emmanouil; Zensus, J.

2018-04-01

We present the first results of an ongoing intra-day variability (IDV) flux density monitoring program of 107 blazars, which were selected from a sample of RadioAstron space very long baseline interferometry (VLBI) targets. The~IDV observations were performed with the Effelsberg 100-m radio telescope at 4.8\\,GHz, focusing on the statistical properties of IDV in a relatively large sample of compact active galactic nuclei (AGN). We investigated the dependence of rapid ($<$3 day) variability on various source properties through a likelihood approach. We found that the IDV amplitude depends on flux density and that fainter sources vary by about a factor of 3 more than their brighter counterparts. We also found a significant difference in the variability amplitude between inverted- and flat-spectrum radio sources, with the former exhibiting stronger variations. $\\gamma$-ray loud sources were found to vary by up to a factor 4 more than $\\gamma$-ray quiet ones, with 4$\\sigma$ significance. However a galactic latitude dependence was barely observed, which suggests that it is predominantly the intrinsic properties (e.g., angular size, core-dominance) of the blazars that determine how they scintillate, rather than the directional dependence in the interstellar medium (ISM). We showed that the uncertainty in the VLBI brightness temperatures obtained from the space VLBI data of the RadioAstron satellite can be as high as $\\sim$70\\% due to the presence of the rapid flux density variations. Our statistical results support the view that IDV at centimeter wavelengths is predominantly caused by interstellar scintillation (ISS) of the emission from the most compact, core-dominant region in an AGN.

Relativistic corrections and non-Gaussianity in radio continuum surveys

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

Maartens, Roy; Zhao, Gong-Bo; Bacon, David

Forthcoming radio continuum surveys will cover large volumes of the observable Universe and will reach to high redshifts, making them potentially powerful probes of dark energy, modified gravity and non-Gaussianity. We consider the continuum surveys with LOFAR, WSRT and ASKAP, and examples of continuum surveys with the SKA. We extend recent work on these surveys by including redshift space distortions and lensing convergence in the radio source auto-correlation. In addition we compute the general relativistic (GR) corrections to the angular power spectrum. These GR corrections to the standard Newtonian analysis of the power spectrum become significant on scales near andmore » beyond the Hubble scale at each redshift. We find that the GR corrections are at most percent-level in LOFAR, WODAN and EMU surveys, but they can produce O(10%) changes for high enough sensitivity SKA continuum surveys. The signal is however dominated by cosmic variance, and multiple-tracer techniques will be needed to overcome this problem. The GR corrections are suppressed in continuum surveys because of the integration over redshift — we expect that GR corrections will be enhanced for future SKA HI surveys in which the source redshifts will be known. We also provide predictions for the angular power spectra in the case where the primordial perturbations have local non-Gaussianity. We find that non-Gaussianity dominates over GR corrections, and rises above cosmic variance when f{sub NL}∼>5 for SKA continuum surveys.« less

Two active states of the narrow-line gamma-ray-loud AGN GB 1310+487

DOE PAGES

Sokolovsky, K. V.

2014-04-28

Context. Previously unremarkable, the extragalactic radio source GB1310+487 showed a γ-ray flare on 2009 November 18, reaching a daily flux of ~ 10 -6 photons cm -2 s -1 at energies E > 100MeV and became one of the brightest GeV sources for about two weeks. Its optical spectrum shows strong forbidden-line emission while lacking broad permitted lines, which is not typical for a blazar. Instead, the spectrum resembles those of narrow emission-line galaxies. Aims. We investigate changes in the object’s radio-to-GeV spectral energy distribution (SED) during and after the prominent γ-ray flare with the aim of determining the naturemore » of the object and of constraining the origin of the variable high-energy emission. Methods. The data collected by the Fermi and AGILE satellites at γ-ray energies; Swift at X-ray and ultraviolet (UV); the Kanata, NOT, and Keck telescopes at optical; OAGH andWISE at infrared (IR); and IRAM30m, OVRO 40m, Effelsberg 100m, RATAN-600, and VLBA at radio are analyzed together to trace the SED evolution on timescales of months. Results. The γ-ray/radio-loud narrow-line active galactic nucleus (AGN) is located at redshift z = 0.638. It shines through an unrelated foreground galaxy at z = 0.500. The AGN light is probably amplified by gravitational lensing. The AGN SED shows a two-humped structure typical of blazars and γ-ray-loud narrow-line Seyfert 1 galaxies, with the high-energy (inverse-Compton) emission dominating by more than an order of magnitude over the low-energy (synchrotron) emission during γ-ray flares. The difference between the two SED humps is smaller during the low-activity state. Fermi observations reveal a strong correlation between the γ-ray flux and spectral index, with the hardest spectrum observed during the brightest γ-ray state. The γ-ray flares occurred before and during a slow rising trend in the radio, but no direct association between γ-ray and radio flares could be established. Conclusions. If the γ-ray flux is a mixture of synchrotron self-Compton (SSC) and external Compton (EC) emission, the observed GeV spectral variability may result from varying relative contributions of these two emission components. This explanation fits the observed changes in the overall IR to γ-ray SED.« less

MAGIC observations and multifrequency properties of the flat spectrum radio quasar 3C 279 in 2011

DOE PAGES

Aleksic, J.

2014-07-01

Aims. We present a study of the very high energy (VHE; E>100 GeV) γ-ray emission of the blazar PKS 1424+240 observed with the MAGIC telescopes. The primary aim of this paper is the multiwavelength spectral characterization and modeling of this blazar, which is made particularly interesting by the recent discovery of a lower limit of its redshift of z ≥ 0.6 and makes it a promising candidate to be the most distant VHE source. Methods. The source has been observed with the MAGIC telescopes in VHE rays for a total observation time of ~33.6 h from 2009 to 2011. Amore » detailed analysis of its γ-ray spectrum and time evolution has been carried out. Moreover, we have collected and analyzed simultaneous and quasi-simultaneous multiwavelength data. Results. The source was marginally detected in VHE rays during 2009 and 2010, and later, the detection was confirmed during an optical outburst in 2011. The combined significance of the stacked sample is ~7.2σ. The differential spectra measured during the different campaigns can be described by steep power laws with the indices ranging from 3.5 ± 1.2 to 5.0 ± 1.7. The MAGIC spectra corrected for the absorption due to the extragalactic background light connect smoothly, within systematic errors, with the mean spectrum in 2009-2011 observed at lower energies by the Fermi-LAT. The absorption-corrected MAGIC spectrum is flat with no apparent turn down up to 400 GeV. The multiwavelength light curve shows increasing flux in radio and optical bands that could point to a common origin from the same region of the jet. The large separation between the two peaks of the constructed non-simultaneous spectral energy distribution also requires an extremely high Doppler factor if an one zone synchrotron self-Compton model is applied. We find that a two-component synchrotron self-Compton model describes the spectral energy distribution of the source well, if the source is located at z ~ 0.6.« less

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.

Suzaku Observations of the Broad-Line Radio Galaxy 3C390.3

NASA Technical Reports Server (NTRS)

Sambruna, rita

2007-01-01

We present the results of a 100ks Suzaku observation of the BLRG 3C390.3. The observations were performed to attempt to disentangle the contributions to the X-ray emission of this galaxy from an AGN and a jet component, via variability and/or the spectrum. The source was detected at high energies up to 80 keV, with a complex 0.3--80keV spectrum. Preliminary analysis of the data shows significant flux variability, with the largest amplitudes at higher energies. Deconvolution of the spectrum shows that, besides a standard Seyfert-like spectrum dominating the 0.3--8keV emission, an additional, hard power law component is required, dominating the emission above 10 keV. We attribute this component to a variable jet.

47 CFR 214.6 - Postattack procedures and actions.

Code of Federal Regulations, 2013 CFR

2013-10-01

... PROCEDURES FOR THE USE AND COORDINATION OF THE RADIO SPECTRUM DURING A WARTIME EMERGENCY § 214.6 Postattack... Radio Spectrum and the Government Master File; (2) Accomplish such coordination as appropriate and...

The MAVERIC Survey: A Red Straggler Binary with an Invisible Companion in the Galactic Globular Cluster M10

NASA Astrophysics Data System (ADS)

Shishkovsky, Laura; Strader, Jay; Chomiuk, Laura; Bahramian, Arash; Tremou, Evangelia; Li, Kwan-Lok; Salinas, Ricardo; Tudor, Vlad; Miller-Jones, James C. A.; Maccarone, Thomas J.; Heinke, Craig O.; Sivakoff, Gregory R.

2018-03-01

We present the discovery and characterization of a radio-bright binary in the Galactic globular cluster M10. First identified in deep radio continuum data from the Karl G. Jansky Very Large Array, M10-VLA1 has a flux density of 27 ± 4 μJy at 7.4 GHz and a flat-to-inverted radio spectrum. Chandra imaging shows an X-ray source with L X ≈ 1031 erg s‑1 matching the location of the radio source. This places M10-VLA1 within the scatter of the radio-X-ray luminosity correlation for quiescent stellar-mass black holes, and a black hole X-ray binary is a viable explanation for this system. The radio and X-ray properties of the source disfavor, but do not rule out, identification as an accreting neutron star or white dwarf system. Optical imaging from the Hubble Space Telescope and spectroscopy from the SOAR telescope show that the system has an orbital period of 3.339 days and an unusual “red straggler” component: an evolved star found redward of the M10 red giant branch. These data also show UV/optical variability and double-peaked Hα emission characteristic of an accretion disk. However, SOAR spectroscopic monitoring reveals that the velocity semi-amplitude of the red straggler is low. We conclude that M10-VLA1 is most likely either a quiescent black hole X-ray binary with a rather face-on (i < 4°) orientation or an unusual flaring RS Canum Venaticorum variable-type active binary, and discuss future observations that could distinguish between these possibilities.

FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics.

PubMed

Harwood, Jeremy J; Croston, Judith H; Intema, Huib T; Stewart, Adam J; Ineson, Judith; Hardcastle, Martin J; Godfrey, Leith; Best, Philip; Brienza, Marisa; Heesen, Volker; Mahony, Elizabeth K; Morganti, Raffaella; Murgia, Matteo; Orrú, Emanuela; Röttgering, Huub; Shulevski, Aleksandar; Wise, Michael W

2016-06-01

Due to their steep spectra, low-frequency observations of Fanaroff-Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR (LOw Frequency ARray) observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C 452 and 3C 223. We find that the morphology of 3C 452 is that of a standard FR II rather than of a double-double radio galaxy as had previously been suggested, with no remnant emission being observed beyond the active lobes. We find that the low-frequency integrated spectra of both sources are much steeper than expected based on traditional assumptions and, using synchrotron/inverse-Compton model fitting, show that the total energy content of the lobes is greater than previous estimates by a factor of around 5 for 3C 452 and 2 for 3C 223. We go on to discuss possible causes of these steeper-than-expected spectra and provide revised estimates of the internal pressures and magnetic field strengths for the intrinsically steep case. We find that the ratio between the equipartition magnetic field strengths and those derived through synchrotron/inverse-Compton model fitting remains consistent with previous findings and show that the observed departure from equipartition may in some cases provide a solution to the spectral versus dynamical age disparity.

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.

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

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.

A KPC-scale X-ray jet in the BL LAC Source S5 2007+777

NASA Technical Reports Server (NTRS)

Sambruna, Rita; Maraschi, Laura; Tavecchio, Fabrizio

2008-01-01

The BL Lac S3 2007++777, a classical radio-selected BL Lac from the sample of Stirkel et al. exhibiting an extended (19") radio jet. was observed with Chandra revealing an X-ray jet with simi1ar morphology. The hard X-ray spectrum and broad band SED is consistent with an IC/CMB origin for the X-ray emission, implying a highly relativistic flow at small angle to the line of sight with an unusually large deprojected length, 300 kpc. A structured jet consisting of a fast spine and slow wall is consistent with the observations.

Dynamic Spectrum Access for Internet of Things Service in Cognitive Radio-Enabled LPWANs

PubMed Central

Moon, Bongkyo

2017-01-01

In this paper, we focus on a dynamic spectrum access strategy for Internet of Things (IoT) applications in two types of radio systems: cellular networks and cognitive radio-enabled low power wide area networks (CR-LPWANs). The spectrum channel contention between the licensed cellular networks and the unlicensed CR-LPWANs, which work with them, only takes place within the cellular radio spectrum range. Our aim is to maximize the spectrum capacity for the unlicensed users while ensuring that it never interferes with the licensed network. Therefore, in this paper we propose a dynamic spectrum access strategy for CR-LPWANs operating in both licensed and unlicensed bands. The simulation and the numerical analysis by using a matrix geometric approach for the strategy are presented. Finally, we obtain the blocking probability of the licensed users, the mean dwell time of the unlicensed user, and the total carried traffic and combined service quality for the licensed and unlicensed users. The results show that the proposed strategy can maximize the spectrum capacity for the unlicensed users using IoT applications as well as keep the service quality of the licensed users independent of them. PMID:29206215

Dynamic Spectrum Access for Internet of Things Service in Cognitive Radio-Enabled LPWANs.

PubMed

Moon, Bongkyo

2017-12-05

In this paper, we focus on a dynamic spectrum access strategy for Internet of Things (IoT) applications in two types of radio systems: cellular networks and cognitive radio-enabled low power wide area networks (CR-LPWANs). The spectrum channel contention between the licensed cellular networks and the unlicensed CR-LPWANs, which work with them, only takes place within the cellular radio spectrum range. Our aim is to maximize the spectrum capacity for the unlicensed users while ensuring that it never interferes with the licensed network. Therefore, in this paper we propose a dynamic spectrum access strategy for CR-LPWANs operating in both licensed and unlicensed bands. The simulation and the numerical analysis by using a matrix geometric approach for the strategy are presented. Finally, we obtain the blocking probability of the licensed users, the mean dwell time of the unlicensed user, and the total carried traffic and combined service quality for the licensed and unlicensed users. The results show that the proposed strategy can maximize the spectrum capacity for the unlicensed users using IoT applications as well as keep the service quality of the licensed users independent of them.

X-Ray Absorption Toward the Einstein Ring Source PKS 1830-211

NASA Technical Reports Server (NTRS)

Mathur, Smita; Nair, Sunita

1997-01-01

PKS 1830-211 is an unusually radio-loud gravitationally lensed quasar. In the radio spectrum, the system appears as two compact, dominant features surrounded by relatively extended radio emission that forms an Einstein ring. As the line of sight to it passes close to our Galactic center, PKS 1830-211 has not been detected in wave bands other than the radio and X-ray so far. Here we present X-ray data of PKS 1830-211 observed with ROSAT Position Sensitive Proportional Counter. The X-ray spectrum shows that absorption in excess of the Galactic contribution is highly likely, which at the redshift of the lensing galaxy (z(sub t)=0.886) corresponds to N(sub H)=3.5((sup 0.6)(sub -0.5))x10(exp 22) atoms sq cm. The effective optical extinction is large, A(sub V)(observed) is greater than or approximately 5.8. When corrected for this additional extinction, the two-point optical to X-ray slope alpha(sub ox) of PKS 1830-211 lies just within the observed range of quasars. It is argued here that both compact images must be covered by the X-ray absorber(s) that we infer to be the lensing galaxy (galaxies). The dust-to-gas ratio along the line of sight within the lensing galaxy is likely to be somewhat larger than for our Galaxy.

47 CFR 214.4 - Planned actions.

Code of Federal Regulations, 2013 CFR

2013-10-01

... COORDINATION OF THE RADIO SPECTRUM DURING A WARTIME EMERGENCY § 214.4 Planned actions. (a) Whenever it is... the use of the radio spectrum in areas of active combat, where such control is necessary to the...

VizieR Online Data Catalog: The CLASS BL Lac sample (Marcha+, 2013)

NASA Astrophysics Data System (ADS)

Marcha, M. J. M.; Caccianiga, A.

2014-04-01

This paper presents a new sample of BL Lac objects selected from a deep (30mJy) radio survey of flat spectrum radio sources (the CLASS blazar survey). The sample is one of the largest well-defined samples in the low-power regime with a total of 130 sources of which 55 satisfy the 'classical' optical BL Lac selection criteria, and the rest have indistinguishable radio properties. The primary goal of this study is to establish the radio luminosity function (RLF) on firm statistical ground at low radio luminosities where previous samples have not been able to investigate. The gain of taking a peek at lower powers is the possibility to search for the flattening of the luminosity function which is a feature predicted by the beaming model but which has remained elusive to observational confirmation. In this study, we extend for the first time the BL Lac RLF down to very low radio powers ~1022W/Hz, i.e. two orders of magnitude below the RLF currently available in the literature. In the process, we confirm the importance of adopting a broader, and more physically meaningful set of classification criteria to avoid the systematic missing of low-luminosity BL Lacs. Thanks to the good statistics we confirm the existence of weak but significant positive cosmological evolution for the BL Lac population, and we detect, for the first time the flattening of the RLF at L~1025W/Hz in agreement with the predictions of the beaming model. (1 data file).

BROADBAND JET EMISSION IN YOUNG AND POWERFUL RADIO SOURCES: THE CASE OF THE COMPACT STEEP SPECTRUM QUASAR 3C 186

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

Migliori, Giulia; Siemiginowska, Aneta; Celotti, Annalisa, E-mail: migliori@cfa.harvard.edu

2012-04-20

We present the X-ray analysis of a deep ({approx}200 ks) Chandra observation of the compact steep spectrum radio-loud quasar 3C 186 (z = 1.06) and investigate the contribution of the unresolved radio jet to the total X-ray emission. The spectral analysis is not conclusive on the origin of the bulk of the X-ray emission. In order to examine the jet contribution to the X-ray flux, we model the quasar spectral energy distribution, adopting several scenarios for the jet emission. For the values of the main physical parameters favored by the observables, a dominant role of the jet emission in themore » X-ray band is ruled out when a single-zone (leptonic) scenario is adopted, even including the contribution of the external photon fields as seed photons for inverse Compton emission. We then consider a structured jet, with the blazar component that-although not directly visible in the X-ray band-provides an intense field of seed synchrotron photons Compton-scattered by electrons in a mildly relativistic knot. In this case, the whole X-ray emission can be accounted for if we assume a blazar luminosity within the range observed from flat spectrum radio quasars. The X-ray radiative efficiency of such a (structured) jet is intimately related to the presence of a complex velocity structure. The jet emission can provide a significant contribution in X-rays if it decelerates within the host galaxy on kiloparsec scales. We discuss the implications of this model in terms of jet dynamics and interaction with the ambient medium.« less

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.

IKT 16: the first X-ray confirmed composite SNR in the SMC

NASA Astrophysics Data System (ADS)

Maitra, C.; Ballet, J.; Filipović, M. D.; Haberl, F.; Tiengo, A.; Grieve, K.; Roper, Q.

2015-12-01

Aims: IKT 16 is an X-ray and radio-faint supernova remnant (SNR) in the Small Magellanic Cloud (SMC). A detailed X-ray study of this SNR with XMM-Newton confirmed the presence of a hard X-ray source near its centre, indicating the detection of the first composite SNR in the SMC. With a dedicated Chandra observation we aim to resolve the point source and confirm its nature. We also acquire new ATCA observations of the source at 2.1 GHz with improved flux density estimates and resolution. Methods: We perform detailed spatial and spectral analysis of the source. With the highest resolution X-ray and radio image of the centre of the SNR available today, we resolve the source and confirm its pulsar wind nebula (PWN) nature. Further, we constrain the geometrical parameters of the PWN and perform spectral analysis for the point source and the PWN separately. We also test for the radial variations of the PWN spectrum and its possible east west asymmetry. Results: The X-ray source at the centre of IKT 16 can be resolved into a symmetrical elongated feature centring a point source, the putative pulsar. Spatial modelling indicates an extent of 5.2'' of the feature with its axis inclined at 82° east from north, aligned with a larger radio feature consisting of two lobes almost symmetrical about the X-ray source. The picture is consistent with a PWN which has not yet collided with the reverse shock. The point source is about three times brighter than the PWN and has a hard spectrum of spectral index 1.1 compared to a value 2.2 for the PWN. This points to the presence of a pulsar dominated by non-thermal emission. The expected Ė is ~1037 erg s-1 and spin period <100 ms. However, the presence of a compact nebula unresolved by Chandra at the distance of the SMC cannot completely be ruled out. The reduced images (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A41

Jets, arcs, and shocks: NGC 5195 at radio wavelengths

NASA Astrophysics Data System (ADS)

Rampadarath, H.; Soria, R.; Urquhart, R.; Argo, M. K.; Brightman, M.; Lacey, C. K.; Schlegel, E. M.; Beswick, R. J.; Baldi, R. D.; Muxlow, T. W. B.; McHardy, I. M.; Williams, D. R. A.; Dumas, G.

2018-05-01

We studied the nearby, interacting galaxy NGC 5195 (M 51b) in the radio, optical and X-ray bands. We mapped the extended, low-surface-brightness features of its radio-continuum emission; determined the energy content of its complex structure of shock-ionized gas; constrained the current activity level of its supermassive nuclear black hole. In particular, we combined data from the European Very Long Baseline Interferometry Network (˜1-pc scale), from our new e-MERLIN observations (˜10-pc scale), and from the Very Large Array (˜100-1000-pc scale), to obtain a global picture of energy injection in this galaxy. We put an upper limit to the luminosity of the (undetected) flat-spectrum radio core. We find steep-spectrum, extended emission within 10 pc of the nuclear position, consistent with optically thin synchrotron emission from nuclear star formation or from an outflow powered by an active galactic nucleus (AGN). A linear spur of radio emission juts out of the nuclear source towards the kpc-scale arcs (detected in radio, Hα and X-ray bands). From the size, shock velocity, and Balmer line luminosity of the kpc-scale bubble, we estimate that it was inflated by a long-term-average mechanical power ˜3-6 × 1041 erg s-1 over the last 3-6 Myr. This is an order of magnitude more power than can be provided by the current level of star formation, and by the current accretion power of the supermassive black hole. We argue that a jet-inflated bubble scenario associated with previous episodes of AGN activity is the most likely explanation for the kpc-scale structures.

High Resolution Rapid Response Observations of Compact Radio Sources with the Ceduna Hobart Interferometer (CHI)

NASA Technical Reports Server (NTRS)

Blanchard, Jay M.; Lovell, James E. J.; Ojha, Roopesh; Kadler, Matthias; Dickey, John M.; Edwards, Philip G.

2011-01-01

Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including Active Galactic Nuclei. A key tool of such studies is the ability to observe an object when it flares i.e. exhibits a rapid and significant increase in its flux density. Aims. We describe the specific observational procedures and the calibration techniques that have been developed and tested to create a single baseline radio interferometer. that can rapidly observe a flaring object. This is the only facility that is dedicated to rapid high resolution radio observations of an object south of -30 degrees declination. An immediate application is to provide rapid contemporaneous radio coverage of AGN flaring at y-ray frequencies detected by the Fermi Gamma-ray Space Telescope. Methods. A single baseline interferometer was formed with radio telescopes in Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up at the University of Tasmania to correlate these data. Results. Measurements of the flux densities of flaring objects can be made using our observing strategy within half an hour of a triggering event. These observations can be calibrated with amplitude errors better than 20%. Lower limits to the brightness temperatures of the sources can also be calculated using CHI. Key words. instrumentation:interferometers - galaxies:active - galaxies:jets - galaxies:nuclei quasars:general gamma rays:galaxies- 1.

Marine asset security and tracking (MAST) system

DOEpatents

Hanson, Gregory Richard [Clinton, TN; Smith, Stephen Fulton [Loudon, TN; Moore, Michael Roy [Corryton, TN; Dobson, Eric Lesley [Charleston, SC; Blair, Jeffrey Scott [Charleston, SC; Duncan, Christopher Allen [Marietta, GA; Lenarduzzi, Roberto [Knoxville, TN

2008-07-01

Methods and apparatus are described for marine asset security and tracking (MAST). A method includes transmitting identification data, location data and environmental state sensor data from a radio frequency tag. An apparatus includes a radio frequency tag that transmits identification data, location data and environmental state sensor data. Another method includes transmitting identification data and location data from a radio frequency tag using hybrid spread-spectrum modulation. Another apparatus includes a radio frequency tag that transmits both identification data and location data using hybrid spread-spectrum modulation.

NASA Radio Frequency Spectrum Management Manual

NASA Technical Reports Server (NTRS)

1989-01-01

The Radio Frequency (RF) Spectrum Management Manual sets forth procedures and guidelines for the management requirements for controlling the use of radio frequencies by the National Aeronautics and Space Administration. It is applicable to NASA Headquarters and field installations. NASA Management Instruction 1102.3 assigns the authority for management of radio frequencies for the National Aeronautics and Space Administration to the Associate Administrator for Space Operations, NASA Headquarters. This manual is issued in loose-leaf form and will be revised by page changes.

The Peculiar Galactic Center Neutron Star X-Ray Binary XMM J174457-2850.3

NASA Technical Reports Server (NTRS)

Degenaar, N.; Wijnands, R.; Reynolds, M. T.; Miller, J. M.; Altamirano, D.; Kennea, J.; Gehrels, N.; Haggard, D.; Ponti, G.

2014-01-01

The recent discovery of a milli-second radio pulsar experiencing an accretion outburst similar to those seen in low mass X-ray binaries, has opened up a new opportunity to investigate the evolutionary link between these two different neutron star manifestations. The remarkable X-ray variability and hard X-ray spectrum of this object can potentially serve as a template to search for other X-ray binary radio pulsar transitional objects. Here we demonstrate that the transient X-ray source XMM J174457-2850.3 near the Galactic center displays similar X-ray properties. We report on the detection of an energetic thermonuclear burst with an estimated duration of 2 hr and a radiated energy output of 5E40 erg, which unambiguously demonstrates that the source harbors an accreting neutron star. It has a quiescent X-ray luminosity of Lx5E32 ergs and exhibits occasional accretion outbursts during which it brightens to Lx1E35-1E36 ergs for a few weeks (2-10 keV). However, the source often lingers in between outburst and quiescence at Lx1E33-1E34 ergs. This unusual X-ray flux behavior and its relatively hard X-ray spectrum, a power law with an index of 1.4, could possibly be explained in terms of the interaction between the accretion flow and the magnetic field of the neutron star.

Transmit-reference methods in software defined radio platforms for communication in harsh propagation environments and systems thereof

DOEpatents

Dowla, Farid U; Nekoogar, Faranak

2015-03-03

A method for adaptive Radio Frequency (RF) jamming according to one embodiment includes dynamically monitoring a RF spectrum; detecting any undesired signals in real time from the RF spectrum; and sending a directional countermeasure signal to jam the undesired signals. A method for adaptive Radio Frequency (RF) communications according to another embodiment includes transmitting a data pulse in a RF spectrum; and transmitting a reference pulse separated by a predetermined period of time from the data pulse; wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated. A method for adaptive Radio Frequency (RF) communications according to yet another embodiment includes receiving a data pulse in a RF spectrum; and receiving a reference pulse separated in time from the data pulse, wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated; and demodulating the pulses.

Transmit-reference methods in software defined radio platforms for communication in harsh propagation environments and systems thereof

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

Dowla, Farid; Nekoogar, Faranak

A method for adaptive Radio Frequency (RF) jamming according to one embodiment includes dynamically monitoring a RF spectrum; detecting any undesired signals in real time from the RF spectrum; and sending a directional countermeasure signal to jam the undesired signals. A method for adaptive Radio Frequency (RF) communications according to another embodiment includes transmitting a data pulse in a RF spectrum; and transmitting a reference pulse separated by a predetermined period of time from the data pulse; wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated. A method for adaptive Radio Frequency (RF) communications accordingmore » to yet another embodiment includes receiving a data pulse in a RF spectrum; and receiving a reference pulse separated in time from the data pulse, wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated; and demodulating the pulses.« less

Q-Learning and p-persistent CSMA based rendezvous protocol for cognitive radio networks operating with shared spectrum activity

NASA Astrophysics Data System (ADS)

Watson, Clifton L.; Biswas, Subir

2014-06-01

With an increasing demand for spectrum, dynamic spectrum access (DSA) has been proposed as viable means for providing the flexibility and greater access to spectrum necessary to meet this demand. Within the DSA concept, unlicensed secondary users temporarily "borrow" or access licensed spectrum, while respecting the licensed primary user's rights to that spectrum. As key enablers for DSA, cognitive radios (CRs) are based on software-defined radios which allow them to sense, learn, and adapt to the spectrum environment. These radios can operate independently and rapidly switch channels. Thus, the initial setup and maintenance of cognitive radio networks are dependent upon the ability of CR nodes to find each other, in a process known as rendezvous, and create a link on a common channel for the exchange of data and control information. In this paper, we propose a novel rendezvous protocol, known as QLP, which is based on Q-learning and the p-persistent CSMA protocol. With the QLP protocol, CR nodes learn which channels are best for rendezvous and thus adapt their behavior to visit those channels more frequently. We demonstrate through simulation that the QLP protocol provides a rendevous capability for DSA environments with different dynamics of PU activity, while attempting to achieve the following performance goals: (1) minimize the average time-to-rendezvous, (2) maximize system throughput, (3) minimize primary user interference, and (4) minimize collisions among CR nodes.

Superconducting cosmic string loops as sources for fast radio bursts

NASA Astrophysics Data System (ADS)

Cao, Xiao-Feng; Yu, Yun-Wei

2018-01-01

The cusp burst radiation of superconducting cosmic string (SCS) loops is thought to be a possible origin of observed fast radio bursts with the model-predicted radiation spectrum and the redshift- and energy-dependent event rate, we fit the observational redshift and energy distributions of 21 Parkes fast radio bursts and constrain the model parameters. It is found that the model can basically be consistent with the observations, if the current on the SCS loops has a present value of ˜1016μ179 /10 esu s-1 and evolves with redshift as an empirical power law ˜(1 +z )-1.3 , where μ17=μ /1017 g cm-1 is the string tension. This current evolution may provide a clue to probe the evolution of the cosmic magnetic fields and the gathering of the SCS loops to galaxy clusters.

Simultaneous Chandra X ray, Hubble Space Telescope Ultraviolet, and Ulysses Radio Observations of Jupiter's Aurora

NASA Technical Reports Server (NTRS)

Elsner, R. F.; Lugaz, N.; Waite, J. H., Jr.; Cravens, T. E.; Gladstone, G. R.; Ford, P.; Grodent, D.; Bhardwaj. A.; MacDowall, R. J.; Desch, M. D. 8;

Radio frequency spectrum management

NASA Astrophysics Data System (ADS)

Sujdak, E. J., Jr.

1980-03-01

This thesis is a study of radio frequency spectrum management as practiced by agencies and departments of the Federal Government. After a brief introduction to the international agency involved in radio frequency spectrum management, the author concentrates on Federal agencies engaged in frequency management. These agencies include the National Telecommunications and Information Administration (NTIA), the Interdepartment Radio Advisory Committee (IRAC), and the Department of Defense (DoD). Based on an analysis of Department of Defense frequency assignment procedures, recommendations are given concerning decentralizing military frequency assignment by delegating broader authority to unified commanders. This proposal includes a recommendation to colocate the individual Service frequency management offices at the Washington level. This would result in reduced travel costs, lower manpower requirements, and a common tri-Service frequency management data base.

A luminous hot accretion flow in the low-luminosity active galactic nucleus NGC 7213

NASA Astrophysics Data System (ADS)

Xie, Fu-Guo; Zdziarski, Andrzej A.; Ma, Renyi; Yang, Qi-Xiang

2016-12-01

The active galactic nucleus (AGN) NGC 7213 shows a complex correlation between the monochromatic radio luminosity LR and the 2-10 keV X-ray luminosity LX, I.e. the correlation is unusually weak with p ˜ 0 (in the form L_R∝ L_X^p) when LX is below a critical luminosity, and steep with p > 1 when LX is above that luminosity. Such a hybrid correlation in individual AGNs is unexpected as it deviates from the Fundamental Plane of AGN activity. Interestingly, a similar correlation pattern is observed in the black hole X-ray binary H1743-322, where it has been modelled by switching between different modes of accretion. We propose that the flat LR-LX correlation of NGC 7213 is due to the presence of a luminous hot accretion flow, an accretion model whose radiative efficiency is sensitive to the accretion rate. Given the low luminosity of the source, LX ˜ 10-4 of the Eddington luminosity, the viscosity parameter is determined to be small, α ≈ 0.01. We also modelled the broad-band spectrum from radio to γ-rays, the time lag between the radio and X-ray light curves, and the implied size and the Lorentz factor of the radio jet. We predict that NGC 7213 will enter into a two-phase accretion regime when LX ≳ 1.5 × 1042 erg s- 1. When this happens, we predict a softening of the X-ray spectrum with the increasing flux and a steep radio/X-ray correlation.

The TANAMI Multiwavelength Program: Dynamic spectral energy distributions of southern blazars

DOE PAGES

Krauß, F.; Wilms, J.; Kadler, M.; ...

2016-06-28

Simultaneous broadband spectral and temporal studies of blazars are an important tool for investigating active galactic nuclei (AGN) jet physics. Aims. Here, we study the spectral evolution between quiescent and flaring periods of 22 radio-loud AGN through multiepoch, quasi-simultaneous broadband spectra. For many of these sources these are the first broadband studies. We also use a Bayesian block analysis of Fermi/LAT light curves to determine time ranges of constant flux for constructing quasi-simultaneous spectral energy distributions (SEDs). The shapes of the resulting 81 SEDs are described by two logarithmic parabolas and a blackbody spectrum where needed. The peak frequencies andmore » luminosities agree well with the blazar sequence for low states with higher luminosity implying lower peak frequencies. This is not true for sources in high states. The γ-ray photon index in Fermi/LAT correlates with the synchrotron peak frequency in low and intermediate states. No correlation is present in high states. The black hole mass cannot be determined from the SEDs. Surprisingly, the thermal excess often found in FSRQs at optical/UV wavelengths can be described by blackbody emission and not an accretion disk spectrum. The so-called harder-when-brighter trend, typically seen in X-ray spectra of flaring blazars, is visible in the blazar sequence. Furthermore, our results for low and intermediate states, as well as the Compton dominance, are in agreement with previous results. Black hole mass estimates using recently published parameters are in agreement with some of the more direct measurements. For two sources, estimates disagree by more than four orders of magnitude, possibly owing to boosting effects. The shapes of the thermal excess seen predominantly in flat spectrum radio quasars are inconsistent with a direct accretion disk origin.« less

Advances in solar radio astronomy

NASA Technical Reports Server (NTRS)

Kundu, M. R.

1982-01-01

The status of the observations and interpretations of the sun's radio emission covering the entire radio spectrum from millimeter wavelengths to hectometer and kilometer wavelengths is reviewed. Emphasis is given to the progress made in solar radio physics as a result of recent advances in plasma and radiation theory. It is noted that the capability now exists of observing the sun with a spatial resolution of approximately a second of arc and a temporal resolution of about a millisecond at centimeter wavelengths and of obtaining fast multifrequency two-dimensional pictures of the sun at meter and decameter wavelengths. A summary is given of the properties of nonflaring active regions at millimeter, centimeter, and meter-decameter wavelengths. The properties of centimeter wave bursts are discussed in connection with the high spatial resolution observations. The observations of the preflare build-up of an active region are reviewed. High spatial resolution observations (a few seconds of arc to approximately 1 arcsec) are discussed, with particular attention given to the one- and two-dimensional maps of centimeter-wavelength burst sources.

Maser Emission from Gravitational States on Isolated Neutron Stars

NASA Astrophysics Data System (ADS)

Tepliakov, Nikita V.; Vovk, Tatiana A.; Rukhlenko, Ivan D.; Rozhdestvensky, Yuri V.

2018-04-01

Despite years of research on neutron stars, the source of their radio emission is still under debate. Here we propose a new coherent mechanism of pulsar radio emission based on transitions between gravitational states of electrons confined above the pulsar atmosphere. Our mechanism assumes that the coherent radiation is generated upon the electric and magnetic dipole transitions of electrons falling onto the polar caps of the pulsar, and predicts that this radiation occurs at radio frequencies—in full agreement with the observed emission spectra. We show that while the linearly polarized electric dipole radiation propagates parallel to the neutron star surface and has a fan-shape angular spectrum, the magnetic dipole emission comes from the magnetic poles of the pulsar in the form of two narrow beams and is elliptically polarized due to the spin–orbit coupling of electrons confined by the magnetic field. By explaining the main observables of the pulsar radio emission, the proposed mechanism indicates that gravitational quantum confinement plays an essential role in the physics of neutron stars.

Cognitive radio based optimal channel sensing and resources allocation

NASA Astrophysics Data System (ADS)

Vijayasarveswari, V.; Khatun, S.; Fakir, M. M.; Nayeem, M. N.; Kamarudin, L. M.; Jakaria, A.

2017-03-01

Cognitive radio (CR) is the latest type of wireless technoloy that is proposed to mitigate spectrum saturation problem. İn cognitve radio, secondary user will use primary user's spectrum during primary user's absence without interupting primary user's transmission. This paper focuses on practical cognitive radio network development process using Android based smart phone for the data transmission. Energy detector based sensing method was proposed and used here because it doesnot require primary user's information. Bluetooth and Wi-fi are the two available types of spectrum that was sensed for CR detection. Simulation showed cognitive radio network can be developed using Android based smart phones. So, a complete application was developed using Java based Android Eclipse program. Finally, the application was uploaded and run on Android based smart phone to form and verify CR network for channel sensing and resource allocation. The observed efficiency of the application was around 81%.

Circumnuclear starbursts in Seyfert galaxies

NASA Technical Reports Server (NTRS)

Wilson, Andrew S.

1987-01-01

Observational diagnostics for the recognition of circumnuclear star formation in Seyfert galaxies are described and illustrated. These methods include: (1) spatially resolved optical spectroscopy, which allows the emission lines for HII regions to be separated from those originating in gas ionized by the Seyfert nucleus; (2) radio continuum mapping, where the linear radio sources characteristic of the nuclear activity may be distinguished from the diffuse morphology of multiple supernova remnants generated in a starburst; (3) infrared spectroscopic searches for emission features of dust, which are seen in starbursts but not in Seyfert nuclei; (4) the shape of the IRAS spectrum. These various diagnostics agree well as to the presence or absence of ongoing star formation. The IRAS spectra of a significant fraction of Seyferts are dominated by emission from dust heated by stars, not the Seyfert nucleus itself. In these cases, the spectrum is curved, being steep between 25 and 60 microns and flatter between 60 and 100 microns. When the Seyfert nucleus dominates, the 25 to 100 micron spectrum is much flatter. It is suggested that the location of a Seyfert galaxy in the IRAS color-color diagram reflects primarily the relative contributions of the active nucleus and dust heated by stars to the infrared fluxes.

MAGIC gamma-ray and multi-frequency observations of flat spectrum radio quasar PKS 1510-089 in early 2012

DOE PAGES

Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; ...

2014-09-17

Aims. We report amongst more than fifty blazars detected in very high energy (VHE, E> 100 GeV) γ rays, only three belong to the subclass of flat spectrum radio quasars (FSRQs). The detection of FSRQs in the VHE range is challenging, mainly because of their soft spectra in the GeV-TeV regime. MAGIC observed PKS 1510-089 (z = 0.36) starting 2012 February 3 until April 3 during a high activity state in the high energy (HE, E> 100 MeV) γ-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 standard deviationsmore » (σ). We study the multi-frequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO, and VLBA telescopes), X-ray (Swift satellite), and HE γ-ray frequencies. Methods. We study the VHE γ-ray emission, together with the multi-frequency light curves, 43 GHz radio maps, and spectral energy distribution (SED) of the source. The quasi-simultaneous multi-frequency SED from the millimetre radio band to VHE γ rays is modelled with a one-zone inverse Compton model. We study two different origins of the seed photons for the inverse Compton scattering, namely the infrared torus and a slow sheath surrounding the jet around the Very Long Baseline Array (VLBA) core. Results. We find that the VHE γ-ray emission detected from PKS 1510-089 in 2012 February-April agrees with the previous VHE observations of the source from 2009 March-April. We find no statistically significant variability during the MAGIC observations on daily, weekly, or monthly time scales, while the other two known VHE FSRQs (3C 279 and PKS 1222+216) have shown daily scale to sub-hour variability. The γ-ray SED combining AGILE, Fermi and MAGIC data joins smoothly and shows no hint of a break. The multi-frequency light curves suggest a common origin for the millimetre radio and HE γ-ray emission, and the HE γ-ray flaring starts when the new component is ejected from the 43 GHz VLBA core and the studied SED models fit the data well. However, the fast HE γ-ray variability requires that within the modelled large emitting region, more compact regions must exist. Lastly, we suggest that these observed signatures would be most naturally explained by a turbulent plasma flowing at a relativistic speed down the jet and crossing a standing conical shock.« 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.

Medium Access Control Protocols for Cognitive Radio Ad Hoc Networks: A Survey

PubMed Central

Islam, A. K. M. Muzahidul; Baharun, Sabariah; Mansoor, Nafees

2017-01-01

New wireless network paradigms will demand higher spectrum use and availability to cope with emerging data-hungry devices. Traditional static spectrum allocation policies cause spectrum scarcity, and new paradigms such as Cognitive Radio (CR) and new protocols and techniques need to be developed in order to have efficient spectrum usage. Medium Access Control (MAC) protocols are accountable for recognizing free spectrum, scheduling available resources and coordinating the coexistence of heterogeneous systems and users. This paper provides an ample review of the state-of-the-art MAC protocols, which mainly focuses on Cognitive Radio Ad Hoc Networks (CRAHN). First, a description of the cognitive radio fundamental functions is presented. Next, MAC protocols are divided into three groups, which are based on their channel access mechanism, namely time-slotted protocol, random access protocol and hybrid protocol. In each group, a detailed and comprehensive explanation of the latest MAC protocols is presented, as well as the pros and cons of each protocol. A discussion on future challenges for CRAHN MAC protocols is included with a comparison of the protocols from a functional perspective. PMID:28926952

Spatially Resolving the Very High Energy Emission from MGRO J2019+37 with VERITAS

NASA Astrophysics Data System (ADS)

Aliu, E.; Aune, T.; Behera, B.; Beilicke, M.; Benbow, W.; Berger, K.; Bird, R.; Bouvier, A.; Buckley, J. H.; Bugaev, V.; Cerruti, M.; Chen, X.; Ciupik, L.; Connolly, M. P.; Cui, W.; Dumm, J.; Dwarkadas, V. V.; Errando, M.; Falcone, A.; Federici, S.; Feng, Q.; Finley, J. P.; Fleischhack, H.; Fortin, P.; Fortson, L.; Furniss, A.; Galante, N.; Gillanders, G. H.; Gotthelf, E. V.; Griffin, S.; Griffiths, S. T.; Grube, J.; Gyuk, G.; Hanna, D.; Holder, J.; Hughes, G.; Humensky, T. B.; Johnson, C. A.; Kaaret, P.; Kargaltsev, O.; Kertzman, M.; Khassen, Y.; Kieda, D.; Krennrich, F.; Lang, M. J.; Madhavan, A. S.; Maier, G.; McArthur, S.; McCann, A.; Millis, J.; Moriarty, P.; Mukherjee, R.; Nieto, D.; O'Faoláin de Bhróithe, A.; Ong, R. A.; Otte, A. N.; Pandel, D.; Park, N.; Pohl, M.; Popkow, A.; Prokoph, H.; Quinn, J.; Ragan, K.; Rajotte, J.; Reyes, L. C.; Reynolds, P. T.; Richards, G. T.; Roache, E.; Roberts, M.; Sembroski, G. H.; Shahinyan, K.; Smith, A. W.; Staszak, D.; Telezhinsky, I.; Tucci, J. V.; Tyler, J.; Vincent, S.; Wakely, S. P.; Weinstein, A.; Welsing, R.; Wilhelm, A.; Williams, D. A.; Zitzer, B.

2014-06-01

We present very high energy (VHE) imaging of MGRO J2019+37 obtained with the VERITAS observatory. The bright extended (~2°) unidentified Milagro source is located toward the rich star formation region Cygnus-X. MGRO J2019+37 is resolved into two VERITAS sources. The faint, point-like source VER J2016+371 overlaps CTB 87, a filled-center remnant (SNR) with no evidence of a supernova remnant shell at the present time. Its spectrum is well fit in the 0.65-10 TeV energy range by a power-law model with photon index 2.3 ± 0.4. VER J2019+378 is a bright extended (~1°) source that likely accounts for the bulk of the Milagro emission and is notably coincident with PSR J2021+3651 and the star formation region Sh 2-104. Its spectrum in the range 1-30 TeV is well fit with a power-law model of photon index 1.75 ± 0.3, among the hardest values measured in the VHE band, comparable to that observed near Vela-X. We explore the unusual spectrum and morphology in the radio and X-ray bands to constrain possible emission mechanisms for this source.

The X-ray emitting galaxy Centaurus A

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.; Serlemitsos, P. J.; Boldt, E. A.; Holt, S. S.; Becker, R. H.

1978-01-01

OSO-8 X-ray observations of Cen A in 1975 and 1976 are reported. The source spectrum can be well fitted in both years by a power law of number index 1.66 and absorption due to 1.3 by 10 to the 23rd power atoms/sq cm. The total flux varied by a factor of 2 between 1975 and 1976. In 1976 there were flux variations of approximately 40% on a time scale of days. Measurements of the 6.4-keV Fe fluorescent line and the 7.1-keV absorption edge imply Fe/H of approximately 0.000016. Simultaneous radio measurements show variation in phase with X-ray variability. Consideration of radio, millimeter, infrared, and X-ray data shows that all the data can be accounted for by a model in which the X-rays are due to a synchrotron self-Compton source embedded in a cold H2 cloud.

The X-ray emitting galaxy Cen-A

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.; Sercemitsos, P. J.; Becker, R. H.; Boldt, E. A.; Holt, S. S.

1977-01-01

OSO-8 X-ray observations of Cen-A in 1975 and 1976 are reported. The source spectrum is well fit in both years by a power law of number index 1.62 and absorption due to 1.3 x 10 to the 23rd power at/sq cm. The total flux varied by a factor 2 between 1975 and 1976. In 1976 there were approximately 40% flux variations on a time scale of days. The 6.4 keV Fe fluorescent line and the 7.1 keV absorption edge were measured implying Fe/H approximately equals .000016. Simultaneous radio measurements show variation in phase with X-ray variability. Models considering radio, milimeter, IR and X-ray data show that all the data can be accounted for by a model in which the X-rays are due to a synchrotron self-Compton source embedded in a cold H(2) cloud.

RADIO OBSERVATIONS OF THE STAR FORMATION ACTIVITIES IN THE NGC 2024 FIR 4 REGION

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

Choi, Minho; Kang, Miju; Lee, Jeong-Eun, E-mail: minho@kasi.re.kr

Star formation activities in the NGC 2024 FIR 4 region were studied by imaging centimeter continuum sources and water maser sources using several archival data sets from the Very Large Array. The continuum source VLA 9 is elongated in the northwest–southeast direction, consistent with the FIR 4 bipolar outflow axis, and has a flat spectrum in the 6.2–3.6 cm interval. The three water maser spots associated with FIR 4 are also distributed along the outflow axis. One of the spots is located close to VLA 9, and another one is close to an X-ray source. Examinations of the positions ofmore » compact objects in this region suggest that the FIR 4 cloud core contains a single low-mass protostar. VLA 9 is the best indicator of the protostellar position. VLA 9 may be a radio thermal jet driven by this protostar, and it is unlikely that FIR 4 contains a high-mass young stellar object (YSO). A methanol 6.7 GHz maser source is located close to VLA 9, at a distance of about 100 AU. The FIR 4 protostar must be responsible for the methanol maser action, which suggests that methanol class II masers are not necessarily excited by high-mass YSOs. Also discussed are properties of other centimeter continuum sources in the field of view and the water masers associated with FIR 6n. Some of the continuum sources are radio thermal jets, and some are magnetically active young stars.« less

Spectrum sensing algorithm based on autocorrelation energy in cognitive radio networks

NASA Astrophysics Data System (ADS)

Ren, Shengwei; Zhang, Li; Zhang, Shibing

2016-10-01

Cognitive radio networks have wide applications in the smart home, personal communications and other wireless communication. Spectrum sensing is the main challenge in cognitive radios. This paper proposes a new spectrum sensing algorithm which is based on the autocorrelation energy of signal received. By taking the autocorrelation energy of the received signal as the statistics of spectrum sensing, the effect of the channel noise on the detection performance is reduced. Simulation results show that the algorithm is effective and performs well in low signal-to-noise ratio. Compared with the maximum generalized eigenvalue detection (MGED) algorithm, function of covariance matrix based detection (FMD) algorithm and autocorrelation-based detection (AD) algorithm, the proposed algorithm has 2 11 dB advantage.

An Energy-Efficient Game-Theory-Based Spectrum Decision Scheme for Cognitive Radio Sensor Networks

PubMed Central

Salim, Shelly; Moh, Sangman

2016-01-01

A cognitive radio sensor network (CRSN) is a wireless sensor network in which sensor nodes are equipped with cognitive radio. In this paper, we propose an energy-efficient game-theory-based spectrum decision (EGSD) scheme for CRSNs to prolong the network lifetime. Note that energy efficiency is the most important design consideration in CRSNs because it determines the network lifetime. The central part of the EGSD scheme consists of two spectrum selection algorithms: random selection and game-theory-based selection. The EGSD scheme also includes a clustering algorithm, spectrum characterization with a Markov chain, and cluster member coordination. Our performance study shows that EGSD outperforms the existing popular framework in terms of network lifetime and coordination overhead. PMID:27376290

An Energy-Efficient Game-Theory-Based Spectrum Decision Scheme for Cognitive Radio Sensor Networks.

PubMed

Salim, Shelly; Moh, Sangman

2016-06-30

A cognitive radio sensor network (CRSN) is a wireless sensor network in which sensor nodes are equipped with cognitive radio. In this paper, we propose an energy-efficient game-theory-based spectrum decision (EGSD) scheme for CRSNs to prolong the network lifetime. Note that energy efficiency is the most important design consideration in CRSNs because it determines the network lifetime. The central part of the EGSD scheme consists of two spectrum selection algorithms: random selection and game-theory-based selection. The EGSD scheme also includes a clustering algorithm, spectrum characterization with a Markov chain, and cluster member coordination. Our performance study shows that EGSD outperforms the existing popular framework in terms of network lifetime and coordination overhead.

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.

Prospects for Pulsar Studies with the GLAST Large Area Telescope

NASA Technical Reports Server (NTRS)

Harding, Alice K.

2007-01-01

The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST), due to launch in November 2007, will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered p ulsars. As the only presently known galactic GeV source class, pulsar s will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma-ray pulsar s, including millisecond pulsars, giving much better statistics for e lucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric partic le acceleration and radiation mechanisms, by comparing data with theo retical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all un identified EGRET sources, to possibly uncover more radio-quiet Geming a-like pulsars.

Prospects for Pulsar Studies with the GLAST Large Area Telescope

NASA Technical Reports Server (NTRS)

Harding, Alice K.

2007-01-01

The Large Area Telescope (LAT) on the Gamma-ray Large Area Space Telescope (GLAST), due to launch in November 2007, will have unprecedented sensitivity and energy resolution for gamma-rays in the range of 30 MeV to 200 GeV. GLAST is therefore expected to provide major advances in the understanding of high-energy emission from rotation-powered pulsars. As the only presently known galactic GeV source class; pulsars will be one of the most important sources for study with GLAST. The main science goals of the LAT for pulsar studies include an increase in the number of detected radio-loud and radio-quiet gamma-ray pulsars, including millisecond pulsars, giving much better statistics for elucidating population characteristics, measurement of the high-energy spectrum and the shape of spectral cutoffs and determining pulse profiles for a variety of pulsars of different age. Further, measurement of phase-resolved spectra and energy dependent pulse profiles of the brighter pulsars should allow detailed tests of magnetospheric particle acceleration and radiation mechanisms, by comparing data with theoretical models that have been developed. Additionally, the LAT will have the sensitivity to allow blind pulsation searches of nearly all unidentified EGRET sources, to possibly uncover more radio-quiet Geminga-like pulsars.

Chandra Confirmation of a Pulsar Wind Nebula in DA 495

NASA Technical Reports Server (NTRS)

Arzoumanian, Z.; Safi-Harb, S.; Landecker, T.L.; Kothes, R.; Camilo, F.

2008-01-01

As part of a multiwavelength study of the unusual radio supernova remnant DA 495, we present observations made with the Chandra X-ray Observatory. Imaging and spectroscopic analysis confirms the previously detected X-ray source at the heart of the annular radio nebula, establishing the radiative properties of two key emission components: a soft unresolved source with a blackbody temperature of 1 MK consistent with a neutron star, surrounded by a nontherma1 nebula 40" in diameter exhibiting a power-law spectrum with photon index Gamma = 1.63, typical of a pulsar wind nebula. Morphologically, the nebula appears to be slightly extended along a direction, in projection on the sky, previously demonstrated to be of significance in radio and ASCA observations; we argue that this represents the orientation of the pulsar spin axis. At smaller scales, a narrow X-ray feature is seen extending out 5" from the point source, but energetic arguments suggest that it is not the resolved termination shock of the pulsar wind against the ambient medium. Finally, we argue based on synchrotron lifetimes in the nebular magnetic field that DA 495 represents the first example of a pulsar wind nebula in which electromagnetic flux makes up a significant part, together with particle flux, of the neutron star's wind.

Deep 20-GHz survey of the Chandra Deep Field South and SDSS Stripe 82: source catalogue and spectral properties

NASA Astrophysics Data System (ADS)

Franzen, Thomas M. O.; Sadler, Elaine M.; Chhetri, Rajan; Ekers, Ronald D.; Mahony, Elizabeth K.; Murphy, Tara; Norris, Ray P.; Waldram, Elizabeth M.; Whittam, Imogen H.

2014-04-01

We present a source catalogue and first results from a deep, blind radio survey carried out at 20 GHz with the Australia Telescope Compact Array, with follow-up observations at 5.5, 9 and 18 GHz. The Australia Telescope 20 GHz (AT20G) deep pilot survey covers a total area of 5 deg2 in the Chandra Deep Field South and in Stripe 82 of the Sloan Digital Sky Survey. We estimate the survey to be 90 per cent complete above 2.5 mJy. Of the 85 sources detected, 55 per cent have steep spectra (α _{1.4}^{20} < -0.5) and 45 per cent have flat or inverted spectra (α _{1.4}^{20} ≥ -0.5). The steep-spectrum sources tend to have single power-law spectra between 1.4 and 18 GHz, while the spectral indices of the flat- or inverted-spectrum sources tend to steepen with frequency. Among the 18 inverted-spectrum (α _{1.4}^{20} ≥ 0.0) sources, 10 have clearly defined peaks in their spectra with α _{1.4}^{5.5} > 0.15 and α 9^{18} < -0.15. On a 3-yr time-scale, at least 10 sources varied by more than 15 per cent at 20 GHz, showing that variability is still common at the low flux densities probed by the AT20G-deep pilot survey. We find a strong and puzzling shift in the typical spectral index of the 15-20-GHz source population when combining data from the AT20G, Ninth Cambridge and Tenth Cambridge surveys: there is a shift towards a steeper-spectrum population when going from ˜1 Jy to ˜5 mJy, which is followed by a shift back towards a flatter-spectrum population below ˜5 mJy. The 5-GHz source-count model by Jackson & Wall, which only includes contributions from FRI and FRII sources, and star-forming galaxies, does not reproduce the observed flattening of the flat-spectrum counts below ˜5 mJy. It is therefore possible that another population of sources is contributing to this effect.

Receiver Statistics for Cognitive Radios in Dynamic Spectrum Access Networks

DTIC Science & Technology

2012-02-28

SNR) are employed by many protocols and processes in direct-sequence ( DS ) spread-spectrum packet radio networks, including soft-decision decoding...adaptive modulation protocols, and power adjustment protocols. For DS spread spectrum, we have introduced and evaluated SNR estimators that employ...obtained during demodulation in a binary CDMA receiver. We investigated several methods to apply the proposed metric to the demodulator’s soft-decision

Digital processing of RF signals from optical frequency combs

NASA Astrophysics Data System (ADS)

Cizek, Martin; Smid, Radek; Buchta, Zdeněk.; Mikel, Břetislav; Lazar, Josef; Cip, Ondřej

2013-01-01

The presented work is focused on digital processing of beat note signals from a femtosecond optical frequency comb. The levels of mixing products of single spectral components of the comb with CW laser sources are usually very low compared to products of mixing all the comb components together. RF counters are more likely to measure the frequency of the strongest spectral component rather than a weak beat note. Proposed experimental digital signal processing system solves this problem by analyzing the whole spectrum of the output RF signal and using software defined radio (SDR) algorithms. Our efforts concentrate in two main areas: Firstly, using digital servo-loop techniques for locking free running continuous laser sources on single components of the fs comb spectrum. Secondly, we are experimenting with digital signal processing of the RF beat note spectrum produced by f-2f 1 technique used for assessing the offset and repetition frequencies of the comb, resulting in digital servo-loop stabilization of the fs comb. Software capable of computing and analyzing the beat-note RF spectrums using FFT and peak detection was developed. A SDR algorithm performing phase demodulation on the f- 2f signal is used as a regulation error signal source for a digital phase-locked loop stabilizing the offset frequency of the fs comb.

Digital processing of signals from femtosecond combs

NASA Astrophysics Data System (ADS)

Čížek, Martin; Šmíd, Radek; Buchta, Zdeněk.; Mikel, Břetislav; Lazar, Josef; Číp, Ondrej

2012-01-01

The presented work is focused on digital processing of beat note signals from a femtosecond optical frequency comb. The levels of mixing products of single spectral components of the comb with CW laser sources are usually very low compared to products of mixing all the comb components together. RF counters are more likely to measure the frequency of the strongest spectral component rather than a weak beat note. Proposed experimental digital signal processing system solves this problem by analyzing the whole spectrum of the output RF signal and using software defined radio (SDR) algorithms. Our efforts concentrate in two main areas: Firstly, we are experimenting with digital signal processing of the RF beat note spectrum produced by f-2f 1 technique and with fully digital servo-loop stabilization of the fs comb. Secondly, we are using digital servo-loop techniques for locking free running continuous laser sources on single components of the fs comb spectrum. Software capable of computing and analyzing the beat-note RF spectrums using FFT and peak detection was developed. A SDR algorithm performing phase demodulation on the f- 2f signal is used as a regulation error signal source for a digital phase-locked loop stabilizing the offset and repetition frequencies of the fs comb.

Multi-wavelength Observations of the Dissociative Merger in the Galaxy Cluster CIZA J0107.7+5408

NASA Astrophysics Data System (ADS)

Randall, S. W.; Clarke, T. E.; van Weeren, R. J.; Intema, H. T.; Dawson, W. A.; Mroczkowski, T.; Blanton, E. L.; Bulbul, E.; Giacintucci, S.

2016-06-01

We present results based on X-ray, optical, and radio observations of the massive galaxy cluster CIZA J0107.7+5408. We find that this system is a post-core-passage, dissociative, binary merger, with the optical galaxy density peaks of each subcluster leading their associated X-ray emission peaks. This separation occurs because the diffuse gas experiences ram pressure forces, while the effectively collisionless galaxies (and presumably their associated dark matter (DM) halos) do not. This system contains double-peaked diffuse radio emission, possibly a double radio relic with the relics lying along the merger axis and also leading the X-ray cores. We find evidence for a temperature peak associated with the SW relic, likely created by the same merger shock that is powering the relic radio emission in this region. Thus, this system is a relatively rare, clean example of a dissociative binary merger, which can in principle be used to place constraints on the self-interaction cross-section of DM. Low-frequency radio observations reveal ultra-steep spectrum diffuse radio emission that is not correlated with the X-ray, optical, or high-frequency radio emission. We suggest that these sources are radio phoenixes, which are preexisting non-thermal particle populations that have been re-energized through adiabatic compression by the same merger shocks that power the radio relics. Finally, we place upper limits on inverse Compton emission from the SW radio relic.

MULTI-WAVELENGTH OBSERVATIONS OF THE DISSOCIATIVE MERGER IN THE GALAXY CLUSTER CIZA J0107.7+5408

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

Randall, S. W.; Weeren, R. J. van; Clarke, T. E.

We present results based on X-ray, optical, and radio observations of the massive galaxy cluster CIZA J0107.7+5408. We find that this system is a post-core-passage, dissociative, binary merger, with the optical galaxy density peaks of each subcluster leading their associated X-ray emission peaks. This separation occurs because the diffuse gas experiences ram pressure forces, while the effectively collisionless galaxies (and presumably their associated dark matter (DM) halos) do not. This system contains double-peaked diffuse radio emission, possibly a double radio relic with the relics lying along the merger axis and also leading the X-ray cores. We find evidence for amore » temperature peak associated with the SW relic, likely created by the same merger shock that is powering the relic radio emission in this region. Thus, this system is a relatively rare, clean example of a dissociative binary merger, which can in principle be used to place constraints on the self-interaction cross-section of DM. Low-frequency radio observations reveal ultra-steep spectrum diffuse radio emission that is not correlated with the X-ray, optical, or high-frequency radio emission. We suggest that these sources are radio phoenixes, which are preexisting non-thermal particle populations that have been re-energized through adiabatic compression by the same merger shocks that power the radio relics. Finally, we place upper limits on inverse Compton emission from the SW radio relic.« less

Multi-wavelength Observations of the Dissociative Merger in the Galaxy Cluster CIZA J0107.7+5408

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

Randall, S. W.; Clarke, T. E.; Weeren, R. J. van

We present results based on X-ray, optical, and radio observations of the massive galaxy cluster CIZA J0107.7+5408. We find that this system is a post-core-passage, dissociative, binary merger, with the optical galaxy density peaks of each subcluster leading their associated X-ray emission peaks. This separation occurs because the diffuse gas experiences ram pressure forces, while the effectively collisionless galaxies (and presumably their associated dark matter (DM) halos) do not. This system contains double-peaked diffuse radio emission, possibly a double radio relic with the relics lying along the merger axis and also leading the X-ray cores. We find evidence for amore » temperature peak associated with the SW relic, likely created by the same merger shock that is powering the relic radio emission in this region. Thus, this system is a relatively rare, clean example of a dissociative binary merger, which can in principle be used to place constraints on the self-interaction cross-section of DM. Low-frequency radio observations reveal ultra-steep spectrum diffuse radio emission that is not correlated with the X-ray, optical, or high-frequency radio emission. Here, we suggest that these sources are radio phoenixes, which are preexisting non-thermal particle populations that have been re-energized through adiabatic compression by the same merger shocks that power the radio relics. Finally, we place upper limits on inverse Compton emission from the SW radio relic.« less

Multi-wavelength Observations of the Dissociative Merger in the Galaxy Cluster CIZA J0107.7+5408

DOE PAGES

Randall, S. W.; Clarke, T. E.; Weeren, R. J. van; ...

2016-05-25

We present results based on X-ray, optical, and radio observations of the massive galaxy cluster CIZA J0107.7+5408. We find that this system is a post-core-passage, dissociative, binary merger, with the optical galaxy density peaks of each subcluster leading their associated X-ray emission peaks. This separation occurs because the diffuse gas experiences ram pressure forces, while the effectively collisionless galaxies (and presumably their associated dark matter (DM) halos) do not. This system contains double-peaked diffuse radio emission, possibly a double radio relic with the relics lying along the merger axis and also leading the X-ray cores. We find evidence for amore » temperature peak associated with the SW relic, likely created by the same merger shock that is powering the relic radio emission in this region. Thus, this system is a relatively rare, clean example of a dissociative binary merger, which can in principle be used to place constraints on the self-interaction cross-section of DM. Low-frequency radio observations reveal ultra-steep spectrum diffuse radio emission that is not correlated with the X-ray, optical, or high-frequency radio emission. Here, we suggest that these sources are radio phoenixes, which are preexisting non-thermal particle populations that have been re-energized through adiabatic compression by the same merger shocks that power the radio relics. Finally, we place upper limits on inverse Compton emission from the SW radio relic.« less

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⊙.

LOW-FREQUENCY OBSERVATIONS OF THE MOON WITH THE MURCHISON WIDEFIELD ARRAY

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

McKinley, B.; Briggs, F.; Kaplan, D. L.

2013-01-01

A new generation of low-frequency radio telescopes is seeking to observe the redshifted 21 cm signal from the epoch of reionization (EoR), requiring innovative methods of calibration and imaging to overcome the difficulties of wide-field low-frequency radio interferometry. Precise calibration will be required to separate the expected small EoR signal from the strong foreground emission at the frequencies of interest between 80 and 300 MHz. The Moon may be useful as a calibration source for detection of the EoR signature, as it should have a smooth and predictable thermal spectrum across the frequency band of interest. Initial observations of themore » Moon with the Murchison Widefield Array 32 tile prototype show that the Moon does exhibit a similar trend to that expected for a cool thermally emitting body in the observed frequency range, but that the spectrum is corrupted by reflected radio emission from Earth. In particular, there is an abrupt increase in the observed flux density of the Moon within the internationally recognized frequency modulated (FM) radio band. The observations have implications for future low-frequency surveys and EoR detection experiments that will need to take this reflected emission from the Moon into account. The results also allow us to estimate the equivalent isotropic power emitted by the Earth in the FM band and to determine how bright the Earth might appear at meter wavelengths to an observer beyond our own solar system.« less

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.

Report to the President: Realizing the Full Potential of Government-Held Spectrum to Spur Economic Growth

DTIC Science & Technology

2012-07-01

managing the use of the Radio Frequency (RF) spectrum to ensure reliable emergency, civil, and government communications . At that time, when the rules of...or equipment and/or radio frequencies to provide electronic communication services under standard conditions (a class license) or authorizing the...Cognitive Radio Networks.” IEEE Communications Magazine (2008). Circular A- 11 : Preparation, Submission, and Execution of the Budget. Executive Office

Observation of a metric type N solar radio burst

DOE PAGES

Kong, Xiangliang; Chen, Yao; Feng, Shiwei; ...

2016-10-10

Type III and type-III-like radio bursts are produced by energetic electron beams guided along coronal magnetic fields. As a variant of type III bursts, Type N bursts appear as the letter "N" in the radio dynamic spectrum and reveal a magnetic mirror effect in coronal loops. Here, we report a well-observed N-shaped burst consisting of three successive branches at metric wavelength with both fundamental and harmonic components and a high brightness temperature (>10 9 K). We verify the burst as a true type N burst generated by the same electron beam from three aspects of the data. First, durations ofmore » the three branches at a given frequency increase gradually and may be due to the dispersion of the beam along its path. Second, the flare site, as the only possible source of non-thermal electrons, is near the western feet of large-scale closed loops. Third, the first branch and the following two branches are localized at different legs of the loops with opposite senses of polarization. We also find that the sense of polarization of the radio burst is in contradiction to the O-mode and there exists a fairly large time delay (~3–5 s) between the fundamental and harmonic components. Possible explanations accounting for these observations are presented. Finally, assuming the classical plasma emission mechanism, we can infer coronal parameters such as electron density and magnetic field near the radio source and make diagnostics on the magnetic mirror process.« less

Los Angeles FOT spread spectrum radio traffic signal interconnect evaluation task : final report on full deployment

DOT National Transportation Integrated Search

1998-10-01

The use of a spread spectrum radio network (SSRN) as an alternative to hard-wired communications between field equipment and the City of Los Angeless Automated Traffic Surveillance and Control (ATSAC) system has been investigated. The aim of using...

Gamma-Ray Emision from the Broad-Line Radio Galaxy 3C 111

NASA Technical Reports Server (NTRS)

Hartman, Robert C.; Kadler, Matthias; Tueller, Jack

2008-01-01

The broad-line radio galaxy 3C 111 has been suggested as the counterpart of the Gamma-ray source 3EGJ0416+3650. While 3C 111 meets most of the criteria for a high-probability identification, like a bright fla t-spectrum radio core and a blazarlike broadband SED, in the Third EG RET Catalog, the large positional offset of about 1.5 degrees put 3C1 11 outside the 99% probability region for 3EG J0416+3650, making this association questionable. We present a re-analysis of all available data for 3C111 from the EGRET archives, resulting in probable detection of high-energy Gamma-ray emission above 1000MeV from a position clo se to the nominal position of 3C 111, in two separate viewing periods (VPs), at a 3sigma level in each. A new source, GROJ0426+3747, appea rs to be present nearby, seen only in the >1000MeV data. For >100MeV, the data are in agreement with only one source (at the original cata log position) accounting for most of the EGRET-detected emission of 3 EGJ0416+3650. A follow-up Swift UVOT/XRT observation reveals one mode rately bright X-ray source in the error box of 3EGJ0416+3650, but bec ause of the large EGRET position uncertainty, it is not certain that the X-ray and Gamma-ray sources are associated. A Swift observation of GROJ0426+3747 detected no X.ray source nearby.

When all else fails: 21st century Amateur Radio as an emergency communications medium.

PubMed

Nollet, Kenneth E; Ohto, Hitoshi

2013-12-01

Twenty-first century demand for radio spectrum continues to increase with the explosive growth of wireless devices, but authorities reserve slices of the spectrum for licensed Amateur Radio operators, recognizing their value to the public, particularly with respect to providing emergency communications. Blood banking and transfusion medicine are among the specialties that should also recognize the value of Amateur Radio as an emergency communications medium, because blood collection, testing, processing, storage, and transfusion are life-saving activities that in modern times can be separated by considerable distance. Copyright © 2013 Elsevier Ltd. All rights reserved.

AGN jets under the microscope: A divide? Doctoral Thesis Award Lecture 2011

NASA Astrophysics Data System (ADS)

Karouzos, M.; Britzen, S.; Witzel, A.; Zensus, A. J.; Eckart, A.

2012-06-01

A new paradigm for active galactic jet kinematics has emerged through detailed investigations of BL Lac objects using very long baseline radio interferometry. In this new scheme, most, if not all, jet components appear to remain stationary with respect to the core but show significant non-radial motions. This paper presents results from our kinematic investigation of the jets of a statistically complete sample of radio-loud flat-spectrum active galaxies, focusing on the comparison between the jet kinematic properties of BL Lacs and flat-spectrum radio-quasars. It is shown that there is a statistically significant difference between the kinematics of the two AGN classes, with BL Lacs showing more bent jets, that are wider and show slower movement along the jet axis, compared to flat-spectrum radio-quasars. This is interpreted as evidence for helically structured jets.

Constraining the location of rapid gamma-ray flares in the flat spectrum radio quasar 3C 273 [Constraining the location of rapid gamma-ray flares in the FSRQ 3C 273

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

Rani, B.; Lott, B.; Krichbaum, T. P.

2013-09-02

Here, we present a γ-ray photon flux and spectral variability study of the flat-spectrum radio quasar 3C 273 over a rapid flaring activity period between September 2009 to April 2010. Five major flares were observed in the source during this period. The most rapid flare observed in the source has a flux doubling time of 1.1 hr. The rapid γ-ray flares allow us to constrain the location and size of the γ-ray emission region in the source. The γγ-opacity constrains the Doppler factor δ γ ≥ 10 for the highest energy (15 GeV) photon observed by the Fermi-Large Area Telescopemore » (LAT). Causality arguments constrain the size of the emission region to 1.6 × 10 15 cm. The γ-ray spectra measured over this period show clear deviations from a simple power law with a break in the 1–2 GeV energy range. We discuss possible explanations for the origin of the γ-ray spectral breaks. Our study suggests that the γ-ray emission region in 3C 273 is located within the broad line region (< 1.6 pc). As a result, the spectral behavior and temporal characteristics of the individual flares indicate the presence of multiple shock scenarios at the base of the jet.« less

AGN coronal emission models - I. The predicted radio emission

NASA Astrophysics Data System (ADS)

Raginski, I.; Laor, Ari

2016-06-01

Accretion discs in active galactic nucleus (AGN) may be associated with coronal gas, as suggested by their X-ray emission. Stellar coronal emission includes radio emission, and AGN corona may also be a significant source for radio emission in radio quiet (RQ) AGN. We calculate the coronal properties required to produce the observed radio emission in RQ AGN, either from synchrotron emission of power-law (PL) electrons, or from cyclosynchrotron emission of hot mildly relativistic thermal electrons. We find that a flat spectrum, as observed in about half of RQ AGN, can be produced by corona with a disc or a spherical configuration, which extends from the innermost regions out to a pc scale. A spectral break to an optically thin power-law emission is expected around 300-1000 GHz, as the innermost corona becomes optically thin. In the case of thermal electrons, a sharp spectral cut-off is expected above the break. The position of the break can be measured with very long baseline interferometry observations, which exclude the cold dust emission, and it can be used to probe the properties of the innermost corona. Assuming equipartition of the coronal thermal energy density, the PL electrons energy density, and the magnetic field, we find that the energy density in a disc corona should scale as ˜R-1.3, to get a flat spectrum. In the spherical case the energy density scales as ˜R-2, and is ˜4 × 10-4 of the AGN radiation energy density. In Paper II we derive additional constraints on the coronal parameters from the Gudel-Benz relation, Lradio/LX-ray ˜ 10- 5, which RQ AGN follow.

A METHOD TO EXTRACT THE ANGULAR POWER SPECTRUM OF THE EPOCH OF REIONIZATION FROM LOW-FREQUENCY RADIO INTERFEROMETERS

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

Zheng Qian; Wu Xiangping; Gu Junhua

2012-10-10

The redshifted 21 cm signal of neutral hydrogen from the epoch of reionization (EoR) is extremely weak and its first detection is therefore expected to be statistical with first-generation low-frequency radio interferometers. In this Letter, we propose a method to extract the angular power spectrum of the EoR from the visibility correlation coefficients p{sub ij} (u, v), instead of the visibilities V{sub ij} (u, v) measured directly by radio interferometers in conventional algorithm. The visibility correlation coefficients are defined as p{sub ij}(u,v)=V{sub ij}(u,v)/{radical}(|V{sub ii}||V{sub jj}|) by introducing the autocorrelation terms V{sub ii} and V{sub jj} such that the angular powermore » spectrum C{sub l} can be obtained through C{sub l} = T {sup 2}{sub 0}(|p{sub ij} (u, v)|{sup 2}), independently of the primary beams of antennas. This also partially removes the influence of receiver gains in the measurement of C{sub l} because the amplitudes of the gains cancel each other out in the statistical average operation of (|p{sub ij} (u, v)|{sup 2}). We use the average system temperature T{sub 0} as a calibrator of C{sub l}, which is dominated by the Milky Way and extragalactic sources in the frequency range that we are interested in, below 200 MHz. Finally, we demonstrate the feasibility of this novel method using the simulated sky maps as targets and the 21 CentiMeter Array (21CMA) as interferometer.« less

A Spectrum Access Based on Quality of Service (QoS) in Cognitive Radio Networks.

PubMed

Zhai, Linbo; Wang, Hua; Gao, Chuangen

2016-01-01

The quality of service (QoS) is important issue for cognitive radio networks. In the cognitive radio system, the licensed users, also called primary users (PUs), are authorized to utilize the wireless spectrum, while unlicensed users, also called secondary users (SUs), are not authorized to use the wireless spectrum. SUs access the wireless spectrum opportunistically when the spectrum is idle. While SUs use an idle channel, the instance that PUs come back makes SUs terminate their communications and leave the current channel. Therefore, quality of service (QoS) is difficult to be ensured for SUs. In this paper, we first propose an analysis model to obtain QoS for cognitive radio networks such as blocking probability, completed traffic and termination probability of SUs. When the primary users use the channels frequently, QoS of SUs is difficult to be ensured, especially the termination probability. Then, we propose a channel reservation scheme to improve QoS of SUs. The scheme makes the terminated SUs move to the reserved channels and keep on communications. Simulation results show that our scheme can improve QoS of SUs especially the termination probability with a little cost of blocking probability in dynamic environment.

A Strategic Bargaining Game for a Spectrum Sharing Scheme in Cognitive Radio-Based Heterogeneous Wireless Sensor Networks.

PubMed

Mao, Yuxing; Cheng, Tao; Zhao, Huiyuan; Shen, Na

2017-11-27

In Wireless Sensor Networks (WSNs), unlicensed users, that is, sensor nodes, have excessively exploited the unlicensed radio spectrum. Through Cognitive Radio (CR), licensed radio spectra, which are owned by licensed users, can be partly or entirely shared with unlicensed users. This paper proposes a strategic bargaining spectrum-sharing scheme, considering a CR-based heterogeneous WSN (HWSN). The sensors of HWSNs are discrepant and exist in different wireless environments, which leads to various signal-to-noise ratios (SNRs) for the same or different licensed users. Unlicensed users bargain with licensed users regarding the spectrum price. In each round of bargaining, licensed users are allowed to adaptively adjust their spectrum price to the best for maximizing their profits. . Then, each unlicensed user makes their best response and informs licensed users of "bargaining" and "warning". Through finite rounds of bargaining, this scheme can obtain a Nash bargaining solution (NBS), which makes all licensed and unlicensed users reach an agreement. The simulation results demonstrate that the proposed scheme can quickly find a NBS and all players in the game prefer to be honest. The proposed scheme outperforms existing schemes, within a certain range, in terms of fairness and trade success probability.

Signal Identification and Isolation Utilizing Radio Frequency Photonics

DTIC Science & Technology

2017-09-01

analyzers can measure the frequency of signals and filters can be used to separate the signals apart from one another. This report will review...different techniques for spectrum analysis and isolation. 15. SUBJECT TERMS radio frequency, photonics, spectrum analyzer, filters 16. SECURITY CLASSIFICATION...Analyzers .......................................................................................... 3 3.2 Frequency Identification using Filters

Goldstone radio spectrum protection. [deep space network

NASA Technical Reports Server (NTRS)

Gaudian, B. A.; Cushman, R. B.

1980-01-01

Potential electromagnetic interference to the Goldstone tracking receivers due to neighboring military installations is discussed. Coordination of the military and NASA Goldstone activities in the Mojave Desert area is seen to be an effective method to protect the Goldstone radio spectrum while maintaining compatible operations for the military and Goldstone.

LOFAR discovery of an ultra-steep radio halo and giant head-tail radio galaxy in Abell 1132

NASA Astrophysics Data System (ADS)

Wilber, A.; Brüggen, M.; Bonafede, A.; Savini, F.; Shimwell, T.; van Weeren, R. J.; Rafferty, D.; Mechev, A. P.; Intema, H.; Andrade-Santos, F.; Clarke, A. O.; Mahony, E. K.; Morganti, R.; Prandoni, I.; Brunetti, G.; Röttgering, H.; Mandal, S.; de Gasperin, F.; Hoeft, M.

2018-01-01

Low-Frequency Array (LOFAR) observations at 144 MHz have revealed large-scale radio sources in the unrelaxed galaxy cluster Abell 1132. The cluster hosts diffuse radio emission on scales of ∼650 kpc near the cluster centre and a head-tail (HT) radio galaxy, extending up to 1 Mpc, south of the cluster centre. The central diffuse radio emission is not seen in NRAO VLA FIRST Survey, Westerbork Northern Sky Survey, nor in C & D array VLA observations at 1.4 GHz, but is detected in our follow-up Giant Meterwave Radio Telescope (GMRT) observations at 325 MHz. Using LOFAR and GMRT data, we determine the spectral index of the central diffuse emission to be α = -1.75 ± 0.19 (S ∝ να). We classify this emission as an ultra-steep spectrum radio halo and discuss the possible implications for the physical origin of radio haloes. The HT radio galaxy shows narrow, collimated emission extending up to 1 Mpc and another 300 kpc of more diffuse, disturbed emission, giving a full projected linear size of 1.3 Mpc - classifying it as a giant radio galaxy (GRG) and making it the longest HT found to date. The head of the GRG coincides with an elliptical galaxy (SDSS J105851.01+564308.5) belonging to Abell 1132. In our LOFAR image, there appears to be a connection between the radio halo and the GRG. The turbulence that may have produced the halo may have also affected the tail of the GRG. In turn, the GRG may have provided seed electrons for the radio halo.

Fermi LAT detection of a GeV flare from blazar TXS 0943+105

NASA Astrophysics Data System (ADS)

Ciprini, S.

2014-07-01

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 flat spectrum radio quasar TXS 0943+105, also known as GB6 J0946+1016, MG1 J094636+1017 and 2FGL J0946.5+1015 in the second Fermi LAT catalog (2FGL, Nolan et al. ...

Understanding the radio spectral indices of galaxy cluster relics by superdiffusive shock acceleration

NASA Astrophysics Data System (ADS)

Zimbardo, Gaetano; Perri, Silvia

2018-06-01

Galaxy cluster merger shocks are the likely source of relativistic electrons, but many observations do not fit into the standard acceleration models. In particular, there is a long-standing discrepancy between the radio derived Mach numbers M_radio and the Mach numbers derived from X-ray measurements, M_X. Here, we show how superdiffusive electron transport and superdiffusive shock acceleration (SSA) can help to solve this problem. We present a heuristic derivation of the superlinear time growth of the mean square displacement of particles, ⟨Δx2⟩∝tβ, and of the particle energy spectral index in the framework of SSA. The resulting expression for the radio spectral index α is then used to determine the superdiffusive exponent β from the observed values of α and of the compression ratio for a number of radio relics. Therefore, the fact that M_radio>M_X can be explained by SSA without the need to make assumptions on the energy spectrum of the seed electrons to be re-accelerated. We also consider the acceleration times obtained in the diffusive case, based both on the Bohm diffusion coefficient and on the quasilinear diffusion coefficient. While in the latter case the acceleration time is consistent with the estimated electron energy loss time, the former case it is much shorter.

Cognitive radio wireless sensor networks: applications, challenges and research trends.

PubMed

Joshi, Gyanendra Prasad; Nam, Seung Yeob; Kim, Sung Won

2013-08-22

A cognitive radio wireless sensor network is one of the candidate areas where cognitive techniques can be used for opportunistic spectrum access. Research in this area is still in its infancy, but it is progressing rapidly. The aim of this study is to classify the existing literature of this fast emerging application area of cognitive radio wireless sensor networks, highlight the key research that has already been undertaken, and indicate open problems. This paper describes the advantages of cognitive radio wireless sensor networks, the difference between ad hoc cognitive radio networks, wireless sensor networks, and cognitive radio wireless sensor networks, potential application areas of cognitive radio wireless sensor networks, challenges and research trend in cognitive radio wireless sensor networks. The sensing schemes suited for cognitive radio wireless sensor networks scenarios are discussed with an emphasis on cooperation and spectrum access methods that ensure the availability of the required QoS. Finally, this paper lists several open research challenges aimed at drawing the attention of the readers toward the important issues that need to be addressed before the vision of completely autonomous cognitive radio wireless sensor networks can be realized.

G0.9 + 0.1 and the emerging class of composite supernova remnants

NASA Technical Reports Server (NTRS)

Helfand, D. J.; Becker, R. H.

1987-01-01

High-resolution, multifrequency maps of a bright extended radio source near the Galactic center have revealed it to be a classic example of a composite supernova remnant. A steep-spectrum shell of emission, about 8 arcmin in diameter, surrounds a flat-spectrum, highly polarized Crab-like core about 2 arcmin across. The two components have equal flux densities at about 6 cm, marking this source as having the highest core-to-shell ratio among the about 10 composite remnants identified to date. X-ray and far-infrared data on the source are used to constrain the energetics and evolutionary state of the remnant and its putative central pulsar. It is argued that the total energy contained in the Crab-like components requires that the pulsars powering them were all born with periods shorter than 50 ms, and that if a substantial number of neutron stars with slow initial rotation rates exist, their birthplaces have not yet been found.

Fermi-LAT detection of a gamma-ray flaring source in the vicinity of PKS 0507+17

NASA Astrophysics Data System (ADS)

D'Ammando, F.; Orienti, M.

2013-04-01

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flux from a source positionally consistent with PKS 0507+17 (also known as 2FGL J0509.9+1802, Nolan et al. 2012, ApJS, 199, 31; R.A.= 05h10m02.3691s, Dec.= +18d00m41.582s, J2000.0, Johnston et al. 1995, AJ, 110, 880), a flat spectrum radio quasar at redshift z = 0.416 (Perlman et al.

Radio-to-Gamma-Ray Monitoring of the Narrow-line Seyfert 1 Galaxy PMN J0948+0022 from 2008 to 2011

NASA Technical Reports Server (NTRS)

Foschini, L.; Angelakis, E.; Fuhrmann, L.; Ghisellini, G.; Hovatta, T.; Lahteenmaki, A.; Lister, M. L.; Braito, V.; Gallo, L.; Hamilton, T. S.;

Radio-to- γ-ray monitoring of the narrow-line Seyfert 1 galaxy PMN J0948 + 0022 from 2008 to 2011

DOE PAGES

Foschini, L.; Angelakis, E.; Fuhrmann, L.; ...

2012-11-30

Here, we present more than three years of observations at different frequencies, from radio to high-energy γ-rays, of the Narrow-Line Seyfert 1 (NLS1) Galaxy PMN J0948 + 0022 (z = 0.585). This source is the first NLS1 detected at energies above 100 MeV and therefore can be considered the prototype of this emerging new class of γ-ray emitting active galactic nuclei (AGN). The observations performed from 2008 August 1 to 2011 December 31 confirmed that PMN J0948 + 0022 generates a powerful relativistic jet, which is able to develop an isotropic luminosity at γ-rays of the order of 10 48more » erg s -1, at the level of powerful quasars. The evolution of the radiation emission of this source in 2009 and 2010 followed the canonical expectations of relativistic jets with correlated multiwavelength variability (γ-rays followed by radio emission after a few months), but it was difficult to retrieve a similar pattern in the light curves of 2011. The comparison of γ-ray spectra before and including 2011 data suggested that there was a softening of the high-energy spectral slope. We selected five specific epochs to be studied by modelling the broad-band spectrum, which are characterised by an outburst at γ-rays or very low/high flux at other wavelengths. The observed variability can largely be explained by changes in the injected power, the bulk Lorentz factor of the jet, or the electron spectrum. The characteristic time scale of doubling/halving flux ranges from a few days to a few months, depending on the frequency and the sampling rate. The shortest doubling time scale at γ-rays is 2.3 ± 0.5 days. Finally, these small values underline the need of highly sampled multiwavelength campaigns to better understand the physics of these sources.« less

RADIO-WEAK BL LAC OBJECTS IN THE FERMI ERA

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

Massaro, F.; Marchesini, E. J.; D’Abrusco, R.

2017-01-10

The existence of “radio-weak BL Lac objects” (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak emission line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated bymore » the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]–[4.6]–[12] μ m color–color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that of the BL Lac population.« less

Radio-weak BL Lac Objects in the Fermi Era

NASA Astrophysics Data System (ADS)

Massaro, F.; Marchesini, E. J.; D'Abrusco, R.; Masetti, N.; Andruchow, I.; Smith, Howard A.

2017-01-01

The existence of “radio-weak BL Lac objects” (RWBLs) has been an open question, and has remained unsolved since the discovery that quasars could be radio-quiet or radio-loud. Recently, several groups identified RWBL candidates, mostly found while searching for low-energy counterparts of the unidentified or unassociated gamma-ray sources listed in the Fermi catalogs. Confirming RWBLs is a challenging task since they could be confused with white dwarfs (WDs) or weak emission line quasars (WELQs) when there are not sufficient data to precisely draw their broadband spectral energy distribution, and their classification is mainly based on a featureless optical spectra. Motivated by the recent discovery that Fermi BL Lacs appear to have very peculiar mid-IR emission, we show that it is possible to distinguish between WDs, WELQs, and BL Lacs using the [3.4]-[4.6]-[12] μm color-color plot built using the WISE magnitudes when the optical spectrum is available. On the basis of this analysis, we identify WISE J064459.38+603131 and WISE J141046.00+740511.2 as the first two genuine RWBLs, both potentially associated with Fermi sources. Finally, to strengthen our identification of these objects as true RWBLs, we present multifrequency observations for these two candidates to show that their spectral behavior is indeed consistent with that of the BL Lac population.

Deep H.E.S.S. observations of the supernova remnant RX J0852.0-4622

NASA Astrophysics Data System (ADS)

Sushch, Iurii; Paz Arribas, Manuel; Komin, Nukri; Schwanke, Ullrich

2016-06-01

The largest TeV source, RX J0852.0-4622 (Vela Jr.), is one of the few supernova remnants (SNRs) with well resolved shell-like morphology at very-high-energy (VHE; E>100 GeV) gamma-rays. Strong non-thermal emission across the electromagnetic spectrum from radio to VHE gamma-rays, young age and proximity of the remnant makes it one of the prime objects for the study of particle acceleration aiming to test the paradigm of SNRs being sources of Galactic cosmic rays. Here we present deep H.E.S.S. observations of RX J0852.0-4622 with roughly doubled exposure comparing to previously published results. Improved statistics together with new analysis techniques result in a firm determination of the cut-off in the gamma-ray spectrum and allow the spatially resolved spectroscopy studies. A smooth connection of the H.E.S.S. spectrum to the spectrum at GeV energies as reported by Fermi/LAT provides an exciting opportunity to recover the present-time parent particle population in both leptonic and hadronic scenarios directly from the gamma-ray data alone. These new observations provide us a deeper insight and better understanding of the physical processes in SNRs.

Properties of centralized cooperative sensing in cognitive radio networks

NASA Astrophysics Data System (ADS)

Skokowski, Paweł; Malon, Krzysztof; Łopatka, Jerzy

2017-04-01

Spectrum sensing is a functionality that enables network creation in the cognitive radio technology. Spectrum sensing is use for building the situation awareness knowledge for better use of radio resources and to adjust network parameters in case of jamming, interferences from legacy systems, decreasing link quality caused e.g. by nodes positions changes. This paper presents results from performed tests to compare cooperative centralized sensing versus local sensing. All tests were performed in created simulator developed in Matlab/Simulink environment.

A Study of the 2012 January 19 Complex Type II Radio Burst Using Wind, SOHO, and STEREO Observations*

NASA Technical Reports Server (NTRS)

Teklu, T. B.; Gholap, A. V.; Gopalswamy, N.; Yashiro, S.; Makela, P.; Akiyama, S.; Thakur, N.; Xie, H.

2016-01-01

We report on a case study of the complex type II radio burst of 2012 January 19 and its association with a white-light coronal mass ejection (CME). The complexity can be described as the appearance of an additional type II burst component and strong intensity variation. The dynamic spectrum shows a pair of type II bursts with fundamental harmonic structures, one confined to decameter-hectometric (DH) wavelengths and the other extending to kilometric (km) wavelengths. By comparing the speeds obtained from white-light images with that speed of the shock inferred from the drift rate, we show that the source of the short-lived DH component is near the nose.

Population density effect on radio frequencies interference (RFI) in radio astronomy

NASA Astrophysics Data System (ADS)

Umar, Roslan; Abidin, Zamri Zainal; Ibrahim, Zainol Abidin; Hassan, Mohd Saiful Rizal; Rosli, Zulfazli; Hamidi, Zety Shahrizat

2012-06-01

Radio astronomical observation is infected by wide range of Radio Frequency Interference (RFI). We will also use information gathered from on-site RFI level measurements on selected 'good' areas generated by this study. After investigating a few suitable sites we will commence to the site and construct the RFI observation. Eventually, the best area we will be deciding from the observations soon. The result of this experiment will support our planning to build the first radio telescope in Malaysia. Radio observatories normally are located in remote area, in order to combat RFI from active spectrum users and radio noise produced in industrial or residential areas. The other solution for this problem is regulating the use of radio frequencies in the country (spectrum management). Measurement of RFI level on potential radio astronomical site can be done to measure the RFI levels at sites. Seven sites are chosen divide by three group, which is A, B and C. In this paper, we report the initial testing RFI survey for overall spectrum (0-2GHz) for those sites. The averaged RFI level above noise level at the three group sites are 19.0 (+/-1.79) dBm, 19.5 (+/-3.71) dBm and 17.0 (+/-3.71) dBm and the averaged RFI level above noise level for without main peaks are 20.1 (+/-1.77) dBm, 19.6 (+/-3.65) dBm and 17.2 (+/-1.43) dBm respectively.

Estimation of a coronal mass ejection magnetic field strength using radio observations of gyrosynchrotron radiation

NASA Astrophysics Data System (ADS)

Carley, Eoin P.; Vilmer, Nicole; Simões, Paulo J. A.; Ó Fearraigh, Brían

2017-12-01

Coronal mass ejections (CMEs) are large eruptions of plasma and magnetic field from the low solar corona into interplanetary space. These eruptions are often associated with the acceleration of energetic electrons which produce various sources of high intensity plasma emission. In relatively rare cases, the energetic electrons may also produce gyrosynchrotron emission from within the CME itself, allowing for a diagnostic of the CME magnetic field strength. Such a magnetic field diagnostic is important for evaluating the total magnetic energy content of the CME, which is ultimately what drives the eruption. Here, we report on an unusually large source of gyrosynchrotron radiation in the form of a type IV radio burst associated with a CME occurring on 2014-September-01, observed using instrumentation from the Nançay Radio Astronomy Facility. A combination of spectral flux density measurements from the Nançay instruments and the Radio Solar Telescope Network (RSTN) from 300 MHz to 5 GHz reveals a gyrosynchrotron spectrum with a peak flux density at 1 GHz. Using this radio analysis, a model for gyrosynchrotron radiation, a non-thermal electron density diagnostic using the Fermi Gamma Ray Burst Monitor (GBM) and images of the eruption from the GOES Soft X-ray Imager (SXI), we were able to calculate both the magnetic field strength and the properties of the X-ray and radio emitting energetic electrons within the CME. We find the radio emission is produced by non-thermal electrons of energies >1 MeV with a spectral index of δ 3 in a CME magnetic field of 4.4 G at a height of 1.3 R⊙, while the X-ray emission is produced from a similar distribution of electrons but with much lower energies on the order of 10 keV. We conclude by comparing the electron distribution characteristics derived from both X-ray and radio and show how such an analysis can be used to define the plasma and bulk properties of a CME.

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

The BL Lac Classification

NASA Astrophysics Data System (ADS)

Landt, H.; Padovani, P.

1999-12-01

In the optical wavelength range the distinction between a radio galaxy and a BL Lac object is mainly based on the Ca II H and K break observed in the optical spectrum. Marchã et al. (1996, MNRAS, 281, 425) have expanded on the previously used division by suggesting objects with Ca II break values lower than 0.4 to be classified as BL Lacs and sources with values higher than 0.4 to be classified as galaxies. We present new evidence that there is a smooth transition between BL Lac objects and Fanaroff-Riley type I radio galaxies. We find an increase in X-ray and radio core luminosity as the Ca II break gets more and more diluted. This suggests that the only difference between BL Lac objects and their parent population lies in orientation. The closer the jet of the radio galaxy to the observer's line of sight, the more its luminosity gets amplified and the object becomes BL Lac-like. We will address the question of the BL Lac parent population and will propose to unify the beamed and unbeamed objects in nomenclature.

Simultaneous Chandra and NuSTAR Observations of the Highly Obscured AGN Candidate in NGC660.

NASA Astrophysics Data System (ADS)

Annuar, Ady

2014-09-01

We are using NuSTAR to undertake a detailed investigation of the obscured AGN population at D<15Mpc. Our latest target is NGC660 where the presence of an AGN has been ambiguous. However, recently it was observed to undergo a radio outburst which reveals a bright continuum source (Argo et al. 2015), coincident with Chandra 2-8 keV emission from one of the three point sources near the nucleus (<5"). This confirms and pinpoints the X-ray position of the AGN. Comparisons of the Chandra flux with the radio emission and other multiwavelength luminosity indicators indicate that the X-ray flux is suppressed, suggesting that it is absorbed by a high column of gas. A NuSTAR observation for this object has been scheduled as part of our program. The requested Chandra observation is essential to unambiguously constrain the AGN and isolate it from other sources at <8 keV. When combined with NuSTAR, we will then be able to accurately characterise the 0.5-30 keV spectrum of the AGN for the first time.

GRO J1655-40: Early Stages of the 2005 Outburst

NASA Technical Reports Server (NTRS)

Shaposhnikov, N.; Swank, Jean; Shrader, C. R.; Rupen, M.; Beckmann, V.; Markwardt, C. B.; Smith, D. A.

2007-01-01

The black-hole X-ray binary transient GRO J1655-40 underwent an outburst beginning in early 2005. We present the results of our multi-wavelength observational campaign to study the early outburst spectral and temporal evolution, which combines data from X-ray (RXTE, INTEGRAL), radio (VLA) and optical (ROTSE, SMARTS) instruments. During the reported period the source left quiescence and went through four major accreting black hole states: low-hard, hard intermediate, soft intermediate and high-soft. We investigated dipping behavior in the RXTE band and compare our results to the 1996-1997 case, when the source was predominantly in the high-soft state, finding significant differences. We consider the evolution of the low frequency quasi-periodic oscillations and find that the frequency strongly correlates with the spectral characteristics, before shutting off prior to the transition to the high-soft state. We model the broad-band high-energy spectrum in the context of empirical models, as well as more physically motivated thermal and bulk-motion Comptonization and Compton reflection models. RXTE and INTEGRAL data together support a statistically significant high energy cut-off in the energy spectrum at approximately equal to 100 - 200 keV during the low-hard state. The RXTE data alone also show it very significantly during the transition, but cannot see one in the high-soft state spectra. We consider radio, optical and X-ray connections in the context of possible synchrotron and synchrotron self-Compton origins of X-ray emission in low-hard and intermediate states. In this outburst of GRO J1655-40, the radio flux does not rise strongly with the X-ray flux.

Supercluster simulations: impact of baryons on the matter power spectrum and weak lensing forecasts for Super-CLASS

NASA Astrophysics Data System (ADS)

Peters, Aaron; Brown, Michael L.; Kay, Scott T.; Barnes, David J.

2018-03-01

We use a combination of full hydrodynamic and dark matter only simulations to investigate the effect that supercluster environments and baryonic physics have on the matter power spectrum, by re-simulating a sample of supercluster sub-volumes. On large scales we find that the matter power spectrum measured from our supercluster sample has at least twice as much power as that measured from our random sample. Our investigation of the effect of baryonic physics on the matter power spectrum is found to be in agreement with previous studies and is weaker than the selection effect over the majority of scales. In addition, we investigate the effect of targeting a cosmologically non-representative, supercluster region of the sky on the weak lensing shear power spectrum. We do this by generating shear and convergence maps using a line-of-sight integration technique, which intercepts our random and supercluster sub-volumes. We find the convergence power spectrum measured from our supercluster sample has a larger amplitude than that measured from the random sample at all scales. We frame our results within the context of the Super-CLuster Assisted Shear Survey (Super-CLASS), which aims to measure the cosmic shear signal in the radio band by targeting a region of the sky that contains five Abell clusters. Assuming the Super-CLASS survey will have a source density of 1.5 galaxies arcmin-2, we forecast a detection significance of 2.7^{+1.5}_{-1.2}, which indicates that in the absence of systematics the Super-CLASS project could make a cosmic shear detection with radio data alone.

Observation of hectometric auroral radio emissions in Iceland

NASA Astrophysics Data System (ADS)

Sato, Y.; Ono, T.; Iizima, M.; Sato, N.

2006-12-01

The Earth's auroral region is an active radio source at frequencies from a few hertz to several megahertz. In the hectometric range, it was found that Terrestrial Hectometric Radiation (THR) is related to auroras by observations of the Ohzora satellite [Oya et al.(1985)]. In resent research, Shinbori et al. [2003] showed that occurrence of THR follows SC by several minutes using the Akebono satellite data. On the ground, auroral roar and MF burst were discovered by Kellogg and Monson [1979, 1984] and Weatherwax et al. [1994] in the northern Canada, respectively. Because there is not enough physical and geophysical characterization of these radio emissions, the physical mechanism of these phenomena in the auroral ionosphere has not been fully understood yet. We set up new observation system at Husafell station in Iceland in September, 2005 and have started to observe auroral radio emissions. Radio signals, which are received by the cross loop antennas, are converted into left- and right- handed polarized components within the frequency range from 1 MHz to 5 MHz. Based on the calibration of system, it was found that the possibility of occurence would be smaller than expected due to the low sensitivity because average power spectrum densities of auroral roar and MF burst are 50-100 nV/m/Hz^1/2. So, the system was planed to be upgraded in this September, which makes it possible to detect auroral roar and MF burst. It is expected that the detail physical process will be elucidated by clarifying the spectrum, polarization, dependence on the geomagnetic activity, and so on. In this presentation, we will show the improved points of the new system and preliminary observation results. There is a basic question whether auroral roar and MF burst observed on the ground are generated by the same process as THR observed by satellites. By comparing the results from the ground-based observation and the Akebono satellite observation of THR, it becomes possible to obtain a new picture of auroral radio emissions.

The Shklovsky phenomenon

NASA Astrophysics Data System (ADS)

Kardashev, N. S.; Marochnik, L. S.

Joseph Samuelovich Shklovsky was born in the town of Glukhov in Ukraine. In 1933 he entered the physicsmath department of Vladivostok University and two years later transferred to the physics department of Moscow University (MGU). In 1938 this young physicist-optician was accepted as a graduate student by the astrophysics department of the P.K. Shternberg State Astronomical Institute (GAISh) at MGU, an institute with which he was to be associated his entire life.Then there followed the start of the war, evacuation to Ashkhabad (because of his poor eyesight he was not sent to the front), then his return to Moscow and GAISh, where he worked for many years at the leading edge of the post-war revolution in astronomy. The last forty years have been characterized by unprecedented development of observational methods and technology such as radio telescopes and interferometers and infrared, ultraviolet, X-ray, and gamma-ray astronomy. New classes of objects have been discovered: radio stars, radio galaxies, quasars, infrared sources, pulsars, cosmic ray bursters, sources of gamma bursts, background radiation at all wave- lengths, and, in particular, background radio radiation. "The question `What is this?' must be central." This is the main testament that Shklovsky left to younger researchers. He was one of the first astronomers to recognize the necessity of studying any astronomical object at all wavelengths in the electromagnetic spectrum. Only under such conditions can one hope to construct a proper model and understand the object's nature. His study of galactic radio emissions appeared in 1947. In that same year he participated in an expedition to observe the total star eclipse in Brazil, the first such expedition to be equipped with a radio telescope. Beginning in 1950 Shklovsky took part in the first infrared observations using an image convertor. His pioneering work: Galactic Infrared Radiation, was published in 1953.

The average X-ray/gamma-ray spectra of Seyfert galaxies from Ginga and OSSE and the origin of the cosmic X-ray background

NASA Technical Reports Server (NTRS)

Zdziarski, Andrzej A.; Johnson, W. Neil; Done, Chris; Smith, David; Mcnaron-Brown, Kellie

1995-01-01

We have obtained the first average 2-500 keV spectra of Seyfert galaxies, using the data from Ginga and Compton Gamma-Ray Observatory's (CGRO) Oriented Scintillation Spectrometer Experiment (OSSE). Our sample contains three classes of objects with markedly different spectra: radio-quiet Seyfert 1's and 2's, and radio-loud Seyfert 1's. The average radio-quiet Seyfert 1 spectrum is well-fitted by a power law continuum with the energy spectral index alpha approximately equals 0.9, a Compton reflection component corresponding to a approximately 2 pi covering solid angle, and ionized absorption. There is a high-energy cutoff in the incident power law continuum: the e-folding energy is E(sub c) approximately equals 0.6(sup +0.8 sub -0.3) MeV. The simplest model that describes this spectrum is Comptonization in a relativistic optically-thin thermal corona above the surface of an accretion disk. Radio-quiet Seyfert 2's show strong netural absorption, and there is an indication that their X-ray power laws are intrinsically harder. Finally, the radio-loud Seyfert spectrum has alpha approximately equals 0.7, moderate neutral absorption E(sub C) = 0.4(sup +0.7 sub -0.2) MeV, and no or little Compton reflection. This is incompatible with the radio-quiet Seyfert 1 spectrum, and probably indicating that the X-rays are beamed away from the accretion disk in these objects. The average spectra of Seyferts integrated over redshift with a power-law evolution can explain the hard X-ray spectrum of the cosmic background.

Blazar flaring patterns (B-FlaP) classifying blazar candidate of uncertain type in the third Fermi-LAT catalogue by artificial neural networks

NASA Astrophysics Data System (ADS)

Chiaro, G.; Salvetti, D.; La Mura, G.; Giroletti, M.; Thompson, D. J.; Bastieri, D.

2016-11-01

The Fermi-Large Area Telescope (LAT) is currently the most important facility for investigating the GeV γ-ray sky. With Fermi-LAT, more than three thousand γ-ray sources have been discovered so far. 1144 (˜40 per cent) of the sources are active galaxies of the blazar class, and 573 (˜20 per cent) are listed as blazar candidate of uncertain type (BCU), or sources without a conclusive classification. We use the empirical cumulative distribution functions and the artificial neural networks for a fast method of screening and classification for BCUs based on data collected at γ-ray energies only, when rigorous multiwavelength analysis is not available. Based on our method, we classify 342 BCUs as BL Lacs and 154 as flat-spectrum radio quasars, while 77 objects remain uncertain. Moreover, radio analysis and direct observations in ground-based optical observatories are used as counterparts to the statistical classifications to validate the method. This approach is of interest because of the increasing number of unclassified sources in Fermi catalogues and because blazars and in particular their subclass high synchrotron peak objects are the main targets of atmospheric Cherenkov telescopes.

Synoptic observations of Jupiter's radio emissions: Average Statistical properties observed by Voyager

NASA Technical Reports Server (NTRS)

Alexander, J. K.; Carr, T. D.; Thieman, J. R.; Schauble, J. J.; Riddle, A. C.

1980-01-01

Observations of Jupiter's low frequency radio emissions collected over one month intervals before and after each Voyager encounter were analyzed. Compilations of occurrence probability, average power flux density and average sense of circular polarization are presented as a function of central meridian longitude, phase of Io, and frequency. The results are compared with ground based observations. The necessary geometrical conditions are preferred polarization sense for Io-related decametric emission observed by Voyager from above both the dayside and nightside hemispheres are found to be essentially the same as are observed in Earth based studies. On the other hand, there is a clear local time dependence in the Io-independent decametric emission. Io appears to have an influence on average flux density of the emission down to below 2 MHz. The average power flux density spectrum of Jupiter's emission has a broad peak near 9MHz. Integration of the average spectrum over all frequencies gives a total radiated power for an isotropic source of 4 x 10 to the 11th power W.

Radio and γ-ray follow-up of the exceptionally high-activity state of PKS 1510-089 in 2011

DOE PAGES

Orienti, M.; Koyama, S.; D'Ammando, F.; ...

2012-11-09

In this paper, we investigate the radio and γ-ray variability of the flat spectrum radio quasar PKS 1510-089 in the time range between 2010 November and 2012 January. In this period the source showed an intense activity, with two major γ-ray flares detected in 2011 July and October. During the latter episode both the γ-ray and the radio flux density reached their historical peak. Multiwavelength analysis shows a rotation of about 380° of the optical polarization angle close in time with the rapid and strong γ-ray flare in 2011 July. An enhancement of the optical emission and an increase ofmore » the fractional polarization both in the optical and in radio bands are observed about three weeks later, close in time with another γ-ray outburst. On the other hand, after 2011 September a huge radio outburst has been detected, first in the millimetre regime followed with some time delay at centimetre down to decimetre wavelengths. This radio flare is characterized by a rising and a decaying stage, in agreement with the formation of a shock and its evolution, as a consequence of expansion and radiative cooling. Lastly, if the γ-ray flare observed in 2011 October is related to this radio outburst, then this strongly indicates that the region responsible for the γ-ray variability is not within the broad line, but a few parsecs downstream along the jet.« less

Surprises from a Deep ASCA Spectrum of the Broad Absorption Line Quasar PHL 5200

NASA Technical Reports Server (NTRS)

Mathur, Smita; Matt, G.; Green, P. J.; Elvis, M.; Singh, K. P.

2002-01-01

We present a deep (approx. 85 ks) ASCA observation of the prototype broad absorption line quasar (BALQSO) PHL 5200. This is the best X-ray spectrum of a BALQSO yet. We find the following: (1) The source is not intrinsically X-ray weak. (2) The line-of-sight absorption is very strong, with N(sub H) = 5 x 10(exp 23)/sq cm. (3) The absorber does not cover the source completely; the covering fraction is approx. 90%. This is consistent with the large optical polarization observed in this source, implying multiple lines of sight. The most surprising result of this observation is that (4) the spectrum of this BALQSO is not exactly similar to other radio-quiet quasars. The hard X-ray spectrum of PHL 5200 is steep, with the power-law spectral index alpha approx. 1.5. This is similar to the steepest hard X-ray slopes observed so far. At low redshifts, such steep slopes are observed in narrow-line Seyfert 1 (NLS1) galaxies, believed to be accreting at a high Eddington rate. This observation strengthens the analogy between BALQSOs and NLS1 galaxies and supports the hypothesis that BALQSOs represent an early evolutionary state of quasars. It is well accepted that the orientation to the line of sight determines the appearance of a quasar: age seems to play a significant role as well.

Simultaneous Chandra X-ray, HST UV, and Ulysses Radio Observations of Jupiter's Aurora

NASA Technical Reports Server (NTRS)

R. Elsner; Bhardwaj, A.; Waite, H.; Lugaz, N.; Majeed, T.; Cravens, T.; Gladstone, G.; Ford, P.; Grodent, D.; MacDowell, R.

2004-01-01

Observations of Jupiter carried out by the Chandra ACIS-S instrument over 24-26 February, 2003, show that the auroral X-ray spectrum consists of line emission consistent with high-charge states of precipitating ions, and not a continuum as might be expected from remsstrahlung. The part of the spectrum due to oxygen peaks around 650 eV, which indicates a high fraction of fully-stripped oxygen in the precipitating ion flux. The OVIII emission lines at 653 eV and 774 eV, as well as the OVII emission lines at 561 eV and 666 eV, are clearly identified. There is also line emission at lower energies in the spectral region extending from 250 to 350 eV for which sulfur and carbon lines are possible candidates. The Jovian auroral spectra differ significantly from measured cometary X-ray spectra. The charge state distribution of the oxygen ion emission evident in the measured auroral spectra strongly suggests that, independent of the source of the energetic ions (magnetospheric or solar wind) the ions have undergone additional acceleration. For the magnetospheric case, acceleration to energies exceeding 10 MeV is apparently required. The ion acceleration also helps to explain the high intensities of the X-rays observed. The phase space densities of unaccelerated source populations of either solar wind or magnetospheric ions are orders of magnitude too small to explain the observed emissions. The Chandra X-ray observations were executed simultaneously with observations at ultraviolet wavelengths by the Hubble Space Telescope and at radio wavelengths by the Ulysses spacecraft. These additional data sets provide interesting hints as to the location of the source region and the acceleration characteristics of the generation mechanism. The combined observations suggest that the source of the X rays is magnetospheric in origin, and that strong field-aligned electric fields are present which simultaneously create both the several-MeV energetic ion population and the relativistic electrons believed to be responsible for the generation of approximately 40 minute quasi-periodic radio outbursts.

The Spectrum of the Universe.

PubMed

Hill, Ryley; Masui, Kiyoshi W; Scott, Douglas

2018-05-01

Cosmic background (CB) radiation, encompassing the sum of emission from all sources outside our own Milky Way galaxy across the entire electromagnetic spectrum, is a fundamental phenomenon in observational cosmology. Many experiments have been conceived to measure it (or its constituents) since the extragalactic Universe was first discovered; in addition to estimating the bulk (cosmic monopole) spectrum, directional variations have also been detected over a wide range of wavelengths. Here we gather the most recent of these measurements and discuss the current status of our understanding of the CB from radio to γ-ray energies. Using available data in the literature, we piece together the sky-averaged intensity spectrum and discuss the emission processes responsible for what is observed. We examine the effect of perturbations to the continuum spectrum from atomic and molecular line processes and comment on the detectability of these signals. We also discuss how one could, in principle, obtain a complete census of the CB by measuring the full spectrum of each spherical harmonic expansion coefficient. This set of spectra of multipole moments effectively encodes the entire statistical history of nuclear, atomic, and molecular processes in the Universe.

The Spectrum of the Universe

NASA Astrophysics Data System (ADS)

Hill, Ryley; Masui, Kiyoshi W.; Scott, Douglas

2018-05-01

The cosmic background (CB) radiation, encompassing the sum of emission from all sources outside our own Milky Way galaxy across the entire electromagnetic spectrum, is a fundamental phenomenon in observational cosmology. Many experiments have been conceived to measure it (or its constituents) since the extragalactic Universe was first discovered; in addition to estimating the bulk (cosmic monopole) spectrum, directional variations have also been detected over a wide range of wavelengths. Here we gather the most recent of these measurements and discuss the current status of our understanding of the CB from radio to $\\gamma$-ray energies. Using available data in the literature we piece together the sky-averaged intensity spectrum, and discuss the emission processes responsible for what is observed. We examine the effect of perturbations to the continuum spectrum from atomic and molecular line processes and comment on the detectability of these signals. We also discuss how one could in principle obtain a complete census of the CB by measuring the full spectrum of each spherical harmonic expansion coefficient. This set of spectra of multipole moments effectively encodes the entire statistical history of nuclear, atomic and molecular processes in the Universe.

Galactic plane gamma-radiation

NASA Technical Reports Server (NTRS)

Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Fichtel, C. E.; Ogelman, H. B.; Tumer, T.; Ozel, M. E.

1979-01-01

Analysis of the SAS 2 data together with the COS B results shows that the distribution of galactic gamma-radiation has several similarities to that of other large-scale tracers of galactic structure. The radiation is primarily confined to a thin disc which exhibits offsets from b = 0 degrees similar to warping at radio frequencies. The principal distinction of the gamma-radiation is a stronger contrast in intensity between the region from 310 to 45 degrees in longitude and the regions away from the center that can be attributed to a variation in cosmic-ray density as a function of position in Galaxy. The diffuse galactic gamma-ray energy spectrum shows no significant variation in direction, and the spectrum seen along the plane is the same as that for the galactic component of the gamma-radiation at high altitudes. The uniformity of the galactic gamma-ray spectrum, the smooth decrease in intensity as a function of altitude, and the absence of any galactic gamma-ray sources at high altitudes indicate a diffuse origin for bulk of the galactic gamma-radiation rather than a collection of localized sources.

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

NASA Astrophysics Data System (ADS)

Falcke, Heino; Moscibrodzka, Monika

2018-06-01

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

The EMBLA 2000 Mission in Hessdalen

NASA Astrophysics Data System (ADS)

Teodorani, M.; Montebugnoli, S.; Monari, J.

2000-11-01

In August 2000 a team of italian physical scientists, working in collaboration with norwegian colleagues from Østfold College, carried out an instrumental expedition in Hessdalen (Norway), which was just the first of a series of future scientific missions planned by the joint italian-norwegian EMBLA Project. The mission was aimed at studying unexplained anomalous atmospheric luminous phenomena occurring in the Hessdalen valley since about 20 years, and it was firstly devoted to the monitor of the radio spectrum in the UHF, VLF and ELF wavelength ranges, secondly to the study of the typology of luminous phenomena. This paper presents an ample introduction describing the analysis of the data acquired in the period 1998-2000 by means of the norwegian automatic videocamera of the Hessdalen Interactive Observatory: the hourly and monthly statistics of the luminous phenomenon and its spatial distribution over the celestial sphere are shown. The paper is then focussed into the results which were obtained with the employed radio spectrum analyzers of the EMBLA team, in particular the discovery of highly anomalous periodic signals of unknown origin which were caracterized by a spike-like and a Doppler-like morphology and which were mostly detected in the VLF radio range. It is shown that the Doppler shift, supposed to be due to a `particle-like' emitting source, ranges in a very short time from 10.000 up-to 100.000 km/sec with a frequency shift which is both red-wards and blue-wards, by changing periodically. Subsequently the physical interpretation is presented and discussed: (a) the occurrence of spike-like signals may be due to the pulsation of a radio-emitting source or alternatively to the rotation of a spheroidal source with a radio-emitting spot on its surface; (b) the very high measured velocities involved in the Doppler-like signals, together with the periodic inversion of the Doppler shift, are hypothesized to be due to a physical mechanism involving the magnetically collimated acceleration of high-energy particles modulated by the rotation of a self-contained `plasma spheroid' whose magnetic axis is misaligned in comparison with its rotation axis. Moreover, a detailed description of the luminous phenomena which were sighted during the many planned skywatching sessions, is presented, together with photo-analysis and point-spread functions of enhanced frames. Finally, a detailed plan for future optical observations and analysis is shown in the appendix, in which photometric and spectroscopic techniques by means of portable scout instrumentation are described.

Increased Gamma-ray Activity from the FSRQ PKS 1424-41

NASA Astrophysics Data System (ADS)

Ojha, Roopesh; Dutka, Michael

2012-10-01

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope has observed increased gamma-ray emission from a source positionally coincident with the flat spectrum radio quasar PKS 1424-41 (1424-418; 2FGL J1428.0-4206, Nolan et al. 2012, ApJS, 199, 31). PKS 1424-41 has the coordinates RA=14h27m56.3s, DEC= -42d06'19.4", J2000, (Johnston et al. 1995, AJ, 110, 880).

HESS and Fermi-LAT discovery of γ-rays from the blazar 1ES 1312-423

DOE PAGES

Abramowski, A.; Acero, F.; Aharonian, F.; ...

2013-08-01

In this study, a deep observation campaign carried out by the High Energy Stereoscopic System (HESS) on Centaurus A enabled the discovery of γ-rays from the blazar 1ES 1312-423, 2° away from the radio galaxy. With a differential flux at 1 TeV of (Φ1 TeV) = (1.9 ± 0.6stat ± 0.4sys) × 10 -13 cm -2 s -1 TeV -1 corresponding to 0.5 percent of the Crab nebula differential flux and a spectral index Γ = 2.9 ± 0.5stat ± 0.2sys, 1ES 1312-423 is one of the faintest sources ever detected in the very high energy (E > 100 GeV)more » extragalactic sky. A careful analysis using three and a half years of Fermi Large Area Telescope (Fermi-LAT) data allows the discovery at high energies (E > 100 MeV) of a hard spectrum (Γ = 1.4 ± 0.4stat ± 0.2sys) source coincident with 1ES 1312-423. Radio, optical, UV and X-ray observations complete the spectral energy distribution of this blazar, now covering 16 decades in energy. Lastly, the emission is successfully fitted with a synchrotron self-Compton model for the non-thermal component, combined with a blackbody spectrum for the optical emission from the host galaxy.« less

Sensivity studies for the Cherenkov Telescope Array

NASA Astrophysics Data System (ADS)

Collado, Tarek Hassan

2015-06-01

Since the creation of the first telescope in the 17th century, every major discovery in astrophysics has been the direct consequence of the development of novel observation techniques, opening new windows in the electromagnetic spectrum. After Karl Jansky discovered serendipitously the first radio source in 1933, Grote Reber built the first parabolic radio telescope in his backyard, planting the seed of a whole new field in astronomy. Similarly, new technologies in the 1950s allowed the establishment of other fields, such as the infrared, ultraviolet or the X-rays. The highest energy end of the electromagnetic spectrum, the γ-ray range, represents the last unexplored window for astronomers and should reveal the most extreme phenomena that take place in the Universe. Given the technical complexity of γ-ray detection and the extremely relative low fluxes, γ-ray astronomy has undergone a slower development compared to other wavelengths. Nowadays, the great success of consecutive space missions together with the development and refinement of new detection techniques from the ground, has allowed outstanding scientific results and has brought gamma-ray astronomy to a worthy level in par with other astronomy fields. This work is devoted to the study and improvement of the future Cherenkov Telescope Array (CTA), the next generation of ground based γ-ray detectors, designed to observe photons with the highest energies ever observed from cosmic sources.

Performance Evaluation of Relay Selection Schemes in Beacon-Assisted Dual-Hop Cognitive Radio Wireless Sensor Networks under Impact of Hardware Noises.

PubMed

Hieu, Tran Dinh; Duy, Tran Trung; Dung, Le The; Choi, Seong Gon

2018-06-05

To solve the problem of energy constraints and spectrum scarcity for cognitive radio wireless sensor networks (CR-WSNs), an underlay decode-and-forward relaying scheme is considered, where the energy constrained secondary source and relay nodes are capable of harvesting energy from a multi-antenna power beacon (PB) and using that harvested energy to forward the source information to the destination. Based on the time switching receiver architecture, three relaying protocols, namely, hybrid partial relay selection (H-PRS), conventional opportunistic relay selection (C-ORS), and best opportunistic relay selection (B-ORS) protocols are considered to enhance the end-to-end performance under the joint impact of maximal interference constraint and transceiver hardware impairments. For performance evaluation and comparison, we derive the exact and asymptotic closed-form expressions of outage probability (OP) and throughput (TP) to provide significant insights into the impact of our proposed protocols on the system performance over Rayleigh fading channel. Finally, simulation results validate the theoretical results.

Cognitive Radio Wireless Sensor Networks: Applications, Challenges and Research Trends

PubMed Central

Joshi, Gyanendra Prasad; Nam, Seung Yeob; Kim, Sung Won

2013-01-01

A cognitive radio wireless sensor network is one of the candidate areas where cognitive techniques can be used for opportunistic spectrum access. Research in this area is still in its infancy, but it is progressing rapidly. The aim of this study is to classify the existing literature of this fast emerging application area of cognitive radio wireless sensor networks, highlight the key research that has already been undertaken, and indicate open problems. This paper describes the advantages of cognitive radio wireless sensor networks, the difference between ad hoc cognitive radio networks, wireless sensor networks, and cognitive radio wireless sensor networks, potential application areas of cognitive radio wireless sensor networks, challenges and research trend in cognitive radio wireless sensor networks. The sensing schemes suited for cognitive radio wireless sensor networks scenarios are discussed with an emphasis on cooperation and spectrum access methods that ensure the availability of the required QoS. Finally, this paper lists several open research challenges aimed at drawing the attention of the readers toward the important issues that need to be addressed before the vision of completely autonomous cognitive radio wireless sensor networks can be realized. PMID:23974152

Reconciling CME Kinematics using Radio and White-light Observations from STEREO and SOHO

NASA Astrophysics Data System (ADS)

Gopalswamy, Nat; Yashiro, Seiji; Xie, Hong; Makela, Pertti; Akiyama, Sachiko; Reiner, Michael; MacDowall, Robert

2014-05-01

We study the characteristics of nonthermal radio emission associated with coronal mass ejections (CMEs) observed by STEREO, SOHO, and Wind spacecraft. In particular, we examine three backside CMEs associated with type II radio bursts at frequencies below 16 MHz. These bursts are known to be excellent indicators of solar energetic particle events. We use the universal drift rate spectrum of type II radio bursts and the inferred density scale heights in the corona and interplanetary medium o estimate the speed of the shock waves that produce the type II radio bursts. We find that the radio bursts can provide an accurate estimate of the CME speeds. We consider three backside events and a cannibalism event to show the usefulness of radio dynamic spectrum in inferring CME kinematics. We use radio direction finding technique to show that CME-CME interaction results in enhanced nonthermal radio emission. The radio data also provide constraints on the particle acceleration mechanisms and the reason for the energetic particles observed at wide-ranging longitudes. Finally we infer the shape and extent of the shock associated with one of the biggest solar energetic particle events in the space era.

Interplanetary plasma scintillation parameters measurements retrieved from the spacecraft observations.

NASA Astrophysics Data System (ADS)

Molera Calvés, Guifré; Pogrebenko, S. V.; Wagner, J.; Maccaferri, G.; Colucci, G.; Kronschnabl, G.; Scilliro, F.; Bianco, G.; Pérez Ayúcar, M.; Cosmovici, C. B.

2010-05-01

Measurement of the Interplanetary Scintillations (IPS) of radio signals propagating through the plasma in the Solar System by the radio astronomical instruments is a powerful tool to characterise and study the spatial and temporal variation of the electron density in the Solar wind. Several techniques based on the observation of natural and artificial radio sources have been developed during the last 50 years. Here we report our results of the IPS parameters measurement based on the multi-station observations of the planetary mission spacecraft. The ESA Venus Express spacecraft was observed at X-band (8.4 GHz) by several European VLBI stations - Metsähovi Radio Observatory (Aalto University , FI), Medicina (INAF-RA, IT), Matera (ASI, IT), Wettzell (BKG, DE), Noto (INAF-IRA, IT) and Yebes (OAN-IGN, ES) during a 2008-2010 campaign in a framework of the PRIDE (Planetary Radio Interferometry and Doppler Experiments) project as a preparatory stage for the European Radio Astronomy VLBI facilities participation in the planned ESA planetary missions (EJSM, TESM, EVE and others). Observational data were processed at Metsähovi Radio Observatory with the on-purpose developed high performance, ultra-high spectral resolution and spacecraft tracking capable software spectrometer-correlator and analysed at the Joint Institute for VLBI in Europe (JIVE, NL). High quality of acquired and analysed data enables us to study and define several parameters of the S/C signal and accompanying "ranging" tones with milli-Hz accuracy, among which the phase fluctuations of the spacecraft signal carrier line can be used to characterise the interplanetary plasma density fluctuations along the signal propagation line at different spatial and temporal scales at different Solar elongations and which exhibits a near-Kolmogorov spectrum. Such essential parameters as the phase scintillation index and bandwidth of scintillations and their dependence on the solar elongation, distance to the target, positions of the source in the Solar system and Solar activity index were retrieved from our measurements and are reported. This study is focused on the technique of the measurements and data analysis, leaving the physical interpretation of the measurement results to the upcoming studies when more observational data is collected. Our measurements of the phase scintillations from the sources within the Solar system are complementary to the classical measurements of the power level scintillations of signals from the natural radio sources. The results presented in this paper are promising and observations will continue during 2010.

Performance evaluation of cognitive radio in advanced metering infrastructure communication

NASA Astrophysics Data System (ADS)

Hiew, Yik-Kuan; Mohd Aripin, Norazizah; Din, Norashidah Md

2016-03-01

Smart grid is an intelligent electricity grid system. A reliable two-way communication system is required to transmit both critical and non-critical smart grid data. However, it is difficult to locate a huge chunk of dedicated spectrum for smart grid communications. Hence, cognitive radio based communication is applied. Cognitive radio allows smart grid users to access licensed spectrums opportunistically with the constraint of not causing harmful interference to licensed users. In this paper, a cognitive radio based smart grid communication framework is proposed. Smart grid framework consists of Home Area Network (HAN) and Advanced Metering Infrastructure (AMI), while AMI is made up of Neighborhood Area Network (NAN) and Wide Area Network (WAN). In this paper, the authors only report the findings for AMI communication. AMI is smart grid domain that comprises smart meters, data aggregator unit, and billing center. Meter data are collected by smart meters and transmitted to data aggregator unit by using cognitive 802.11 technique; data aggregator unit then relays the data to billing center using cognitive WiMAX and TV white space. The performance of cognitive radio in AMI communication is investigated using Network Simulator 2. Simulation results show that cognitive radio improves the latency and throughput performances of AMI. Besides, cognitive radio also improves spectrum utilization efficiency of WiMAX band from 5.92% to 9.24% and duty cycle of TV band from 6.6% to 10.77%.

THE UNUSUAL RADIO AFTERGLOW OF THE ULTRA-LONG GAMMA-RAY BURST GRB 130925A

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

Horesh, Assaf; Cenko, S. Bradley; Perley, Daniel A.

2015-10-10

GRB 130925A is one of the recent additions to the growing family of ultra-long gamma-ray bursts (GRBs; T90 ≳1000 s). While the X-ray emission of ultra-long GRBs have been studied extensively in the past, no comprehensive radio data set has been obtained so far. We report here the early discovery of an unusual radio afterglow associated with the ultra-long GRB 130925A. The radio emission peaks at low-frequencies (∼7 GHz) at early times, only 2.2 days after the burst occurred. More notably, the radio spectrum at frequencies above 10 GHz exhibits a rather steep cut-off, compared to other long GRB radiomore » afterglows. This cut-off can be explained if the emitting electrons are either mono-energetic or originate from a rather steep, dN/dE ∝ E{sup −4}, power-law energy distribution. An alternative electron acceleration mechanism may be required to produce such an electron energy distribution. Furthermore, the radio spectrum exhibits a secondary underlying and slowly varying component. This may hint that the radio emission we observed is comprised of emission from both a reverse and a forward shock. We discuss our results in comparison with previous works that studied the unusual X-ray spectrum of this event and discuss the implications of our findings on progenitor scenarios.« less

Solar Rotation Stereoscopy in Microwaves

NASA Astrophysics Data System (ADS)

Aschwanden, Markus J.; Lim, Jeremy; Gary, Dale E.; Klimchuk, James A.

1995-11-01

We present here the first stereoscopic altitude measurements of active region sources observed at microwave frequencies (10-14 GHz The active region NOAA 7128 was observed with the Owens Valley Radio Observatory (OVRO) on 1992 April 13, 14, 15, and 16 as it passed through the central meridian. From white-light data of the underlying sunspot we determined the rotation rate of the active region, which was found to have a relative motion of dL/dt = +0°.240 day-1 with respect to the standard photospheric differential rotation rate. Based on this rotation rate we determine for the microwave sources stereoscopic altitudes of 3.3-11.0 Mm above the photosphere. The altitude spectrum h(v) of the right circular polarization (RCP) main source shows a discontinuity at 12 GHz and can be satisfactorily fitted with a dipole model with a transition from the second to the third harmonic level at 12 GHz. The dominance of the third harmonic for frequencies above 12 GHz occurs because the second harmonic level drops below the transition region, at a height of 2.6±0.6 Mm according to the microwave data. The altitude spectrum h(v) serves also to invert the temperature profile T(h) from the optically thick parts of the radio brightness temperature spectrum TB(ν[h]). The microwave emission in both circular polarizations can be modeled with gyroresonance emission, with x-mode for RCP and o-mode in LCP, with the same harmonics at each frequency, but different emission angles in both modes. The contributions from free-free emission are negligible in both polarizations, based on the peak emission measure of EM ≍ 6 × 1028 cm-5 observed in soft X-rays by Yohkoh/SXT. This study demonstrates that the height dependence of the coronal magnetic field B(h) and the plasma temperature T(h) in an active region can be inverted from the stereoscopic altitude spectra h(v) and the observed brightness temperature spectra TB(ν).

NuSTAR and XMM-Newton Observations of the Hard X- Ray Spectrum of Centaurus A

NASA Technical Reports Server (NTRS)

Furst, F.; Muller, C.; Madsen, K. K.; Lanz, L.; Rivers, E.; Brightman, M.; Arevalo, P.; Balokovic, M.; Beuchert, T.; Zhang, W.

2016-01-01

We present simultaneous XMM-Newton and Nuclear Spectroscopic Telescope Array (NuSTAR) observations spanning 3-78 keV of the nearest radio galaxy, Centaurus A (Cen A). The accretion geometry around the central engine in Cen A is still debated, and we investigate possible configurations using detailed X-ray spectral modeling. NuSTAR imaged the central region of Cen A with subarcminute resolution at X-ray energies above 10 keV for the first time, but found no evidence for an extended source or other off-nuclear point sources. The XMM-Newton and NuSTAR spectra agree well and can be described with an absorbed power law with a photon index Gamma = 1.8150 +/- 0.005 and a fluorescent Fe Kaline in good agreement with literature values. The spectrum is greater than 1 MeV. A thermal Comptonization continuum describes the data well, with parameters that agree with values measured by INTEGRAL, in particular an electron temperature kTe between approximately 100-300 keV and seed photon input temperatures between 5 and 50 eV. We do not find evidence for reflection or a broad iron line and put stringent upper limits of R is less than 0.01 on the reflection fraction and accretion disk illumination. We use archival Chandra data to estimate the contribution from diffuse emission, extra-nuclear point sources, and the outer X-ray jet to the observed NuSTAR and XMM-Newton X-ray spectra and find the contribution to be negligible. We discuss different scenarios for the physical origin of the observed hard X-ray spectrum and conclude that the inner disk is replaced by an advection-dominated accretion flow or that the X-rays are dominated by synchrotron self-Compton emission from the inner regions of the radio jet or a combination thereof.

Recombining Plasma and Gamma-Ray Emission in the Mixed-morphology Supernova Remnant 3C 400.2

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

Ergin, T.; Sezer, A.; Sano, H.

3C 400.2 belongs to the mixed-morphology supernova remnant class, showing center-filled X-ray and shell-like radio morphology. We present a study of 3C 400.2 with archival Suzaku and Fermi -LAT observations. We find recombining plasma (RP) in the Suzaku spectra of north–east and south–east regions. The spectra of these regions are well described by two-component thermal plasma models: the hard component is in RP, while the soft component is in collisional ionization equilibrium (CIE) conditions. The RP has enhanced abundances, indicating that the X-ray emission has an ejecta origin, while the CIE has solar abundances associated with the interstellar material. Themore » X-ray spectra of north–west and south–west regions are best fitted by a two-component thermal plasma model: an ionizing and a CIE plasma. We have detected GeV gamma-ray emission from 3C 400.2 at the level of ∼5 σ , assuming a point-like source model with a power-law (PL) type spectrum. We have also detected a new GeV source at the level of ∼13 σ, assuming a Gaussian extension model with a PL-type spectrum in the neighborhood of the supernova remnant. We report the analysis results of 3C 400.2 and the new extended gamma-ray source, and discuss the nature of gamma-ray emission of 3C 400.2 in the context of existing NANTEN CO data, Dominion Radio Astrophysical Observatory H i data, and the Suzaku X-ray analysis results.« 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

Automated isotope identification algorithm using artificial neural networks

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

Kamuda, Mark; Stinnett, Jacob; Sullivan, Clair

There is a need to develop an algorithm that can determine the relative activities of radio-isotopes in a large dataset of low-resolution gamma-ray spectra that contains a mixture of many radio-isotopes. Low-resolution gamma-ray spectra that contain mixtures of radio-isotopes often exhibit feature over-lap, requiring algorithms that can analyze these features when overlap occurs. While machine learning and pattern recognition algorithms have shown promise for the problem of radio-isotope identification, their ability to identify and quantify mixtures of radio-isotopes has not been studied. Because machine learning algorithms use abstract features of the spectrum, such as the shape of overlapping peaks andmore » Compton continuum, they are a natural choice for analyzing radio-isotope mixtures. An artificial neural network (ANN) has be trained to calculate the relative activities of 32 radio-isotopes in a spectrum. Furthermore, the ANN is trained with simulated gamma-ray spectra, allowing easy expansion of the library of target radio-isotopes. In this paper we present our initial algorithms based on an ANN and evaluate them against a series measured and simulated spectra.« less

Automated isotope identification algorithm using artificial neural networks

DOE PAGES

Kamuda, Mark; Stinnett, Jacob; Sullivan, Clair

2017-04-12

There is a need to develop an algorithm that can determine the relative activities of radio-isotopes in a large dataset of low-resolution gamma-ray spectra that contains a mixture of many radio-isotopes. Low-resolution gamma-ray spectra that contain mixtures of radio-isotopes often exhibit feature over-lap, requiring algorithms that can analyze these features when overlap occurs. While machine learning and pattern recognition algorithms have shown promise for the problem of radio-isotope identification, their ability to identify and quantify mixtures of radio-isotopes has not been studied. Because machine learning algorithms use abstract features of the spectrum, such as the shape of overlapping peaks andmore » Compton continuum, they are a natural choice for analyzing radio-isotope mixtures. An artificial neural network (ANN) has be trained to calculate the relative activities of 32 radio-isotopes in a spectrum. Furthermore, the ANN is trained with simulated gamma-ray spectra, allowing easy expansion of the library of target radio-isotopes. In this paper we present our initial algorithms based on an ANN and evaluate them against a series measured and simulated spectra.« less

The Serendip II design. [narrowband astronautical radio signal search for extraterrestrial intelligence

NASA Technical Reports Server (NTRS)

Werthimer, D.; Tarter, J.; Bowyer, S.

1985-01-01

Serendip II is an automated system designed to perform a real time search for narrow band radio signals in the spectra of sources in a regularly scheduled, non-Seti, astronomical observing program. Because Serendip II is expected to run continuously without requiring dedicated observing time, it is hoped that a large portion of the sky will be surveyed at high sensitivity and low cost. Serendip II will compute the power spectrum using a 65,536 channel fast Fourier transform processor with a real time bandwidth of 128 KHz and 2 Hz per channel resolution. After searching for peaks in a 100 KHz portion of the radio telescope's IF band, Serendip II will move to the next 100 KHz portion using a programmable frequency synthesizer; when the whole IF band has been scanned, the process will start again. Unidentified peaks in the power spectra are candidates for further study and their celestial coordinates will be recorded along with the time and power, IF and RF frequency, and bandwidth of the peak.

Bayesian analysis of X-ray jet features of the high redshift quasar jets observed with Chandra

NASA Astrophysics Data System (ADS)

McKeough, Kathryn; Siemiginowska, Aneta; Kashyap, Vinay; Stein, Nathan; Cheung, Chi C.

2015-01-01

X-ray emission of powerful quasar jets may be a result of the inverse Compton (IC) process in which the Cosmic Microwave Background (CMB) photons gain energy by interactions with the jet's relativistic electrons. However, there is no definite evidence that IC/CMB process is responsible for the observed X-ray emission of large scale jets. A step toward understanding the X-ray emission process is to study the Radio and X-ray morphologies of the jet. Results from Chandra X-ray and multi-frequency VLA imaging observations of a sample of 11 high- redshift (z > 2) quasars with kilo-parsec scale radio jets are reported. The sample consists of a set of four z ≥ 3.6 flat-spectrum radio quasars, and seven intermediate redshift (z = 2.1 - 2.9) quasars comprised of four sources with integrated steep radio spectra and three with flat radio spectra.We implement a Bayesian image analysis program, Low-count Image Reconstruction and Analysis (LIRA) , to analyze jet features in the X-ray images of the high redshift quasars. Out of the 36 regions where knots are visible in the radio jets, nine showed detectable X-ray emission. Significant detections are based on the upper bound p-value test based on LIRA simulations. The X-ray and radio properties of this sample combined are examined and compared to lower-redshift samples.This work is supported in part by the National Science Foundation REU and the Department of Defense ASSURE programs under NSF Grant no.1262851 and by the Smithsonian Institution, and by NASA Contract NAS8-39073 to the Chandra X-ray Center (CXC). This research has made use of data obtained from the Chandra Data Archive and Chandra Source Catalog, and software provided by the CXC in the application packages CIAO, ChIPS, and Sherpa. Work is also supported by the Chandra grant GO4-15099X.

VLSI Technology for Cognitive Radio

NASA Astrophysics Data System (ADS)

VIJAYALAKSHMI, B.; SIDDAIAH, P.

2017-08-01

One of the most challenging tasks of cognitive radio is the efficiency in the spectrum sensing scheme to overcome the spectrum scarcity problem. The popular and widely used spectrum sensing technique is the energy detection scheme as it is very simple and doesn’t require any previous information related to the signal. We propose one such approach which is an optimised spectrum sensing scheme with reduced filter structure. The optimisation is done in terms of area and power performance of the spectrum. The simulations of the VLSI structure of the optimised flexible spectrum is done using verilog coding by using the XILINX ISE software. Our method produces performance with 13% reduction in area and 66% reduction in power consumption in comparison to the flexible spectrum sensing scheme. All the results are tabulated and comparisons are made. A new scheme for optimised and effective spectrum sensing opens up with our model.

Cognitive Radio Cloud Networks: Assured Access In The Future Electromagnetic Operating Environment

DTIC Science & Technology

2017-04-04

AIR COMMAND AND STAFF COLLEGE AIR UNIVERSITY COGNITIVE RADIO CLOUD NETWORKS: ASSURED ACCESS IN THE FUTURE ELECTROMAGNETIC OPERATING...3 Abstract The electromagnetic spectrum is a finite resource that is critical to the United States military’s...ability to gain superiority in the other five warfighting domains. The Department of Defense’s electromagnetic strategy is spectrum access when and

GLAST Large Area Telescope Multiwavelength Planning

NASA Technical Reports Server (NTRS)

Thompson, D. J.; Cameron, R. A.; Digel, S. W.; Wood, K. S.

2006-01-01

Because gamma-ray astrophysics depends in many ways on multiwavelength studies, the GLAST Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority needs include: (1) radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-spectrum blazar flare measurements; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for unidentified gamma-ray sources. Work on the first three of these activities is needed before launch. The GLAST Large Area Telescope is an international effort, with U.S. funding provided by the Department of Energy and NASA.

RF Spectrum Sensing Based on an Overdamped Nonlinear Oscillator Ring for Cognitive Radios.

PubMed

Tang, Zhi-Ling; Li, Si-Min; Yu, Li-Juan

2016-06-09

Existing spectrum-sensing techniques for cognitive radios require an analog-to-digital converter (ADC) to work at high dynamic range and a high sampling rate, resulting in high cost. Therefore, in this paper, a spectrum-sensing method based on a unidirectionally coupled, overdamped nonlinear oscillator ring is proposed. First, the numerical model of such a system is established based on the circuit of the nonlinear oscillator. Through numerical analysis of the model, the critical condition of the system's starting oscillation is determined, and the simulation results of the system's response to Gaussian white noise and periodic signal are presented. The results show that once the radio signal is input into the system, it starts oscillating when in the critical region, and the oscillating frequency of each element is fo/N, where fo is the frequency of the radio signal and N is the number of elements in the ring. The oscillation indicates that the spectrum resources at fo are occupied. At the same time, the sampling rate required for an ADC is reduced to the original value, 1/N. A prototypical circuit to verify the functionality of the system is designed, and the sensing bandwidth of the system is measured.

Fermi LAT detection of a gamma-ray flare from FSRQ S5 1044+71

NASA Astrophysics Data System (ADS)

Ojha, Roopesh; Carpenter, Bryce; Dutka, Michael

2013-04-01

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar S5 1044+71 (also known as 2FGL J1048.3+7144, Nolan et al. 2012, ApJS, 199, 31). Localization analysis has ruled out the nearby source 2FGL J1049.7+7240 as a possible counterpart. S5 1044+71 has coordinates RA=10h48m27.6199s DEC=+71d43m35.938s, J2000, (Johnston et al.

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.

Optical-NIR spectroscopy of the puzzling γ-ray source 3FGL 1603.9-4903/PMN J1603-4904 with X-Shooter

NASA Astrophysics Data System (ADS)

Goldoni, P.; Pita, S.; Boisson, C.; Müller, C.; Dauser, T.; Jung, I.; Krauß, F.; Lenain, J.-P.; Sol, H.

2016-02-01

Context. The Fermi/LAT instrument has detected about two thousand extragalactic high energy (E ≥ 100 MeV) γ-ray sources. One of the brightest is 3FGL J1603.9-4903; it is associated to the radio source PMN J1603-4904. Its nature is not yet clear, it could be either a very peculiar BL Lac or a compact symmetric object radio source which are considered as the early stage of a radio galaxy. The latter, if confirmed, would be the first detection in γ-rays for this class of objects. A redshift z = 0.18 ± 0.01 has recently been claimed on the basis of the detection of a single X-ray line at 5.44 ± 0.05 keV which has been interpreted as a 6.4 keV (rest frame) fluorescent line. Aims: We aim to investigate the nature of 3FGL J1603.9-4903/PMN J1603-4904 using optical-to near-IR (NIR) spectroscopy. Methods: We observed PMN J1603-4904 with the UV-NIR VLT/X-Shooter spectrograph for two hours. We extracted spectra in the visible and NIR range that we calibrated in flux and corrected for telluric absorption. We systematically searched for absorption and emission features. Results: The source was detected starting from ~6300 Å down to 24 000 Å with an intensity similar to that of its 2MASS counterpart and a mostly featureless spectrum. The continuum lacks absorption features and thus is non-stellar in origin and most likely non-thermal. In addition to this spectrum, we detected three emission lines that we interpret as the Hα-[NII] complex, the [SII]λ,λ6716, 6731 doublet and the [SIII]λ 9530 line; we obtain a redshift estimate of z = 0.2321 ± 0.0004. The line ratios suggest that a LINER/Seyfert nucleus powers the emission. This new redshift measurement implies that the X-ray line previously detected should be interpreted as a 6.7 keV line which is very peculiar. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under program 095.B-0400(A). The raw FITS data files are available in the ESO archive.

Physics of compact nonthermal sources. III - Energetic considerations. [electron synchrotron radiation

NASA Technical Reports Server (NTRS)

Burbidge, G. R.; Jones, T. W.; Odell, S. L.

1974-01-01

The energy content of the compact incoherent electron-synchrotron sources 3C 84, 3C 120, 3C 273, 3C 279, 3C 454.3, CTA 102, 3C 446, PKS 2134+004, VRO 42.22.01 and OJ 287 is calculated on the assumption that the low-frequency turnovers in the radio spectrum are due to self-absorption and that the electron distribution is isotropic. The dependence of the source parameters on various modifications of the standard assumptions is determined. These involve relativistic motions, alternate explanations for the low-frequency turnover, proton-synchrotron radiation, and distance to the source. The canonical interpretation is found to be accurate in many respects; some of the difficulties and ways of dealing with them are discussed in detail.

Spectrum sharing in cognitive radio networks--an auction-based approach.

PubMed

Wang, Xinbing; Li, Zheng; Xu, Pengchao; Xu, Youyun; Gao, Xinbo; Chen, Hsiao-Hwa

2010-06-01

Cognitive radio is emerging as a promising technique to improve the utilization of the radio frequency spectrum. In this paper, we consider the problem of spectrum sharing among primary (or "licensed") users (PUs) and secondary (or "unlicensed") users (SUs). We formulate the problem based on bandwidth auction, in which each SU makes a bid for the amount of spectrum and each PU may assign the spectrum among the SUs by itself according to the information from the SUs without degrading its own performance. We show that the auction is a noncooperative game and that Nash equilibrium (NE) can be its solution. We first consider a single-PU network to investigate the existence and uniqueness of the NE and further discuss the fairness among the SUs under given conditions. Then, we present a dynamic updating algorithm in which each SU achieves NE in a distributed manner. The stability condition of the dynamic behavior for this spectrum-sharing scheme is studied. The discussion is generalized to the case in which there are multiple PUs in the network, where the properties of the NE are shown under appropriate conditions. Simulations were used to evaluate the system performance and verify the effectiveness of the proposed algorithm.

Performance analysis of multi-radio routing protocol in cognitive radio ad hoc networks under different path failure rate

NASA Astrophysics Data System (ADS)

Che-Aron, Z.; Abdalla, A. H.; Abdullah, K.; Hassan, W. H.

2013-12-01

In recent years, Cognitive Radio (CR) technology has largely attracted significant studies and research. Cognitive Radio Ad Hoc Network (CRAHN) is an emerging self-organized, multi-hop, wireless network which allows unlicensed users to opportunistically access available licensed spectrum bands for data communication under an intelligent and cautious manner. However, in CRAHNs, a lot of failures can easily occur during data transmission caused by PU (Primary User) activity, topology change, node fault, or link degradation. In this paper, an attempt has been made to evaluate the performance of the Multi-Radio Link-Quality Source Routing (MR-LQSR) protocol in CRAHNs under different path failure rate. In the MR-LQSR protocol, the Weighted Cumulative Expected Transmission Time (WCETT) is used as the routing metric. The simulations are carried out using the NS-2 simulator. The protocol performance is evaluated with respect to performance metrics like average throughput, packet loss, average end-to-end delay and average jitter. From the simulation results, it is observed that the number of path failures depends on the PUs number and mobility rate of SUs (Secondary Users). Moreover, the protocol performance is greatly affected when the path failure rate is high, leading to major service outages.

Stochastic Particle Acceleration in the Hot Spots of FRII Radio Galaxies

NASA Astrophysics Data System (ADS)

Liu, Siming; Fan, Z.; Wang, J.; Fryer, C. L.; Li, H.

2007-12-01

Chandra, XMM-Newton, and HST observations of FRII radio galaxies, in combination with traditional radio studies, have advanced our understanding of the nature of jets, hot spots, and lobes significantly. The observed radio to optical emission has been attributed to the synchrotron processes. The X-ray emission can be produced through synchrotron, synchrotron self-Comptonization, and inverse Comptonization of the CMB or other background photos. Phenomenologically modelings of the observed broadband spectra have led to good constraints on the magnetic field and electron distribution. However, the matter and energy contents of the relativistic outflows driven by the central black holes, which power these sources, are still not well-constrained, and we also lack an understanding of the physical processes that determine the energy partition between the electrons and the magnetic field, the low energy cutoff of the electron spectrum, and the electron acceleration rate in these strongly magnetized relativistic plasmas. In the context of stochastic particle acceleration, we propose a model for the hot spots of radio galaxies and show how it may help us to address the above issues. This work was funded in part under the auspices of the US Department of Energy, and supported by its contract W-7405-ENG-36 to Los Alamos National Laboratory.

THE {gamma}-RAY EMISSION REGION IN THE FANAROFF-RILEY II RADIO GALAXY 3C 111

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

Grandi, P.; Torresi, E.; Stanghellini, C., E-mail: grandi@iasfbo.inaf.it, E-mail: torresi@iasfbo.inaf.it, E-mail: cstan@ira.inaf.it

The broad-line radio galaxy 3C 111, characterized by a Fanaroff-Riley II (FRII) radio morphology, is one of the sources of the misaligned active galactic nucleus sample, consisting of radio galaxies and steep spectrum radio quasars, recently detected by the Fermi Large Area Telescope (LAT). Our analysis of the 24 month {gamma}-ray light curve shows that 3C 111 was only occasionally detected at high energies. It was bright at the end of 2008 and faint, below the Fermi-LAT sensitivity threshold, for the rest of the time. A multifrequency campaign of 3C 111, ongoing in the same period, revealed an increase ofmore » the millimeter, optical, and X-ray fluxes in 2008 September-November, interpreted by Chatterjee et al. as due to the passage of a superluminal knot through the jet core. The temporal coincidence of the millimeter-optical-X-ray outburst with the GeV activity suggests a cospatiality of the events, allowing, for the first time, the localization of the {gamma}-ray dissipative zone in an FRII jet. We argue that the GeV photons of 3C 111 are produced in a compact region confined within 0.1 pc and at a distance of about 0.3 pc from the black hole.« less

The ``X component'' of the radio background

NASA Astrophysics Data System (ADS)

Semenova, T. A.; Pariiskii, Yu. N.; Bursov, N. N.

2009-01-01

The recent publication of evidence for a new mechanism producing background radio emission of the Galaxy at centimeter wavelengths (in addition to synchrotron radiation, free—free transitions in ionized gas, and the weak radio emission of standard dust) gave rise to a strong reaction among observers, and requires independent experimental verification. This signal is of special concern in connection with studies of the polarization of the cosmic microwave background (CMB) using new-generation experiments. We have derived independent estimates of the validity of the “spinning-dust” hypothesis (dipole emission of macromolecules) using multi-frequency RATAN-600 observations. Test studies in the Perseus molecular cloud show evidence for anomalous extended emission in the absence of strong radio sources (compact HII regions) that could imitate an anomalous radio spectrum in this region. A statistical analysis at centimeter wavelengths over the Ratan Zenith Field shows that the upper limit for the polarized noise from this new component in the spinning-dust hypothesis is unlikely to exceed 1 µK at wavelengths of 1 cm or shorter on the main scales of the EE mode of Sakharov oscillations. Thus, this emission should not hinder studies of this mode, at least to within several percent of the predicted level of polarization of the CMB emission.

Characterizing X-Ray and Radio Emission in the Black Hole X-Ray Binary V404 Cygni During Quiescence

NASA Technical Reports Server (NTRS)

Rana, Vikram; Loh, Alan; Corbel, Stephane; Tomsick, John A.; Chakrabarty, Deepto; Walton, Dominic J.; Barret, Didier; Boggs, Steven E.; Christensen, Finn E.; Craig, William;

Swift detection of increased X-ray activity from gamma-ray flaring blazar PKS 1424-41

NASA Astrophysics Data System (ADS)

Ciprini, Stefano; Cutini, Sara

2013-01-01

Following enduring gamma-ray flaring activity of the flat spectrum radio quasar PKS 1424-41 (also known as 2FGL J1428.0-4206, Nolan et al. 2012, ApJS, 199, 31) detected by Fermi LAT during January 2013, two Swift target of opportunity observations were performed on January 24 and 27, 2013. Recent gamma-ray and X-ray flaring activity from the source was observed on January 6 and January 7 (ATel#4714 and ATel #4717).

Fermi LAT detection of increased gamma-ray activity from the blazar TXS 1318+225

NASA Astrophysics Data System (ADS)

Torresi, E.; D'Ammando, F.; Tanaka, Y.

2012-11-01

The Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope, has observed an increase in the gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar TXS 1318+225 (z=0.943, Sowards-Emmerd et al. 2003, ApJ, 590, 109; RA=200.2966771 deg, Dec=22.2700300 deg, J2000), also known as 2FGL J1321.1+2215 (Nolan et al. 2012, ApJS, 199, 31).

Hard Fusion Based Spectrum Sensing over Mobile Fading Channels in Cognitive Vehicular Networks

PubMed Central

Hao, Li; Ni, Dadong; Tran, Quang Thanh

2018-01-01

An explosive growth in vehicular wireless applications gives rise to spectrum resource starvation. Cognitive radio has been used in vehicular networks to mitigate the impending spectrum starvation problem by allowing vehicles to fully exploit spectrum opportunities unoccupied by licensed users. Efficient and effective detection of licensed user is a critical issue to realize cognitive radio applications. However, spectrum sensing in vehicular environments is a very challenging task due to vehicle mobility. For instance, vehicle mobility has a large effect on the wireless channel, thereby impacting the detection performance of spectrum sensing. Thus, gargantuan efforts have been made in order to analyze the fading properties of mobile radio channel in vehicular environments. Indeed, numerous studies have demonstrated that the wireless channel in vehicular environments can be characterized by a temporally correlated Rayleigh fading. In this paper, we focus on energy detection for spectrum sensing and a counting rule for cooperative sensing based on Neyman-Pearson criteria. Further, we go into the effect of the sensing and reporting channel conditions on the sensing performance under the temporally correlated Rayleigh channel. For local and cooperative sensing, we derive some alternative expressions for the average probability of misdetection. The pertinent numerical and simulating results are provided to further validate our theoretical analyses under a variety of scenarios. PMID:29415452

Interpretation of the Arcade 2 Absolute Sky Brightness Measurement

NASA Technical Reports Server (NTRS)

Seiffert, M.; Fixsen, D. J.; Kogut, A.; Levin, S. M.; Limon, M.; Lubin, P. M.; Mirel, P.; Singal, J.; Villela, T.; Wollack, E.;

Galactic synchrotron radiation from radio to microwaves, and its relation to cosmic-ray propagation models: past, present and future

NASA Astrophysics Data System (ADS)

Orlando, Elena

2016-04-01

Galactic synchrotron radiation observed from radio to microwaves is produced by cosmic-ray (CR) electrons propagating in magnetic fields (B-fields). The low-frequency foreground component separated maps by WMAP and Planck depend on the assumed synchrotron spectrum. The synchrotron spectrum varies for different line of sights as a result of changes on the CR spectrum due to propagation effects and source distributions. Our present knowledge of the CR spectrum at different locations in the Galaxy is not sufficient to distinguish various possibilities in the modeling. As a consequence uncertainties on synchrotron emission models complicate the foreground component separation analysis with Planck and future microwave telescopes. Hence, any advancement in synchrotron modeling is important for separating the different foreground components.The first step towards a more comprehensive understanding of degeneracy and correlation among the synchrotron model parameters is outlined in our Strong et al. 2011 and Orlando et al. 2013 papers. In the latter the conclusion was that CR spectrum, propagation models, B-fields, and foreground component separation analysis need to be studied simultaneously in order to properly obtain and interpret the synchrotron foreground. Indeed for the officially released Planck maps, we use only the best spectral model from our above paper for the component separation analysis.Here we present a collections of our latest results on synchrotron, CRs and B-fields in the context of CR propagation, showing also our recent work on B-fields within the Planck Collaboration. We underline also the importance of using the constraints on CRs that we obtain from gamma ray observations. Methods and perspectives for further studies on the synchrotron foreground will be addressed.

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

Murray, S. G.; Trott, C. M.; Jordan, C. H.

We present a sophisticated statistical point-source foreground model for low-frequency radio Epoch of Reionization (EoR) experiments using the 21 cm neutral hydrogen emission line. Motivated by our understanding of the low-frequency radio sky, we enhance the realism of two model components compared with existing models: the source count distributions as a function of flux density and spatial position (source clustering), extending current formalisms for the foreground covariance of 2D power-spectral modes in 21 cm EoR experiments. The former we generalize to an arbitrarily broken power law, and the latter to an arbitrary isotropically correlated field. This paper presents expressions formore » the modified covariance under these extensions, and shows that for a more realistic source spatial distribution, extra covariance arises in the EoR window that was previously unaccounted for. Failure to include this contribution can yield bias in the final power-spectrum and under-estimate uncertainties, potentially leading to a false detection of signal. The extent of this effect is uncertain, owing to ignorance of physical model parameters, but we show that it is dependent on the relative abundance of faint sources, to the effect that our extension will become more important for future deep surveys. Finally, we show that under some parameter choices, ignoring source clustering can lead to false detections on large scales, due to both the induced bias and an artificial reduction in the estimated measurement uncertainty.« less

Fast radio bursts and the stochastic lifetime of black holes in quantum gravity

NASA Astrophysics Data System (ADS)

Barrau, Aurélien; Moulin, Flora; Martineau, Killian

2018-03-01

Nonperturbative quantum gravity effects might allow a black-to-white hole transition. We revisit this increasingly popular hypothesis by taking into account the fundamentally random nature of the bouncing time. We show that if the primordial mass spectrum of black holes is highly peaked, the expected signal can in fact match the wavelength of the observed fast radio bursts. On the other hand, if the primordial mass spectrum is wide and smooth, clear predictions are suggested and the sensitivity to the shape of the spectrum is studied.

Extraction and Use of Noise Models from Production-Mode Transient Electromagnetic Data

NASA Astrophysics Data System (ADS)

Rasmussen, S.; Nyboe, N. S.; Larsen, J. J.

2016-12-01

In the interpretation of data acquired using the Transient Electromagnetic Method (TEM), noise in the measurements from external sources, such as the power grid, spherics and radio transmitters and from internal sources in the TEM system itself is unavoidable. This noise lowers the data quality, and it is therefore desirable to know the noise conditions.Typically, the noise spectrum is measured one or more times during a survey with the transmitter turned off, i.e. with no TEM signal present.In production-mode, when the pulses of alternating signs are continually transmitted, the TEM signal contributes powerful, narrow spikes to the spectrum at the odd harmonics of the waveform repetition rate.In between these TEM-spikes, the noise spectrum is preserved. Using a simple interpolation method and an appropriate spectral estimation method, we show how to recover an estimate of the clean noise spectrum from short intervals of production-mode data.The resulting estimate can be used for in-field tailoring the data acquisition strategy to the present conditions, specifically gating scheme, stacking scheme and repetition rate, such that less noise enters the measurements.Another application is in the interpretation phase, where the noise level for each gate can be computed and used as input to the inversion code.

XTE Proposal #20102--"SS 433's High Energy Spectrum"

NASA Technical Reports Server (NTRS)

Band, David L.; Blanco, P.; Rothschild, R.; Kawai, N.; Kotani, T.; Oka, T.; Wagner, R. M.; Hjellming, R.; Rupen, M.; Brinkmann, W.

1999-01-01

We observed the jet-producing compact binary system SS 433 with RXTE during three multiwavelength campaigns, the first in conjunction with ASCA observations, the second simultaneous with a VLA-VLBA-MERLIN campaign, and the third associated with a Nobeyama millimeter-band campaign. All these campaigns included optical observations. Occurring at different jet precession and binary phases, the observations also monitored the system during a radio flare. The data provide SS 433's X-ray spectrum over more than an energy decade, and track the spectral variations as the X-ray source was partially eclipsed. The continuum can be modeled as a power law with an exponential cutoff, which can be detected to approximately 50 keV. Strong line emission is evident in the 5-10 keV range which can be modeled as a broad line whose energy is precession independent and a narrow line whose energy does vary with jet precession phase; this line model is clearly an over simplification since the PCA does not have sufficient energy resolution to detect the lines ASCA observed. The eclipses are deeper at high energy and at jet precession phases when the jets are more inclined towards and away from us. A large radio flare occurred between two sets of X-ray monitoring observations; an X-ray observation at the peak of the flare found a softer spectrum with a flux approximately 1/3 that of the quiescent level.

Possible interaction between baryons and dark-matter particles revealed by the first stars

NASA Astrophysics Data System (ADS)

Barkana, Rennan

2018-03-01

The cosmic radio-frequency spectrum is expected to show a strong absorption signal corresponding to the 21-centimetre-wavelength transition of atomic hydrogen around redshift 20, which arises from Lyman-α radiation from some of the earliest stars. By observing this 21-centimetre signal—either its sky-averaged spectrum or maps of its fluctuations, obtained using radio interferometers—we can obtain information about cosmic dawn, the era when the first astrophysical sources of light were formed. The recent detection of the global 21-centimetre spectrum reveals a stronger absorption than the maximum predicted by existing models, at a confidence level of 3.8 standard deviations. Here we report that this absorption can be explained by the combination of radiation from the first stars and excess cooling of the cosmic gas induced by its interaction with dark matter. Our analysis indicates that the spatial fluctuations of the 21-centimetre signal at cosmic dawn could be an order of magnitude larger than previously expected and that the dark-matter particle is no heavier than several proton masses, well below the commonly predicted mass of weakly interacting massive particles. Our analysis also confirms that dark matter is highly non-relativistic and at least moderately cold, and primordial velocities predicted by models of warm dark matter are potentially detectable. These results indicate that 21-centimetre cosmology can be used as a dark-matter probe.

Possible interaction between baryons and dark-matter particles revealed by the first stars.

PubMed

Barkana, Rennan

2018-02-28

The cosmic radio-frequency spectrum is expected to show a strong absorption signal corresponding to the 21-centimetre-wavelength transition of atomic hydrogen around redshift 20, which arises from Lyman-α radiation from some of the earliest stars. By observing this 21-centimetre signal-either its sky-averaged spectrum or maps of its fluctuations, obtained using radio interferometers-we can obtain information about cosmic dawn, the era when the first astrophysical sources of light were formed. The recent detection of the global 21-centimetre spectrum reveals a stronger absorption than the maximum predicted by existing models, at a confidence level of 3.8 standard deviations. Here we report that this absorption can be explained by the combination of radiation from the first stars and excess cooling of the cosmic gas induced by its interaction with dark matter. Our analysis indicates that the spatial fluctuations of the 21-centimetre signal at cosmic dawn could be an order of magnitude larger than previously expected and that the dark-matter particle is no heavier than several proton masses, well below the commonly predicted mass of weakly interacting massive particles. Our analysis also confirms that dark matter is highly non-relativistic and at least moderately cold, and primordial velocities predicted by models of warm dark matter are potentially detectable. These results indicate that 21-centimetre cosmology can be used as a dark-matter probe.

PKS 2123-463: A Confirmed Gamma-ray Blazar at High Redshift

NASA Technical Reports Server (NTRS)

DAmmando, F.; Rau, A.; Schady, P.; Finke, J.; Orienti, M.; Greiner, J.; Kann, D. A.; Ojha, R.; Foley, A. R.; Stevens, J.;

The Radio Frequency Environment at 240-270 MHz with Application to Signal-of-Opportunity Remote Sensing

NASA Technical Reports Server (NTRS)

Piepmeier, Jeffrey R.; Vega, Manuel; Fritts, Matthew; Du Toit, Cornelis; Knuble, Joseph; Lin, Yao-Cheng; Nold, Benjamin; Garrison, James

2017-01-01

Low frequency observations are desired for soil moisture and biomass remote sensing. Long wavelengths are needed to penetrate vegetation and Earths land surface. In addition to the technical challenges of developing Earth observing spaceflight instruments operating at low frequencies, the radio frequency spectrum allocated to remote sensing is limited. Signal-of-opportunity remote sensing offers the chance to use existing signals exploiting their allocated spectrum to make Earth science measurements. We have made observations of the radio frequency environment around 240-270 MHz and discuss properties of desired and undesired signals.

The High Time Resolution Radio Sky

NASA Astrophysics Data System (ADS)

Thornton, D.

2013-11-01

Pulsars are laboratories for extreme physics unachievable on Earth. As individual sources and possible orbital companions can be used to study magnetospheric, emission, and superfluid physics, general relativistic effects, and stellar and binary evolution. As populations they exhibit a wide range of sub-types, with parameters varying by many orders of magnitude signifying fundamental differences in their evolutionary history and potential uses. There are currently around 2200 known pulsars in the Milky Way, the Magellanic clouds, and globular clusters, most of which have been discovered with radio survey observations. These observations, as well as being suitable for detecting the repeating signals from pulsars, are well suited for identifying other transient astronomical radio bursts that last just a few milliseconds that either singular in nature, or rarely repeating. Prior to the work of this thesis non-repeating radio transients at extragalactic distances had possibly been discovered, however with just one example status a real astronomical sources was in doubt. Finding more of these sources was a vital to proving they were real and to open up the universe for millisecond-duration radio astronomy. The High Time Resolution Universe survey uses the multibeam receiver on the 64-m Parkes radio telescope to search the whole visible sky for pulsars and transients. The temporal and spectral resolution of the receiver and the digital back-end enable the detection of relatively faint, and distant radio sources. From the Parkes telescope a large portion of the Galactic plane can be seen, a rich hunting ground for radio pulsars of all types, while previously poorly surveyed regions away from the Galactic plane are also covered. I have made a number of pulsar discoveries in the survey, including some rare systems. These include PSR J1226-6208, a possible double neutron star system in a remarkably circular orbit, PSR J1431-471 which is being eclipsed by its companion with each orbit, PSR J1729-2117 which is an unusual isolated recycled pulsar, and PSR J2322-2650 which has a companion of very low mass - just 7 × 10^{-4} {M}_{⊙}, amongst others. I begin this thesis with the study of these pulsars and discuss their histories. In addition, I demonstrate that optical observations of the companions to some of the newly discovered pulsars in the High Time Resolution Universe survey may result in a measurement of their age and that of the pulsar. I have discovered five new extragalactic single radio bursts, confirming them as an astronomical population. These appear to occur frequently, with a rate of 1.0^{+0.6}_{-0.5} × 10^4 sky^{-1} day^{-1}. The sources are likely at cosmological distances - with redshifts between 0.45 and 1.45, making them more than half way to the Big Bang in the most distant case. This implies their luminosities must be enormous, 10^{31} to 10^{33} J emitted in just a few milliseconds. Their source is unknown but I present an analysis of the options. I also perform a population simulation of the bursts which demonstrates how their intrinsic spectrum could be measured, even for unlocalised FRBs: early indications are that the spectral index of FRBs < 0.

47 CFR 18.101 - Basis and purpose.

Code of Federal Regulations, 2012 CFR

2012-10-01

... industrial, scientific, and medical equipment (ISM) that emits electromagnetic energy on frequencies within the radio frequency spectrum in order to prevent harmful interference to authorized radio...

47 CFR 18.101 - Basis and purpose.

Code of Federal Regulations, 2013 CFR

2013-10-01

... industrial, scientific, and medical equipment (ISM) that emits electromagnetic energy on frequencies within the radio frequency spectrum in order to prevent harmful interference to authorized radio...

47 CFR 18.101 - Basis and purpose.

Code of Federal Regulations, 2010 CFR

2010-10-01

... industrial, scientific, and medical equipment (ISM) that emits electromagnetic energy on frequencies within the radio frequency spectrum in order to prevent harmful interference to authorized radio...

47 CFR 18.101 - Basis and purpose.

Code of Federal Regulations, 2011 CFR

2011-10-01

... industrial, scientific, and medical equipment (ISM) that emits electromagnetic energy on frequencies within the radio frequency spectrum in order to prevent harmful interference to authorized radio...

47 CFR 18.101 - Basis and purpose.

Code of Federal Regulations, 2014 CFR

2014-10-01

... industrial, scientific, and medical equipment (ISM) that emits electromagnetic energy on frequencies within the radio frequency spectrum in order to prevent harmful interference to authorized radio...

On the Direct Correlation between Gamma-Rays and PeV Neutrinos from Blazars

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

Gao, Shan; Pohl, Martin; Winter, Walter, E-mail: shan.gao@desy.de

We study the frequently used assumption in multi-messenger astrophysics that the gamma-ray and neutrino fluxes are directly connected because they are assumed to be produced by the same photohadronic production chain. An interesting candidate source for this test is the flat-spectrum radio quasar PKS B1424-418, which recently called attention to a potential correlation between an IceCube PeV neutrino event and its burst phase. We simulate both the multi-waveband photon and the neutrino emission from this source using a self-consistent radiation model. We demonstrate that a simple hadronic model cannot adequately describe the spectral energy distribution for this source, but amore » lepto-hadronic model with a subdominant hadronic component can reproduce the multi-waveband photon spectrum observed during various activity phases of the blazar. As a conclusion, up to about 0.3 neutrino events may coincide with the burst, which implies that the leptonic contribution dominates in the relevant energy band. We also demonstrate that the time-wise correlation between the neutrino event and burst phase is weak.« less

The missing links of neutron star evolution in the eROSITA all-sky X-ray survey

NASA Astrophysics Data System (ADS)

Pires, A. M.

2017-12-01

The observational manifestation of a neutron star is strongly connected with the properties of its magnetic field. During the star’s lifetime, the field strength and its changes dominate the thermo-rotational evolution and the source phenomenology across the electromagnetic spectrum. Signatures of magnetic field evolution are best traced among elusive groups of X-ray emitting isolated neutron stars (INSs), which are mostly quiet in the radio and γ-ray wavelengths. It is thus important to investigate and survey INSs in X-rays in the hope of discovering peculiar sources and the long-sought missing links that will help us to advance our understanding of neutron star evolution. The Extended Röntgen Survey with an Imaging Telescope Array (eROSITA), the primary instrument on the forthcoming Spectrum-RG mission, will scan the X-ray sky with unprecedented sensitivity and resolution. The survey has thus the unique potential to unveil the X-ray faint end of the neutron star population and probe sources that cannot be assessed by standard pulsar surveys.

Extragalactic Ultra-High Energy Cosmic-Rays - Part One - Contribution from Hot Spots in Fr-II Radio Galaxies

NASA Astrophysics Data System (ADS)

Rachen, J. P.; Biermann, P. L.

1993-05-01

The hot spots of Fanaroff-Riley class II radio galaxies, considered as working surfaces of highly collimated plasma jets, are proposed to be the dominant sources of the cosmic rays at energies above 1 EeV^a^. We apply the model of first order Fermi acceleration at strong, nonrelativistic shock waves to the hot spot region. The strength of the model has been demonstrated by Biermann & Strittmatter (1987) and by Meisenheimer et al. (1989), who explain their radio-to optical spectra and infer the physical conditions of the radiating plasma. Using synchrotron radiating electrons as a trace, we can calculate the spectrum and the maximum energy of protons accelerated under the same conditions. For simplicity, we disregard heavy nuclei, but their probable role is discussed. The normalization of proton flux injected in extragalactic space is performed by using estimates from Rawlings & Saunders (1991) for the total energy stored in relativistic particles inside the jets and radio galaxy evolution models given by Peacock (1985). We calculate the spectral modifications due to interactions of the protons with the microwave background photons in an evolving universe, following Berezinsky & Grigor'eva (1988). Constraints on the extragalactic magnetic field can be imposed, since it must permit an almost homogeneous filling of the universe with energetic protons. The observed ultra-high energy cosmic ray spectrum is reproduced in slope and flux, limited at high energies by the Greisen-cutoff at about 80 EeV. The requirements on the content of relativistic protons in jets and the constraints to the extragalactic magnetic field are consistent with common estimates. The data beyond the Greisen cutoff for protons may be explained by including heavy nuclei in our model, since they can propagate over cosmological distances up to more than 100 EeV.

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.

The Impact of Radio Interference on Future Radio Telescopes

NASA Astrophysics Data System (ADS)

Mitchell, Daniel A.; Robertson, Gordon J.; Sault, Robert J.

While future radio telescopes will require technological advances from the communications industry interference from sources such as satellites and mobile phones is a serious concern. In addition to the fact that the level of interference is growing constantly the increased capabilities of next generation instruments make them more prone to harmful interference. These facilities must have mechanisms to allow operation in a crowded spectrum. In this report some of the factors which may limit the effectiveness of these mechanisms are investigated. Radio astronomy is unique among other observing wavelengths in that the radiation can be fully sampled at a rate which completely specifies the electromagnetic environment. Knowledge of phases and antennae gain factors affords one the opportunity to attempt to mitigate interference from the astronomical data. At present several interference mitigation techniques have been demonstrated to be extremely effective. However the observational scales of the new facilities will push the techniques to their limits. Processes such as signal decorrelation varying antenna gain and instabilities in the primary beam will have a serious effect on some of the algorithms. In addition the sheer volume of data produced will render some techniques computationally and financially impossible.

Synchrotron Spectral Curvature from 22 MHZ to 23 GHZ

NASA Technical Reports Server (NTRS)

Kogut, Alan J.

2012-01-01

We combine surveys of the radio sky at frequencies 22 MHz to 1.4 GHz with data from the ARCADE-2 instrument at frequencies 3 GHz to 10 GHz to characterize the frequency spectrum of diffuse synchrotron emission in the Galaxy. The radio spectrum steepens with frequency from 22 MHz to 10 GHz. The projected spectral index at 23 GHz derived from the low-frequency data agrees well with independent measurements using only data at frequencies 23 GHz and above. Comparing the spectral index at 23 GHz to the value from previously published analyses allows extension of the model to higher frequencies. The combined data are consistent with a power-law index beta = -2.64 +/-= 0.03 at 0.31 GHz, steepening by an amount of Delta-beta = 0.07 every octave in frequency. Comparison of the radio data to models including the cosmic-ray energy spectrum suggests that any break in the synchrotron spectrum must occur at frequencies above 23 GHz.

A Fast Radio Burst Search Method for VLBI Observation

NASA Astrophysics Data System (ADS)

Liu, Lei; Tong, Fengxian; Zheng, Weimin; Zhang, Juan; Tong, Li

2018-02-01

We introduce the cross-spectrum-based fast radio burst (FRB) search method for Very Long Baseline Interferometer (VLBI) observation. This method optimizes the fringe fitting scheme in geodetic VLBI data post-processing, which fully utilizes the cross-spectrum fringe phase information and therefore maximizes the power of single-pulse signals. Working with cross-spectrum greatly reduces the effect of radio frequency interference compared with using auto-power spectrum. Single-pulse detection confidence increases by cross-identifying detections from multiple baselines. By combining the power of multiple baselines, we may improve the detection sensitivity. Our method is similar to that of coherent beam forming, but without the computational expense to form a great number of beams to cover the whole field of view of our telescopes. The data processing pipeline designed for this method is easy to implement and parallelize, which can be deployed in various kinds of VLBI observations. In particular, we point out that VGOS observations are very suitable for FRB search.

Precise γ-ray timing and radio observations of 17 FERMI γ-ray pulsars

DOE PAGES

Ray, Paul S.; Kerr, M.; Parent, D.; ...

2011-04-29

Here, we present precise phase-connected pulse timing solutions for 16 γ-ray-selected pulsars recently discovered using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope plus one very faint radio pulsar (PSR J1124–5916) that is more effectively timed with the LAT. We describe the analysis techniques including a maximum likelihood method for determining pulse times of arrival from unbinned photon data. A major result of this work is improved position determinations, which are crucial for multiwavelength follow-up. For most of the pulsars, we overlay the timing localizations on X-ray images from Swift and describe the status of X-ray counterpartmore » associations. We report glitches measured in PSRs J0007+7303, J1124–5916, and J1813–1246. We analyze a new 20 ks Chandra ACIS observation of PSR J0633+0632 that reveals an arcminute-scale X-ray nebula extending to the south of the pulsar. We were also able to precisely localize the X-ray point source counterpart to the pulsar and find a spectrum that can be described by an absorbed blackbody or neutron star atmosphere with a hard power-law component. Another Chandra ACIS image of PSR J1732–3131 reveals a faint X-ray point source at a location consistent with the timing position of the pulsar. Finally, we present a compilation of new and archival searches for radio pulsations from each of the γ-ray-selected pulsars as well as a new Parkes radio observation of PSR J1124–5916 to establish the γ-ray to radio phase offset.« less

The Quasar Fraction in Low-Frequency Selected Complete Samples and Implications for Unified Schemes

NASA Technical Reports Server (NTRS)

Willott, Chris J.; Rawlings, Steve; Blundell, Katherine M.; Lacy, Mark

2000-01-01

Low-frequency radio surveys are ideal for selecting orientation-independent samples of extragalactic sources because the sample members are selected by virtue of their isotropic steep-spectrum extended emission. We use the new 7C Redshift Survey along with the brighter 3CRR and 6C samples to investigate the fraction of objects with observed broad emission lines - the 'quasar fraction' - as a function of redshift and of radio and narrow emission line luminosity. We find that the quasar fraction is more strongly dependent upon luminosity (both narrow line and radio) than it is on redshift. Above a narrow [OII] emission line luminosity of log(base 10) (L(sub [OII])/W) approximately > 35 [or radio luminosity log(base 10) (L(sub 151)/ W/Hz.sr) approximately > 26.5], the quasar fraction is virtually independent of redshift and luminosity; this is consistent with a simple unified scheme with an obscuring torus with a half-opening angle theta(sub trans) approximately equal 53 deg. For objects with less luminous narrow lines, the quasar fraction is lower. We show that this is not due to the difficulty of detecting lower-luminosity broad emission lines in a less luminous, but otherwise similar, quasar population. We discuss evidence which supports at least two probable physical causes for the drop in quasar fraction at low luminosity: (i) a gradual decrease in theta(sub trans) and/or a gradual increase in the fraction of lightly-reddened (0 approximately < A(sub V) approximately < 5) lines-of-sight with decreasing quasar luminosity; and (ii) the emergence of a distinct second population of low luminosity radio sources which, like M8T, lack a well-fed quasar nucleus and may well lack a thick obscuring torus.

Disc-jet Coupling in the 2009 Outburst of the Black Hole Candidate H1743-322

NASA Technical Reports Server (NTRS)

Miller-Jones, J. C. A.; Sivakoff, G. R.; Altamirano, D.; Coriat, M.; Corbel, S.; Dhawan, V.; Krimm, H. A.; Remillard, R. A.; Rupen, M. P.; Russell, D. M.;

THE RADIO/GAMMA-RAY CONNECTION IN ACTIVE GALACTIC NUCLEI IN THE ERA OF THE FERMI LARGE AREA TELESCOPE

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

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

We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the largest data sets ever used for this purpose. We use both archival interferometric 8.4 GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15 GHz measurements from the Owens Valley Radio Observatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using amore » surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the centimeter radio and the broadband (E > 100 MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability of <10{sup -7} for the correlation appearing by chance. Using the OVRO data, we find that concurrent data improve the significance of the correlation from 1.6 x 10{sup -6} to 9.0 x 10{sup -8}. Our large sample size allows us to study the dependence of correlation strength and significance on specific source types and gamma-ray energy band. We find that the correlation is very significant (chance probability < 10{sup -7}) for both flat spectrum radio quasars and BL Lac objects separately; a dependence of the correlation strength on the considered gamma-ray energy band is also present, but additional data will be necessary to constrain its significance.« less

The radio/gamma-ray connection in active galactic nuclei in the era of the Fermi Large Area Telescope

DOE PAGES

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

2011-10-12

We present a detailed statistical analysis of the correlation between radio and gamma-ray emission of the active galactic nuclei (AGNs) detected by Fermi during its first year of operation, with the largest data sets ever used for this purpose. We use both archival interferometric 8.4 GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15 GHz measurements from the Owens Valley Radio Observatory (OVRO, for a sub sample of 199 objects). Our unprecedentedly large sample permits us to assess with high accuracy the statistical significance of the correlation, using amore » surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities. We find that the statistical significance of a positive correlation between the centimeter radio and the broadband (E > 100 MeV) gamma-ray energy flux is very high for the whole AGN sample, with a probability of <10 –7 for the correlation appearing by chance. Using the OVRO data, we find that concurrent data improve the significance of the correlation from 1.6 × 10 –6 to 9.0 × 10 –8. Our large sample size allows us to study the dependence of correlation strength and significance on specific source types and gamma-ray energy band. As a result, we find that the correlation is very significant (chance probability < 10 –7) for both flat spectrum radio quasars and BL Lac objects separately; a dependence of the correlation strength on the considered gamma-ray energy band is also present, but additional data will be necessary to constrain its significance.« less

The Radio/Gamma-Ray Connection in Active Galactic Nuclei in the Era of the Fermi Large Area Telescope

NASA Technical Reports Server (NTRS)

Ackermann, M.; Ajello, M.; Allafort, A.; Angelakis, E.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.;

Theoretical Interpretation of Pass 8 Fermi -LAT e + + e - Data

DOE PAGES

Di Mauro, M.; Manconi, S.; Vittino, A.; ...

2017-08-17

The flux of positrons and electrons (e + + e -) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. Here, we discuss a number of interpretations of Pass 8 Fermi-LAT e + + e - spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We also found that the Fermi-LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positrons from cataloged PWNe, and amore » secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e + + e - Fermi-LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green's catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e + + e - Fermi-LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e + + e -spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

Theoretical Interpretation of Pass 8 Fermi -LAT e + + e - Data

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

Di Mauro, M.; Manconi, S.; Vittino, A.

The flux of positrons and electrons (e + + e -) has been measured by the Fermi Large Area Telescope (LAT) in the energy range between 7 GeV and 2 TeV. Here, we discuss a number of interpretations of Pass 8 Fermi-LAT e + + e - spectrum, combining electron and positron emission from supernova remnants (SNRs) and pulsar wind nebulae (PWNe), or produced by the collision of cosmic rays (CRs) with the interstellar medium. We also found that the Fermi-LAT spectrum is compatible with the sum of electrons from a smooth SNR population, positrons from cataloged PWNe, and amore » secondary component. If we include in our analysis constraints from the AMS-02 positron spectrum, we obtain a slightly worse fit to the e + + e - Fermi-LAT spectrum, depending on the propagation model. As an additional scenario, we replace the smooth SNR component within 0.7 kpc with the individual sources found in Green's catalog of Galactic SNRs. We find that separate consideration of far and near sources helps to reproduce the e + + e - Fermi-LAT spectrum. However, we show that the fit degrades when the radio constraints on the positron emission from Vela SNR (which is the main contributor at high energies) are taken into account. We find that a break in the power-law injection spectrum at about 100 GeV can also reproduce the measured e + + e -spectrum and, among the CR propagation models that we consider, no reasonable break of the power-law dependence of the diffusion coefficient can modify the electron flux enough to reproduce the observed shape.« less

Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs

PubMed Central

Posada-Roman, Julio E.; Garcia-Souto, Jose A.; Poiana, Dragos A.; Acedo, Pablo

2016-01-01

Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal. PMID:27898043

Fast Interrogation of Fiber Bragg Gratings with Electro-Optical Dual Optical Frequency Combs.

PubMed

Posada-Roman, Julio E; Garcia-Souto, Jose A; Poiana, Dragos A; Acedo, Pablo

2016-11-26

Optical frequency combs (OFC) generated by electro-optic modulation of continuous-wave lasers provide broadband coherent sources with high power per line and independent control of line spacing and the number of lines. In addition to their application in spectroscopy, they offer flexible and optimized sources for the interrogation of other sensors based on wavelength change or wavelength filtering, such as fiber Bragg grating (FBG) sensors. In this paper, a dual-OFC FBG interrogation system based on a single laser and two optical-phase modulators is presented. This architecture allows for the configuration of multimode optical source parameters such as the number of modes and their position within the reflected spectrum of the FBG. A direct read-out is obtained by mapping the optical spectrum onto the radio-frequency spectrum output of the dual-comb. This interrogation scheme is proposed for measuring fast phenomena such as vibrations and ultrasounds. Results are presented for dual-comb operation under optimized control. The optical modes are mapped onto detectable tones that are multiples of 0.5 MHz around a center radiofrequency tone (40 MHz). Measurements of ultrasounds (40 kHz and 120 kHz) are demonstrated with this sensing system. Ultrasounds induce dynamic strain onto the fiber, which generates changes in the reflected Bragg wavelength and, hence, modulates the amplitude of the OFC modes within the reflected spectrum. The amplitude modulation of two counterphase tones is detected to obtain a differential measurement proportional to the ultrasound signal.

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

Fang, Ke; Linden, Tim, E-mail: kefang@umd.edu, E-mail: linden.70@osu.edu

Radio observations at multiple frequencies have detected a significant isotropic emission component between 22 MHz and 10 GHz, commonly termed the ARCADE-2 Excess. The origin of this radio emission is unknown, as the intensity, spectrum and isotropy of the signal are difficult to model with either traditional astrophysical mechanisms or novel physics such as dark matter annihilation. We posit a new model capable of explaining the key components of the excess radio emission. Specifically, we show that the re-acceleration of non-thermal electrons via turbulence in merging galaxy clusters are capable of explaining the intensity, spectrum, and isotropy of the ARCADE-2more » data. We examine the parameter spaces of cluster re-acceleration, magnetic field, and merger rate, finding that the radio excess can be reproduced assuming reasonable assumptions for each. Finally, we point out that future observations will definitively confirm or rule-out the contribution of cluster mergers to the isotropic radio background.« less

Fermi LAT detection of a GeV gamma-ray flare from blazar CGRaBS J0809+5341 (87GB 080551.6+535010)

NASA Astrophysics Data System (ADS)

Gasparrini, Dario

2017-10-01

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray emission from a source positionally consistent with the flat spectrum radio quasar CGRaBS J0809+5341 (also known as 87GB 080551.6+535010, BZQ J0809+5341 and 3FGL J0809.5+5342) with radio coordinates (J2000) R.A.: 122.4238862 deg, Dec.: 53.6903033 deg (Petrov et al. 2011, AJ, 142, 89). This blazar has a redshift z = 2.133 (Healey et al. 2008, ApJS, 175, 97). Preliminary analysis indicates that on 2017 October 26, CGRaBS J0809+5341 was in a high state with a daily averaged gamma-ray flux (E > 100 MeV) of (0.23+/-0.15) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 20 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue.

Monitoring Mars for Electrostatic Disturbances

NASA Technical Reports Server (NTRS)

Compton, D.

2011-01-01

The DSN radio telescope DSS-13 was used to monitor Mars for electrostatic discharges from 17 February to 11 April, 2010, and from 19 April to 4 May, 2011, over a total of 72 sessions. Of these sessions, few showed noteworthy results and no outstanding electrostatic disturbances were observed on Mars from analyzing the kurtosis of radio emission from Mars. Electrostatic discharges on mars were originally detected in June of 2006 by Ruf et al. using DSS-13. he kurtosis (normalized fourth moment of the electrical field strength) is sensitive to non-thermal radiation. Two frequencies bands, either 2.4 and 8.4 GHz or 8.4 and 32 GHz were used. The non-thermal radiation spectrum should have peaks at the lowest three modes of the theoretical Schumann Resonances of Mars. The telescope was pointed away from Mars every 5 minutes for 45 seconds to confirm if Mars was indeed the sources of any events. It was shown that by including a down-link signal in one channel and by observing when the kurtosis changed as the telescope was pointed away from the source that the procedure can monitor Mars without the need of extra equipment monitoring a control source.

Supernova Remnant Kesteven 27: Interaction with A Neighbor HI Cloud Viewed by Fermi

NASA Astrophysics Data System (ADS)

Xing, Yi; Wang, Zhongxiang; Zhang, Xiao; Chen, Yang

2015-05-01

We report on the likely detection of γ-ray emission from the supernova remnant (SNR) Kesteven 27 (Kes 27). We analyze 5.7 yr Fermi Large Area Telescope data of the SNR region and find an unresolved source at a position consistent with the radio brightness peak and the X-ray knot of Kes 27, which is located in the eastern region of the SNR and caused by its interaction with a nearby Hi cloud. The source’s emission is best fit with a power-law spectrum with a photon index of 2.5 ± 0.1 and a >0.2 GeV luminosity of 5.8× {{10}34} erg s-1 assuming a distance of 4.3 kpc, as derived from radio observations of the nearby Hi cloud. Comparing the properties of the source with that of other SNRs that are known to be interacting with nearby high-density clouds, we discuss the origin of the source’s emission. The spectral energy distribution of the source can be described by a hadronic model that considers the interaction of energetic protons escaping from the shock front of Kes 27 with a high-density cloud.

Final Results from the BIMA CMB Anisotropy Survey and Search for Signature of the SZ Effect

NASA Technical Reports Server (NTRS)

Dawson, K. S.; Holzapfel, W. L.; Carlstrom, J. E.; Joy, M.; LaRoque, S. J.

2006-01-01

We report the final results of our study of the cosmic microwave background (CMB) with the BIMA array. Over 1000 hours of observation were dedicated to this project exploring CMB anisotropy on scales between 1' and 2' in eighteen 6'.6 FWHM fields. In the analysis of the CMB power spectrum, the visibility data is divided into two bins corresponding to different angular scales. Modeling the observed excess power as a flat band of average multipole l(sub eff)= 5237, we find deltaT(sup 2)(sub 1) = 220(sup +140)(sub -120) mu K(sup 2) at 68% confidence and deltaT(sup 2)(sub 1) greater than 0 muK(sup 2) with 94.7% confidence. In a second band with average multipole of l(sub eff) = 8748, we find deltaT(sup 2)(sub 2) consistent with zero, and an upper limit 880 muK(sup 2) at 95% confidence. An extensive series of tests and supplemental observations with the VLA provide strong evidence against systematic errors or radio point sources being the source of the observed excess power. The dominant source of anisotropy on these scales is expected to arise from the Sunyaev-Zel'dovich (SZ) effect in a population of distant galaxy clusters. If the excess power is due to the SZ effect, we can place constraints on the normalization of the matter power spectrum sigma(sub 8) = 1.03(sup +0.20)(sub -0.29) at 68% confidence. The distribution of pixel fluxes in the BIMA images are found to be consistent with simulated observations of the expected SZ background and rule out instrumental noise or radio sources as the source of the observed excess power with similar confidence to the detection of excess power. Follow-up optical observations to search for galaxy over-densities anti-correlated with flux in the BIMA images, as might be expected from the SZ effect, proved to be inconclusive.

Radio Wavelength Studies of the Galactic Center Source N3, Spectroscopic Instrumentation For Robotic Telescope Systems, and Developing Active Learning Activities for Astronomy Laboratory Courses

NASA Astrophysics Data System (ADS)

Ludovici, Dominic Alesio

2017-08-01

The mysterious radio source N3 appears to be located within the vicinity of the Radio Arc region of the Galactic Center. To investigate the nature of this source, we have conducted radio observations with the VLA and the VLBA. Continuum observations between 2 and 50 GHz reveal that N3 is an extremely compact and bright source with a non-thermal spectrum. Molecular line observations with the VLA reveal a compact molecular cloud adjacent to N3 in projection. The properties of this cloud are consistent with other galactic center clouds. We are able to rule out several hypotheses for the nature of N3, though a micro-blazar origin cannot be ruled out. Robotic Telescope systems are now seeing widespread deployment as both teaching and research instruments. While these systems have traditionally been able to produce high quality images, these systems have lacked the capability to conduct spectroscopic observations. To enable spectroscopic observations on the Iowa Robotic Observatory, we have developed a low cost (˜ 500), low resolution (R ˜ 300) spectrometer which mounts inside a modified filter wheel and a moderate cost (˜ 5000), medium resolution (R ˜ 8000) fiber-fed spectrometer. Software has been developed to operate both instruments robotically and calibration pipelines are being developed to automate calibration of the data. The University of Iowa offers several introductory astronomy laboratory courses taken by many hundreds of students each semester. To improve student learning in these laboratory courses, we have worked to integrate active learning into laboratory activities. We present the pedagogical approaches used to develop and update the laboratory activities and present an inventory of the current laboratory exercises. Using the inventory, we make observations of the strengths and weaknesses of the current exercises and provide suggestions for future refinement of the astronomy laboratory curriculum.

IGR J12319-0749: Evidence for Another Extreme Blazar Found with INTEGRAL

NASA Technical Reports Server (NTRS)

Bassani, L.; Landi, R.; Marshall, F. E.; Malizia, A.; Bazzano, A.; Bird, A. J.; Gehrels, N.; Ubertini, P.; Masetti, N.

2012-01-01

We report on the identification of a new soft gamma-ray source, IGR J12319-0749, detected with the IBIS imager on board the INTEGRAL satellite. The source, which has an observed 20-100 keV flux of approx 8.3 × 10(exp -12) erg/sq. cm/ s, is spatially coincident with an active galactic nucleus (AGN) at redshift z = 3.12. The broad-band continuum, obtained by combining XRT and IBIS data, is flat (Gamma = 1.3) with evidence for a spectral break around 25 keV (100 keV in the source restframe). X-ray observations indicate flux variability, which is also supported by a comparison with a previous ROSAT measurement. IGR J12319-0749 is also a radio-emitting object likely characterised by a flat spectrum and high radio loudness; optically it is a broad-line emitting object with a massive black hole (2.8 × 10(exp 9) solar masses) at its centre. The source spectral energy distribution is similar to another high-redshift blazar, 225155+2217 at z = 3.668: both objects are bright, with a high accretion disk luminosity and a Compton peak located in the hard X-ray/soft gamma-ray band. IGR J12319-0749 is likely the second-most distant blazar detected so far by INTEGRAL.

IGR J12319-0749: Evidence for Another Extreme Blazar Found with INTEGRAL

NASA Technical Reports Server (NTRS)

Bassani, L.; Landi, R.; Marshall, F. E.; Malizia, A.; Bazzano, A.; Bird, A. J.; Gehrels, N.; Ubertini, P.; Masetti, N.

2012-01-01

We report on the identification of a new soft gamma-ray source, IGR J12319 C0749, detected with the IBIS imager on board the INTEGRAL satellite. The source, which has an observed 20 C100 keV flux of 8.3 10.12 erg cm.2 s.1, is spatially coincident with an AGN at redshift z = 3.12. The broad-band continuum, obtained by combining XRT and IBIS data, is flat ( =1.3) with evidence for a spectral break around 25 keV (100 keV in the source rest frame). X-ray observations indicate flux variability which is further supported by a comparison with a previous ROSAT measurement. IGR J12319 C0749 is also a radio emitting object likely characterized by a flat spectrum and high radio loudness; optically it is a broad-line emitting object with a massive black hole (2.8 109 solar masses) at its center. The source Spectral Energy Distribution is similar to another high redshift blazar, 225155+2217 at z = 3.668: both objects are bright, with a large accretion disk luminosity and a Compton peak located in the hard X-ray/soft gamma-ray band. IGR J12319 C0749 is likely the second most distant blazar detected so far by INTEGRAL.

Alternative licensing arrangements and spectrum economics: The case of multipoint distribution service

NASA Technical Reports Server (NTRS)

Agnew, C. E.

1981-01-01

At present, the Federal Communications Commission assigns radio licenses following a determination of the public interest. Whenever mutually conflicting license applications are filed, the Commission holds a comparative hearing. This assignment mechanism is criticized as cumbersome and unrealiable, and three alternatives are proposed: increasing the available spectrum, and either auctions or lotteries of radio licenses. An analysis is presented of the present system and these alternative arrangments for assigning rights to the frequency spectrum for the Multipoint Distribution Service (MDS). Although MDS is a relatively minor radio service, it serves as a prototype for message distribution services with a large potential for use in business communications. Moreover, the way in which the initial batch of MDS licenses was assigned provides a unique opportunity for empirical work on the economics of the licensing process.

Optimized Beam Sculpting with Generalized Fringe-rate Filters

NASA Astrophysics Data System (ADS)

Parsons, Aaron R.; Liu, Adrian; Ali, Zaki S.; Cheng, Carina

2016-03-01

We generalize the technique of fringe-rate filtering, whereby visibilities measured by a radio interferometer are re-weighted according to their temporal variation. As the Earth rotates, radio sources traverse through an interferometer’s fringe pattern at rates that depend on their position on the sky. Capitalizing on this geometric interpretation of fringe rates, we employ time-domain convolution kernels to enact fringe-rate filters that sculpt the effective primary beam of antennas in an interferometer. As we show, beam sculpting through fringe-rate filtering can be used to optimize measurements for a variety of applications, including mapmaking, minimizing polarization leakage, suppressing instrumental systematics, and enhancing the sensitivity of power-spectrum measurements. We show that fringe-rate filtering arises naturally in minimum variance treatments of many of these problems, enabling optimal visibility-based approaches to analyses of interferometric data that avoid systematics potentially introduced by traditional approaches such as imaging. Our techniques have recently been demonstrated in Ali et al., where new upper limits were placed on the 21 {cm} power spectrum from reionization, showcasing the ability of fringe-rate filtering to successfully boost sensitivity and reduce the impact of systematics in deep observations.

A phenomenological pulsar model

NASA Technical Reports Server (NTRS)

Michel, F. C.

1978-01-01

Particle injection energies and rates previously calculated for the stellar wind generation by rotating magnetized neutron stars are adopted. It is assumed that the ambient space-charge density being emitted to form this wind is bunched. These considerations immediately place the coherent radio frequency luminosity from such bunches near 10 to the 28th erg/s for typical pulsar parameters. A comparable amount of incoherent radiation is emitted for typical (1 second) pulsars. For very rapid pulsars, however, the latter component grows more rapidly than the available energy sources. The comparatively low radio luminosity of the Crab and Vela pulsars is attributed to both components being limited in the same ratio. The incoherent radiation essentially has a synchotron spectrum and extends to gamma-ray energies; consequently the small part of the total luminosity that is at optical wavelengths is unobservable. Assuming full coherence at all wavelengths short of a critical length gives a spectral index for the flux density of -8/3 at higher frequencies. The finite energy available from the injected particles would force the spectrum to roll over below about 100 MHz, although intrinsic morphological factors probably enter for any specific pulsar as well.

Cascade model of gamma-ray bursts: Power-law and annihilation-line components

NASA Technical Reports Server (NTRS)

Harding, A. K.; Sturrock, P. A.; Daugherty, J. K.

1988-01-01

If, in a neutron star magnetosphere, an electron is accelerated to an energy of 10 to the 11th or 12th power eV by an electric field parallel to the magnetic field, motion of the electron along the curved field line leads to a cascade of gamma rays and electron-positron pairs. This process is believed to occur in radio pulsars and gamma ray burst sources. Results are presented from numerical simulations of the radiation and photon annihilation pair production processes, using a computer code previously developed for the study of radio pulsars. A range of values of initial energy of a primary electron was considered along with initial injection position, and magnetic dipole moment of the neutron star. The resulting spectra was found to exhibit complex forms that are typically power law over a substantial range of photon energy, and typically include a dip in the spectrum near the electron gyro-frequency at the injection point. The results of a number of models are compared with data for the 5 Mar., 1979 gamma ray burst. A good fit was found to the gamma ray part of the spectrum, including the equivalent width of the annihilation line.

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09

NASA Astrophysics Data System (ADS)

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.; Mitra, D.; Rankin, J. M.; Stappers, B. W.; Wright, G. A. E.; Basu, R.; Szary, A.; van Leeuwen, J.

2017-04-01

We report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09 with ESA's XMM-Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822-09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2-1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ˜0.15 at 0.3 keV to ˜0.6 at 1 keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ˜0.96 × 106 K, hotspot radius R ˜2.0 km) and a hot component (T ˜2.2 × 106 K, R ˜100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822-09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055-52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822-09, which might be a pulsar wind nebula.

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822$-$09

DOE PAGES

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.; ...

2016-12-05

Here, we report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822–09 with ESA's XMM–Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822–09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2–1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1more » keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~0.96 × 10 6 K, hotspot radius R ~2.0 km) and a hot component (T ~2.2 × 10 6 K, R ~100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822–09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055–52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822–09, which might be a pulsar wind nebula.« less

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822$-$09

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

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.

Here, we report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822–09 with ESA's XMM–Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822–09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2–1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1more » keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~0.96 × 10 6 K, hotspot radius R ~2.0 km) and a hot component (T ~2.2 × 10 6 K, R ~100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822–09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055–52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822–09, which might be a pulsar wind nebula.« less

XMM-Newton X-ray Observatory Guest Observer program (AO-1) at CASA

NASA Technical Reports Server (NTRS)

Skinner, Stephen L.

2003-01-01

In this research program, we obtained and analyzed X-ray observations of the Wolf-Rayet (WR) star WR 110 (HD 165688) using the XMM-Newton space-based observatory. Radio observations were also obtained using the Very Large Array (VLA) radio telescope located in New Mexico and operated by the Natl. Radio Astronomy Observatory (NRAO). This star was targeted for observations primarily because it is believed to be a single WR star without a companion. Single WR stars are thought to emit X-rays from cool plasma in shocks distributed throughout their powerful stellar winds. However, there has been little observational work done to test this idea since single WR stars are relatively weak X-ray sources and have been difficult to detect with previous generation telescopes. The launch of XMM-Newton provides a new telescope that is much more sensitive than its predecessors, allowing single WR stars to be studied in detail for the first time. X-ray emission was clearly detected from WR 110. Analysis of its spectrum yields a surprising result. Its X-ray emitting plasma is distributed over a range of temperatures and is dominated by relatively cool plasma with a characteristic temperature T is approximately 6 million K. Such plasma can be explained by existing theoretical wind shock models. However, the spectrum also shows hotter plasma whose temperature is uncertain but is thought to be in excess of T approximately 30 million K. The origin of this hotter plasma is yet unknown, but possible mechanisms are identified

Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies in the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Paliya, Vaidehi S.; Ajello, M.; Rakshit, S.; Mandal, Amit Kumar; Stalin, C. S.; Kaur, A.; Hartmann, D.

2018-01-01

The detection of significant γ-ray emission from radio-loud narrow-line Seyfert 1 (NLSy1s) galaxies enables us to study jets in environments different than those in blazars. However, due to the small number of known γ-ray-emitting NLSy1 (γ-NLSy1) galaxies, a comprehensive study could not be performed. Here, we report the first detection of significant γ-ray emission from four active galactic nuclei (AGNs), recently classified as NLSy1 from their Sloan Digital Sky Survey (SDSS) optical spectrum. Three flat-spectrum radio quasars (FSRQs) present in the third Large Area Telescope AGN catalog (3LAC) are also found as γ-NLSy1 galaxies. Comparing the γ-ray properties of these objects with 3LAC blazars reveals their spectral shapes to be similar to FSRQs, however, with low γ-ray luminosity (≲1046–47 erg s‑1). In the Wide-field Infrared Survey Explorer color–color diagram, these objects occupy a region mainly populated by FSRQs. Using the H β emission line parameters, we find that on average γ-NLSy1 have smaller black hole masses than FSRQs at similar redshifts. In the low-resolution SDSS image of one of the γ-NLSy1 source, we find the evidence of an extended structure. We conclude by noting that overall many observational properties of γ-NLSy1 sources are similar to FSRQs, and therefore these objects could be their low black hole mass counterparts, as predicted in the literature.

FBQS J1644+2619: multiwavelength properties and its place in the class of γ-ray emitting Narrow Line Seyfert 1s

NASA Astrophysics Data System (ADS)

Larsson, J.; D'Ammando, F.; Falocco, S.; Giroletti, M.; Orienti, M.; Piconcelli, E.; Righini, S.

2018-05-01

A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be γ-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multifrequency analysis of FBQS J1644+2619, one of the most recently discovered γ-ray emitting NLSy1s. We analyse an ˜80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multiwavelength observations covering the radio-γ-ray range. The spectral energy distribution of the source is similar to the other γ-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterized by a hard photon index (Γ = 1.66) above 2 keV and a soft excess at lower energies. The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonization in a warm, optically thick corona. We discuss our results in the context of the other γ-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s.

RF Spectrum Sensing Based on an Overdamped Nonlinear Oscillator Ring for Cognitive Radios

PubMed Central

Tang, Zhi-Ling; Li, Si-Min; Yu, Li-Juan

2016-01-01

Existing spectrum-sensing techniques for cognitive radios require an analog-to-digital converter (ADC) to work at high dynamic range and a high sampling rate, resulting in high cost. Therefore, in this paper, a spectrum-sensing method based on a unidirectionally coupled, overdamped nonlinear oscillator ring is proposed. First, the numerical model of such a system is established based on the circuit of the nonlinear oscillator. Through numerical analysis of the model, the critical condition of the system’s starting oscillation is determined, and the simulation results of the system’s response to Gaussian white noise and periodic signal are presented. The results show that once the radio signal is input into the system, it starts oscillating when in the critical region, and the oscillating frequency of each element is fo/N, where fo is the frequency of the radio signal and N is the number of elements in the ring. The oscillation indicates that the spectrum resources at fo are occupied. At the same time, the sampling rate required for an ADC is reduced to the original value, 1/N. A prototypical circuit to verify the functionality of the system is designed, and the sensing bandwidth of the system is measured. PMID:27294928

The Far-Infrared Emission of Radio Loud and Radio Quiet Quasars

NASA Technical Reports Server (NTRS)

Polletta, M.; Courvoisier, T. J.-L.; Wilkes, B. J.; Hooper, E. J.

2000-01-01

Continuum observations at radio, millimeter, infrared and soft X-ray energies are presented for a sample of 22 quasars, consisting of flat and steep spectrum radio loud, radio intermediate and radio quiet objects. The primary observational distinctions, among the different kinds of quasars in the radio and IR energy domains are studied using large observational datasets provided by ISOPHOT on board the Infrared Space Observatory, by the IRAM interferometer, by the sub-millimetre array SCUBA on JCMT, and by the European Southern Observatory (ESO) facilities IRAC1 on the 2.2 m telescope and SEST. The spectral energy distributions of all quasars from radio to IR energies are analyzed and modeled with non-thermal and thermal spectral components. The dominant mechanism emitting in the far/mid-IR is thermal dust emission in all quasars, with the exception of flat spectrum radio loud quasars for which the presence of thermal IR emission remains rather uncertain, since it is difficult to separate it from the bright non-thermal component. The dust is predominantly heated by the optical/ultraviolet radiation emitted from the external components of the AGN. A starburst contributes to the IR emission at different levels, but always less than the AGN (<= 27%). The distribution of temperatures, sizes, masses, and luminosities of the emitting dust are independent of the quasar type.

47 CFR 90.813 - Partitioned licenses and disaggregated spectrum.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 47 Telecommunication 5 2014-10-01 2014-10-01 false Partitioned licenses and disaggregated spectrum... Specialized Mobile Radio Service § 90.813 Partitioned licenses and disaggregated spectrum. (a) Eligibility.... Spectrum may be disaggregated in any amount. (3) Combined partitioning and disaggregation. The Commission...

47 CFR 90.813 - Partitioned licenses and disaggregated spectrum.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 5 2012-10-01 2012-10-01 false Partitioned licenses and disaggregated spectrum... Specialized Mobile Radio Service § 90.813 Partitioned licenses and disaggregated spectrum. (a) Eligibility.... Spectrum may be disaggregated in any amount. (3) Combined partitioning and disaggregation. The Commission...

47 CFR 90.813 - Partitioned licenses and disaggregated spectrum.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 5 2011-10-01 2011-10-01 false Partitioned licenses and disaggregated spectrum... Specialized Mobile Radio Service § 90.813 Partitioned licenses and disaggregated spectrum. (a) Eligibility.... Spectrum may be disaggregated in any amount. (3) Combined partitioning and disaggregation. The Commission...

47 CFR 90.813 - Partitioned licenses and disaggregated spectrum.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 47 Telecommunication 5 2013-10-01 2013-10-01 false Partitioned licenses and disaggregated spectrum... Specialized Mobile Radio Service § 90.813 Partitioned licenses and disaggregated spectrum. (a) Eligibility.... Spectrum may be disaggregated in any amount. (3) Combined partitioning and disaggregation. The Commission...

An Improved Statistical Point-source Foreground Model for the Epoch of Reionization

NASA Astrophysics Data System (ADS)

Murray, S. G.; Trott, C. M.; Jordan, C. H.

2017-08-01

We present a sophisticated statistical point-source foreground model for low-frequency radio Epoch of Reionization (EoR) experiments using the 21 cm neutral hydrogen emission line. Motivated by our understanding of the low-frequency radio sky, we enhance the realism of two model components compared with existing models: the source count distributions as a function of flux density and spatial position (source clustering), extending current formalisms for the foreground covariance of 2D power-spectral modes in 21 cm EoR experiments. The former we generalize to an arbitrarily broken power law, and the latter to an arbitrary isotropically correlated field. This paper presents expressions for the modified covariance under these extensions, and shows that for a more realistic source spatial distribution, extra covariance arises in the EoR window that was previously unaccounted for. Failure to include this contribution can yield bias in the final power-spectrum and under-estimate uncertainties, potentially leading to a false detection of signal. The extent of this effect is uncertain, owing to ignorance of physical model parameters, but we show that it is dependent on the relative abundance of faint sources, to the effect that our extension will become more important for future deep surveys. Finally, we show that under some parameter choices, ignoring source clustering can lead to false detections on large scales, due to both the induced bias and an artificial reduction in the estimated measurement uncertainty.

PKS 2155-304 relativistically beamed synchrotron radiation from BL LAC object

NASA Technical Reports Server (NTRS)

Urry, C. M.; Mushotzky, R. F.

1981-01-01

The newly discovered BL Lacertae object, PKS 2155-304, was observed with the medium and high intensity energy detectors of the HEAO-1 A2 experiment. The variability by a factor of two in less than a day reported by Snyder, et al (1979) is confirmed. Two spectra, obtained a year apart, while the satellite was in scanning mode, are well fit by simple power laws with energy spectral index alpha sub 1 equals approximately 1.4. A third spectrum, of higher statistical quality, obtained while the satellite was pointed at its source, has has two components. An acceptable fit was obtained using a two power law model, with indices alpha sub 1 equals 2.0 (+1.2, -0.6) and alpha sub 2 equals -1.5 (+1.5, -2.3). An interpretation of the overall spectrum from radio through X-rays in terms of a synchrotron self-Compton model gives a good description of the data if allowance is made for relativistic beaming. Thus, from a consideration of the spectrum, combined with an estimate of the size of the source, the presence of jets is inferred without their observation.

The telecommunications and data acquisition report

NASA Technical Reports Server (NTRS)

1980-01-01

Progress in the development and operations of the Deep Space Network is reported. Developments in Earth based radio technology as applied to geodynamics, astrophysics, and radio astronomy's use of the deep space stations for a radio search for extraterrestrial intelligence in the microwave region of the electromagnetic spectrum are reported.

X-ray characteristics of the Lupus Loop and SN 1006 supernova remnants

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

Toor, A.

1980-01-01

The spatial extent of the Lupus Loop and spectra for the Lupus Loop and SN1006 supernova remnants have been determined with a rocket-borne payload. The Lupus Loop is an extended source of soft X-rays (approx. 300' diam) that shows a correlation between its brightest x-ray and radio-emission regions. Its spectrum is characterized by a temperature of 350 eV. Thus, the Lupus Loop appears similar to Vela X and Cygnus Loop, although much weaker. Emission from SN1006 is spatially unresolved and exhibits a harder spectrum than that of the Lupus Loop. All spectral data (0.2 to 10 keV) from our observationmore » and previous observations are satisfactorily fit with a power law (index = 2.15). This spectral dependence suggests the possibility that a rotating neutron star is the underlying source of the radiated energy although such an interpretation appears inconsistent with the remnant's morphology.« less