Strength of cosmic radio sources.
Cosmic radio source strength, explaining spectral output from substructures of 3C-273
QUASI-STELLAR RADIO SOURCE /QSO/↗
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Results for “COSMIC RADIO SOURCES”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Flat-spectrum radio sources - Cosmic conspiracy or relativistic neutrons?
The intensity spectrum of the core of radio-loud AGN varies smoothly from 10 exp 8.5 to 10 to the 16th Hz, and is flat between 10 to the 9th and 10 to the 10th Hz, implying that a single emission mechanism is responsible. It is proposed here that energy is transported from the central source by relativistic neutrons which travel freely over a large volume and decay into relativistic protons. The protons produce secondary electrons which generate the observed radiation. The photon spectra thus produced are largely model-independent and flat.
Giovanoni, Peter M.↗
A search for high-energy photons from discrete sources of cosmic radio emission
Search for high energy photons from celestial radio sources
COSMIC RADIATION↗
MODELING MULTI-WAVELENGTH PULSE PROFILES OF THE MILLISECOND PULSAR PSR B1821–24
PSR B1821–24 is a solitary millisecond pulsar that radiates multi-wavelength pulsed photons. It has complex radio, X-ray, and γ-ray pulse profiles with distinct peak phase separations that challenge the traditional caustic emission models. Using the single-pole annular gap model with a suitable magnetic inclination angle (α = 40°) and viewing angle (ζ = 75°), we managed to reproduce its pulse profiles of three wavebands. It is found that the middle radio peak originated from the core gap region at high altitudes, and the other two radio peaks originated from the annular gap region at relatively low altitudes. Two peaks of both X-ray and γ-ray wavebands basically originated from the annular gap region, while the γ-ray emission generated from the core gap region contributes somewhat to the first γ-ray peak. Precisely reproducing the multi-wavelength pulse profiles of PSR B1821–24 enables us to understand emission regions of distinct wavebands and justify pulsar emission models.
79 ASTRONOMY AND ASTROPHYSICS↗
Perspectives on Gamma-Ray Pulsar Emission
Pulsars are powerful sources of radiation across the electromagnetic spectrum. This paper highlights some theoretical insights into non-thermal, magnetospheric pulsar gamma-ray radiation. These advances have been driven by NASA's Fermi mission, launched in mid-2008. The Large Area Telescope (LAT) instrument on Fermi has afforded the discrimination between polar cap and slot gap/outer gap acceleration zones in young and middle-aged pulsars. Altitude discernment using the highest energy pulsar photons will be addressed, as will spectroscopic interpretation of the primary radiation mechanism in the LAT band, connecting to both polar cap/slot gap and outer gap scenarios. Focuses will mostly be on curvature radiation and magnetic pair creation, including population trends that may afford probes of the magnetospheric accelerating potential.
79 ASTRONOMY AND ASTROPHYSICS↗
CANGAROO-III OBSERVATION OF TeV GAMMA RAYS FROM THE UNIDENTIFIED GAMMA-RAY SOURCE HESS J1614-518
We report the detection, with the CANGAROO-III imaging atmospheric Cherenkov telescope array, of a very high energy gamma-ray signal from the unidentified gamma-ray source HESS J1614-518, which was discovered in the H.E.S.S. Galactic plane survey. Diffuse gamma-ray emission was detected above 760 GeV at the 8.9{sigma} level during an effective exposure of 54 hr from 2008 May to August. The spectrum can be represented by a power law: (8.2 {+-} 2.2{sub stat} {+-} 2.5{sub sys}) x 10{sup -12} x (E/1 TeV){sup -}{gamma} cm{sup -2} s{sup -1} TeV{sup -1} with a photon index {gamma} of 2.4 {+-} 0.3{sub stat} {+-} 0.2{sub sys}, which is compatible with that of the H.E.S.S. observations. By combining our result with multiwavelength data, we discuss the possible counterparts for HESS J1614-518 and consider radiation mechanisms based on hadronic and leptonic processes for a supernova remnant (SNR), stellar winds from massive stars, and a pulsar wind nebula (PWN). Although a leptonic origin from a PWN driven by an unknown pulsar remains possible, hadronic-origin emission from an unknown SNR is preferred.
79 ASTRONOMY AND ASTROPHYSICS↗
DISCOVERY OF GAMMA-RAY EMISSION FROM THE SUPERNOVA REMNANT Kes 17 WITH FERMI LARGE AREA TELESCOPE
We report the discovery of GeV emission at the position of supernova remnant Kes 17 by using the data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Kes 17 can be clearly detected with a significance of {approx}12{sigma} in the 1-20 GeV range. Moreover, a number of {gamma}-ray sources were detected in its vicinity. The {gamma}-ray spectrum of Kes 17 can be described well by a simple power law with a photon index of {Gamma} {approx} 2.4. Together with the multiwavelength evidence for its interactions with the nearby molecular cloud, the {gamma}-ray detection suggests that Kes 17 is a candidate acceleration site for cosmic rays.
79 ASTRONOMY AND ASTROPHYSICS↗
IDENTIFICATION OF THE INFRARED NON-THERMAL EMISSION IN BLAZARS
Blazars constitute the most interesting and enigmatic class of extragalactic {gamma}-ray sources dominated by non-thermal emission. In this Letter, we show how the Wide Infrared Survey Explorer (WISE) infrared data make it possible to identify a distinct region of the [3.4]-[4.6]-[12] {mu}m color-color diagram where the sources dominated by the thermal radiation are separated from those dominated by non-thermal emission, in particular the blazar population. This infrared non-thermal region, which we indicate as the WISE blazar strip (WBS), will constitute a new powerful diagnostic tool when the full WISE survey data are released. The WBS can be used to extract new blazar candidates, to identify those of uncertain type and also to search for the counterparts of unidentified {gamma}-ray sources. We show one example of the value of the use of the WBS identifying the TeV source VER J0648+152, recently discovered by VERITAS.
79 ASTRONOMY AND ASTROPHYSICS↗
SUPERNOVA-ENHANCED COSMIC-RAY IONIZATION AND INDUCED CHEMISTRY IN A MOLECULAR CLOUD OF W51C
Cosmic rays (CRs) pervade the Galaxy and are thought to be accelerated in supernova shocks. The interaction of CRs with dense interstellar matter has two important effects: (1) high-energy ({approx}>1 GeV) protons produce {gamma}-rays by {pi}{sup 0}-meson decay and (2) low-energy ({approx}<1 GeV) CRs (protons and electrons) ionize the gas. We present here new observations toward a molecular cloud close to the W51C supernova remnant and associated with a recently discovered TeV {gamma}-ray source. Our observations show that the cloud ionization degree is highly enhanced, implying a CR ionization rate {approx}10{sup -15} s{sup -1}, i.e., 100 times larger than the standard value in molecular clouds. This is consistent with the idea that the cloud is irradiated by an enhanced flux of freshly accelerated low-energy CRs. In addition, the observed high CR ionization rate leads to an instability in the chemistry of the cloud, which keeps the electron fraction high, {approx}10{sup -5}, in a large fraction (A {sub v} {>=} 6 mag) of the cloud and low, {approx}10{sup -7}, in the interior. The two states have been predicted in the literature as high- and low-ionization phases (HIP and LIP). This is the observational evidence of their simultaneous presence in a cloud.
79 ASTRONOMY AND ASTROPHYSICS↗
Magnetar-like X-Ray Bursts Suppress Pulsar Radio Emission
Rotation-powered pulsars and magnetars are two different observational manifestations of neutron stars: rotation-powered pulsars are rapidly spinning objects that are mostly observed as pulsating radio sources, while magnetars, neutron stars with the highest known magnetic fields, often emit short-duration X-ray bursts. Here, we report simultaneous observations of the high-magnetic-field radio pulsar PSR J1119−6127 at X-ray, with XMM-Newton and NuSTAR , and at radio energies with the Parkes radio telescope, during a period of magnetar-like bursts. The rotationally powered radio emission shuts off coincident with the occurrence of multiple X-ray bursts and recovers on a timescale of ∼70 s. These observations of related radio and X-ray phenomena further solidify the connection between radio pulsars and magnetars and suggest that the pair plasma produced in bursts can disrupt the acceleration mechanism of radio-emitting particles.
79 ASTRONOMY AND ASTROPHYSICS↗
THE EVOLUTION OF RADIO GALAXIES AND X-RAY POINT SOURCES IN COMA CLUSTER PROGENITORS SINCE z {approx} 1.2
Using Chandra imaging spectroscopy and Very Large Array (VLA) L-band radio maps, we have identified radio sources at P{sub 1.4GHz} {>=} 5 x 10{sup 23} W Hz{sup -1} and X-ray point sources (XPSs) at L{sub 0.3-8 keV} {>=} 5 x 10{sup 42} erg s{sup -1} in L > L* galaxies in 12 high-redshift (0.4 < z < 1.2) clusters of galaxies. The radio galaxies and XPSs in this cluster sample, chosen to be consistent with Coma Cluster progenitors at these redshifts, are compared to those found at low-z analyzed in Hart et al. Within a projected radius of 1 Mpc of the cluster cores, we find 17 cluster radio galaxies (11 with secure redshifts, including one luminous FR II radio source at z = 0.826, and six more with host galaxy colors similar to cluster ellipticals). The radio luminosity function (RLF) of the cluster radio galaxies as a fraction of the cluster red-sequence (CRS) galaxies reveals significant evolution of this population from high-z to low-z, with higher power radio galaxies situated in lower temperature clusters at earlier epochs. Additionally, there is some evidence that cluster radio galaxies become more centrally concentrated than CRS galaxies with cosmic time. Within this same projected radius, we identify seven spectroscopically confirmed cluster XPSs, all with CRS host galaxy colors. Consistent with the results from Martini et al., we estimate a minimum X-ray active fraction of 1.4% {+-} 0.8% for CRS galaxies in high-z clusters, corresponding to an approximate 10-fold increase from 0.15% {+-} 0.15% at low-z. Although complete redshift information is lacking for several XPSs in z > 0.4 cluster fields, the increased numbers and luminosities of the CRS radio galaxies and XPSs suggest a substantial (9-10-fold) increase in the heat injected into high-redshift clusters by AGNs compared to the present epoch.
79 ASTRONOMY AND ASTROPHYSICS↗
TRACING THE SOURCES OF COSMIC RAYS WITH MOLECULAR IONS
The rate of ionization by cosmic rays (CRs) in interstellar gas directly associated with {gamma}-ray-emitting supernova remnants (SNRs) is for the first time calculated to be several orders of magnitude larger than the Galactic average. Analysis of ionization-induced chemistry yields the first quantitative prediction of the astrophysical H{sup +} {sub 2} emission line spectrum, which should be detectable together with H{sup +} {sub 3} lines. The predicted coincident observation of those emission lines and {gamma}-rays will help prove that SNRs are sources of CRs.
79 ASTRONOMY AND ASTROPHYSICS↗
Radio and γ -Ray Variability in the BL Lac PKS 0219−164: Detection of Quasi-periodic Oscillations in the Radio Light Curve
In this work, we explore the long-term variability properties of the blazar PKS 0219−164 in the radio and the γ -ray regime, utilizing the OVRO 15 GHz and the Fermi /LAT observations from the period 2008–2017. We found that γ -ray emission is more variable than the radio emission implying that γ -ray emission possibly originated in more compact regions while the radio emission represented continuum emission from the large-scale jets. Also, in the γ -ray, the source exhibited spectral variability, characterized by the softer-when-brighter trend, a less frequently observed feature in the high-energy emission by BL Lacs. In radio, using Lomb–Scargle periodogram and weighted wavelet z -transform, we detected a strong signal of quasi-periodic oscillation (QPO) with a periodicity of 270 ± 26 days with possible harmonics of 550 ± 42 and 1150 ± 157 day periods. At a time when detections of QPOs in blazars are still under debate, the observed QPO with high statistical significance (∼97%–99% global significance over underlying red-noise processes) and persistent over nearly 10 oscillations could make one of the strongest cases for the detection of QPOs in blazar light curves. We discuss various blazar models that might lead to the γ -ray and radio variability, QPO, and the achromatic behavior seen in the high-energy emission from the source.
79 ASTRONOMY AND ASTROPHYSICS↗
X-RAY AND RADIO OBSERVATIONS OF THE MASSIVE STAR-FORMING REGION IRAS 20126+4104
We present results from Chandra ACIS-I and Karl G. Jansky Very Large Array 6 cm continuum observations of the IRAS 20126+4104 massive star-forming region. We detect 150 X-ray sources within the 17′ × 17′ ACIS-I field, and a total of 13 radio sources within the 9.′2 primary beam at 4.9 GHz. Among these observtions are the first 6 cm detections of the central sources reported by Hofner et al., namely, I20N1, I20S, and I20var. A new variable radio source is also reported. Searching the 2MASS archive, we identified 88 near-infrared (NIR) counterparts to the X-ray sources. Only four of the X-ray sources had 6 cm counterparts. Based on an NIR color–color analysis and on the Besançon simulation of Galactic stellar populations, we estimate that approximately 80 X-ray sources are associated with this massive star-forming region. We detect an increasing surface density of X-ray sources toward the massive protostar and infer the presence of a cluster of at least 43 young stellar objects within a distance of 1.2 pc from the massive protostar.
79 ASTRONOMY AND ASTROPHYSICS↗
DISCOVERY OF DRAMATIC OPTICAL VARIABILITY IN SDSS J1100+4421: A PECULIAR RADIO-LOUD NARROW-LINE SEYFERT 1 GALAXY?
We present our discovery of dramatic variability in SDSS J1100+4421 by the high-cadence transient survey Kiso Supernova Survey. The source brightened in the optical by at least a factor of three within about half a day. Spectroscopic observations suggest that this object is likely a narrow-line Seyfert 1 galaxy (NLS1) at z = 0.840, however, with unusually strong narrow emission lines. The estimated black hole mass of ∼10{sup 7} M {sub ☉} implies bolometric nuclear luminosity close to the Eddington limit. SDSS J1100+4421 is also extremely radio-loud, with a radio loudness parameter of R ≅ 4 × 10{sup 2}-3 × 10{sup 3}, which implies the presence of relativistic jets. Rapid and large-amplitude optical variability of the target, reminiscent of that found in a few radio- and γ-ray-loud NLS1s, is therefore produced most likely in a blazar-like core. The 1.4 GHz radio image of the source shows an extended structure with a linear size of about 100 kpc. If SDSS J1100+4421 is a genuine NLS1, as suggested here, this radio structure would then be the largest ever discovered in this type of active galaxies.
79 ASTRONOMY AND ASTROPHYSICS↗
BURST AND PERSISTENT EMISSION PROPERTIES DURING THE RECENT ACTIVE EPISODE OF THE ANOMALOUS X-RAY PULSAR 1E 1841-045
The Swift/Burst Alert Telescope detected the first burst from 1E 1841-045 in 2010 May with intermittent burst activity recorded through at least 2011 July. Here we present Swift and Fermi/Gamma-ray Burst Monitor observations of this burst activity and search for correlated changes to the persistent X-ray emission of the source. The T {sub 90} durations of the bursts range between 18 and 140 ms, comparable to other magnetar burst durations, while the energy released in each burst ranges between (0.8-25) x 10{sup 38} erg, which is on the low side of soft gamma repeater bursts. We find that the bursting activity did not have a significant effect on the persistent flux level of the source. We argue that the mechanism leading to this sporadic burst activity in 1E 1841-045 might not involve large-scale restructuring (either crustal or magnetospheric) as seen in other magnetar sources.
79 ASTRONOMY AND ASTROPHYSICS↗
DIFFUSIVE SHOCK ACCELERATION SIMULATIONS OF RADIO RELICS
Recent radio observations have identified a class of structures, so-called radio relics, in clusters of galaxies. The radio emission from these sources is interpreted as synchrotron radiation from GeV electrons gyrating in {mu}G-level magnetic fields. Radio relics, located mostly in the outskirts of clusters, seem to associate with shock waves, especially those developed during mergers. In fact, they seem to be good structures to identify and probe such shocks in intracluster media (ICMs), provided we understand the electron acceleration and re-acceleration at those shocks. In this paper, we describe time-dependent simulations for diffusive shock acceleration at weak shocks that are expected to be found in ICMs. Freshly injected as well as pre-existing populations of cosmic-ray (CR) electrons are considered, and energy losses via synchrotron and inverse Compton are included. We then compare the synchrotron flux and spectral distributions estimated from the simulations with those in two well-observed radio relics in CIZA J2242.8+5301 and ZwCl0008.8+5215. Considering that CR electron injection is expected to be rather inefficient at weak shocks with Mach number M {approx}< a few, the existence of radio relics could indicate the pre-existing population of low-energy CR electrons in ICMs. The implication of our results on the merger shock scenario of radio relics is discussed.
79 ASTRONOMY AND ASTROPHYSICS↗
THE CHANDRA SURVEY OF EXTRAGALACTIC SOURCES IN THE 3CR CATALOG: X-RAY EMISSION FROM NUCLEI, JETS, AND HOTSPOTS IN THE CHANDRA ARCHIVAL OBSERVATIONS
As part of our program to build a complete radio and X-ray database of all Third Cambridge catalog extragalactic radio sources, we present an analysis of 93 sources for which Chandra archival data are available. Most of these sources have already been published. Here we provide a uniform re-analysis and present nuclear X-ray fluxes and X-ray emission associated with radio jet knots and hotspots using both publicly available radio images and new radio images that have been constructed from data available in the Very Large Array archive. For about 1/3 of the sources in the selected sample, a comparison between the Chandra and radio observations was not reported in the literature: we find X-ray detections of 2 new radio jet knots and 17 hotspots. We also report the X-ray detection of extended emission from the intergalactic medium for 15 galaxy clusters.
79 ASTRONOMY AND ASTROPHYSICS↗