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Start Over Subject gamma-ray astronomy
291. Proton synchrotron gamma-rays in blazars
ID:
ivo://CDS.VizieR/J/ApJ/893/L20
Title:
Proton synchrotron gamma-rays in blazars
Short Name:
J/ApJ/893/L20
Date:
21 Oct 2021
Publisher:
CDS
Description:
The origin of high-energy emission in blazars jets (i.e., leptonic versus hadronic) has been a longstanding matter of debate. Here, we focus on one variant of hadronic models where proton synchrotron radiation accounts for the observed steady {gamma}-ray blazar emission. Using analytical methods, we derive the minimum jet power (P_j,min_) for the largest blazar sample analyzed to date (145 sources), taking into account uncertainties of observables and jet's physical parameters. We compare P_j,min_ against three characteristic energy estimators for accreting systems, i.e., the Eddington luminosity, the accretion disk luminosity, and the power of the Blandford-Znajek process, and find that P_j,min_ is about 2 orders of magnitude higher than all energetic estimators for the majority of our sample. The derived magnetic field strengths in the emission region require either large amplification of the jet's magnetic field (factor of 30) or place the {gamma}-ray production site at sub-pc scales. The expected neutrino emission peaks at ~0.1-10EeV, with typical peak neutrino fluxes ~10^-4^ times lower than the peak {gamma}-ray fluxes. We conclude that if relativistic hadrons are present in blazar jets, they can only produce a radiatively subdominant component of the overall spectral energy distribution of the blazar's steady emission.
292. PSR J0537-6910 gamma-ray emission
ID:
ivo://CDS.VizieR/J/A+A/545/L2
Title:
PSR J0537-6910 gamma-ray emission
Short Name:
J/A+A/545/L2
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the significant detection of the first extragalactic pulsar wind nebula (PWN) detected in gamma rays, N157B, located in the large Magellanic Cloud (LMC). Pulsars with high spin-down luminosity are found to power energised nebulae that emit gamma rays up to energies of several tens of TeV. N157B is associated with PSRJ0537-6910, which is the pulsar with the highest known spin-down luminosity. The High Energy Stereoscopic System telescope array observed this nebula on a yearly basis from 2004 to 2009 with a dead-time corrected exposure of 46h. The gamma-ray spectrum between 600GeV and 12TeV is well-described by a pure power-law with a photon index of 2.8+/-0.2stat+/-0.3syst and a normalisation at 1TeV of (8.2+/-0.8stat+/-2.5syst)x10^-13^/cm^2^/s/TeV. A leptonic multi-wavelength model shows that an energy of about 4x10^49^erg is stored in electrons and positrons. The apparent efficiency, which is the ratio of the TeV gamma-ray luminosity to the pulsar's spin-down luminosity, 0.08%+/-0.01%, is comparable to those of PWNe found in the Milky Way. The detection of a PWN at such a large distance is possible due to the pulsar's favourable spin-down luminosity and a bright infrared photon-field serving as an inverse-Compton-scattering target for accelerated leptons. By applying a calorimetric technique to these observations, the pulsar's birth period is estimated to be shorter than 10ms.
293. Pulsars in {gamma}-ray sources
ID:
ivo://CDS.VizieR/J/MNRAS/424/2832
Title:
Pulsars in {gamma}-ray sources
Short Name:
J/MNRAS/424/2832
Date:
21 Oct 2021
Publisher:
CDS
Description:
Machine learning, algorithms designed to extract empirical knowledge from data, can be used to classify data, which is one of the most common tasks in observational astronomy. In this paper, we focus on Bayesian data classification algorithms using the Gaussian mixture model and show two applications in pulsar astronomy. After reviewing the Gaussian mixture model and the related expectation-maximization algorithm, we present a data classification method using the Neyman-Pearson test. To demonstrate the method, we apply the algorithm to two classification problems. First, it is applied to the well-known period-period derivative diagram. Our second example is to calculate the likelihood of unidentified Fermi point sources being pulsars.
294. Pulsar Timing for Fermi Gamma-ray Space Telescope
ID:
ivo://CDS.VizieR/J/A+A/492/923
Title:
Pulsar Timing for Fermi Gamma-ray Space Telescope
Short Name:
J/A+A/492/923
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe a comprehensive pulsar monitoring campaign for the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST). The detection and study of pulsars in gamma rays give insights into the populations of neutron stars and supernova rates in the Galaxy, into particle acceleration mechanisms in neutron star magnetospheres, and into the "engines" driving pulsar wind nebulae. LAT's unprecedented sensitivity between 20MeV and 300GeV together with its 2.4sr field-of-view makes detection of many gamma-ray pulsars likely, justifying the monitoring of over two hundred pulsars with large spin-down powers. To search for gamma-ray pulsations from most of these pulsars requires a set of phase-connected timing solutions spanning a year or more to properly align the sparse photon arrival times. We describe the choice of pulsars and the instruments involved in the campaign.
295. Quasi-periodic pulsations in solar flares
ID:
ivo://CDS.VizieR/J/ApJ/833/284
Title:
Quasi-periodic pulsations in solar flares
Short Name:
J/ApJ/833/284
Date:
21 Oct 2021
Publisher:
CDS
Description:
The nature of quasi-periodic pulsations (QPP) in solar flares is poorly constrained, and critically the general prevalence of such signals in solar flares is unknown. Therefore, we perform a large-scale search for evidence of signals consistent with QPP in solar flares, focusing on the 1-300s timescale. We analyze 675 M- and X-class flares observed by the Geostationary Operational Environmental Satellite (GOES) series in 1-8 A soft X-rays between 2011 February 1 and 2015 December 31. Additionally, over the same era we analyze Fermi/Gamma-ray Burst Monitor (GBM) 15-25keV X-ray data for each of these flares associated with a Fermi/GBM solar flare trigger, a total of 261 events. Using a model comparison method, we determine whether there is evidence for a substantial enhancement in the Fourier power spectrum that may be consistent with a QPP signature, based on three tested models; a power-law plus a constant, a broken power-law plus constant, and a power-law-plus-constant with an additional QPP signature component. From this, we determine that ~30% of GOES events and ~8% of Fermi/GBM events show strong signatures consistent with classical interpretations of QPP. For the remaining events either two or more tested models cannot be strongly distinguished from each other, or the events are well-described by single power-law or broken power-law Fourier power spectra. For both instruments, a preferred characteristic timescale of ~5-30s was found in the QPP-like events, with no dependence on flare magnitude in either GOES or GBM data. We also show that individual events in the sample show similar characteristic timescales in both GBM and GOES data sets. We discuss the implications of these results for our understanding of solar flares and possible QPP mechanisms.
296. Radio afterglow observations of GRBs
ID:
ivo://CDS.VizieR/J/ApJ/746/156
Title:
Radio afterglow observations of GRBs
Short Name:
J/ApJ/746/156
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a catalog of radio afterglow observations of gamma-ray bursts (GRBs) over a 14 year period from 1997 to 2011. Our sample of 304 afterglows consists of 2995 flux density measurements (including upper limits) at frequencies between 0.6 GHz and 660 GHz, with the majority of data taken at 8.5 GHz frequency band (1539 measurements). We use this data set to carry out a statistical analysis of the radio-selected sample. The detection rate of radio afterglows has stayed unchanged almost at 31% before and after the launch of the Swift satellite. The canonical long-duration GRB radio light curve at 8.5 GHz peaks at three to six days in the source rest frame, with a median peak luminosity of 10^31^ erg/s/Hz. The peak radio luminosities for short-hard bursts, X-ray flashes, and the supernova-GRB classes are an order of magnitude or more fainter than this value. There are clear relationships between the detectability of a radio afterglow and the fluence or energy of a GRB, and the X-ray or optical brightness of the afterglow. However, we find few significant correlations between these same GRB and afterglow properties and the peak radio flux density. We also produce synthetic light curves at centimeter and millimeter bands using a range of blast wave and microphysics parameters derived from multiwavelength afterglow modeling, and we use them to compare to the radio sample. Finding agreement, we extrapolate this behavior to predict the centimeter and millimeter behavior of GRBs observed by the Expanded Very Large Array and the Atacama Large Millimeter Array.
297. Radio core dominance of Fermi/LAT-detected AGNs
ID:
ivo://CDS.VizieR/VIII/108
Title:
Radio core dominance of Fermi/LAT-detected AGNs
Short Name:
VIII/108
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a sample of 4388 AGNs with available radio core-dominance parameters-defined as the ratio of the core flux densities to the extended ones, R=S_core_/S_ext._ - which includes 630 Fermi-detected AGNs from the fourth source catalog (4FGL) of the Fermi Large Area Telescope (Fermi/LAT); the rest are non-Fermi-detected AGNs. In our sample, 584 blazars are Fermi-detected and 1310 are not. The sample also contains other subclasses, such as Seyferts, Fanaroff-Riley I/II galaxies, and normal galaxies. We investigate various properties of the Fermi-detected and non-Fermi-detected AGNs by using core-dominance parameters, capitalizing on a previous study which showed that R is a good indicator of beaming. We then calculate radio spectral indices for the whole sample, and adopt {gamma}-ray-photon indices for the Fermi AGNs from the 4FGL catalog to discuss the properties of different subclasses. We obtain a relation between the core-dominance parameters and the radio spectral indices for both Fermi and non-Fermi sources, assuming a two-component model in the radio band. Our previous study ruled out the assumption that the core-dominance parameters and radio spectral indices are quite different for different AGN subclasses. This holds not only for Fermi sources but also for non-Fermi sources. In particular, R is, on average, greater for the former AGNs than for the latter. In this study, we enlarge our sample with available values of R to 4388 AGNs, and the obtained conclusions are consistent with our previous study. We assume that the same two-component model holds for the {gamma}-ray band as for the radio band, and therefore, adopt the same relation between the core-dominance parameters and the {gamma}-ray-photon indices for Fermi AGNs. Our fitting results indicate that the {gamma}-ray emissions of Fermi blazars originate mainly from the jet, and therefore, we conclude that the Fermi blazars are beamed.
298. Radio detections of 3G sources
ID:
ivo://CDS.VizieR/J/A+A/482/247
Title:
Radio detections of 3G sources
Short Name:
J/A+A/482/247
Date:
21 Oct 2021
Publisher:
CDS
Description:
A considerable fraction of the gamma-ray sources discovered with the Energetic Gamma-Ray Experiment Telescope (EGRET) remain unidentified. The EGRET sources that have been properly identified are either pulsars or variable sources at both radio and gamma-ray wavelengths. Most of the variable sources are strong radio blazars. However, some low galactic-latitude EGRET sources, with highly variable gamma-ray emission, lack any evident counterpart according to the radio data available until now. The primary goal of this paper is to identify and characterise the potential radio counterparts of four highly variable gamma-ray sources in the galactic plane through mapping the radio surroundings of the EGRET confidence contours and determining the variable radio sources in the field whenever possible. We have carried out a radio exploration of the fields of the selected EGRET sources using the Giant Metrewave Radio Telescope (GMRT) interferometer at 21 cm wavelength, with pointings being separated by months.
299. Radio follow-up on 3FGL unassociated sources
ID:
ivo://CDS.VizieR/J/ApJ/838/139
Title:
Radio follow-up on 3FGL unassociated sources
Short Name:
J/ApJ/838/139
Date:
21 Oct 2021
Publisher:
CDS
Description:
The third Fermi Large Area Telescope {gamma}-ray source catalog (3FGL) contains over 1000 objects for which there is no known counterpart at other wavelengths. The physical origin of the {gamma}-ray emission from those objects is unknown. Such objects are commonly referred to as unassociated and mostly do not exhibit significant {gamma}-ray flux variability. We performed a survey of all unassociated {gamma}-ray sources found in 3FGL using the Australia Telescope Compact Array and Very Large Array in the range 4.0-10.0 GHz. We found 2097 radio candidates for association with {gamma}-ray sources. The follow-up with very long baseline interferometry for a subset of those candidates yielded 142 new associations with active galactic nuclei that are {gamma}-ray sources, provided alternative associations for seven objects, and improved positions for another 144 known associations to the milliarcsecond level of accuracy. In addition, for 245 unassociated {gamma}-ray sources we did not find a single compact radio source above 2 mJy within 3{sigma} of their {gamma}-ray localization. A significant fraction of these empty fields, 39%, are located away from the Galactic plane. We also found 36 extended radio sources that are candidates for association with a corresponding {gamma}-ray object, 19 of which are most likely supernova remnants or H II regions, whereas 17 could be radio galaxies.
300. Radio/{gamma}-ray correlation in AGN
ID:
ivo://CDS.VizieR/J/ApJ/741/30
Title:
Radio/{gamma}-ray correlation in AGN
Short Name:
J/ApJ/741/30
Date:
21 Oct 2021
Publisher:
CDS
Description:
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 8.4GHz data (from the Very Large Array and ATCA, for the full sample of 599 sources) and concurrent single-dish 15GHz 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 a surrogate data method designed to simultaneously account for common-distance bias and the effect of a limited dynamical range in the observed quantities.