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Start Over Subject gamma-ray astronomy
91. 3FGL Blazar of Unknown Type classification
ID:
ivo://CDS.VizieR/J/MNRAS/462/3180
Title:
3FGL Blazar of Unknown Type classification
Short Name:
J/MNRAS/462/3180
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Fermi-Large Area Telescope (LAT) is currently the most important facility for investigating the GeV {gamma}-ray sky. With Fermi-LAT, more than three thousand {gamma}-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 {gamma}-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.
92. 2FGL J0846.0+2820 opt. counterpart follow-up
ID:
ivo://CDS.VizieR/J/ApJ/851/31
Title:
2FGL J0846.0+2820 opt. counterpart follow-up
Short Name:
J/ApJ/851/31
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present optical photometric and spectroscopic observations of the likely stellar counterpart to the unassociated Fermi Large Area Telescope (LAT) {gamma}-ray source 2FGL J0846.0+2820, selected for study based on positional coincidences of optical variables with unassociated LAT sources. Using optical spectroscopy from the SOAR telescope, we have identified a late-G giant in an eccentric (e=0.06) 8.133-day orbit with an invisible primary. Modeling the spectroscopy and photometry together led us to infer a heavy neutron star primary of ~2M_{sun}_ and a partially stripped giant secondary of ~0.8M_{sun}_. H{alpha} emission is observed in some of the spectra, perhaps consistent with the presence of a faint accretion disk. We find that the {gamma}-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009, accompanied by an increased variation in the optical brightness, and since then, it has not been detected by Fermi. The long period and giant secondary are reminiscent of the {gamma}-ray bright binary 1FGL J1417.7-4407, which hosts a millisecond pulsar (MSP) apparently in the final stages of the pulsar recycling process. The discovery of 2FGL J0846.0+2820 suggests the identification of a new subclass of MSP binaries that are the likely progenitors of typical field MSPs.
93. 2FGL sources observed between 5-9GHz
ID:
ivo://CDS.VizieR/J/ApJS/217/4
Title:
2FGL sources observed between 5-9GHz
Short Name:
J/ApJS/217/4
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of an all-sky radio survey between 5 and 9GHz of sky areas surrounding all unassociated {gamma}-ray objects listed in the Fermi Large Area Telescope Second Source Catalog (2FGL). The goal of these observations is to find all new {gamma}-ray active galactic nucleus (AGN) associations with radio sources >10mJy at 8GHz. We observed with the Very Large Array and the Australia Telescope Compact Array the areas around unassociated sources, providing localizations of weak radio point sources found in 2FGL fields at arcmin scales. Then we followed-up a subset of those with the Very Long Baseline and the Long Baseline Arrays to confirm detections of radio emission on parsec-scales. We quantified association probabilities based on known statistics of source counts and assuming a uniform distribution of background sources. In total we found 865 radio sources at arcsec scales as candidates for association and detected 95 of 170 selected for follow-up observations at milliarcsecond resolution. Based on this we obtained firm associations for 76 previously unknown {gamma}-ray AGNs. Comparison of these new AGN associations with the predictions from using the Wide-field Infrared Survey Explorer color-color diagram shows that half of the associations are missed. We found that 129 out of 588 observed {gamma}-ray sources at arcmin scales not a single radio continuum source was detected above our sensitivity limit within the 3{sigma} {gamma}-ray localization. These "empty" fields were found to be particularly concentrated at low Galactic latitudes. The nature of these Galactic {gamma}-ray emitters is not yet determined.
94. 3FGL sources statistical classifications
ID:
ivo://CDS.VizieR/J/ApJ/820/8
Title:
3FGL sources statistical classifications
Short Name:
J/ApJ/820/8
Date:
21 Oct 2021
Publisher:
CDS
Description:
We apply a number of statistical and machine learning techniques to classify and rank gamma-ray sources from the Third Fermi Large Area Telescope Source Catalog (3FGL), according to their likelihood of falling into the two major classes of gamma-ray emitters: pulsars (PSR) or active galactic nuclei (AGNs). Using 1904 3FGL sources that have been identified/associated with AGNs (1738) and PSR (166), we train (using 70% of our sample) and test (using 30%) our algorithms and find that the best overall accuracy (>96%) is obtained with the Random Forest (RF) technique, while using a logistic regression (LR) algorithm results in only marginally lower accuracy. We apply the same techniques on a subsample of 142 known gamma-ray pulsars to classify them into two major subcategories: young (YNG) and millisecond pulsars (MSP). Once more, the RF algorithm has the best overall accuracy (~90%), while a boosted LR analysis comes a close second. We apply our two best models (RF and LR) to the entire 3FGL catalog, providing predictions on the likely nature of unassociated sources, including the likely type of pulsar (YNG or MSP). We also use our predictions to shed light on the possible nature of some gamma-ray sources with known associations (e.g., binaries, supernova remnants/pulsar wind nebulae). Finally, we provide a list of plausible X-ray counterparts for some pulsar candidates, obtained using Swift, Chandra, and XMM. The results of our study will be of interest both for in-depth follow-up searches (e.g., pulsar) at various wavelengths and for broader population studies.
95. 4FGL sources with IR/Rad associations
ID:
ivo://CDS.VizieR/J/ApJS/248/23
Title:
4FGL sources with IR/Rad associations
Short Name:
J/ApJS/248/23
Date:
09 Nov 2021 09:30:22
Publisher:
CDS
Description:
Associating {gamma}-ray sources to their low-energy counterparts is one of the major challenges of modern {gamma}-ray astronomy. In the context of the Fourth Fermi Large Area Telescope Source Catalog (4FGL), the associations rely mainly on parameters such as apparent magnitude, integrated flux, and angular separation between the {gamma}-ray source and its low-energy candidate counterpart. In this work, we propose a new use of the likelihood ratio (LR) and a complementary supervised learning technique to associate {gamma}-ray blazars in 4FGL, based only on spectral parameters such as the {gamma}-ray photon index, mid-infrared colors, and radio-loudness. In the LR approach, we crossmatch the Wide-field Infrared Survey Explorer Blazar-Like Radio-Loud Sources catalog with 4FGL and compare the resulting candidate counterparts with the sources listed in the {gamma}-ray blazar locus to compute an association probability (AP) for 1138 counterparts. In the supervised learning approach, we train a random forest algorithm with 869 high-confidence blazar associations and 711 fake associations and then compute an AP for 1311 candidate counterparts. A list with all 4FGL blazar candidates of uncertain type associated by our method is provided to guide future optical spectroscopic follow-up observations.
96. First AGILE catalog of gamma-ray sources
ID:
ivo://CDS.VizieR/J/A+A/506/1563
Title:
First AGILE catalog of gamma-ray sources
Short Name:
J/A+A/506/1563
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first catalog of high-confidence {gamma}-ray sources detected by the AGILE satellite during observations performed from July 9, 2007 to June 30, 2008. Cataloged sources were detected by merging all the available data over the entire time period. AGILE, launched in April 2007, is an ASI mission devoted to {gamma}-ray observations in the 30MeV-50GeV energy range, with simultaneous X-ray imaging capability in the 18-60keV band. This catalog is based on Gamma-Ray Imaging Detector (GRID) data for energies greater than 100MeV. For the first AGILE catalog, we adopted a conservative analysis, with a high-quality event filter optimized to select {gamma}-ray events within the central zone of the instrument field of view (radius of 40{deg}). This is a significance-limited (4{sigma}) catalog, and it is not a complete flux-limited sample due to the non-uniform first-year AGILE sky coverage. The catalog includes 47 sources, 21 of which are associated with confirmed or candidate pulsars, 13 with blazars (7 FSRQ, 4 BL Lacs, 2 unknown type), 2 with HMXRBs, 2 with SNRs, 1 with a colliding-wind binary system, and 8 with unidentified sources.
97. First COMPTEL source catalogue
ID:
ivo://CDS.VizieR/J/A+AS/143/145
Title:
First COMPTEL source catalogue
Short Name:
J/A+AS/143/145
Date:
21 Oct 2021
Publisher:
CDS
Description:
The imaging Compton telescope COMPTEL aboard NASA's Compton Gamma-Ray Observatory (CGRO) has opened the MeV gamma-ray band as a new window to astronomy. COMPTEL provided the first complete all-sky survey in the energy range 0.75 to 30MeV. The catalogue, presented here, is largely restricted to published results. It contains firm as well as marginal detections of continuum and line emitting sources and presents upper limits for various types of objects. The numbers of the most significant detections are 32 for steady sources and 31 for gamma-ray bursters. Among the continuum sources, detected so far, are spin-down pulsars, stellar black-hole candidates, supernova remnants, interstellar clouds, nuclei of active galaxies, gamma-ray bursters, and the Sun during solar flares. Line detections have been made in the light of the 1.809MeV ^26^Al line, the 1.157MeV ^44^Ti line, the 847 and 1238keV ^56^Co lines, and the neutron capture line at 2.223MeV. For the identification of galactic sources, a modelling of the diffuse galactic emission is essential. Such a modelling at this time does not yet exist at the required degree of accuracy. Therefore, a second COMPTEL source catalogue will be produced after a detailed and accurate modelling of the diffuse interstellar emission has become possible.
98. First Fermi-LAT AGN catalog (1LAC)
ID:
ivo://CDS.VizieR/J/ApJ/715/429
Title:
First Fermi-LAT AGN catalog (1LAC)
Short Name:
J/ApJ/715/429
Date:
21 Oct 2021
Publisher:
CDS
Description:
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 {gamma}-ray sources located at high Galactic latitudes (|b|>10{deg}) 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 blazars 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.
99. First Fermi-LAT Inner Galaxy point source catalog
ID:
ivo://CDS.VizieR/J/ApJ/819/44
Title:
First Fermi-LAT Inner Galaxy point source catalog
Short Name:
J/ApJ/819/44
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy {gamma}-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1-100GeV from a 15{deg}x15{deg} region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the {gamma}-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ~1kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15{deg}x15{deg} region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with {gamma}-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.
100. First IBIS Catalog: 20-100keV
ID:
ivo://CDS.VizieR/J/ApJ/607/L33
Title:
First IBIS Catalog: 20-100keV
Short Name:
J/ApJ/607/L33
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the first high-energy survey catalog obtained with the IBIS gamma-ray imager on board INTEGRAL. The analysis has been performed on the first-year Core Program ISGRI data comprising both Galactic Plane Scan and Galactic Centre Deep Exposure pointings for a total exposure time exceeding 5Ms. This initial survey has revealed the presence of ~120 sources detected with the unprecedented sensitivity of ~1mCrab in the energy range 20-100keV. Each source is located to an accuracy between 1' and 3', depending on its brightness. The outstanding IBIS capability to locate soft {gamma}-ray emitters has allowed us to identify most of the detected sources with already known Galactic X-ray binary systems, while 28 of the objects are of unknown nature.