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71. Fermi LAT third source catalog (3FGL)
ID:
ivo://CDS.VizieR/J/ApJS/218/23
Title:
Fermi LAT third source catalog (3FGL)
Short Name:
J/ApJS/218/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in the 100MeV-300GeV range. Based on the first 4yr of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the Second Fermi LAT catalog, the 3FGL catalog incorporates twice as much data, as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse {gamma}-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources above 4{sigma} significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 238 sources are considered as identified based on angular extent or correlated variability (periodic or otherwise) observed at other wavelengths. For 1010 sources we have not found plausible counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. From source counts of Galactic sources we estimate that the contribution of unresolved sources to the Galactic diffuse emission is ~3% at 1GeV.
72. Fermi sources with massive YSO associations
ID:
ivo://CDS.VizieR/J/A+A/530/A72
Title:
Fermi sources with massive YSO associations
Short Name:
J/A+A/530/A72
Date:
21 Oct 2021
Publisher:
CDS
Description:
Massive protostars have associated bipolar outflows that can produce strong shocks when they interact with the surrounding medium. At these shocks, particles can be accelerated up to relativistic energies. Relativistic electrons and protons can then produce gamma-ray emission, as some theoretical models predict. To identify young galactic objects that may emit gamma rays, we crossed the Fermi First Year Catalog with some catalogs of known massive young stellar objects (MYSOs), early type stars, and OB associations, and we implemented Monte Carlo simulations to find the probability of chance coincidences. We obtained a list of massive MYSOs that are spatially coincident with Fermi sources.
73. Fermi superluminal sources
ID:
ivo://CDS.VizieR/IX/60
Title:
Fermi superluminal sources
Short Name:
IX/60
Date:
07 Mar 2022 07:19:31
Publisher:
CDS
Description:
Paper I (2019SCPMA..62l9811X): Active galactic nuclei (AGNs) have been attracting research attention due to their special observable properties. Specifically, a majority of AGNs are detected by Fermi-LAT missions, but not by Fermi-LAT, which raises the question of weather any differences exist between the two. To answer this issue, we compile a sample of 291 superluminal AGNs (189 FDSs and 102 non-FDSs) from available multi-wavelength radio, optical, and X-ray (or even {gamma}-ray) data and Doppler factors and proper motion ({mu}) (or apparent velocity ({beta}app)); calculated the apparent velocity from their proper motion, Lorentz factor ({GAMMA}), viewing angle ({phi}) and co-moving viewing angle ({phi}co) for the sources with available Doppler factor ({delta}); and performed some statistical analyses for both types. Our study indicated that (1) in terms of average values, FDSs have higher proper motions ({mu}), apparent velocities ({beta}_app_), Doppler factor ({delta}), Lorentz factor ({GAMMA}), and smaller viewing angle ({phi}). Nevertheless, there is no clear difference in co-moving viewing angles ({phi}_co_). The results reveal that FDSs show stronger beaming effect than non-FDSs. (2) In terms of correlations: 1) both sources show positive, mutually correlated fluxes, which become closer in de-beamed fluxes; 2) with respect to apparent velocities and {gamma}-ray luminosity, there is a tendency for the brighter sources to have higher velocities; 3) with regard to viewing angle and observed {gamma}-ray luminosity, log{phi}=-(0.23+/-0.04)logL{gamma}+(11.14+/-1.93), while for the co-moving viewing angle and the intrinsic {gamma}-ray luminosity, log{phi}_co_=(0.09+/-0.01)logL^in^_(gamma)_-(1.73+/-0.48). These correlations show that the luminous {gamma}-ray sources have smaller viewing angles and a larger co-moving viewing angle, which indicate a stronger beaming effect in {gamma}-ray emissions. Paper II (2020AN....341..462X): In our previous work in Xiao et al. (SCPMA, 2019, 62, 129811), we suggested that six superluminal sources could be {gamma}-ray candidates, and in fact, five of them have been confirmed in the fourth Fermi-LAT source catalog (4FGL). In this work, based on the 4FGL, we report a sample of 229 Fermi detected superluminal sources (FDSs), including 40 new FDSs and 62 non-FDSs. Thus, we believe that all superluminal sources should have {gamma}-ray emissions, and superluminal motion could also be a clue to detect {gamma}-ray emission from active galactic nuclei. We present a new approach of Doppler factor estimate through the study of the {gamma}-ray luminosity (L{gamma}) and of the viewing angle ({phi}). Paper III (2020A&C....3200387X): In this work, Machine Learning (ML) methods are used to efficiently identify the unassociated sources and the Blazar Candidate of Uncertain types (BCUs) in the Fermi-LAT Third Source Catalog (3FGL). The aims are twofold: (1) to distinguish the Active Galactic Nuclei (AGNs) from others (non-AGNs) in the unassociated sources; (2) to identify BCUs into BL Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs). Two dimensional reduction methods are presented to decrease computational complexity, where Random Forest (RF), Multilayer Perceptron (MLP) and Generative Adversarial Nets (GAN) are trained as individual models. In order to achieve better performance, the ensemble technique is further explored. It is also demonstrated that grid search method is of help to choose the hyperparameters of models and decide the final predictor, by which we have identified 748 AGNs out of 1010 unassociated sources, with an accuracy of 97.04%. Within the 573 BCUs, 326 have been identified as BL Lacs and 247 as FSRQs, with an accuracy of 92.13%.
74. 4FGL blazar classification neural network
ID:
ivo://CDS.VizieR/J/MNRAS/493/1926
Title:
4FGL blazar classification neural network
Short Name:
J/MNRAS/493/1926
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Fermi Large Area Telescope (LAT) has detected more than 5000 gamma-ray sources in its first 8 years of operation. More than 3000 of them are blazars. About 60 per cent of the Fermi-LAT blazars are classified as BL Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs), while the rest remain of uncertain type. The goal of this study was to classify those blazars of uncertain type, using a supervised machine learning method based on an artificial neural network, by comparing their properties to those of known gamma-ray sources. Probabilities for each of 1329 uncertain blazars to be a BL Lac or FSRQ are obtained. Using 90 per cent precision metric, 801 can be classified as BL Lacs and 406 as FSRQs while 122 still remain unclassified. This approach is of interest because it gives a fast preliminary classification of uncertain blazars. We also explored how different selections of training and testing samples affect the classification and discuss the meaning of network outputs.
75. 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.
76. 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.
77. 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.
78. 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.
79. 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.
80. 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.

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