Radio Follow-up on all Unassociated Gamma-ray Sources from the Third Fermi Large Area Telescope Source Catalog

Abstract

The third Fermi Large Area Telescope (LAT) $\gamma$-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 of 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 of 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 AGN associations with $\gamma$-ray sources, provided alternative associations for 7 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 HII regions, whereas 17 could be radio galaxies.

14 pages, 9 figures, 6 tables, 5 machine readable tables, accepted for publication in ApJS

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• Fermi Large Area Telescope Fourth Source Catalog
• The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope
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• The Second LBA Calibrator Survey of southern compact extragalactic radio sources - LCS2
• A ring accelerator? Unusual jet dynamics in the IceCube candidate PKS 1502+106
• An optical overview of blazars with LAMOST I: Hunting changing-look blazars and new redshift estimates
• A multi-wavelength investigation of candidate milli-second pulsars in unassociated $\gamma$-ray sources
• VLBI ecliptic plane survey: VEPS-1
• Classification of Fermi-LAT unidentified gamma-ray sources using CatBoost gradient boosting decision trees
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• Optical spectroscopic observations of low-energy counterparts of Fermi-LAT gamma-ray sources
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• The HI absorption zoo: JVLA extension to $z\sim 0.4$
• Radio Counterpart Candidates to 4FGL-DR2 Unassociated Sources
• Multiwavelength evidence for a new flare-mode transitional millisecond pulsar
• Probing the unidentified Fermi blazar-like population using optical polarization and machine learning
• Redshift prediction of Fermi-LAT gamma-ray sources using CatBoost gradient boosting decision trees
• A Combined Radio Multi-Survey Catalog of Fermi Unassociated Sources
• New Identifications and Multi-wavelength Properties of Extragalactic Fermi Gamma-Ray Sources in the SPT-SZ Survey Field
• Search for AGN counterparts of unidentified Fermi-LAT sources with optical polarimetry: Demonstration of the technique
• COBIPULSE: A Systematic Search for Compact Binary Millisecond Pulsars
• Multiwavelength Evidence for Two New Candidate Transitional Millisecond Pulsars in the Sub-luminous Disk State: 4FGL J0639.1--8009 and 4FGL J1824.2+1231
• The loud and the quiet: searching for radio counterparts of two radio-weak BL Lac candidates with VLBI
• TANAMI: Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry. III. First-epoch S band images
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• Search for the multiwavelength counterparts to extragalactic unassociated Fermi γ-ray sources
• Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2
• Exploring the nature of Galactic unassociated sources detected by the Fermi-LAT