Unveiling the nature of the unidentified gamma-ray sources II: radio, infrared and optical counterparts of the gamma-ray blazar candidates

Abstract

A significant fraction (~30%) of the high-energy gamma-ray sources listed in the second Fermi LAT catalog (2FGL) are still of unknown origin, being not yet associated with counterparts at low energies. We recently developed a new association method to identify if there is a gamma-ray blazar candidate within the positional uncertainty region of a generic 2FGL source. This method is entirely based on the discovery that blazars have distinct infrared colors with respect to other extragalactic sources found thanks, to the Wide-field Infrared Survey Explorer (WISE) all-sky observations. Several improvements have been also performed to increase the efficiency of our method in recognizing gamma-ray blazar candidates. In this paper we applied our method to two different samples, the first constituted by the unidentified gamma-ray sources (UGSs) while the second by the active galaxies of uncertain type (AGUs), both listed in the 2FGL. We present a catalog of IR counterparts for ~20% of the UGSs investigated. Then, we also compare our results on the associated sources with those present in literature. In addition, we illustrate the extensive archival research carried out to identify the radio, infrared, optical and X-ray counterparts of the WISE selected, gamma-ray blazar candidates. Finally, we discuss the future developments of our method based on ground-based follow-up observations.

31 page, 3 figures, 11 tables, ApJS accepted for publication

References in corpus (9)

• The Sloan Digital Sky Survey Quasar Catalog IV. Fifth Data Release
• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• Roma-BZCAT: A multifrequency catalogue of Blazars
• The Sloan Digital Sky Survey quasar catalog: ninth data release
• A Systematic Analysis of Fe II Emission in Quasars: Evidence for Inflow to the Central Black Hole
• Unveiling the nature of INTEGRAL objects through optical spectroscopy. VI. A multi-observatory identification campaign
• Unveiling the nature of the unidentified gamma-ray sources I: a new method for the association of gamma-ray blazars
• Unveiling the nature of INTEGRAL objects through optical spectroscopy. VII. Identification of 20 Galactic and extragalactic hard X-ray sources
• 0FGL J1830.3+0617: A Fermi Blazar Near the Galactic Plane

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• Optical spectroscopic observations of gamma-ray blazars candidates I: preliminary results
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• Optical spectroscopic observations of blazars and gamma-ray blazar candidates in the Sloan Digital Sky Survey Data Release Nine
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• Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere
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• The Gamma-ray Blazar Quest: new optical spectra, state of art and future perspectives
• Hunting for treasures among the Fermi unassociated sources: a multi-wavelength approach
• Search for gamma-ray-emitting active galactic nuclei in the Fermi-LAT unassociated sample using machine learning
• Optical spectroscopic observations of gamma-ray blazar candidates IV. Results of the 2014 follow-up campaign
• Unveiling the nature of the unidentified gamma-ray sources V: analysis of the radio candidates with the kernel density estimation
• Refining the associations of the Fermi Large Area Telescope Source Catalogs
• Research and characterisation of blazar candidates among the Fermi/LAT 3FGL catalogue using multivariate classifications
• The Infrared-Gamma-Ray Connection: A WISE View of the Extragalactic Gamma-Ray Sky
• Optical Spectroscopic Observations of Gamma-Ray Blazar Candidates. VII. Follow-up Campaign in the Southern Hemisphere
• BL Lacertae identifications in a ROSAT-selected sample of Fermi unidentified objects
• The low-frequency radio catalog of flat spectrum sources
• Multiband Diagnostics of Unidentified 1FGL Sources with Suzaku and Swift X-ray Observations
• Optical archival spectra of blazar candidates of uncertain type in the 3${}^{rd}$ Fermi Large Area Telescope Catalog
• Unveiling the nature of the unidentified gamma-ray sources VI: gamma-ray blazar candidates in the WISH survey and their radio properties
• X-ray and Optical Study of the Gamma-ray Source 3FGL J0838.8$-$2829: Identification of a Candidate Millisecond Pulsar Binary and an Asynchronous Polar
• Optical spectroscopic observations of gamma-ray blazar candidates VIII: the 2016-2017 follow up campaign carried out at SPM, NOT, KPNO and SOAR telescopes
• Infrared properties of blazars: putting the GASP-WEBT sources into context
• An optical overview of blazars with LAMOST I: Hunting changing-look blazars and new redshift estimates
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• Optical spectroscopic observations of gamma-ray blazar candidates. IX. Optical archival spectra and further observations from SOAR and OAGH
• Swift/XRT counterparts to unassociated Fermi high-energy LAT sources
• Optical spectroscopic observations of gamma-ray blazar candidates. X. Results from the 2018--2019 SOAR and OAN-SPM observations of blazar candidates of uncertain type
• Optical spectroscopic observations of low-energy counterparts of Fermi-LAT gamma-ray sources
• Identification of New Gamma-Ray Blazar Candidates With Multifrequency Archival Observations
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• New blazars from the cross-match of recent multi-frequency catalogs
• ZBLLAC -- A spectroscopic database of BL Lacertae objects
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