Optical spectroscopic observations of low-energy counterparts of Fermi-LAT gamma-ray sources

Abstract

A significant fraction of all $\gamma$-ray sources detected by the Large Area Telescope aboard the \fer\ satellite is still lacking a low-energy counterpart. In addition, there is still a large population of $\gamma$-ray sources with associated low-energy counterparts that lack firm classifications. In the last 10 years we have undertaken an optical spectroscopic campaign to address the problem of unassociated/unidentified $\gamma$-ray sources (UGSs), mainly devoted to observing blazars and blazar candidates because they are the largest population of $\gamma$-ray sources associated to date. Here we describe the overall impact of our optical spectroscopic campaign on sources associated in \fer-LAT catalogs, coupled with objects found in the literature. In the literature search, we kept track of efforts by different teams that presented optical spectra of counterparts or potential counterparts of \fer-LAT catalog sources. Our summary includes an analysis of an additional 30 newly-collected optical spectra of counterparts or potential counterparts of \fer-LAT sources of previously unknown nature.New spectra were acquired at the Blanco 4-m and OAN-SPM 2.1-m telescopes, and those available in the Sloan Digital Sky Survey (data release 15) archive. All new sources with optical spectra analyzed here are classified as blazars. Thanks to our campaign, we altogether discovered and classified 394 targets with an additional 123 objects collected from a literature search. We began our optical spectroscopic campaign between the release of the second and third \fer-LAT source catalogs (2FGL and 3FGL, respectively), and classified about 25\% of the sources with uncertain nature and discovered a blazar-like potential counterpart for $\sim$10\% of UGSs listed therein. In the 4FGL catalog, about 350 \fer-LAT sources are classified to date thanks to our campaign. [incomplete abstract]

31 pages, 12 tables, 32 figures, 2 appendices, accepted for publication on A&A (pre-proofs version)

References in corpus (42)

• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• Roma-BZCAT: A multifrequency catalogue of Blazars
• The 5th edition of the Roma-BZCAT. A short presentation
• The Imprint of The Extragalactic Background Light in the Gamma-Ray Spectra of Blazars
• MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. VIII. Faraday rotation in parsec-scale AGN jets
• The Origin of the Extragalactic Gamma-Ray Background and Implications for Dark-Matter Annihilation
• The WISE Blazar-Like Radio-Loud Sources: An All-Sky Catalog Of Candidate Gamma-Ray Blazars
• Two new catalogs of blazar candidates in the WISE infrared sky
• Optical spectroscopic observations of gamma-ray blazars candidates I: preliminary results
• Optical spectroscopic observations of $\gamma$-ray blazar candidates VI. Further observations from TNG, WHT, OAN, SOAR and Magellan telescopes
• 1WHSP: an IR-based sample of $\sim$1,000 VHE $\gamma$-ray blazar candidates
• Optical spectroscopic observations of blazars and gamma-ray blazar candidates in the Sloan Digital Sky Survey Data Release Nine
• Unveiling the nature of the unidentified gamma-ray sources IV: the $\text{Swift}$ catalog of potential X-ray counterparts
• Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere
• New Associations of Gamma-Ray Sources from the Fermi Second Source Catalog
• Optical Spectroscopic Observations of Gamma-ray Blazar Candidates. V. TNG, KPNO, and OAN Observations of Blazar Candidates of Uncertain Type in the Northern Hemisphere
• Optical spectroscopic observations of gamma-ray blazar candidates III. The 2013/2014 campaign in the Southern Hemisphere
• The Gamma-ray Blazar Quest: new optical spectra, state of art and future perspectives
• Optical spectroscopic observations of gamma-ray blazar candidates IV. Results of the 2014 follow-up campaign
• Optical spectroscopic survey of a sample of Unidentified Fermi objects
• Refining the associations of the Fermi Large Area Telescope Source Catalogs
• Optical Spectroscopic Observations of Gamma-Ray Blazar Candidates. VII. Follow-up Campaign in the Southern Hemisphere
• The Infrared-Gamma-Ray Connection: A WISE View of the Extragalactic Gamma-Ray Sky
• 3FGLzoo. Classifying 3FGL Unassociated Fermi-LAT Gamma-ray Sources by Artificial Neural Networks
• The soft X-ray properties of AGN from the CJF sample; A correlation analysis between soft X-ray and VLBI properties
• 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
• Spectroscopy of 10 gamma-ray BL Lac objects at high redshift
• Spectroscopy of BL Lac objects of extraordinary luminosity
• Optical spectroscopic observations of gamma-ray blazar candidates VIII: the 2016-2017 follow up campaign carried out at SPM, NOT, KPNO and SOAR telescopes
• Radio Weak BL Lac objects in the Fermi era
• Looking for blazars in a sample of unidentified high-energy emitting Fermi sources
• Optical spectroscopic observations of gamma-ray blazar candidates. IX. Optical archival spectra and further observations from SOAR and OAGH
• 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
• Identifying the 3FHL catalog: CTIO results
• Optical characterization of WISE selected blazar candidates
• Multi-scale time- and frequency-domain likelihood analysis with photon weights
• 0FGL J1830.3+0617: A Fermi Blazar Near the Galactic Plane
• Optical spectroscopy of microquasar candidates at low galactic latitudes
• The $\gamma$-ray sky seen at X-ray energies II: the Swift hunt of Fermi BL Lac objects among unidentified gamma-ray sources
• Probing the unidentified Fermi blazar-like population using optical polarization and machine learning
• On the physical association of Fermi-LAT blazars with their low-energy counterparts

Cited by in corpus (15)

• Incremental Fermi Large Area Telescope Fourth Source Catalog
• The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope -- Data Release 3
• The Central Engines of Fermi Blazars
• MOJAVE XIX: Brightness Temperatures and Intrinsic Properties of Blazar Jets
• An optical overview of blazars with LAMOST I: Hunting changing-look blazars and new redshift estimates
• Optical spectroscopy of Blazars for the Cherenkov Telescope Array
• Constraints on the antistar fraction in the Solar system neighborhood from the 10-years Fermi Large Area Telescope gamma-ray source catalog
• Optical Spectroscopy of Blazars for the Cherenkov Telescope Array -- II
• Identifying the 3FHL catalog: V. Results of the CTIO-COSMOS optical spectroscopy campaign 2019
• Powerful Radio Sources in the Southern Sky. I. Optical Identifications
• Powerful Radio Sources in the Southern Sky. II. A SWIFT X-Ray Perspective
• Disentangling the nature of the prototype radio weak BL Lac: Contemporaneous multifrequency observations of WISE J141046.00 + 740511.2
• Swift-XRT follow-up analysis of unidentified hard X-ray sources
• IGR J18249-3243: a new GeV-emitting FR II and the emerging population of high energy radio galaxies
• On the origin of mid-infrared colors in $\gamma$-ray blazars