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

Author(s):Show less -

Pena-Herazo, H. A. ^{[1, 2, 3, 4]} ; Amaya-Almazan, R. A. ^[4] ; Massaro, F. ^{[1, 2, 3, 5]} ; de Menezes, R. ^{[2, 6]} ; Marchesini, E. J. ^{[7, 2, 3, 8, 9]} ; Chavushyan, V. ^[4] ; Paggi, A. ^{[3, 5]} ; Landoni, M. ^{[10, 11]} ; Masetti, N. ^{[12, 8]} ; Ricci, F. ^{[13, 14]} ; D'Abrusco, R. ^[15] ; Cheung, C. C. ^[16] ; La Franca, F. ^[17] ; Smith, H. A. ^[16] ; Milisavljevic, D. ^[18] ; Jimenez-Bailon, E. ^[19] ; Patino-Alvarez, V. M. ^{[20, 4]} ; Tosti, G. ^[21]

Affiliation:Show less -

^[1] Ist Nazl Fis Nucl, Sez Torino, I-10125 Turin - Italy

^[2] Univ Torino, Dipartimento Fis, Via Pietro Giuria 1, I-10125 Turin - Italy

^[3] INAF, Osservatorio Astrofis Torino, Via Osservatorio 20, I-10025 Pino Torinese - Italy

^[4] Inst Nacl Astrofis Opt & Electr, Apartado Postal 51-216, Puebla 72000 - Mexico

^[5] Consorzio Interuniv Fis Spaziale CIFS, Via Pietro Giuria 1, I-10125 Turin - Italy

^[6] Univ Sao Paulo, Dept Astron, BR-05508090 Sao Paulo, SP - Brazil

^[7] Univ Nacl La Plata, Fac Ciencias Astron & Geofis, La Plata - Argentina

^[8] INAF, Osservatorio Astrofis & Sci Spazio, Via Gobetti 93-3, I-40129 Bologna - Italy

^[9] CCT La Plata, UNLP, CONICET, Inst Astrofis La Plata, La Plata - Argentina

^[10] INAF, Osservatorio Astron Brera, Via Emilio Bianchi 46, I-23807 Merate - Italy

^[11] INAF, Osservatorio Astron Cagliari, Via Sci 5, Selargius, CA - Italy

^[12] Univ Andres Bello, Dept Ciencias Fis, Fernandez Concha 700, Santiago - Chile

^[13] Pontificia Univ Catolica Chile, Fac Fis, Inst Astrofis, Casilla 306, Santiago 22 - Chile

^[14] Pontificia Univ Catolica Chile, Fac Fis, Ctr Astroingn, Casilla 306, Santiago 22 - Chile

^[15] Harvard & Smithsonian, Ctr Astrophys, 60 Garden St, Cambridge, MA 02138 - USA

^[16] Naval Res Lab, Div Space Sci, Code 7650, Washington, DC 20375 - USA

^[17] Univ Roma Tre, Dipartimento Matemat & Fis, Via Vasca Navale 84, I-00146 Rome - Italy

^[18] Purdue Univ, Dept Phys & Astron, 525 Northwestern Ave, W Lafayette, IN 47907 - USA

^[19] Univ Nacl Autonoma Mexico, Inst Astron, Apdo Postal 877, Ensenada 22800, Baja California - Mexico

^[20] Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn - Germany

^[21] Univ Perugia, Dipartimento Fis, I-06123 Perugia - Italy

• Document type: Journal article
• Source: Astronomy & Astrophysics; v. 643, NOV 9 2020.
• Web of Science Citations: 0

Abstract

Context. A significant fraction of all gamma-ray sources detected by the Large Area Telescope aboard the Fermi 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 or 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.Aims. Here we describe the overall impact of our optical spectroscopic campaign on sources associated in Fermi-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 Fermi-LAT catalog sources. Our summary includes an analysis of additional 30 newly collected optical spectra of counterparts or potential counterparts of Fermi-LAT sources of a previously unknown nature.Methods. 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.Results. All new sources with optical spectra analyzed here are classified as blazars. Thanks to our campaign, altogether we 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 Fermi-LAT source catalogs (2FGL and 3FGL, respectively), classified about 25% of the sources that had uncertain nature and discovered a blazar-like potential counterpart for similar to 10% of UGSs listed therein. In the 4FGL catalog, about 350 Fermi-LAT sources have been classified to date thanks to our campaign.Conclusions. The most elusive class of blazars are found to be BL Lacs since the largest fraction of Fermi-LAT sources targeted in our observations showed a featureless optical spectrum. The same conclusion applied to the literature spectra. Finally, we confirm the high reliability of mid-IR color-based methods to select blazar-like candidate counterparts of unassociated or unidentified gamma-ray sources. (AU)

• FAPESP's process: 18/24801-6 - Multislit spectroscopy of unidentified gamma-ray sources
• Grantee: Raniere Maciel de Menezes
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 16/25484-9 - Optical observations of blazar candidates and unknown gamma-ray sources
• Grantee: Raniere Maciel de Menezes
• Support Opportunities: Scholarships in Brazil - Doctorate