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

MASSARO, F.; CHAVUSHYAN, V.; MASETTI, N.; CHEUNG, C. C.; MILISAVLJEVIC, D.; TOSTI, G.; PEÑA-HERAZO, H. A.; DE MENEZES, R.; PAGGI, A.; RICCI, F.; LA FRANCA, F.; JIMÉNEZ-BAILÓN, E.; AMAYA-ALMAZÁN, R. A.; MARCHESINI, E. J.; LANDONI, M.; D?ABRUSCO, R.; SMITH, H. A.; PATIÑO-ÁLVAREZ, V. M.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Año: 2020 vol. 643

0004-6361

A significant fraction of all γ-ray sources detected by the Large AreaTelescope aboard the er satellite is still lacking a low-energy counterpart.In addition, there is still a large population of γ-ray sources withassociated low-energy counterparts that lack firm classifications. In the last10 years we have undertaken an optical spectroscopic campaign to address theproblem of unassociated/unidentified γ-ray sources (UGSs), mainlydevoted to observing blazars and blazar candidates because they are the largestpopulation of γ-ray sources associated to date. Here we describe theoverall impact of our optical spectroscopic campaign on sources associated iner-LAT catalogs, coupled with objects found in the literature. In theliterature search, we kept track of efforts by different teams that presentedoptical spectra of counterparts or potential counterparts of er-LAT catalogsources. Our summary includes an analysis of an additional 30 newly-collectedoptical spectra of counterparts or potential counterparts of er-LAT sourcesof previously unknown nature.New spectra were acquired at the Blanco 4-m andOAN-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 hereare classified as blazars. Thanks to our campaign, we altogether discovered andclassified 394 targets with an additional 123 objects collected from aliterature search. We began our optical spectroscopic campaign between therelease of the second and third er-LAT source catalogs (2FGL and 3FGL,respectively), and classified about 25% of the sources with uncertain natureand discovered a blazar-like potential counterpart for ∼10% of UGSslisted therein. In the 4FGL catalog, about 350 er-LAT sources are classifiedto date thanks to our campaign.