New blazars from the cross-match of recent multi-frequency catalogs

Abstract

Blazars are radio-loud active galactic nuclei well known for their non thermal emission spanning a wide range of frequencies. The Roma-BZCAT is, to date, the most comprehensive list of these sources. We performed the cross-match of several catalogs obtained from recent surveys at different frequencies to search for new blazars. We cross-matched the 1 st Swift XRT Point Source catalog with the spectroscopic sample of the 9 th Data Release of the Sloan Digital Sky Survey. Then, we performed further cross-matches with the catalogs corresponding to the Faint Images of the Radio Sky at Twenty cm survey and to the AllWISE Data re- lease, focusing on sources with infrared colors similar to those of confirmed γ-ray blazars included in the Second Fermi-LAT catalog. As a result, we obtained a preliminary list of objects with all the elements needed for a proper blazar classification according to the prescriptions of the Roma-BZCAT. We carefully investigated additional properties such as their morphology and the slope of their spectral energy distribution in the radio domain, the features shown in their optical spectrum, and the luminosity in the soft X rays to exclude generic active galactic nuclei and focus on authentic blazar-like sources. At the end of our screening we obtained a list of 15 objects with firmly established blazar properties.

Investigation of Two Fermi-LAT Gamma-Ray Blazars Coincident with High-energy Neutrinos Detected by IceCube

“…Among the remaining 37 neutrino events, besides the IceCube-170922A/TXS 0506+056 occurrence, one additional spatial coincidence with a gamma-ray source is confirmed in this search (see also Aartsen et al 2018a). The gamma-ray source 3FGL J1040.4+0615 , which is associated with GB6 J1040+0617, is a BL Lac object with redshift 0.7351±0.0045 (Ahn et al 2012;Maselli et al 2015). We note that the redshift measurement might be unreliable given that the automatic extraction was flagged by the SDSS pipeline, which indicates a poorly determined redshift.…”

Fermi Large Area Telescope Fourth Source Catalog

“…In addition, to assess the real nature and classify all newly associated sources, it has been crucial to perform additional spectroscopic optical observations, which, for extragalactic objects, were also able to provide estimates of their cosmological distances (see, e.g., Shaw et al 2013aShaw et al , 2013bPaggi et al 2014;Landoni et al 2015aLandoni et al , 2015bMassaro et al 2015aMassaro et al , 2015bRicci et al 2015;Álvarez Crespo et al 2016aÁlvarez Crespo et al , 2016cChiaro et al 2016;Paiano et al 2017aPaiano et al , 2017cPaiano et al , 2017dPeña-Herazo et al 2017;Landoni et al 2018;Marchesi et al 2018;Marchesini et al 2019). These campaigns are continuously updated including searches in the optical databases of the major surveys (see, e.g., Cowperthwaite et al 2013;Massaro et al 2014Maselli et al 2015;Álvarez Crespo et al 2016b;de Menezes et al 2019).…”

Optical spectroscopic observations of gamma-ray blazar candidates. VII. Follow-up campaign in the southern hemisphere

“…It is worth highlighting that blazars are the dominant class of sources in the γ-ray extragalactic sky, being about 85 % of the associated sources in 3FGL (Acero et al 2015), therefore we expect a significant fraction of UGSs at high Galactic latitudes (|b| > 30 • ) to be blazars. Thus, in recent years, several methods and follow up observations were developed and used to search for blazar-like sources that, lying within the positional uncertainty region of UGSs, could be their low-energy counterparts (Cowperthwaite et al 2013;Maselli et al 2015;Massaro et al 2015a).…”