Optical Counterparts of Undetermined Type [gamma]-Ray Active Galactic Nuclei with Blazar-Like Spectral Energy Distributions

• Published in: Journal of astrophysics and astronomy 2015-12, Vol.36 (4), p.447
• Main Authors: Mura, Giovanni La, Chiaro, Graziano, Ciroi, Stefano, Rafanelli, Piero, Salvetti, David, Berton, Marco, Cracco, Valentina
• Format: Article
• Language: English
• Subjects: Astronomy; Emissions; Quasars; Radio telescopes; Stars & galaxies; Wavelengths
• ISSN: 0250-6335; 0973-7758
• DOI: 10.1007/s12036-015-9357-6

Issue Title: Special Issue on Spectral Line Shapes in Astrophysics During its first four years of scientific observations, the Fermi Large Area Telescope (Fermi-LAT) detected 3033 γ-ray sources above a 4 σ significance level. Although most of the extra-galactic sources are active galactic nuclei (AGN) of the blazar class, other families of AGNs are observed too, while a still high fraction of detections (30%) remains with uncertain association or classification. According to the currently accepted interpretation, the AGN γ-ray emission arises from inverse Compton (IC) scattering of low energy photons by relativistic particles confined in a jet, which, in the case of blazars, is oriented very close to our line-of-sight. Taking advantage of data from radio and X-ray wavelengths, which we expect to be produced together with γ-rays, providing a much better source localization potential, we focused our attention on a sample of γ-ray Blazar Candidates of Undetermined type (BCUs), starting a campaign of optical spectroscopic observations. The main aims of our investigation include a census of the AGN families that contribute to γ-ray emission and a study of their redshift distribution, with the subsequent implications on the intrinsic source power. We furthermore analyze which γ-ray properties can better constrain the nature of the source, thus helping in the study of objects not yet associated with a reliable low frequency counterpart. Here we report on the instruments and techniques used to identify the optical counterparts of γ-ray sources, we give an overview on the status of our work, and we discuss the implications of a large scale study of γ-ray emitting AGNs.