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    • Keywords


      Catalogues; galaxies: active; galaxies: jets; quasars: emission lines.

    • Abstract


      During its first four years of scientific observations, the Fermi Large Area Telescope (Fermi-LAT) detected 3033 𝛾-ray sources above a 4𝜎 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.

    • Author Affiliations


      Giovanni La Mura1 Graziano Chiaro1 Stefano Ciroi1 Piero Rafanelli1 David Salvetti2 Marco Berton1 Valentina Cracco1 Fermi-LAT collaboration

      1. Dipartimento di Fisica e Astronomia G. Galilei, Università degli Studi di Padova, Vicolo dell'Osservatorio 3, 35122 Padova, Italy.
      2. IASF Milano – Istituto di Astrofisica Spaziale e Fisica Cosmica, Via E. Bassini 15, 20133 Milano, Italy.
    • Dates

  • Journal of Astrophysics and Astronomy | News

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      Posted on January 27, 2016

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