Fermilarge Area Telescope Observations of the Active Galaxy 4c +55.17: Steady, Hard Gamma-ray Emission and Its Implications
Year: 2011
Type: article
Abstract: We report Fermi Large Area Telescope (LAT) observations and broadband spectral modeling of the radio-loud active galaxy 4C +55.17 ( z = 0.896), formally classified as a flat-spectrum radio quasar. Using 19 months of all-sky survey Fermi -LAT data, we detect a γ-ray continuum extending up to an observed energy of 145 GeV, and furthermore we find no evidence of γ-ray variability in the source over its observed history. We illustrate the implications of these results in two different domains. First, we investigate the origin of the steady γ-ray emission, where we re-examine the common classification of 4C +55.17 as a quasar-hosted blazar and consider instead its possible nature as a young radio source. We analyze and compare constraints on the source physical parameters in both blazar and young radio source scenarios by means of a detailed multiwavelength analysis and theoretical modeling of its broadband spectrum. Second, we show that the γ-ray spectrum may be formally extrapolated into the very high energy (VHE, ⩾100 GeV) range at a flux level detectable by the current generation of ground-based Cherenkov telescopes. This enables us to place constraints on models of extragalactic background light within LAT energies and features the source as a promising candidate for VHE studies of the universe at an unprecedented redshift of z = 0.896.
Source: The Astrophysical Journal
Institutions: Goddard Space Flight Center, University of Maryland, College Park, Istituto Nazionale di Fisica Nucleare, Istituto Nazionale di Fisica Nucleare, Sezione di Torino, Center for Astrophysics Harvard & Smithsonian, University of Turin, University of Pennsylvania, Nicolaus Copernicus Astronomical Center, Jagiellonian University, Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, National Academy of Sciences, National Academies of Sciences, Engineering, and Medicine, SLAC National Accelerator Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, University of California, Santa Cruz, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, United States Naval Research Laboratory, Naval Research Laboratory Space Science Division, Istituto di Radioastronomia di Bologna, University of Bologna, University of Chicago
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W1997017457