Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications

McConville, W.; Ostorero, L.; Moderski, R.; Stawarz, Ł.; Cheung, C. C.; Ajello, M.; Bouvier, A.; Bregeon, J.; Donato, D.; Finke, J.; Furniss, A.; McEnery, J. E.; Monzani, M. E.; Orienti, M.; Reyes, L. C.; Rossetti, A.; Williams, D. A.

doi:10.1088/0004-637X/738/2/148

Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications

Journal Article · Fri Aug 19 00:00:00 EDT 2011 · The Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/738/2/148· OSTI ID:1357198

McConville, W. ^[1]; Ostorero, L. ^[2]; Moderski, R. ^[3]; Stawarz, Ł. ^[4]; Cheung, C. C. ^[5]; Ajello, M. ^[6]; Bouvier, A. ^[7]; Bregeon, J. ^[8]; Donato, D. ^[1]; Finke, J. ^[9]; Furniss, A. ^[7]; McEnery, J. E. ^[1]; Monzani, M. E. ^[6]; Orienti, M. ^[10]; Reyes, L. C. ^[11]; Rossetti, A. ^[12]; Williams, D. A. ^[7]

NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland, College Park, MD (United States)
Univ. degli Studi di Torino, Torino (Italy); Istituto Nazionale di Fisica Nucleare (INFN), Torino (Italy); Univ. of Pennsylvania, Philadelphia, PA (United States); Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)
Nicolaus Copernicus Astronomical Center, Warsaw (Poland)
Institute of Space and Astronautical Science, Kanagawa (Japan); Jagiellonian Univ., Krakow (Poland)
National Academy of Science, Washington, D.C. (United States); Naval Research Lab., Washington, D.C. (United States)
Stanford Univ., Stanford, CA (United States)
Univ. of California, Santa Cruz, CA (United States)
Istituto Nazionale di Fisica Nucleare, Pisa (Italy)
Naval Research Lab., Washington, D.C. (United States)
Univ. di Bologna, Bologna (Italy); Istituto di Radioastronomia INAF, Bologna (Italy)
Univ. of Chicago, Chicago, IL (United States)
Istituto di Radioastronomia INAF, Bologna (Italy)

Here, 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.

View Accepted Manuscript (DOE)

Research Organization:: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: AC02-76SF00515

OSTI ID:: 1357198

Journal Information:: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 2 Vol. 738; ISSN 0004-637X

Publisher:: Institute of Physics (IOP)Copyright Statement

Country of Publication:: United States

Language:: English

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