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Title: Broad-line radio galaxies observed with Fermi-LAT: The origin of the GeV γ-ray emission

Here, we report on a detailed investigation of the γ-ray emission from 18 broad-line radio galaxies (BLRGs) based on two years of Fermi Large Area Telescope data. We confirm the previously reported detections of 3C 120 and 3C 111 in the GeV photon energy range; a detailed look at the temporal characteristics of the observed γ-ray emission reveals in addition possible flux variability in both sources. No statistically significant γ-ray detection of the other BLRGs was found, however, in the considered data set. Though the sample size studied is small, what appears to differentiate 3C 111 and 3C 120 from the BLRGs not yet detected in γ-rays is the particularly strong nuclear radio flux. This finding, together with the indications of the γ-ray flux variability and a number of other arguments presented, indicates that the GeV emission of BLRGs is most likely dominated by the beamed radiation of relativistic jets observed at intermediate viewing angles. In this paper we also analyzed a comparison sample of high-accretion-rate Seyfert 1 galaxies, which can be considered radio-quiet counterparts of BLRGs, and found that none were detected in γ-rays. A simple phenomenological hybrid model applied for the broadband emission of the discussed radio-loud andmore » radio-quiet type 1 active galaxies suggests that the relative contribution of the nuclear jets to the accreting matter is ≥ 1% on average for BLRGs, whereas it is ≤ 0.1% for Seyfert 1 galaxies.« less
Authors:
 [1] ;  [2] ;  [1] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [8] ;  [1] ;  [1] ;  [9] ;  [10] ;  [4] ;  [11] ;  [12] ;  [13]
  1. Waseda Univ., Tokyo (Japan)
  2. Institute of Space and Astronautical Science, Kanagawa (Japan); Jagiellonian Univ., Krakow (Poland)
  3. National Academy of Sciences, Washington, D.C. (United States); Naval Research Lab., Washington, D.C. (United States)
  4. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.
  5. INAF-IASF, Bologna (Italy)
  6. Univ. of Washington, Seattle, WA (United States)
  7. Scuola Internazionale Superiore di Studi Avanzati (SISSA), Trieste (Italy)
  8. Ecole Polytechnique, Palaiseau (France)
  9. Univ. of New Mexico, Albuquerque, NM (United States)
  10. Istituto Nazionale di Fisica Nucleare, Perugia (Italy); Univ. degli Studi di Perugia, Perugia (Italy)
  11. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland, College Park, MD (United States)
  12. Naval Research Lab., Washington, D.C. (United States)
  13. IASF Palermo, Palermo (Italy); INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Roma (Italy)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 740; Journal Issue: 1; Journal ID: ISSN 0004-637X
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies: active; galaxies: individual (3C 120 3C 111); galaxies: jets; gamma rays: galaxies; radiation mechanisms: non-thermal; X-rays: galaxies
OSTI Identifier:
1356802