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

Abstract

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 promisingmore » candidate for VHE studies of the universe at an unprecedented redshift of z = 0.896.« less

Authors:
 [1];  [2];  [3];  [4];  [5];  [6];  [7];  [8];  [1];  [9];  [7];  [1];  [6];  [10];  [11];  [12];  [7]
  1. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland, College Park, MD (United States)
  2. 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)
  3. Nicolaus Copernicus Astronomical Center, Warsaw (Poland)
  4. Institute of Space and Astronautical Science, Kanagawa (Japan); Jagiellonian Univ., Krakow (Poland)
  5. National Academy of Science, Washington, D.C. (United States); Naval Research Lab., Washington, D.C. (United States)
  6. Stanford Univ., Stanford, CA (United States)
  7. Univ. of California, Santa Cruz, CA (United States)
  8. Istituto Nazionale di Fisica Nucleare, Pisa (Italy)
  9. Naval Research Lab., Washington, D.C. (United States)
  10. Univ. di Bologna, Bologna (Italy); Istituto di Radioastronomia INAF, Bologna (Italy)
  11. Univ. of Chicago, Chicago, IL (United States)
  12. Istituto di Radioastronomia INAF, Bologna (Italy)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1357198
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 738; Journal Issue: 2; Journal ID: ISSN 0004-637X
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies: active; galaxies: individual (4C+55.17); galaxies: jets; gamma rays: galaxies; radiation mechanisms: non-thermal

Citation Formats

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., and Williams, D. A. Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications. United States: N. p., 2011. Web. doi:10.1088/0004-637X/738/2/148.
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. Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications. United States. doi:10.1088/0004-637X/738/2/148.
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., and Williams, D. A. Fri . "Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications". United States. doi:10.1088/0004-637X/738/2/148. https://www.osti.gov/servlets/purl/1357198.
@article{osti_1357198,
title = {Fermi Large Area Telescope observations of the active galaxy 4C +55.17: Steady, hard gamma-ray emission and its implications},
author = {McConville, W. and Ostorero, L. and Moderski, R. and Stawarz, Ł. and Cheung, C. C. and Ajello, M. and Bouvier, A. and Bregeon, J. and Donato, D. and Finke, J. and Furniss, A. and McEnery, J. E. and Monzani, M. E. and Orienti, M. and Reyes, L. C. and Rossetti, A. and Williams, D. A.},
abstractNote = {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.},
doi = {10.1088/0004-637X/738/2/148},
journal = {Astrophysical Journal},
number = 2,
volume = 738,
place = {United States},
year = {2011},
month = {8}
}

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