FERMI LARGE AREA TELESCOPE OBSERVATIONS OF THE ACTIVE GALAXY 4C +55.17: STEADY, HARD GAMMA-RAY EMISSION AND ITS IMPLICATIONS

Journal Article · Sat Sep 10 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/738/2/148; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)· OSTI ID:21584890

McConville, W; McEnery, J E ^[1]; Ostorero, L ^[2]; Moderski, R ^[3]; Stawarz, L ^[4]; Cheung, C C ^[5]; Ajello, M; Monzani, M E ^[6]; Bouvier, A ^[7]; Bregeon, J ^[8]; Donato, D ^[9]; Finke, J ^[10]; Furniss, A; Williams, D A ^[11]; Orienti, M ^[12]; Reyes, L C ^[13]; Rossetti, A ^[14]

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1. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
2. Dipartimento di Fisica Generale 'Amedeo Avogadro', Universita degli Studi di Torino, Via P. Giuria 1, I-10125 Torino (Italy)
3. Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw (Poland)
4. Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)
5. National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001 (United States)
6. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
7. Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States)
8. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
9. Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
10. Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)
11. Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064 (United States)
12. Dipartimento di Astronomia, Universita di Bologna, via Ranzani 1, I-40127, Bologna (Italy)
13. Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637 (United States)
14. Istituto di Radioastronomia INAF, via Gobetti 101, 40129 Bologna (Italy)

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 {gamma}-ray continuum extending up to an observed energy of 145 GeV, and furthermore we find no evidence of {gamma}-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 {gamma}-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 {gamma}-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.

• OSTI ID: 21584890
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 738; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ELECTROMAGNETIC RADIATION
EMISSION
GALAXIES
GAMMA RADIATION
GAMMA SPECTRA
IONIZING RADIATIONS
RADIATIONS
SIMULATION
SPECTRA