Astron. Astrophys. 326, 51-58 (1997)

A spectral study of gamma-ray emitting active galactic nuclei

M. Pohl ¹, R.C. Hartman ², B.B. Jones ³ and P. Sreekumar <sup>2, 4

1</sup> Max-Planck-Institut für Extraterrestrische Physik, Postfach 1603, D-85740 Garching, Germany
² NASA/Goddard Space Flight Center, Code 660, Greenbelt, MD 20771, USA
³ W.W. Hansen Expt. Physics Lab., Stanford Univ., Stanford, CA 94305-4085, USA
⁴ Universities Space Research Association, USA

Received 4 November 1996 / Accepted 12 March 1997

Abstract

In this paper we present a statistical analysis of the -ray spectra of flat-spectrum radio quasars (FSRQ) compared to those of BL Lacs. The average spectra and possible systematic deviations from power-law behaviour are investigated by summing up the intensity and the power-law fit statistic for both classes of objects. We also compare the time-averaged spectrum to that at the time of -ray outbursts.

The spectrum of the average AGN is softer than that of the extragalactic -ray background. It may be that BL Lacs, which on average have a harder spectrum than FSRQs, make up the bulk of the extragalactic background.

We also find apparent cut-offs at both low and high energies in the spectra of FSRQs at the time of -ray outbursts. While the cut-off at high energies may have something to do with opacity, the cut-off at low energies may be taken as indication that the -ray emission of FSRQs is not a one component spectrum.

Key words: methods: statistical BL Lacertae objects: general quasars: general Gamma-rays: observations

Send offprint requests to: http://www.dsri.dk/ mkp/

SIMBAD Objects

Contents

• 1. Introduction
• 2. The average source
• 3. The peak spectra
  • 3.1. Possible systematics
• 4. Discussion
  • 4.1. The deficit at low energies
  • 4.2. The cut-off at high energies
  • 4.3. The relation to the diffuse -ray background
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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