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

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A spectral study of gamma-ray emitting active galactic nuclei

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

1 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 [FORMULA] -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 [FORMULA] -ray outbursts.

The spectrum of the average AGN is softer than that of the extragalactic [FORMULA] -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 [FORMULA] -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 [FORMULA] -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/ [FORMULA] mkp/

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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