Astron. Astrophys. 326, 51-58
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A spectral study of gamma-ray emitting active galactic nuclei
M. Pohl1, R.C. Hartman2, B.B. Jones3, and P. Sreekumar2,4
1Max-Planck-Institut für Extraterrestrische Physik,
D-85740 Garching, Germany
Received 4 November 1996 / Accepted 12 March 1997
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
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© European Southern Observatory (ESO) 1997
Online publication: September 9, 1997