A spectral study of gamma-ray emitting AGN
  In this paper I investigate the $\gamma$-ray spectra of AGN by summing up the intensity and the power-law fit statistic of Quasars and OVV's and BL Lac's separately. The spectrum of the average AGN is softer than that of the extragalactic $\gamma$-ray background. It may be that BL Lac's, of which the average has a harder spectrum than Quasars, make up the bulk of the extragalactic background. We also find cut-offs both at low and at high energies in the spectra of Quasars and OVV's, however only at the time of $\gamma$-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 $\gamma$-ray emission of Quasars is not a one component spectrum. 
Martin Pohl