RADIO-LOUD AGN AND THE EXTRAGALACTIC GAMMA-RAY BACKGROUND

We estimate the contribution of radio-loud active galactic nuclei to the gamma-ray background using the recent detections by GRO of BL Lacs and flat-spectrum radio quasars at energies > 100 MeV From the recently derived radio luminosity functions of these objects, together with the observed mean values of the gamma-ray to radio luminosity, we derive contributions of about 30 and 35 per cent, respectively, at 100 MeV. The total contribution of radio-loud sources is 66(-24)+31 per cent, leaving little room for a substantial contribution from radio-quiet active galactic nuclei, none of which has been detected so far. Our results assume that the detected sources are typical of the radio-loud population and not strongly variable; further gamma-ray detections and variability studies should allow a refinement of our estimate.