Extragalactic photon background above GeV energies: High peaked BL lacertae objects or dark matter?

Abstract

Blazars produce a large fraction of the observed extragalactic gamma ray background between 100 MeV and 100 GeV. The average spectrum of the resolved blazars in the 3rd EGRET catalogue is too steep to be consistent with the shape of the background spectrum above 1 GeV. The most proliferant emitters above 100 GeV, the high-peaked blazars, which are too faint to have been detected with EGRET, but of which an increasing number is now being detected with imaging air Cherenkov telescopes such as MAGIC, H.E.S.S., and VERITAS, could supply a substantial contribution to the background above GeV energies. We show that dark matter annihilation in clumpy halos could naturally produce an emission component peaking at ∼20 GeV. Adding this to the blazar-origin component, a best-fit model for the extragalactic gamma ray background is obtained. © 2008 Springer-Verlag Berlin Heidelberg.