The Gamma-Ray Background from Blazars: A New Look
  We present the results of a new model calculation of the gamma-ray background produced by unresolved blazars, using the second EGRET catalogue and taking account of flaring. These results are compared to the preliminary gamma-ray background spectrum reported recently by the EGRET team. We find that blazars can account for the entire extragalactic gamma-ray background observed by EGRET. In addition, the EGRET spectrum shows some evidence of a signature for the blazar background, in the form of a concavity in the spectrum. 
F.W. Stecker and M.H. Salamon