"The Contribution of Active Galactic Nuclei to the Diffuse Gamma Ray   Background"
  We consider the emission of high energy to very high energy $\gamma$-rays in radio-quiet active galactic nuclei (AGN) or the central regions of radio-loud AGN. We use our results to estimate the $\gamma$-ray flux from the central regions of nearby AGN, and then to calculate the contribution to the diffuse $\gamma$-ray flux from unresolved AGN. 
P.A. Johnson, A. Mastichiadis, R.J. Protheroe, T.S. Stanev and A.P.   Szabo