Can Flat Spectrum Radio Quasars make most of the overall gamma--ray   background ?
  The contribution of discrete sources to the gamma--ray background is modeled. Flat spectrum radio quasars are known to make a substantial contribution to the hard (E > 100 MeV) background. The so called ``MeV bump", however, cannot be accounted for in terms of known classes of sources even taking into account the newly discovered class of objects with a broad band spectrum sharply peaked in the MeV range (``MeV blazars"). Even in the most optimistic case the predicted intensity falls short of at least a factor three. 
A. Comastri(1), T. Di Girolamo(2), G. Setti(2,3) ((1) Osservatorio   Astronomico di Bologna, (2) Dipartimento di Astronomia ...