Rolling down from the 30 keV peak: modelling the hard X-ray and   gamma-ray backgrounds
  We will briefly discuss the importance of sensitive X-ray observations above a few tens of keV for a better understanding of the physical mechanisms associated to the Supermassive Black Hole primary emission in both radio quiet and radio loud AGN and to the cosmological evolution of the most obscured sources. 
Andrea Comastri, Roberto Gilli, Guenther Hasinger