How is the blazar GeV emission really produced?
  We show that the external Compton (EC) model for the production of the GeV emission in blazars makes specific predictions for the spectrum and variability of those blazars characterized by a high Compton dominance (Compton to synchrotron luminosity ratio). These unavoidable features have not been observed, casting doubt on the validity of this popular model. We argue that synchrotron-self Compton (SSC) models including the higher orders of Compton scattering are more promising, and we briefly discuss the implications of our findings for the geometry of the broad line region (BLR). 
Markos Georganopoulos, Eric Perlman, Demosthenes Kazanas, & Brian   Wingert