Using the SED to locate the Gamma-ray emission site of powerful blazars
  The location of the Gamma-ray emission of powerful blazars is a matter of active debate. Is the location within the UV emitting sub-pc scale broad line region, or farther out at pc scales where the molecular torus IR emission dominates? We present a diagnostic that connects three observables, the synchrotron and external Compton peak frequencies and the Compton dominance (the ratio of Compton to synchrotron luminosity) to the seed photon energy and energy density. We discuss encouraging preliminary results and discuss how to use our diagnostic to understand the location of the Gamma-ray emission as a function of source power through the use of multiwavelength observations. 
M. Georganopoulos, E. T. Meyer, G. Fossati
astro-ph.HE