Fermi Gamma-ray Space Telescope

The seed factor: how a combination of four observables can unveil the location of the blazar GeV emission.

Adam Harvey
(Eileen T. Meyer)


We present here a method for constraining the emission location of gamma-rays in powerful, lined blazars (i.e., flat spectrum radio quasars (FSRQs)). We develop a diagnostic criteria, which we term the seed factor, to differentiate between gamma-ray emission due to external Compton (EC) scattering in the broad line region (BLR) and the molecular torus (MT). The seed factor is determined entirely by four observable quantities; the synchrotron and inverse Compton (IC) peak frequencies, and the respective peak luminosities. It may thus be possible to use the seed factor to constrain the emission location in a model-independent way. We present the results of our analysis of multiple samples of multiwavelength observations. We find that the MT is implicated as the most likely emission location of gamma-rays from EC scattering in FSRQs.