Discerning the $\gamma$-ray emitting region in the flat spectrum radio quasars

Understand

A model-dependent method is proposed to determine the location of the $\gamma$-ray emitting region for a given flat spectrum radio quasar (FSRQ).

• In the model, the extra-relativistic electrons are injected at the base of the jet and non-thermal photons are produced by both synchrotron radiation and inverse-Comtpon (IC) scattering in the energy dissipation region.
• The target photons dominating inverse-Comtpon scattering originate from both synchrotron photons and external ambient photon fields, and the energy density of external radiation field is a function of the distance between the position of dissipation region and a central super-massive black hole, and their spectra are seen in the comoving frame.
• Moreover, the energy dissipation region could be determined by the model parameter through reproducing the $\gamma$-ray spectra.