ON COMPTON-SCATTERING SCENARIOS FOR BLAZAR FLARES

The synchrotron reflection scenario recently proposed to explain gamma -ray flares observed from blazar jets is studied. Our analysis takes i nto account the angular distribution of the beamed radiation, the fini te extent of the scattering region, and light-travel-time effects. We compare energy densities and powers for synchrotron, synchrotron self- Compton, reflected synchrotron (RSy), and external Compton scattering processes. If the width of the scattering layer is much larger than Ga mma R-B', where Gamma and R-B' denote the bulk Lorentz factor and the comoving frame radius of the plasma blob, respectively, then the ratio of the RSy and synchrotron energy densities is similar to 4 Gamma(3)n (BLR)sigma(T)R(B)' where n(BLR) is the mean particle density in the br oad line region (BLR). Our results imply that Thomson-thick scattering regions of narrow extent must be present for the synchrotron reflecti on mechanism to operate effectively. This process seems unlikely to ca use flares in lineless BL Lac sources, where X-ray and TeV flares are common and the BLR is thought to be weak or absent. We sketch time pro files of flares for Various scenarios.