The origin and emission mechanism of VHE (>100GeV) emission from FSRQs

摘要

Flat Spectrum Radio Quasars, unlike BL Lac objects, are blazars that show prominent line-emission and strong thermal components associated with the accretion disk, the broad-line region (BLR), and/or the dusty torus. The low energy peak in the continuum is from synchrotron emission (of electrons), and the high energy peak is well explained by external-Compton emission. In these models the relativistic electrons in the jet up-scatter photons from the thermal photon fields up to GeV energies. Beyond a few tens of GeV such models predict cutoffs due to Klein-Nishina effect and internal absorption via pair production. While more than 300 FSRQs have been seen with Fermi-LAT (between 100MeV?30GeV), only three have been detected at VHE (Very High Energy, E > 100 GeV) with Cherenkov telescopes. The detection of VHE emission constrains the location of the blazar zone based on internal absorption estimates, but challenges the emission models that predict cutoffs. While a number of GeV flaring states (in various FSRQs) have been observed with Cherenkov telescopes only few have resulted in detection of a VHE signal. The broadband emission characteristics of VHE FSRQs (including the VHE-detected FSRQs) are studied and put in context to better understand their location and emission mechanism.