Modification of the gamma-ray spectra by internal absorption in OVV blazars: The example cases of 3C 273 and 3C 279

Abstract

Recent observations with the low threshold Cherenkov telescopes proved that sub-TeV gamma-rays are able to arrive from active galaxies at relatively large distances in spite of expected severe absorption in the extragalactic background light (EBL). We calculate the gamma-ray spectra at TeV energies from two example OVV quasars, 3C 273 and 3C 279, assuming that gamma-rays are injected in the inner parts of the jets launched by the accretion disks. It is assumed that gamma-rays in the broad energy range (from MeV up to TeV) are produced in these blazars with the power law spectrum with the spectral index as observed from these objects by the EGRET telescope at GeV energies. We take into account the internal absorption of these gamma-rays by considering a few different models for the radiation field surrounding the jet. The classical picture of the relativistic blob in jet model for the injection of primary gamma-rays is considered with the injection rate of gamma-rays as observed by the EGRET telescope in the GeV energy range. The results of calculations are compared with positive detection and the upper limits on the sub-TeV gamma-ray fluxes from these two sources. It is concluded that even with the Stecker EBL model, the level of the gamma-ray emission from 3C~279 is close to the recent measurements in the sub-TeV gamma-ray energies provided that the injected gamma-ray spectrum extends from the GeV energies over the next two decades with this same spectral index. We also suggest that a few day time scale flare from 3C 273 can be detected by the MAGIC II stereo telescopes.