Possible GeV Emission from TeV Blazars

Abstract

We propose a model to account for possible GeV emission from TeV blazars. In this model, the possible GeV emission from a TeV blazar can consist of two components. One, the source component, is produced in the source through the synchrotron self-Compton (SSC) mechanism; the other, the external component, is produced on the way from the source to us by the inverse Compton (IC) scattering of e± pairs with the cosmic microwave background (CMB), where the e± are created through the interaction of TeV gamma rays emitted from the TeV blazar with the diffuse IR-UV background. We apply the model to study the possible GeV emission from Mrk 501, which is a strong TeV emitter. We calculate self-consistently the spectra of high-energy gamma rays of these two components for three different activities of Mrk 501 in 1997. Our results indicate that (1) the GeV gamma-ray emission of the external component can dominate that of the source component if the intergalactic magnetic field (IGMF) strength is not greater than 10−19 G; (2) the shape of the photon spectra of the external component depends on both the observed variation time and the IGMF strength, particularly in the lower part of GeV energy range; (3) the flux level of TeV photons determines that of the spectrum of the external component; and (4) GeV emission from different activity in Mrk 501 should be detectable by the upcoming satellite GLAST.