Modelling the TeV gamma-ray spectra of two low redshift AGNs: Mkn 501 and Mkn 421

Abstract

We discuss the results of modelling the TeV gamma-ray spectra of two AGNs, Mkn 501 and Mkn 421 that have almost the same redshifts: z=0.031 and z=0.034, respectively. The effect of intergalactic gamma-ray absorption is treated as an uncertainty in the measurement of the intrinsic spectrum. Although the objects differ, we obtain satisfactory fits for both of them in a synchrotron self-Compton scenario. Compared to previous models, our fits are characterised by higher values of the Doppler factor (>= 50) and an electron injection spectrum extending to higher energies (Gmax = 1.5x10^5). In the case of Mkn 421, the observed difference in spectral slope in X-rays and TeV gamma-rays between the high and low states can be explained as a variation of a single parameter - the maximum energy Gmax mc^2 at which electrons are injected.