Modeling the TeV Gamma‐Ray Spectra of Two Low‐Redshift Active Galactic Nuclei: Markarian 501 and Markarian 421

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 anuncertainty in the measurement of the intrinsic spectrum. Although the objectsdiffer, we obtain satisfactory fits for both of them in a synchrotronself-Compton scenario. Compared to previous models, our fits are characterisedby higher values of the Doppler factor (>= 50) and an electron injectionspectrum extending to higher energies (Gmax = 1.5x10^5). In the case of Mkn421, the observed difference in spectral slope in X-rays and TeV gamma-raysbetween the high and low states can be explained as a variation of a singleparameter - the maximum energy Gmax mc^2 at which electrons are injected.Comment: 28 pages, 7 figures, accepted for publication in The Astrophysical Journa