Top left: photon-photon absorption correction (exp [τ_γγ]) for the source MKN 501 at z = 0.034, based on our improved EBL model. Bottom left: observed (open black) and absorption-corrected (filled red) spectrum. Data are taken from Aharonian et al. (2001; see also Aharonian et al. 1999). The intrinsic spectrum is fitted by a broken power-law with relatively flat photon spectral indices, as indicated in the insert. Top right: absorption correction for the source MKN 421 at z = 0.03 . Bottom right: observed (open black) and absorption-corrected (filled red) spectrum. Data are taken from Aharonian et al. (2002). The intrinsic spectrum was fitted by a steep broken power-law. Spectral indices are indicated.