SIMBAD references

We present a new calculation of the intergalactic γ-ray pair-production absorption coefficient as a function of both energy and redshift. In reexamining this problem, we make use of a new empirially based calculation (as opposed to previous model calculations) of the intergalactic infrared radiation field (IIRF). We find smaller opacities than those given previously (Stecker & De Jager, 1997ApJ...476..712S). We apply our results to the new observations of the flaring γ-ray spectra of Mrk421 and Mrk501, both at a redshift of ∼0.03. Our new calculations indicate that there should be no significant curvature in the spectra of these sources for energies below 10TeV, as indicated by recent observations. However, the intrinsic spectra of these sources should be harder by amounts of ∼0.25 to 0.45 in the spectral index (in the 1-10TeV range), with an intergalactic absorption cutoff above ∼20TeV.