On the Absorption of High‐Energy Gamma Rays by Intergalactic Infrared Radiation

We present a new calculation of the intergalactic $\gamma$-raypair-production absorption coefficient as a function of both energy andredshift up to the redshift of 3C279, z = 0.54. In reexamining this problem, wemake use of new observational data on the intergalactic infrared radiationfield (IIRF), together with recent theoretical models of the galactic spectralenergy distributions of the IIRF from stars and dust reradiation and estimatesof the IIRF from galaxy counts and {\it COBE} results. We present our resultsfor two fairly well defined IIRF spectral energy distributions, one of which iswithin $1 \sigma $ of our previous estimate of the IIRF at $ \sim 20$ $\mu$m.We then apply our results to the $\gamma$-ray spectrum of Mrk 421, and obtaingood agreement with the observational data, including the recent results of the{\it HEGRA} group.Comment: Plain TeX file with text in abs96.tex, 3 postscript figures (Fig. 1 - ircobe.eps, Fig. 2 - taupl.eps, Fig. 3 - mki.eps), stylefile epsf.sty included, accepted for publication in the Astrophysical Journa