On the Absorption of High Energy Gamma-rays by Intergalactic Infrared Radiation

We present a new calculation of the intergalactic γ-ray pair-production absorption coefficient as a function of both energy and redshift up to the redshift of 3C279, z = 0.54. In reexamining this problem, we make use of new observational data on the intergalactic infrared radiation field (IIRF), together with recent theoretical models of the galactic spectral energy distributions of the IIRF from stars and dust reradiation and estimates of the IIRF from galaxy counts and COBE results. We present our results for two fairly well defined IIRF spectral energy distributions, one of which is within 1σ of our previous estimate of the IIRF at ∼ 20 μm. We then apply our results to the γ-ray spectrum of Mrk 421, and obtain good agreement with the observational data, including the recent results of the HEGRA group. Subject headings: γ-rays:theory – infrared:general – quasars:general – quasars:individual (Markarian 421, 3C279)