Intergalactic Extinction of High Energy Gamma-Rays


We discuss the determination of the intergalactic pair-production absorption coefficient as derived by Stecker and De Jager by making use of a new empirically based calculation of the spectral energy distribution of the intergalactic infrared radiation field as given by Malkan and Stecker. We show that the results of the Malkan and Stecker calculation agree well with recent data on the infrared background. We then show that Whipple observations of the flaring γ-ray spectrum of Mrk 421 hint at extragalactic absorption and that the HEGRA observations of the flaring spectrum of Mrk 501 appear to strongly indicate extragalactic absorption. We also discuss the determination of the γ-ray opacity at higher redshifts, following the treatment of Salamon and Stecker. We give a predicted spectrum, with absorption included for PKS 2155-304. This XBL lies at a redshift of 0.12,the highest redshift source yet observed at an energy above 0.3 TeV. This source should have its spectrum steepened by ∼ 1 in its spectral index between ∼ 0.3 and ∼ 3 TeV and should show an absorption cutoff above ∼ 6 TeV.

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@inproceedings{Stecker1998IntergalacticEO, title={Intergalactic Extinction of High Energy Gamma-Rays}, author={Floyd W. Stecker}, year={1998} }