Absorption of High Energy Gamma Rays by Interactions With Starlight Photons in Extragalactic Space at High Redshifts and the High Energy Gamma-Ray Background

摘要

We calculate the absorption of 10-500 GeV gamma-rays at high redshifts. Thiscalculation requires the determination of the high-redshift evolution of theintergalactic starlight photon field, including its IR-UV spectral energydistribution. To estimate this evolution, we have followed a recent analysis ofFall, Charlot and Pei which gives results consistent with recent data. We giveour results for the gamma-ray opacity as a function of redshift out to aredshift of 3. We also give predicted gamma-ray spectra for selected blazarsand give an extragalactic unresolved blazar background spectrum up to 500 GeV.Our results indicate that this background should steepen significantly above 20GeV owing to intergalactic absorption. Future observations of this steepeningwould provide a test for the blazar background origin hypothesis. We have usedour results to discuss upper limits on the redshifts of gamma-ray bursts. Wenote that the 17 Feb. 1994 burst observed by EGRET must have originated at aredshift less than 2. We also use our estimates of the background to determinethe observability of multi-GeV gamma-ray lines from the annihilation ofsupersymmetric dark matter particles in the galactic halo.