ELECTRON-PHOTON CASCADING OF VERY-HIGH-ENERGY GAMMA-RAYS IN THE INFRARED BACKGROUND

Soon after the detection by the Compton Gamma Ray Observatory of gamma -rays above 100 MeV from the optically violent variable 3C 279 at a re dshift of z = 0.54, Stecker et al. pointed out that TeV gamma-rays fro m large-redshift sources would be attenuated by photon-photon interact ions in the intergalactic infrared (IR) background radiation. In this paper, we consider the case in which the produced pairs inverse-Compto n-scatter low-energy photons up to gamma-ray energies and start a pair -Compton cascade in the IR/microwave background. The simulation of suc h cascades over the enormous distances from high-redshift sources requ ired us to develop a new matrix method to carry out the propagation. W e find that the TeV gamma-ray fluxes are only marginally higher for th e case with cascading than they are for the case of absorption only. H owever, the greatest difference occurs at lower energies, around 1 GeV , where the pile-up of photons below the absorption feature results in a significant flattening in the observed spectrum relative to the emi ssion spectrum.