The Possibility of Investigating Ultra-High-Energy Cosmic-Ray Sources Using Data on the Extragalactic Diffuse Gamma-Ray Emission

Abstract: We provide our estimates of the intensity of the gamma-ray emission with an energy near 0.1 TeV generated in inrergalactic space in the interactions of cosmic rays with background emissions. We assume that the cosmic ray sources are point-like and these are active galactic nuclei. The following pjssible types of sources are considered: remote and powerful ones, at redshifts up to z=1.1, with a monoenergetic particle spectrum, E=10^21 eV; the same objects, but with a power-law particle spectrum; and nearby sources with redshifts 0<z<=0.0092, i.e. at distances no larger than 50 Mpc also with a power-law particle spectrum. The contribution of cosmic rays to to the extragalactic diffuse gamma-ray background at an energy of 0.1 TeV has been found to depend on the type of sources or, more specifically, the contribution ranges from f<<10^-4 to f of about 0.1. depending on the source model. We conclude that the data on the extragalactic background gamma-ray emission can be used to determine the characteristics of cosmic-ray sources, i.e. their distances and the pattern of the particle energy spectrum. Keywords: cosmic rays, diffuse gamma-ray emission, active galactic nuclei. To be published in: Astronomy Letters, 2017, vol. 43, No.8, pp. 529-535.