Contribution of Cosmic Rays from Sources with a Monoenergetic Proton Spectrum to the Extragalactic Diffuse Gamma-Ray Emission

TL;DR

This paper investigates how ultra-high-energy cosmic rays from specific extragalactic sources, like certain active galactic nuclei, can significantly contribute to the diffuse gamma-ray background observed by Fermi LAT, providing new constraints on source populations.

Contribution

It demonstrates that cosmic rays from monoenergetic proton sources can produce detectable gamma-ray fluxes and establishes constraints on the fraction of such sources among known AGNs.

Findings

Cosmic rays from these sources can produce a noticeable gamma-ray flux.

Constraints on the fraction of specific AGNs contributing to gamma-ray emission.

Ultra-high-energy cosmic rays can significantly influence the extragalactic gamma-ray background.

Abstract

The extragalactic sources of ultra-high-energy (E > 4x10^19 eV) cosmic rays that make a small contribution to the flux of particles recorded by ground-based arrays are discussed. We show that cosmic rays from such sources can produce a noticeable diffuse gamma-ray flux in intergalactic space compared to the the data obtained with Fermi LAT (onboard the Fermi space observatory). A possible type of active galactic nuclei (AGNs) in which cosmic-ray protons can be accelerated to energies 1021 eV is considered as an illustration of such sources. We conclude that ultra-high-energy cosmic rays from the AGNs being discussed can contribute significantly to the extragalactic diffuse gamma-ray emission. In addition, a constraint on the fraction of the AGNs under consideration relative to the BL Lac objects and radio galaxies has been obtained from a comparison with the Fermi LAT data.