Constraints on secondary 10-100 EeV gamma ray flux in the minimal bottom-up model of Ultra High Energy Cosmic Rays

TL;DR

This paper constrains the flux of secondary ultra-high energy gamma rays within a minimal proton-based model of cosmic rays above 10 EeV, using observational data and theoretical calculations.

Contribution

It provides the first detailed constraints on gamma ray fluxes in a minimal, proton-only cosmic ray model considering various radio backgrounds and magnetic fields.

Findings

Limits on gamma ray fluxes derived for different radio background models.

Quantitative predictions of gamma ray fluxes based on the minimal model.

Implications for the composition and sources of ultra-high energy cosmic rays.

Abstract

In a recently proposed model the cosmic rays spectrum at energies above EeV can be fitted with a minimal number of unknown parameters assuming that the extragalactic cosmic rays are only protons with a power law source spectrum. Within this minimal model, after fitting the observed HiRes spectrum with four parameters (proton injection spectrum power law index, maximum energy, minimum distance to sources and evolution parameter) we compute the flux of ultra-high energy photons due to photon-pion production and e+e- pair production by protons for several radio background models and a range of average extragalactic magnetic fields.