GZK photons in the minimal ultra-high energy cosmic rays model

In a recently proposed model the cosmic rays spectrum at energies above 1018 eV 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 ∼E−α and α ≃ 2.6. Within this minimal model, after fitting the observed HiRes spectrum with four parameters (proton injection spectrum power law index and maximum energy, minimum distance to sources and evolution parameter) we compute the flux of ultra-high energy photons due to photon-pion production, the GZK photons, for several radio background models and average extragalactic magnetic fields with amplitude between 10−11 G and 10−9 G. We find the photon fraction to be between 10−4 and 10−3 in cosmic rays at energies above 1019 eV. These small fluxes could only be detected in future experiments like Auger North plus South, EUSO and OWL.