Cascade photons as test of protons in UHECR

Understand

An isotropic component of high energy $\gamma$-ray spectrum measured by Fermi LAT constrains the proton component of UHECR.

• The strongest restriction comes from the highest, $(580-820)$ GeV, energy bin.
• One more constraint on the proton component is provided by the IceCube upper bound on ultrahigh energy cosmogenic neutrino flux.
• We study the influence of these restrictions on the source properties, such as evolution and distribution of sources, their energy spectrum and admixture of nuclei.