دانلود رایگان مقاله فوتون آبشاری به عنوان آزمون پروتون ها در UHECR

ABSTRACT

An isotropic component of high energy γ -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. We also study the sensitivity of restrictions to various Fermi LAT galactic foreground models (model B being less restrictive), to the choice of extragalactic background light model and to overall normalization of the energy spectrum. We claim that the γ -ray-cascade constraints are stronger than the neutrino ones, and that however many proton models are viable. The basic parameters of such models are relatively large γ g and not very large zmax . The allowance for He4 admixture also relaxes the restrictions. However we foresee that future CTA measurements of γ -ray spectrum at Eγ (600 − 800) GeV, as well as resolving of more individual γ -ray sources, may rule out the proton-dominated cosmic ray models.

3. Discussion

Modern UHECR experiments in which mass composition of UHECR is measured using atmospheric shower properties such as depth of shower maximum, result in contradictory conclusions. For this reason the indirect methods facilitating discrimination of various UHECR composition models obtain the considerable importance. In this work we use the method based on calculation of diffuse fluxes of secondary γ -rays and neutrinos generated by UHECR during their propagation. We consider first the models with pure proton composition which are consistent with TA and HiRes data and then the mixed composition of protons and Helium with different ratios. These models include also the dip model which explains the observed feature, the dip at (1 − 40) EeV by e+e− pair production. We demonstrate that many proton models are severely constrained by the Fermi LAT IGRB observations, but there are many models that successfully survive. The first selection of the proton-dominated models follows from the condition of describing the TA or HiRes energy spectra; among these models we choose those with generation indexes γ g, zmax and cosmological evolution (1 + z)m up to maximum redshift zmax which do not overproduce the Fermi LAT γ -ray radiation.