The obscured gamma-ray and UHECR universe

TL;DR

This paper explores how the extragalactic background light influences gamma-ray and ultra-high energy cosmic ray observations, suggesting a CNO composition for UHECRs above 60 EeV and discussing implications for their sources.

Contribution

It links gamma-ray spectra and UHECR clustering through EBL effects, proposing a CNO composition for the highest energy cosmic rays, which is a novel interpretation.

Findings

UHECRs above 60 EeV are likely CNO group nucleons.

EBL causes the GZK cutoff and affects gamma-ray and UHECR observations.

Implications for UHECR source models are discussed.

Abstract

Auger results on clustering of > 60 EeV ultra-high energy cosmic ray (UHECR) ions and the interpretation of the gamma-ray spectra of TeV blazars are connected by effects from the extragalactic background light (EBL). The EBL acts as an obscuring medium for gamma rays and a reprocessing medium for UHECR ions and protons, causing the GZK cutoff. The study of the physics underlying the coincidence between the GZK energy and the clustering energy of UHECR ions favors a composition of > 60 EeV UHECRs in CNO group nucleons. This has interesting implications for the sources of UHECRs. We also comment on the Auger analysis.