Unmasking the ultrahigh-energy cosmic ray origin

TL;DR

This paper reviews a general model explaining ultrahigh-energy cosmic ray spectrum and composition, highlighting starburst galaxies as plausible sources, and addresses the spectral features around the ankle energy.

Contribution

It introduces a comprehensive model of cosmic ray origins based on photo-disintegration in sources, with starburst galaxies as a key example.

Findings

The model reproduces the observed spectrum and composition of extragalactic cosmic rays.

Starburst galaxies are identified as promising sources for ultrahigh-energy cosmic rays.

The model explains the spectral ankle feature through source-related processes.

Abstract

The sharp change in slope of the ultrahigh-energy cosmic ray spectrum around 10^{9.6} GeV (the ankle), combined with evidence of a light but extragalactic component near and below the ankle which evolves to intermediate/heavy composition above, has proved exceedingly challenging to understand theoretically. Recently, we introduced a very general model in which, for a range of source conditions, photo-disintegration of ultrahigh-energy nuclei in the region surrounding the accelerator naturally accounts for the observed spectrum and composition of the entire extragalactic component, which dominates above about 10^{8.5} GeV. In this communication we review the generalities of the model and show that starburst galaxies provide a compelling source example.