The need for a local source of UHE CR nuclei

TL;DR

This paper investigates the local sources of ultra-high energy cosmic ray nuclei, finding that nearby sources within 60-80 Mpc are necessary to explain observed heavy composition trends, especially considering magnetic fields.

Contribution

It provides an analytic framework linking UHE CR composition data to the distribution of local sources within 80 Mpc, emphasizing the need for nearby sources.

Findings

Sources of intermediate-to-heavy nuclei are consistent with observed spectra.

Nearby sources within 60-80 Mpc are required for silicon and iron nuclei.

Local magnetic fields strengthen the case for local sources.

Abstract

Recent results of the Pierre Auger (Auger) fluorescence detectors indicate an increasingly heavy composition of ultra-high energy (UHE) cosmic rays (CRs). Assuming that this trend continues up to the highest energies observed by the Auger surface detectors we derive the constraints this places on the local source distribution of UHE CR nuclei. Utilizing an analytic description of UHE CR propagation we derive the expected spectra and composition for a wide range of source emission spectra. We find that sources of intermediate-to-heavy nuclei are consistent with the observed spectra and composition data above the ankle. This consistency requires the presence of nearby sources within 60 Mpc and 80 Mpc for silicon and iron only sources, respectively. The necessity of these local sources becomes even more compelling in the presence nano-Gauss local extragalactic magnetic fields.