UHECR correlations taking account of composition and Galactic magnetic deflections

TL;DR

This study models ultra-high-energy cosmic ray arrival directions considering Galactic magnetic deflections, source types, and compositions, showing that significant structure persists even with heavy or mixed compositions, aiding correlation analyses.

Contribution

It introduces a method to incorporate Galactic magnetic field deflections at low rigidities into UHECR correlation studies, accounting for various source and composition hypotheses.

Findings

Correlations are feasible with low-rigidity deflections.

Arrival directions show structure even with heavy compositions.

The model supports local universe origin hypotheses.

Abstract

We predict the arrival direction distribution of cosmic rays including their deflection in the Galactic magnetic field, for several combinations of source and composition hypotheses: the sources are hard X-ray AGNs or uniformly sample the matter distribution of galaxies, and the composition at the source is pure proton or is the Galactic cosmic ray composition measured by CREAM. We use the regular component of the Jansson-Farrar 2012 model for the GMF and allow for rigidities as low as 2 EeV. We report the correlations of published UHECRs, rescaling event energies so as to reconcile the spectra of the different experiments and taking the overall energy uncertainty into account; different composition hypotheses are considered. This work demonstrates the feasibility of calculating GMF deflections to low enough rigidities to allow for heavy composition in correlation studies, and that non-trivial arrival direction structure should be expected even for mixed or heavy composition, as long as UHECRs come from the local universe.