Role of Galactic sources and magnetic fields in forming the observed energy-dependent composition of ultrahigh-energy cosmic rays

TL;DR

This paper explores how Galactic sources and magnetic fields influence the energy-dependent composition of ultrahigh-energy cosmic rays, suggesting diffusion times and recent bursts shape observed patterns.

Contribution

It proposes a model where Galactic gamma-ray bursts and supernovae explain the composition and anisotropy of UHECRs based on diffusion differences.

Findings

Heavy element fraction increases at higher energies.

Anisotropy towards the Galactic Center is a few percent.

Recent nearby bursts may correlate with UHECR clusters.

Abstract

Recent results from Pierre Auger Observatory, showing energy dependent chemical composition of ultrahigh-energy cosmic rays (UHECRs) with a growing fraction of heavy elements at high energies, suggest a possible non-negligible contribution of the Galactic sources. We show that, in the case of UHECRs produced by gamma-ray bursts (GRBs) or rare types of supernova explosions that took place in Milky Way in the past, the change in UHECR composition can result from the difference in diffusion times for different species. The anisotropy in the direction of the Galactic Center is expected to be a few per cent on average, but the locations of the most recent/closest bursts can be associated with observed clusters of UHECRs.