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

Abstract

Recent results from the 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 or rare types of supernova explosions that took place in the 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 or closest bursts can be associated with observed clusters of UHECRs.