Origin of the Ultrahigh-Energy Cosmic Rays and their Spectral Break

TL;DR

This paper proposes that ultrahigh-energy cosmic rays originate from Galactic gamma-ray bursts rather than extragalactic sources, explaining the spectral break as a Galactic escape threshold rather than the GZK cutoff.

Contribution

It introduces a Galactic origin model for UHECRs, challenging the conventional extragalactic assumption and explaining the spectral features through local acceleration and escape mechanisms.

Findings

UHECRs above 50 EeV may originate from Galactic sources.

The spectral break is interpreted as a Galactic escape threshold.

UHECR nuclei should point back to Galactic sources rather than extragalactic ones.

Abstract

The energy spectrum, composition and arrival directions of ultrahigh energy cosmic rays (UHECRs) with energy above the cosmic ray ankle, measured by the Pierre Auger Observatory, are inconsistent if their origin is assumed to be extragalactic. Their observed properties, however, are those expected from UHECRs accelerated by the highly relativistic jets emitted in Galactic gamma ray bursts, most of which are beamed away from Earth. If this alternative interpretation is correct, the observed break in the energy spectrum of UHECRs around 50 EeV is not the Greisen-Zatsepin-Kuzmin cutoff but the energy threshold for free escape of ultrahigh energy iron cosmic rays from the Galaxy and above their respective free-escape threshold-energies, UHECR nuclei should point back to their Galactic sources or their remnants rather than to active galactic nuclei (AGN) within the GZK horizon.