On Gamma Ray Burst and Blazar AGN Origins of the Ultra-High Energy Cosmic Rays in Light of First Results from Auger

TL;DR

This paper discusses the astrophysical origins of ultra-high energy cosmic rays, highlighting gamma-ray bursts and AGNs as primary sources, supported by recent Auger Observatory findings and theoretical considerations.

Contribution

It provides new insights into the sources and acceleration mechanisms of UHECRs, integrating observational data with theoretical models to identify likely astrophysical origins.

Findings

Clustering of >60 EeV UHECRs towards nearby AGNs supports extragalactic origins.

UHECR ions can survive photodisintegration within AGN environments.

Predicted gamma-ray and neutrino signatures can help identify UHECR sources.

Abstract

The discoveries of the GZK cutoff with the HiRes and Auger Observatories and the discovery by Auger of clustering of >~60 EeV ultra-high energy cosmic rays (UHECRs) towards nearby <~75 Mpc) AGNs along the supergalactic plane establishes the astrophysical origin of the UHECRs. The likely sources of the UHECRs are gamma-ray bursts and radio-loud AGNs because: (1) they are extragalactic; (2) they are sufficiently powerful; (3) acceleration to ultra-high energies can be achieved in their relativistic ejecta; (4) anomalous X-ray and gamma-ray features can be explained by nonthermal hadron acceleration in relativistic blast waves; and (5) sources reside within the GZK radius. Two arguments for acceleration to UHE are presented, and limits on UHECR ion acceleration are set. UHECR ions are shown to be able to survive without photodisintegrating while passing through the AGN scattered radiation field, even if launched deep in the broad line region. UHECR injection throughout cosmic time fits the measured energy spectrum of UHECRs, at least for protons. Local UHECR proton and ion interaction and energy-loss mean free paths are calculated using an empirical fit to the extragalactic background light (EBL) at IR and optical energies. Minimum intergalactic magnetic (IGM) fields ~1e-11 G are derived from clustering assuming specific source origins, e.g., Cen A, nearby AGNs, or GRBs for the super-GZK CRs seen with Auger. Besides distinct cosmic-ray induced gamma-ray signatures that should be observed with the Gamma ray Large Area Space Telescope (GLAST), source and GZK neutrino detections and the arrival distribution of UHECR in direction and time can finally decide the sources of cosmic rays at the highest energies.