Evidence that a cluster of UHECRs was produced by a burst or flare

TL;DR

This paper suggests that a cluster of ultrahigh energy cosmic rays likely originated from a short-duration burst or flare from a nearby source, based on their energies, angular distribution, and magnetic deflections.

Contribution

It provides evidence supporting a burst or flare origin for a UHECR cluster and estimates magnetic field properties and energy output of the source.

Findings

Cluster of 5 UHECRs has low probability of chance occurrence.

Data favors a burst or flare source over continuous emission.

Estimated magnetic field strength and source energy output.

Abstract

The angular clustering of 5 Ultrahigh Energy Cosmic Rays (UHECRs) in the combined published AGASA-HiRes data has a probability of ~ 2 10^-3 of occurring by chance. A first analysis of the implications of the event energies and angular spreading is presented, which is applicable if the source is close enough that GZK losses can be ignored. Under this assumption, the observed energies of the events in this cluster favor a bursting rather than continuously emitting source, with the events emitted on a time scale short compared with 300 D_Mpc years. Assuming the UHECRs experience many incoherent small magnetic deflections enroute from source to Earth, the arrival direction distribution allows estimation that < B^2 lambda > D ~ 7.7 nG^2 Mpc^2, where lambda is the coherence length of the field and D is the source distance. If the spectrum at the source ~ E^{-2}, the total isotropic equivalent energy emitted in UHECRs is > 10^43 D_Mpc^3 ergs.