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

The angular clustering of 5 Ultrahigh Energy Cosmic Rays (UHECRs) in the combined published AGASA-HiRes data has a probability of 2103 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 300DMpc years. Assuming the UHECRs experience many incoherent small magnetic deflections enroute from source to Earth, the arrival direction distribution allows estimation that hB2iD 7.7 nG2Mpc2. If the spectrum at the source E2, the total isotropic equivalent energy emitted in UHECRs is 1043 D3 Mpc ergs.