A Cluster of Ultrahigh Energy Cosmic Rays

Abstract

Five ultrahigh energy cosmic rays in the combined AGASA and HiRes stereo data are analyzed to test whether they come from a single source. The quad above 37 EeV in the 94-event high energy dataset can be analyzed without considering magnetic dispersion. The probability that it is a chance association is 10^-3. Assuming the source is continuous, the random magnetic deflections these UHECRs accumulated en route from their source can be used to estimate \sqrt{B^2 λD} ~ 1 nG-Mpc. A quintuplet including a HiRes event between 10 and 30 EeV is well fit with this value. Galactic magnetic deflection appears to be smaller than in some models.

Reformatted as AASTex preprint; 12 pp. An obvious but serious typo in the units of the field-strength constraint is corrected. Chance probability estimates are updated with results of more extensive Monte Carlo simulations, strengthening conclusions. Clarity of the text is improved, treatment of galactic magnetic deflection is generalized, and some other points are elaborated