Possible Association of Ultra–High-Energy Cosmic-Ray Events with Strong Gamma-Ray Bursts

Abstract

We point out that each of the error boxes of the two highest-energy\ncosmic-ray shower events known, overlaps with that of a strong gamma-ray burst\n(GRB). The GRBs precede the cosmic rays by 5.5, and 11 months respectively. In\none case the strongest known cosmic ray is paired with the strongest gamma-ray\nburst in the BATSE catalogue. The probability of this to have occurred by\nchance seems rather small. Without building on post-factum statistics, we think\nthe above is remarkable enough to suggest that the cosmic ray and gamma-ray\nburst were produced by the same outburst. A time delay (and a small positional\ndisparity) is expected, since the trajectory of a charged cosmic-ray particle\nis wriggled by intervening magnetic fields. We estimate that the Galaxy's field\nalone may produce a delay of the order observed. We discuss some of the\nimplications that follow if such an association is confirmed. For example, the\nupper limit on the distance to the cosmic-ray source, combined with a\nmuch-better-determined position of the gamma-ray burst source, narrows greatly\nthe volume in which to look for an optical counterpart. There is also useful\ninformation in the time delay regarding, e.g., intergalactic magnetic fields.\n