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 cosmic-ray shower events known, overlaps with that of a strong gamma-ray burst (GRB). The GRBs precede the cosmic rays by 5.5, and 11 months respectively. In one case the strongest known cosmic ray is paired with the strongest gamma-ray burst in the BATSE catalogue. The probability of this to have occurred by chance seems rather small. Without building on post-factum statistics, we think the above is remarkable enough to suggest that the cosmic ray and gamma-ray burst were produced by the same outburst. A time delay (and a small positional disparity) is expected, since the trajectory of a charged cosmic-ray particle is wriggled by intervening magnetic fields. We estimate that the Galaxy's field alone may produce a delay of the order observed. We discuss some of the implications that follow if such an association is confirmed. For example, the upper limit on the distance to the cosmic-ray source, combined with a much-better-determined position of the gamma-ray burst source, narrows greatly the volume in which to look for an optical counterpart. There is also useful information in the time delay regarding, e.g., intergalactic magnetic fields.