POSSIBLE ASSOCIATION OF ULTRA-HIGH-ENERGY COSMIC-RAY EVENTS WITH STRONG GAMMA-RAY BURSTS

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 catalog. The probability of this occurring 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, are 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. With similar energies going into gamma rays and cosmic rays, we expect only a few times 10% of the strongest GRBs to be followed by a detection of an ultra-high-energy (E > 10(20) eV) cosmic ray in existing experiments. We discuss some of the implications that follow if such an association is confirmed. For example, the upper limit on the distance of the cosmic-ray source, combined with a much better determined position of the gamma-ray burst source, reduces greatly the volume in which to look for an optical counterpart. The need to produce ultra-high-energy cosmic rays in the GRB source imposes additional constraints on the physical conditions in it. There is also useful information in the time delay regarding, e.g., intergalactic magnetic fields.