GB 811016 and EXO 0748-676

J. G. Laros, E. E. Fenimore, M. M. Fikani and R. W. Klebesadel, Los Alamos National Laboratory, report: "Contrary to what might be concluded from IAUC 4047, the transient x-ray source EXO 0748-676 apparently is not associated with the gamma-ray burst (GRB) GB 811016. In fact, EXO 0748-676 is not in the original error box presented by Katoh et al. (1984, AIP Proc. 115, 390), unless the Pioneer Venus Orbiter (PVO)-Hakucho time-of-arrival annulus is arbitrarily ignored. A refined PVO-Hakucho annulus and a new PVO-International Cometary Explorer annulus are both in agreement with the earlier time-of-arrival work. The new annuli miss EXO 0748-676 by more than ten times their half-widths. The only conceivable systematic effect that would allow the two sources to coincide is a 3-s PVO timing error. However, PVO has demonstrated in other GRB analyses a timing accuracy better than 0.010 s, and several PVO clock correlations taken up to +/- 1 month from GB 811016 showed no irregularities. Therefore, it seems almost certain that we are dealing with a chance coincidence involving only the 3 deg**2 Hakucho collimator-determined error box, and not a real association between an x-ray source and a GRB."