A serendipitous observation of the gamma-ray burst GRB 921013b field with EUVE

Abstract

We report a serendipitous extreme ultraviolet observation by EUVE of the field containing GRB 921013b, ~ 11 hours after its occurrence. This burst was detected on 1992 October 13 by the WATCH and PHEBUS on Granat, and by the GRB experiment on Ulysses. The lack of any transient (or quiescent) EUV source imposes a 2sigma upper limit of 1.3 x 10(-12) erg \ s(-1) \ cm(-2) in the 58-174 Angstroms bandpass. In the likely case that GRB 921013b was extragalactic, and assuming the existence of an X-ray afterglow similar to those observed for GRB 970228 and GRB 970828, the resulting EUV flux 11 hours after the burst is 1.8 x 10(-16) \ erg \ s(-1) \ cm(-2) after correction for absorption by the Galactic interstellar medium. Even if we exclude an intrinsic absorption, this is well below the detection limit of the EUVE measurement. Although it is widely accepted that gamma-ray bursts are at cosmological distances, if the source of GRB 921013b would be a galactic neutron star, the data presented here place a lower limit to its distance of ~ 30 pc.