GAMMA-RAY BURSTER COUNTERPARTS - HUBBLE-SPACE-TELESCOPE BLUE AND ULTRAVIOLET DATA

The surest solution of the gamma-ray burst (GRB) mystery is to find an unambiguous low-energy quiescent counterpart. However, to date no rea sonable candidates have been identified in the X-ray, optical, infrare d, or radio ranges. The Hubble Space Telescope (HST) has now allowed f or the first deep ultraviolet searches for quiescent counterparts. Thi s paper reports on multiepoch ultraviolet searches of five GRB positio ns with HST. We found no sources with significant ultraviolet excesses , variability, parallax, or proper motion in any of the burst error re gions. In particular, we see no sources similar to that proposed as a counterpart to the GRB 970228. While this negative result is disappoin ting, it still has good utility for its strict limits on the no-host-g alaxy problem in cosmological models of GRBs. For most cosmological mo dels (with peak luminosity 6 x 10(50) ergs s(-1)), the absolute B magn itude of any possible host galaxy must be fainter than -15.5 to -17.4. These smallest boxes for some of the brightest bursts provide the mos t critical test, and our limits are a severe problem for all published cosmological burst models.