The expected rates of X-ray flashes from GRBs in ROSAT and preliminary search results

The recent long (up to days) and relatively bright soft X-ray afterglows from GRBs detected by BeppoSAX raise the possibility of detecting similar events in the ROSAT database. We perform detailed calculations on the expected number of ROSAT events based on the extended halo scenario. We use the realistic ROSAT capabilities and the actual exposure time on bright nearby galaxies. We find that the expected number of X-ray events is quite low, ∼1, and depends on the peak X-ray luminosity. Thus a nondetection of such events from nearby galaxies (within 12 Mpc) can not rule out most of the viable halo models. We also present the preliminary search results from the ROSAT PSPC database.