1998ApJ...505L.123V

We search for faint X-ray bursts with duration 10-300 s in the ROSAT PSPC pointed observations with a total exposure of 1.6x10⁷ s. We do not detect any events shorter than ∼100 s, i.e., those that could be related to the classic gamma-ray bursts (GRBs). At the same time, we detect a number of long flares with durations of several hundred seconds. Most, but not all, of the long flares are associated with stars. If even a small number of those long flares, which cannot be identified with stars, are X-ray afterglows of GRBs, the number of X-ray afterglows greatly exceeds the number of BATSE GRBs. This would imply that the beaming factor of gamma rays from the burst should be greater than 100. The nondetection of any short bursts in our data constrains the GRB counts at the fluences to 10-300 times fainter than the BATSE limit. The constrained burst counts are consistent with the extrapolation of the BATSE logN-logS relation. Finally, our results do not confirm the reality of short X-ray flashes found in the Einstein IPC data by Gotthelf, Hamilton, & Helfand.