Search for GRB X-ray afterglows in the ROSAT all-sky survey

摘要

We describe a search for X-ray afterglows from gamma-ray bursts using theROSAT all-sky survey (RASS) data. If the emission in the soft X-ray band issignificantly less beamed than in the gamma-ray band, we expect to detect manyafterglows in the RASS. We found 23 afterglow candidates, where about 4detections are predicted. However, follow-up spectroscopy of severalcounterpart candidates strongly suggests a flare star origin of the RASS eventsin many cases. We conclude that the RASS data are consistent with comparablebeaming angles in the X-ray (within a few hours of the burst) and gamma-raybands. However, models predicting a large amount of energy emerging as a nearlyisotropic X-ray component of the early afterglow are severely constrained bythe ROSAT data. In particular, a so far undetected class of ``dirty fireballs''and delayed ``rebursts'' are constrained.