In order to more accurately determine the fraction f and thus the expected number of events, a distribution function of power-law indices of GRB X-ray afterglow decays as measured by BeppoSAX is highly needed.
We finally note that GRBs from directions within a few degrees of the galactic plane will suffer absorption, thus compromising the sensitivity of the ROSAT detection. However, this effect concerns only a few percent of the sky, and mainly applies to single peak events, because any multi-peak event should have a first peak count rate high enough to still be detectable.
We are indebted to E. Costa and J. in 't Zand for providing X-ray afterglow light curves in digital form. JG is supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DLR) under contract No. 50OR96098. The ROSAT project is supported by BMBF/DLR and the Max-Planck-Society. This research has made use of the Simbad database, operated at CDS, Strasbourg, France and the Digitized Sky Survey (DSS) produced at the Space Telescope Science Institute under US Government grant NAG W-2166.
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