The WATCH GRB catalogue provides a set of 47 burster positions, 39 of which have a total (statistical plus systematic) uncertainty of less than 1 deg. For 13 events error boxes with radii smaller than 30 arcmin are now available. The WATCH sample thus contributes to the currently available list of moderately accurate GRB positions a number of locations comparable to that accumulated by the interplanetary satellite networks and never before obtained with any stand-alone instrument. We therefore hope that the new data presented here will be useful for burster counterpart searches in different energy ranges as well as for studying possible correlations in GRB positions.
The WATCH GRBs appear distributed both isotropically on the celestial sphere and homogeneously in space. These two results seem to be consistent with the implications from the third BATSE catalogue, as WATCH is about an order of magnitude less sensitive than the large-area detectors of BATSE, and the brighter bursts in the BATSE catalogue also show both isotropy and homogeneity (Meegan et al. 1996).
The light curves of most bursts observed by WATCH show hardening of the energy spectrum near the burst maxima. Several bursts demonstrate a significant 8-20 keV activity in the absence of hard X-ray flux either before or after the GRB. To all appearances, these X-ray events accompanying gamma-ray bursts are higher energy manifestations of the soft X-ray precursors and tails observed at 1.5-10 keV by GINGA.
Acknowledgements
We thank all specialists involved in the GRANAT/WATCH experiment,
in particular: the staffs of the Lavochkin Association, the Evpatoria
Deep Space Control Center and the group of B.S. Novikov maintaining
the instrument operations; the group of A.V. Dyachkov at IKI RAN
processing telemetry data; N.G. Havenson and E.M. Churazov for their
assistance in determining the spacecraft attitude. The participation
of the russian co-authors in this project was
supported by Russian
Basic Research Foundation grant
No. 95-02-05938 and INTAS grant
93-3364. SS acknowledges the hospitality of the Max-Planck-Institut
für Astrophysik
where the final manuscript of this paper was finished.