GRB050925: Swift-BAT detection of a short burst

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 4034
SUBJECT: GRB050925: Swift-BAT detection of a short burst
DATE: 05/09/25 10:05:01 GMT
FROM: Scott Barthelmy at NASA/GSFC Scott@lheamail.gsfc.nasa.gov

S.T. Holland (GSFC/USRA), S. Barthelmy (GSFC), A. Beardmore (U. Leicester), N. Gehrels (GSFC), J. Kennea (PSU), K. Page (U. Leicester), D. Palmer (LANL), S. Rosen (MSSL) on behalf of the Swift team:

At 09:04:33 UT, Swift-BAT triggered and located GRB050925 (trigger=156838). The BAT on-board calculated location is RA,Dec 303.445d,+34.334d {20h 13m 47s,+34d 20′ 04″} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). We note that the galactic latitude is -0.1. The BAT light curve shows a single-peak structure with a total duration of less than 128 msec. The peak count rate was ~8000 counts/sec (15-350 keV), for the 128-msec binning at 0.00 seconds after the trigger.

The spacecraft slewed immediately and the XRT began observing the GRB at 09:06:05 UT, 92 sec after the BAT trigger. The on-board detection algorithm failed to centroid on a source, so no prompt X-ray position is available. The XRT prompt spectra and lightcurve show no signficant X-ray emission in the field, suggesting that any X-ray counterpart to this burst is faint.

The UVOT began observing this field 91 sec after the BAT trigger. The small UVOT TDRSS image covers 25% of the BAT error circle. However, the full-field UVOT source list contains only catalogued sources, and in particular no uncatalogued source is found inside the BAT error circle. At the present time it is not possible to determine a limiting magnitude for this field. The V-band extinction in this direction is A_V = 7.05 mag.

We note that this burst has soft emission in BAT which may not be consistent with it being in the short-hard class of GRB. At low galactic latitude it is possible that it is a new SGR. At this point we can not be sure of its classification.