NASA SWIFT: GRB050730: Swift-BAT detection of a weak burst

TITLE: GCN GRB OBSERVATION REPORT
NUMBER: 3704
SUBJECT: GRB050730: Swift-BAT detection of a weak burst
DATE: 05/07/30 21:00:41 GMT
FROM: Scott Barthelmy at NASA/GSFC Scott@lheamail.gsfc.nasa.gov

S.T. Holland (GSFC/USRA), S. Barthelmy (GSFC), D.N. Burrows (PSU), C. Gronwall (PSU), J. Kennea (PSU), N. Gehrels (GSFC), D. Palmer (LANL), A. Parsons (GSFC), P. Schady (MSSL), on behalf of the Swift team:

At 19:58:23 UT, Swift-BAT triggered and located GRB050730 (trigger=148225). The spacecraft slewed immediately. The BAT on-board calculated location is RA,Dec 212.065d,-3.762d {14h 08m 16s,-03d 45′ 41″} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys). The BAT light curve shows a broad weak bump with a total duration of 30-40 sec. The peak count rate was ~500 counts/sec (15-350 keV).

The XRT began observing at 20:00:33 UT, 130 seconds after the BAT trigger. XRT was unable to centroid on any source, however the downlinked lightcurve shows a bright variable source is present in the XRT field of view. There are no catalogued X-ray sources in the field, suggesting that this bright source is the GRB afterglow.

The Swift Ultra-Violet/Optical Telescope (UVOT) observations began at 20:00:22 UT, 119 seconds after the BAT trigger. The first data taken in the V band after the spacecraft settled was a 100 sec exposure. A comparison against the DSS catalogue reveals a possible new source inside the BAT error circle at 14h 08m 17.09s,-3d 46′ 18.9″ +- 1 arcsec (radius, sys+stat, 90% c.l., J2000). The V band magnitude was 17.62 +- 0.22.

It is noted that the position of this GRB lies in the direction of the Galaxy Cluster ZwCl 1406-0334 (z=0.088). The s/c is currently in the gap of downlink passes, so further analysis will not be forthcoming for at least 5 hours.