GCN Circular 3788

A. Retter (PSU), L. Barbier (GSFC), S. Barthelmy (GSFC), A. Blustin (MSSL),
D. Burrows (PSU), A. Cucchiara (PSU), N. Gehrels (GSFC), 
O. Godet (U. Leicester), J. Kennea (PSU), C. Markwardt (GSFC/UMD),
D. Morris (PSU), D. Palmer (LANL), J. Racusin (PSU), P. Roming (PSU)
on behalf of the Swift team, report:
 
At 06:45:09.8 UT, Swift-BAT triggered and located GRB050813
(trigger=150139).  The spacecraft slewed immediately.  The BAT
on-board calculated location is RA,Dec 242.010, +11.252 {+16h 08m 02s, 
+11d 15' 07"} (J2000), with an uncertainty of 3 arcmin (radius,
90% containment, stat+sys).  There is a single peak with an
approximate duration of 0.7 sec FWHM.  The peak rate is approx 2000
ct/s in the 15-350 keV band.

At 06:46:23 UT XRT attempted to centroid on the BAT position, 73 secs
after the BAT trigger. No position was acquired by the onboard
software and the TDRSS lightcurve shows no evidence for a decaying
x-ray source.  We can not rule out the presence of a weak x-ray source
like that seen for the early afterglow of short GRB 050509b.  We await
ground analysis of the early XRT data following the first Malindi
pass.

The UVOT began observing this trigger at 06:46:52.0 UT, 102 seconds
after the BAT trigger. No new source (compared to the DSS image) is
observed in the 100 second V-band UVOT GeNI image down to a 5-sigma
upper limit of 18.15 mag.

This trigger (=150139) appears to be a real GRB, as opposed to the
recently retracted trigger (=150131).