[vsnet-grb-info 2444] GRB 051117B: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4281
SUBJECT: GRB 051117B: Swift detection of a burst
DATE:    05/11/17 13:59:44 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

D. Band (PSU), S. Barthelmy (GSFC), A. Beardmore (U Leicester),
D. Burrows (PSU), J. Cummings (GSFC/NRC), S.T. Holland (GSFC/USRA),
M. Goad (U. Leicester), O. Godet (U. Leicester), N. Gehrels (GSFC),
C. Gronwall (PSU), J. Kennea (PSU), H. Krimm (GSFC/USRA),
J. Osborne (U Leicester), K. Page (U Leicester)
on behalf of the Swift team:

At 13:22:54 UT, Swift-BAT triggered and located GRB 051117B (trigger=164279).
The BAT on-board calculated location is RA,Dec 85.225d,-19.245d
{05h 40m 54s,-19d 14' 41"} (J2000), with an uncertainty of 3 arcmin
(radius, 90% containment, stat+sys).  The BAT light curve shows
a multi-peak structure with a total duration of ~25 sec.  The peak count
rate was ~800 counts/sec (15-350 keV), at ~2 seconds after the trigger.

The spacecraft slewed immediately and the XRT began observing the GRB at
13:25:09 UT, 135 sec after the BAT trigger.  The on-board detection algorithm
did not centroid on a source due to insufficient counts, so no prompt X-ray
position is available.  However, the XRT prompt light curve and raw spectrum
look like a faint GRB.  More information will be available around 16:30 UT,
after the next Malindi ground-station pass.

UVOT took a finding chart exposure of 200 sec with the V filter
starting 133 sec after the BAT trigger.  No afterglow candidate
has been found in the initial data products.  The sub-image covers 19%
of the BAT error circle.  No afterglow candidate is found in the list
of sources generated on-board, which covers 89% of the BAT error circle.
The list of sources is typically complete to about 17th mag.  No correction
has been made for the expected visual extinction of about 0.19 magnitudes.