[vsnet-grb-info 2443] GRB 051117: Swift detection of a bright burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4280
SUBJECT: GRB 051117: Swift detection of a bright burst
DATE:    05/11/17 11:44:49 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

D. Band (GSFC), S. Barthelmy (GSFC), A. Beardmore (U Leicester),
D. Burrows (PSU), N. Gehrels (GSFC), M. Goad (U. Leicester)
O. Godet (U. Leicester), C. Gronwall (PSU), J. Kennea (PSU),
K. Page (U Leicester), E. Rol (U. Leicester)
on behalf of the Swift team:

At 10:51:20 UT, Swift-BAT triggered and located GRB 051117 (trigger=164268).
The spacecraft slewed immediately.  The BAT on-board calculated location
is RA,Dec 228.405d, +30.870d {+15h 13m 37s, +30d 52' 11"} (J2000),
with an uncertainty of 3 arcmin (radius, 90% containment, stat+sys).
The BAT light curve shows a single peak with a total duration
of about 20 sec.  The peak count rate was ~1500 counts/sec (15-350 keV),
at ~3 sec after the trigger.

XRT began observing at 10:53:07 UT, 107 seconds after the BAT trigger. 
We find a bright, rapidly fading, uncataloged source at RA 15h 13m 33.7s 
Dec +30d 52' 22.0" (J2000) with a positional uncertainty of 5.8 arcsec
(90% containment).  This is 46 arcsec from the BAT position.  The 
approximate initial flux is 1.0e-8 erg/cm2/sec (0.2-10 keV).  The XRT
preliminary raw spectrum is well fit by an absorbed powerlaw with a
photon index of 2.2+/- 0.1 with an excess NH of 2e21 cm^-2.

UVOT began observing at UT 10:53:10, 111 seconds after the BAT trigger.
In a 200 sec V image, we detect a faint source just outside the XRT 
error circle at an approximate position of RA=15h 13m 33.6s, Dec=30d 52' 15.2"
(J2000) that is not present in the DSS.  The magnitude is 19.9 mag.
The extinction in this direction is A_V = 0.08.