[vsnet-grb-info 1987] GRB050819: Swift-BAT detection of a weak burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3826
SUBJECT: GRB050819: Swift-BAT detection of a weak burst
DATE:    05/08/19 17:23:53 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

M. De Pasquale (MSSL), S. Barthelmy (GSFC), A.P. Beardmore (U Leicester),
D. Burrows (PSU), M. Chester (PSU), A. Cucchiara (PSU), J. Cummings (GSFC/NRC),
N. Gehrels (GSFC), M.R. Goad (U Leicester), J. Kennea (PSU), H. Krimm (GSFC/USRA),
S.T. Holland (GSFC/USRA), S. Hunsberger (PSU), F. Marshall (GSFC),
C. Markwardt (GSFC/UMD), J.P. Osborne (U Leicester), K.L. Page (U Leicester),
D. Palmer (LANL), A. Parsons (GSFC), P. Roming (PSU), T. Sakamoto (GSFC),
M. Still (GSFC)
on behalf of the Swift team:

At 16:23:55 UT, Swift-BAT triggered and located GRB050819 (trigger 151131).
The BAT on-board calculated location is RA,Dec 358.735d,+24.854d
{23h 54m 56s,+24d 51' 13"} (J2000), with an uncertainty of 2 arcmin
(radius, 90% containment, stat+sys).  The BAT light curve
shows a very broad shallow peak of about 40 seconds duration. 
The peak count rate was ~400 counts/sec (15-350 keV) at ~10 seconds
after the trigger.

The spacecraft slewed immediately and the XRT began taking data at
16:26:15.8, 141 seconds after the BAT trigger.  There were not enough
counts in the first 2.5 s image for a successful on-board centroid.
However, the light-curve shows evidence for a decaying X-ray source
in the field of view and the spectrum appears consistent with that of a GRB.

The UVOT began observing the position of the trigger at 16:26:13.5 UT,
138 s after the BAT trigger.  In a 100 s V-band image, no new source
is detected with respect to the DSS down to a 5 sigma upper limit
of 18.1 mag.  The estimated extinction in this direction is A_V ~ 0.4
magnitudes.  The UVOT image gives 50% coverage assuming a BAT error circle
of 2 arcmin radius.