[vsnet-grb-info 1991] Subject: GRB 050820: Swift detection of a GRB

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3830
SUBJECT: Subject: GRB 050820: Swift detection of a GRB
DATE:    05/08/20 07:29:30 GMT
FROM:    David Burrows at PSU/Swift  <dxb15 at psu.edu>

M. Page (UCL-MSSL), D. Burrows (PSU), A. Beardmore (U. Leicester), D. 
Palmer (LANL),
J, Kennea (PSU), N. Gehrels (GSFC), C. Markwardt (GSFC/UMD), K. Page (U. 
Leicester),
T. Sakamoto (GSFC/NRC), M. Chester (PSU), P. Boyd (GSFC) report on behalf 
of the Swift team:

At 06:34:53 BAT triggered, located, and immediately slewed to GRB
050820 (trigger=151207).  The BAT on-board calculated position is
RA,Dec 337.400d, +19.578d {22h 29m 36s, 19d 34' 42"} (J2000) with an
uncertainty of 2 arcmin (radius, 90% containment, stat+sys).  The BAT
light curve shows a broad double-humped structure about 20 seconds
long, with peaks around T+1s and T+14 s, with a peak count rate
of ~1500 counts  per second (15-350 keV) at ~1 second after the trigger.

XRT began observing at 06:36:13 UT, 80s after the BAT trigger. A bright 
uncatalogued source was found in the field, which XRT was able to centroid 
on. The on-board calculated coordinates of this source are: 
RA(J2000):  22:29:37.8, Dec(J2000): 19:33:32.7, with an uncertainty of 7 
arcseconds radius (90% containment). This position lies 73 arcseconds from 
the center of the BAT error circle, and 6.2 arcseconds from the P60 
position (GCN 3829).

The UVOT began observations at 06:36:13 UT, 80s after the BAT trigger. 
There is no new source detected in the preliminary UVOT data in the XRT 
error circle.