TITLE:   GCN CIRCULAR
NUMBER:  5778
SUBJECT: GRB 061102B: Swift detection of a possible burst
DATE:    06/11/02 06:41:41 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

S. T. Holland (GSFC/USRA), A. M. Parsons (GSFC),
L. M. Barbier (NASA/GSFC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), C. Gronwall (PSU),
C. B. Markwardt (GSFC/UMD), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. Stamatikos (NASA/ORAU) report on behalf of
the Swift Team:

At 06:13:16 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possible GRB 061102B (trigger=236481).  Swift slewed immediately
to the burst.  The BAT on-board calculated location is 
RA,Dec 309.881, +15.179 {20h 39m 31s, +15d 10' 44"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  This is a 32 msec trigger and the TDRSS lightcurve
shows nothing significant.  Therefore, it is possible that this trigger is
due to a cosmic ray shower event in the spacecraft.  We will not be able
to separate the burst and shower possibilities until we receive the
full data set in 2 hours. 

The XRT began taking data at 06:14:38 UT, 83 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in
the image and no prompt position is available. There is no source in
the quicklook downlinked data products, which have an exposure time
of about 250 s, giving us a rough upper limit of 2E-12 ergs/cm2/s for
any point source in the field of view. We are waiting for full
down-linked data to make a more sensitive search for a possible point
source. 

The UVOT began observing at 06:14:44, 89 s after the BAT trigger with
the White (160-650 nm) filter. No source is detected inside the BAT
error circle. The 3-sigma upper limit is approximately V = 18 mag. No
correction has been made for the expected Galactic extinction of
E_{B-V} = 0.09 mag.