TITLE:   GCN CIRCULAR
NUMBER:  10301
SUBJECT: Trigger 381591: Swift detection of a possible burst
DATE:    09/12/31 18:14:26 GMT
FROM:    David Burrows at PSU/Swift  <dxb15@psu.edu>

C. B. Markwardt (CRESST/GSFC/UMD), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
K. L. Page (U Leicester), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC), R. L. C. Starling (U Leicester) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 17:44:17 UT, the Swift Burst Alert Telescope (BAT) triggered and
located a possible source (trigger=381591).  Swift slewed immediately 
to the source position.  The BAT on-board calculated location is 
RA, Dec 235.079, -8.738 which is 
   RA(J2000) = 15h 40m 19s
   Dec(J2000) = -08d 44' 15"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed several peaks over
the interval T-450 to T+150 sec in the low energy band (15-25 keV).  The
later peak was during the slew to the source, so it may not be real.  
The peak count rate was ~600 counts/sec (15-350 keV), at ~100 sec after 
the trigger. 

The XRT began observing the field at 17:46:26.3 UT, 128.9 seconds after
the BAT trigger.   The observation lasted only a few minutes before we 
slewed away due to an Earth limb constraint.  No source was detected in 
the promptly available XRT data.  We are waiting for the full dataset 
following the next ground pass to detect and localise any XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White   
filter starting 132 seconds after the BAT trigger. UVOT took a second 
finding chart exposure of 181 seconds with the u filter starting 290 
seconds after the BAT trigger. No credible afterglow candidate has  
been found in the initial data products. The 2.7'x2.7' sub-images 
cover 25% of the BAT error circle. The typical 3-sigma upper limit 
has been about 19.6 mag in White and 19.2 in u.  The 8'x8' region for
the list of sources generated on-board covers 100% of the BAT error
circle. The list of sources is typically complete to about 18.0
mag. No correction has been made for the expected extinction
corresponding to E(B-V) of 0.14. 

The next ground pass is at 1956 UT.  Ground analysis of data from that
pass will be required to determine the nature of this source. 

Burst Advocate for this burst is C. B. Markwardt (Craig.Markwardt AT nasa.gov). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)