[vsnet-grb-info 8797] Trigger 381434: Swift detection of a possible burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10296
SUBJECT: Trigger 381434: Swift detection of a possible burst
DATE:    09/12/29 02:31:32 GMT
FROM:    David Burrows at PSU/Swift  <dxb15 at psu.edu>

V. Mangano (INAF-IASFPA), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), B. Sbarufatti (INAF-IASFPA),
M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 02:07:04 UT, the Swift Burst Alert Telescope (BAT) triggered and
located trigger=381434.  Swift slewed immediately to the position. 
The BAT on-board calculated location is 
RA, Dec 74.816, -55.042 which is 
   RA(J2000) = 04h 59m 16s
   Dec(J2000) = -55d 02' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The trigger duration was 64 ms with a 
significance of 6.56 sigma; the BAT light curve shows a weak peak of 
~500 cts/sec in the highest band with a duration of <0.1s near T+0. 

The XRT began observing the field at 02:08:04.5 UT, 60.4 seconds after
the BAT trigger. No source was detected in the promptly available XRT
data. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 64 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
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 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.02. 

Because the BAT trigger is weak and the XRT did not find a
counterpart, we cannot say whether this trigger is a GRB,
an astrophysical source or spurious. Further analysis using 
data downlinked through the ground station will be required 
for a definitive determination. 

Burst Advocate for this burst is V. Mangano (vanessa AT ifc.inaf.it). 
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.)