[vsnet-grb-info 8328] GRB 090831B: Swift detection of a possible burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9851
SUBJECT: GRB 090831B: Swift detection of a possible burst
DATE:    09/08/31 18:26:54 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

M. De Pasquale (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL),
P. Romano (INAF-IASFPA), 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 18:01:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located possible GRB 090831B (trigger=361477).  Swift slewed immediately 
to the location.  The BAT on-board calculated location is 
RA, Dec 3.619, +27.970 which is 
   RA(J2000)  =  00h 14m 29s
   Dec(J2000) = +27d 58' 12"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows nothing significant
as is typical for an image trigger. 

The XRT began observing the field at 18:03:44.9 UT, 149.9 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 153 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
0.03. 

Due to the lack of detection by XRT, we cannot confirm
that this is a true astrophysical source.  Further analysis
of the downlinked data (available in ~3 hours) will be required. 

Burst Advocate for this burst is M. De Pasquale (mdp AT mssl.ucl.ac.uk). 
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.)