[vsnet-grb-info 12042] Swift detection of GRB 120711B or a new Galactic transient

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13431
SUBJECT: Swift detection of GRB 120711B or a new Galactic transient
DATE:    12/07/11 03:40:19 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

M. J. Page (UCL-MSSL), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), N. Gehrels (NASA/GSFC),
F. E. Marshall (NASA/GSFC), S. R. Oates (UCL-MSSL),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC) and T. N. Ukwatta (MSU) report on behalf
of the Swift Team:

At 03:11:02.58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located what may be GRB 120711B (trigger=526270).  Swift slewed immediately
to the position. The BAT on-board calculated location is 
RA, Dec 331.668, +60.020 which is 
   RA(J2000) = 22h 06m 40s
   Dec(J2000) = 60d 01' 10"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve does not show any obvious
variation, which is typical for an image trigger (64 second duration). 

The XRT began observing the field at 03:13:05.6 UT, 123.1 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source located at RA, Dec 331.69037, 60.02173 which
is equivalent to:
   RA(J2000)  = 22h 06m 45.69s
   Dec(J2000) = +60d 01' 18.2"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 40 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data does not constrain the column density. 

The initial flux in the 2.5 s image was 8.75e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 260 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 100% of
the XRT 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
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the large, but uncertain extinction expected. 

Due to the proximity of the source to the Galactic plane (3.46 degrees),
the fact that this source was detected in the first image following
the SAA, and the relative constancy of the XRT light curve, we
believe that this is more likely to be a previously-unknown
Galactic source rather than a GRB.  However we will need the 
complete downlinked data to determine the nature of the source. 

Burst Advocate for this burst is M. J. Page (mjp 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.)