[vsnet-grb-info 6910] GRB 081109: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8500
SUBJECT: GRB 081109: Swift detection of a burst
DATE:    08/11/09 07:22:59 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

S. Immler (CRESST/GSFC/UMD), A. P. Beardmore (U Leicester),
J. R. Cummings (NASA/UMBC), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), S. D. Hunsberger (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL),
M. Stamatikos (NASA/ORAU), R. L. C. Starling (U Leicester),
T. N. Ukwatta (GSFC/GWU) and L. Vetere (PSU) report on behalf of the
Swift Team:

At 07:02:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081109 (trigger=334112).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 330.787, -54.719 which is 
   RA(J2000) = 22h 03m 09s
   Dec(J2000) = -54d 43' 06"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a triangular
structure with a duration of about 40 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at 20 sec after the trigger. 

The XRT began observing the field at 07:03:12.2 UT, 65.6 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 330.7911, -54.7114 which is equivalent to:
   RA(J2000)  = 22h 03m 09.86s
   Dec(J2000) = -54d 42' 41.0"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 28 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 4.78e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 75 seconds after the BAT trigger. 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 expected extinction corresponding to
E(B-V) of 0.02. No afterglow candidate has been detected. 

Burst Advocate for this burst is S. Immler (immler AT milkyway.gsfc.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.)