[vsnet-grb-info 2618] GRB 060109: Swift Detection of a long burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4455
SUBJECT: GRB 060109:  Swift Detection of a long burst
DATE:    06/01/09 17:31:48 GMT
FROM:    Jay R. Cummings at NASA/GSFC/Swift  <jayc at milkyway.gsfc.nasa.gov>

M. De Pasquale (MSSL), S. Barthelmy (GSFC), A. Beardmore (U. Leicester),
J. Cummings (GSFC/ORAU), N. Gehrels (GSFC), M.R. Goad (U. Leicester),
O. Godet (U. Leicester), J. Kennea (PSU), H. Krimm (GSFC/USRA),
F. Marshall (GSFC), K. Page (U. Leicester), D. Palmer (LANL),
T. Sakamoto (GSFC),
on behalf of the Swift Team:

At 16:54:41 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060109 (trigger=176620).   The BAT on-board calculated
location is RA,Dec 282.710, +31.989 {18h 50m 50s, +31d 59' 22"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 10 sec.  The peak count rate was
~1000 counts/sec (15-350 keV), at ~8 sec after the trigger.

The XRT began observing the burst at 16:56:22 UT, 101 sec after the BAT
trigger.  A bright (0.2-10 keV flux of 4.8e-09 erg/cm2/sec), fading,
uncatalogued source was found by the on-board centroiding algorithm at
RA(J2000)= 18h 50m 43.9s
DEC(J2000)= +31d 59' 34.7"
with an uncertainty of 5.8 arcsec radius (90% containment).  This
uncertainty includes a systematic error of about 5 arcsec in the
on-board calculated positions due to the XRT boresight offset.  This
position lies 84 arcsec from the centre of the BAT error circle.

UVOT took a finding chart exposure of 200 seconds with the V filter
starting 104 sec after the BAT trigger. No 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 18th 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 19.0 mag. No correction has been made for
the expected visual extinction of about 0.5 magnitudes.