[vsnet-grb-info 3694] GRB 060906: Swift detection of a probable burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5528
SUBJECT: GRB 060906: Swift detection of a probable burst
DATE:    06/09/06 09:12:48 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

J. L. Racusin (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB),
S. D. Hunsberger (PSU), V. Mangano (INAF-IASFPA), D. C. Morris (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL), E. Rol (U Leicester),
P. Romano (INAF-OAB), G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU)
and H. Z. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 08:32:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060906 (trigger=228316).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 40.748, +30.349 {02h 42m 60s, +30d 20' 58"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve is complicated by the fact
that the spacecraft was slewing just prior to the image trigger.  There
appears to be an ~5 sec wide peak starting at T_zero.  There are possibly
two smaller peaks at T-15 and T-21 sec, but these are during the slew
and may be caused by the slew.  The peak count rate
is ~1000 counts/sec (15-350 keV), at ~5 sec after the trigger. 

The XRT began taking data at 08:35:15 UT, 148 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in
the image but ground analysis of 5 seconds of flight data available 
at this time reveals a possible faint source at the following coordinates:   
RA(J2000): 2h 43m 00.9s
Dec(J2000): +30 21 38.95   
with an error of 8 arcseconds (90% confidence). Further analysis of 
ground data is necessary to determine the properties of the possible
source. 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 152 seconds after the BAT trigger. No
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 18.5 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  0.20. 

We will have the full data set downlinked and processed by ~11:00 UT.