GCN Circular 5502

D. Grupe (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
M. M. Chester (PSU), N. Gehrels (NASA/GSFC),
S. T. Holland (GSFC/USRA), S. D. Hunsberger (PSU),
J. A. Kennea (PSU), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), M. Stamatikos (NASA/ORAU) and M. C. Stroh (PSU)
report on behalf of the Swift Team:

At 01:03:21 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060904 (trigger=227996).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 237.743, +44.966 {15h 50m 58s, +44d 57' 57"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows 3 little peaks
starting out and then a large peak at T+55 sec and a total burst duration
of about 85 sec.  The peak count rate was ~9000 counts/sec (15-350 keV),
at ~55 sec after the trigger. 

The XRT began observing the field at 01:04:27 UT, 66 seconds after the
BAT trigger. XRT found a bright, fading, uncatalogued X-ray source
located at RA(J2000) = 15h 50m 54.9s, Dec(J2000) = +44d 59' 07.8", with an
estimated uncertainty of 5.4 arcseconds (90% confidence radius). 
This location is 79 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 0.1s image was
2.7e-08 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 75 seconds 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 18.5 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.