GCN Circular 5590

M. Stamatikos (NASA/ORAU), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), M. Capalbi (ASDC), M.L. Conciatore (ASDC),
N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB),
S. T. Holland (GSFC/USRA), J. A. Kennea (PSU),
C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), M. Perri (ASDC),
T. Sakamoto (NASA/ORAU), D. E. Vanden Berk (PSU) and
H. Ziaeepour (UCL-MSSL) report on behalf of the Swift Team:

At 11:38:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060923B (trigger=230702).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 238.201, -30.907 {15h 52m 48s, -30d 54' 25"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single peak
with a duration of about 10 sec.  The peak count rate
was ~1500 counts/sec (15-350 keV), at ~4 sec after the trigger. 

The XRT began observing the field at 11:40:00 UT, 114 seconds after
the BAT trigger. XRT centroided on a cosmic ray on-board, so the
position sent out in our first, automated XRT Position Notice is
incorrect. From preliminary ground analysis of photon-counting mode
data, XRT did find an uncatalogued X-ray source located at RA(J2000)
= 15h 52m 46.83s, Dec(J2000) = -30d 54' 12.6", with an estimated
uncertainty of 6.5 arcseconds (90% confidence radius). This position
was sent out via BACODINE in a second XRT Position Notice with the
correct position. This location is 21 arcseconds from the BAT
on-board position, within the BAT error circle. The initial flux in
the 2.5s image was 2.4e-11 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of nominal 200 seconds with the
White (160-650 nm) filter starting 122 seconds after the BAT trigger. 
No afterglow candidate has been found in the initial data products. 
Image catalog data are not available at this time. 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. The overlap of the sub-image and the XRT error circle is 100%. 
No source is seen in the XRT error circle to a magnitude of
approximately 18.5.  No correction has been made for the expected
extinction corresponding to E(B-V) of 0.15.