GCN Circular 5442

A. Moretti (INAF-OAB), S. D. Barthelmy (GSFC),
J. R. Cummings (NASA/UMD), C. Guidorzi (Univ Bicocca&INAF-OAB),
C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), P. Romano (INAF-OAB) and D. E. Vanden Berk (PSU)
report on behalf of the Swift Team:

At 22:50:22 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060813 (trigger=224364).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA,Dec 111.868, -29.851 {07h 27m 28s, -29d 51' 01"} (J2000)
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single,
roughly square peak with a duration of about 10 sec.  The peak count rate
was ~10,000 counts/sec (15-350 keV), at ~7 sec after the trigger. 

The XRT began observing the field at 22:51:38 UT, 76 seconds after the
BAT trigger. XRT found a variable, uncatalogued X-ray source
located at RA(J2000) = 07h 27m 34.9s, Dec(J2000) = -29d 50' 54.6", with an
estimated uncertainty of 5.8 arcseconds (90% confidence radius). 
This location is 87 arcseconds from the BAT on-board position, within
the BAT error circle. The initial flux in the 2.5s image was
6.5e-10 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 83 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. The
field is fairly crowded.  No correction has been made for the 
expected extinction corresponding to E(B-V) of 0.33.