GCN Circular 11102

S. R. Oates (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC),
N. Gehrels (NASA/GSFC), J. M. Gelbord (PSU), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), O. M. Littlejohns (U Leicester),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL),
C. J. Saxton (UCL-MSSL), M. Stamatikos (OSU/NASA/GSFC) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:

At 00:37:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100816A (trigger=431764).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 351.740, +26.561 which is 
   RA(J2000) = 23h 26m 58s
   Dec(J2000) = +26d 33' 38"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single symmetric
peak structure with a duration of about 2 sec.  There is possible
further activity at around T+80s.  The peak count rate
was ~13000 counts/sec (15-350 keV), at ~0.5 sec after the trigger. 

The XRT began observing the field at 00:39:14.2 UT, 82.8 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 351.7381, +26.5785 which is equivalent to:
   RA(J2000)  = 23h 26m 57.15s
   Dec(J2000) = +26d 34' 42.6"
with an uncertainty of 5.5 arcseconds (radius, 90% containment). This
location is 63 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 91 seconds after the BAT trigger. The refined UVOT 
position is    
     RA (J2000)  23:26:57.56  
    Dec (J2000)  26:34:42.9      with an estimated uncertainty of 0.5
arcsec (radius, 90% confidence). This position is 5.5 arc sec. from
the  center of the XRT error circle. The estimated magnitude is 17.00
with  a 1-sigma error of about 0.03. No correction has been made for
the  expected extinction corresponding to E(B-V) of 0.09. 

There were no real-time GCN Notices on this burst because the block2world
filter was still in place due to the earlier episode of the startracker
loss-of-lock problem.  The MOC had just gotten the startracker back to lock
and BAT triggers restored when the trigger occurred.  But the block2world
had not yet been removed.  BAT_POSITION and XRT_POSITION notices were manually
generated and distributed. 

Burst Advocate for this burst is S. R. Oates (sro AT mssl.ucl.ac.uk). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)