TITLE:   GCN CIRCULAR
NUMBER:  11004
SUBJECT: GRB 100728A: Swift detection of a burst
DATE:    10/07/28 02:30:01 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

J. K. Cannizzo (NASA/UMBC), W. H. Baumgartner (GSFC/UMBC),
P. A. Evans (U Leicester), J. M. Gelbord (PSU),
S. T. Holland (CRESST/USRA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
O. M. Littlejohns (U Leicester), C. B. Markwardt (CRESST/GSFC/UMD),
F. E. Marshall (NASA/GSFC), C. Pagani (U Leicester),
K. L. Page (U Leicester), D. M. Palmer (LANL),
A. Rowlinson (U Leicester), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC) and R. L. C. Starling (U Leicester)
report on behalf of the Swift Team:

At 02:18:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 100728A (trigger=430151).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 88.743, -15.262 which is 
   RA(J2000) = 05h 54m 58s
   Dec(J2000) = -15d 15' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of at least 200 sec, although the burst was
already in progress when the spacecraft slewed to the original position.  
The peak count rate was ~11,000 counts/sec (15-350 keV), at ~25 sec after
the trigger. 

The XRT began observing the field at 02:19:41.0 UT, 76.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 88.7610, -15.2561 which is equivalent to:
   RA(J2000)  = 05h 55m 02.63s
   Dec(J2000) = -15d 15' 21.9"
with an uncertainty of 5.8 arcseconds (radius, 90% containment). This
location is 64 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. 

The initial flux in the 0.1 s image was 2.01e-08 erg cm-2 s-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 86 seconds after the BAT trigger. No credible 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 19.6 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
0.18. 

Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.nasa.gov). 
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.)