TITLE:   GCN CIRCULAR
NUMBER:  12292
SUBJECT: GRB 110820A: Swift-BAT refined analysis
DATE:    11/08/21 01:52:10 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC), T. Sakamoto (GSFC/UMBC), M. Stamatikos (OSU),
E. Troja (NASA/GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (MSU)
(i.e. the Swift-BAT team):
 
Using the data set from T-119 to T+296 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 110820A (trigger #501095)
(Troja, et al., GCN Circ. 12288).  The BAT ground-calculated position is
RA, Dec = 343.203, 70.298 deg, which is 
   RA(J2000)  =  22h 52m 48.8s 
   Dec(J2000) = +70d 17' 51.2" 
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 99%.
 
The mask-weighted light curve shows two main peaks.  The first started at ~T-5 sec,
peaking at ~T+2 sec, and ending at ~T+35 sec.  The second starts at ~T+195 sec,
peaking at ~T+230, and ending at ~T+285 sec.  T90 (15-350 keV) is 256 +- 50 sec
(estimated error including systematics).
 
The time-averaged spectrum from T-7.07 to T+264.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.92 +- 0.28.  The fluence in the 15-150 keV band is 8.2 +- 1.5 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.43 sec in the 15-150 keV band
is 0.4 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 
 
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/501095/BA/