TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3840
SUBJECT: SUBJECT:  GRB050820B:  Refined analysis of the Swift-BAT burst 
DATE:    05/08/21 02:33:16 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori@milkyway.gsfc.nasa.gov>

E. Fenimore (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC), 
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), D. Hullinger (GSFC/UMD), 
K. Hurley (Berkeley), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), 
J. Norris (GSFC), D. Palmer (LANL), A. Parsons (GSFC), 
T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC) 
on behalf of the Swift-BAT team: 
 
Using the full data set from the recent telemetry downlink, we report 
further analysis of Swift-BAT GRB 050820B (trigger #151334) 
(Page, et al., GCN 3839).  The ground-analysis position is 
RA,Dec 135.594,-72.639 (J2000) with an uncertainty of 2 arcmin 
(radius, 90%, stat+sys). 
The light curve show a peak at T+1 sec and a cluster of merged  
peaks at T+8 sec.  T90 is 13 +/-2 sec. 
Fitting a cutoff power law over the interval from T+0.2 to T+17.3 sec, 
the photon index is 0.5 +/- 0.2 and Epeak is 100 (-10/+15) keV 
with a fluence of 2.8 +/- 0.2 x 10^-6 erg/cm^2 in the 15-350 keV 
band (90% c.l.). The peak flux in a 1-sec wide window starting at 
T+8.7 seconds is 4.7 +/- 0.3 ph/cm^2/sec (15-350 keV).