TITLE:   GCN CIRCULAR
NUMBER:  9593
SUBJECT: GRB 090628: Swift-BAT refined analysis
DATE:    09/06/29 12:43:06 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

C. B. Markwardt (GSFC/UMD), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
H. A. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA), D. M. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+649 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090628 (trigger #355942)
(Mangano, et al., GCN Circ. 9585).  The BAT ground-calculated position is
RA, Dec = 237.038, -15.969 deg, which is 
   RA(J2000)  =  15h 48m 09.0s 
   Dec(J2000) = -15d 58' 09.0" 
with an uncertainty of 1.7 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 63%.
 
The mask-weighted light curve shows a weak 1-sec wide precursor peak
at ~T-7.5 sec that then returns almost to background levels, and the
main peak starting at ~T-0.3 sec, peaking at ~T+1 sec, and ending 
at ~T+6 sec.  T90 (15-350 keV) is 20.1 +- 4.6 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-25.0 to T+4.0 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.36 +- 0.20.  The fluence in the 15-150 keV band is 7.0 +- 0.8 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T+0.05 sec in the 15-150 keV band
is 1.5 +- 0.2 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/355942/BA/