TITLE:   GCN CIRCULAR
NUMBER:  8967
SUBJECT: GRB 090309, Swift-BAT refined analysis
DATE:    09/03/10 14:02:00 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori.sakamoto-1@nasa.gov>

D. M. Palmer (LANL), 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), C. B. Markwardt (GSFC/UMD), A. M. Parsons (GSFC),
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+362 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090309 (trigger #345945)
(Evans, et al., GCN Circ. 8964).  The BAT ground-calculated position is
RA, Dec = 284.978, -25.274 deg which is 
   RA(J2000)  =  18h 59m 55.5s 
   Dec(J2000) = -25d 16' 42.0" 
with an uncertainty of 2.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 61%.
 
The mask-weighted light curve shows a single peak starting at T-1 sec, 
peaking around T+1 sec, and ending at T+2 sec.  
T90 (15-350 keV) is 3.0 +- 1.4 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.8 to T+2.2 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.36 +- 0.33.  The fluence in the 15-150 keV band is 1.3 +- 0.3 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+0.18 sec in the 15-150 keV band
is 0.9 +- 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/345945/BA/