TITLE:   GCN CIRCULAR
NUMBER:  10089
SUBJECT: GRB 091026: Swift-BAT refined analysis
DATE:    09/10/26 23:31:38 GMT
FROM:    Craig Markwardt at NASA/GSFC/UMD  <craigm@milkyway.gsfc.nasa.gov>

T. N. Ukwatta (GWU), 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), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS),
M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC)
(i.e. the Swift-BAT team):
 
Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 091026 (trigger #373871)
(Markwardt, et al., GCN Circ. 10081).  The BAT ground-calculated position is
RA, Dec = 276.657, -86.113 deg which is 
   RA(J2000)  =  18h 26m 37.7s 
   Dec(J2000) = -86d 06' 47.2" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 36%.
 
The mask-weighted light curve shows a single FRED-like peak which starts
to rise around T-5 sec, peaks near T+0 sec, and has a long tail extending 
to about T+120 sec.  T90 (15-350 keV) is 41.6 +- 7.2 sec (estimated error 
including systematics).
 
The time-averaged spectrum from T-3.7 to T+47.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.53 +- 0.11.  The fluence in the 15-150 keV band is 1.8 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.18 sec in the 15-150 keV band
is 2.2 +- 0.3 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/373871/BA/