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GCN Circular 9890

Subject

GRB 090904B: Swift-BAT refined analysis

Date

2009-09-04T13:27:29Z (16 years ago)

From

Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>

T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), V. D'Elia (ASDC), E. E. Fenimore (LANL),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD),
D. M. Palmer (LANL), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC),
T. N. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-119 to T+303 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090904B (trigger #361831)
(D'Elia, et al., GCN Circ. 9881Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 264.194, -25.219 deg, which is 
   RA(J2000)  =  17h 36m 46.5s 
   Dec(J2000) = -25d 13' 09.0" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 8%.
 
The mask-weighted light curve shows the burst starting at ~T-30 sec, with
several overlapping peaks between T-5 to T+20 sec and another series
from T+30 to T+50 sec. The burst is over by ~T+70 sec  T90 (15-350 keV)
is 47.0 +- 1.7 sec (estimated error including systematics).
 
The time-averaged spectrum from T-2.5 to T+49.7 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.59 +- 0.07.  The fluence in the 15-150 keV band is 1.1 +- 0.0 x 10^-5 erg/cm2.
The 1-sec peak photon flux measured from T+12.42 sec in the 15-150 keV band
is 5.3 +- 0.9 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/361831/BA/