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GCN Circular 9204

Subject
GRB 090423: Swift-BAT refined analysis
Date
2009-04-23T12:45:50Z (15 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.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-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 090423 (trigger #350184)
(Krimm, et al., GCN Circ. 9198).  The BAT ground-calculated position is
RA, Dec = 148.891, 18.165 deg, which is 
   RA(J2000)  =  09h 55m 33.8s 
   Dec(J2000) = +18d 09' 55.7" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 92%.
 
The mask-weighted light curve shows a couple overlapping peaks starting
at ~T-2 sec, peaking at T+4 sec, and ending at ~T+15 sec.
T90 (15-350 keV) is 10.3 +- 1.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.7 to T+11.7 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.80 +- 0.50, 
and Epeak of 48.6 +- 6.2 keV (chi squared 41.4 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 5.9 +- 0.4 x 10^-7 erg/cm2
and the 1-sec peak flux measured from T+3.50 sec in the 15-150 keV band is
1.7 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.90 +- 0.10 (chi squared 59.9 for 57 d.o.f.).  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/350184/BA/
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