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GCN Circular 9195

Subject
GRB 090422: Swift-BAT refined analysis
Date
2009-04-22T17:39:45Z (15 years ago)
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), D. M. Palmer (LANL), 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 090422 (trigger #349931)
(Ukwatta, et al., GCN Circ. 9185).  The BAT ground-calculated position is
RA, Dec = 294.746, 40.398 deg which is 
   RA(J2000)  =  19h 38m 59.1s 
   Dec(J2000) = +40d 23' 52.1" 
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 72%.
 
The mask-weighted light curve shows two main peaks at T0 and T+8 sec.
They are each about 1 sec wide. There is a third, weaker peat at ~T=50 sec.
T90 (15-350 keV) is 8.5 +- 0.4 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.4 to T+8.5 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.72 +- 0.30.  The fluence in the 15-150 keV band is 2.3 +- 0.4 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.37 sec in the 15-150 keV band
is 1.7 +- 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/349931/BA/
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