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GCN Circular 13806

Subject
GRB 120922A: Swift-BAT refined analysis
Date
2012-09-23T13:36:02Z (12 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (GSFC/UMBC),
G. Sato (ISAS), M. Stamatikos (OSU), J. Tueller (GSFC),
T. N. Ukwatta (MSU), V. N. Yershov (UCL-MSSL)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+303 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 120922A (trigger #534394)
(Yershov, et al., GCN Circ. 13793).  The BAT ground-calculated position is
RA, Dec = 234.758, -20.181 deg, which is 
   RA(J2000)  =  15h 39m 02.0s 
   Dec(J2000) = -20d 10' 51.8" 
with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 33%.
 
The mask-weighted light curve shows low-level emission starting at T-200 sec,
possibly sooner before the data capture started, with peaks at ~T_0, ~T+60, & ~T+105 sec,
and ending at ~T+205 sec.  T90 (15-350 keV) is 173 +- 33 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-22.58 to T+215.73 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.58 +- 0.36, 
and Epeak of 38.2 +- 0.0 keV (chi squared 54.3 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 6.2 +- 0.7 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+99.21 sec in the 15-150 keV band is
2.0 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 2.09 +- 0.08 (chi squared 61.1 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/534394/BA/
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