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GCN Circular 9157

Subject
GRB 090418: Swift-BAT refined analysis
Date
2009-04-18T17:54:33Z (15 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
E. E. Fenimore (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA),
C. B. Markwardt (GSFC/UMD), V. Mangano (INAF-IASFPA), 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-240 to T+705 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 090418 (trigger #349510)
(Mangano, et al., GCN Circ. 9149).  The BAT ground-calculated position is
RA, Dec = 269.320, 33.407 deg, which is 
   RA(J2000)  =  17h 57m 16.8s 
   Dec(J2000) = +33d 24' 24.4" 
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 31%.
 
The mask-weighted light curve shows two clusters of peaks.  The first
starts at ~T-8 sec, peaks at ~T+1 sec, and reaches a minimum at T+15 sec.
The second cluster peaks at around T+40 sec and returns to background
at ~T+70 sec.  T90 (15-350 keV) is 56 +- 5 sec (estimated error
including systematics).
 
The time-averaged spectrum from T-8.5 to T+61.1 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.48 +- 0.07.  The fluence in the 15-150 keV band is 4.6 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+0.06 sec in the 15-150 keV band
is 1.9 +- 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/349510/BA/
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