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GCN Circular 7640

Subject
GRB 080426, Swift-BAT refined analysis
Date
2008-04-26T18:37:17Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD), D. Palmer (LANL),
T. Sakamoto (GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), T. Ukwatta (GWU), H. Ziaeepour (UCL-MSSL)
(i.e. the Swift-BAT team):
 
Using the data set from T-119 to T+183 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 080426 (trigger #310219)
(Ziaeepour, et al., GCN Circ. 7639).  The BAT ground-calculated position is
RA, Dec = 26.510, 69.469 deg which is 
   RA(J2000)  =  01h 46m 02.4s 
   Dec(J2000) = +69d 28' 07.9" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 43%.
 
The mask-weighted light curve shows a single spike starting at T+0 and
ending at T+2.0 sec.  The lag analysis yields:
  Lag31 = 88 +/- 9 ms  (50-100 to 15-25 keV bands)
  Lag21 = 74 +/- 6 ms  (25-50  to 15-25 keV bands)
T90 (15-350 keV) is 1.7 +- 0.4 sec (estimated error including systematics).
While the T90 value puts this burst in the middle of the long and Short burst
T90-distribution peaks, the lag value puts this burst in the Long burst class.
 
The time-averaged spectrum from T+0.1 to T+2.3 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.98 +- 0.13.  The fluence in the 15-150 keV band is 3.7 +- 0.3 x 10^-7 erg/cm2.
The 1-sec peak photon flux measured from T-0.08 sec in the 15-150 keV band
is 4.8 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level. 

We note that this is an unusual burst.  The T90 for the 50-300 keV  
BATSE range is 1.3 sec which would put it in the short class in that  
era.  However, the long lag and a spectrum that is not hard lead us  
to believe it is in the long class.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/310219/BA/
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