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GCN Circular 6954

Subject
GRB 071020, Swift-BAT refined analysis
Date
2007-10-20T16:46:43Z (16 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. Tueller (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), S. T. Holland (CRESST/USRA/GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), J. Norris (U. Denver),
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):
 
Using the data set from T-239 to T+625 sec from recent telemetry downlinks,
we report further analysis of BAT GRB 071020 (trigger #294835)
(Holland, et al., GCN Circ. 6949).  The BAT ground-calculated position is
RA, Dec = 119.666, 32.857 deg, which is 
   RA(J2000)  = 07h 58m 39.9s 
   Dec(J2000) = 32d 51' 25" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 90%.
 
The mask-weighted lightcurve shows at least 8 overlapping pulses in the initial
burst.  They all have approximately the same peak flux values.  This emission
starts at ~T-3 sec, peaks at ~T-1.5 sec, and ends at ~T+0.9 sec.
T90 (15-350 keV) is 4.2 +- 0.2 sec (estimated error including systematics).

The spectral lag for this burst is:
59 +7-9 msec for the 150-300 to 25-50 keV bands, and
10 +8-7 msec for the 50-100 to 15-25 keV bands.
 
The time-averaged spectrum from T-3.0 to T+7.4 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.11 +- 0.05.  The fluence in the 15-150 keV band is 2.3 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.36 sec in the 15-150 keV band
is 8.4 +- 0.3 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

Folding in the borderline results of the T90, the hardness ratio,
the spectral lag, and very marginal detection of extended emission in the lightcurve;
we think this is a Long burst, but we can not rule out the possibility
of a SHB classification.
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