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GCN Circular 21832

Subject
GRB 170906C: Swift-BAT refined analysis
Date
2017-09-06T14:56:29Z (6 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (CPI),
H. A. Krimm (NSF/USRA), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), M. H. Siegel (PSU), M. Stamatikos (OSU),
T. N. Ukwatta (LANL) (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 170906C (trigger #770981)
(Siegel, et al., GCN Circ. 21826).  The BAT ground-calculated position is
RA, Dec = 128.659, 70.805 deg, which is
   RA(J2000)  =  08h 34m 38.1s
   Dec(J2000) = +70d 48' 16.7"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 32%.

The mask-weighted light curve shows multiple overlapping peaks starting at
~T-40 sec, peaking at ~T+7 sec, and returning to baseline at ~T+100 sec.
T90 (15-350 keV) is 48.4 +- 4.7 sec (estimated error including systematics).

The time-averaged spectrum from T-35.21 to T+39.22 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.30 +- 0.22,
and Epeak of 104.8 +- 43.0 keV (chi squared 47.9 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 8.8 +- 0.3 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+6.18 sec in the 15-150 keV band is
7.2 +- 0.5 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.67 +- 0.05 (chi squared 56.9 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/770981/BA/
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