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GCN Circular 21838

Subject
GRB 170906A: Swift-BAT refined analysis
Date
2017-09-06T20:53:57Z (7 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. R. Cummings (CPI), S. D. Barthelmy (GSFC), H. A. Krimm (NSF/USRA),
A. Y. Lien (GSFC/UMBC), 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-239 to T+603 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 170906A (trigger #770957)
(Siegel, et al., GCN Circ. 21821).  The BAT ground-calculated position is
RA, Dec = 203.949, -47.088 deg, which is 
   RA(J2000)  =  13h 35m 47.7s 
   Dec(J2000) = -47d 05' 18.3" 
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 67%.
 
The mask-weighted light curve shows multiple peaks starting at ~T-40 sec,
with a max peak at ~T+30, and returning to baseline at ~T+170 sec.
T90 (15-350 keV) is 88.1 +- 1.5 sec (estimated error including systematics).
 
The time-averaged spectrum from T-44.9 to T+121.5 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.21 +- 0.10, 
and Epeak of 205.4 +- 71.9 keV (chi squared 36.4 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 3.2 +- 0.0 x 10^-5 erg/cm2
and the 1-sec peak flux measured from T+29.82 sec in the 15-150 keV band is
10.9 +- 0.4 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.45 +- 0.02 (chi squared 52.7 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/770957/BA/
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