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GCN Circular 18256

Subject
GRB 150907B: Swift-BAT refined analysis
Date
2015-09-08T12:27:43Z (9 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. G. R. Roegiers (PSU), T. Sakamoto (AGU),
M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from the recent telemetry downlinks,
we report further analysis of BAT GRB 150907B (trigger #654803)
(Roegiers, et al., GCN Circ. 18249).  The BAT ground-calculated position is
RA, Dec = 255.265, -63.798 deg, which is 
   RA(J2000)  =  17h 01m 03.5s 
   Dec(J2000) = -63d 47' 51.6" 
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 50%.
 
The mask-weighted light curve shows a Fred-like starting at ~T-1 sec,
peaking at ~T+1 sec, and ending around T+100 sec.
T90 (15-350 keV) is 62.0 +- 11.1 sec (estimated error including systematics).
 
The time-averaged spectrum from T-1.48 to T+64.53 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 0.17 +- 1.03, 
and Epeak of 67.4 +- 29.7 keV (chi squared 53.2 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.1 +- 0.2 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+0.59 sec in the 15-150 keV band is
1.0 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.47 +- 0.18 (chi squared 59.8 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/654803/BA/
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