GCN Circular 41924

R. Gupta (GSFC), S. D. Barthelmy (GSFC), 
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), D. M. Palmer (LANL),
T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC),
T. Sakamoto (AGU) (i.e. the Swift-BAT team):
 
Using the data set from T-240 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250920C (trigger #1351039)
(R. Gupta, et al., GCN Circ. 41904
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 ).  The BAT ground-calculated position is
RA, Dec = 51.465, -29.646 deg which is 
   RA(J2000)  =  03h 25m 51.6s 
   Dec(J2000) = -29d 38' 46.7" 
with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 15%.
 
The BAT mask-weighted light curve exhibits a bright initial peak followed by multiple
structured emission episodes, lasting for about 40 sec from the trigger time.
T90 (15-350 keV) is 38.02 +- 1.27 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.44 to T+40.49 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.09 +- 0.18, 
and Epeak of 133.4 +- 43.9 keV (chi squared 45.87 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.3 +- 0.0 x 10^-05 erg/cm2
and the 1-sec peak flux measured from T-0.12 sec in the 15-150 keV band is
16.9 +- 1.0 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.48 +- 0.04 (chi squared 60.21 for 57 d.o.f.).  All the quoted errors
are at the 90% confidence level. 
 
The results of the batgrbproduct analysis are available at
https://swift.gsfc.nasa.gov/results/batgrbcat/BAT_refined_circular/1351039