TITLE:   GCN CIRCULAR
NUMBER:  41923
SUBJECT: GRB 250920B: Swift-BAT refined analysis
DATE:    25/09/21 02:14:23 GMT
FROM:    Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), 
R. Gupta (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), (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 250920B (trigger #1351008)
(R. Gupta, et al., GCN Circ. 41898).  The BAT ground-calculated position is
RA, Dec = 187.316, 47.843 deg which is 
   RA(J2000)  =  12h 29m 15.8s 
   Dec(J2000) = +47d 50' 33.6" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 57%.
 
The BAT mask-weighted light curve shows multiple emission episodes
extending over ~150 sec. T90 (15-350 keV) is 128.44 +- 1.00 sec 
(estimated error including systematics).

The time-averaged spectrum from T-4.83 to T+149.43 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.31 +- 0.15, 
and Epeak of 182.2 +- 153.0 keV (chi squared 36.64 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.1 +- 0.0 x 10^-05 erg/cm2
and the 1-sec peak flux measured from T+0.29 sec in the 15-150 keV band is
5.0 +- 0.3 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.52 +- 0.04 (chi squared 42.79 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/1351008