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GCN Circular 41812

Subject

GRB 250911A: Swift-BAT refined analysis

Event

GRB 250911A

Date

2025-09-12T10:16:27Z (5 hours ago)

From

Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>

Via

Web form

D. M. Palmer (LANL), S. D. Barthelmy (GSFC), 
R. Gupta (GSFC),  N. J. Klingler (GSFC/UMBC/CRESSTII),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
M. J. Moss (GSFC), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):

 
Using the data set from T-239 to T+200 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250911 A (trigger #1348587)
(Klingler, et al., GCN Circ. 41781Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 263.752, -16.841 deg which is 
   RA(J2000)  =  17h 35m 00.6s 
   Dec(J2000) = -16d 50' 28.0" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 29%.


The mask-weighted BAT light curve shows two emission episodes 
(a precursor followed by main emission) separated by quiescent 
gap of ~ 80 sec. T90 (15-350 keV) is 128.42 +- 87.23 sec 
(estimated error including systematics).
 
 
The time-averaged spectrum from T-1.35 to T+147.24 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.00 +- 0.20, 
and Epeak of 170.5 +- 84.5 keV (chi squared 56.83 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 1.5 +- 0.0 x 10^-05 erg/cm2
and the 1-sec peak flux measured from T+103.94 sec in the 15-150 keV band is
8.6 +- 0.6 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.35 +- 0.05 (chi squared 66.73 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/1348587