GCN Circular 41494

A. Y. Lien (U Tampa), S. D. Barthelmy (GSFC),
S. Dichiara (PSU), R. Gupta (GSFC),
H. A. Krimm (NSF), S. Laha (GSFC/UMBC),
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+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250821A (trigger #1344131)
(Dichiara, et al., GCN Circ. 41462
Loading...
 
 ).  The BAT ground-calculated position is
RA, Dec = 358.427, -28.631 deg which is
   RA(J2000)  =  23h 53m 42.6s
   Dec(J2000) = -28d 37' 53.3"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 64%.

The mask-weighted BAT light curve exhibits a short-duration main emission
starting from ~T-0.5 to ~T+1.2 sec, followed by a weaker, extended emission
which last up to ~ T+18 sec.
T90 (15-350 keV) is 1.52 +- 0.37 sec (estimated error including systematics).

The time-averaged spectrum from T-0.46 to T+1.20 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
0.83 +- 0.41.  The fluence in the 15-150 keV band is 1.3 +- 0.3 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+0.06 sec in the 15-150 keV band
is 0.9 +- 0.2 ph/cm2/sec.  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/1344131