TITLE:   GCN CIRCULAR
NUMBER:  39471
SUBJECT: GRB 250221A: Swift-BAT refined analysis
DATE:    25/02/25 14:19:03 GMT
FROM:    Mike Moss at NASA GSFC <mikejmoss3@gmail.com>

D. M. Palmer (LANL), S. D. Barthelmy (GSFC),
R. Caputo (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), T. Parsotan (GSFC),
D. Sadaula (GSFC/UMBC), T. Sakamoto (AGU)
(i.e. the Swift-BAT team):

Using the data set from T-479 to T+600 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250221A (trigger #1290305)
(R. Caputo, et al., GCN Circ. 39396).  The BAT ground-calculated position is
RA, Dec = 59.476, -15.137 deg which is 
   RA(J2000)  =  03h 57m 54.4s 
   Dec(J2000) = -15d 08' 11.8" 
with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 19%.
 
The mask-weighted light curve displays a single short pulse.
T90 (15-350 keV) is 1.80 +- 0.32 sec (estimated error including systematics).
 
The time-averaged spectrum from T-0.22 to T+1.84 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.43 +- 0.23.  The fluence in the 15-150 keV band is 3.9 +- 0.6 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+0.42 sec in the 15-150 keV band
is 2.9 +- 0.5 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/1290305