TITLE:   GCN CIRCULAR
NUMBER:  39821
SUBJECT: GRB 250321A: Swift-BAT refined analysis
DATE:    25/03/21 18:34:55 GMT
FROM:    Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>


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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250321A (trigger #1297508)
(Gupta, et al., GCN Circ. 39794).  The BAT ground-calculated position is
RA, Dec = 295.100, 21.055 deg which is
   RA(J2000)  =  19h 40m 23.9s
   Dec(J2000) = +21d 03' 16.4"
with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 24%.

The mask-weighted BAT light curve shows a sharp peak at the trigger time, followed by a rapid decline.
T90 (15-350 keV) is 6.21 +- 1.36 sec (estimated error including systematics).

The time-averaged spectrum from T-0.14 to T+7.35 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.61 +- 0.19.  The fluence in the 15-150 keV band is 6.7 +- 0.8 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-0.16 sec in the 15-150 keV band
is 3.2 +- 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/1297508