TITLE:   GCN CIRCULAR
NUMBER:  40056
SUBJECT: GRB 250331B Swift-BAT refined analysis
DATE:    25/04/04 16:16:25 GMT
FROM:    Mike Moss at NASA GSFC <mikejmoss3@gmail.com>

S. Laha (GSFC/UMBC), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC),  R. Gupta (GSFC),
H. A. Krimm (NSF), 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-240 to T+842 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250331B (trigger #1299965)
(Cenko, et al., GCN Circ. 39958).  The BAT ground-calculated position is
RA, Dec = 71.377, 43.794 deg which is
   RA(J2000)  =  04h 45m 30.4s
   Dec(J2000) = +43d 47' 39.1"
with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 55%.

The mask-weighted light curve displays a single dim pulse.
The T90 (15-350 keV) is 3.95 +- 0.77 sec (estimated error including systematics).

The time-averaged spectrum from T-0.72 to T+3.76 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.61 +- 0.38.  The fluence in the 15-150 keV band is 1.5 +- 0.3 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+1.28 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/1299965