TITLE:   GCN CIRCULAR
NUMBER:  40057
SUBJECT: GRB 250331C Swift-BAT refined analysis
DATE:    25/04/04 16:17:44 GMT
FROM:    Mike Moss at NASA GSFC <mikejmoss3@gmail.com>

A. Y. Lien (U Tampa), S. D. Barthelmy (GSFC),
S. B. Cenko (GSFC), 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-239 to T+963 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 250331C (trigger #1299967)
(Cenko, et al., GCN Circ. 39959).  The BAT ground-calculated position is
RA, Dec = 80.963, 33.068 deg which is
   RA(J2000)  =  05h 23m 51.0s
   Dec(J2000) = +33d 04' 03.4"
with an uncertainty of 2.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows a dim pulse of emission with some possible
complex structure. The T90 (15-350 keV) is 70.10 +- 11.70 sec (estimated error
including systematics).

The time-averaged spectrum from T-12.59 to T+66.67 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.88 +- 0.23.  The fluence in the 15-150 keV band is 6.6 +- 1.0 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T-3.19 sec in the 15-150 keV band
is 0.3 +- 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/1299967