TITLE:   GCN CIRCULAR
NUMBER:  38629
SUBJECT: GRB 241218A: Swift-BAT refined analysis
DATE:    24/12/18 22:02:20 GMT
FROM:    Mike Moss at NASA GSFC <mikejmoss3@gmail.com>

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), M. A. Williams (PSU)
(i.e. the Swift-BAT team):

Using the data set from T-520 to T+962 sec from the recent telemetry downlink,
we report further analysis of BAT GRB 241218A (trigger #1275005)
(M. A. Williams, et al., GCN Circ. 38601). The BAT ground-calculated position is
RA, Dec = 185.687, 29.984 deg which is
   RA(J2000)  =  12h 22m 44.8s
   Dec(J2000) = +29d 59' 04.2"
with an uncertainty of 2.1 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 52%.

The mask-weighted light curve shows a single pulse of emission lasting 40 seconds
with a possible second pulse at T+70 seconds.
The T90 (15-350 keV) is 23.31 +- 4.19 sec (estimated error including systematics).

The time-averaged spectrum from T-1.82 to T+26.16 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.31 +- 0.26.  The fluence in the 15-150 keV band is 5.5 +- 1.0 x 10^-07 erg/cm2.
The 1-sec peak photon flux measured from T+16.64 sec in the 15-150 keV band
is 0.6 +- 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/1275005