TITLE:   GCN CIRCULAR
NUMBER:  35761
SUBJECT: GRB 240218A: Swift-BAT refined analysis
DATE:    24/02/20 16:00:46 GMT
FROM:    Tyler Parsotan  at NASA GSFC <tyler.parsotan@nasa.gov>

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),

T. Sakamoto (AGU), (i.e. the Swift-BAT team):



Using the data set from T-240 to T+200 sec from the recent telemetry downlink,

we report further analysis of BAT GRB 240218A (trigger #1215912)

(Page, et al., GCN Circ. 35742).  The BAT ground-calculated position is

RA, Dec = 161.810, 1.295 deg which is

   RA(J2000)  =  10h 47m 14.4s

   Dec(J2000) = +01d 17' 40.2"

with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).

The partial coding was 36%.



The mask weighted light curve shows two major pulses, one that is broad and the other

which is narrow.

T90 (15-350 keV) is 66.93 +- 11.28 sec (estimated error including systematics).



The time-averaged spectrum from T-38.93 to T+63.55 sec is best fit by a power law

with an exponential cutoff.  This fit gives a photon index 1.00 +- 0.32,

and Epeak of 103.1 +- 45.5 keV (chi squared 62.59 for 56 d.o.f.).  For this

model the total fluence in the 15-150 keV band is 5.2 +- 0.3 x 10^-06 erg/cm2

and the 1-sec peak flux measured from T+21.62 sec in the 15-150 keV band is

3.0 +- 0.3 ph/cm2/sec.  A fit to a simple power law gives a photon index

of 1.51 +- 0.07 (chi squared 71.30 for 57 d.o.f.).  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/1215912/