TITLE:   GCN CIRCULAR
NUMBER:  29537
SUBJECT: GRB 210218A: Swift-BAT refined analysis
DATE:    21/02/19 02:01:49 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

M. Stamatikos (OSU), S. D. Barthelmy (GSFC),
J. R. Cummings (CPI), H. A. Krimm (NSF),
S. Laha (GSFC/UMBC), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), B. Sbarufatti (PSU),
T. N. Ukwatta (LANL) (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 210218A (trigger #1033328)
(Sbarufatti et al., GCN Circ. 29529).  The BAT ground-calculated position is
RA, Dec = 47.318, 35.322 deg which is
   RA(J2000)  =  03h 09m 16.3s
   Dec(J2000) = +35d 19' 18.9"
with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 57%.

The mask-weighted light curve shows a multi-peaked structure that
starts at ~T-15 s and peaks at ~T0. The burst emission lasted
until the burst went out of the BAT FOV at T+287 s.
Using the available data, the lower limit of T90 is ~ 240 s.

The time-averaged spectrum from T-14.27 to T+266.26 sec is best fit by
a power law with an exponential cutoff.  This fit gives a photon
index 0.77 +- 0.49, and Epeak of 91.3 +- 48.2 keV (chi squared 50.53
for 56 d.o.f.).  For this model the total fluence in the 15-150 keV
band is 4.3 +- 0.3 x 10^-6 erg/cm2 and the 1-sec peak flux measured
from T+0.09 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec.
A fit to a simple power law gives a photon index of 1.46 +- 0.11
(chi squared 57.43 for 57 d.o.f.).  All the quoted errors are at
the 90% confidence level.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/1033328/BA/