GCN Circular 33254

H. A. Krimm (NSF), S. D. Barthelmy (GSFC), S. Dichiara (PSU),
S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Parsotan (GSFC/UMBC), T. Sakamoto (AGU),
M. Stamatikos (OSU) (i.e. the Swift-BAT team):

Using the data set from T-60 to T+243 sec from the recent telemetry downlink,
we report further analysis of BAT  GRB 221216A (trigger #1144698)
(Dichiara, et al., GCN Circ. 33067
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 ).  The BAT ground-calculated position is
RA, Dec = 326.023, -34.394 deg which is
   RA(J2000)  =  21h 44m 05.6s
   Dec(J2000) = -34d 23' 37.4"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.

The mask-weighted light curve shows two broad peaks, one centered around T+0,
and the other at T+165 seconds.  There is a third, more narrow and weaker peak
at T+50 seconds and some possible subsidiary peaks.  Note that not all of the event
data is available, so it is possible that the burst extended before or after this period.
T90 (15-350 keV) is 174.48 +- 5.26 sec (estimated error including systematics).

The time-averaged spectrum from -9.68 to T+175.22 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.02 +- 0.36,
and Epeak of 91.0 +- 44.0 keV (chi squared 37.14 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 4.6 +- 0.3 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+0.23 sec in the 15-150 keV band is
1.8 +- 0.2 ph/cm2/sec.  A fit to a simple power law gives a photon index
of 1.56 +- 0.08 (chi squared 44.55 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/1144698/BA/