GCN Circular 31289

S. D. Barthelmy (GSFC), H. A. Krimm (NSF), 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-239 to T+963 sec sec from the recent telemetry
downlink, we report further analysis of BAT GRB 211221A (trigger #1090472)
(Page et al., GCN 31273
Not found
 
 
).  The BAT ground-calculated position is RA, Dec =
78.906, 0.902 deg which is

   RA(J2000)  =  05h 15m 37.4s

   Dec(J2000) = +00d 54' 06.2"

with an uncertainty of 2.6 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 97%.


The BAT light curve showed a complex peak structure with a duration of
about 20 sec. There may be hints of precursor activity and low-level
post-peak emission from the GRB as seen in the mask weighted light curve.
The post-peak emission lasts beyond the available event data (which ends at
T+963). T90 (15-350 keV) is 671.67 +- 105.96 sec (estimated error including
systematics).


The time-averaged spectrum from T-129.40 to T+688.36 sec is best fit by a
simple power-law model.  The power law index of the time-averaged spectrum
is 1.48 +- 0.13.  The fluence in the 15-150 keV band is 4.0 +- 0.3 x 10^-06
erg/cm2. The 1-sec peak photon flux measured from T-0.27 sec in the 15-150
keV band is 0.5 +- 0.1 ph/cm2/sec.  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/1090472/BA/