TITLE:   GCN CIRCULAR
NUMBER:  26607
SUBJECT: GRB 191228A: Swift-BAT refined analysis
DATE:    19/12/28 17:38:12 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@milkyway.gsfc.nasa.gov>

T. N. Ukwatta (LANL) S. D. Barthelmy (GSFC), M. G. Bernardini (INAF-OAB),
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), M. Stamatikos (OSU),
(i.e. the Swift-BAT team):
 
Using the data set from T-60 to T+243 sec from the recent telemetry downlinks,
we report further analysis of BAT GRB 191228A (trigger #946476)
(Bernardini, et al., GCN Circ. 26601).  The BAT ground-calculated position is
RA, Dec = 5.341, -8.650 deg, which is 
   RA(J2000)  =  00h 21m 21.9s 
   Dec(J2000) = -08d 38' 58.3" 
with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 90%.
 
The mask-weighted light curve] shows 3 broad peaks starting at T-50 sec
with peaks at ~T+5, ~T+55, and ~T+130 sec, and ending at T+190 sec.
T90 (15-350 keV) is 166.9 +- 10.2 sec (estimated error including systematics).
 
The time-averaged spectrum from T-39.2 to T+138.9 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
2.06 +- 0.14.  The fluence in the 15-150 keV band is 2.0 +- 0.2 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+54.59 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
http://gcn.gsfc.nasa.gov/notices_s/946476/BA/