GCN Circular 18752

H. A. Krimm (GSFC/USRA), S. D. Barthelmy (GSFC), J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC),
D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL)
(i.e. the Swift-BAT team):
 
Using the data set from T-61 to T+243 sec from the recent telemetry downlinks,
we report further analysis of BAT GRB 151228B (trigger #668641)
(Lien, et al., GCN Circ. 18739
Not found
 
 
).  The BAT ground-calculated position is
RA, Dec = 344.431, 8.081 deg, which is 
   RA(J2000)  =  22h 57m 43.4s 
   Dec(J2000) = +08d 04' 52.4" 
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 100%.
 
The mask-weighted light curve shows a FreD-like peak starting at ~T-10 sec,
peaking at ~T+3 sec, and ending at ~T+65 sec.  T90 (15-350 keV) is
48.0 +- 16.0 sec (estimated error including systematics).
 
The time-averaged spectrum from T-12.56 to T+67.44 sec is best fit by a power law
with an exponential cutoff.  This fit gives a photon index 1.09 +- 0.34, 
and Epeak of 78.1 +- 27.0 keV (chi squared 52.3 for 56 d.o.f.).  For this
model the total fluence in the 15-150 keV band is 2.4 +- 0.1 x 10^-6 erg/cm2
and the 1-sec peak flux measured from T+10.94 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 1.66 +- 0.08 (chi squared 61.6 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/668641/BA/