TITLE:   GCN CIRCULAR
NUMBER:  19113
SUBJECT: GRB 160228A: Swift-BAT refined analysis
DATE:    16/02/29 04:53:26 GMT
FROM:    Amy Lien at GSFC  <amy.y.lien@nasa.gov>

M. Stamatikos (OSU), S. D. Barthelmy (GSFC),  J. R. Cummings (GSFC/UMBC),
N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC),
D. Malesani (DARK/NBI), C. B. Markwardt (GSFC), D. M. Palmer (LANL),
T. Sakamoto (AGU), 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 160228A (trigger #676595)
(Malesani et al., GCN Circ. 19107).  The BAT ground-calculated position is
RA, Dec = 107.311, 26.946 deg which is
  RA(J2000)  =  07h 09m 14.6s
  Dec(J2000) = +26d 56' 45.3"
with an uncertainty of 1.3 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 81%.

The mask-weighted light curve shows a short spike from ~T0 to ~T+3 s, followed
by an extended emission till ~T+120 s. This structure is similar to those short
GRBs with extended emission (e.g., Norris et al. 2006). T90 (15-350 keV) is
98.36 +- 23.35 sec (estimated error including systematics).

The time-averaged spectrum from T-0.01 to T+116.104 sec is best fit by a simple
power-law model.  The power law index of the time-averaged spectrum is
1.31 +- 0.11.  The fluence in the 15-150 keV band is (2.0 +- 0.1) x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T-0.01 sec in the 15-150 keV band
is 1.2 +- 0.1 ph/cm2/sec.  All the quoted errors are at the 90% confidence
level.

Moreover, spectral analyses for the short pulse and extended emission intervals
show that the short pulse is harder than the extended emission. Both the
short-pulse spectrum (T0-0.008 to T0+3.188 s) and the extended-emission spectrum
(T0+3.188 to T0+116.104 s) are best fit by the simple power-law model,
with the power-law index of (0.88 +/- 0.17) and (1.35 +/- 0.12), respectively.

The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/676595/BA/