TITLE:   GCN CIRCULAR
NUMBER:  18866
SUBJECT: Konus-Wind observation of GRB 151231A
DATE:    16/01/14 14:07:57 GMT
FROM:    Anastasia Tsvetkova at Ioffe Institute  <tsvetkova@mail.ioffe.ru>

S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A. Lysenko, A. Kozlova and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, intense GRB 151231A
(Fermi GBM observation: Veres, C Meegan & von Kienlin, GCN 18787;
CALET Gamma-Ray Burst Monitor detection: Moriyama et al., GCN18810;
IPN triangulation: Hurley et al., GCN 18855)
triggered Konus-Wind at T0=38267.351 s UT (10:37:47.351).

The burst light curve shows two emission episodes
with a total duration of ~91 s.
The emission is seen up to ~15 MeV.

As observed by Konus-Wind, the burst
had a fluence of 9.03(-0.64,+0.65)x10^-5 erg/cm2,
and a 64-ms peak energy flux, measured from T0+5.952 s,
of 1.27(-0.19,+0.19)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+77.056 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.81(-0.09,+0.10),
the high energy photon index beta = -2.57(-0.21,+0.14),
the peak energy Ep = 163(-10,+11) keV,
chi2 = 95/96 dof.

The spectrum near the peak count rate
(measured from T0 to T0+7.424 s)
is best fit in the 20 keV - 3 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.07(-0.07,+0.07),
the high energy photon index beta = -2.40(-0.19,+0.13),
the peak energy Ep = 216(-20,+22) keV,
chi2 = 61/63 dof.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB151231_T38267/

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.