GCN Circular 18854

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, extremely intense GRB 151229B
(IPN triangulation: Golenetskii et al., GCN Circ. 18852
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triggered Konus-Wind at T0=77056.981 s UT (21:24:16.981).

The burst light curve shows a bright multi-peaked pulse
with a duration of ~10 s (from ~T0+5 s to ~T0+15 s).
This extremely bright phase of the event passes into a weaker decaying
tail, which can be traced out to ~T0+100 s.
The emission in the main pulse is seen up to ~15 MeV.

As observed by Konus-Wind, the burst
had a fluence of 4.2(-0.1,+0.1)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+10.064 s,
of 7.1(-0.6,+0.6)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+28.672 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 = -0.65(-0.06,+0.06),
the high energy photon index beta = -2.12(-0.03,+0.03),
the peak energy 262(-13,+14) keV
(chi2 = 120/93 dof)

The spectrum near the maximum count rate
(measured from T0+9.984 to T0+10.240 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 = -0.33(-0.14,+0.16),
the high energy photon index beta = -2.51(-0.18,+0.14),
the peak energy 290(-30,+33) keV
(chi2 = 44/54 dof)

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB151229_T77056/

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