TITLE:   GCN CIRCULAR
NUMBER:  14104
SUBJECT: Konus-Wind observation of GRB 121225B
DATE:    12/12/26 16:21:17 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The intense long-duration hard-spectrum GRB 121225B
(Fermi-LAT detection: Kocevski et al., GCN 14101;
Fermi-GBM detection: Tierney et al., GCN 14102;
IPN detection and localization: Hurley et al., GCN 14103)
triggered Konus-Wind at T0=36066.467s UT (10:01:06.467)

The burst light curve shows a hard multi-peaked structure
from ~T0-18s to ~T0+15s followed by a softer complex pulse
from ~T0+23s to ~T0+56s. The total duration of the burst is ~75s.
The emission is seen up to 15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB121225_T36066/

As observed by Konus-Wind, the burst
had a fluence of (9.0 ± 0.7)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+4.288 s,
of (9.9 ± 0.9)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst (measured T0 to T0+55.296 s)
is best fit in the 20 keV - 17 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.00 ± 0.08,
the high energy photon index beta = -2.3 ± 0.1,
the peak energy Ep = 230 ± 20 keV,
chi2 = 102.0/95 dof.

The spectrum at the maximum count rate (measured T0 to T0+6.144 s)
is best fit in the 20 keV - 17 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = +0.85 ± 0.07,
the high energy photon index beta = -2.3 ± 0.1,
the peak energy Ep = 410 ± 40 keV,
chi2 = 89.7/93 dof.

All the quoted results are preliminary.