TITLE:   GCN CIRCULAR
NUMBER:  12790
SUBJECT: Konus-Wind observation of GRB 111228A
DATE:    11/12/31 11:38:24 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 long GRB 111228A (Swift-BAT trigger #510649:
Ukwatta et al., GCN 12737; Cummings et al., GCN 12749)
triggered Konus-Wind at T0=56736.171s UT (15:45:36.171).

The light curve shows two groups of pulses separated by ~45 s.
A total duration of the burst is ~50 s.
The emission is seen up to ~1500 keV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB111228_T56736/

As observed by Konus-Wind the burst
had a fluence of (7.5 ± 1.3)x10-6 erg/cm2,
and a 256-ms peak flux, measured from T0+3.584 s,
of (2.0 ± 0.3)x10-6 erg/cm2/s
(both in the 20 keV - 2000 MeV energy range).

The time-integrated spectrum of the burst (measured from T0 to T0+49.408 s)
is best fit in the 20 keV - 2000 keV range
by a simple power law function with the photon
index of (2.4 ± 0.2), chi2 = 53.7/62 dof.

The spectrum at the maximum count rate (measured from T0 to T0+8.448 s)
is also best fit in the 20 keV - 2000 keV range
by a simple power law function with the photon
index of (2.25 ± 0.15), chi2 = 77.1/62 dof.

Assuming the redshift z~0.715 (Dittman et al., GCN 12759;
Cucchiara et al., GCN 12761; Palazzi et al., GCN 12765;
Xu et al., GCN 12764) and a standard cosmology model
with H_0 = 71 km/s/Mpc, Omega_M = 0.27, Omega_Lambda = 0.73,
the isotropic energy release E_iso is (1.0 ± 0.2)x10^52 erg, and
the isotropic peak luminosity L_iso_max is (4.6 ± 0.7)x10^51 erg/s.

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