TITLE: GCN CIRCULAR NUMBER: 14010 SUBJECT: Konus-Wind observation of GRB 121128A DATE: 12/11/28 12:12:07 GMT FROM: Dmitry Frederiks at Ioffe Institute 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-duration soft GRB 121128A (Swift-BAT trigger #539866: Oates et al., GCN 14007) triggered Konus-Wind at T0=18353.307s UT (05:05:53.307) The burst light curve shows a multi-peaked structure with a total duration of ~30 s. The emission is seen up to 6 MeV. As observed by Konus-Wind, the burst had a fluence of (7.0 ± 0.6)x10-6 erg/cm2, and a 64-ms peak flux, measured from T0+5.568 s, of (2.05 ± 0.15)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+16.640 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.94 ± 0.14, the high energy photon index beta = -3.36 ± 0.48, the peak energy Ep = 76 ± 4 keV, chi2 = 82.6/87 dof. The spectrum at the maximum count rate (measured T0 to T0+8.848 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = +0.87 ± 0.13, the high energy photon index beta = -3.32 ± 0.46, the peak energy Ep = 87 ± 4 keV, chi2 = 69.4/60 dof. Assuming the Gemini North redshift of z=2.20 (Tanvir et al., GCN 14009) 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 (8.2 ± 0.7)x10^52 erg, the isotropic peak luminosity L_iso_max is (7.7 ± 0.6)x10^52 erg/s, and Ep_rest is (243 ± 13) keV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB121128_T18353/ All the quoted results are preliminary.