TITLE: GCN CIRCULAR NUMBER: 18781 SUBJECT: Konus-Wind observation of GRB 151227B DATE: 15/12/31 08:50:48 GMT FROM: Anastasia Tsvetkova at Ioffe Institute 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 151227B (Fermi GBM detection: Toelge & Bissaldi, GCN 18727; IPN Triangulation: Hurley et al., GCN 18773) triggered Konus-Wind at T0=18827.479 s UT (05:13:47.479). The burst light curve shows three emission episodes with a total duration of ~48 s. The emission is seen up to ~15 MeV. As observed by Konus-Wind, the burst had a fluence of 6.49(-0.72,+0.72)x10^-5 erg/cm2, and a 64-ms peak energy flux, measured from T0+29.728 s, of 1.11(-0.20,+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+43.776 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 = -1.19(-0.08,+0.10), the high energy photon index beta = -2.11(-0.18,+0.11), the peak energy Ep = 228(-40,+46) keV, chi2 = 110/97 dof. The spectrum near the peak count rate (measured from T0+24.832 to T0+35.584 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 = -1.25(-0.05,+0.05), the high energy photon index beta = -2.57(-1.09,+0.28), the peak energy Ep = 353(-44,+52) keV, chi2 = 111/93 dof. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB151227_T18827/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.