TITLE: GCN CIRCULAR NUMBER: 13979 SUBJECT: Konus-Wind observation of GRB 121118B DATE: 12/11/21 10:33:10 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 intense GRB 121118B (IPN detection and localization: Hurley et al., GCN 13977) triggered Konus-Wind at T0=80847.239s UT (22:27:27.239) The light curve shows multiple pulses with increasing amplitude in the time interval starting at ~60s before KW trigger and ending at ~T0+40s. The emission is seen up to 9 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB121118_T80847/ As observed by Konus-Wind the burst had a fluence of (8.5 ± 0.3)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+13.696 s, of (1.0 ± 0.6)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the triggered part of the burst (measured T0 to T0+32.512 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 = -1.30 ± 0.05, the high energy photon index beta = -3.05 ± 0.70, the peak energy Ep = 520 ± 64 keV, chi2 = 78.4/82 dof. The spectrum at the maximum count rate (measured T0+8.448 to T0+16.128 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff (CPL) model, for which: the photon index alpha = -1.18 ± 0.04 and the peak energy Ep = 599 ± 52 keV, chi2 = 91.4/83 dof. Fitting this spectrum with the Band function yields the same alpha and Ep with only an upper limit for beta <-3.0 (90% conf.) All the quoted results are preliminary.