TITLE: GCN CIRCULAR NUMBER: 13758 SUBJECT: Konus-Wind observation of GRB 120911B DATE: 12/09/13 06:51:03 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 hard GRB 120911B (IPN detection and localization: Hurley at al., GCN 13755; Fermi-LAT detection: Racusin et. al., GCN 13756; Fermi-GBM observation: Gruber et. al., GCN 13757) triggered Konus-Wind at T0=23172.213s UT (06:26:12.213) The light curve shows a bright hard pulse with a duration of ~30 s followed by a tail of weaker and softer extended emission during the next ~150 s; additionally, a soft weak precursor is observed around T0-55 s. The emission in the main bursting episode is seen up to 9 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB120911_T23172/ As observed by Konus-Wind, the burst had a fluence of 3.0(-0.1,+0.1)x10-4 erg/cm2, and a 64-ms peak flux, measured from T0+15.232 s, of 3.8(-0.4,+0.4)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the main emission episode (measured from T0 to T0+34.048 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 = -0.86 (-0.03, +0.03), the high energy photon index beta = -2.6 (-0.2, +0.2), the peak energy Ep = 950(-50, +50) keV, chi2 = 78.4/82 dof. The spectrum at the maximum count rate (measured from T0+14.080 to T0+15.616 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 = -0.63 (-0.08, +0.09), the high energy photon index beta = -2.9 (-1.6, +0.3), the peak energy Ep = 1000(-120, +130) keV, chi2 = 81.1/82 dof. All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.