TITLE: GCN CIRCULAR NUMBER: 11251 SUBJECT: Konus-Wind observation of GRB 100906A DATE: 10/09/07 10:27:34 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 GRB 100906A, (Swift/BAT trigger=433509: Markwardt et.al, GCN 11227; Barthelmy et.al, GCN 11233) triggered Konus-Wind at T0=49770.732s UT (13:49:30.732) The burst light curve started with a complex ~20s-long structure, followed by a weaker softer emission episode starting at ~T0+100 s. The total duration of the burst is ~150 s. The emission is seen up to 2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB100906_T49770/ As observed by Konus-Wind the burst had a fluence of (2.6 ± 0.4)x10-5 erg/cm2, and a 256-ms peak flux, measured from T0+9.728s, of (2.7 ± 0.3)x10-6 erg/cm2/s (both in the 20 keV - 2 MeV energy range). The time-integrated spectrum of the burst (from T0 to T0+139.264 s) is best fit in the 20 keV - 2 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -1.5 (-0.2, +0.4), the high energy photon index beta = -2.3 (<-2.0), the peak energy Ep = 142(-60, +119) keV (chi2 = 84/60 dof). The spectrum of the most intense part of the burst (measured from T0+0.256 to T0+16.384 s) is best fit in the 20 keV - 2 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -1.1 (-0.1, +0.1), the high energy photon index beta = -2.2 (-0.3, +0.2), the peak energy Ep = 180(-40, +45) keV (chi2 = 68/60 dof). The spectrum of the second bursting episode (measured from T0+98.304 to T0+122.880 s) is best fit in the 20 keV - 2 MeV range by the simple power law model with the photon index = 2.55 (-0.2, +0.25), chi2 = 63/62 dof. Assuming z=1.727 (Tanvir, Wiersema, and Levan et al., GCN 11230) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27, Omega_Lambda = 0.73, the isotropic energy release E_iso = (2.2 ± 0.4)x1053 erg, the peak luminosity (L_iso)_max = (5.7 ± 0.6)x1052 erg/s. All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.