TITLE: GCN CIRCULAR NUMBER: 21859 SUBJECT: Konus-Wind observation of GRB 170906A DATE: 17/09/11 16:11:07 GMT FROM: Anastasia Tsvetkova at Ioffe Institute A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik, M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 170906A (Swift-BAT trigger #770957: Siegel et al., GCN 21821; Cummings et al., GCN 21838; Fermi-LAT detection: Bissaldi et al., GCN 21827; Fermi GBM detection: Hamburg & Meegan, GCN 21839; AstroSat CZTI(Veto) detection: Sharma et al., GCN 21856) triggered Konus-Wind at T0=2607.999 s UT (00:43:27.999). The burst light curve shows a double-peaked structure started at ~T0-23 s with a total duration of ~91 s, followed by a weaker emission seen up to ~T0+135 s. The KW data above 1.5 MeV are largely contaminated by high solar particle background. As observed by Konus-Wind, the burst had a fluence of 1.19(-0.21,+0.22)x10^-4 erg/cm2, and a 64-ms peak energy flux, measured from T0+11.184 s, of 9.25(-2.67,+2.97)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+68.608 s) is best fit in the 20 keV - 1.5 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.91(-0.10,+0.12), the high energy photon index beta = -2.41(-0.94,+0.28), the peak energy Ep = 274(-37,+43) keV, chi2 = 86/59 dof. The spectrum near the peak count rate (measured from T0+6.400 to T0+16.384 s) is best fit in the 20 keV - 1.5 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.60(-0.12,+0.15), the high energy photon index beta = -2.36(-0.75,+0.31), the peak energy Ep = 360(-54,+58) keV, chi2 = 64/59 dof. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB170906_T02607/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.