TITLE: GCN CIRCULAR NUMBER: 21767 SUBJECT: Konus-Wind observation of GRB 170826B DATE: 17/08/30 15:05:24 GMT FROM: Anna Kozlova at Ioffe Institute A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 170826B (Fermi GBM observation: Poolakkil et al., GCN 21717; Insight-HXMT detection: Li et al., GCN 21739; IPN Triangulation: Hurley et al., GCN 21753) triggered Konus-Wind at T0=70742.555 s UT (19:39:02.555). The burst light curve shows a multipeaked structure which starts at ~T0-3.9 s and has a total duration of ~23.6 s. The emission is seen up to ~10 MeV. As observed by Konus-Wind, the burst had a fluence of 5.70(-0.53,+0.53)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+1.728 s, of 1.62(-0.29,+0.30)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+14.592 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.73(-0.14,+0.15), the high energy photon index beta = -2.12(-0.14,+0.10), the peak energy Ep = 261(-32,+46) keV (chi2 = 87/83 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+6.400 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.54(-0.19,+0.20), the high energy photon index beta = -2.05(-0.13,+0.09), the peak energy Ep = 259(-36,+53) keV (chi2 = 99/83 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB170826_T70742/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.