TITLE: GCN CIRCULAR NUMBER: 15125 SUBJECT: Konus-Wind observation of GRB 130821A DATE: 13/08/26 16:46:37 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, 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 130821A (Fermi-GBM detection: Jenke, GCN 15113; Fermi-LAT detection: Kocevski, et al., GCN 15115) triggered Konus-Wind at T0=58258.022 s UT (16:10:58.022). The light curve shows multiple pulses from ~T0-40 to ~T0+80 s. 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/GRB130821_T58258/ As observed by Konus-Wind, the burst had a fluence of (9.9 ± 0.9)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+6.784 s, of (1.3 ± 0.1)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum (measured from T0 to T0+78.080 s) is best fit in the 20 keV - 18 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.33 ± 0.11, the high energy photon index beta = -2.25 ± 0.19, the peak energy Ep = 260 ± 47 keV, chi2 = 84.6/97 dof. The spectrum at the maximum count rate (measured from T0 to T0+12.544 s) is best fit in the 20 keV - 18 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.11 ± 0.07, the high energy photon index beta = -2.33 ± 0.10, the peak energy Ep = 255 ± 22 keV, chi2 = 96.9/97 dof. All the quoted results are preliminary.