TITLE: GCN CIRCULAR NUMBER: 19462 SUBJECT: Konus-Wind observation of GRB 160521B DATE: 16/05/25 12:53:34 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 160521B (Fermi-GBM detection: Yu and Veres, GCN 19443; Fermi-LAT detection: Axelsson et al., GCN 19444) triggered Konus-Wind at T0=33237.337 s UT (09:13:57.337). The burst light curve shows a broad, multi-peaked pulse started at ~T0-0.3 s with a total duration of ~6.4 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/GRB160521_T33237/ As observed by Konus-Wind, the burst had a fluence of 1.32(-0.15,+0.17)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+1.504 s, of 1.01(-0.14,+0.14)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+9.984 s) is best fit in the 20 keV - 2 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.65(-0.14,+0.16), the high energy photon index beta = -2.72(-0.49,+0.26), the peak energy Ep = 165(-16,+17) keV (chi2 = 49/61 dof) The spectrum near the maximum count rate (measured from T0+0.256 to T0+1.792 s) is best fit in the 20 keV - 2 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.43(-0.12,+0.14), the high energy photon index beta = -3.62(-6.38,+0.62), the peak energy Ep = 190(-15,+15) keV (chi2 = 56/50 dof) All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.