TITLE: GCN CIRCULAR NUMBER: 21045 SUBJECT: Konus-Wind observation of GRB 170428A DATE: 17/04/28 18:30:50 GMT FROM: Dmitry Svinkin at Ioffe Institute A. Tsvetkova, S. Golenetskii, R. Aptekar, D. Frederiks, D. Svinkin, P. Oleynik, M. Ulanov, A. Lysenko, A.Kozlova, and T. Cline on behalf of the Konus-Wind team, report: The short-duration, bright GRB 170428A (Swift-BAT detection: Beardmore et al., GCN Circ. 21042) triggered Konus-Wind at T0=33218.719 s UT (09:13:38.719). The burst light curve shows a multipeaked structure which starts at ~T0-0.02 s and has a total duration of ~0.14 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB170428_T33218/ As observed by Konus-Wind, the burst had a fluence of 4.20(-0.90,+0.91)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0+0.056 s, of 5.00(-1.52,+1.53)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+0.128 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 = -0.47(-0.21,+0.28), the high energy photon index beta = -2.46(-7.54,+0.52), the peak energy Ep = 982(-355,+394) keV (chi2 = 31/37 dof). Fitting this spectrum by a power law with exponential cutoff model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -0.53(-0.18,+0.21) and Ep = 1134(-268,+368) keV (chi2 = 33/38 dof). All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.