TITLE: GCN CIRCULAR NUMBER: 27883 SUBJECT: Konus-Wind observation of GRB200528A DATE: 20/06/02 09:06:41 GMT FROM: Anastasia Tsvetkova at Ioffe Institute A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Lysenko, A. Ridnaia and T. Cline on behalf of the Konus-Wind team, report: The long-duration, soft-spectrum GRB200528A (Swift detection: Ambrosi et al., GCN 27832; Barthelmy et al., GCN 27839; Fermi GBM Observation: Fletcher, von Kienlin & Meegan, GCN 27841; CALET Gamma-Ray Burst Monitor detection: Pal'shin et al., GCN 27855) triggered Konus-Wind at T0=37675.256 s UT (10:27:55.256). The burst light curve shows a complex structure which starts at ~T0-33.8 s, with a total duration of~60.0 s, and comprises two double-peaked emission episodes. The emission is seen up to ~1 MeV. As observed by Konus-Wind, the burst had a fluence of 2.12(-0.07,+0.07)x10^-5 erg/cm2, and a 64-ms peak energy flux, measured from T0+1.696 s, of 2.38(-0.35,+0.35)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+33.024 s) is best fit in the 20 keV - 1 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with  alpha = -1.41(-0.14,+0.14), and Ep = 64(-5,+5) keV (chi2 = 50/60 dof). Fitting by the GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.89 (chi2 = 49/59 dof). The spectrum near the peak count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 1 MeV range by the power law with exponential cutoff model with  alpha = -1.14(-0.15,+0.16), and Ep = 75(-4,+5) keV (chi2 = 52/60 dof). Fitting by the GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.03 (chi2 = 51/59 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB200528_T37675/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.