TITLE: GCN CIRCULAR NUMBER: 31964 SUBJECT: Konus-Wind detection of GRB 220427A DATE: 22/04/28 14:20:52 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long GRB 220427A (Swift detection: D'Ai et al., GCN Circ. 31960) triggered Konus-Wind (KW) at T0=75645.009 s UT (21:00:45.009). The burst light curve shows a single pulse, which starts at ~T0-3 s and has a total duration of ~15 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/GRB220427_T75645/ As observed by Konus-Wind, the burst had a fluence of (1.0 ± 0.3)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 0.256 s, of (2.5 ± 0.7)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). A time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is well fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.04(-0.30,+0.43) and Ep = 503(-204,+757) keV (chi2 = 77/97 dof). A fit to this spectrum by the Band GRB function is poorly constrained, it results in the best fit values of alpha~-0.6, Ep~260 keV, and the high energy photon index beta ~ -2.0 (chi2 = 77/96 dof). All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.