TITLE: GCN CIRCULAR NUMBER: 25274 SUBJECT: Konus-Wind observation of GRB 190731A DATE: 19/08/05 15:36:05 GMT FROM: Anastasia Tsvetkova at Ioffe Institute A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline on behalf of the Konus-Wind team, report: The long-duration, hard-spectrum, very bright GRB 190731A (Fermi-LAT detection: Ohno et al., GCN 25244; CALET Gamma-Ray Burst Monitor detection: Asaoka�� et al., GCN 25246; Fermi GBM detection: Roberts & Meegan, GCN 25248; IPN Triangulation: Hurley et al., GCN 25250; AstroSat CZTI detection: Ghumatkar et al., GCN 25258) triggered Konus-Wind at T0=81504.082 s UT (22:38:24.082). The burst light curve shows a multi-peaked structure which starts at ~T0-1.5 s and has a total duration of~22.0 s. The emission is seen up to ~5 MeV. As observed by Konus-Wind, the burst had a fluence of 1.32(-0.08,+0.08)x10^-4 erg/cm2, and a 64-ms peak energy flux, measured from T0+0.944 s, of 3.89(-0.46,+0.46)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+23.808 s) is best fit in the 20 keV - 5 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.69(-0.05,+0.06), the high energy photon index beta = -2.30(-0.13,+0.11), the peak energy Ep = 406(-30,+30) keV, chi2 = 121/98 dof. The spectrum near the peak count rate (measured from T0+0.256 to T0+1.536 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.63(-0.07,+0.08), the high energy photon index beta = -2.69(-0.50,+0.29), the peak energy Ep = 875(-118,+120) keV, chi2 = 107/69 dof. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB190731_T81504/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.