TITLE: GCN CIRCULAR NUMBER: 25285 SUBJECT: Konus-Wind observation of GRB 190805B DATE: 19/08/08 05:42:10 GMT FROM: Anna Kozlova at Ioffe Institute A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 190805B (MAXI/GSC detection: Sato et al., GCN Circ. 25271; Fermi/GBM detection: Hamburg & Meegan, GCN Circ. 25277) triggered Konus-Wind at T0=17159.354 s UT (04:45:59.354). The burst light curve shows a multipeaked structure which starts at ~T0-6.1 s and has a total duration of ~27.9 s. The emission is seen up to ~6 MeV. As observed by Konus-Wind, the burst had a fluence of 1.46(-0.16,+0.24)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+14.832 s, of 4.76(-1.60,+8.56)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+24.832 s) is best fit in the 20 keV - 6 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.07(-0.23,+0.26) and Ep = 315(-73,+148) keV (chi2 = 66/79 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.0 (chi2 = 65/78 dof). The spectrum near the maximum count rate (measured from T0+8.448 to T0+16.640 s) is best fit in the 20 keV - 6 MeV range by a power law with exponential cutoff model with alpha = -1.28(-0.44,+0.55) and Ep = 281(-118,-281) keV (chi2 = 45/78 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.7 (chi2 = 44/77 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB190805_T17159/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.