TITLE: GCN CIRCULAR NUMBER: 26089 SUBJECT: Konus-Wind observation of GRB 191025B DATE: 19/10/29 12:34:07 GMT FROM: Anna Kozlova at Ioffe Institute A. Ridnaia, 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 short-duration GRB 191025B (Insight-HXMT detection: Luo et al., GCN Circ. 26081; IPN triangulation: Svinkin et al., GCN Circ. 26086) triggered Konus-Wind at T0=67331.034 s UT (18:42:11.034). The burst light curve shows a single pulse started at ~T0 with a total duration of ~0.2 s. The emission is seen up to ~10 MeV. As observed by Konus-Wind, the burst had a fluence of 8.41(-1.44,+1.52)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0-0.006 s, of 1.32(-0.32,+0.33)x10^-4 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+0.128 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.84(-0.11,+0.13) and Ep = 2184(-608,+812) keV (chi2 = 23/26 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.9 (chi2 =22/25 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB191025_T67331/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.