TITLE: GCN CIRCULAR NUMBER: 26951 SUBJECT: Konus-Wind observation of GRB 200125B DATE: 20/01/31 16:11:49 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, M. Ulanov, A. Tsvetkova, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team, report: The long-duration, very bright GRB 200125B (Fermi-GBM observations: The Fermi GBM team, GCN Circ. 26879; Veres et al., GCN Circ. 26893; BALROG localization: Biltzinger et al., GCN Circ. 26880; Insight-HXMT/HE detection: Cai et al., GCN Circ. 26888; IPN triangulation: Svinkin et al., GCN Circ. 26918) triggered Konus-Wind at T0=74611.206 s UT (20:43:31.206). The burst light curve shows a multipeaked structure which starts at ~T0-0.5 s and has a total duration of ~10 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB200125_T74611/ As observed by Konus-Wind, the burst had a fluence of 6.01(-0.36,+0.37)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+1.312 s, of 3.92(-0.44,+0.46)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+12.288 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.91(-0.06,+0.07), the high energy photon index beta = -2.48(-0.15,+0.12), the peak energy Ep = 211(-15,+16) keV (chi2 = 98/97 dof). The spectrum near the maximum count rate (measured from T0+1.280 to T0+1.536 s) is best fit in the 20 keV - 4 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.43(-0.14,+0.16), the high energy photon index beta = -2.64(-0.34,+0.21), the peak energy Ep = 295(-36,+39) keV (chi2 = 63/51 dof). All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.