TITLE: GCN CIRCULAR NUMBER: 23809 SUBJECT: Konus-Wind observation of extremely bright GRB 190129B DATE: 19/01/29 18:31:05 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, R.Aptekar, A. Kozlova, A.Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The extremely bright, long GRB 190129B (IPN triangulation: Hurley et al., GCN 23808) triggered Konus-Wind (KW) at T0=44134.335 s UT (12:15:34.335). The light curve of the burst shows a multi-peaked pulse, which started at ~T0-10 s and had a duration of ~ 60s, which was followed by a weaker and softer pulse around ~T0+130 s. The emission is seen up to ~20 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB190129_T44134/ As observed by Konus-Wind, the burst had a fluence of (5.59 ± 0.40)x10^-4 erg/cm2 and a 64-ms peak energy flux, measured from T0+17.344, of (1.19 ± 0.04)x10^-4 erg/cm2 (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+152.832 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.85 (-0.06,+0.06), the high energy photon index beta = -2.18 (-0.16,+0.11), the peak energy Ep = 561 (-53,+56) keV, chi2 = 107/97 dof. The spectrum near the peak count rate (measured from T0+17.152 s to T0+18.432 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.64 (-0.06,+0.06), the high energy photon index beta = -2.13 (-0.08,+0.07), the peak energy Ep = 717 (-62,+66) keV, chi2 = 89/77 dof. All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.