Konus-Wind detection of GRB 210406A

The long GRB 210406A (INTEGRAL detection, T0 = T0(IBIS/ISGRI)= 17:11:28 UT: Mereghetti, et al., GCN 29767; Fermi/GBM detection: Malacaria & Meegan, GCN 29771) was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a >10 sigma count rate increase over background in the interval from ~T0-0.470 s to ~T0+73.130 s. As observed by Konus-Wind, the burst had a fluence of 9.13(-1.16,+1.40)x10^-6 erg/cm2 and a 2.944-s peak flux, measured in the interval starting from ~T0+5.418 s, of 5.74(-0.84,+0.97)x10^-7 erg/cm2/s (both in the 10 keV - 10 MeV energy range). Modeling the K-W 3-channel time-integrated spectrum (from ~T0-0.470 s to ~T0+73.130 s) by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.04(-0.20,+0.35) and Ep = 176(-36,+54) keV. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB210406A/ All the quoted errors are estimated at the 1 sigma confidence level. All the presented results are preliminary.