TITLE: GCN CIRCULAR NUMBER: 5748 SUBJECT: Konus-Wind observation of GRB 061021 DATE: 06/10/23 14:22:58 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and T. Cline on behalf of the Konus-Wind team report: The long GRB 061021 (Swift-BAT trigger #234905: Moretti et al., GCN 5743; Palmer et al., GCN 5744) triggered Konus-Wind at T0=56348.304 s UT (15:39:08.304). As observed by Konus-Wind the burst shows a single pulse with a duration of ~10 s, followed by a weak tail seen up to T-T0 ~60 s. The spectrum of the pulse integrated from T0 to T0+8.448 s is well fitted (in the 20 keV - 2 MeV range) by a power law with exponential cutoff model: dN/dE ~ E^(-alpha) * exp(-(2-alpha)*E/Ep) with alpha = 1.22(-0.14, +0.12) and Ep = 777 (-237, +549) keV (chi2 = 58/59 dof). The fluence of this part is 9.93(-4.14, +0.69)x10^-6 erg/cm2 (in the 20 keV - 2 MeV range). The spectrum of the tail integrated from T0+8.448 s to T0+57.600 s can be fitted (in the 20 keV - 2 MeV range) by a simple power law with the photon index 1.93(-0.27, +0.32) (chi2 = 77/60 dof). The fluence of this part is 3.43(-2.20, +0.83)x10^-6 erg/cm2 (in the 20 keV - 2 MeV range). We note that because of the derived photon index is ~2, this fluence value is very sensitive to the upper boundary of the energy range. The total burst fluence is 1.34(-0.47, +0.11)x10^-5 erg/cm2, and the 256-ms peak flux measured from T0+0.608 s 3.72(-1.62, +0.53)x10^-6 erg/cm2/s (both in the 20 keV - 2 MeV energy range). All the quoted errors are at the 90% confidence level.