TITLE: GCN CIRCULAR NUMBER: 5837 SUBJECT: Konus-Wind and Konus-A observations of GRB 061121 DATE: 06/11/22 18:00:35 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 and Konus-A teams report: The second, brightest pulse of the long GRB 061121 (Swift-BAT trigger #239899: Page et al., GCN 5823; Fenimore et al., GCN 5831) triggered Konus-Wind at T0=55412.445 s UT(15:23:32.445). The first pulse which triggered Swift-BAT was detected by Konus-Wind in the waiting mode. The Konus-Wind spectrum integrated over the main episode of emission (from T0 to T0+21.504 s) can be fitted (in the 20 keV - 5 MeV range) by a power law with exponential cutoff model: dN/dE ~ E^(-alpha) * exp(-(2-alpha)*E/Ep) with alpha = 1.32(-0.05, +0.04) and Ep = 606(-72, +90) keV (chi2 = 95/75 dof). The fluence of this part is 5.67(-0.50, +0.30)x10^-5 erg/cm2 and the 64-ms peak flux measured from T0+12.960 s 1.28(-0.19, +0.16)x10^-5 erg/cm2/s (both in the 20 keV - 5 MeV range). The fluence of the precursor is estimated as ~10^-6 erg/cm2, so the total burst fluence equals to the fluence of the main episode in the limits of its uncertainty. Assuming z = 1.314 (Bloom, Perley, and Chen, GCN 5826) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.3, Omega_\Lambda = 0.7, the isotropic bolometric energy release is E_iso ~2.5x10^53 erg, and the maximum bolometric luminosity is (L_iso)_max ~1.3x10^53 erg/s. All the quoted errors are at the 90% confidence level. The GRB 061121 also triggered Konus-A at T0=55350.15 s UT (15:22:10.15) (so Konus-A triggered on the precursor). The Konus-A instrument has been operating onboard Cosmos-2421 spacecraft since June 25, 2006. The instrument consists of 3 NaI(Tl) detectors 200 mm in diameter and 50 mm in height with beryllium entrance windows. It is designed to study temporal and spectral characteristics of gamma-ray bursts in the wide energy range from 10 keV up to 10 MeV. The Konus-Wind and Konus-A light curves of this GRB are available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB061121_T55412/