TITLE: GCN CIRCULAR NUMBER: 10882 SUBJECT: Konus-Wind observation of GRB 100621A DATE: 10/06/23 10:22:55 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report: The long GRB 100621A (Swift-BAT trigger=425151; Ukwatta et al., GCN 10870; Ukwatta et al., GCN 10875) triggered Konus-Wind at T0=11013.352s UT (03:03:33.352) The burst light curve shows multiple overlapping peaks with a total duration of ~80 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB100621_T11013/ As observed by Konus-Wind the burst had a fluence of 3.6(+/-0.4)x10-5 erg/cm2, and a 256-ms peak flux measured from T0+26.880s of 1.70(+/-0.13)x10-6 erg/cm2/s (both in the 20 keV - 2 MeV energy range). The time-integrated spectrum of the burst (from T0 to T0+73.984 s) is best fit in the 20 keV - 2 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -1.70 (+/-0.13), the high energy photon index beta = -2.45 ( <-2.3 ), the peak energy Ep = 95(-13, +18)keV (chi2 = 65/57 dof). The spectrum at the maximum count rate (measured from T0+24.832 to T0+33.024 s) is best fit in the 20 keV - 2 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -1.15 (-0.2/+0.3), the high energy photon index beta = -2.8 (-0.7/+0.3), the peak energy Ep = 83(+/-9)keV (chi2 = 64/57 dof). Assuming z=0.542 (Milvang-Jensen et al., GCN 10876) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27, Omega_Lambda = 0.73, the isotropic energy release E_iso = 2.8(+/-0.3)x10^52 erg, the peak luminosity (L_iso)_max = (2.04+/-0.16)x10^51 erg/s. All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.