TITLE: GCN CIRCULAR NUMBER: 6766 SUBJECT: Konus-Wind observation of very bright GRB 070821 DATE: 07/08/28 15:42:39 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: The very bright long GRB 070821 localized by the IPN (Hurley et al., GCN 6764) triggered Konus-Wind at T0=46164.332 s UT (12:49:24.332). The Konus-Wind light curve shows a soft precursor started at T-T0 ~-6 s (with a duration of ~8 s), followed by a very intense multipeaked pulse at T-T0 ~120 s and a weaker pulse at T-T0 ~180 s (there is an emission between these two intense pulses). The total burst duration is ~215 s. As observed by Konus-Wind the burst had a fluence of 1.02(-0.04, +0.03)x10^-4 erg/cm2, and a 256-ms peak flux measured from T0+126.720 s of 1.38(-0.11, +0.09)x10^-5 erg/cm2/s (both in the 20 keV - 2 MeV energy range). The time-integrated spectrum of the main episode (from T0+114.944 s to T0+203.776 s) can be fitted (in the 20 keV - 2 MeV range) by a power law with exponential cutoff model: dN/dE ~ E^(-alpha)*exp(-E*(2-alpha)/Ep) with alpha = 1.299 +/- 0.037 and Ep = 268 (-17, +19) keV (chi2 = 67.8/59 dof). The spectrum of the most intense pulse (accumulated from T0+114.944 s to T0+146.432 s) is well fitted (in the 20 keV - 2 MeV range) by a power law with exponential cutoff model with alpha = 1.215 +/- 0.030 and Ep = 289 (-14, +15) keV (chi2 = 68.3/59 dof). This pulse had a fluence of 8.34(-0.24, +0.17)x10^-5 erg/cm2. All the quoted errors are at the 90% confidence level. The Konus-Wind light curve of this GRB is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB070821_T46164/