[vsnet-grb-info 5059] Konus-Wind observation of very bright GRB 070821

[GCN Circulars]

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  <val at mail.ioffe.ru>

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/