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GCN Circular 4394

Subject
Konus-Wind observation of GRB 051221A
Date
2005-12-24T15:51:40Z (18 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team report:

The GRB 051221A (Swift-BAT trigger #173780;
Parsons et al., GCN 4363; Cummings et al., GCN 4365;
Norris et al., GCN 4388)
triggered Konus-Wind at T0=6672.976 s UT (01:51:12.976).

The Konus-Wind light curve consists of a soft weak precursor
and the main episode with five ~15-ms peaks.
The first peak at T0-16 ms to T0+10 is
substantially softer than the others
(there is no emission in the 380-1160 keV energy range).
After T0+0.250 sec a weak soft emission is marginally seen only
in the G1 (18-70 keV) range up to ~1 sec .

As observed by Konus-Wind the burst had
a fluence of 3.2(-1.7, +0.1)x10^-6 erg/cm2 and
peak flux on 4-ms time scale  4.6(-2.5, +0.2)x10^-5 erg/cm2/sec
(both in the 20 keV - 2 MeV energy range).

The time-integrated spectrum of the GRB (from T0 to T0+0.256 sec)
is well fitted (in the 20 keV - 2 MeV range)
by a power law with exponential cutoff model:
dN/dE ~ E^(-alpha) * exp(-E/E0)
with alpha = 1.08(-0.14, +0.13)
and E0 = 436(-116, +165) keV (chi2 = 65/69dof).
The peak energy Ep = 402(-72, +93) keV.
The fitting by a single power law gives an unacceptable
result: chi2 = 152/70dof (null hypothesis probability = 5.423E-08).

All the quoted errors are at the 90% confidence level.

Assuming z = 0.5465 (Berger and Soderberg, GCN 4384)
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.3, Omega_\Lambda = 0.7,
the isotropic energy release is E_iso ~2.5x10^51 erg,
the maximum luminosity is (L_iso)_max ~5.5x10^52 erg/sec.

The Konus-Wind light curve of this GRB can be seen
at http://www.ioffe.rssi.ru/LEA/GRBs/GRB051221_T06672/
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