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GCN Circular 9296

Subject
Konus-Wind observation of very bright GRB 090427
Date
2009-04-29T16:16:22Z (15 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@mail.ioffe.ru>
S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P.
Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind
team, report:

The very bright GRB 090427 localized by IPN (Pal'shin et al., GCN
9277) triggered Konus-Wind at T0=84392.051 s UT (23:26:32.051).

As observed by Konus-Wind the burst
had a fluence of (1.03 +/- 0.05)x10^-4 erg/cm2,
and a 16-ms peak flux measured from T0+9.200 s
of (1.10 +/- 0.13)x10^-4 erg/cm2/s
(both in the 20 keV - 8 MeV energy range).

The time-integrated spectrum of the burst
(from T0 to T0+17.920 s) can be fitted (in the 20 keV - 8 MeV
range) by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -1.31 +/- 0.04,
and Ep = 751(-67, +78) keV (chi2 = 90.5/85 dof).
Fitting by GRB (Band) model yields the same alpha and Ep,
and only an upper limit on the high energy
photon index: beta < -2.8 (chi2 = 90.4/84 dof).
All the quoted errors are at the 90% confidence level.

The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090427_T84392/
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