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GCN Circular 13272

Subject
Konus-Wind observation of GRB 120427A
Date
2012-04-28T17:04:53Z (12 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
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:

GRB 120427A (IPN localization: Hurley at al., GCN 13271)
triggered Konus-Wind at T0=04651.927s UT (01:17:31.927)

The light curve shows a broad pulse with
a total duration of ~5 s.
The emission is seen up to ~5 MeV.
A spectral lag between the G2(90-300 keV)
and the G1(25-90 keV) instrument's light curves
is estimated to 0.51 � 0.07 s (1 sigma).

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB120427_T04651/

As observed by Konus-Wind the burst
had a fluence of (7.8 � 1.1)x10-6 erg/cm2,
and a 64-ms peak flux, measured from T0+1.600 s,
of (2.6 � 0.4)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fitted in the 20 keV - 10 MeV range
with the GRB (Band) model, for which:
the low-energy photon index alpha = -0.77 (-0.20, +0.23),
the high energy photon index beta = -2.9 (-1.1, +0.3),
the peak energy Ep = 133(-14, +7) keV,
chi2 = 97.5/81 dof.

We note a curious resemblance, both in the light curves
and in the spectral properties, between GRB 120427A and
the one-day older GRB 120426A (Golenetskii et al., GCN 13268).
However, a ~126 deg angular distance between their IPN
localization boxes (GCN 13265, GCN 13271) leaves
no chance for a lensed event.

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