[vsnet-grb-info 12645] Konus-Wind observation of GRB 121122A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14005
SUBJECT: Konus-Wind observation of GRB 121122A
DATE:    12/11/27 12:04:59 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at 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:

The long-duration intense GRB 121122A
(IPN detection and localization: Hurley et al., GCN 14001)
triggered Konus-Wind at T0=76497.048s UT (21:14:57.048)

The burst light curve is formed by three overlapped FRED-like pulses;
a total duration of the burst is ~12 s.
A behavior of hardness ratios between the instrument's light curves
in different energy bands suggests a strong hard-to-soft spectral evolution.
The emission is seen up to 7 MeV.

As observed by Konus-Wind, the burst
had a fluence of (4.1 ± 0.1)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0+1.728 s,
of (1.0 ± 0.1)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst (measured T0 to T0+15.616 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.53 ± 0.05,
the high energy photon index beta = -3.3 ± 0.2,
the peak energy Ep = 183 ± 4 keV,
chi2 = 106/91 dof.

The spectrum at the maximum count rate (measured T0 to T0+1.792 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = +0.58 ± 0.12,
the high energy photon index beta = -3.0 ± 0.2,
the peak energy Ep = 308 ± 13 keV,
chi2 = 69.4/60 dof.

The time-resolved spectral analysis reveals
a steady decrease of Ep from ~700 keV to ~100 keV
during the first 8 seconds of the burst,
which can be described by a power law with
the temporal decay index of ~0.6 .

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB121122_T76497/

All the quoted results are preliminary.