[vsnet-grb-info 12650] Konus-Wind observation of GRB 121128A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14010
SUBJECT: Konus-Wind observation of GRB 121128A
DATE:    12/11/28 12:12:07 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 soft GRB 121128A
(Swift-BAT trigger #539866: Oates et al., GCN 14007)
triggered Konus-Wind at T0=18353.307s UT (05:05:53.307)

The burst light curve shows a multi-peaked structure with
a total duration of ~30 s.
The emission is seen up to 6 MeV.

As observed by Konus-Wind, the burst
had a fluence of (7.0 ± 0.6)x10-6 erg/cm2,
and a 64-ms peak flux, measured from T0+5.568 s,
of (2.05 ± 0.15)x10-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst (measured T0 to T0+16.640 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 = -0.94 ± 0.14,
the high energy photon index beta = -3.36 ± 0.48,
the peak energy Ep = 76 ± 4 keV,
chi2 = 82.6/87 dof.

The spectrum at the maximum count rate (measured T0 to T0+8.848 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 = +0.87 ± 0.13,
the high energy photon index beta = -3.32 ± 0.46,
the peak energy Ep = 87 ± 4 keV,
chi2 = 69.4/60 dof.

Assuming the Gemini North redshift of z=2.20 (Tanvir et al., GCN 14009)
and a standard cosmology model with H_0 = 71 km/s/Mpc, Omega_M = 0.27,
Omega_Lambda = 0.73:
the isotropic energy release E_iso is (8.2 ± 0.7)x10^52 erg,
the isotropic peak luminosity L_iso_max is (7.7 ± 0.6)x10^52 erg/s,
and Ep_rest is (243 ± 13) keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB121128_T18353/

All the quoted results are preliminary.