TITLE:   GCN CIRCULAR
NUMBER:  15398
SUBJECT: Konus-Wind observation of GRB 131028A
DATE:    13/10/29 15:50:06 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin,
P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf
of the Konus-Wind team, report:

The bright, long-duration, hard-spectrum GRB 131028A
(Fermi GBM detection: von Kienlin, GCN 15396;
IPN triangulation: Hurley at al., GCN 15397)
triggered Konus-Wind at T0=6546.966 s UT (01:49:06.966).

The burst light curve shows a bright, hard pulse from ~T0 to ~T0+20 s,
followed by a tail of softer emission in next ~50 s.
The emission in the main pulse is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB131028_T06546/

As observed by Konus-Wind, the burst
had a fluence of (2.41 ± 0.05)x10-4 erg/cm2,
and a 64-ms peak flux, measured from T0+5.760 s,
of (6.6 ± 0.3)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+20.736 s)
is best fit in the 50 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.82 ± 0.02,
the high energy photon index beta = -3.07 ± 0.17,
the peak energy Ep = 901 ± 25 keV,
chi2 = 97.2/93 dof.

The spectrum near the maximum count rate
(measured from T0+5.376 s to T0+6.400 s)
is best fit in the 50 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.56 ± 0.06,
the high energy photon index beta = -3.18 ± 0.42,
the peak energy Ep = 1277 ± 91 keV,
chi2 = 119/86 dof.

All the quoted values are preliminary.