[vsnet-grb-info 14166] Konus-Wind observation of GRB 131108A

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15480
SUBJECT: Konus-Wind observation of GRB 131108A
DATE:    13/11/10 12:05:37 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at 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 long-duration, bright, hard-spectrum GRB 131108A
(Fermi-LAT detection: Racusin, et al., GCN 15464; Vianello, et al., GCN 15472;
IPN triangulation: Hurley at al., GCN 15466;
Fermi-GBM observation: Younes, GCN 15477;
AGILE/GRID observation: Giuliani, et al., GCN 15479)
triggered Konus-Wind at T0=74512.947 s UT (20:41:52.947).

The light curve shows a mult-peaked structure from ~T0 to ~T0+20 s.
The emission is seen up to ~12 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB131108_T74512/

As observed by Konus-Wind, the burst
had a fluence of (4.15 ± 0.25)x10-5 erg/cm2,
and a 64-ms peak flux, measured from T0,
of (2.10 ± 0.15)x10-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+23.04 s)
is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.11 ± 0.05,
the high energy photon index beta = -2.72 ± 0.06,
the peak energy Ep = 340 ± 11 keV,
chi2 = 69.2/95 dof.

The spectrum of the brightest initial spike
(measured from T0 to T0+0.256 s)
is best fit in the 50 keV - 15 MeV range
by the cutoff power law with the following model parameters:
the photon index alpha = -1.21 ± 0.11,
and the peak energy Ep = 1326 ± 382 keV,
chi2 = 52.9/70 dof.

Assuming the redshift z=2.40 (de Ugarte Postigo, et al., GCN 15470;
Xu, et al., GCN 15471),
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.27, and Omega_Lambda = 0.73,
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is (5.8 ± 0.4)x10^53 erg,
the peak luminosity L_iso is (1.0 ± 0.07)x10^54 erg/s,
and the rest-frame peak energy Ep,i = (1160 ± 40) keV

All the quoted results are preliminary.