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 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.