TITLE: GCN CIRCULAR NUMBER: 12008 SUBJECT: Konus-Wind observation of GRB 110503A DATE: 11/05/05 09:50:41 GMT FROM: Dmitry Frederiks at Ioffe Institute 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 GRB 110503A, (Swift/BAT trigger=452685: Stamatikos et al., GCN 11991; Sakamoto et.al, GCN 11995) triggered Konus-Wind at T0=63341.862s UT (17:35:41.862) The burst light curve consists of a single pulse with a total duration of ~12 s. The emission is seen up to ~4 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB110503_T63341/ As observed by Konus-Wind the burst had a fluence of (2.6 ± 0.2)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+2.304 s, of (1.0 ± 1)x10-5 erg/cm2/s (both in the 20 keV - 5 MeV energy range). The time-integrated spectrum of the burst (from T0 to T0+10.752 s) is best fitted in the 20 keV - 5 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -0.98 (-0.08, +0.09), the high energy photon index beta = -2.7 (-0.5, +0.2), the peak energy Ep = 219(-19, +20) keV, chi2 = 69.5/76 dof. The spectrum at the maximum count rate (measured from T0+1.792 s to T0+2.560 s) can be fitted in the 20 keV - 5 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -0.44 (-0.16, +0.19), the high energy photon index beta = -2.75 (-0.4, +0.3), the peak energy Ep = 211(-23, +25) keV, chi2 = 55.4/48 dof. Assuming the afterglow redshift z = 1.61 (de Ugarte Postigo et al., GCN 11993; D'Avanzo et al., GCN 11997) 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 (1.77 ± 0.15)x10^53 erg, the peak luminosity L_iso_max is (1.83 ± 0.18)x10^53 erg/s, and Ep_rest is 570 ± 50 keV. All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.