TITLE: GCN CIRCULAR NUMBER: 11951 SUBJECT: Konus-Wind observation of GRB 110420A DATE: 11/04/21 13:41:09 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report: The long soft GRB 110420A (Swift-BAT trigger #451757: Mangano et al., GCN 11941; Krimm et al., GCN 11945) triggered Konus-Wind at T0(KW)=39750.543 s UT (11:02:30.543). The burst light curve shows a single pulse started at ~T0(KW)-9 s with a duration of ~18 s. As observed by Konus-Wind the burst had a fluence of 6.54(-0.53, +0.64)x10^-6 erg/cm2, and a 256-ms peak flux measured from T0-0.320 s of (1.11 +/- 0.17)x10^-6 erg/cm2/s (both in the 20 - 500 keV energy range). The time-integrated spectrum of the burst (from T0 to T0+8.448 s) is well fitted (in the 20 - 500 keV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.71(-0.26, +0.31), and Ep = 43(-18, +17) keV (chi2 = 31.1/39 dof). Fitting by GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.61 (chi2 = 31.1/38 dof). All the quoted errors are at the 90% confidence level. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB110420_T39750/