TITLE: GCN CIRCULAR NUMBER: 16719 SUBJECT: Konus-Wind observation of GRB 140818A DATE: 14/08/19 14:37:57 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline on behalf of the Konus-Wind team, report: A long duration GRB 140818A (MAXI/GSC detection: Honda et al., GCN 16702, 16705; Fermi-GBM detection: Roberts, GCN 16708) triggered Konus-Wind at T0=19880.472 s UT (05:31:20.472). The burst light curve shows a rather weak pulse at ~T0-83 s followed by the main emission episode at ~T0-15 s. The total duration of the burst is ~126 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB140818_T19880/ As observed by Konus-Wind, the burst had a fluence of 3.68(-0.21,+0.22)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+24.304 s, of (2.29+/-0.49)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 3 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.11 (-0.13,+0.14) and Ep = 219 (-21,+26) keV (chi2 = 68/68 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.7 (chi2 = 68/67 dof) All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.