TITLE: GCN CIRCULAR NUMBER: 15939 SUBJECT: Konus-Wind observation of GRB 140306A DATE: 14/03/07 12:17:50 GMT FROM: Dmitry Svinkin at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 140306A (localized by IPN: Golenetskii et al., GCN 15938; GBM detection: Fitzpatrick, GCN 15935) triggered Konus-Wind at T0=12581.686 s UT (03:29:41.686). The burst light curve shows an bright multi-peaked pulse with a duration of ~75 s. The emission is seen up to ~8 MeV. As observed by Konus-Wind, the burst had a fluence of (1.35 +/- 0.12)x10^-4 erg/cm2, and a 256-ms peak flux, measured from T0+4.592 s, of (2.3 +/- 0.2)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+78.848 s) is best fit (in the 20 keV - 15 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.21 (-0.04, 0.05) and Ep = 1305 (-210,+273) keV (chi2 = 106/98 dof). Fit with the GRB (Band) model yields the same alpha and Ep, and only an upper limit on the high energy photon index: beta < -2.37 (chi2 = 106/97 dof). The spectrum near the maximum count rate (measured from T0 to T0+6.656 s) is best fit (in the 20 keV - 15 MeV range) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.77 (-0.05, 0.05) and Ep = 1524 (-142,+158) keV (chi2 = 76/98 dof). Fit with the GRB (Band) model yields the same alpha and Ep, and only an upper limit on the high energy photon index: beta < -2.74 (chi2 = 76/97 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB140306_T12581/ All the quoted errors are at the 90% confidence level. All the quoted results are preliminary.