TITLE: GCN CIRCULAR NUMBER: 18180 SUBJECT: Konus-Wind observation of GRB 150819B DATE: 15/08/20 12:46:07 GMT FROM: Dmitry Svinkin at Ioffe Institute S. Golenetskii, R. Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline on behalf of the Konus-Wind team, report: The short-duration, very intense GRB 150819B (IPN triangulation: Golenetskii et al., GCN 18176; Fermi GBM detection: Yu and Burns, GCN 18178) triggered Konus-Wind at T0=38000.750 s UT (10:33:20.750). The burst light curve shows at least three separate peaks. A total duration of the burst is ~1.2 s. The emission is seen up to ~3 MeV. As observed by Konus-Wind, the burst had a fluence of 6.61(-0.88,+1.10)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0+0.008 s, of 1.20(-0.17,+0.19)x10^-4 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.03(-0.21,+0.24) and Ep = 348(-70,+116) keV (chi2 = 74/89 dof). Fitting by the GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.3 (chi2 = 74/88 dof). The spectrum near the maximum count rate (measured from T0 to T0+0.064 s) is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model with alpha = -0.41(-0.15,+0.17) and Ep = 618(-86,+95) keV (chi2 = 57/43 dof). Fitting by the GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.8 (chi2 = 57/42 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB150819_T38000/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.