TITLE: GCN CIRCULAR NUMBER: 17641 SUBJECT: Konus-Wind observation of GRB 150323B DATE: 15/03/25 16:39:15 GMT FROM: Anastasia Tsvetkova at Ioffe Institute 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: The long-duration GRB 150323B (Swift-BAT trigger #635929: Cummings, GCN 17619; Fermi-GBM observation: von Kienlin, GCN 17623) triggered Konus-Wind at T0=34121.196 s UT (09:28:41.196). The burst light curve shows several bright peaks during first ~60 s after the trigger. In the instrument's soft energy channel, the flaring can be traced up to ~T0+150 s. As observed by Konus-Wind, the burst had a fluence of 2.0(-0.1,+0.2)x10^-5 erg/cm2, and a 64-ms peak energy flux, measured from T0+22.656 s, of 1.4(-0.6,+0.6)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+65.792 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 = -1.53(-0.10,+0.11), and Ep = 109(-12,+15) keV (chi2 = 109/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.90 (chi2 = 109/97 dof). The spectrum near the peak count rate (measured from T0+16.640 to T0+24.832 s) is best fit in the 20 keV - 1 MeV range by the power law with exponential cutoff model with alpha = -1.15(-0.25,+0.29), and Ep = 215(-51,+108) keV (chi2 = 35/59 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -1.97 (chi2 = 35/58 dof). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB150323_T34121/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.