TITLE: GCN CIRCULAR NUMBER: 16854 SUBJECT: Konus-Wind observation of GRB 140928A DATE: 14/09/30 15:33:47 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, intense GRB 140928A (Fermi-LAT detection: Desiante et al., GCN 16847; Fermi-GBM detection: von Kienlin and Meegan, GCN 16850; IPN triangulation: Hurley et al., GCN 16852) triggered Konus-Wind at T0=37793.602 s UT (10:29:53.602). The burst light curve shows two emission episodes with a total duration of ~69 s. The first emission episode lasts from ~T0-6 s to ~T0+15 s and the second episode lasts from ~T0+42 s to ~T0+63 s (Fermi-GBM missed the second episode probably due to the Earth occultation). The IPN data confirm the second episode belongs to the same GRB. The emission is seen up to ~15 MeV. As observed by Konus-Wind, the burst had a fluence of 8.6(-1.4,+1.3)x10^-5 erg/cm2, and a 64-ms peak energy flux, measured from T0+9.248 s, of 1.7(-0.3,+0.3)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+57.856 s) is best fit in the 20 keV - 10 MeV range by a GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.17(-0.09,+0.12), the high energy photon index beta = -2.09(-0.32,+0.16), the peak energy Ep = 304(-66,+80) keV, chi2 = 73/84 dof. The spectrum near the peak count rate (measured from T0+6.912 to T0+16.896 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.11(-0.08,+0.09), the high energy photon index beta = -2.27(-0.34,+0.17), the peak energy Ep = 318(-46,+59) keV, chi2 = 84/93 dof. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB140928_T37793/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.