TITLE: GCN CIRCULAR NUMBER: 15589 SUBJECT: Konus-Wind observation of GRB 131209A DATE: 13/12/10 13:08:14 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 131209A (Fermi LAT detection: Vianello & Omodei, GCN 15587; IPN triangulation: Hurley at al., GCN 15588) triggered Konus-Wind at T0=47280.491 s UT (13:08:00.491). The burst light curve shows a broad pulse from ~T0-3 s to ~T0+17 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB131209_T47280/ As observed by Konus-Wind, the burst had a fluence of (1.4 ± 0.1)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+7.744 s, of (3.2 ± 0.3)x10-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum (measured from T0 to T0+16.640 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.49 ± 0.19, the high energy photon index beta = -2.68 ± 0.46, the peak energy Ep = 235 ± 29 keV, chi2 = 91.2/97 dof. The spectrum near the maximum count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.17 ± 0.17, the high energy photon index beta = -2.49 ± 0.22, the peak energy Ep = 246 ± 18 keV, chi2 = 87.2/97 dof. All the quoted values are preliminary.