TITLE: GCN CIRCULAR NUMBER: 10166 SUBJECT: Konus-Wind and Konus-RF observations of GRB 091031 DATE: 09/11/13 12:14:19 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin, P. Oleynik, M. Ulanov, and D. Svinkin on behalf of Konus-Wind and Konus-RF teams, and T. Cline on behalf of the Konus-Wind team, report: The long GRB 091031 (Fermi-GBM trigger 278683230/091031500, McBreen and Chaplin, 10115) localized by Fermi-LAT (de Palma et al., GCN 10163) triggered Konus-Wind at T0=43232.687s UT (12:00:32.687) and Konus-RF onboard Coronas-Photon s/c at T0=43230.291s UT (12:00:30.291). The burst light curve shows a complex structure with a total duration of ~40 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB091031_T43232/ As observed by Konus-Wind the burst had a fluence of (1.94 ± 0.2)x10-5 erg/cm2, and a 256-ms peak flux measured from T0 + 4.608s of (2.74 ± 0.35)x10-6 erg/cm2/s (both in the 20 keV - 2 MeV energy range). The time-integrated spectrum of the burst (from T0 to T0+41.216 s) is well fitted in the 20 keV - 2 MeV range by a power law with exponential cutoff model, for which: alpha = 0.93 (-0.08, +0.09), and Epeak = 477 (-91, +138) keV, Chi2 = 31/58 dof. Fitting by a GRB (Band) model yiels the same alpha and Epeak values with high energy spectral index beta of -9.4 (<-2.4) All the quoted values are preliminary. All the quoted errors are at the 90% confidence level.