TITLE: GCN CIRCULAR NUMBER: 20292 SUBJECT: Konus-Wind observation of GRB 161218A DATE: 16/12/19 12:03:31 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline, on behalf of the Konus-Wind team, report: The long GRB 161218A (Swift-BAT detection: D'Ai et al., GCN 20283; POLAR observation: Li et al., GCN 20287) triggered Konus-Wind at T0=13651.970 s UT (03:47:31.970). The burst light curve shows a single pulse with a total duration of ~7 s. The emission is seen up to ~10 MeV. As observed by Konus-Wind, the burst had a fluence of (1.24 ± 0.10)x10^-5 erg/cm2 and a 64-ms peak energy flux, measured from T0+0.640, of (4.6 ± 0.4)x10^-5 erg/cm2 (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+10.496 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 = -0.28 (-0.21,+0.25), the high energy photon index beta = -3.40 (-1.17,+0.43), the peak energy Ep = 128 (-8,+8) keV, chi2 = 110/97 dof. The spectrum near the peak count rate (measured from T0+0.256 to T0+2.304 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 = +0.08 (-0.26,+0.29), the high energy photon index beta = -3.18 (-0.59,+0.31), the peak energy Ep = 135 (-9,+10) keV, chi2 = 84/74 dof. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB161218_T13651/ All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.