TITLE: GCN CIRCULAR NUMBER: 23557 SUBJECT: Konus-Wind observation of GRB 181222B DATE: 18/12/25 10:36:09 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, M. Ulanov, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline on behalf of the Konus-Wind team, report: The short-duration, extremely bright GRB 181222B (Fermi-GBM detection: Veres, GCN Circ. 23551; IPN triangulation: Svinkin et al., GCN Circ. 23556) triggered Konus-Wind at T0=72694.563 s UT (20:11:34.563). The burst light curve shows a single pulse which starts at about T0 and has a total duration of ~2.1 s. The emission is seen up to ~15 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB181222_T72694/ As observed by Konus-Wind, the burst had a fluence of 3.70(-0.17,+0.18)x10^-5 erg/cm2, and a 16-ms peak flux, measured from T0+0.166 s, of 2.72(-0.25,+0.26)x10^-4 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+0.512 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.52(-0.08,+0.08), the high energy photon index beta = -2.95(-0.30,+0.20), the peak energy Ep = 365(-26,+27) keV (chi2 = 53/56 dof). Among ~300 bursts from the Konus catalog of short GRBs (Svinkin et al., ApJS 224, 10, 2016), GRB 181222B is within top 2% in the terms of 16-ms peak energy flux and within top 2% in the terms of the total energy fluence, both in the 20 keV - 10 MeV range. All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.