TITLE: GCN CIRCULAR NUMBER: 23363 SUBJECT: Konus-Wind observation of GRB 181020A DATE: 18/10/22 14:49:57 GMT FROM: Anastasia Tsvetkova at Ioffe Institute A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline on behalf of the Konus-Wind team, report: The  GRB 181020A  (Swift-BAT detection: Moss et al., GCN 23349; Sakamoto  et al., GCN 23357; Fermi-LAT detection: Axelsson, GCN 23350; Fermi GBM detection: Veres, GCN 23352) triggered Konus-Wind at T0=68437.284 s UT (19:00:37.284). The burst light curve shows a single pulse with a total duration of ~26 s. The emission is seen up to ~5 MeV. As observed by Konus-Wind, the burst had a fluence of 4.17(-0.54,+0.58)x10^-5 erg/cm2, and a 64-ms peak energy flux, measured from T0+7.552 s, of 8.27(-1.99,+2.05)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+15.360 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.73(-0.11,+0.13), the high energy photon index beta = -2.35(-0.41,+0.22), the peak energy Ep = 371(-52,+57) keV, chi2 = 80/97 dof. Assuming the redshift z=2.938 (Fynbo et al., GCN 23356) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.27, and Omega_Lambda = 0.73, we estimate the following rest-frame parameters: the isotropic energy release E_iso is 8.28(-1.07,+1.16)x10^53 erg, the peak luminosity L_iso is 6.47(-1.56,+1.60)x10^53 erg/s, and the rest-frame peak energy of the time-integrated spectrum, Ep,i, is 1461(-205,+225) keV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB181020_T68437/ All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.