TITLE: GCN CIRCULAR NUMBER: 42765 SUBJECT: Konus-Wind detection of GRB 251118С (EP251118a) DATE: 25/11/19 16:58:51 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaia, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: A long-duration GRB 251118C was detected by Konus-Wind (KW) in the waiting mode at T0=T0(KW)~16:44:49 UT. A Bayesian block analysis of the KW data in the 20-1500 keV band reveals a ~17 sigma count rate increase in the interval from ~T0-0.5 s to ~T0+23 s. Corrected for the propagation time, the burst started ~140 s after the start time of the fast X-ray transient EP251118a (T0(EP)=16:42:29 UT; Jiang et al., GCN 42749). The burst source is located in the southern ecliptic hemisphere at a low ecliptic latitude, which is consistent with the EP251118a localization. The positional and temporal coincidence of GRB 251118C with the EP251118a supports the conclusion that both events have a common origin. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251118C/ The time-integrated spectrum of the burst, measured from T0-0.5 s to T0+23 s, can be described by a simple power function with the photon index (2.29 ± 0.11). The total burst fluence is (5.08 ± 0.40)x10^-6 erg/cm^2, and the 2.944 s peak energy flux, measured from T0-1.96 s, is (4.84 ± 0.38)x10^-7 erg/cm^2(both in the 20 - 1500 keV energy range). Assuming the redshift z=1.216 (An et al., GCN 42756) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the burst isotropic energy release E_iso to (2.06 ± 0.16)x10^52 erg, the isotropic peak luminosity L_iso to (4.34 ± 0.34)x10^51 erg/s. All the quoted errors are estimated at the 68% confidence level. All the presented results are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/42765. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...