TITLE: GCN CIRCULAR NUMBER: 35758 SUBJECT: Konus-Wind detection of GRB 240218A DATE: 24/02/20 02:33:53 GMT FROM: Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru> D. Svinkin, D. Frederiks, A.Lysenko, A. Ridnaia, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 240218A (Swift-BAT detection: Page et al., GCN 35742; Fermi-GBM detection: Veres and Meegan, GCN 35755) was detected by Konus-Wind (KW) in the waiting mode. A Bayesian block analysis of the KW waiting mode data in the 20-400 keV band reveals a >10 sigma count rate increase in the interval from T0-12.646 s to T0+25.626 s, where T0 = T0(BAT) = 02:00:00 UT. The burst light curve shows a multi-peaked structure with the brightest peak around ~T0(BAT)+20 s. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB240218_T07200/ As observed by Konus-Wind, the burst had a total fluence of 7.62(-2.22,+1.72)x10^-6 erg/cm^2 and a 2.944-s peak energy flux, measured from T0+19.738 s, of 5.29(-1.49,+2.21)x10^-7 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). Modelling the 3-channel time-integrated spectrum of the burst (measured from T0-12.646 s to T0+25.626 s) by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha > -0.56 and Ep = 180(-74,+77) keV. Modelling the 3-channel spectrum near the peak count rate (measured from T0+19.738 to T0+25.626 s) by the CPL model yields alpha = -1.33(-0.29,+0.53) and Ep = 293(-120,+207) keV. Assuming the redshift z=6.782 (Saccardi et al., GCN 35756) 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 5.4(-1.6,+1.2)x10^53 erg, the isotropic peak luminosity L_iso to 2.9(-0.8,+1.2)x10^53 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to 1401(-576,+599) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to 2280(-934,+1611) keV. With the obtained estimates, GRB 240218A is inside 68% prediction band for both 'Amati' and 'Yonetoku' relations derived for the sample of

300 long KW GRBs with known redshifts (Tsvetkova et al., 2017; Tsvetkova et al., 2021), see http://www.ioffe.ru/LEA/GRBs/GRB240218_T07200/GRB240218A_rest_frame.pdf

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/35758. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...