TITLE: GCN CIRCULAR NUMBER: 40164 SUBJECT: Konus-Wind detection of GRB 250403A DATE: 25/04/17 17:43:37 GMT FROM: Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru> D. Frederiks, A.Lysenko, A. Ridnaya, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report The long GRB 250403A (Fermi GBM detection: Fermi GBM team, GCN 40025; Veres et al., GCN 40060; SVOM detection: Julacanti et al., GCN 40026; AstroSat CZTI detection: Tembhurnikar et al., GCN 40077) 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 ~12 sigma count-rate increase in the interval from T0-0.4 s to T0+11.5 s where T0 = 15:15:22 UT. The KW light curve of this burst is available at http://www.ioffe.ru/LEA/GRBs/GRB250403A/ Modeling the time-integrated spectrum of the burst by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.14 (-0.23, + 0.23) and Ep = 83(-6,+6) keV. In the 10 keV -10 MeV band, standard for the KW analysis, the burst fluence is (2.55 ± 0.18)x10^-6 erg/cm^2 and the 2.944 s peak energy flux is (2.51 ± 0.22)x10^-7 erg/cm^2/s. Assuming the redshift z=1.847 (de Ugarte Postigo et al., GCN 40162) 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 (2.2 ± 0.2)x10^52 erg, the isotropic peak luminosity L_iso to (6.3 ± 0.6)x10^51 erg/s, and the rest-frame peak spectral energy Ep,z to (236 ± 11) keV. With the obtained estimates, GRB 250403A is consistent (inside 68% prediction bands) of both 'Amati' and 'Yonetoku' relations 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/GRB250403A/GRB250403A_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/40164. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...