TITLE: GCN CIRCULAR NUMBER: 43214 SUBJECT: Konus-Wind detection of GRB 251222A / EP251222b DATE: 25/12/23 12:47:21 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: The long-duration GRB 251222A (Fermi-GBM detection: The Fermi GBM team, GCN 43186; SVOM detection: Yang et al., GCN 43188, Wang et al., GCN 43202), associated with the Einstein Probe X-ray transient EP251222b (Guo et al., GCN 43201), triggered Konus-Wind (KW) at T0=61605.670 s UT (17:06:45.670). The burst shows multiple emission pulses in the interval from T0-50 s to T0+33 s and has a total duration of ~83 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251222_T61605/ As observed by Konus-Wind, the burst had the fluence of (9.92 ± 0.94)x10^-6 erg/cm^2 and the 64-ms peak energy flux, measured from T0 + 4.864 s, of (2.51 ± 0.32)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the brightest part of the burst (measured from T0 to T0+33.024 s) is best fit in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.45 (-0.21, + 0.24) and Ep = 102(-16,+17) keV, chi^2 = 94/98 dof. The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 15 MeV range by a CPL model with alpha = -1.23 (-0.20, + 0.23)and Ep = 131(-14,+18) keV, chi^2 = 69/83 dof. Assuming the redshift z=3.121 (Saccardi et al., GCN 43204) 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 (2.15 ± 0.20)x10^53 erg, the isotropic peak luminosity L_iso to (2.24 ± 0.28)x10^53 erg/s, the rest-frame peak energy of the time-integrated spectrum Ep,i,z to (420 ± 68) keV, and the rest-frame peak energy at the peak of the emission Ep,p,z to (540 ± 66) keV. With the obtained estimates, GRB 251222A is consistent with 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/GRB251222_T61605/GRB251222A_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/43214. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...