TITLE: GCN CIRCULAR NUMBER: 41166 SUBJECT: Konus-Wind detection of GRB 250725A DATE: 25/07/25 15:53:14 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 GRB 250525A (Fermi-GBM detection: The Fermi GBM team, GCN 41150; Swift detection: Evans et al., GCN 41152; SVOM/GRM observation: Wang et al., GCN 41164) triggered Konus-Wind (KW) at T0=6698.029 s UT (01:51:38.029). The burst shows a multi-peaked structure with a total duration of ~12 s. The emission is seen up to ~1.5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250725_T06698/ As observed by Konus-Wind, the burst had a fluence of (1.19 ± 0.10)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 0.512 s, of (4.16 ± 0.41)x10^-6 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+16.640 s) is best fit in the 20 keV - 15 MeV range by a GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.41 (-0.13,+0.15), the high energy photon index beta = -2.75 (-0.25,+0.18), the peak energy Ep = 155 (-9,+9) keV, chi2 = 89/97 dof. Assuming the redshift z=5.26 (Thakur et al., GCN 41160) 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 (5.85 ± 0.49)x10^53 erg, the isotropic peak luminosity L_iso to (1.30 ± 0.13)x10^52 erg/s, and the rest-frame peak spectral energy Ep,z to (970 ± 56) keV. With the obtained estimates, GRB 250725A 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/GRB250725_T06698/GRB250725A_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/41166. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...