TITLE: GCN CIRCULAR NUMBER: 40121 SUBJECT: Konus-Wind detection of GRB 250407A DATE: 25/04/08 16:13:31 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 250407A ( Fermi-GBM detection: The Fermi GBM team, GCN 40104; Mukherjee & Meegan, GCN 40114; SVOM/GRM observation: Wang et al., GCN 20120) triggered Konus-Wind (KW) at T0=56895.249 s UT (15:48:15.249). The burst afterglow was detected and localized by SRG/ART-XC (Molkov et al. 2025, GCN 40110) and Swift-XRT (Dichiara et al. 2025, GCN 40113). The burst light curve shows a bright pulse which starts at ~T0-6 s and has a total duration of ~20 s. A weaker emission can be traced at least to ~T0+50 s. The emission in the main pulse is seen up to ~15 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250407_T56895/ As observed by Konus-Wind, the burst had a fluence of (1.57 ± 0.04)x10^-4 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 5.292 s, of (1.41 ± 0.05)x10^-4 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+15.616 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 = -1.02 (-0.03,+0.03), the high energy photon index beta = -2.27 (-0.07,+0.06), the peak energy Ep = 648 (-44,+46) keV, chi2 = 162/97 dof. The spectrum near the peak count rate (measured from T0+5.888 s to T0+7.424 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 = -0.76 (-0.06,+0.07), the high energy photon index beta = -2.38 (-0.14,+0.11), the peak energy Ep = 833 (-99,+106) keV, chi2 = 78/65 dof. 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/40121. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...