TITLE: GCN CIRCULAR NUMBER: 41942 SUBJECT: Konus-Wind detection of GRB 250920B DATE: 25/09/22 18:37:52 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 250920B (Fermi-GBM detection: The Fermi GBM team, GCN 41897; Sonawane and Meegan, GCN 41919; Swift-BAT detection: Gupta et al., GCN 41898; Sakamoto et al., GCN 41923; Glowbug detection: Cheung et al., GCN 41937) triggered Konus-Wind at T0=31587.304 s UT (08:46:27.304). The burst light curve shows a multipeaked structure which starts at ~T0-3.0 s and has a total duration of ~141 s. The emission is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250920_T31587/ As observed by Konus-Wind, the burst had the total fluence of 3.80(-0.78,+0.93)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+6.368 s, of 6.72(-1.17,+1.16)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+131.328 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.41(-0.10,+0.11), the high energy photon index beta = -2.41(-7.59,+0.35), the peak energy Ep = 310(-69,+94) keV (chi2 = 94/97 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.06(-0.10,+0.10), the high energy photon index beta = -2.33(-0.38,+0.18), the peak energy Ep = 296(-38,+52) keV (chi2 = 87/81 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/41942. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...