TITLE: GCN CIRCULAR NUMBER: 42448 SUBJECT: Konus-Wind detection of GRB 251016B DATE: 25/10/25 20:36:05 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru> A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long-duration GRB 251016B (Ferm-GBM detection: The Fermi GBM team, GCN 42316; Godwin and Meegan, GCN 42383; CALET-GBM detection: Yamaoka et al., GCN 42320; AstroSat-CZTI detection: Harsha et al., GCN 42324; IPN triangulation: Kozyrev et al., GCN 42403) triggered Konus-Wind at T0=86340.495 s UT (23:59:00.495). The burst light curve shows a single pulse which starts at ~T0-0.5 s and has a total duration of ~18.5 s. The emission is seen up to ~6 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB251016_T86340/ As observed by Konus-Wind, the burst had a fluence of 3.50(-0.18,+0.18)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+2.320 s, of 1.22(-0.11,+0.11)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+11.520 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 = -0.98(-0.06,+0.06), the high energy photon index beta = -2.29(-0.10,+0.08), the peak energy Ep = 226(-18,+19) keV (chi2 = 93/85 dof). The spectrum near the maximum count rate (measured from T0+0.256 to T0+3.328 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 = -0.85(-0.05,+0.06), the high energy photon index beta = -2.41(-0.11,+0.09), the peak energy Ep = 294(-21,+21) keV (chi2 = 67/67 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/42448. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...