TITLE: GCN CIRCULAR NUMBER: 41508 SUBJECT: Konus-Wind detection of GRB 250821B DATE: 25/08/23 16:06:36 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 bright, long-duration GRB 250821B (Ferm-GBM detection: The Fermi GBM team, GCN 41473; Smith and Meegan, GCN 41477; SVOM-GRM detection: Tan et al., GCN 41486; IPN localization Kozyrev et al., GCN 41498) triggered Konus-Wind (KW) at T0=58069.135 s UT (16:07:49.135). The burst light curve shows a single emission pulse with a total duration of ~2.5 s. The emission is seen up to ~5 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB250821_T58069/ As observed by Konus-Wind, the burst had a fluence of (1.34 ± 0.13)x10^-5 erg/cm^2 and a 64-ms peak energy flux, measured from T0 + 0.512 s, of (1.77 ± 0.17)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+8.448 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 = -0.60 (-0.14,+0.15), the high energy photon index beta = -2.24 (-0.13,+0.10), the peak energy Ep = 193(-18,+21) keV, chi2 = 70/96 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/41508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...