TITLE: GCN CIRCULAR NUMBER: 30921 SUBJECT: Konus-Wind detection of GRB 210928A DATE: 21/10/04 12:37:31 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru> A. Ridnaia, D. Frederiks, S. Golenetskii, A. Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 210928A (Fermi-LAT detection: Axelsson et al., GCN 30912; Fermi-GBM observation: Fletcher & Meegan, GCN 30913) triggered Konus-Wind at T0=7234.398 s UT (02:00:34.398). The burst light curve shows a single multi-peaked pulse started at ~T0-4.3 s with a total duration of ~27.3 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/GRB210928_T07234/ As observed by Konus-Wind, the burst had a fluence of 6.79(-0.66,+0.71)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+14.416 s, of 6.45(-1.72,+1.77)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+24.320 s) is best fit in the 20 keV - 6 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.34(-0.15,+0.16), the high energy photon index beta = -2.55(-0.35,+0.21), the peak energy Ep = 361(-33,+38) keV (chi2 = 61/78 dof). The spectrum near the maximum count rate (measured from T0+8.448 to T0+16.128 s) is best fit in the 20 keV - 6 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.07(-0.21,+0.23), the high energy photon index beta = -2.73(-0.55,+0.28), the peak energy Ep = 328(-30,+36) keV (chi2 = 75/78 dof). All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.