TITLE: GCN CIRCULAR NUMBER: 43864 SUBJECT: Konus-Wind detection of GRB 260226A DATE: 26/02/27 13:52:56 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 bright, long-duration GRB 260226A (Fermi-GBM detection: The Fermi GBM team, GCN 43840; Bissaldi eat al., GCN 43851; BALROG localization: Preis and Greiner, GCN 43843; Fermi-LAT detection: Depalo et al., GCN 43844, 43850; AstroSat-CZTI detection: Harsha et al., GCN 43846; NuSTAR-ACS detection: Waratkar et al., GCN 43854; Glowbug detection: Woolf et al., GCN 43855; CALET-GBM detection: Kobayashi et al., GCN 43860) triggered Konus-Wind at T0=38287.440 s UT (10:38:07.440). The burst light curve shows a very bright, multi-peaked emission pulse which starts at ~T0-9 s and has a duration of ~30 s. This pulse is followed by a weaker, smoothly decaying emission tail, visible up to the end of the KW triggered data record (~T0+250 s). The emission is seen up to ~20 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260226_T38287/ As observed by Konus-Wind, the burst had the total fluence of 7.27(-0.17,+0.17)x10^-4 erg/cm2, and the 64-ms peak flux, measured from T0+10.688 s, of 1.33(-0.06,+0.06)x10^-4 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+142.080 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 = -0.93(-0.02,+0.03), the high energy photon index beta = -2.33(-0.07,+0.06), the peak energy Ep = 613(-25,+26) keV (chi2 = 118/97 dof). The spectrum near the maximum count rate (measured from T0+10.240 to T0+10.752 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 = -0.64(-0.06,+0.07), the high energy photon index beta = -2.11(-0.08,+0.07), the peak energy Ep = 772(-77,+80) keV (chi2 = 48/57 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/43864. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...