TITLE: GCN CIRCULAR NUMBER: 43703 SUBJECT: Konus-Wind detection of GRB 260209B DATE: 26/02/11 19:06:19 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 long-duration, hard-spectrum GRB 260209B triggered Konus-Wind (KW) at T0=66273.996 s UT (18:24:33.996). The burst consists of two bright, multi-peaked emission pulses and has a total duration of ~26 s. The emission is seen up to ~7 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB260209_T66273/ As observed by Konus-Wind, the burst had the fluence of (3.44 ± 0.35)x10^-5 erg/cm^2 and the 64-ms peak energy flux, measured from T0 + 2.880 s, of (3.70 ± 0.28)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+24.832 s) is best fitted in the 20 keV - 15 MeV range by a power law with exponential cutoff (CPL) model dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -1.34 (-0.04, + 0.05) and Ep = 1340(-257,+343) keV, chi^2 = 112/98 dof. Fitting this spectrum by a Band GRB function yields the same values of alpha and Ep, and only an upper limit on the high energy photon index beta of -2.7 The spectrum near the peak count rate (measured from T0 to T0+8.448 s) is best fitted in the 20 keV - 15 MeV range by a CPL model with alpha = -1.25 (-0.3, + 0.04)and Ep = 1704(-233,+277) keV, chi^2 = 97/85 dof. Fitting this spectrum by a Band function yields the same values of alpha and Ep, and only an upper limit on the high energy photon index beta of -2.8 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/43703. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...