GCN Circular 43703

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