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.