TITLE:   GCN CIRCULAR
NUMBER:  30157
SUBJECT: Konus-Wind detection of GRB 210606B
DATE:    21/06/09 10:06:48 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

D. Frederiks, S. Golenetskii, A.Lysenko, A. Ridnaia,
D. Svinkin, A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long GRB 210606B (GECAM detection: Cai et al., GCN 30138;
BALROG localization: Kunzweiler et al., GCN Circ. 30139;
AGILE detection: Ursi et al., GCN 30142;
Fermi GBM detection:  Malacaria & Meegan, GCN 30147;
IPN localization: Hurley et al., GCN Circ. 30154;)
triggered Konus-Wind (KW) at T0=81665.249 s UT (22:41:05.249).

The burst light curve contains two major emission episodes:
a bright, multi-peaked emission complex in the interval from ~T0-2 s to ~T0+30 s;
and the second, much weaker episode, which starts at ~T0+195 s, and has a duration of ~70 s.
The emission in the main episode is seen up to ~2 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210606_T81665/

As observed by Konus-Wind, the burst had
a fluence of (8.1 ± 0.7)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 4.224 s,
of (1.7 ± 0.2)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The spectrum of the main episode (measured from T0 to T0+33.024 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.04 (-0.06,+0.07),
the high energy photon index beta = -2.61 (-0.54,+0.24),
the peak energy Ep = 309 (-27,+31) keV,
chi2 = 80/97 dof.

The spectrum of the second episode (measured from T0+193.536 to T0+259.072 s)
is best fit in the 20 keV - 20 MeV range
by the a simple power law with the photon index of 2.1 (-0.14,+0.15), chi2 = 94/99 dof.

The spectrum near the peak count rate (measured from T0+0.256
to T0+13.824 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.08 (-0.07,+0.08),
the high energy photon index beta = -2.67 (-1.76,+0.33),
the peak energy Ep = 345 (-42,+48) keV,
chi2 = 84/97 dof.

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.