TITLE:   GCN CIRCULAR
NUMBER:  30144
SUBJECT: Konus-Wind detection of GRB 210605A (short/hard)
DATE:    21/06/07 13:07:38 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 short/hard GRB 210605A (Fermi GBM Final Real-time Localization:
Fermi GBM team, GCN 30127; IPN localization: Svinkin et al., GCN 30143)
triggered Konus-Wind (KW) at T0=18539.058 s UT (05:08:59.058).

The burst light curve shows a single, hard-spectrum pulse,
which starts at ~T0-0.038 s, peaks at ~T0-0.032 s,
and has the total duration of ~0.35 s (T100, 20-1500 keV).
The emission in this pulse is seen up to ~10 MeV.
In the soft 20-100 keV KW band, we note a hint for an extended emission up to ~T0+25 s.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210605_T18539/

As observed by Konus-Wind, the burst had
a fluence of (4.2 ± 1.1)x10^-6 erg/cm^2 and
a 16-ms peak energy flux, measured from T0-0.032,
of (5.7 ± 1.4)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst (measured from T0 to T0+0.256 s)
is best fit 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 = -0.75(-0.18,+0.21) and Ep = 2079(-614,+986) keV (chi2 = 23/44 dof).
Fitting this spectrum by a Band function yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.1 (chi2 = 23/43 dof).

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