TITLE:   GCN CIRCULAR
NUMBER:  30599
SUBJECT: Konus-Wind detection of a burst from SGR 1935+2154 on 2021 August 5
DATE:    21/08/07 06:42:27 GMT
FROM:    Anna Ridnaia at Ioffe Institute  <ridnaia@mail.ioffe.ru>

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

The short, soft burst from SGR 1935+2154
(IPN triangulation: Svinkin et al., GCN 30598)
triggered Konus-Wind on 2021 August 5 at
T0=539.958 s UT (00:08:59.958).

The burst light curve shows a single pulse
started at ~T0-70 ms with a total duration of ~165 ms.
The emission is seen up to ~200 keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/SGRs/210805_T00539/

As observed by Konus-Wind, the burst
had a fluence of 1.29(-0.08,+0.08)x10^-6 erg/cm2,
and a 2-ms peak flux, measured from T0-0.014 s,
of 1.62(-0.35,+0.35)x10^-5 erg/cm2/s
(both in the 20 - 500 keV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+0.064 s)
is best fit in the 20 - 200 keV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = 0.39(-0.99,+1.12)
and Ep = 33(-6,+4) keV (chi2 = 11/12 dof).

All the quoted errors are at the 90% confidence level.
All the quoted values are preliminary.