TITLE:   GCN CIRCULAR
NUMBER:  30866
SUBJECT: Konus-Wind detection of a burst from SGR 1935+2154 on 2021 September 22
DATE:    21/09/23 12:31:24 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:

A short, soft, SGR-like burst
triggered Konus-Wind on 2021 September 22 at
T0=72739.639 s UT (20:12:19.639).

The Konus-Wind ecliptic latitude response is consistent
with the SGR 1935+2154 position. So, taking in account
the ongoing bursting activity of this source, burst
time history, and softness of its spectrum (as observed
by Konus-Wind), we suggest that this burst is likely
originated from SGR 1935+2154.

The burst light curve shows a single pulse
started at ~T0-100 ms with a total duration of ~172 ms.
The emission is seen up to ~200 keV.

The Konus-Wind light curve of this burst is available at
http://www.ioffe.ru/LEA/SGRs/210922_T72739/

As observed by Konus-Wind, the burst
had a fluence of 1.46(-0.08,+0.08)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.024 s,
of 1.59(-0.16,+0.16)x10^-5 erg/cm2/s
(both in the 20 - 500 keV energy range).

The 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 = -0.13(-0.76,+0.85)
and Ep = 37(-6,+4) keV (chi2 = 12/14 dof).

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