TITLE:   GCN CIRCULAR
NUMBER:  31513
SUBJECT: Konus-Wind detection of an intermediate flare from SGR 1935+2154 on January 20
DATE:    22/01/21 16:42:21 GMT
FROM:    Anna Ridnaia at Ioffe Institute  <ridnaia@mail.ioffe.ru>

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

The bright burst from SGR 1935+2154
(IPN triangulation: Kozyrev et al., GCN Circ. 31512)
triggered Konus-Wind at T0=35475.962 s UT (09:51:15.962)
on 2021 January 20.

The light curve shows a single pulse with a sharp(<10 ms) rise
and a total duration of ~1.2 s.
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/220120_T35475/

As observed by Konus-Wind, the burst
had a fluence of 7.54(-0.19,+0.19)x10^-6 erg/cm2,
and a 16-ms peak flux, measured from T0+0.012 s,
of 1.08(-0.11,+0.11)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+1.024 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 = 0.17(-0.26,+0.27)
and Ep = 43(-1,+1) keV (chi2 = 44/25 dof).

The rather long duration of the event along with the
large measured energy fluence put the burst in the class
of "intermediate" SGR flares.

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