GCN Circular 31325

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

The very bright burst from SGR 1935+2154
(AGILE observations: Ursi et al., GCN Circ. 31296
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 ;
Swift-BAT detection: Palmer et al., ATel #15141)
triggered Konus-Wind at T0=13350.516 s UT (03:42:30.516)
on 2021 December 24.

The light curve shows a single pulse with a sharp(<10 ms) rise
and a total duration of ~1.3 s.
The emission is seen up to ~250 keV

The Konus-Wind light curve of this SGR is available at
http://www.ioffe.ru/LEA/SGRs/211224_T13350/

As observed by Konus-Wind, the burst
had a fluence of 1.09(-0.02,+0.02)x10^-5 erg/cm2,
and a 16-ms peak flux, measured from T0+0.640 s,
of 1.33(-0.09,+0.09)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+8.448 s)
is best fit in the 20 - 250 keV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = 0.32(-0.26,+0.27)
and Ep = 36(-1,+1) keV (chi2 = 35/29 dof).
The 2BB fit to this spectrum yields
the cool BB temperature kT1 = 5.2 (-1.5,+1.9) keV
and the hot BB temperature kT2 = 11.3 (-0.6,+1.3) keV
(chi2=37/28 dof).

The rather long duration of the burst along with the
large measured energy fluence put the burst in the class
of "intermediate" SGR bursts. Among 43 bright bursts
from SGR 1935+2154 detected by KW so far this event is
the fourth most fluent. The measured spectral
parameters are in typical range for bright short and
intermediate SGR bursts.

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