[vsnet-grb-info 25531] Konus-Wind observation of a bright burst from SGR 1935+2154

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27631
SUBJECT: Konus-Wind observation of a bright burst from SGR 1935+2154
DATE:    20/04/23 13:21:05 GMT
FROM:    Anna Ridnaia at Ioffe Institute  <ridnaia at mail.ioffe.ru>

A. Ridnaia, S. Golenetskii, R. Aptekar, 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
(CALET-GRBM detection: Cherry et al., GCN Circ. 27623;
IPN triangulation: Hurley et al., GCN Circ. 27625)
triggered Konus-Wind at T0=31996.933 s UT (08:53:16.933)
on 2020 April 22.

The light curve shows a single pulse with a sharp rise
and a total duration of ~0.6 s.
The emission is seen up to ~250 keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/SGRs/200422_T31996/

As observed by Konus-Wind, the burst
had a fluence of 1.15(-0.03,+0.03)x10^-5 erg/cm2,
and a 16-ms peak flux, measured from T0+0.072 s,
of 2.75(-0.23,+0.23)x10^-5 erg/cm2/s
(both in the 20 - 200 keV energy range).

The burst spectrum (measured from T0 to T0+0.256 s)
is well fit by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.06(-0.24,+0.25)
and Ep = 52(-2,+2) keV (chi2 = 30/25 dof).

A double blackbody function fits this spectrum less well
(chi2 = 40/24 dof), with
the cold BB temperature of 9.4 (-4.5,+1.9) keV and
the hot BB temperature of 18.9 (-3.7,+5.3) keV.

Among 17 bright bursts from SGR 1935+2154 detected by KW
so far this event is the second most fluent (after
the April 12, 2015 Intermediate Flare; Kozlova et al. 2016,
MNRAS 460, 2008) and the second most luminous (after
the November 5, 2019 burst; Ridnaia et al., GCN 26242).
Also, the spectrum of the burst is characterized by the
hardest peak energy so far; a typical Ep(CPL) for the
KW sample is in the 30-40 keV range.

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