[vsnet-grb-info 25567] Konus-Wind observation of a very intense bursting activity of SGR 1935+2154

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27667
SUBJECT: Konus-Wind observation of a very intense bursting activity of SGR 1935+2154
DATE:    20/04/28 18:47:28 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 onset of a new period of activity of SGR 1935+2154
(Swift-BAT detection: Barthelmy et al., GCN Circ. 27657,
Palmer, GCN Circ. 27665;
Fermi-GBM observation: Fletcher, GCN Circ. 27659;
MAXI-GSC detection: Sugawara et al., GCN Circ. 27661;
CALET-GBM observation: Ricciarini et al., GCN Circ. 27663;
AstroSat-CZTI detection: Marathe et al., GCN Circ. 27664)
has been detected by Konus-Wind on 2020 April 27.

A series of several tens of bursts triggered Konus-Wind at
66696.729 s UT (18:31:36.729). The series consists of
two very crowded clusters:
from -0.252 s to 8 s and
from 77 s to 116 s relative to the trigger time
(numerous weaker bursts are seen between intense bursts).

The most intense episode of the cluster started at ~85 s
after trigger time. It had a duration of ~23.6 s,
a fluence of 1.09(-0.02,+0.02)x10^-4 erg/cm2,
and a 64-ms peak flux, measured from T0+95.680 s,
of 2.28(-0.27,+0.29)x10^-5 erg/cm2/s
(both in the 20 - 200 keV energy range).

The time-integrated spectrum of this cluster
(measured from T0+74.496 to T0+91.392)
is well fit by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.48(-0.17,+0.18)
and Ep = 35(-1,+1) keV (chi2 = 47/29 dof).
A double blackbody function fits this spectrum equally well
(chi2 = 38/28 dof), with
the cold BB temperature of 4.7 (-0.5,+0.6) keV and
the hot BB temperature of 12.5 (-0.4,+0.5) keV.

The Konus-Wind light curve of this trigger is available at
http://www.ioffe.ru/LEA/SGRs/200427_T66696/

Further SGR 1935+2154 bursts have triggered KW on 2020
April 27, so far, at 71024.348 s UT (19:43:44.348),
79162.174 s UT (21:59:22.174), and 85471.654 s UT
(23:44:31.654).

This burst cluster resembles the series of bursts from
SGR 1900+14 and SGR 1806-20 detected about three months
before giant flares from these sources observed on
1998 August 27 and 2004 December 27, respectively
(Aptekar et al., ApJSS v. 137, p. 227, 2001, Golenetskii
et al., GCN Circ. 2769, Golenetskii et al., GCN Circ. 2896).

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