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GCN Circular 19613

Subject
Konus-Wind observation of a bright burst from SGR 1935+2154
Date
2016-06-28T14:29:17Z (8 years ago)
From
Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>
D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov,
D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline,
on behalf of the Konus-Wind team, report:

The bright burst from SGR 1935+2154 (Swift detection:
Barthelmy et al., GCN 19590; Cummings et al., GCN 19596;
Fermi/GBM detection: Younes et al., GCN 19598)
triggered Konus-Wind at T0=50073.909 s UT (13:54:33.909)
on 2016 June 26.

The light curve shows a single pulse with a sharp rise
and a total duration of ~0.8 s.
The emission is seen up to ~200 keV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/SGRs/160626_T50073/

As observed by Konus-Wind, the burst had a fluence
of 1.28(-0.02,+0.02)x10^-5 erg/cm2, and a 16-ms peak flux,
measured from T0, of 2.1(-0.1,+0.1)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 = -0.17(-0.16,+0.16),
and Ep = 37.5(-1.1,+1.0) keV
(c-stat = 16.1/25 dof).
A double blackbody function fits this spectrum equally well
(c-stat = 17.3/26 dof), with
the cold BB temperature of 6.6 (-0.6,+0.6) keV and
the hot BB temperature of 13.9 (-0.6,+0.8) keV.

This event continues a series of about a dozen bright bursts
from SGR 1935+2154 detected by Konus-Wind in May-June, 2016.
Varying in their durations and energy fluences,
these bursts demonstrate spectral properties and peak
luminosities similar to those of the 1.7s-long "intermediate"
flare (IF) from this source (Kozlova et al. 2016, MNRAS 460, 2008).

All the quoted errors are at the 1 sigma confidence level.
All the quoted values are preliminary.
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