[vsnet-grb-info 16422] Konus-Wind observation of a bright burst from SGR 1935+2154

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17703
SUBJECT: Konus-Wind observation of a bright burst from SGR 1935+2154
DATE:    15/04/14 15:02:18 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred at mail.ioffe.ru>

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

A bright, short-duration, soft burst which is likely originated from
SGR 1935+2154 (IPN triangulation: Golenetskii et al., GCN 17699)
triggered Konus-Wind at T0=41064.683 s UT (11:24:24.683).

The light curve shows a single pulse with a sharp(<10 ms) rise
and a total duration of ~1.7 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/150412_T41064/

As observed by Konus-Wind, the burst had a fluence
of 2.60(-0.03,+0.03)x10^-5 erg/cm2, and a 16-ms peak flux,
measured from T0+0.800 s, of 2.3(-0.1,+0.1)x10^-5 erg/cm2/s
(both in the 20 - 200 keV energy range).

The time-averaged spectrum (measured from T0 to T0+9.472 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 = +0.21(-0.13,+0.13),
and Ep = 36.5(-0.6,+0.6) keV
(chi2 = 28.6/31 dof).
A double blackbody fit to this spectrum yields
the lower temperature kT1 = 6.4 (-0.7,+0.7) keV and
the higher temperature kT2 = 12.3 (-0.6,+0.7) keV
(chi2=36.3/30 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.
The measured spectral parameters are in typical range for
bright short and intermediate SGR bursts;
also, they resemble the fits reported by Swift/BAT
and Fermi/GBM for much weaker and shorter bursts detected
during the recent SGR 1935+2154 activity in February, 2015
(Lien et al., GCN 17490; Burns & Younes, GCN 17496).

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