[vsnet-grb-info 17990] Konus-Wind observation of a bright burst from SGR 1935+2154

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19438
SUBJECT: Konus-Wind observation of a bright burst from SGR 1935+2154
DATE:    16/05/19 14:45:17 GMT
FROM:    Anna Kozlova at Ioffe Institute  <ann_kozlova at mail.ioffe.ru>

A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko, and T. Cline,
on behalf of the Konus-Wind team, report:

The bright, short-duration burst from SGR 1935+2154
(Swift-BAT trigger #686761: D'Avanzo et al., GCN Circ. 19433;
Fermi GBM trigger #bn160518382: Younes, GCN Circ. 19437)
triggered Konus-Wind at T0=32964.102 s UT (09:09:24.102).

The burst light curve shows a single pulse with a total
duration of 150 ms. 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/160518_T32964/

As observed by Konus-Wind, the burst had a fluence
of 1.62(-0.07,+0.07)x10^-6 erg/cm2, and a 16-ms peak flux,
measured from T0+0.014 s, of 1.53(-0.15,+0.15)x10^-5 erg/cm2/s
(both in the 20 - 200 keV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+0.128 s)
is equally well fit in the 20 - 200 keV range
by a power law with exponential cutoff (CPL) model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
and by a sum of two blackbody functions (2BB).
The CPL model best fit parameters are:
alpha = 0.23 (-0.55,+0.61)
and Ep = 29 (-3,+2) keV (chi2 = 8/15 dof).
The 2BB fit to this spectrum yields
the cool BB temperature kT1 = 4.9 (-2.2,+2.1) keV
and the hot BB temperature kT2 = 9.8 (-1.0,+2.5) keV
(chi2=8/14 dof).

Assuming isotropic emission and  the distance to the source
of 9.1 kpc (Gaensler, GCN Circ.16533; Pavlovic et al., 2013;
Kozlova et al., 2016, arXiv:1605.02993), we estimate the
total energy release in the burst E_tot is ~1.6x10^40 erg
and the peak luminosity, L_max, is ~1.5x10^41 erg/s
(both in the 20-200 keV range).

Although this burst is more than order of magnitude less
energetic than the 1.7s-long "intermediate" flare (IF) from
this source on 2015 April 12 (Kozlova et al., 2016), its peak
luminosity is almost comparable to that of the IF.

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