GCN Circular 27669

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 short burst from SGR 1935+2154
(INTEGRAL detection: Mereghetti et al., GCN Circ. 27668
Not found
 
 
,
Atel #13685; AGILE detection: Tavani et al., Atel #13686)
triggered Konus-Wind at T0=52464.084 s UT (14:34:24.084)
on 2020 April 28. The burst Earth-crossing time,
T0Earth = 52464.444 s UTC (14:34:24.444), is consistent
with the radio burst from SGR 1935+2154 reported in
Scholz, ATel #13681 and Bochenek et al., Atel #13684.

The light curve shows a multipeaked structure
started at ~T0-0.2 s with a total duration of ~0.5 s.
The emission is seen up to ~250 keV.

The Konus-Wind light curve of this burst is available at
http://www.ioffe.ru/LEA/SGRs/200428_T52464/

As observed by Konus-Wind, the burst
had a fluence of 7.63(-0.75,+0.75)x10^-7 erg/cm2,
and a 16-ms peak flux, measured from T0+0.004 s,
of 9.10(-2.29,+2.29)x10^-6 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 = -0.52(-0.50,+0.57)
and Ep = 82(-9,+12) keV (chi2 = 14/24 dof).

A double blackbody function fits this spectrum equally well
(chi2 = 15/23 dof), with
the cold BB temperature of 9.9 (-4.3,+3.9) keV and
the hot BB temperature of 27.4 (-5.1,+9.2) keV.

The burst temporal structure and hardness differ from a
typical SGR burst and resemble the short hard bursts
(Ep ~ 80 - 100 keV) associated with SGR 1900+14,
observed on 1998 October 22 at 15:40:47.4 UT and on
1999 January 10 at 08:39:01.4 UT (Woods et al., ApJL 527,
47, 1999, Aptekar et al., ApJSS 137, 227, 2001), suggesting
a possibly different emission mechanism of such SGR bursts.

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