Konus-Wind observation of hard X-ray counterpart of the radio burst from SGR 1935+2154

ATel #13688; A. Ridnaia, S. Golenetskii, R. Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Tsvetkova, A. Lysenko (Ioffe Institute), and T. Cline
on 29 Apr 2020; 19:42 UT
Credential Certification: Anna Kozlova (ann_kozlova@mail.ioffe.ru)

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The short burst from SGR 1935+2154 (GCN #27668, Atel: #13685, #13686, #13687) 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 ATel: #13681, #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.

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.

This Atel is a copy of circular distributed via GCN

Konus-Wind is a gamma-ray spectrometer operating onboard the NASA GGS-WIND spacecraft since November 1994. It contains two NaI scintillation detectors continuously observing the whole sky and covers the energy band from ~20 keV to ~15 MeV.

Konus-Wind light curve of the SGR 1935+2154 burst