INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154

S. Mereghetti; V. Savchenko; C. Ferrigno; D. Götz; M. Rigoselli; A. Tiengo; A. Bazzano; E. Bozzo; A. Coleiro; T. J. -L. Courvoisier; M. Doyle; A. Goldwurm; L. Hanlon; E. Jourdain; A. von Kienlin; A. Lutovinov; A. Martin-Carrillo; S. Molkov; L. Natalucci; F. Onori; F. Panessa; J. Rodi; J. Rodriguez; C. Sánchez-Fernández; R. Sunyaev; P. Ubertini

doi:10.3847/2041-8213/aba2cf

paper

INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154

arXiv:2005.06335 · doi:10.3847/2041-8213/aba2cf

Abstract

We report on INTEGRAL observations of the soft $γ$ -ray repeater SGR 1935+2154 performed between 2020 April 28 and May 3. Several short bursts with fluence of $\sim 1 0^{- 7} - 1 0^{- 6}$ erg cm $^{- 2}$ were detected by the IBIS instrument in the 20-200 keV range. The burst with the hardest spectrum, discovered and localized in real time by the INTEGRAL Burst Alert System, was spatially and temporally coincident with a short and very bright radio burst detected by the CHIME and STARE2 radio telescopes at 400-800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by $\sim$ 29 ms time intervals, superimposed on a broad pulse lasting $\sim$ 0.6 s. The brightest peak had a delay of 6.5 $\pm$ 1.0 ms with respect to the 1.4 GHz radio pulse (that coincides with the second and brightest component seen at lower frequencies). The burst spectrum, an exponentially cut-off power law with photon index $Γ = 0. 7_{- 0.2}^{+ 0.4}$ and peak energy $E_{p} = 65 \pm 5$ keV, is harder than those of the bursts usually observed from this and other magnetars. By the analysis of an expanding dust scattering ring seen in X-rays with the {\it Neil Gehrels Swift Observatory} XRT instrument, we derived a distance of 4.4 $_{- 1.3}^{+ 2.8}$ kpc for SGR 1935+2154, independent of its possible association with the supernova remnant G57.2+0.8. At this distance, the burst 20-200 keV fluence of $(6.1 \pm 0.3) \times 1 0^{- 7}$ erg cm $^{- 2}$ corresponds to an isotropic emitted energy of $\sim 1.4 \times 1 0^{39}$ erg. This is the first burst with a radio counterpart observed from a soft $γ$ -ray repeater and it strongly supports models based on magnetars that have been proposed for extragalactic fast radio bursts.

Accepted for publication on The Astrophysical Journal Letters - revised accepted version

INTEGRAL discovery of a burst with associated radio emission from the magnetar SGR 1935+2154

Abstract

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