INTEGRAL Discovery of a Burst with Associated Radio Emission from the Magnetar SGR 1935+2154

Abstract

We report on International Gamma-Ray Astrophysics Laboratory (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 erg cm−2 were detected by the Imager on-board INTEGRAL (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 Canadian Hydrogen Intensity Mapping Experiment (CHIME) and Survey for Transient Astronomical Radio Emission 2 (STARE2) radio telescopes at 400–800 MHz and 1.4 GHz, respectively. Its lightcurve shows three narrow peaks separated by ∼29 ms time intervals, superimposed on a broad pulse lasting ∼0.6 s. The brightest peak had a delay of 6.5 ± 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 cutoff power law with photon index and peak energy , 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 Neil Gehrels Swift Observatory X-ray Telescope (XRT) instrument, we derived a distance of 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 erg cm−2 corresponds to an isotropic emitted energy of 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.

Constraining the X-Ray–Infrared Spectral Index of Second-timescale Flares from SGR 1935+2154 with Palomar Gattini-IR

“…As the only other X-ray burst from SGR 1935+2154 that has been reported with a multiwavelength (radio) counterpart, we compare the NIR limits to the observed spectral energy distribution (SED) of FRB 200428. The striking time coincidence between two X-ray pulses observed in the X-ray burst associated with FRB 200428 (Li et al 2020a;Mereghetti et al 2020) with the two radio pulses detected by CHIME (The CHIME/FRB Collaboration et al 2020) potentially suggests a common emission source extending from the X-ray to radio frequencies. Li et al (2020a) show that the HXMT X-ray burst associated FRB 200428 was characterized with a hard powerlaw spectrum with a photon index of Γ≈1.5, corresponding to a flux density dependence of f ν ∝ν −0.5 and fluence dependence of n µ  0.5 .…”

Implications of a Fast Radio Burst from a Galactic Magnetar

“…The observational situation changed abruptly with the recent discovery of a luminous millisecond radio burst from the Galactic magnetar SGR 1935+2154 (Bochenek et al 2020c;CHIME/FRB Collaboration et al 2020b). The double-peaked burst, detected independently by CHIME (Bandura et al 2014) and STARE2 (Bochenek et al 2020b), was temporally coincident with an X-ray burst of significantly larger fluence Mereghetti et al 2020a;Ridnaia et al 2020e;Tavani et al 2020). This FRB is still a factor of ∼10 less energetic than the weakest FRB previously detected from any localized cosmological FRB source.…”

“…The source is associated with supernova remnant (SNR) G57.2+0.8 (Gaensler 2014). Distance estimates are uncertain, ranging from 4.4 to 12.5 kpc (Sun et al 2011;Pavlović et al 2013;Kothes et al 2018;Mereghetti et al 2020a;Zhou et al 2020), and throughout this paper, we adopt a distance of = d d 10 kpc…”

“…This burst's long duration of~1.7 s and large fluence of´-2.5 10 5 erg cm −2 (radiated energy~10 41 erg) place it in the rare class of "intermediate" SGR flares (Mazets et al 1999;Feroci et al 2003;Mereghetti et al 2009;Göǧüś et al 2011). The trend that the bursts from SGR 1935+2154 have become progressively more energetic in the years since its initial discovery (Younes et al 2017) persists with the recent outburst, which is the most energetic yet (Mereghetti et al 2020a;Zhang et al 2020a). Similar behavior was previously observed for SGR1806-20, which culminated with its production of the most energetic magnetar giant flare seen to date (Younes et al 2015).…”

What does FRB light-curve variability tell us about the emission mechanism?

“…However, the origin of FRBs remains an unsolved puzzle. The nature of the underlying object has been identified to be magnetars only very recently by observing a FRB in the Galaxy in the radio and X-ray bands simultaneously (The CHIME/FRB Collaboration et al 2020;Bochenek et al 2020;Mereghetti et al 2020;Li et al 2020;Pearlman et al 2020;Ridnaia et al 2020;Tavani et al 2020). Although this observation is a major landmark for FRB science, many emission models remain valid (Lu et al 2020;Lyutikov & Popov 2020;Margalit et al 2020a;Katz 2020).…”