Persistent Emission Properties of SGR J1935+2154 During Its 2020 Active Episode

TL;DR

This study analyzes the persistent X-ray emission of SGR J1935+2154 during its 2020 active episode, revealing complex magnetic field topology and detailed spectral and timing properties after a burst storm including an associated fast radio burst.

Contribution

It provides the first detailed spectral and temporal analysis of SGR J1935+2154's emission during its 2020 active phase, highlighting a likely highly non-dipolar magnetic field topology.

Findings

Detection of pulsed X-ray emission in XMM-Newton data

Average spin-down rate of 1.6×10⁻¹¹ s s⁻¹

Surface magnetic field strengths exceeding 4.4×10¹⁴ G in localized regions

Abstract

We present detailed spectral and temporal characteristics of the persistent X-ray emission of SGR J1935+2154 based on our XMM-Newton and Chandra observations taken in the aftermath of its April 2020 burst storm, during which hundreds of energetic X-ray bursts were emitted, including one associated with an extraordinary fast radio burst. We clearly detect the pulsed X-ray emission in the XMM-Newton data. An average spin-down rate of 1.6$\times$10$^{-11}$ s s$^{-1}$ is obtained using our spin period measurement combined with three earlier values reported from the same active episode. Our investigations of the XMM-Newton and Chandra spectra with a variety of phenomenological and physically-motivated models, concluded that the magnetic field topology of SGR J1935+2154 is most likely highly non-dipolar. The spectral models indicate that surface field strengths in somewhat localized regions substantially exceed the polar value of 4.4$\times$10$^{14}$ G inferred from a spin-down torque associated with a rotating magnetic dipole.