The X-Ray Reactivation of the Radio Bursting Magnetar SGR J1935+2154

• Published in: Astrophysical journal. Letters 2020-10, Vol.902 (1), p.L2
• Main Authors: Borghese, A., Zelati, F. Coti, Rea, N., Esposito, P., Israel, G. L., Mereghetti, S., Tiengo, A.
• Format: Article
• Language: English
• Subjects: Activation; Blackbody; Gamma rays; Luminosity; Magnetars; Magnetic properties; Neutron stars; Radio bursts; Radio pulsars; Spectroscopic telescopes; X ray spectra; X-ray bursts; X-ray transient sources
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/aba82a

A few years after its discovery as a magnetar, SGR J1935+2154 started a new burst-active phase on 2020 April 27, accompanied by a large enhancement of its X-ray persistent emission. Radio single bursts were detected during this activation, strengthening the connection between magnetars and fast radio bursts. We report on the X-ray monitoring of SGR J1935+2154 from ∼3 days prior to ∼3 weeks after its reactivation, using Swift, the Nuclear Spectroscopic Telescope Array (NuSTAR), and the Neutron Star Interior Composition Explorer (NICER). We detected X-ray pulsations in the NICER and NuSTAR observations, and constrained the spin period derivative to s s −1 (3 σ c.l.). The pulse profile showed a variable shape switching between single and double-peaked as a function of time and energy. The pulsed fraction decreased from ∼34% to ∼11% (5–10 keV) over ∼10 days. The X-ray spectrum was well fit by an absorbed blackbody model with temperature decreasing from kT BB  ∼ 1.6 to 0.45–0.6 keV, plus a nonthermal power-law component (Γ ∼ 1.2) observed up to ∼25 keV with NuSTAR. The 0.3–10 keV X-ray luminosity increased in less than 4 days from erg s −1 to about erg s −1 and then decreased again to erg s −1 over the following 3 weeks of the outburst, where d 6.6 is the source distance in units of 6.6 kpc. We also detected several X-ray bursts, with properties typical of short magnetar bursts.