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  • The X-Ray Reactivation of t...
    Borghese, A.; Zelati, F. Coti; Rea, N.; Esposito, P.; Israel, G. L.; Mereghetti, S.; Tiengo, A.

    Astrophysical journal. Letters, 10/2020, Volume: 902, Issue: 1
    Journal Article

    Abstract 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.