Swift observation of the magnetar SGR 1935+2154 following the detection of several bursts

ATel #14388; A. Borghese, F. Coti Zelati, N. Rea (ICE-CSIC, IEEC), P. Esposito (IUSS), G. L. Israel (INAF), on behalf of a larger collaboration
on 12 Feb 2021; 12:00 UT
Credential Certification: Alice Borghese ([email protected])

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The magnetar SGR 1935+2154 emitted several hard X-ray bursts between 2021 January 27 and February 7 (GCN #29363, #29373, #29374, #29381, #29425, Atel #14359). These bursts represent the first flaring activity detected in the X-ray band since the last outburst, which started on 2020 April 27 (Borghese et al. 2020, ApJL, 902, L2; Younes et al. 2020, ApJL, 904, L21).

Here, we report the results of a Swift/XRT observation of SGR 1935+2154 performed on 2021 February 11, as soon as the source became visible again.

The source is detected with a net count rate of 0.034(6) counts/s in the 0.3-10 keV energy interval. The spectrum is well described by an absorbed blackbody model. The hydrogen column density was fixed to 2.3 x 10²² cm^-2, which is the value derived from archival high signal-to-noise Chandra and XMM-Newton data (Coti Zelati et al. 2018, MNRAS, 474, 961). The best-fitting temperature and radius for the thermal component are 0.47(8) keV and 1.5(5) km (assuming a distance of 6.6 kpc; Zhou et al. 2020, ApJ, 905, 99). Uncertainties are at 1 sigma confidence level.

We measured a slight enhancement of the persistent X-ray flux. The observed flux was about 1 x 10^-12 erg cm^-2 s^-1 (0.3-10 keV), a factor of about 2 higher than the quiescent level and a factor of about 5 lower than the flux measured at the peak of the 2020 outburst.