X-ray monitoring of the active magnetar SGR 1935+2154

ATel #13720; A. Borghese, N. Rea, F. Coti Zelati (ICE-CSIC, IEEC), G. L. Israel (INAF), P. Esposito (IUSS), on behalf of a larger collaboration.
on 8 May 2020; 16:49 UT
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Credential Certification: Alice Borghese (borghese@ice.csic.es)

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After the re-activation of the magnetar SGR 1935+2154 (e.g., ATEL #13675, #13678), we are monitoring it with NuSTAR, NICER and Swift. Several ms-long X-ray bursts were detected, showing that the source is still in a burst-active phase.

The NuSTAR observation was performed on 2020 May 2, and the NICER pointing was acquired on 2020 April 29-30. We are planning further observations with both satellites in the coming weeks.

The source was detected up to 25 keV in the NuSTAR data. The 3-25 keV background-subtracted spectrum is well described by a power law with photon index of 1.43 +/- 0.04 (1 sigma c.l.). The observed flux was about 5e-12 erg/s/cm2 (3-25 keV). We detect the spin period of SGR 1935+2154 at P = 3.247331(3) s (1 sigma c.l.). The pulse profile is double-peaked, differently from the single-peaked profile observed in previous epochs (Israel et al. 2016, MNRAS 457, 3448), with a pulsed fraction of about 23%.

The X-ray Telescope on board Swift is monitoring the source with a daily cadence, both in the photon counting and windowed timing modes. In the last 4-ks observation on May 7, the observed flux was about 1.5e-12 erg/s/cm2 (0.3-10 keV), still a factor of 2.5 brighter than the last pre-outburst observation performed on April 23. Additional observations are scheduled for the next few days.

To facilitate coordination of simultaneous radio and X-ray observations of this target, we encourage interested research teams to contact us for more details on the schedule of future X-ray observations.

We thank the NuSTAR, NICER and Swift teams for the prompt reaction after our trigger, and for the large effort in planning these and our future observations.