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arXiv · 2507.19698

The Timing Evolution of the Magnetar Swift J1818.0-1607 During a Period of Reduced Activity

Moaz Abdelmaguid·Paulo C. C. Freire·Joseph D. Gelfand·Yogesh Maan·Samayra Straal·J. A. J. Alford
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Abstract

We report results from an observational campaign of the radio-loud magnetar Swift J1818.0-1607 using the Green Bank Telescope (GBT) at 2.0 GHz, which began in November 2021 during a period of reduced activity approximately 20 months after its March 2020 outburst. Over the 60-day duration reported here, the integrated pulse profile remained consistently stable, exhibiting a single, narrow peak with with a small precursor component and no evidence of a postcursor one. This pulse profile is in sharp contrast to the double-peaked morphology observed during an observing campaign approximately 120 days preceding ours. Along with this change in the integrated pulse profile shape, we also measure a slower spin-down rate compared to the end of that preceding campaign. Together, these differences suggest that a mode-switching event likely occurred between the end of that campaign and the start of ours. Finally, we derived a phase-connected timing solution from our data, from which we inferred a characteristic age of approximately 2500 years, about 2.5 times older than the most recent published estimate, and a surface dipole magnetic field strength of roughly 1 x 10^14 G, nearly three times weaker. These updated estimates reflect the short-term variations in the magnetar's spin-down rate, from which both its age and magnetic field strength are inferred, rather than intrinsic changes in the magnetar itself.

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Moaz Abdelmaguid, Paulo C. C. Freire, Joseph D. Gelfand, Yogesh Maan, Samayra Straal, J. A. J. Alford. 2025-07-25. The Timing Evolution of the Magnetar Swift J1818.0-1607 During a Period of Reduced Activity. https://arxiv.org/abs/2507.19698

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