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arXiv · 2512.12995

The disk precession in a Be star-magnetar binary and its application to the rotation measure of FRB 20201124A

Ying-ze Shan·Wei-Hua Lei·Hao-Tian Lan·Shao-yu Fu·Jumpei Takata·Yuan-chuan Zou·Jia-xin Liu·Long-xuan Zhang·Tong-lun Wang·Fa-Yin Wang
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Abstract

Fast radio bursts (FRBs) are bright, millisecond-duration radio bursts with poorly known origins. Most FRB sources are detected only once, while some are repeaters. Variation patterns observed in the rotation measure (RM) of some repeaters -- indicate that the local magneto-ionic environments of these FRB sources are highly dynamic. It has been suggested that a Be star-magnetar binary system is a possible origin for such variation. FRB 20201124A is notable among these sources since it is the most active one and exhibits substantial temporal variations of RM measured by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The physics behind this long-term behavior is poorly understood. Here we propose that, within the framework of the Be star-magnetar binary scenario, the observed variation of RM is attributed to a combination of orbital motion and the precession of the circumstellar disk of the Be star. While a ~785-day precession of the disk contributes to the observed decrease in the amplitude of the variation, our model predicts that the amplitude oscillates with this period.

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Ying-ze Shan, Wei-Hua Lei, Hao-Tian Lan, Shao-yu Fu, Jumpei Takata, Yuan-chuan Zou, Jia-xin Liu, Long-xuan Zhang, Tong-lun Wang, Fa-Yin Wang. 2025-12-15. The disk precession in a Be star-magnetar binary and its application to the rotation measure of FRB 20201124A. https://arxiv.org/abs/2512.12995

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