Repeating fast radio burst 20201124A originates from a magnetar/Be star binary

Abstract

Fast radio bursts (FRBs) are cosmic sources emitting millisecond-duration radio bursts. Although several hundreds FRBs have been discovered, their physical nature and central engine remain unclear. The variations of Faraday rotation measure and dispersion measure, due to local environment, are crucial clues to understanding their physical nature. The recent observations on the rotation measure of FRB 20201124A show a significant variation on a day time scale. Intriguingly, the oscillation of rotation measure supports that the local contribution can change sign, which indicates the magnetic field reversal along the line of sight. Here we present a physical model that explains observed characteristics of FRB 20201124A and proposes that repeating signal comes from a binary system containing a magnetar and a Be star with a decretion disk. When the magnetar approaches the periastron, the propagation of radio waves through the disk of the Be star naturally leads to the observed varying rotation measure, depolarization, large scattering timescale, and Faraday conversion. This study will prompt to search for FRB signals from Be/X-ray binaries.

Rotation Measure Variations and Reversals of Repeating FRBs in Massive Binary Systems

“…A similar RM evolution has been found through the periastron passage of PSR B1259 −63/LS 2883 (e.g., Johnston et al 1996Johnston et al , 2005. Wang et al (2022a) proposed that FRB 20201124A and FRB 20190520B may reside in a magnetar/Be star binary system. The fastrotating Be star will form a decretion disk.…”

“…Second, similar RM variations and reversals of repeating FRBs have been observed both in repeating FRBs (Anna-Thomas et al 2022;Dai et al 2022;Xu et al 2022) and in a binary system containing a pulsar and a massive Be star (PSR B1259−63/LS 2883; Johnston et al 1996Johnston et al , 2005. Wang et al (2022a) found that RM variations and reversals can be well understood in a magnetar/Be star binary system. Third, short-time RM variations have been measured in the pulsar binary system PSR B1744−24A (Li et al 2022).…”

“…The inhomogeneities of the density and magnetic field in clumps would lead to stochastic DM and RM variations, which have been detected (Pleunis et al 2021;Mckinven et al 2022). The minor structures of the RM evolution of FRB 20201124A are considered to be caused by the clumps in the disk (Wang et al 2022a). We will give the DM and RM contributions only from the density inhomogeneities of clumps (Melatos et al 1995).…”

“…Third, short-time RM variations have been measured in the pulsar binary system PSR B1744−24A (Li et al 2022). Massive stars usually have strong stellar winds, which is not discussed in detail in previous works (Wang et al 2022a;Yang et al 2022b). More importantly, the interactions between the stellar wind and the pulsar wind will form a bow shock cavity, which will play an essential role in the orbital modulations of the RM, DM, and free-free absorption process.…”

Deep Synoptic Array science I: discovery of the host galaxy of FRB 20220912A

“…The detection of microstructure in bursts from FRB 20200120E (Majid et al 2021;Nimmo et al 2022), together with its association with a globular cluster of M81 (Kirsten et al 2022), suggest an origin in a recycled pulsar system. Despite its origin in an inter-arm region of its late-type host galaxy (Xu et al 2022), FRB 20201124A illuminates extreme variability of its sub-AU magneto-ionic environment, suggestive of a magnetar/Be-star binary (Wang et al 2022). Such observational diversity among the small sample of just eight localized sources motivates the characterization of a larger sample of host galaxies and environments of repeating FRBs.…”