“Second-scale periodicity in FRB 20201124A: Coincident with critical rotation measure evolution epochs and its possible implication” (2026), by Wen-Long Zhang et al. Physics and Astronomy research paper. Original abstract below, unchanged. A free PDF is available.

Second-scale periodicity in FRB 20201124A: Coincident with critical rotation measure evolution epochs and its possible implication

Wen-Long Zhang, Chen-Ran Hu, Chen Du et al. · November 5, 2026 · Physics and Astronomy

Abstract

Second-timescale periodicity (∼1.7,s) has been reported in the repeating fast radio burst FRB,20201124A at two epochs, MJD,59310 and MJD,59347. We find that these two epochs coincide with the days on which the Faraday rotation measure (RM) of the source passes through the transition between the quasi-steady and the strongly varying phases that are predicted by the magnetar+Be star binary model. To examine whether this coincidence could arise by chance, we re-fitted the secular RM evolution within the same binary framework and estimated the probability of a chance coincidence, ̊m CC Independently, and in order to cross-validate the reported periodicity, we carried out a coherent joint period search on the bursts of the two epochs, assuming a simple linear evolution of the spin period; we obtain P₀=1.70603,s and dot P =6.1 ,s,s-1 at the reference epoch, with a Gaussian significance of and . -10 consistent with the previous measurement. We propose that the two periodic epochs correspond to passages of the magnetar through the decretion disk of the Be-star companion. The captured disk material suppresses low-latitude magnetospheric emission, such that the polar-cap emission dominates and the spin period becomes detectable; alternatively, because the disk material carries substantial angular momentum, accretion increases the magnetic obliquity and thereby amplifies the periodic modulation of the polar-cap emission. The synchronisation between the burst periodicity and the magneto-ionic transition points to a link between burst activity and the dynamical evolution of the source environment. The details of the binary-model fit and of the period search are given in Appendices

Free PDF DOI: 10.1051/0004-6361/202556750