Xiaohui Liu, Heng Xu, Jiarui Niu, Yongkun Zhang, Jinchen Jiang, Dejiang Zhou, Jinlin Han, Weiwei Zhu, Kejia Lee, Di Li, Wei-Yang Wang, Bing Zhang, Xuelei Chen, Jia-Wei Luo, Rui Luo, Chenhui Niu, Yuanhong Qu, Bojun Wang, Fayin Wang, Pei Wang, Tiancong Wang, Qin Wu, Ziwei Wu, Jiangwei Xu, Yuan-Pei Yang, Jun-Shuo Zhang

Fast radio bursts (FRBs), typically highly polarized, usually have a nearly constant polarization position angle (PA) during each burst. Some bursts show significant PA variations, and one of them was claimed to have a PA variation pattern consistent with the prediction of the rotating vector model (RVM) commonly adopted to fit the PA variations in radio pulsars. We systematically study the PA evolution pattern of 1727 bursts from three active repeating FRB sources monitored by the Five-hundred-meter Aperture Spherical Telescope (FAST). We identify 46 bursts whose PA variations are fully consistent with the RVM. However, the inferred geometrical parameters and rotation periods derived from these RVM fitting are inconsistent from each other. This suggests that the magnetosphere of the FRB central engine is constantly distorted by the FRB emitter, and the magnetic configuration is dynamically evolving.