The magneto-active environment near FRBs and pulsars

Fast radio bursts are short-duration radio bursts whose origins are not fully understood. Some FRBs show exotic polarization behavior, providing constrain on the circumburst environment.
Recently, fast rotation measure (RM) variations are seen on a repeating FRB 20211112A. Moreover, a small fraction of the bursts is observed to have oscillation in polarization fraction (P), linear polarization (L), and circular polarization(V), which are a unique clue of the magneto-environment close to the source. In this talk, I will first discuss the required multi-layer circumburst environment near this FRB to explain the polarization measurement. Moreover, we have recently observed fast variation of RM and change of V and P in a pulsar binary system. With a known physical scale, clean comparison of pulse profile in front of and behind the companion, the pulsar binary system provides a great test field to study the radio transfer effects. I will discuss the new constraints we have on the pulsar binary system and compare it with the FRB 20211112A.