On the Circular Polarization of Repeating Fast Radio Bursts

Fast spinning (e.g., sub-second) neutron star with ultra-strong magnetic fields (or so-called magnetar) is one of the promising origins repeating fast radio bursts (FRBs). Here we discuss circularly polarised emissions produced by propagation effects in magnetosphere magnetars. We argue that polarisation-limiting region well beyond light cylinder, suggesting wave mode coupling are unlikely to produce strong circular polarisation for Cyclotron absorption could be significant if secondary plasma density high. However, high degrees can only large asymmetries electrons and positrons. draw attention non-detection current observations known FRBs. suggest FRBs provide key information on their help distinguish different radiation mechanisms.