Rotation Measure Evolution of the Repeating Fast Radio Burst Source FRB 180301
Zhang, Chunfeng
Study the polarization and Faraday rotation measure (RM) of repeating FRB 180301 with FAST. During the nine-hour observation session, about 30 radio pulses were detected from FRB 180301, moreover, the polarization and RM results of five bright pulses were obtained. The max linear polarization degree is 47%, the average RM value is about 200rad/m^2. Considered the historical data observed by FAST, the polarization of bursts from the source dropped below the FAST detection in March 2021 and appeared again in September 2021. It is found that its RM values has been changed since 2019, the RM variation in the local rest frame of FRB 180301 is \Delta RM ~ 1500 rad /m^2, and the time scale is \tau ~ 700 day, accepted a typical value 100 km/s of binary motion or proper motion of neutron stars, the corresponding size of the source region is estimated to be \Delta X ~ 40AU, thus the average apparent magnetic field along the line of sight is estimated to be larger than <B_\parallel> \geq 15 \mu G. This indicates dynamical evolving, magnetized medium surrounding the source.