Rotation Measure Evolution of the Repeating Fast Radio Burst Source FRB 121102

The repeating fast radio burst source FRB 121102 has been shown to have an exceptionally high and variable Faraday rotation measure (RM), which must be imparted within its host galaxy and likely by or within its local environment. In the redshifted (z=0.193 source reference frame, the RM decreased from 1.46\times10^5rad~m^{-2}to 1.33\times10^5rad~m^{-2}between January and August 2017, showing day-timescale variations of...