FRB 20180916B polarization PA variability

We use the calibrated burst dataset detected by uGMRT in Band 4 (650MHz) which have been published in our earlier work. We transform the PA measured at 650MHz to infinite frequency such that PAs measured in different observations are consistent, and finally measure the changes within and across active windows. We find that PA of the bursts vary according to the periodicity of the source.

We constrain the PA variability to be less than seven degrees on timescales less than four hours for all MJDs. We also tentatively find that the PA varies within an active window with a variability of few degrees per hour. In addition, we also tentatively note the PA measured at the same phase in the active window varies from one cycle to another.

Using the findings, we constrain rotational, precession and binary progenitor models involving compact objects, where the emission is originating from the magnetosphere of the compact object. Rotational model partially agrees with observed PA variability but requires further study to be fully constrained. We robustly rule out all flavors of precessional models where precession of neutron star either explains the periodicity of the FRB or the variability from one cycle to another.

We can rule out relativistic spin precession binary model. Lastly, we draw similarities between FRB 20180916B and a X-ray binary system, Her X 1, and explicitly note that both the sources exhibit a similar form of PA variability.