Polarization sweeps in rotation-powered pulsars

We reexamine the characteristic polarization angle sweep of rotation-powered pulsars and calculate the expected deviations from this sweep caused by aberrational effects and by polar-cap current flow. We find that in addition to the previously known phase shift of the entire sweep by Delta Phi = -4r/R-L (when R-L is the light cylinder distance), aberration shifts the polarization angle itself by Delta Psi = -(10/3)(r/R-L) cos alpha. Similarly, current flow above the polar cap shifts the polarization sweep by Delta Psi = (10/3)(r/R-L) (J/J(GL)) cos alpha, potentially providing a method of directly measuring the magnitude of the current. The competition between these two effects produces a potentially observable signature in the polarization angle sweep. Although these effects may appear similar to orthogonal mode shifts, they are an independent phenomenon with distinct observational characteristics.