Pulsar radio polarization and the magnetic-field twist effect

The electromagnetic braking torque that slows the spin of a pulsar will twist the magnetic field lines opposite to the sense of rotation. If this torque stems mainly from ''recoil'' of the magnetic dipole radiation, one can calculate how the open magnetic field-line cone should be distorted relative to the undisturbed dipole field, as perceived by relativistic particles traveling along the field lines. In the polar-cap neutron star model, the twist of the cone will asymmetrize the curve phi/sub p/(theta) for the linear-polarization position angle as a function of longitude along the average radio-pulse profile: the point where phi/sub p/(theta) is steepest (its center of symmetry) will shift away from the center toward the leading edge of the profile by an angle ..delta..theta which increases swiftly with distance r from the star. Analysis of polarimetric data reveals that the shift ..delta..theta does depend on the pulsar period P and the radio frequency ..nu.. in the manner predicted: Vertical Bar..delta..theta(P, ..nu..)Vertical Bar increases as either P or ..nu.. diminishes. Radio-emission heights r/sub ..nu../ in the pulsar magnetosphere are estimated from the amplitude and character of the ..delta..theta(P, ..nu..) relation: rMHz> or approx. =1.5 x 10/sup 8/ cm, r/sub 400/roughly-equal3 x 10/supmore » 8/ cm, r/sub 160/roughly-equal4 x 10/sup 8/ cm for PSR 0833-45, 1929+10, 0628-28, respectively.« less