POLARIMETRY OF MILLISECOND PULSARS

Polarization measurements of millisecond pulsars test theories of pulsar magnetic field geometry and the pulsar emission mechanism under extreme conditions. We have measured the mean polarization profiles of several fast pulsars. Observations of pulsar PSR 1937 + 21 are similar to previously published results, except that we find a shallower position angle swing across the pulse at low frequency and for the first time explicitly demonstrate the occurrence of orthogonal mode switching at all frequencies. Contrary to previous reports we show that PSR 1953 + 29 is substantially linearly polarized in its first and third components. We also present the first polarization measurements of the recently discovered millisecond pulsar PSR 1957 + 20. We find no evidence that the polarization properties of these "recycled" pulsars differ from those of their slower counterparts. Available data on the spectral development of millisecond pulsar profiles is also reviewed. We emphasize that millisecond pulsars severely test phenomenological models such as the one proposed by Rankin.