A multifrequency polarization study of millisecond pulsars

Based on the second data release of multifrequency observations from the Parkes Pulsar Timing Array (PPTA) project, we conduct a detailed polarization analysis of eight millisecond pulsars observed at 732, 1369, and 3100 MHz as part of the PPTA. Using polarization-calibrated data, we present high signal-to-noise ratio pulse profiles, and study individual profile components and their evolution with frequency. We find that the pulse profiles of certain pulsars at low frequencies exhibit significant discrepancies compared to previously published results. The pulse components follow a complex evolutionary behavior with frequency. All millisecond pulsars in this study exhibit broad pulse profiles, with 7 of them showing pulse widths exceeding 50% of their pulse periods at 1369 MHz. The evolution of polarization properties is similarly intricate, for instance, the fractional linear polarizations of pre- and post-cursor components are often higher than the main pulse. By jointly fitting the data across the three frequency bands, we determined the spectral index and rotation measure for each pulsar. While most spectra can reasonably well follow a single power-law and their position angles generally follow a λ² relation, clear deviations are observed in some frequency bands or subbands of some pulsars. In addition, we present measurements of phase-resolved spectral index, fractional linear polarization, and rotation measure, which show systematic variations across the pulse profile. These results provide important insights into the emission mechanisms of millisecond pulsars and the formation of distinct radiation components within pulsar magnetosphere.