Wang et al. report on the broadband polarization behaviour of the millisecond pulsar B1937+21 (J1939+2134), using high-quality observations made with the ultra-wideband low (UWL) receiver on Murriyang, the Parkes radio telescope. Observations spanning approximately 3 yr are carefully calibrated and integrated to produce high signal-to-noise-ratio pulse profiles. Updated and accurate interstellar medium parameters toward the pulsar are obtained. The temporal variability of the dispersion measure (DM), the Faraday rotation measure, and the flux density are analyzed from their corresponding structure functions. The spectra of the mean flux density follow a high-frequency cutoff power law, with the interpulse spectra being steeper than the main pulse. The pulse width decreases with increasing frequency, further confirming that the emission height decreases with frequency, consistent with the results obtained from relativistic effects. These findings will contribute to a deeper understanding of the underlying emission mechanisms.

The upper panel above shows the temporal evolution of the topocentric DM toward pulsar B1937+21, measured from the Parkes UWL observations. The annual variation of the DM is consistent with the expected Doppler effect caused by the Earth’s motion in its orbit around the Sun, which modifies the signal frequency measured at the telescope compared to its value in the interstellar medium.The model and measured values are indicated by the blue curve and red dots, respectively. The lower panel shows the DM variation with time. The red and green dots represent the DM measurements obtained using structure-optimization and template-alignment techniques, respectively.