The impact of polarization calibration on pulsar timing noise in FAST’s observations

Pulsar timing arrays (PTAs) have made significant progress in the detection of nano-Hertz gravitational waves, with the Chinese Pulsar Timing Array (CPTA) achieving the highest-confidence results to date. As such, the demand for improved pulsar timing precision will continue to grow. In this study, we investigated the impact of polarization calibration on pulsar timing accuracy using polarization observation data of globular cluster pulsars obtained with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We selected four pulsars—M3D, M5E, M53A, and NGC6760A—for detailed analysis. The results show that polarization calibration can reduce TOA (time-of-arrival) uncertainties by an average of tens to hundreds of nanoseconds. Specifically, the average TOA uncertainties for M3D and M5E were reduced by 642 and 89 ns, respectively, corresponding to 1.7 and 2.2 times their standard deviations—indicating a significant improvement in timing precision. Additionally, polarization calibration reduces the root-mean-square (RMS) of timing residuals, with M3D showing a reduction of up to 390 ns, further confirming its beneficial impact. Changes in pulse profiles before and after calibration suggest that the improvement in TOA precision is likely associated with narrower pulse widths, rather than changes in pulse sharpness or signal-to-noise ratio (S/N). Overall, polarization calibration enhances both TOA measurement accuracy and timing residual RMS, making it an essential step for high-precision pulsar timing with FAST. These findings provide important technical support for precision pulsar timing with FAST, particularly in the context of PTA-based nano-Hertz gravitational wave detection.