Spider pulsars are a unique class of millisecond pulsar binary systems, characterized by eclipses observed in the radio band. In such systems, the pulsar's radiation and high-energy particle winds irradiate the companion star, gradually evaporating its mass. This process provides important insights into pulsar evolution and the formation of isolated millisecond pulsars. Although spider pulsars have been studied for decades, observational sensitivity limitations have restricted investigations of their eclipse-inducing media to only a few bright sources. This small sample size has constrained progress in this field.

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Wang Shuangqiang, a special research associate at the Xinjiang Astronomical Observatory, Chinese Academy of Sciences, conducted high-sensitivity observations of some spider pulsars. By measuring the shift of the linear polarization position angle, the study successfully determined the magnetic field strengths of the eclipse medium in three spider pulsars — PSRs B1957+20, J2055+3829, and J1544+4937 — and revealed a reversal in their Faraday rotation measures (see Figure 1).

Prior to this work, direct measurements of magnetic fields in eclipse media had only been reported for three other spider pulsars. This study significantly expands the current sample. The results show that the magnetic field strengths in the eclipse regions range from tens to hundreds of milligauss, indicating common physical characteristics across different systems.

Furthermore, by analyzing variations in dispersion measure near the eclipse, the researchers estimated the mass loss rates of the companions of 10^(-13) - 10^(-12) solar mass per year, suggesting that some spider pulsars may still evolve into isolated millisecond pulsars within the Hubble time scale.

Notably, in the case of PSR J1544+4937, the researchers found that the eclipse is nearly absent at 1.25 GHz, yet the linear polarization signal disappears during the corresponding phase. This finding suggests that methods relying solely on total intensity to identify spider pulsars may underestimate their true population. Therefore, multi-dimensional analysis incorporating polarization information is crucial for accurately identifying such systems.

This work was supported by grants from the National Natural Science Foundation of China and the National Key R&D Program of China.

                                                         Figure 1: The polarization properties of PSRs B1957+20, J2055+3829, and J1544+4937 versus orbital phases.