Study on the polarimetric pulse emission from the millisecond pulsar B1937+21 with the Five-hundred-meter Aperture Spherical radio Telescope
Abstract
The millisecond pulsar B1937+21, known for its exceptional rotational stability and complex polarization features, serves as a prime target for investigating emission mechanisms. Using unprecedented high-sensitivity observational data from China's Five-hundred-meter Aperture Spherical radio Telescope (FAST), this study systematically analyzes the polarimetric pulse emission characteristics and frequency-dependent evolution of this pulsar within the 1000–1500 MHz band for the first time. Beyond the main pulse (MP) and interpulse (IP), we have detected faint emission components within the off-pulse window of PSR B1937+21 for the first time, identified as the MP precursor and IP precursor components. The polarization position angles of both the MP and IP follow power-law growth trends with increasing frequency, characterized by spectral indices of 4.59±0.84 and 1.25±0.07, respectively. Notably, their fractional linear polarization exhibits a striking divergence in frequency evolution: the IP's linear polarization degree increases with a spectral index of 1.44±0.10, while the MP's decreases with a spectral index of -0.69±0.18.The widths of both the MP and IP exhibit a power-law decrease with increasing frequency, indicating that the emission height at higher frequencies is lower than that at lower frequencies. The single-pulse energies of the MP and IP follow normal distributions and show a significantly positive correlation, with the MP's mean energy being approximately 1.7 times that of the IP. These observational results reveal fundamental differences in the radiation mechanisms or magnetospheric geometries between the MP and IP.
