Distinct polarization properties for two emission states of four pulsars

Four pulsars, PSRs J1838+1523, J1901+0510, J1909+0007, and J1929+1844, are found to exhibit bright and weak emission states from sensitive observations made using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). New FAST observations have measured the polarization properties for the two states, and reveal that the polarization profiles, linear polarization percentage, and polarization position angle curves, as well as circular polarization percentage, are partially or entirely different in the two emission states. Remarkably, PSR J1838+1523 has very different slopes for the polarization position angle curves. PSR J1901+0510 has a wider profile and a higher linear polarization in the weak state than in the bright state. PSR J1909+0007 has very distinct polarization angle curves for the two modes. While in the case of PSR J1929+1844, the central profile component evolves with frequency in the bright state, and the senses of circular polarization are opposite in the two modes. The different polarization properties of the two emission states provide valuable insights into the physical processes and emission conditions in the pulsar magnetosphere.