Sun et al. present polarisation profiles of 23 pulsars exhibiting interpulse (IP) emissions using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). By applying the rotating vector model (RVM), the inclination and impact angles were measured for 16 pulsars, enabling investigation of their beam geometries. The analysis indicates that, for 5 pulsars, the IP emissions likely originate from the same magnetic pole as the main pulse (MP), whereas for the remaining 11 pulsars, the IP and MP emissions originate from opposite magnetic poles. For the 7 pulsars that do not conform to the RVM, it was not possible to determine whether the IP emissions originate from the same or opposite magnetic pole as the MPs. Through analysis of the beam configurations, it was found that the emission within the beam is not fully active across both longitude and latitude. For pulsars with opposite-pole IP emissions, filling factors ranging from 0.27 to 0.99 were obtained, suggesting that emission heights may be underestimated when using the geometrical method. The study also finds that the emissions for MPs and IPs occur at different heights within the pulsar magnetosphere, with differences ranging from tens to thousands of kilometers. Additionally, some pulsars exhibit wide emission beams, implying that radio emission may occur at high altitudes within the magnetosphere.

The image above shows the polarisation profiles for 23 pulsars with interpulse (IP) emissions. In the top panels, the PPAs of the average profile are shown as red dots, superimposed on the PPAs of single pulses are shown as black dots. Only PPAs with uncertainties smaller than 7° are included. The middle panels display the total intensity (black line), linear polarisation (red line), and circular polarisation (blue line). The bottom panels provide zoomed-in views of the polarisation profiles for more detailed inspection.