Magnetic dipolar geometry unveiled from a long-period radio pulsar

The radio emission observed from rotating compact objects like radio pulsars and ultralong period radio transients (LPTs) is not fully understood, as coherent radiation is thought to be difficult to produce without sufficient spin-down power. PSR J0901-4046 is a radio pulsar with the longest period of 76 seconds known to date, and may act as a "transition state" between known radio pulsars and LPTs. Here we present the key results from a synergic monitoring program for PSR J0901-4046 with the Parkes radio telescope and the MPG/ESO 2.2-metre optical telescope. We detected a series of single pulses, among which one event perfectly follows the quasi-periodicity correlation established by radio-emitting neutron stars. For the first time, we have successfully folded the integrated pulse profile by timing the pulsar and then measured its polarization properties. Using the rotating vector model that depicts the geometry of a moving dipolar magnetic field, we fitted the key parameters and unveiled its geometry. The peculiar radiation characteristics of PSR J0901-4046 possibly provide constraints for the coherent radiation theory of radio pulsars. All the findings favour a canonical neutron-star framework for this pulsar.