Geometry of radio pulsar signals: The origin of pulsation modes and nulling

Radio pulsars exhibit an enormous diversity of single pulse behaviour that involves sudden changes in pulsation mode and nulling occurring on timescales of tens or hundreds of spin periods. The pulsations appear both chaotic and quasi-regular, which has hampered their interpretation for decades. Here I show that the pseudo-chaotic complexity of single pulses is caused by the viewing of a relatively simple radio beam that has a sector structure traceable to the magnetospheric charge distribution. The slow E x B drift of the sector beam, when sampled by the line of sight, produces the classical drift-period-folded patterns known from observations. The drifting azimuthal zones of the beam produce the changes in pulsation modes and both the intermodal and sporadic nulling at timescales of beating between the drift and the star spin. The axially symmetric conal beams are thus a superficial geometric illusion, and the standard carousel model of pulsar radio beams does not apply. The beam suggests a particle flow structure that involves inward motions with possible inward emission.

Automated summary

This study reveals that the complex behavior of single radio pulses from pulsars is mainly a result of the sector structure of the observed relatively simple radio beam, leading to a diversity of pulsation modes and nulling. The research also demonstrates that the classical drift-period-folded patterns are caused by the slow drift of the sector beam.