Pulsar nulling and drifting subpulse phase memory

Abstract

A qualitative analysis is presented to account for the nulling phenomena observed pulsar radio emissions, which also feature an associated phase memory. The problem is that the radio signals are present in the form of a subpulse phase which is nulled for a fixed period, then return exactly in phase with the drifting subpulses occurring before the null. The discussion is limited to the Ruderman and Sutherland (1975) model and its modifications. Considering only old pulsars, it is argued that the dot product of the vectors E and B in the gaps under plasma flux tubes is higher than present along neighboring field lines outside the tubes. The nulling feature is then a manifestation of a continuous discharge in the polar gap of the pulsars instead of a cessation of sparking. The absence of radio emissions during nulling is then the lack of coherent structure. Mode changing arises due to the changing of certain regions of the polar gaps from active to nulling conditions, and from nulling to active states.