SIMBAD references

We propose that in some pulsars the magnetosphere has different states with different geometries or/and different distributions of currents; it occasionally switches between them. These states have different spin-down rates and emission beams; in some of the states no radio emission is produced at all. Switching into a different state manifests as a mode change when we see different parts of the emission beam or the beams in different states have significantly different geometries; it manifests as nulling when either we miss the new beam or no radio emission is generated in the new state. We show that modest variations in the beam shape can be accompanied by large variations in the pulsar spin-down rate W - the dependence of W on the opening angle of the emission beam α can be as strong as W ∝ α⁴. We speculate about physical mechanisms which may cause reconfiguration of the magnetosphere.