2006MNRAS.370..673R

Unusual single-pulse behaviour has been identified in two pulsars, B0919+06 and B1859+07. Both stars normally emit bright subpulses in a region near the trailing edge of their profile. However, they occasionally undergo `events', whereby the emission longitude gradually decreases by about their profile width, remains in this position for typically several tens of pulses, and then gradually returns over a few pulses to the usual longitude. The effect bears some resemblance to a profile `mode change', but here the effect is gradual and episodic. On close inspection, the separate profiles of the normal and `event' in each pulsar emission reveal a broad and complex structure - but one which may be understood in terms of the geometry of a conical beam. Possibly the effect entails an extreme example of variable `absorption' within the magnetosphere, as suspected in other pulsars. Alternatively, it may be caused by intrinsic changes in the emission within the pulsar's beam.