2004MNRAS.351..813W

Aberration and retardation of the radiation within a pulsar magnetosphere enable a single corotating absorbing region in the outer magnetosphere to give rise to a `double notch' in the pulsar observed radio profile. This effect requires that a pulsar has not only absorbing but also emitting regions at heights that are a significant proportion of the light cylinder radius. The known presence of double notches in the weak secondary emission of three nearby pulsars suggests that this emission comes from open field lines well above their poles and that an obscuring region extending over no more than 5 per cent of the light cylinder radius is located at or near the light cylinder.