Periodic nulls in the pulsar B1133+16

Numerous studies of the brightest Cambridge pulsar, B1133+16, have revealed little order in its individual pulses, apart from a weak 30-odd-rotation-period fluctuation feature and that some 15 per cent of the star's pulsars are `nulls'. New Arecibo observations confirm this fluctuation feature and that it modulates all the emission, not simply the `saddle' region. By replacing each pulse with a scaled version of the average profile, we were able to quench all subpulse modulation and thereby demonstrate that the star's `null' pulses exhibit a similar periodicity. A subbeam carousel model with a sparse and irregular `beamlet' population appears to be compatible with these characteristics.