On the long and short nulls, modes and interpulse emission of radio pulsar B1944+17

We present a single pulse study of pulsar B1944+17, whose non-random nulls dominate nearly 70 per cent of its pulses and usually occur at mode boundaries. When not in the null state, this pulsar displays four bright modes of emission, three of which exhibit drifting subpulses. B1944+17 displays a weak interpulse whose position relative to the main pulse (Δφ
IP-MP
) we find to be frequency independent. Its emission is nearly 100 per cent polarized, its polarization-angle traverse is very shallow and opposite in direction to that of the main pulse and it nulls approximately two-thirds of the time. Geometric modelling indicates that this pulsar is a nearly aligned rotator whose α value is hardly 2°– i.e. its magnetic axis is so closely aligned with its rotation axis that its sightline orbit remains within its conal beam. The star's nulls appear to be of two distinct types: those with lengths less than about eight rotation periods appear to be pseudo-nulls – i.e. produced by ‘empty’ sightline traverses through the conal beam system; whereas the longer nulls appear to represent actual cessations of the pulsar's emission engine.