Null transition times, quantized drift modes, and no memory across nulls for PSR 1944 + 17

The authors have studied the behavior of the drifting subpulses and nulling in PSR 1944+17 (P = 0.441 s), an object which allows a large number of null transitions to be examined, since 60% of the pulses are null pulses. No evidence for phase memory is found, but there are differences between the last pulse before a null and the other pulses in a burst. Two time scales are observed for the onset of a null. There is a decline of the pulse intensity for several pulse periods, followed by a rapid drop to the null state on a time scale 2 ms < τ < 30 ms. The implications of the measurements are briefly discussed in terms of polar cap models.