Drifting Subpulses in PSR B0826-34

We analyze single pulse data from PSR B0826-34 showing apparent changes of subpulse drift direction, inconsistent with basic pulsar electrodynamics. We demonstrate that this unusual behaviour is not genuine, and results from aliasing in sampling of the intensity fluctuations. Aliasing resolved, drifting subpulses in PSR B0826-34 provide first direct evidence of a system of sparks circulating on the polar cap.