Drifting subpulses in PSR B0943+10

Drifting subpulses in PSR 0943+10 are analyzed within a framework of the Ruderman & Sutherland spark model. This pulsar was extensively studied by Deshpande & Rankin by means of a fluctuation spectral analysis, and they argued that its drifting subpulse pattern observed at 430 MHz can be understood as resulting from a system of 20 equidistant subbeams circulating around the magnetic axis in an interval (P) over cap (3) of about 37 pulsar periods or about 41 s. Assuming implicitly that all subbeams circulate at the same distance from the magnetic axis, they found that some subbeams are stronger than others and maintain these intensity differences over several circulation times P-3. However, the origin of a mechanism that controls the amplitude of subbeam intensity is unknown. We propose an alternative and more natural model in which spark-associated subbeams of subpulse emission fluctuate randomly in intensity over timescales shorter than one pulsar period, but each spark (subbeam) circulates at slightly different distance from the magnetic axis. A similar idea was already mentioned by Asgekar & Deshpande, who argued that an analysis of their pulse sequence observed at 35 MHz may imply some nonuniformity in the spacing of the subbeams.