2023MNRAS.526..691B

We report the observations of single pulse emission from the pulsar B0809+74 at 150 MHz using the Polish LOFAR station, PL-611. The three major phenomena of subpulse drifting, nulling, and mode changing associated with single pulse variations are prominently seen in these observations. The pulsar has a single-component conal profile and the single pulses are primarily in the 'normal' drift mode with periodicity (P₃) 11.1 ± 0.5 P for 96 per cent of the observing duration, while the shorter duration 'slow-drift' mode has P₃ = 15.7 ± 1.2 P. We were able to measure the phase behaviour associated with drifting from the fluctuation spectral analysis that showed identical linear phase variations across the pulse window for both modes despite their different periodic behaviour. Earlier studies reported that the transitions from the normal state to the slow-drift mode were preceded by the presence of nulling with typical durations of 5 to 10 periods. Our observations however seem to suggest that the transition to nulling follows shortly after the pulsar switches to the slow-drift mode and not at the boundary between the modes, with one instance of complete absence of nulling between mode switching. In addition, we also detected a second type of short-duration nulls not associated with the mode changing that showed quasi-periodic behaviour with periodicity P_N ∼ 44 ± 7. The variety of features revealed in the single pulse sequence makes PSR B0809+74 an ideal candidate to understand the physical processes in the Partially Screened Gap dominated by non-dipolar magnetic fields.