2023MNRAS.520.4562S

We report on the subpulse modulation properties of 1198 pulsars using the Thousand-Pulsar-Array programme on MeerKAT. About 35 per cent of the analysed pulsars exhibit drifting subpulses that are more pronounced towards the death line, consistent with previous studies. We estimate that this common phenomenon is detectable in 60 per cent of the overall pulsar population if high-quality data were available for all. This large study reveals the evolution of drifting subpulses across the pulsar population in unprecedented detail. In particular, we find that the modulation period P₃ follows a V-shaped evolution with respect to the characteristic age τ_c, such that the smallest P₃ values, corresponding to the Nyquist period P₃ ≃ 2, are found at τ_c ≃ 10^7.5 yr. The V-shaped evolution can be interpreted and reproduced if young pulsars possess aliased fast intrinsic P₃, which monotonically increase, ultimately achieving a slow unaliased P₃. Enhancement of irregularities in intrinsic subpulse modulation by aliasing in small-τ_c pulsars would explain their observed less well defined P₃'s and weaker spectral features. Modelling these results as rotating subbeams, their circulation must slow down as the pulsar evolves. This is the opposite to that expected if circulation is driven by $\boldsymbol{E}\times \boldsymbol{B}$ drift. This can be resolved if the observed P₃ periodicity is due to a beat between an $\boldsymbol{E}\times \boldsymbol{B}$ system and the pulsar period. As a by-product, we identified the correct periods and spin-down rates for 12 pulsars, for which harmonically related values were reported in the literature.