2025MNRAS.544..299C

We study the single-pulse variability of pulsar PSR J0535$-$0231, which was discovered by the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) as part of the Commensal Radio Astronomy FAST Survey (CRAFTS) at 1.25 GHz. Through pulsar timing, we obtain precise measurements of this pulsar's position, rotational parameters, and dispersion measure. The integrated pulse profile of this pulsar exhibits at least three distinct emission components, namely the leading, central, and trailing components. The emission from the leading component is notably anticorrelated with that from the trailing component. A Gaussian mixture model (GMM) analysis shows that PSR J0535$-$0231 does not exhibit significant pulse nulling. From the examination of the total intensity and polarization profiles, we speculate that the leading component may originate from core emission, while the central and trailing components are associated with conal emission. Fluctuation spectral analysis reveals that this pulsar shows time-varying and different subpulse modulation phenomenon, including drifting modulation, phase-stationary amplitude modulation, and diffuse modulation. The traditional carousel model fails to fully account for these behaviours of PSR J0535$-$0231. Therefore, the emission characteristics of PSR J0535$-$0231 could shed light on the mechanisms underlying coherent radio emission in pulsars and serve as important constraints on theoretical models.