Component-dependent Periodic Emission Variations of PSR J1857+0943 Observed with FAST

Abstract Single-pulse studies of millisecond pulsars provide an important way to probe the plasma processes responsible for their radio emission, but such studies remain rare because of the weak emission and short rotation periods of these objects. Using the high sensitivity of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), we investigate the pulse-to-pulse variability of PSR J1857+0943 and report the first detection of distinct fluctuation behavior across its main pulse and interpulse. The integrated main pulse and interpulse each show multiple emission components with markedly different variability properties. Pulse longitude–resolved fluctuation analysis reveals quasiperiodic intensity modulation in both pulse regions, with the interpulse showing a characteristic modulation timescale approximately twice that observed in the trailing part of the main pulse. A longitude-resolved cross-correlation analysis further reveals a weak anticorrelation between the trailing main pulse emission and the interpulse at a lag of one rotation period, suggesting that these widely separated pulse longitude ranges may be influenced by a common magnetospheric process. The polarization properties of the single pulses in the same longitude range also differ from those of the adjacent main pulse components, supporting the presence of component-dependent emission behavior. In addition, we measure a 1 hr jitter noise of σ J,1h = 73.2 ± 1.5 ns at 1.25 GHz, consistent with previous measurements. These results demonstrate that PSR J1857+0943 exhibits complex single-pulse variability and provide new observational constraints on the magnetospheric structure of interpulse millisecond pulsars.