Investigating the subpulse drifting and periodic nulling behavior of the long-period pulsar PSR J1831-1223 with FAST

PSR J1831-1223 is an old, long-period pulsar located in the death valley region, which was discovered in the Parkes Multibeam Pulsar Survey. We report new observations of PSR J1831-1223 obtained with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) at 1250 MHz. The pulsar exhibits a variety of single-pulse emission phenomena, including pulse nulling, subpulse drifting, and sporadic bright pulses. We estimate a nulling fraction of 25.40_ -1.37 ^ +1.41 %. Further analysis shows that the transitions between the null and burst states are periodically modulated with a characteristic periodicity of approximately 32 rotation periods. Fluctuation spectral analysis of the single-pulse sequence reveals two prominent periodic modulation features. The longer-period feature is associated with periodic nulling across the emission window, while the shorter-period modulation feature is detected in both the leading and trailing components, with modulation periods of P_3 = 3.61 ± 0.11,P_1 and 3.71 ± 0.19,P_1, respectively. We also compare the mean profiles of the first active pulses (FAPs) and last active pulses (LAPs), and find that their emission in the third and fourth components is significantly weaker than that of the overall burst-pulse profile, while the LAP profile is stronger than the FAP profile. In addition, we identify five bright pulses whose single-pulse peaks are concentrated primarily in the leading component. Polarization analysis reveals a moderate degree of linear polarization, while some individual pulses exhibit polarization position angle jumps of approximately 90^̧irc. The coexistence of periodic nulling and subpulse drifting places PSR J1831-1223 in a relatively small subclass of pulsars. These observational results provide important clues for understanding the radio emission mechanism of pulsars.