PSR J1914+2636: Quasiperiodic Nulling and Bright-pulse Emission from an Old Pulsar in the Death Valley

In this paper, we report high-sensitivity single-pulse observations of PSR J1914+2636 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). By combining our FAST observations with archival timing data, we obtained an improved phase-connected timing solution for this pulsar. The single-pulse analysis reveals the coexistence of quasiperiodic nulling, weak emission below the single-pulse detection threshold, and sporadic bright pulses. The pulsar exhibits a characteristic nulling periodicity of 63.57 ± 14.67 P _0 . The integrated profiles of pulses classified as nulls still show weak residual emission. A total of 88 bright pulses were detected within 45 minutes, with peak flux densities exceeding 10 times that of the integrated pulse profile. The peak-flux distribution exhibits a pronounced high-intensity tail that can be approximately described by either power-law or lognormal statistics, while the waiting-time distribution deviates significantly from Poisson behavior and is better described by Weibull or gamma models, indicative of clustered burst activity. In the period–period-derivative diagram, PSR J1914+2636 lies near the lower boundary of the pulsar death valley and is currently the oldest known pulsar exhibiting the coexistence of quasiperiodic nulling and bright-pulse emission. Interestingly, the currently known pulsars exhibiting the coexistence of quasiperiodic nulling and bright pulse emission are also located within the “death valley” region. The coexistence of quasiperiodic nulling, weak emission, and clustered bright pulses in PSR J1914+2636 suggests that old pulsars near the death valley may undergo intermittent magnetospheric state switching. Our results provide further insight into the late-stage evolution of pulsar radio emission and the origin of intermittent emission behaviour in old pulsars.