Revealing the Unseen: The Discovery of Long-awaited Radiation from the Intermittent Pulsar PSR B1931+24

Abstract Pulsars are typically characterized by their stable, highly magnetized, and fast-rotating nature, which underpins their persistent radio emissions. However, the discovery of prolonged radio-quiet (“off”) states in intermittent pulsars, such as PSR B1931+24, has been challenging the fundamental theory of pulsar magnetospheric emission. Despite long-term monitoring with several telescopes over 20 yr, the observations of PSR B1931+24 had not detected any significant emission during its “off” states. Recently, sensitive observations via the Five-hundred-meter Aperture Spherical radio Telescope revealed the mysterious weak emissions containing occasional faint bursting pulses during the “off” states of PSR B1931+24, signifying the theory of pulsar magnetospheric emission that the pulsar cannot remain off for long unless it truly dies. Along with a substantial decrease in flux density, a contraction and change in the integrated pulse profile are measured in the “off” state compared to the radio-loud (“on”) state, indicating alterations in the plasma supply and magnetospheric structure. Additionally, previously unobserved asynchronous, nonuniform emission patterns are found in both states, implying a spatially inhomogeneous pair-cascade associated with the coherent radio emission of the pulsar. Furthermore, statistical comparisons between the faint off-state bursts and the on-state emission show that the faint bursts cannot be explained simply as a scaled-down version of the on-state emission. Instead, they constitute a distinct emission mode, plausibly linked to changes in plasma supply and the magnetospheric configuration of PSR B1931+24. These findings greatly advance our understanding of pulsar magnetospheric dynamics and emission mechanisms.