A possible link among pulsar timing noise intermittency and hidden ultra-compact binaries

The quasi-periodic feature of 1-10 years exhibited in pulsar timing noise has not been well understood since 1980. The recently demonstrated correlation between timing noise and variation of pulse profile motivates us to further investigate its origins. We suggest that the quasi-periodicity feature of timing noise, with rapid oscillations lying on lower frequency structure, comes from the geodetic precession of an unseen binary system, which induces additional motion of the pulsar spin axis. The resultant change of azimuth and latitude at which the observer's line of sight crosses the emission beam is responsible for the variation of timing noise and pulse profile respectively. The first numerical simulation to both timing noise and pulse profile variation are thus performed, from which the orbital periods of these pulsars are of 1-35 minutes. Considering the existence of the ultracompact binary white dwarf of orbital period of 5.4 minute, HM Cancri, such orbital periods to pulsar binaries are not strange. The change of latitude of the magnetic moment exceeding the range of emission beam of a pulsar results in the intermittency, which explains the behavior of PSR B1931+24. Therefore, it provides not only a mechanism of the quasi-periodic feature displayed on some ``singular" pulsars, like timing noise, variation of pulse profile and intermittency; but also a new approach of searching ultra-compact binaries, possibly pulsar-black hole binary systems.