A long-term single-pulse study of the Vela pulsar

The mechanisms of emission and changes in rotation frequency (glitches) of the Vela pulsar (J0835-4510) are a fascinating area of study. Further insight into these mechanisms can be achieved by long-term studies of integrated pulse width, timing residuals, and bright pulse rates. We have undertaken an intensive observing campaign of Vela and collected over 14000 hours of single-pulse data. The data shows that the pulse width changes with time, including marked jumps in width after micro-glitches. The abundance of bright pulses also changes after some micro-glitches, but not all. The secular changes in pulse width have cyclic periods, some of which match with X-Ray periodicities of a helical jet that are interpreted as free precession. Some radio pulsars make excellent natural clocks because of their fast rotation and immense angular inertia. However the Vela pulsar, which has rotation frequency \\(v\\) = 11:2 Hz, suddenly speeds up by ‚Äöv†vú/‚Äöv†vú\\(v\\) ‚Äöv¢v† 10\\(^{-6}\\) during a glitch which happens roughly every three years. Glitches have never been observed with a telescope and receiver sensitive enough to detect individual pulses, from Vela or any other pulsar, until now. On 2016-12-12 at UT 11:36 a glitch with magnitude ‚Äöv†vú/‚Äöv†vú\\(v\\) = 1:431 x 10\\(^{-6}\\) was captured by the University of Tasmania's 26m and 30m telescopes at a frequency of 1376 MHz and a bandwidth of 64 MHz. Here we show that just near the glitch epoch, the pulse shape shows a sudden change. One pulse is a null, i.e. there is no emission detected, and the pulse before the null is very broad. Just after the null there is a 2.6 second interval when the pulsar shows decreased pulse frequency, i.e. an effect in the opposite direction to the glitch. Along with the slight spin-down during these 2.6 seconds, the variance of the pulse arrival time decreases, suggesting that either or both the magnetic field configuration and the crustal rotation period have been stabilised during this interval, perhaps by a brief but strong dynamical connection between the superfluid interior and the outer layers of the pulsar. The null pulse and the change in arrival time statistics are both extremely rare; that they are nearly simultaneous with the glitch strongly suggests that all three are aspects of a single event.