Pulsars and neutron stars/Noise in pulsar timing residuals

Jitter
It is often assumed that if a sufficient number of individual pulses are added together then the resulting pulse profile will be stable. However, as the pulsar timing array projects push the limits of timing precision it is found that observations of some pulsars do not improve with increased telescope sensitivity. This is caused by "jitter noise" (the intrinsic variability in the shape of individual pulses from a pulsar). For instance, Osowski et al. (2011) showed that, even with a large telescope, the timing precision for PSR J0437-4715 could never be better than ~40ns with a 1-hour observation. Shannon & Cordes (2012) found similar results using Arecibo observations of PSR J1713+0747. Shannon et al. (2014) determined the jitter noise level for many of the millisecond pulsars observed at the Parkes observatory.

Shannon & Cordes (2012) provide an order-of-magnitude estimate of the amount of jitter noise for a given pulsar which depends upon the pulse width, W, period, P, and the observation time, t:

$$\sigma_J \approx 0.2W\sqrt{\frac{P}{t}}$$

(where all parameters are measured in seconds).