Time-Correlated Structure in Pulsar Spin Fluctuations

I will present evidence for time-correlated structure in the pulsar spin-rate fluctuations known as timing noise. Such evidence has not been found in previous studies of timing noise power spectra, which have revealed no sign of deviations from rigid body rotation. We use two statistics to measure correlations in the time domain: the auto-correlation function and the lagged distribution function. This analysis indicates that pulse arrival time fluctuations are correlated over a correlation time of $\sim$10 days, beyond which no correlation is observed. We interpret this to be the signature of a damped rotational mode in the star, arising from frictional coupling of the solid crust and liquid interior.