Time-Correlated Structure in Spin Fluctuations in Pulsars

TL;DR

This paper introduces new time-domain analysis methods to study pulse arrival time variations in pulsars, revealing correlated fluctuations and potential neutron star interior dynamics.

Contribution

It presents robust analysis techniques for timing noise and applies them to pulsar data, providing evidence for internal neutron star processes.

Findings

Detection of correlated fluctuations over 10-20 days in two pulsars.

Evidence for relaxation processes possibly related to crust-core interactions.

Observation of quasi-periodic oscillations in one pulsar.

Abstract

We study statistical properties of stochastic variations in pulse arrival times, timing noise, in radio pulsars using a new analysis method applied in the time domain. The method proceeds in two steps. First, we subtract low-frequency wander using a high-pass filter. Second, we calculate the discrete correlation function of the filtered data. As a complementary method for measuring correlations, we introduce a statistic that measures the dispersion of the data with respect to the data translated in time. The analysis methods presented here are robust and of general usefulness for studying arrival time variations over timescales approaching the average sampling interval. We apply these methods to timing data for 32 pulsars. In two radio pulsars, PSRs B1133+16 and B1933+16, we find that fluctuations in arrival times are correlated over timescales of 10 - 20 d with the distinct signature of a relaxation process. Though this relaxation response could be magnetospheric in origin, we argue that damping between the neutron star crust and interior liquid is a more likely explanation. Under this interpretation, our results provide the first evidence independent from pulsar spin glitches of differential rotation in neutron stars. PSR B0950+08, shows evidence for quasi-periodic oscillations that could be related to mode switching.