Crust-superfluid coupling plays an important role in neutron star rotation, particularly with respect to timing noise and glitches. Here, we present new timing-noise-based estimates of the crust-superfluid coupling time-scale \(\tau\) for 105 radio pulsars in the UTMOST dataset, by Kalman filtering the pulse times of arrival. The 105 objects are selected because they favor a two-component, crust-superfluid model over a one-component model with log Bayes factor \(\ln \mathfrak{ B}_{ \rm BF} \geq 5\). The median estimate of \(\tau\) ranges from \(10^{ 4.6\pm0.4}\)\,s for PSR J2241$-$5236 to \(10^{ 7.7^{ +0.7}_{ -0.4}}\)\,s for PSR J1644$-$4559 among 28 out of 105 objects with sharply peaked \(\tau\) posteriors. A hierarchical Bayesian analysis is performed on 101 out of 105 objects that are canonical (i.e.\ neither recycled nor magnetars) and reside in the populous core of the \(\Omega_{ \rm c}\)-\(\dot{ \Omega}_{ \rm c}\) plane. It returns the population-level scaling \(\tau \propto \Omega_{ \rm c}^{ 0.19^{ +0.50}_{ -0.52}} |\dot{ \Omega}_{ \rm c}|^{ 0.18^{ +0.18}_{ -0.19}}\), where \(\Omega_{ \rm c}\) and \(\dot{ \Omega}_{ \rm c}\) are the angular velocity and spin-down rate of the crust respectively. The variances of the stochastic crust and superfluid torques are also estimated hierarchically, with \(Q_{ \rm c} \propto \Omega_{ \rm c}^{ 1.23^{ +0.80}_{ -0.75}} |\dot{ \Omega}_{ \rm c}|^{ 0.49^{ +0.27}_{ -0.32}}\) and \(Q_{ \rm s} \propto \Omega_{ \rm c}^{ 0.71^{ +0.76}_{ -0.78}} |\dot{ \Omega}_{ \rm c}|^{ 1.27^{ +0.30}_{ -0.28}}\) respectively. Implications for the physical origin of crust-superfluid coupling, e.g.\ through mutual friction, are discussed briefly.
Categories: astro-ph.HE