Pulsar Glitch in a Strangeon Star Model. III. The recovery

TL;DR

This paper models the recovery process of pulsar glitches within the strangeon star framework, showing how viscous flows after starquakes can explain observed exponential recoveries and relate glitch size to cracking depth.

Contribution

It introduces a viscous flow model for glitch recovery in strangeon stars, linking glitch size to cracking depth and fitting observational data with exponential decay.

Findings

Viscous flow causes exponential recovery of spin frequency after glitches.

Recovery timescale and cracking depth can be fitted from observational data.

The model's predictions align with observed glitch recovery magnitudes.

Abstract

Strangeon star model has passed various observational tests, such as the massive pulsars and the tidal deformability during binary mergers. Pulsar glitch, as a useful probe for studying the interior structure of pulsars, has also been studied in strangeon star model in our previous papers, including the recovery coefficient, the waiting time of glitches and glitch activity. In this paper, the recovery process of a glitch is described in the strangeon star model, based on the starquake picture established in Paper I. After the starquake, the inner motion of the stellar matter would reduce the tangential pressure in the cracked places at the equatorial plane. The recovery (increase) of the tangential pressure would be achieved by a viscous flow towards the cracked places at equatorial plane, which leads to the exponential recovery of the spin frequency. A uniform viscous flow can reproduce the single exponential decay observed in some glitches, and the viscous time-scale $\tau$ and the depth $h$ of the cracking place below the surface can be fitted by the recovery data. It is found that $h$ increases with glitch size $\Delta\nu/\nu$, which is expected in the glitch scenario of strangeon stars. The magnitude of the recovery predicted in this recovery model is also consistent with that derived from observations. The single exponential decay reproduced by a uniform viscous flow can be generalized to two or more exponentials by the multi-component of viscous flows.