Avalanche dynamics of radio pulsar glitches

TL;DR

This study supports the hypothesis that radio pulsar glitches are caused by an avalanche process, with statistical evidence from a large pulsar glitch dataset showing scale-invariant sizes and mostly exponential waiting times, indicating a self-organized critical state.

Contribution

It provides the first comprehensive statistical analysis of pulsar glitches supporting the avalanche model and characterizes the distribution of glitch sizes and waiting times across multiple pulsars.

Findings

Glitch size distribution is scale-invariant, consistent with avalanche behavior.

Waiting times are exponential in most pulsars, indicating a Poisson process.

Some pulsars show quasiperiodic glitching, deviating from randomness.

Abstract

We test statistically the hypothesis that radio pulsar glitches result from an avalanche process, in which angular momentum is transferred erratically from the flywheel-like superfluid in the star to the slowly decelerating, solid crust via spatially connected chains of local, impulsive, threshold-activated events, so that the system fluctuates around a self-organised critical state. Analysis of the glitch population (currently 285 events from 101 pulsars) demonstrates that the size distribution in individual pulsars is consistent with being scale invariant, as expected for an avalanche process. The waiting-time distribution is consistent with being exponential in seven out of nine pulsars where it can be measured reliably, after adjusting for observational limits on the minimum waiting time, as for a constant-rate Poisson process. PSR J0537$-$6910 and PSR J0835$-$4510 are the exceptions; their waiting-time distributions show evidence of quasiperiodicity. In each object, stationarity requires that the rate $\lambda$ equals $- \epsilon \dot{\nu} / <\Delta\nu>$, where $\dot{\nu}$ is the angular acceleration of the crust, $<\Delta\nu>$ is the mean glitch size, and $\epsilon\dot{\nu}$ is the relative angular acceleration of the crust and superfluid. There is no evidence that $\lambda$ changes monotonically with spin-down age. The rate distribution itself is fitted reasonably well by an exponential for $\lambda \geq 0.25 {\rm yr^{-1}}$. For $\lambda < 0.25 {\rm yr^{-1}}$, its exact form is unknown; the exponential overestimates the number of glitching pulsars observed at low $\lambda$, where the limited total observation time exercises a selection bias.