Self-organized criticality in a spherically closed cellular automaton: Modeling soft gamma repeater bursts driven by magnetic reconnection

TL;DR

This paper introduces a spherical cellular automaton model to simulate self-organized criticality in soft gamma repeater bursts, highlighting magnetic reconnection as a key mechanism and aligning with observed energy distributions.

Contribution

It presents a novel spherical CA model for SGR bursts that incorporates magnetic reconnection and demonstrates SOC behavior consistent with observations.

Findings

Energy distributions follow a power law with cutoff

SOC state depends on nonzero expectation value of perturbations

Power-law index varies with perturbation amplitude

Abstract

A new cellular automaton (CA) model is presented for the self-organized criticality (SOC) in recurrent bursts of soft gamma repeaters (SGRs), which are interpreted as avalanches of reconnection in the magnetosphere of neutron stars. The nodes of a regular dodecahedron and a truncated icosahedron are adopted as spherically closed grids enclosing a neutron star. It is found that the system enters the SOC state if there are sites where the expectation value of the added perturbation is nonzero. The energy distributions of SOC avalanches in CA simulations are described by a power law with a cutoff, which is consistent with the observations of SGR 1806-20 and SGR 1900+14. The power-law index is not universal and depends on the amplitude of the perturbation. This result shows that the SOC of SGRs can be illustrated not only by the crust quake model but also by the magnetic reconnection model.