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

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.

Distributions of Energy, Luminosity, Duration, and Waiting Times of Gamma-Ray Burst Pulses with Known Redshift Detected by Fermi/GBM

“…One of the main accomplishments of SOC theory is the successful and exhaustive description of solar flares (Lu & Hamilton 1991;Charbonneau et al 2001;Aschwanden & Aschwanden 2008a, 2008bAschwanden & McTiernan 2010;Wang & Dai 2013). A body of evidence for SOC behavior was also found in the case of soft gamma-ray repeaters (SGRs) or magnetars (Nakazato 2014), which are also GRB engine candidates. It is worth noting that SOC behavior in the case of a BH surrounded by an accretion disk was also investigated as well as for the X-ray flaring activity of the Galactic center, Sgr A * (Li et al 2015;Yuan et al 2018).…”