The Power-Law Distribution of Flare Kernels and Fractal Current Sheets in a Solar Flare

TL;DR

This study analyzes the fine structure and temporal evolution of flare kernels during a solar flare, revealing power-law distributions indicative of self-organized criticality and fractal current sheets in magnetic reconnection.

Contribution

It provides detailed observational evidence linking flare kernel properties to power-law distributions, supporting models of self-organized criticality in solar flares.

Findings

C IV kernels correlate with Ha and HXR emissions

Kernel intensities follow power-law distributions

Evidence for fractal current sheets in reconnection region

Abstract

We report a detailed examination of the fine structure inside flare ribbons and the temporal evolution of this fine structure during the X2.5 solar flare that occurred on 2004 November 10. We examine elementary bursts of the C IV (1550{\AA}) emission lines seen as local transient brightenings inside the flare ribbons in the ultraviolet (1600{\AA}) images taken with Transition Region and Coronal Explorer, and we call them C IV kernels. This flare was also observed in Ha with the Sartorius 18 cm Refractor telescope at Kwasan observatory, Kyoto University, and in hard X-rays (HXR) with Reuven Ramaty High Energy Solar Spectroscopic Imager. Many C IV kernels, whose sizes were comparable to or less than 2", were found to brighten successively during the evolution of the flare ribbon. The majority of them were well correlated with the Ha kernels in both space and time, while some of them were associated with the HXR emission. These kernels were thought to be caused by the precipitation of nonthermal particles at the footpoints of the reconnecting flare loops. The time profiles of the C IV kernels showed intermittent bursts, whose peak intensity, duration, and time interval were well described by power-law distribution functions. This result is interpreted as evidence for "self-organized criticality" in avalanching behavior in a single flare event, or for fractal current sheets in the impulsive reconnection region.