Reconnection in the Post-Impulsive Phase of Solar Flares

TL;DR

This paper analyzes the magnetic reconnection rate during the late phase of solar flares, showing that fast reconnection requires mechanisms like localized resistivity or turbulence to shorten the diffusion region.

Contribution

It introduces an analytical method to determine reconnection rates in solar flare models and highlights the importance of additional mechanisms for fast reconnection.

Findings

Reconnection rate remains slow with uniform resistivity and laminar flow.

Short diffusion regions are implied by XRT observations.

Localized resistivity or turbulence can enable fast reconnection.

Abstract

Using a recently developed analytical procedure, we determine the rate of magnetic reconnection in the "standard" model of eruptive solar flares. During the late phase, the neutral line is located near the lower tip of the reconnection current sheet, and the upper region of the current sheet is bifurcated into a pair of Petschek-type shocks. Despite the presence of these shocks, the reconnection rate remains slow if the resistivity is uniform and the flow is laminar. Fast reconnection is achieved only if there is some additional mechanism that can shorten the length of the diffusion region at the neutral line. Observations of plasma flows by the X-Ray Telescope (XRT) on Hinode imply that the diffusion region is in fact quite short. Two possible mechanisms for reducing the length of the diffusion region are localized resistivity and MHD turbulence.