Reconnection Electric Field and Hardness of X-Ray Emission of Solar Flares

TL;DR

This study investigates the relationship between reconnection electric fields and X-ray emission hardness in solar flares, revealing strong correlations that support electron acceleration models based on magnetic reconnection.

Contribution

It presents a novel comparison of reconnection electric field measurements from ribbon motion with X-ray spectral hardness in solar flares.

Findings

Reconnection electric field is strongly anti-correlated with X-ray spectral index.

Reconnection electric field correlates with flare magnitude.

Supports models of electron acceleration driven by reconnection electric fields.

Abstract

Magnetic reconnection is believed to be the prime mechanism to trigger solar flares and accelerate electrons up to energies of MeV. In the classical two-dimensional reconnection model, the separation motion of chromospheric ribbons manifests the successive reconnection that takes place higher up in the corona. Meanwhile, downward traveling energetic electrons bombard the dense chromosphere and create hard X-ray (HXR) emissions, which provide a valuable diagnostic of electron acceleration. Analyses of ribbon dynamics and HXR spectrum have been carried out separately. In this Letter, we report a study of the comparison of reconnection electric field measured from ribbon motion and hardness (spectral index) of X-ray emission derived from X-ray spectrum. Our survey of the maximum average reconnection electric field and the minimum overall spectral index for 13 two-ribbon flares show that they are strongly anti-correlated. The former is also strongly correlated with flare magnitude measured using the peak flux of soft X-ray emissions. These provide strong support for electron acceleration models based on the electric field generated at reconnecting current sheet during flares.