Electron acceleration by cascading reconnection in the solar corona I Magnetic gradient and curvature effects

TL;DR

This study models electron acceleration in the solar corona's magnetic reconnection regions, revealing how magnetic field gradients and curvature influence electron trajectories and resulting X-ray emissions.

Contribution

It introduces a test particle approach combined with high-resolution MHD simulations to analyze electron acceleration and resulting X-ray spectra in cascading magnetic reconnection.

Findings

Magnetic gradients and curvature accelerate electrons in reconnection regions.

Electrons are trapped, precipitate, or are ejected based on initial conditions.

Trapped electrons contribute to observed X-ray bright spots.

Abstract

Aims: We investigate the electron acceleration in convective electric fields of cascading magnetic reconnection in a flaring solar corona and show the resulting hard X-ray (HXR) radiation spectra caused by Bremsstrahlung for the coronal source. Methods: We perform test particle calculation of electron motions in the framework of a guiding center approximation. The electromagnetic fields and their derivatives along electron trajectories are obtained by linearly interpolating the results of high-resolution adaptive mesh refinement (AMR) MHD simulations of cascading magnetic reconnection. Hard X-ray (HXR) spectra are calculated using an optically thin Bremsstrahlung model. Results: Magnetic gradients and curvatures in cascading reconnection current sheet accelerate electrons: trapped in magnetic islands, precipitating to the chromosphere and ejected into the interplanetary space. The final location of an electron is determined by its initial position, pitch angle and velocity. These initial conditions also influence electron acceleration efficiency. Most of electrons have enhanced perpendicular energy. Trapped electrons are considered to cause the observed bright spots along coronal mass ejection CME-trailing current sheets as well as the flare loop-top HXR emissions.