Diffusive Transport of Energetic Electrons in the Solar Corona: X-ray and Radio Diagnostics

TL;DR

This paper uses X-ray and radio observations to study how energetic electrons are transported and trapped in the solar corona during a flare, revealing that their scattering mean free path decreases with energy.

Contribution

It demonstrates that combining X-ray and radio diagnostics effectively investigates electron transport and provides the first estimate of the energy dependence of the scattering mean free path in the solar corona.

Findings

Electrons are trapped in the corona with spectral hardening observed.

Coronal trapping is stronger for radio-emitting electrons.

The scattering mean free path decreases with electron energy between 25-500 keV.

Abstract

Imaging spectroscopy in X-rays with RHESSI provide the possibility to investigate the spatial evolution of the X-ray emitting electron distribution and therefore to study the transport effects on energetic electrons during solar flares. We study the energy dependence of the energetic electron scattering mean free path in the solar corona. We use the imaging spectroscopy technique with RHESSI to study the evolution of energetic electrons distribution in different part of the magnetic loop during the 2004 May 21 flare. These observations are compared with the radio observations of the gyrosynchrotron radiation of the same flare by Kuznetsov and Kontar (2015), and with the predictions of the diffusive transport model described by Kontar et al. (2014). The X-ray analysis shows a trapping of energetic electrons in the corona and a spectral hardening of the energetic electron distribution between the top of the loop and the footpoints. Coronal trapping of electrons is stronger for the radio-emitting electrons than for the X-ray-emitting electrons. These observations can be explained by the diffusive transport model derived by Kontar et al. (2014). We show that the combination of X-ray and radio diagnostics is a powerful tool to study electron transport in the solar corona in different energy domains. We show that the diffusive transport model can explain our observations; and in the range 25-500 keV, the electron scattering mean free path decreases with electron energy. We can estimate for the first time the scattering mean free path dependence on energy in the corona.