Connecting energetic electrons at the Sun and in the heliosphere through X-ray and radio diagnostics

¹ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
² Goddard Planetary Heliophysics Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA
³ Heliospheric Physics Laboratory, Heliophysics Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁴ Radboud Radio Lab, Department of Astrophysics/IMAPP-Radboud University, NL-6500 GL Nijmegen, The Netherlands

^⋆ Corresponding author; david.paipa@obspm.fr

Received: 17 September 2024
Accepted: 12 December 2024

Abstract

Context. Solar flares release huge amounts of energy, a considerable part of which is channeled into particle acceleration in the lower corona. Hard X-ray (HXR) emissions are used to diagnose the accelerated electrons that bombard the chromosphere, while type III radio bursts result from energetic electron beams propagating through the corona and into interplanetary space. The Solar Orbiter mission, launched in 2020, aims to link solar flare remote observations with heliospheric events, thus producing useful observations for our understanding of particle acceleration and propagation from the Sun to the heliosphere.

Aims. While both hard X-Ray and radio emissions result from flare-accelerated electrons, their relationship is not straightforward. By comparing the evolution of the X-ray emitting sites and the timing of type III bursts, our aim is to determine the conditions for associations between X-ray flares and interplanetary (IP) type III bursts.

Methods. We analyzed 15 interplanetary type III bursts that are associated with HXR bursts in the first available period for simultaneous X-ray/radio observations of type III bursts from Solar Orbiter (using the RPW and STIX instruments). X-ray imaging was performed around the onset of the type III bursts, complemented by EUI 174 Å images to assess the magnetic configuration of the corona.

Results. All 15 X-ray flares originated from the same active region on the west limb as observed by Solar Orbiter. In each of the events, a change in X-ray source morphology occurred shortly (< 6 minutes) before the onset of type III radio bursts, indicating a change in the electron acceleration region preceding the radio emission. Considering the delays observed between the two emissions, these findings describe complex scenarios with multiple reconnection episodes, some of which may allow accelerated electrons to escape into IP space when open magnetic field lines are involved (interchange reconnection). In some cases, X-ray source elongations toward open field lines in the UV were observed, reinforcing this idea.