Determining the acceleration regions of in situ electrons using remote radio and X-ray observations

¹ Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland
² Turku Collegium for Science, Medicine and Technology, University of Turku, 20014 Turku, Finland
³ Leibniz Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Department of Physics, University of Helsinki, PO Box 64 FI-00014 Helsinki, Finland
⁵ ASTRON – the Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
⁶ Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, R. Prawochenskiego 9, 10-719 Olsztyn, Poland

^⋆ Corresponding author; diana.morosan@utu.fi

Received: 7 October 2024
Accepted: 2 December 2024

Abstract

Context. Solar energetic particles in the heliosphere are produced by flaring processes on the Sun or by shocks driven by coronal mass ejections. These particles are regularly detected remotely as electromagnetic radiation (X-rays or radio emission), which they generate through various processes, or in situ by spacecraft monitoring the Sun and the heliosphere.

Aims. Our aim is to combine remote-sensing and in situ observations of energetic electrons to determine the origin and acceleration mechanism of these particles.

Methods. Here we investigate the acceleration location, escape, and propagation directions of electron beams producing radio bursts observed with the Low Frequency Array (LOFAR), hard X-ray (HXR) emission, and in situ electrons observed at Solar Orbiter on 3 October 2023. These observations are combined with a three-dimensional (3D) representation of the electron acceleration locations and results from a magnetohydrodynamic (MHD) model of the solar corona in order to investigate the origin and connectivity of electrons observed remotely at the Sun to in situ electrons.

Results. We observed a type II radio burst with good connectivity to Solar Orbiter, where a significant electron event was detected. However, type III radio bursts and hard X-rays were also observed co-temporally with the electron event, but likely connected to Solar Orbiter by different far-side field lines. The injection times of the Solar Orbiter electrons are simultaneous with both the onset of the type II radio burst, the group of type III bursts, and the presence of a second HXR peak; however, the most direct connection to Solar Orbiter is that of the type II burst location. The in situ electron spectra point to shock acceleration of electrons with a short-term connection to the source region.

Conclusions. We propose that there are two contributions to the Solar Orbiter electron fluxes based on the results and magnetic connectivity determined from remote-sensing data: a smaller flare contribution from the far-side of the Sun and a main shock contribution from the region close to the eastern limb as viewed from Earth. We note that these two electron acceleration regions are distinct and separated by a large distance and are connected via two separate field lines to Solar Orbiter.