Bursty acceleration and 3D trajectories of electrons in a solar flare

¹ Astronomy & Astrophysics Section, Dublin Institute for Advanced Studies, Dublin D02 XF86, Ireland
² School of Physics, Trinity College Dublin, College Green, Dublin 2, Ireland
³ European Space Agency, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁴ LIRA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁵ Observatoire Radioastronomique de Nançay, Observatoire de Paris, PSL Research University, CNRS, Univ. Orléans, 18330 Nançay, France

^⋆ Corresponding author; bhunias@tcd.ie

Received: 8 July 2024
Accepted: 2 February 2025

Abstract

Context. During a solar flare, electrons are accelerated to non-thermal energies as a result of magnetic reconnection. These electrons then propagate upwards and downwards from the energy release site along magnetic field lines and produce radio and X-ray emission.

Aims. On 11 November 2022, an M5.1 solar flare was observed by the Spectrometer/Telescope for Imaging X-rays (STIX) on board Solar Orbiter together with various ground- and space-based radio instruments. The flare was associated with several fine hard X-ray (HXR) structures and a complex set of metric radio bursts (type III, J, and narrowband). By studying the evolution of X-ray, extreme ultraviolet, and radio sources, we aim to study the trajectories of the flare-accelerated electrons in the lower solar atmosphere and low corona.

Methods. We used observations from the STIX on board Solar Orbiter to study the evolution of X-ray sources. Using radio imaging from the Nançay Radio heliograph (NRH) and the Newkirk density model, we constructed 3D trajectories of 14 radio bursts.

Results. Imaging of the HXR fine structures shows several sources at different times. The STIX and NRH imaging shows correlated changes in the location of the HXR and radio source at the highest frequency during the most intense impulsive period. Imaging and 3D trajectories of all the bursts show that electrons are getting accelerated at different locations and along several distinct field lines. Some of the trajectories from the same origin show expansion on the order of 4 over a height of ∼110 Mm. The longitude and latitude extent of the trajectories are ∼30″ and ∼152″.

Conclusions. We find that the electrons producing HXR and radio emission have similar acceleration origins. Importantly, our study supports the scenario that the flare acceleration process is temporally and spatially fragmentary, and during each of these small-scale processes, the electron beams are injected into a very fibrous environment and produce complex HXR and radio emission.