Magnetic connectivity of coronal loops and flare-accelerated electrons in a B-class flare

Based on X-ray, EUV (DEM analysis), and type-III radio burst observations

¹ Leibniz Institute for Astrophysics Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
² Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
³ Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, R. Prawocheńskiego 9, 10-719 Olsztyn, Poland
⁴ Center for mathematical Plasma Astrophysics, Department of Mathematics, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
⁵ Solar-Terrestrial Centre of Excellence, Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Uccle, Belgium
⁶ RAL Space, United Kingdom Research and Innovation – Science & Technology Facilities Council – Rutherford Appleton Laboratory, Harwell Campus, Oxfordshire OX11 0QX, UK
⁷ Polish Academy of Sciences, Palace of Culture and Science, Pl. Defilad 1, 00-901 Warsaw, Poland
⁸ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

^⋆ Corresponding authors; malte.broese@fu-berlin.de, cvocks@aip.de

Received: 19 January 2024
Accepted: 7 December 2024

Abstract

Context. In solar flares, non-potential magnetic field energy is transferred to particle acceleration, heating, and radiation. Multi-wavelength observations of the solar corona in extreme ultraviolet (EUV) and X-ray show the consequences of magnetic reconfiguration in lower heights, while radio observations contain information about the access of flare-accelerated electrons to greater heights in the solar atmosphere. Signs of downward and upward particle propagation do not always appear symmetrically, they depend on the acceleration process, the sensitivity of the instruments, and the magnetic connectivity. The magnetic connectivity in various flare phases is therefore a key element to study in order to gain a better understanding of combined flare observations.

Aims. We aim to draw conclusions about the magnetic connectivity of specific coronal loops in the active region, the acceleration region, and the higher corona with respect to different phases of the flare process.

Methods. We investigate the evolution of particle acceleration, loops heated by the energy release, and the trajectories of flare-accelerated electrons observed up to one solar radius (1 R_S) above the active region in a B-class flare on 6 June 2020. We studied the downward particle acceleration and thermal evolution with observations by the Spectrometer/Telescope for Imaging X-rays and with a reconstruction code based on EUV observations. Traces of flare-accelerated electrons, namely, type-III radio bursts, were investigated with a spectroscopic solar dynamic radio imager (LOw Frequency ARray). The radio source positions in heights of 0.4 R_S–1.0 R_S were compared with the thermal evolution of coronal loops and with a solar magnetic field model.

Results. In this flare event, similar magnetic reconnection processes and accompanied heating processes are triggered several times. For loops and periods with access to the higher corona, type-III bursts from similar reconnection process are emitted along similar propagation trajectories. There are no radio bursts associated with the heating process of the main flaring loop.

Conclusions. In this event, the large-scale magnetic field is rather stable and seems not to be affected by the flare. The access to loops reaching heights of half a solar radius or more is suppressed during the main flare phase for flare-accelerated electrons. This may lead to more effective heating and absent type-III radio bursts between 20 MHz and 85 MHz.