A1 Refereed original research article in a scientific journal
Determining the acceleration regions of in situ electrons using remote radio and X-ray observations
Authors: Morosan, D. E.; Dresing, N.; Palmroos, C.; Gieseler, J.; Jebaraj, I. C.; Warmuth, A.; Fedeli, A.; Normo, S.; Pomoell, J.; Kilpua, E. K. J.; Zucca, P.; Dabrowski, B.; Krankowski, A.; Mann, G.; Vocks, C.; Vainio, R.
Publisher: EDP Sciences
Publishing place: LES ULIS CEDEX A
Publication year: 2025
Journal: Astronomy and Astrophysics
Journal name in source: Astronomy & Astrophysics
Journal acronym: ASTRON ASTROPHYS
Article number: A296
Volume: 693
Number of pages: 12
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202452511
Web address : https://doi.org/10.1051/0004-6361/202452511
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/485101664
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.
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Funding information in the publication:
This study has received funding from the European Union’s (EU’s) Horizon 2020 research and innovation programme under grant agreement No. 101004159 (SERPENTINE) and EU’s Horizon Europe research and innovation programme under grant agreement No. 101134999 (SOLER). This research reflects only the authors’ view and the European Commission is not responsible for any use that may be made of the information it contains. D.E.M acknowledges the Research Council of Finland project ‘SolShocks’ (grant number 354409). N.D. and I.C.J. are grateful for support from the Research Council of Finland (SHOCKSEE, grant No. 346902). A.F. acknowledges the Vilho, Yrjö and Kalle Väisälä Foundation of the Finnish Academy of Science and Letters. J.P. acknowledges the Research Council of Finland Project 343581 (SWATCH). The research is performed under the umbrella of the Finnish Centre of Excellence in Research of Sustainable Space (FORESAIL) funded by the Research Council of Finland (grant no. 352847 and 352850). The authors wish to acknowledge CSC – IT Center for Science, Finland, for computational resources. This paper is based (in part) on data obtained with the LOFAR telescope (LOFAR-ERIC) under project code LC20_001. LOFAR (van Haarlem et al. 2013) is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the LOFAR European Research Infrastructure Consortium (LOFAR-ERIC) under a joint scientific policy. The LOFAR-ERIC resources have benefited from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Oréans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland.
