A1 Refereed original research article in a scientific journal
Resolving spatial and temporal shock structures using LOFAR observations of type II radio bursts
Authors: Morosan, Diane E.; Jebaraj, Immanuel Christopher; Zhang, Peijin; Zucca, Pietro; Dabrowski, Bartosz; Gallagher, Peter T.; Krankowski, Andrzej; Vocks, Christian; Vainio, Rami
Publisher: EDP SCIENCES S A
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: A70
Volume: 695
Number of pages: 8
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202452775
Web address : https://doi.org/10.1051/0004-6361/202452775
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/491598706
Context. Collisionless shocks are one of the most powerful particle accelerators in the Universe. In the heliosphere, type II solar radio bursts are signatures of electrons accelerated by collisionless shocks launched at the Sun. Spectral observations of these bursts show a variety of fine structures often composing multiple type II lanes. The origin of these lanes and structures is not well understood and has been attributed to the inhomogeneous environment around the propagating shock.
Aims. Here, we aim to determine the large-scale local structures near a coronal shock wave using high-resolution radio imaging observations of a complex type II radio burst observed on 3 October 2023.
Methods. By using inteferometric imaging from the Low Frequency Array (LOFAR), combined with extreme ultraviolet observations, we investigate the origin of multiple type II lanes at low frequencies (30-80 MHz) relative to the propagating shock wave.
Results. We identify at least three radio sources at metric wavelengths corresponding to a multi-lane type II burst. The type II burst sources propagate outwards with a shock driven by a coronal mass ejection. We find a double radio source that exhibits increasing separation over time, consistent with the expansion rate of the global coronal shock. This suggests that the overall shock expansion is nearly self-similar, with acceleration hotspots forming at various times and splitting at a rate proportional to the shock's expansion.
Conclusions. Our results show the importance of increased spatial resolution in determining either the small-scale spatial properties in coronal shocks or the structuring of the ambient medium. Possible shock corrugations or structuring of the upstream plasma at the scale of 10(5) km can act as hotspots for the acceleration of suprathermal electrons. This can be observed as radiation that exhibits double sources with increasing separation at the same expansion rate as the global shock wave.
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Funding information in the publication:
D.E.M. acknowledges the Research Council of Finland project ‘SolShocks’ (grant number 354409). I.C.J. was funded by the Research Council of Finland project SHOCKSEE (grant No. 346902). This study has received funding from the European Union’s Horizon Europe research and innovation programme under grant agreement No. 101134999 (SOLER). The paper reflects only the authors’ view and the European Commission is not responsible for any use that may be made of the information it contains. 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). The authors wish to acknowledge CSC – IT Center for Science, Finland, for computational resources. This paper is based 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’Orléans, 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.
