Source location and evolution of a multilane type II radio burst

¹ ASTRON – Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
² Center for Solar-Terrestrial Research, New Jersey Institute of Technology, Newark, NJ 07102, USA
³ Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72 Tsarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
⁴ Astronomy & Astrophysics Section, School of Cosmic Physics, Dublin Institute for Advanced Studies, DIAS Dunsink Observatory, Dublin D15 XR2R, Ireland
⁵ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, S. P. Pune University Campus, Pune 411007, India
⁶ Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Badi Road, Udaipur, 313001 Rajasthan, India
⁷ Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
⁸ Cooperative Programs for the Advancement of Earth System Science, University Corporation for Atmospheric Research, Boulder, CO, USA
⁹ Turku Collegium for Science, Medicine and Technology, University of Turku, 20014 Turku, Finland
¹⁰ Space Radio-Diagnostics Research Centre, University of Warmia and Mazury, R. Prawochenskiego 9, 10-719 Olsztyn, Poland
¹¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany

^⋆ Corresponding author: zucca@astron.nl

Received: 3 March 2025
Accepted: 11 October 2025

Abstract

Context. Shocks in the solar corona are capable of accelerating electrons that in turn generate radio emission known as type II radio bursts. The characteristics and morphology of these radio bursts in the dynamic spectrum reflect the evolution of the shock itself, together with the properties of the local corona where the shock propagates.

Aims. In this work we study the evolution of a complex type II radio burst with a multilane structure to find the locations where the radio emission is produced and relate them to the properties of the local environment where the shock propagates.

Methods. Using radio imaging, we were able to separately track each lane composing the type II burst and relate the position of the emission to the properties of the ambient medium, such as density, Alfvén speed, and magnetic field.

Results. We show that the radio burst morphology in the dynamic spectrum changes with time and is related to the complexity of the local environment. The initial stage of the radio emission is characterized by a single broad lane in the spectrum, while the later stages of the radio signature evolve in a multilane scenario. The radio imaging reveals how the initial stage of the radio emission separates with time into different locations along the shock front as the density and orientation of the magnetic field change along the shock propagation. At the time when the spectrum shows a multilane shape, we find a clear separation of the imaged radio sources propagating in regions with different densities.

Conclusions. By combining radio imaging with the properties of the local corona, we describe the evolution of a type II radio burst and, for the first time, identify three distinct radio emission regions above the coronal mass ejection front. Two regions were located at the flanks, producing earlier radio emission than the central position, in accordance with the complexity of density and Alfvén speed values in the regions where radio emission is generated. This unprecedented observation of a triple-source structure provides new insights into the nature of multilane type II bursts.