Source locations of multiple type II solar radio bursts associated with a slow coronal mass ejection

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Abstract
Context. Electrons accelerated by coronal shock waves can be remotely detected as type II solar radio bursts. Radio imaging of these bursts can be used to study the presence of shocks in the solar corona especially when other clear observations of the shock are missing at other wavelengths. Aims. Our aim is to investigate the origin and source locations of two type II solar radio bursts associated with a faint and slow coronal mass ejection (CME) using imaging and spectroscopic observations from the LOw Frequency ARray (LOFAR) together with a magnetohydrodynamic (MHD) model of the solar corona. Methods. We use dynamic spectra of the observed type II bursts to track them in frequency and time. We then use the imaging observations at the corresponding frequencies and times to see where the type II sources are located relative to the Sun. Finally, we combine the imaging observations with a global MHD model of coronal densities and magnetic field to de-project the radio source locations and investigate the properties of the emitting regions. Results. Imaging of the type II bursts shows that they originate from different regions in the corona. Combining LOFAR imaging with the MHD model shows that despite their separate source locations, both type II bursts originate along a coronal streamer characterised by high density and low Alfvèn speed. Conclusions. The different source locations of the type II bursts suggest that a single coronal shock driven by a weak CME can accelerate electrons at multiple separate locations along the shock front. The results indicate that a CME interacting with a streamer can create favourable conditions for the generation of type II bursts. The high density leads to low values of Alfvèn speed, and thus, even a slow CME can drive a shock capable of accelerating electrons in these regions.
Funding Information
  • Research Council of Finland (353309)
  • Väisälän Rahasto
  • Research Council of Finland (374097)
  • Cooperative Programs for the Advancement of Earth System Science (80NSSC22M0097)
  • HORIZON EUROPE Framework Programme (101134999)

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