The effect of scattering on split-band Type II solar radio bursts

Nicolina Chrysaphi, University of Glasgow

Shocks driven by coronal mass ejections (CMEs) can accelerate electrons which through the plasma emission mechanism can produce radio signatures known as Type II solar radio bursts. A characteristic of some Type II bursts is the splitting of a harmonic band into thinner lanes, a phenomenon known as band splitting. We present a detailed imaging and spectroscopic observation of a split-band Type II burst recorded with the LOw-Frequency ARray (LOFAR). We show, for the first time, simultaneous images of the higher- and lower-frequency sub-band sources and find that they experience a large separation. The effect of radio-wave scattering—the dominant process affecting radio waves—is taken into account. We find that the amount by which scattering shifts the true location of a lower-frequency source is larger than the shift of a higher-frequency source such that two sources originating from virtually co-spatial regions will appear to be significantly separated. This provides supporting evidence for band-splitting models that require the emission sources of a split-band Type II burst to originate from nearly the same spatial location, like the model attributing band splitting to radiation emitted from the upstream and downstream regions of a shock front.