A detailed look at a type II radio burst using the Murchison Widefield Array

Abstract:

Type II solar radio bursts are believed to be caused by magnetohydrodynamics (MHD) shock accelerated electrons. Often, a type II burst is seen to have two emission lanes: harmonic and fundamental. Sometimes, both fundamental and harmonic type II emissions are split into a higher and lower sub-band, which is referred to as band splitting. These bands are believed to be coming from downstream and upstream regions of the shockfront respectively. Here we present the results from imaging analysis of a type II radio burst associated with a GOES M class flare observed by the Murchison Widefield Array (MWA). The MWA provides high sensitivity data enabling high-quality spectroscopic snapshot imaging capability spanning the range 80-300 MHz with a time resolution of 0.5 s and frequency resolution of 40 kHz. Curiously, as seen in the Figure, instead of the band splitting, the MWA dynamic spectrum of the harmonic band shows many fine temporal and spectral structures. Upon investigating we have found out that the type II source size approximately scales with λ. Examination of the variation in the location of the compact radio source associated with type II emission as a function of time and frequency shows that these variations are very systematic and very well correlated across neighboring times and frequencies. This suggests that these variations are mostly likely arising due to propagation effects, a combination of scattering and refraction, and not because of the physical motion of the shock location. So, these data can potentially provide an excellent opportunity to use the observed properties of the source to constraint the parameters of coronal turbulence. Our data also include simultaneous imaging of the fundamental and harmonic emission for a small part of the burst, which is believed to arise from the same location. Any apparent differences in their size and location can hence be attributed to propagation effects. We present our preliminary investigations of these aspects.