Abstract Details

Name: Divya Oberoi
Affiliation: National Centre for Radio Asrtophysics - Tata Institute of Fundamental Research
Conference ID: ASI2021_32
Title : Spectroscopic snapshot imaging of solar type II bursts : A new tool for exploring coronal propagation effects
Authors and Co-Authors : Divya Oberoi (NCRA-TIFR)
Abstract Type : Poster
Abstract Category : Sun and the Solar System
Abstract : Type II bursts are the strongest active solar radio emissions. They are usually seen at metrewaves as a pair of drifting emission bands, at frequencies corresponding to the local plasma frequency at the site of origin and its harmonic. They are associated with the faster, more energetic coronal mass ejections (CMEs) and believed to arise from the locations of shocks on the CME front. As the shocks propagates out through the corona, the emission drifts from higher to lower frequencies. These emissions are clearly of great interest from a space weather perspective. However the vast majority of the studies of these bursts have relied on non-imaging observations from solar radio spectrographs, which tends to limit their utility. This emission is highly structured in both time and frequency, and hence their imaging studies require a spectroscopic snapshot imaging capability. This has possible only comparatively recently with the new generation instruments like the Murchison Widefield Array (MWA). We present the first detailed spectroscopic imaging study of a type II burst with the MWA. We find the type II source to be only marginally resolved implying the presence of a localised shock. Very interestingly, for the first time, these high signal-to-noise observations show the location of the type II source to show small scale motions which are very coherent across neighbouring time and frequency slices, but seem quasi-random over larger spans in time or frequency. It is evident that this cannot arise simply because of the motion of the shock through the coronal medium. We believe that these apparent motions arise due to the propagation effects (refraction and scattering) encountered by the plasma emission originating from a compact source as it traverses the highly structured and turbulent corona. These observations hold considerable promise to provide a novel approach to studying coronal turbulence.