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Imaging Spectroscopy of CME-Associated Solar Radio Bursts using OVRO-LWA

Published onAug 18, 2020
Imaging Spectroscopy of CME-Associated Solar Radio Bursts using OVRO-LWA

Radio emission from the solar corona provides a unique perspective on the physical properties of energetic phenomena, such as solar flares and coronal mass ejections (CMEs). We present first results of a solar radio event observed with the new state-of-the-art Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection and an M2.1 GOES soft X-ray flare from 2015 September 20, as well as quiet Sun images before and after the bursts. Images of 9-s cadence are used to analyze the event over a 120-minute period, and solar emission is observed out to a distance of ≈3.5R, over the frequency range of 40-70MHz available at that time. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. A coalignment with the LASCO(C2) coronagraph allows a spatial and temporal comparison with observations of the CME in white light, indicating an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell (GCS) reconstruction of the CME, we constrain the density in the volume. We find that the estimated density values yield an electron plasma frequency lower than, but close to the observed emission frequency, rendering it difficult to completely dismiss the possibility of plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral fitting techniques to estimate the evolving physical conditions during the outward motion of this CME-associated radio burst source.

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