Simultaneous Near-Sun Observations of a Moving Type IV Radio Burst and the Associated White-Light Coronal Mass Ejection

Abstract

We present rare contemporaneous low-frequency ($< 100~\mbox{MHz}$) imaging, spectral, and polarimetric observations of a moving type IV radio burst that had close spatio-temporal association with a white-light coronal mass ejection (CME) near the Sun. We estimate the electron density near the burst region from white-light coronagraph polarized brightness (pB) images of the CME as well as the two-dimensional radio imaging observations of the thermal free-free emission at a typical radio frequency such as 80 MHz. We analyze the burst properties such as the degree of circular polarization, the spectral index, and fine structures using the radio polarimeter and the radio spectral observations. The obtained results suggest that second harmonic plasma emission from the enhanced electron density in the leading edge of the CME is the cause of the radio burst. We determine the strength of the coronal magnetic field ($B$) for the first time based on this interpretation. The estimated value ($B \approx 1$ gauss) in the CME leading edge at a heliocentric distance of $\approx 2.2~R_{\odot }$ agrees well with the similar $B$ values reported earlier based on other types of observations.