Abstract:
We present rare contemporaneous low-frequency (< 100 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 ≈ 1 gauss) in the CME leading edge at a heliocentric distance of ≈ 2.2 R⊙ agrees well
with the similar B values reported earlier based on other types of observations.
