  The geo-effectiveness of coronal mass ejections (CMEs) is determined
primarily by their magnetic fields. Modeling of Gyrosynchrotron (GS) emission
is a promising remote sensing technique to measure the CME magnetic field at
coronal heights. However, faint GS emission from CME flux ropes is hard to
detect in the presence of bright solar emission from the solar corona. With
high dynamic-range spectropolarimetric meter wavelength solar images provided
by the Murchison Widefield Array, we have detected faint GS emission from a CME
out to $\sim 8.3\ R_\odot$, the largest heliocentric distance reported to date.
High-fidelity polarimetric calibration also allowed us to robustly detect
circularly polarized emission from GS emission. For the first time in
literature, Stokes V detection has jointly been used with Stokes I spectra to
constrain GS models. One expects that the inclusion of polarimetric measurement
will provide tighter constraints on GS model parameters. Instead, we found that
homogeneous GS models, which have been used in all prior works, are unable to
model both the total intensity and circular polarized emission simultaneously.
This strongly suggests the need for using inhomogeneous GS models to robustly
estimate the CME magnetic field and plasma parameters.
