Deciphering Faint Gyrosynchrotron Emission from Coronal Mass Ejection using Spectro-polarimetric Radio Imaging

Measurements of the plasma parameters of coronal mass ejections (CMEs), particularly the magnetic field and non-thermal electron population entrained in the CME plasma, are crucial to understand their propagation, evolution, and geo-effectiveness. Spectral modeling of gyrosynchrotron (GS) emission from CME plasma has been regarded as  one of the most promising methods to estimate spatially resolved CME plasma parameters remotely. The very low flux density of CME GS emission, however, makes this rather  challenging. This challenge has recently been overcome using the high dynamic range imaging capability of the Murchison Widefield Array (MWA). Although the detection of GS is now possible routinely, the large number of free parameters of the GS models and some degeneracies between the values of these parameters make it hard to estimate all of them from the observed spectrum alone. These degeneracies can be broken using polarimetric imaging. In this work, we demonstrate this using our newly developed capability of robust polarimetric imaging on the data from the MWA. Very interestingly, we find that spectro-polarimetric imaging not only breaks the degeneracies but also provides tighter constraints on a larger number of plasma parameters than possible with total intensity spectroscopic imaging alone.