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

TL;DR

This paper demonstrates that high-fidelity spectropolarimetric radio imaging with the MWA can effectively constrain CME plasma parameters by breaking model degeneracies, even with limited polarization data.

Contribution

It introduces a novel application of high-fidelity spectropolarimetric imaging to better determine CME plasma parameters, overcoming previous observational challenges.

Findings

Spectropolarimetric imaging constrains CME plasma parameters more tightly than intensity-only methods.

Polarization data helps break degeneracies in gyrosynchrotron emission modeling.

High dynamic range imaging enables detection of faint CME emissions close to the Sun.

Abstract

Measurements of the plasma parameters of coronal mass ejections (CMEs), particularly the magnetic field and nonthermal 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 remote-sensing techniques for estimating spatially resolved CME plasma parameters. Imaging the very low flux density CME GS emission in close proximity to the Sun with orders of magnitude higher flux density has, however, proven to be rather challenging. This challenge has only recently been met using the high dynamic range imaging capability of the Murchison Widefield Array (MWA). Although routine detection of GS is now within reach, the challenge has shifted to constraining the large number of free parameters in GS models, a few of which are degenerate, using the limited number of spectral points at which the observations are typically available. These degeneracies can be broken using polarimetric imaging. For the first time, we demonstrate this using our recently developed capability of high-fidelity polarimetric imaging on the data from the MWA. We show that spectropolarimetric imaging, even when only sensitive upper limits on circularly polarization flux density are available, is not only able to break the degeneracies but also yields tighter constraints on the plasma parameters of key interest than possible with total intensity spectroscopic imaging alone.