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

Abstract

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 remote sensing technique 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, however, has 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, in addition to breaking the degeneracies, spectropolarimetric spectroscopic imaging also yields tighter constraints on the plasma parameters of key interest than possible with total intensity spectroscopic imaging alone.

Space Weather Research using Spectropolarimetric Radio Imaging Combined With Aditya-L1 and PUNCH Missions

“…Mondal et al (2020) demonstrated that with high-dynamic range imaging with the MWA, it is possible to detect GS emission from slow CMEs as well and also at much higher coronal heights (∼ 4.73 R ). In another event, Kansabanik et al (2023) detected GS emission from another two slow CMEs, as shown in Figure 3. The GS radio emission from the southwestern CME is detected up to 8.5 R , the highest heliocentric distance to date.…”

“…) in the presence of CME magnetic elds. Using the ground-based radio observations, these methods can be used to measure the CME-entrained magnetic elds up to ∼ 10 R (Kansabanik et al, 2023).…”

“…The GS radio emission from the southwestern CME is detected up to 8.5 R , the highest heliocentric distance to date. Studies by Mondal et al (2020) and Kansabanik et al (2023) successfully demonstrated that the high-dynamic-range imaging o ered by the MWA data allowed us to detect much fainter GS emissions from the slow CMEs.…”

“…GS model has ten free parameters, which cannot be constraint using Stokes I spectrum alone. Kansabanik et al (2023) have demonstrated that simultaneous use of constrains from Stokes I and V observations break some degeneracies between GS model parameters, the use of multi-vantage point coronagraph observations allow one to independently estimate the geometric parameters of the CME, signi cantly improve the robustness of the magnetic elds and other estimated parameters.…”