Frequency Dependence of Polarization of Zebra Pattern in Type-IV Solar Radio Bursts

TL;DR

This study analyzed the polarization properties of a zebra pattern in a solar radio burst, revealing frequency-dependent polarization degree and delays, supporting the double plasma resonance model and mode conversion effects.

Contribution

It provides the first detailed measurement of polarization delay and frequency dependence in ZP, supporting the double plasma resonance generation mechanism.

Findings

Degree of circular polarization was 50-70%, mostly right-handed.

Left-handed component delayed by 50-70 ms, increasing with frequency.

Results support the double plasma resonance model with mode conversion effects.

Abstract

We investigated the polarization characteristics of a zebra pattern (ZP) in a type-IV solar radio burst observed with AMATERAS on 2011 June 21 for the purpose of evaluating the generation processes of ZP. Analyzing highly resolved spectral and polarization data revealed the frequency dependence of the degree of circular polarization and the delay between two polarized components for the first time. The degree of circular polarization was 50-70 percent right-handed and it varied little as a function of frequency. Cross-correlation analysis determined that the left-handed circularly polarized component was delayed by 50-70 ms relative to the right-handed component over the entire frequency range of the ZP and this delay increased with the frequency. We examined the obtained polarization characteristics by using pre-existing ZP models and concluded that the ZP was generated by the double plasma resonance process. Our results suggest that the ZP emission was originally generated in a completely polarized state in the O-mode and was partly converted into the X-mode near the source. Subsequently, the difference between the group velocities of the O-mode and X-mode caused the temporal delay.