First Robust Detection of Linear Polarization from Metric Solar Emissions: Challenging Established Paradigms

TL;DR

This paper provides the first robust evidence of linear polarization in solar radio emissions at meter wavelengths, challenging decades-old assumptions and improving understanding of solar plasma conditions.

Contribution

It presents the first confirmed detection of linear polarization from solar emissions at meter wavelengths using dual-telescope observations, challenging established paradigms.

Findings

Consistent linear polarization fractions observed with two different telescopes.

Rapid changes in polarization morphology and fraction detected.

Instrumental effects ruled out as the cause of polarization signals.

Abstract

Polarimetric radio observations of the Sun can provide rich information about emission mechanisms and the propagation medium. For the past five decades, solar polarimetric studies at low radio frequencies have almost always assumed the absence of linear polarization. This has been based on the expectations from coronal propagation effects. Here we present the first robust evidence of linear polarization from solar emissions at meter wavelengths using simultaneous measurements with two telescopes of very different designs separated by thousands of kilometers - the Murchison Widefield Array and the upgraded Giant Metrewave Radio Telescope. Both datasets show consistent linear polarization fractions, confirming this detection. Rapid changes in morphology, as well as the fractional linear polarization at small time and frequency spans, further rule out any possibilities of an instrumental origin. Assuming the absence of linear polarization in solar radio emissions can result in incorrect interpretation of solar observations as well as those of other flare stars, which are often guided by learnings from solar studies. This discovery highlights the need for relaxing this assumption, and is essential for precise estimation of polarization signatures, ultimately leading to a better understanding of the plasma conditions in the Sun and other stars.