Thomson scattering above solar active regions and an ad-hoc polarization correction method for the emissive corona

TL;DR

This paper explores using the polarized nature of the solar corona's Thomson scattering to develop an ad-hoc correction method for instrument-induced polarization crosstalk, enhancing measurement accuracy.

Contribution

It introduces a formalism for deriving Stokes parameters of Thomson scattering and proposes a correction technique based on polarized signals and advanced coronal modeling.

Findings

Correction of polarization crosstalk is feasible with the proposed method.

The approach accounts for symmetry-breaking features in the incident radiation.

Simulations show potential for improved polarization measurements in solar observations.

Abstract

Thomson scattered photospheric light is the dominant constituent of the lower solar corona's spectral continuum viewed off-limb at optical wavelengths. Known as the K-corona, it is also linearly polarized. We investigate the possibility of using the a priori polarized characteristics of the K-corona, together with polarized emission lines, to measure and correct instrument-induced polarized crosstalk. First, we derive the Stokes parameters of Thomson scattering of unpolarized light in an irreducible spherical tensor formalism. This allows forward synthesis of the Thomson scattered signal for the more complex scenario of symmetry-breaking features in the incident radiation field, which could limit the accuracy of our proposed technique. For this, we make use of an advanced 3D radiative magnetohydrodynamic coronal model. Together with synthesized polarized signals in the Fe XIII 10746 Angstrom emission line, we find that an ad hoc correction of telescope and instrument-induced polarization crosstalk is possible under the assumption of a non-depolarizing optical system.