White-light observations by the Solar Dynamics Observatory's Helioseismic and Magnetic Imager of a loop-prominence system occurring in the aftermath of an X-class flare on 2013 May 13 near the eastern solar limb show a linearly polarized component, reaching up to ∼20% at an altitude of ∼33 Mm, about the maximal amount expected if the emission were due solely to Thomson scattering of photospheric light by the coronal material. The mass associated with the polarized component was 8.2×1014 g. At 15 Mm altitude, the brightest part of the loop was 3(+/-0.5)% linearly polarized, only about 20% of that expected from pure Thomson scattering, indicating the presence of an additional unpolarized component at wavelengths near Fe I (617.33 nm), probably thermal emission. We estimated the free electron density of the white-light loop system to possibly be as high as 1.8×1012 cm−3.
@article{arxiv.1402.7016,
title = {Helioseismic and Magnetic Imager observations of linear polarization from a loop prominence system},
author = {Pascal Saint-Hilaire and Jesper Schou and Juan-Carlos Martínez Oliveros and Hugh S. Hudson and Säm Krucker and Hazel Bain and Sébastien Couvidat},
journal= {arXiv preprint arXiv:1402.7016},
year = {2015}
}