SN 2020uem: a Possible Thermonuclear Explosion within a Dense Circumstellar Medium (II). The Properties of the CSM from Polarimetry and Light-curve Modeling

Type IIn/Ia-CSM supernovae (SNe IIn/Ia-CSM) are classified by their characteristic spectra, which exhibit narrow hydrogen emission lines originating from a strong interaction with circumstellar medium (CSM) together broad of intermediate-mass elements. We performed intensive follow-up observations SN 2020uem, including photometry, spectroscopy, and polarimetry. In this paper, we focus on the results imaging polarimetry at $66$ days spectropolarimetry $103$ after discovery. 2020uem shows high continuum polarization $1.0-1.5\%$ without wavelength dependence. Besides, degree position angle keep roughly constant. These suggest that is powered confined aspherical CSM. simple modeling, based has an equatorial-disk/torus semi-analytic light-curve modeling estimated CSM mass. revealed mass-loss rate in final few hundred years immediately before explosion range $0.01 - 0.05 {\rm ~M_{\odot}~yr^{-1}}$, total mass $0.5-4 ~M_{\odot}}$. The can be accommodated not only red supergiant (RSG) but giant (RG) or asymptotic-giant-branch (AGB) star. As possible progenitor scenario propose white-dwarf binary system RG, RSG AGB star, especially merger via common envelope evolution, i.e., core-degenerate its variant.