Polarization Properties of Thomson-Scattering Triaxial Ellipsoids

Abstract: Polarimetry is a powerful tool for constraining the geometry of distant astrophysical objects. Continuum polarization induced by Thomson scattering can probe the photospheric geometry of transients and provide insight into their explosion mechanisms. We systematically study continuum polarization from spheroids over a broader range of deformations and viewing angles than considered previously, and generalize the calculation to triaxial ellipsoids. We find that strongly deformed spheroids exhibit a non-monotonic dependence of polarization on viewing angle, a behavior overlooked in previous studies. Triaxial ellipsoids show more diverse polarization signatures, but their qualitative behavior can be understood from the area of surface elements viewed nearly edge-on, where the local polarization is strongest. Our results provide a simple physical understanding of the dependence of polarization on photospheric geometry and help constrain the geometry of astrophysical transients through polarimetric observations. The computational results of this study will be made publicly available for use in future research.