The polarization of supernova light - A measure of deviation from spherical symmetry

Abstract

An observational test of the assumption of spherical symmetry of supernova explosions is suggested, based upon the likelihood that SN atmospheres are scattering dominated and the fact that light from an unresolved, asymmetric, scattering atmosphere is linearly polarized. The net polarization which is to be expected as a function of the degree of asphericity is discussed, and the basic assumptions about the SN atmosphere which are relevant to the emergence of polarized light are summarized. The basic equations and solutions for predicting net polarization are presented, including equations for pure electron scattering, resonance scattering, and a mixture of scattering absorption in a plane-parallel atmosphere, the ellipsoids of revolution and nonuniform surface flux distribution pertaining to the characterization of asymmetry, and the net Stokes parameters. It is found that a mixture of scattering and absorption can yield a significantly higher degree of polarization than that expected from the classical, pure scattering atmosphere. The effects of interstellar dust on observed polarization are also discussed.