A Simple Bipolar Jet Model for the Polarization of Core-Collapse Supernovae

We propose a bipolar jet model for supernova polarization. Light from the main component of the supernova (which we call the bulk supernova for short) scatters off electrons in the jets and is polarized: this polarized light is added to the direct emission from the bulk supernova and causes the overall supernova emission to be polarized. The motivation for the bipolar jet model is to resolve the potential paradox set by an analysis which suggests strong spherical symmetry for Type Ib supernovae and the expectation that Type Ib supernovae should be highly polarized in the continuum up to perhaps about 4 %. For the model we have derived simple, non-relativistic, approximate analytic formulae for relative amount of scattered flux and polarization. The polarization formula qualitatively reproduces two main features observed for at least some supernovae: (1) the rise to a polarization maximum and then decline with time; (2) the inverted P Cygni polarization profiles of lines. The model is strictly axisymmetric and predicts a constant position angle of intrinsic polarization. Since position angle variation of intrinsic polarization is observed, the model cannot account for all the polarization of all supernovae.