Polarization of SN 1987A Revisited

Abstract

The conventional picture for the origin of the polarization of a supernova is based on a model of Thomson or resonance scattering of photons traveling through an aspherical supernova atmosphere. Positive detection of intrinsic polarization in SN 1987A is then interpreted as evidence of an asymmetrical supernova atmosphere. We show here a different view based on the scattering of the supernova by a dusty circumstellar material (CSM), or the light echo effect. At a given epoch after the explosion, the observed photons consist of both those propagating directly from the supernova and those scattered by dust particles in the CSM. Polarized can be produced if the distribution of the dust particles is aspherical. The model can reproduce both the time evolution of the observed broadband polarization of SN 1987A and major features of the polarization spectra. It is also successful in providing a natural model for the early infrared curve, in particular the observed 30 day delay of the IR maximum compared to the maximum of the bolometric curve.