Polarization of SN 1987A Revisited

The conventional picture for the origin of the polarization of a supernova isbased on a model of Thomson or resonance scattering of photons travelingthrough an aspherical supernova atmosphere. Positive detection of intrinsicpolarization in SN 1987A is then interpretated as evidence of an asymmetricalsupernova atmosphere. We show here a different view based on the scattering ofthe supernova light by a dusty circumstellar material (CSM), or the ``lightecho'' effect. At a given epoch after the explosion, the observed photonsconsist of both those propagating directly from the supernova and thosescattered by dust particles in the CSM. Polarized light can be produced if thedistribution of the dust particles is aspherical. The model can reproduce boththe time evolution of the observed broad band polarization of SN 1987A andmajor features of the polarization spectra. It is also successful in providinga natural model for the early infrared light curve, in particular the observed30 day delay of the IR maximum compared to the maximum of the bolometric lightcurve.Comment: 7 pages, 3 Postscript figure