Bi-polar supernova explosions

Abstract

Core-collapse SNe are found to be significantly polarized. Our preliminary results are: (a) Core-collapse supernonae are normally polarized at 1% level; (b) the polarization of core-collapse SNe increases with the mass of the stellar envelope; (c) their polarizations increase as deeper into the ejecta. We discuss here the optical spectropolarimetry of several core-collapse SNe, SN 1996cb (Type IIB), SN 1997X (Type Ic), and SN 1998S (Type IIn). The data show polarization evolution of several spectral features at levels from 0.5% to above 4%. These data suggest that the distribution of ejected matter is highly aspherical. In the case of SN 1998S, the minimum major to minor axis ratio must be larger than 2.5 to 1 if the polarization is 3% from an oblate spheroidal ejecta seen edge on. A well-defined symmetry axis can be deduced from spectropolarimetry for the peculiar Type IIn SN 1998S. The observed degree of polarization of the Type Ic SN 1997X is above 4%. The data reveal a trend that the degree of polariz...