SPECTROPOLARIMETRY OF SN-1993J IN NGC-3031

We have obtained low-resolution optical spectropolarimetry of SN 1993J which shows a high continuum linear polarization and a 0.5% drop in p olarization across the Halpha emission line accompanied by a approxima tely 15-degrees position angle rotation. From these data we infer the presence of two distinct polarization components and conclude that at least part of the polarization is intrinsic to the supernova. We propo se that the polarization observed at Halpha is due to interstellar pol arization within NGC 3031, while the continuum polarization is intrins ic to the object. After correcting the observed Stokes parameters for interstellar polarization, we find that the intrinsic continuum polari zation is high, P = 1.6% +/- 0.1% at 0 = 49-degrees +/- 3-degrees, and is wavelength-independent. The Stokes flux displays blueshifted Halph a absorption which suggests that the polarization is generated primari ly in the underlying continuum source. Comparing our results to the sc attering photosphere models of Shapiro & Sutherland we find that to pr oduce the continuum polarization the ratio between the semimajor and s emiminor axes of the scattering envelope must be greater-than-or-equal -to 1.54 for the oblate case, and greater-than-or-equal-to 2.0 for the prolate case. We also consider the point-source scattering envelope m odels of Brown & McLean, and find that for an oblate scattering envelo pe the models require that the inclination be close to edge-on unless the asymmetry is extreme. On the other hand, the prolate case can prod uce high polarization for a wide range of inclination angles.