Optical Spectropolarimetry of Sn 2002ap: Evidence for a High Velocity Asymmetric Explosion of a Hypernova

We present spectropolarimetry of the energetic Type Ic supernova SN 2002ap, taken with the FOCAS mounted on the Subaru Telescope at two epochs, close to and one month later than the visual maximum (2002 February 8). The data show the development of intrinsic linear polarization, in addition to the steady and smooth interstellar polarization. Distinct polarization profiles were seen only in the O I λ7773 multiplet/Ca II IR triplet absorption trough at maximum light and in the Ca II IR triplet absorption trough a month later, with the latter showing a peak polarization as high as ∼ 2 %. We estimate the interstellar polarization toward the supernova to be pmax = 0.64 ± 0.20 % and θISP = 120 ◦ ± 10. The intrinsic polarization shows three clear position angles: 80 for the February continuum, 120 for the February line feature, and 150 for the March data. Since the position angle varies, the supernova cannot be exactly axisymmetric. We conclude that there are multiple asymmetric components in the ejecta. We suggest that the supernova has a bulk asymmetry with an axial ratio projected on the sky that is different from 1 by of order 10 %. Furthermore, we suggest very speculatively that a jet, or bipolar jets, moving at 0.23c contribute to polarization in the February epoch. Subject headings: polarization — supernovae: individual (SN 2002ap)