Spectropolarimetry of the Type Ib SN 2008D , associated with the XRF 080109 , at two separate epochs , are presented .
The epochs of these observations correspond to V-band light curve maximum and 15 days after light curve maximum ( or 21 and 36 days after the XRF ) .
We find SN 2008D to be significantly polarized , although the largest contribution is due to the interstellar polarization component of Q _ { ISP } = 0 \pm 0.1 \% and U _ { ISP } = -1.2 \pm 0.1 \% .
At the two epochs , the spectropolarimetry of SN 2008D is classified as being D1+L ( He i ) +L ( Ca ii ) .
The intrinsic polarization of continuum wavelength regions is < 0.4 \% , at both epochs , implying an asymmetry of the photosphere of < 10 \% .
Similar to other Type Ibc SNe , such as 2005bf , 2006aj and 2007gr , we observed significant polarization corresponding to the spectral features of Ca ii , He i , Mg i , Fe ii and , possibly , O i \lambda 7774 , about a close-to-spherically-symmetric photosphere .
We introduce a new plot showing the chemically distinct line forming regions in the ejecta and comment on the apparent ubiquity of highly polarized high-velocity Ca ii features in Type Ibc SNe .
The polarization angle of Ca ii IR triplet was significantly different , at both epochs , to those of the other species , suggesting high-velocity Ca ii forms in a separate part of the ejecta .
The apparent structure in the outer layers of SN 2008D has implications for the interpretation of the early-time X-ray emission associated with shock break-out .
We present two scenarios , within the jet-torus paradigm , which explain the lack of an apparent geometry discontinuity between the two observations : 1 ) a jet which punched a hole straight through the progenitor and deposited Ni outside the ejecta and 2 ) a jet which stalled inside the radius of the photosphere as observed at the second epoch .
The lack of a peculiar polarization signature , suggesting strongly asymmetric excitation of the ejecta , and the reported properties of the shock-breakout favour the second scenario .