We present spectropolarimetry of SN 2009ip throughout the evolution of its 2012 explosion .
During the 2012a phase , when the spectrum exhibits broad P-Cygni lines , we measure a V -band polarization of P \approx 0.9 % at a position angle of \theta \approx 166 ^ { \circ } , indicating substantial asphericity for the 2012a outflow .
Near the subsequent peak of the 2012b phase , when the spectrum shows signs of intense interaction with circumstellar material ( CSM ) , we measure P \approx 1.7 % and \theta \approx 72 ^ { \circ } , indicating a separate component of polarization during 2012b , which exhibits a higher degree of asphericity than 2012a and an orthogonal axis of symmetry on the sky .
Around 30 days past peak , coincident with a substantial bump in the declining light curve , we measure P \approx 0.7 % and another significant shift in \theta .
At this point , broad photospheric lines have again become prominent and exhibit significant variations in P relative to the continuum , particularly He i /Na I D. By 60 days past peak the continuum polarization has dropped below 0.2 % , probably declining toward a low value of interstellar polarization .
The results are consistent with a scenario in which a prolate ( possibly bipolar ) explosion launched during the 2012a phase impacts an oblate ( toroidal ) distribution of CSM in 2012b .
Previous calculations that assumed spherical symmetry for the CSM have substantially underestimated the required explosion energy , since only a small fraction of the SN ejecta appears to have participated in strong CSM interaction .
An ejecta kinetic energy of at least \sim 10 ^ { 51 } ergs is difficult to avoid , supporting the interpretation that the 2012 outburst of SN 2009ip was the result of a core-collapse explosion .