2013MNRAS.433L..20M

Spectropolarimetry provides the means to probe the 3D geometries of supernovae (SNe) at early times. We report spectropolarimetric observations of the Type Ia SN 2012fr at four epochs: -11, -5, +2 and +24 d, with respect to B-light-curve maximum. SN 2012fr is a normal Type Ia SN, similar to SNe 1990N, 2000cx and 2005hj (that all exhibit low velocity decline rates for the principal Siii line). The SN displays high-velocity components at -11d that are highly polarized. The polarization of these features decreases as they become weaker from -5d. At +2d, the polarization angles of the low-velocity components of silicon and calcium are identical and oriented at 90° relative to the high-velocity Ca component. In addition to having very different velocities, the high- and low-velocity Ca components have orthogonal distributions in the plane of the sky. The continuum polarization for the SN at all four epochs is low, <0.1percent. We conclude that the low level of continuum polarization is inconsistent with the merger-induced explosion scenario. The simple axial symmetry evident from the polarization angles of the high-velocity and low-velocity Ca components, along with the presence of high-velocity components of Si and Ca, is perhaps more consistent with the pulsating delayed detonation model. We predict that, during the nebular phase, SN 2012fr will display blueshifted emission lines of Fe-group elements.