Top panels: ejecta composition for the N5def^3D model. Density ρ (left) and mass fraction X_i of IMEs (middle) and IGEs (right) are shown in the x–y plane. The x–y projected direction of the 8 viewing angles is shown in the density panel. Bottom panels: flux, Q, U and polarisation spectra (from top to bottom) of the N5def^3D models are shown 4 days before (left) and at maximum light (right) for the 8 different orientations (n₁ −n₈) highlighted in the top left panel. Flux and polarisation P of SN 2005hk is shown in black for comparison, with polarimetric data from Maund et al. (2010, bottom right panel) re-binned of a factor of two to have a similar wavelength resolution (Δλ ~ 50 Å) and polarisation uncertainties (σ_P ~ 0.06 per cent, error bars inbottom panels) as those from Chornock et al. (2006, bottom left panel). Both observed and modelled fluxes are normalised at 6000 Å for presentation purposes.