Predicted radial expansion of a putative PWN associated with SN 2012au for varying radio efficiency factors, η_R, assuming τ₀  ≳  8 yr. The 99.7% confidence interval upper limits imposed by our VLBI observations are overplotted (23 GHz = orange, 5 GHz = maroon; see Table 2). The dashed, gray horizontal line corresponds to the resolvable limit of the global VLBI network at 22 GHz (θ = 250 × 250 μas²) at a 99.7% confidence interval upper limit on the distance of D_A = 32.6 Mpc. We assume E_k = 5 × 10⁵¹ erg and M_ej = 5 M_⊙ inferred from available optical light-curve modeling of SN 2012au, leading to a conservative lower limit on the radial expansion (higher energies and lower masses result in a more rapid radial expansion, becoming resolvable earlier; see the text for details). For η_R  ≲  0.001, in-line with known Galactic systems, the PWN should now be resolvable (∼14 yr post-explosion).