Oblateness parameter posterior probability densities. Black contours mark the 0.5σ, 1.0σ, 1.5σ, and 2.0σ joint confidence levels, and 1D histograms show the marginalized distributions. Constraints on the projected quantities are shown in the top right panel. The constraint on f depends on the values of θ and ϕ, which are unconstrained by the data. For low θ, an oblateness larger than 0.15 can be ruled out with 2σ confidence, whereas for high θ, f is effectively unconstrained. The 95% confidence upper limits on f for two different θ ranges are highlighted in the bottom-right panel. The other parameters in the model were well constrained without significant degeneracies; see Table 1.