MCMC posterior distribution of the arc parameters used to fit the dust continuum observations: the peak amplitude of the arc A_c; the central radius of the arc r_c; the azimuthal location of the arc peak ϕ_c; the arc radial standard deviation σ_r; and the azimuthal standard deviations for the leading and trailing side of the arc σ_ϕ,1 and σ_ϕ,2, respectively. The contour levels in the 2D marginalised distributions correspond to the 68, 95 and 99.7% confidence levels. The dashed vertical lines in the marginalised distributions display the 16th, 50th and 84th percentiles. The red lines represent the best-fit value (lowest χ²). The posterior distribution of the other parameters is presented in Figure B.1.