Marginalised posterior PDF for γ_ext (external shear strength), b_P (strength of primary lens in arcseconds), b_S (strength of satellite lens in arcseconds) and t (truncation radius of satellite in arcseconds) based on extended image surface brightness modelling, plotted on the same scales as in Fig. 4. The three shaded regions show the 68.3%, 95.4% and 99.7% credible regions. For comparison, the lines show the 68.3% credible regions from Fig. 4 with image positions as constraints. In contrast to the full t-degeneracy from image position modelling, extended image modelling allows us to constrain the truncation radius of the satellite galaxy halo to be .