Probability density distribution of the source size r_s using a time delay of Δt = 417 days, a radio-flux ratio of B/A = 0.74, a linear interpolation of image A’s light curve as an intrinsic variability model, and the lens model parameters of Mediavilla et al. (2009) (dotted black line). The dashed lines show the PDFs for various model/data-related analyses as indicated by the legend. These are obtained by multiplying single probability distributions corresponding to different time delays (red), models for the intrinsic variability (orange; see Table 4), and radio measurements (blue; see Table 6). We note that the red and orange distributions overlap.