Left: The same significance map as in Figure 1, but with the exclusion mask covering V4641 Sgr and a colour range which focuses on the background fluctuation scales. Right: The distribution of the significance values outside of an exclusion mask covering V4641 Sgr (red line) and over the entire map (green line). A Gaussian function is fit to the red distribution (black line), with mean −0.020 ± 0.007 and width 1.006 ± 0.007, close to the values of mean 0 and width 1 expected if the background is perfectly modelled.