Significance distributions for hadronic background model fit. The black histogram shows the distribution of significance values of all spatial pixels of the map in Fig. A.2. The dark grey histogram is for all pixels outside the exclusion regions around HESS J1804−216, HESS J1808−204, and HESS J1813−178 (i.e. contains only the excess from HESS J1809−193), and the light grey histogram is for all pixels outside any of the exclusion regions. The blue line shows the result of fitting a Gaussian distribution to the light grey histogram, the fitted width of the Gaussian is given in the upper right corner of the plot.