Stacked residuals of all 45 empty-field observations after fitting the csbkgmodel background model to each individual observation. Left panel: residual count spectrum after summing over the entire field of view. Centre panel: histogram of significances, determined after summing over energy and by sampling the events into bins of 0.2° ×0.2°. Right panel: residual map in the field-of-view coordinate system. The residual map is summed over all energies and was computed for a correlation radius of 0.2°. Residuals are shown in units of significance expressed in Gaussian σ and are computed using Eqs. (A.3) and (A.4).