Illustration of background model construction. We exemplary show the model for the bin with azimuth angle 90° < ϕ <  270° and zenith angle 20° < ϑ <  30°, for energies between 0.8 and 1.1 TeV. a: sum of the number of registered events in each observation, excluding events with a reconstructed direction close to known γ-ray sources. b: effective exposure time of each spatial pixel. The effective exposure time is the summed observation time of all observations, corrected for the exclusion of events from regions around known γ-ray sources. c: averaged background rate, given by the number of registered events divided by effective exposure time, energy interval and solid angle. d: averaged background rate after the application of a spline-based smoothing algorithm. All vertical axis labels refer to the same colour bar.