Simulated and reconstructed signal events per solid angle Ω versus the logarithm of the space angle α in degrees for the burst GRB 110918: muon tracks are plotted in black, shower-like events are drawn in green. The corresponding fit is shown in red (see Eq. (1)). The grey dotted line indicates the median angular spread of events ⟨ α ⟩  = 0.32°. The blue dashed line shows the flat background distribution ℬ(α) as calculated in Sect. 6. Cut values Λ >  − 5.5 and β < 1° are applied here.