Total 1 ms count distribution of the 17 HE-NaI units (green points). This is modelled (green thick line) as the sum of two independent components: in addition to the one that accounts for ∼99% of the total counts with an average count rate of 0.017 counts ms⁻¹ (blue points and orange solid line), there is an additional component (red solid line), which is responsible for the remaining 1% of counts, with an average count rate of 0.7 counts ms⁻¹ and whose exposure is just 2.6  ×  10⁻⁴ times the total net one.