of the background. The background control data sample was normalized to the on-source sample between $0.12\,\mathrm{deg}^2<\theta^2<0.24\,\mathrm{deg}^2$. The reason of the slow but steady drop in the background is the drop in acceptance towards the camera boundary. The observed excess signal of 528 events below $\theta^2<0.04\,\mathrm{deg}^2$ corresponds to an $11\sigma$ excess according to eq. 17 in @LiMa. An independent analysis using other cuts, a different reconstruction algorithm and a different $\gamma$/hadron optimization procedure, revealed a comparable (within statistics) significance. While for the sky map and the $\theta^2$ plot a fixed, tight $h$ cut was applied, the final separation for the spectral analysis and the light curve was done using a looser, energy-dependent cut in $h$, requiring that about 60% of the MC $\gamma$ events survive.

As the analyzed data comprise 21 observation nights, it is possible to check the light curve for possible flux variability. On a diurnal basis, the $\geq$ 200 GeV light curve (Fig. \[fig:lc\]) shows small changes and trends beyond those expected from statistical fluctuations. The structure observed during MJD 53580$-$53600 is compatible with a constant-flux ansatz ($\chi^2/$dof$=6.1/6$), while from MJD 53726.82$-$53726.90 a flux of $2.4\sigma$ above the average flux inferred from the surrounding days MJD 53720$-$53740, $(1.8\pm0.6)\cdot10^{-11}
