Table 2: Results of the best $\chi ^2$ fit to the annual and overall spectra of PG 1553+113 measured by HESS.

Epoch		 $E_{\rm min}$ $E_{\max}$ $\Gamma$ $I_{\circ}$ $\chi ^2$ NDF P($\chi ^2$)
  [TeV] [TeV]   [10-11 cm-2 s-1 TeV-1]      
2005 (AH06)a 0.185 0.585 $3.98\pm0.63_{\rm stat}\pm0.10_{\rm syst}$ $2.59\pm0.47_{\rm stat}\pm0.52_{\rm syst}$ 1.7 2 0.42

2005b		 0.225 1.265 $4.01\pm0.60_{\rm stat}\pm0.10_{\rm syst}$ $5.92\pm1.19_{\rm stat}\pm1.18_{\rm syst}$ 2.1 5 0.84
2006 0.225 0.534 $4.45\pm0.48_{\rm stat}\pm0.10_{\rm syst}$ $4.35\pm0.54_{\rm stat}\pm0.87_{\rm syst}$ 8.5 2 0.014
Total 0.225 1.265 $4.46\pm0.34_{\rm stat}\pm0.10_{\rm syst}$ $4.68\pm0.49_{\rm stat}\pm0.94_{\rm syst}$ 8.4 5 0.13
a The AH06 entry is the previously published HESS result (Aharonian et al. 2006a) for 2005. The AH06 entry was not corrected for long-term changes in the optical efficiency of the system.
b The 2005 entry corresponds to exactly the same data as presented in AH06, but with a correction (see text) applied to account for optical efficiency changes within the data. The 2006 and total entries also have this correction applied.

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