Table 1: Fit results for different spectral models. The differential flux normalisation I0 and the integral flux above 1 TeV $(I({>}1~{\rm TeV}))$ are given in units of $10^{-12}~{\rm cm}^{-2}~{\rm s}^{-1}~{\rm TeV}^{-1}$ and $10^{-12}~{\rm cm}^{-2}~{\rm s}^{-1}$, respectively. The power-law fit is clearly an inappropriate description of the data, a power law with an exponential cutoff (row 2), a power law with an energy dependent photon index (row 3), and a broken power law (row 4; in the formula, the parameter S = 0.4 describes the sharpness of the transition from $\Gamma _1$ to $\Gamma _2$ and it is fixed in the fit) are equally likely descriptions of the HESS data. Note that when fitting a broken power law to the data, some of the fit parameters are highly correlated.
Fit Formula Fit Parameters $\chi ^2$ (d.o.f.) $I({>}1~{\rm TeV})$

$I_0\ E ^ {-\Gamma}$		 $I_0 = 17.1 \pm 0.5$ $\Gamma = 2.26 \pm 0.02$     85.6 (23) $13.5 \pm 0.4$
$I_0\ E ^ {-\Gamma}\ \exp~ (-E / E_{{\rm c}})$ $I_0 = 20.4 \pm 0.8$ $\Gamma = 1.98 \pm 0.05$ $E_{{\rm c}} = 12 \pm 2 $   27.4 (22) $15.5 \pm 1.1$
$I_0\ E ^ {-\Gamma + ~ \beta\ \log E}$ $I_0 = 19.7 \pm 0.6$ $\Gamma = 2.08 \pm 0.04$ $\beta = -0.30 \pm 0.04 $   25.5 (22) $15.6 \pm 0.7$
$I_0\ E / E_{{\rm B}} ^ {-\Gamma_1}\ \left( 1 + E / E_{{\rm B}} ^ {1 / S } \right) ^ {~ S ~ (\Gamma_2 - \Gamma_1)}$ I0 = 0.4+0.6-0.2 $\Gamma_1 = 2.06 \pm 0.05$ $\Gamma_2 = 3.3 \pm 0.5$ $ E_{{\rm B}} = 6.7 \pm 2.7 $ 26.2 (21) $15.4 \pm 0.8$


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