Observed γ-ray spectrum of Mkn 501 during the 1997 active state recorded HEGRA (red symbols). The black solid and dotted orange lines show the observed and the intrinsic spectrum, assuming standard absorption with the D11 (upper panel) and KD10 (lower panel) EBL models. Grey points indicate the observed data points corrected for absorption. Other lines show the predicted spectrum with LIV effects (line styles and colors as in Fig. 2). The violet lines show the 5σ sensitivity curves for CTA (5 h, dashed and 50 h exposure, solid).