Light curve (top) and spectrum (bottom) of PKS 0139-09 at redshift z = 0.733. Green curve in the bottom panel shows a power-law-type model spectrum absorbed on the EBL from Franceschini et al. (2008). Also shown in the bottom panel are sensitivity curves of different ground based γ-ray telescopes: 5@5 (Aharonian et al. 2000), HESS-I and HESS-II (Masbou 2010), and CTA (CTA Consortium 2011). The solid sensitivity curves for HESS-I and HESS-II correspond to spectral index of Γ = 2, dashed – to Γ = 3, and dotted – to Γ = 4. Black and red data points in the lower panel show the spectrum extracted using the likelihood analysis and aperture photometry method, respectively.