Spectral energy distribution of the sources discussed in Sect. 3. The details of the data and sources used in this plot are given in Table 1 and in Sect. 3.2. The dashed black line is the spectral template of elliptical galaxies from Silva et al. (1998) at a distance of 570 Mpc. The dotted (red) line is the blackbody spectrum of a massive star with parameters identical with the companion star in the gamma-ray binary LS 5039 at a distance of 25 kpc. The data in IR (2MASS) and visual (Swift/UVOT) bands were corrected for extinction. For Fermi/LAT we plot both upper limits for Γ = 1.5 (dark brown) and Γ = 2.0 (light brown).