SED of PKS 0447 − 439 during the epoch of HESS observation (November 2009 − January 2010). Red points represent Swift/UVOT, Swift/XRT, Fermi/LAT and de-absorbed (assuming z    =    0.2) HESS data. Cyan data are the observed HESS data. Green symbols report historical data obtained through the ASI/ASDC tools. Green LAT points are from the 1LAC catalogue. The black lines are the result of the one-zone emission leptonic model discussed in the text for two different values of the minimum Lorentz factor of the emitting electrons, γ_min    =    1 (solid) and γ_min    =    3 × 10³ (dashed). See text for details.