H.E.S.S. observations of Active Galactic Nuclei

The array of four imaging atmospheric-Cherenkov telescopes H.E.S.S. has been operating in Namibia since 2003 and during this time it has observed a selected sample of extragalactic γ -ray emitters in the Very High Energy (VHE) domain. All the detected sources are Active Galactic Nuclei (AGN) and almost all belong to the class of BL Lac objects. The brightest blazar observed by H.E.S.S. was PKS 2155-304. An exceptional flare of this source was observed in July 2006 and this detection, which showed one of the fastest VHE variability ever observed, will be described here. Furthermore, the high sensitivity of H.E.S.S. allows the detection of faint sources at the level of a few percent of the Crab flux, yielding a catalogue of 17 BL Lac, nine of which were discovered by H.E.S.S. ly H.E.S.S. has detected two of the most distant BL Lac, 1ES 0229+200 and 1ES 0347-12, and these observations will be described.