Speaker
Francesca Volpe
(Ecole Polytechnique, France)
Description
The array of four imaging atmospheric-Cherenkov telescopes HESS has been operating in Namibia since 2003 and during this time it has observed a selected sample of extragalactic gamma-ray emitters in the Very High Energy domain. All the detected sources are Active Galactic Nuclei and almost all belong to class of BL Lac objects. The high sensitivity of HESS allows the detection of faint sources at the level of a few percentage of the Crab flux, yielding a catalogue up to 12 BL Lac. The study of spectra of objects at different redshift is very important to disentangle the intrinsic acceleration mechanisms of the AGN from their absorption by the EBL. A brief overview of AGN in the HESS catalogue will be presented with a particular emphasis on two of the most distant BL Lac 1ES0229+200 and 1ES0347-121, which have recently been detected by HESS. The exceptional flare of PKS2155-304, characterized by the fastest VHE variability ever observed and detected in July 2006, will be also presented.
Author
Francesca Volpe
(Ecole Polytechnique, France)