Discovery of >160 GeV $\gamma$-rays from 1ES 1101-232 (z = 0.186) with H.E.S.S.

Abstract : The system of four H.E.S.S. (High Energy Stereoscopic System) atmospheric Cherenkov telescopes is complete and operational since December 2003. Since the commissioning of the experiment in June 2002, a considerable amount of observation time has been dedicated to observations and monitoring of active galactic nuclei (AGN). For several objects simultaneous observation campaigns were carried out in other wavelength bands. In addition to the understanding of the intrinsic acceleration mechanisms of these objects, the observations of AGN also provide an indirect measurement of the Extragalactic Background Light (EBL) via the absorption of very high energy (i.e. in the GeV/TeV energy regime) gamma-rays by $e^+e^-$ pair production with EBL photons. To this end it is important to study spectra of AGN at different redshifts. To date, the redshifts of AGN detected at very high energies range from 0.004 to 0.129. Here we report on the detection (9$\sigma$) of the BL Lac object 1ES 1101-232, at a redshift of z = 0.186 , with the H.E.S.S. Cherenkov telescopes.