Aims. To investigate the very high energy (VHE: > 100 GeV) y-ray emission from the high-frequency peaked BL Lac IES 0229+200. Methods. Observations of IES 0229+200 at energies above 580 GeV were performed with the High Energy Stereoscopic System (HESS) in 2005 and 2006. Results. IES 0229+200 is discovered by HESS to be an emitter of VHE photons. A signal is detected at the 6.6σ level in the HESS observations (41.8 h live time). The integral flux above 580 GeV is (9.4 ± 1.5 stat ± 1.9 syst) × 10 -13 cm -2 s -1 corresponding to ∼1.8% of the flux observed from the Crab Nebula. The data show no evidence for significant variability on any time scale. The observed spectrum is characterized by a hard power law (T = 2.50 ± 0.19 stat ± 0.10 syst) from 500 GeV to ∼15 TeV. Conclusions. The high-energy range and hardness of the observed spectrum, coupled with the object's relatively large redshift (z = 0.1396), enable the strongest constraints so far on the density of the Extragalactic Background Light (EBL) in the mid-infrared band. Assuming that the emitted spectrum is not harder than T mt ≈ 1.5, the HESS data support an EBL spectrum σλ -1 and density close to the lower limit from source counts measured by Spitzer, confirming the previous indications from the HEGRA data of IES 1426+428 (z = 0.129). Irrespective of the EBL models used, the intrinsic spectrum of IES 0229+200 is hard, thus locating the high-energy peak of its spectral energy distribution above a few TeV.
- BL lacertae objects: individual: IES 0229+200
- Gamma rays: observations