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Humboldt-Universität zu Berlin - Mathematisch-Naturwissen­schaft­liche Fakultät - Experimentelle Elementarteilchenphysik

Humboldt-Universität zu Berlin | Mathematisch-Naturwissen­schaft­liche Fakultät | Institut für Physik | Experimentelle Elementarteilchenphysik | H.E.S.S. | Talks & Papers | New constraints on the mid-IR EBL from the HESS discovery of VHE gamma-rays from 1ES 0229+200

The H Collaboration (2007)

New constraints on the mid-IR EBL from the HESS discovery of VHE gamma-rays from 1ES 0229+200

aap, 475:L9-L13.

Aims:To investigate the very high energy (VHE: >100 GeV) gamma-ray emission from the high-frequency peaked BL Lac 1ES 0229+200. Methods: Observations of 1ES 0229+200 at energies above 580 GeV were performed with the High Energy Stereoscopic System (HESS) in 2005 and 2006. Results: 1ES 0229+200 is discovered by HESS to be an emitter of VHE photons. A signal is detected at the 6.6sigma 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 (Gamma = 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 Gamma_int ≈ 1.5, the HESS data support an EBL spectrum ∝lambda^-1 and density close to the lower limit from source counts measured by Spitzer, confirming the previous indications from the HEGRA data of 1ES 1426+428 (z=0.129). Irrespective of the EBL models used, the intrinsic spectrum of 1ES 0229+200 is hard, thus locating the high-energy peak of its spectral energy distribution above a few TeV.

Provided by the SAO/NASA Astrophysics Data System