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Aims: The nearby galaxy clusters Abell 496 and Abell 85 are studied in thevery high energy (VHE, E > 100 GeV) band to investigate VHE cosmic rays (CRs)in this class of objects which are the largest gravitationally bound systems inthe Universe. Methods: H.E.S.S., an array of four Imaging Atmospheric CherenkovTelescopes (IACT), is used to observe the targets in the range of VHE gammarays. Results: No significant gamma-ray signal is found at the respectiveposition of the two clusters with several different source size assumptions foreach target. In particular, emission regions corresponding to the high densitycore, to the extension of the entire X-ray emission in these clusters, and tothe very extended region where the accretion shock is expected, areinvestigated. Upper limits are derived for the gamma-ray flux at energies E>570GeV for Abell 496 and E>460 GeV for Abell 85. Conclusions: From thenon-detection in VHE gamma rays, upper limits on the total energy of hadronicCRs in the clusters are calculated. If the cosmic-ray energy density followsthe large scale gas density profile, the limit on the fraction of energy inthese non-thermal particles with respect to the total thermal energy of theintra-cluster medium (ICM) is 51% for Abell 496 and only 8% for Abell 85 due toits larger mass and higher gas density. These upper limits are compared withtheoretical estimates. They predict about ~10% of the thermal energy of the ICMin non-thermal particles. The observations presented here can constrain thesepredictions especially for the case of the Abell 85 cluster.

Very high energy gamma-ray observations of the galaxy clusters Abell 496 and Abell 85 with H.E.S.S