a st ro - p h / 06 07 35 1 v 1 1 5 Ju l 2 00 6 The H . E . S . S . View of the Central 200 Parsecs

The inner few hundred parsecs of our galaxy provide a laboratory for the study of the production and propagation of energetic particles. Very-high-energy γ-rays provide an effective probe of these processes and, especially when combined with data from other wave-bands, γ-rays observations are a powerful diagnostic tool. Within this central region, data from the H.E.S.S. instrument have revealed three discrete sources of very-high-energy γ-rays and diffuse emission correlated with the distribution of molecular material. Here I provide an overview of these recent results from H. 1. Introduction The central 200 pc of our Galaxy is a unique region that harbours many remarkable objects — including several potential sites of effective particle acceleration. Non-thermal emission (particularly in the radio, X-ray and γ-ray bands) can be used to trace the energetic particle populations of this region. X-ray and radio observations of synchrotron emission provide information on the product of the local magnetic field energy density and the density of relativistic electrons. The flux of inverse Compton γ-rays, on the other hand, is proportional to the radiation field density (and the electron density). The combination of γ-ray and X-ray measurements therefore provides a powerful tool for probing both magnetic field strength and energetic particle content. Moreover, γ-rays provide an effective tracer for hadronic particles: proton-proton interactions in the interstellar medium lead to the production and decay of pions and hence γ-ray production. The combination of γ-ray measurements with tracers of atomic and molecular material may be the only way to effectively trace energetic hadrons in our galaxy. The usefulness of γ-ray observations has traditionally been limited by poor angular resolution and modest sensitivity. A major step forward in the very-high-energy (VHE, > 100 GeV) domain has recently been taken with the commissioning of H.E.S.S. (High Energy Stereoscopic System). H.E.S.S. is an array of four, 13 m diameter, imaging Cherenkov telescopes located in the Khomas highlands of Namibia [1], a southern hemisphere location ideal for observations of the Galactic Centre (GC). H.E.S.S. has an angular resolution of a few arc-minutes and a locational accuracy of ∼ 30 ′′ for typical point sources. The instrument reaches an energy flux sensitivity of 10 −12 erg cm −2 s −1 , an order of magnitude lower than the previous generation of VHE instruments. The wide field of view of H.E.S.S. (5 • in diameter) enables us to simultaneously monitor the entire central 200 parsec region. Results from …