Discovery of very-high-energy γ-rays from the Galactic Centre ridge

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The source of Galactic cosmic rays (with energies up to 1015 eV) remains unclear, although it is widely believed that they originate in the shock waves of expanding supernova remnants1,2. At present the best way to investigate their acceleration and propagation is by observing the γ-rays produced when cosmic rays interact with interstellar gas3. Here we report observations of an extended region of very-high-energy (> 1011 eV) γ-ray emission correlated spatially with a complex of giant molecular clouds in the central 200 parsecs of the Milky Way. The hardness of the γ-ray spectrum and the conditions in those molecular clouds indicate that the cosmic rays giving rise to the γ-rays are likely to be protons and nuclei rather than electrons. The energy associated with the cosmic rays could have come from a single supernova explosion around 104 years ago.

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Figure 1: VHE γ-ray images of the Galactic Centre region.
Figure 2: γ-ray emission from the Galactic Centre region.
Figure 3: Energy distribution of Galactic cosmic rays.


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The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of HESS is gratefully acknowledged, as is the support by the German Ministry for Education and Research (BMBF), the Max Planck Society, the French Ministry for Research, the CNRS-IN2P3 and the Astroparticle Interdisciplinary Programme of the CNRS, the UK Particle Physics and Astronomy Research Council (PPARC), the IPNP of Charles University, the South African Department of Science and Technology and National Research Foundation, and by the University of Namibia. We would like to thank M. Tsuboi for providing the CS survey data used here and Y. Moriguchi and Y. Fukui for helpful discussions on molecular tracers.

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Correspondence to J. A. Hinton.

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Aharonian, F., Akhperjanian, A., Bazer-Bachi, A. et al. Discovery of very-high-energy γ-rays from the Galactic Centre ridge. Nature 439, 695–698 (2006) doi:10.1038/nature04467

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