Home > Publications database > Acceleration of petaelectronvolt protons in the Galactic Centre |
Report/Journal Article | PUBDB-2017-00281 |
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2016
Macmillan28177
London
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Please use a persistent id in citations: doi:10.1038/nature17147 doi:10.3204/PUBDB-2017-00281
Report No.: arXiv:1603.07730
Abstract: Galactic cosmic rays reach energies of at least a few Peta-electronvolts (1 PeV =$10^\mathbf{15}$ electron volts). This implies our Galaxy contains PeV accelerators (PeVatrons), but all proposed models of Galactic cosmic-ray accelerators encounter non-trivial difficulties at exactly these energies. Tens of Galactic accelerators capable of accelerating particle to tens of TeV (1 TeV =$10^\mathbf{12}$ electron volts) energies were inferred from recent gamma-ray observations. None of the currently known accelerators, however, not even the handful of shell-type supernova remnants commonly believed to supply most Galactic cosmic rays, have shown the characteristic tracers of PeV particles: power-law spectra of gamma rays extending without a cutoff or a spectral break to tens of TeV. Here we report deep gamma-ray observations with arcminute angular resolution of the Galactic Centre regions, which show the expected tracer of the presence of PeV particles within the central 10~parsec of the Galaxy. We argue that the supermassive black hole Sagittarius A* is linked to this PeVatron. Sagittarius A* went through active phases in the past, as demonstrated by X-ray outbursts and an outflow from the Galactic Centre. Although its current rate of particle acceleration is not sufficient to provide a substantial contribution to Galactic cosmic rays, Sagittarius A* could have plausibly been more active over the last $\gtrsim 10^{6-7}$ years, and therefore should be considered as a viable alternative to supernova remnants as a source of PeV Galactic cosmic rays.
Keyword(s): cosmic radiation: galaxy ; galaxy: model ; particle: acceleration ; accelerator ; gamma ray: VHE ; supernova ; electron ; gamma ray: emission ; p p: interaction ; p: UHE ; angular resolution ; neutrino ; black hole ; spectral ; X-ray
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