Supernova Remnant Paradigm for Cosmic-Ray Origin

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  • 超新星残骸は宇宙線の起源か？
  • チョウシンセイ ザンガイ ワ ウチュウセン ノ キゲン カ?

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Abstract

<p>Galactic Cosmic Rays (CRs), mostly CR protons, are accelerated up to a few PeV energies. While it is widely believed that supernova remnants (SNRs) are the sources of Galactic cosmic rays, unequivocal evidence for the acceleration of high-energy protons in SNRs lacked until recently. Inelastic collisions between high-energy protons with nuclei in the interstellar gas produce neutral pions, which in turn decay into gamma rays whose energy and spatial distributions reflect those of parent protons. This offers a compelling way to reveal the acceleration sites of protons. However, the identification of piondecay gamma rays has been tantalizingly difficult since high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. Recently, the Fermi-LAT Collaboration has reported on the detection of the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, which are known to be interacting with molecular clouds. It provides direct evidence that cosmic-ray protons are accelerated in SNRs. We describe the Fermi-LAT observations of these objects along with gamma-ray observations of some other remnants and discuss their implications to our understanding of the acceleration of the Galactic CRs.</p>

Journal

  • Butsuri

    Butsuri 72 (9), 649-657, 2017-09-05

    The Physical Society of Japan

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