Diffusion of Cosmic Rays in a Multiphase Interstellar Medium Swept-Up by a Supernova Remnant Blast Wave

Abstract

Supernova remnants (SNRs) are one of the most energetic astrophysical events and are thought to be the dominant source of Galactic cosmic rays (CRs). A recent report on observations from the Fermi satellite has shown a signature of pion decay in the gamma-ray spectra of SNRs. This provides strong evidence that high-energy protons are accelerated in SNRs. The actual gamma-ray emission from pion decay should depend on the diffusion of CRs in the interstellar medium. In order to quantitatively analyse the diffusion of high-energy CRs from acceleration sites, we have performed test particle numerical simulations of CR protons using a three-dimensional magnetohydrodynamics (MHD) simulation of an interstellar medium swept-up by a blast wave. We analyse the diffusion of CRs at a length scale of order a few pc in our simulated SNR, and find the diffusion of CRs is precisely described by a Bohm diffusion, which is required for efficient acceleration at least for particles with energies above 30 TeV for a realistic interstellar medium. Although we find the possibility of a superdiffusive process (travel distance proportional to t^0.75) in our simulations, its effect on CR diffusion at the length scale of the turbulence in the SNR is limited.

20 pages, 4 tables, 10 figures

References in corpus (5)

• Detection of the Characteristic Pion-Decay Signature in Supernova Remnants
• Observations of the young supernova remnant RX J1713.7-3946 with the Fermi Large Area Telescope
• Hadronic gamma-rays from RX J1713.7-3946?
• A Possible Link Between the Galactic Center HESS Source and Sgr A*
• Diffuse TeV Emission at the Galactic Centre

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• Stochastic Particle Acceleration in Turbulence Generated by the Magnetorotational Instability
• Direct Numerical Simulations of Cosmic-ray Acceleration at Dense Circumstellar Medium: Magnetic Field Amplification by Bell Instability and Maximum Energy
• Bell-Instability-Mediated Spectral Modulation of Hadronic Gamma Rays from a Supernova Remnant Interacting with a Molecular Cloud
• Using Interstellar Clouds to Search for Galactic PeVatrons: Gamma-ray Signatures from Supernova Remnants
• Interaction between Molecular Clouds and MeV-TeV Cosmic-ray Protons Escaped from Supernova Remnants
• Anomalous Galactic Cosmic Rays in the Framework of AMS-02