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Electron and ion acceleration in relativistic shocks with applications to GRB afterglows

Warren, Donald C. ; Ellison, Donald C. ; Bykov, Andrei M. ; Lee, Shiu-Hang

In: Monthly Notices of the Royal Astronomical Society, 2015, vol. 452, no. 1, p. 431-443

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    Title
    • Electron and ion acceleration in relativistic shocks with applications to GRB afterglows
    Author
    • Warren, Donald C.. Astrophysical Big Bang Laboratory, RIKEN, Saitama 351-0198, Japan
    • Ellison, Donald C.. Physics Department, North Carolina State University, Box 8202, Raleigh, NC 27695, USA
    • Bykov, Andrei M.. Ioffe Institute for Physics and Technology, 194021 St. Petersburg, Russia
    • Lee, Shiu-Hang. Japan Aerospace Exploration Agency (JAXA), Institute of Space and Astronautical Science, Kanagawa 252-5210, Japan
    Document Type
    • Postprint
    Language
    • English
    Published in
    • Monthly Notices of the Royal Astronomical Society, 2015, vol. 452, no. 1, p. 431-443. Oxford University Press
    Other Version
    OAI-PMH Identifier
    • oai:doc.rero.ch:293459
    Summary
    We have modelled the simultaneous first-order Fermi shock acceleration of protons, electrons, and helium nuclei by relativistic shocks. By parametrizing the particle diffusion, our steady-state Monte Carlo simulation allows us to follow particles from particle injection at non-relativistic thermal energies to above PeV energies, including the non-linear smoothing of the shock structure due to cosmic ray (CR) backpressure. We observe the mass-to-charge (A/Z) enhancement effect believed to occur in efficient Fermi acceleration in non-relativistic shocks and we parametrize the transfer of ion energy to electrons seen in particle-in-cell (PIC) simulations. For a given set of environmental and model parameters, the Monte Carlo simulation determines the absolute normalization of the particle distributions and the resulting synchrotron, inverse Compton, and pion-decay emission in a largely self-consistent manner. The simulation is flexible and can be readily used with a wide range of parameters typical of γ-ray burst (GRB) afterglows. We describe some preliminary results for photon emission from shocks of different Lorentz factors and outline how the Monte Carlo simulation can be generalized and coupled to hydrodynamic simulations of GRB blast waves. We assume Bohm diffusion for simplicity but emphasize that the non-linear effects we describe stem mainly from an extended shock precursor where higher energy particles diffuse further upstream. Quantitative differences will occur with different diffusion models, particularly for the maximum CR energy and photon emission, but these non-linear effects should be qualitatively similar as long as the scattering mean-free path is an increasing function of momentum