Astronomy and Astrophysics – Astrophysics – High Energy Astrophysical Phenomena
Scientific paper
2009-09-28
2009 ApJ 706 38-44
Astronomy and Astrophysics
Astrophysics
High Energy Astrophysical Phenomena
8 pages, 6 figures, accepted by ApJ
Scientific paper
Efficient acceleration of cosmic rays (via the mechanism of diffusive shock acceleration) requires turbulent, amplified magnetic fields in the shock's upstream region. We present results of multidimensional particle-in-cell simulations aimed at observing the magnetic field amplification that is expected to arise from the cosmic-ray current ahead of the shock, and the impact on the properties of the upstream interstellar medium. We find that the initial structure and peak strength of the amplified field is somewhat sensitive to the choice of parameters, but that the field growth saturates in a similar manner in all cases: the back-reaction on the cosmic rays leads to modification of their rest-frame distribution and also a net transfer of momentum to the interstellar medium, substantially weakening their relative drift while also implying the development of a modified shock. The upstream medium becomes turbulent, with significant spatial fluctuations in density and velocity, the latter in particular leading to moderate upstream heating; such fluctuations will also have a strong influence on the shock structure.
Niemiec Jacek
Pohl Martin
Stroman Thomas
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