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| Paper: |
Self-Similar Evolution of Cosmic-Ray Modified Shocks |
| Volume: |
429, Numerical Modeling of Space Plasma Flows, Astronum-2009 |
| Page: |
85 |
| Authors: |
Kang, H.; Ryu, D. |
| Abstract: |
Diffusive shock acceleration (DSA) is widely accepted as the primary
mechanism through which cosmic rays (CRs) are produced in a variety of
astrophysical environments. We used kinetic simulations of DSA to study
the time-dependent evolution of the energy spectrum of CRs accelerated
by plane, quasi-parallel shocks. We found that the precursor and subshock
transition approach the time-asymptotic state, and then evolve in an
approximately self-similar fashion, depending only on the similarity
variable, x/(us t). During this self-similar stage, the CR spectrum
at the subshock maintains a characteristic form as it evolves: the
sum of two power-laws with the slopes determined by the subshock and total
compression ratios with an exponential cutoff at the highest accelerated
momentum. This analytic form may represent an approximate solution to
the DSA problem for astrophysical shocks during the self-similar
evolutionary stage. |
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