This content will become publicly available on June 1, 2023
- Award ID(s):
- 1655280
- Publication Date:
- NSF-PAR ID:
- 10355939
- Journal Name:
- The Astrophysical Journal
- Volume:
- 932
- Issue:
- 1
- Page Range or eLocation-ID:
- 65
- ISSN:
- 0004-637X
- Sponsoring Org:
- National Science Foundation
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Abstract Subsonic, compressive turbulence transfers energy to cosmic rays (CRs), a process known as nonresonant reacceleration. It is often invoked to explain the observed ratios of primary to secondary CRs at ∼GeV energies, assuming wholly diffusive CR transport. However, such estimates ignore the impact of CR self-confinement and streaming. We study these issues in stirring box magnetohydrodynamic (MHD) simulations using Athena++, with field-aligned diffusive and streaming CR transport. For diffusion only, we find CR reacceleration rates in good agreement with analytic predictions. When streaming is included, reacceleration rates depend on plasma
β . Due to streaming-modified phase shifts between CR and gas variables, they are slower than canonical reacceleration rates in low-β environments like the interstellar medium but remain unchanged in high-β environments like the intracluster medium. We also quantify the streaming energy-loss rate in our simulations. For sub-Alfvénic turbulence, it is resolution dependent (hence unconverged in large-scale simulations) and heavily suppressed compared to the isotropic loss ratev A· ∇P CR/P CR∼v A/L 0, due to misalignment between the mean field and isotropic CR gradients. Unlike acceleration efficiencies, CR losses are almost independent of magnetic field strength overβ ∼ 1–100 and are, therefore, not the primary factor behind lower acceleration rates when streaming is included. While this paper is primarilymore » -
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