STOCHASTIC PARTICLE ACCELERATION IN TURBULENCE GENERATED BY MAGNETOROTATIONAL INSTABILITY

Journal Article · Tue May 10 00:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/822/2/88· OSTI ID:22663043

Kimura, Shigeo S.; Toma, Kenji ^[1]; Suzuki, Takeru K.; Inutsuka, Shu-ichiro ^[2]

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1. Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai 980-8578 (Japan)
2. Department of Physics, Nagoya University, Nagoya, Aichi 464-8602 (Japan)

We investigate stochastic particle acceleration in accretion flows. It is believed that magnetorotational instability (MRI) generates turbulence inside accretion flows and that cosmic rays (CRs) are accelerated by the turbulence. We calculate equations of motion for CRs in the turbulent fields generated by MRI with the shearing box approximation and without back reaction to the field. Our results show that the CRs randomly gain or lose their energy through interaction with the turbulent fields. The CRs diffuse in the configuration space anisotropically: the diffusion coefficient in the direction of the unperturbed flow is about 20 times higher than the Bohm coefficient, while those in the other directions are only a few times higher than the Bohm. The momentum distribution is isotropic and its evolution can be described by the diffusion equation in momentum space where the diffusion coefficient is a power-law function of the CR momentum. We show that the shear acceleration works efficiently for energetic particles. We also cautiously note that in the shearing box approximation, particles that cross the simulation box many times along the radial direction undergo unphysical runaway acceleration by the Lorentz transformation, which needs to be taken into account with special care.

• OSTI ID: 22663043
• Journal Information: Astrophysical Journal, Vol. 822, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ACCELERATION
ACCRETION DISKS
APPROXIMATIONS
COSMIC RADIATION
DIFFUSION
DIFFUSION EQUATIONS
DISTRIBUTION
EQUATIONS OF MOTION
GALAXIES
GALAXY NUCLEI
INSTABILITY
LORENTZ TRANSFORMATIONS
MAGNETIC PROPERTIES
NMR IMAGING
ROTATION
SIMULATION
SPACE
STOCHASTIC PROCESSES
TURBULENCE