Abstract
Abstract. We have investigated the generation of magnetic fields associated with velocity shear between an unmagnetized relativistic jet and an unmagnetized sheath plasma. We have examined the strong magnetic fields generated by kinetic shear (Kelvin–Helmholtz) instabilities. Compared to the previous studies using counter-streaming performed by Alves et al. (2012), the structure of the kinetic Kelvin–Helmholtz instability (KKHI) of our jet-sheath configuration is slightly different, even for the global evolution of the strong transverse magnetic field. In our simulations the major components of growing modes are the electric field Ez, perpendicular to the flow boundary, and the magnetic field By, transverse to the flow direction. After the By component is excited, an induced electric field Ex, parallel to the flow direction, becomes significant. However, other field components remain small. We find that the structure and growth rate of KKHI with mass ratios mi/me = 1836 and mi/me = 20 are similar. In our simulations saturation in the nonlinear stage is not as clear as in counter-streaming cases. The growth rate for a mildly-relativistic jet case (γj = 1.5) is larger than for a relativistic jet case (γj = 15).
Highlights
A shear flow upstream of a shock can lead to density inhomogeneities via the Magnetohydrodynamics (MHD) Kelvin–Helmholtz instability (KHI), which may provide important scattering sites for particle acceleration
This structure is similar in spirit, not in scale, to that proposed for active galactic nuclei (AGN) relativistic jet cores surrounded by a slower moving sheath, and is relevant to gamma-ray burst (GRB) jets
We have investigated generation of magnetic fields associated with velocity shear between an unmagnetized relativistic jet and an unmagnetized sheath plasma
Summary
In this simulation study we investigate velocity shear in a core-sheath jet instead of the counter-streaming jets used in previous simulations (Alves et al, 2012; Liang et al, 2013). Electric and magnetic field generated by a relativistic electron ion jet core with γj. Asninn.cGe etohpehyDs.C, 31fi,e1l5d35is–1s5t4ro1,n2g0e1r3than the AC field, a kinetic treatment is clearly required in order to fully capture the field structure generated in unmagnetized or weakly mass ratio case keep the system thermal fluctuations smaller, but the kinetic KHI grows . In this RPIC simulation the velocity shear occurs at the edges of a velocity fieldwwwwi.tahnnv-cgoereopphoyisn.ntient/g31i/n15t3h5e/20p1o3s/itive x direction in the middle of the simulation box, with upper and lower quarters of the simulation box containing a velocity field with v pointing in the positive x direction as inlog E. relativistic jet core resulting in a larger Lorentz factor in the “electrostatic” relativistic jet plasma frequency and larger electron inertia in the simulation frame
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