Orateur
Description
Shearing flows give rise to a Fermi-type acceleration and have been proposed to explain e.g. the presence of high-energy electrons along astrophysical jets and to contribute to the acceleration of ultra-high energy cosmic rays.
Particles diffusing along the shearing direction experience a change in the flow speed, which translates to a change in momentum. In a Fokker-Planck picture, shear acceleration can be described by a diffusion and drift in momentum, where assumptions on the particle scattering and flow profile go into the corresponding Fokker-Planck coefficients.
We present a stochastic model, following Lemoine, 2025, where those assumptions can be relaxed, allowing to study non-gradual shear profiles and the influence of anisotropic spatial diffusion. The momentum evolution of a particle is tracked in a comoving frame that moves with the plasma velocity, assuming that perturbations in the magnetic field are carried with the flow. We find that shear acceleration is most efficient in mildly-relativistic jets while high-relativistic jet speeds lead to particle trapping in space and momentum. The latter results in a subdiffusive evolution of the particle momentum leading to power-law spectra that go beyond Fokker-Planck expectations.