Relativistic shear flow between electron-ion and electron-positron plasmas and astrophysical applications
Abstract
We present particle-in-cell simulation results of relativistic shear boundary layers between electron–ion and
electron–positron plasmas and discuss their potential applications to astrophysics. Specifically, we find that in the
case of a fast electron–positron spine surrounded by a slow-moving or stationary electron–ion sheath, lepton
acceleration proceeds in a highly anisotropic manner due to electromagnetic fields created at the shear interface.
While the highest-energy leptons still produce a beaming pattern (as seen in the quasi-stationary frame of the
sheath) of order 1/Γ, where Γ is the bulk Lorentz factor of the spine, for lower-energy particles, the beaming is
much less pronounced. This is in stark contrast to the case of pure electron–ion shear layers, in which anisotropic
particle acceleration leads to significantly narrower beaming patterns than 1/Γ for the highest-energy particles. In
either case, shear-layer acceleration is expected to produce strongly angle-dependent lepton (hence, emanating
radiation) spectra, with a significantly harder spectrum in the forward direction than viewed from larger off-axis
angles, much beyond the regular Doppler boosting effect from a co-moving isotropic lepton distribution. This may
solve the problem of the need for high (and apparently arbitrarily chosen) minimum Lorentz factors of radiating
electrons, often plaguing current blazar and GRB jet modeling efforts
URI
http://hdl.handle.net/10394/25802https://doi.org/10.3847/1538-4357/aa8772
http://iopscience.iop.org/article/10.3847/1538-4357/aa8772