Browsing by Author "Böttcher, Markus"

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    Relativistic Shear Flow between Electron–Ion and Electron–Positron Plasmas and Astrophysical Applications
    (IOP Publishing, 2017) Liang, Edison; Fu, Wen; Böttcher, Markus
    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.
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    Scaling of Relativistic Shear Flows with the Bulk Lorentz Factor
    (IOP Publishing, 2018) Liang, Edison; Fu, Wen; Böttcher, Markus; Roustazadeh, Parisa
    We compare Particle-in-cell simulation results of relativistic electron–ion shear flows with different bulk Lorentz factors, and discuss their implications for spine-sheath models of blazar versus gamma-ray burst (GRB) jets. Specifically, we find that most properties of the shear boundary layer scale with the bulk Lorentz factor: the lower the Lorentz factor, the thinner the boundary layer, and the weaker the self-generated fields. Similarly, the energized electron spectrum peaks at an energy near the ion drift energy, which increases with bulk Lorentz factor, and the beaming of the accelerated electrons along the shear interface gets narrower with increasing Lorentz factor. This predicts a strong correlation between emitted photon energy, angular beaming, and temporal variability with the bulk Lorentz factor. Observationally, we expect systematic differences between the high-energy emissions of blazars and GRB jets.