Evolution of Global Relativistic Jets: Collimations and Expansion with kKHI and the Weibel Instability

TL;DR

This study investigates the initial evolution of relativistic jets, focusing on magnetic field generation, collimation, and particle acceleration, revealing differences between electron-proton and electron-positron jets that affect observable properties.

Contribution

It provides new insights into how kinetic instabilities influence jet collimation, magnetic field structure, and particle acceleration in relativistic jets.

Findings

Magnetic fields from instabilities collimated the jets.

Electrons are accelerated perpendicularly in electron-proton jets.

Distinct magnetic structures in different jet compositions may affect polarization observations.

Abstract

One of the key open questions in the study of relativistic jets is their interaction with the environment. Here, we study the initial evolution of both electron-proton and electron-positron relativistic jets, focusing on their lateral interaction with the ambient plasma. We trace the generation and evolution of the toroidal magnetic field generated by both kinetic Kelvin-Helmholtz (kKH) and Mushroom instabilities (MI). This magnetic field collimates the jet. We show that in electron-proton jet, electrons are perpendicularly accelerated with jet collimation. The magnetic polarity switches from the clockwise to anti-clockwise in the middle of jet, as the instabilities weaken. For the electron-positron jet, we find strong mixture of electron-positron with the ambient plasma, that results in the creation of a bow shock. Merger of magnetic field current filaments generate density bumps which initiate a forward shock. The strong mixing between jet and ambient particles prevents full development of the jet on the studied scale. Our results therefore provide a direct evidence for both jet collimation and particle acceleration in the created bow shock. Differences in the magnetic field structures generated by electron-proton and electron-positron jets may contribute to observable differences in the polarized properties of emission by electrons.