Abstract
Weakly magnetized, relativistic collisionless shock waves are not only the natural offsprings of relativistic jets in high-energy astrophysical sources, they are also associated with some of the most outstanding displays of energy dissipation through particle acceleration and radiation. Perhaps their most peculiar and exciting feature is that the magnetized turbulence that sustains the acceleration process, and (possibly) the secondary radiation itself, is self-excited by the accelerated particles themselves, so that the phenomenology of these shock waves hinges strongly on the microphysics of the shock. In this review, we draw a status report of this microphysics, benchmarking analytical arguments with particle-in-cell simulations, and extract consequences of direct interest to the phenomenology, regarding, in particular, the so-called microphysical parameters used in phenomenological studies.
Highlights
The generation of fast and powerful outflows appears to be a common trait of all high-energy astrophysical sources, often accompanied by outstanding dissipative phenomena observed all across the electromagnetic spectrum
Those shock waves are said to be collisionless because the mean free path for (Coulomb) binary particle interactions far exceeds the relevant length scales, in particular the thickness of the shock, and this very property makes them ideal sites of particle acceleration, e.g., [11], proceeding in rather extreme regimes of relativistic plasma astrophysics [12,13,14]
At the magnetizations that we are interested in (σ . 10−3 ), particle acceleration can take place at relativistic shock waves, it is restricted to a finite range of gyroradii, see [53] for simulations
Summary
The generation of fast and powerful outflows appears to be a common trait of all high-energy astrophysical sources, often accompanied by outstanding dissipative phenomena observed all across the electromagnetic spectrum. It is generally sourced by a central object, which consumes its rotational or magnetic energy reservoir, or which draws hydromagnetic energy from its surroundings Those shock waves are said to be collisionless because the mean free path for (Coulomb) binary particle interactions far exceeds the relevant length scales, in particular the thickness of the shock, and this very property makes them ideal sites of particle acceleration, e.g., [11], proceeding in rather extreme regimes of relativistic plasma astrophysics [12,13,14]. Inside gamma-ray burst outflows, radio-galaxy and blazar outflows, or even microquasars, internal shocks can occur between layers of material propagating at different four-velocities, triggering mildly relativistic [meaning ush ∼ O(1)] shock waves, e.g., [16,17,18,19] In such objects, the magnetization is generally unknown, and may take arbitrarily large or small values. All densities and temperatures are expressed in the proper frame
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