Particle Acceleration Processes in Astrophysical Jets

Dear Colleagues,

Astrophysical jets, the collimated outflows associated with matter accretion onto compact objects, represent one of the most extreme phenomena in the Universe. They have been observed from a variety of cosmic sources, from protostars to distant galaxies, and often determine the major observational features of the parent object. The jet phenomenon appears to be common wherever mass accretion onto a central object occurs. In many cases, the bulk motion of the jet plasma is close to the speed of light, so relativistic effects play an important role in the physical processes in these outflows. Jets become relativistic in the case of accretion onto compact objects, such as neutron stars or black holes, both in Galactic systems and extragalactic systems. The detection of astrophysical jets and our understanding of their physical nature has been closely related to the development of multiwavelength instruments, and improved methods of simulation. However, we still need much effort to make progress in our understanding of the many fundamental aspects of jet physics that are still poorly understood and constrained: the mechanisms of jet launching andacceleration, the connection between these processes and those operating in accretion discs; the physics responsible for jet collimation over tens of thousands to even millions of Schwarzschild radii of the central putative black holes; the role of magnetic fields and reconnection;  the matter content of jets; the location of the region accelerating particles to TeV-PeV energy, and, possibly, even to EeV energies; the physical processes responsible for this particle acceleration; the radiative processes giving rise to the observed multi-wavelength emission; and the topology of magnetic fields and their role in the jet collimation and particle acceleration processes.

This Issue reviews our current understanding of the particle acceleration processes at work in the jets of various extreme Galactic and extragalactic objects: protostars, X-ray binaries, microquasars, Fermi bubbles (as relics of Seyfert-type active Galactic nuclei), blazars, radio galaxies, and gamma-ray bursts. It emphasizes unresolved problems, and the importance of multiwavelength monitoring and high-resolution simulations for insight into the physical processes operating in the jets of various objects over a range of distances from the central engine.

Prof. Bidzina Kapanadze
Prof. Philip Hughes
Guest Editors

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• Jets: relativistic
• collimation
• particle acceleration
• active galactic nuclei
• microquasars
• GRBs
• Seyfert galaxies
• blazars
• quasars
• X-ray binaries