An interplay of various particle acceleration processes in turbulent astrophysical plasma

Abstract

Magneto-hydrodynamic (MHD) turbulence is ubiquitous in astrophysical systems, and it is typically attributed to governing various micro-physical activities in these systems. One of the important manifestations of this astrophysical turbulence is the origin and transport of non-thermal particles, often called cosmic rays (CR). These high-energy CRs, though small in number, play a signi cant and unique role in various astronomical phenomena. While propagating through a turbulent system, CRs acquire energy via Fermi acceleration processes and lose energy due to various loss processes. Among those acceleration mechanisms, di usive shock acceleration (DSA) and stochastic turbulent acceleration (STA) are considered to be operative, particularly in weakly magnetised regions. While DSA is a systematic acceleration process that energises particles in the vicinity of shocks, stochastic turbulent acceleration (STA) is a random energising process where the interaction between cosmic ray particles and electromagnetic uctuations results in particle acceleration. This process is usually interpreted as a biased random walk in energy space. The primary energy loss processes that these non-thermal high-energy CRs undergo are synchrotron and inverse compton (IC) losses. This interplay of particle acceleration processes and radiative losses subsequently shapes the emission features of di erent astrophysical sources.