2018MNRAS.473.3211Z

This paper studies the acceleration processes of background thermal electrons in X-ray binary jets via turbulent stochastic interactions and shock collisions. By considering turbulent magnetized jets mixed with fluctuating magnetic fields and an ordered large-scale magnetic field, and numerically solving the transport equation along the jet axis, we explore the influence on acceleration efficiency of magnetic turbulence, electron injection, the location of the acceleration region and various cooling mechanisms. The results show the following: (1) Dominant turbulent magnetic fields in the jets are necessary to accelerate background thermal electrons to relativistic energies. (2) The acceleration of electrons depends on the type of magnetohydrodynamic turbulence and turbulence with a hard slope can accelerate electrons more effectively. (3) The effective acceleration region is located at a distance >10³R_g away from the central black hole (R_g being the gravitational radius). As a result of acceleration mechanisms competing with various cooling mechanisms, background thermal electrons gain energy and their spectra are broadened beyond the initial distribution to form a thermal-like distribution. (4) The acceleration mechanisms explored in this work can reasonably provide the maximum electron energy required for interpreting high-energy γ-ray observations from microquasars; however, some extreme parameter values are needed for the possible very high-energy γ-ray signals.