The terminal bulk Lorentz factor of relativistic electron-positron jet

We present numerical simulation of bulk Lorentz factor of relativistic electronpositron jet driven by Compton rocket effect from accretion disk radiation. The plasma is assumed to have a power-law distribution ne(γ) ∝ γ −s ( 1 < γ < γmax) and is continuously reheated to compensate radiation losses. We include Klein-Nishina (hereafter KN) corrections, and study the role of energy upper cut-off γmax, spectral index s, and source compactness. We determine terminal bulk Lorentz factor in the case of supermassive black holes relevant to AGN and stellar black holes relevant to galactic microquasars. In the latter case, effects of KN corrections are more important, and induce terminal bulk Lorentz factor γb∞ smaller than in the former case. The result can explain the low bulk Lorentz factors for galactic sources (GRS1915+105, GROJ1655-40) compared to extragalactic ones. We also take into account the influence of the size of the accretion disk; if the external radius is small enough, the bulk Lorentz factor can be as high as 60, which is comparable to the values needed to explain extragalactic gamma-ray bursts.