Appearance of bulk motion Comptonization in the Monte Carlo simulated spectrum. The spectrum is shown in units of keV (keV cm ⁻² s ⁻¹ keV ⁻¹) with absolute values that are multiplied by an arbitrary constant. The dotted line corresponds to a simulation with an assumption that there is no bulk effect in the converging flow zone. The solid line results from the same simulation adding bulk velocity. The effect of bulk motion Comptonization is clearly seen above 20–30 keV. The parameters used are: mass accretion rate in Eddington units , flow electron temperature kT _e = 4.3 keV, C ₁/ C ₀ = 7, and q = 0.01.