The hydrogen-like and helium-like iron Kα line emission from a black hole X-ray binary

The iron Kα line emission from the black hole X-ray binary GX339-4 in the “off” state is calculated. It is shown that the black hole with ADAF (advection-dominated accretion flow) at a very low accretion rate might produce detectable hydrogen-like and helium-like iron Kα lines. Although the ADAF model has been applied successfully in explaining the continuum spectra of many low accretion rate systems, line emission from ADAF has rarely been discussed till now.