The thermal-radiative wind in low-mass X-ray binary H1743−322 – II. Iron line predictions from Monte Carlo radiation transfer

Abstract

We show the best current simulations of the absorption and emission features predicted from thermal-radiative winds produced from X-ray illumination of the outer accretion disc in binary systems. We use the density and velocity structure derived from a radiation hydrodynamic code as input to a Monte Carlo radiation transport calculation. The initial conditions are matched to those of the black hole binary system H1743−322 in its soft, disc dominated state, where wind features are seen in Chandra grating data. Our simulation fits well to the observed line profile, showing that these physical wind models can be the origin of the absorption features seen, rather than requiring a magnetically driven wind. We show how the velocity structure is the key observable discriminator between magnetic and thermal winds. Magnetic winds are faster at smaller radii, whereas thermal winds transition to a static atmosphere at smaller radii. New data from XRISM (due for launch 2022 January) will give an unprecedented view of the physics of the wind launch and acceleration processes, but the existence of static atmospheres in small disc systems already rules out magnetic winds which assume self-similar magnetic fields from the entire disc as the origin of the absorption features seen.