2024MNRAS.527.1093Y

The Fe Kα fluorescent emission line from neutral matter is widely used as a diagnostic tool in X-ray spectroscopy for many astrophysical X-ray sources. The line properties can potentially be used to constrain the geometry, column density, and kinematics of the material in which the line is formed. The intrinsic width and the shape of the intrinsic line profile has been neglected thus far, because it is much smaller than the instrumental broadening in all space-based X-ray detectors before Hitomi. However, the instrumental broadening of X-ray microcalorimeters is comparable to the intrinsic line width. We have performed new calculations based on Monte Carlo simulations of the MYTORUS X-ray reprocessor spectral-fitting model that utilize parametrizations of historical high-precision laboratory measurements of the intrinsic profiles of the Fe Kα and Fe Kβ lines. A publicly available table is provided that can seamlessly replace the existing Fe Kα and Fe Kβ line spectrum in the MYTORUS model. The new table can also be used in a standalone mode (without the MYTORUS model) in order to derive empirical velocity widths, if the line-emitting matter is Compton thin. Neglecting to account for the intrinsic profiles of the Fe Kα and Fe Kβ lines can result in a significant overestimate of the velocity broadening, if the true velocity broadening is less than ${\sim} 2000 \ \rm km \ s^{-1}$. Residual artefacts may also appear in observed line profiles in data with a high signal-to-noise ratio.