Intrinsic line profiles for X-ray fluorescent lines in SKIRT

TL;DR

This paper enhances the SKIRT X-ray radiative transfer code by incorporating intrinsic line profiles of fluorescent lines, enabling more accurate modeling of cold-gas kinematics with upcoming XRISM/Resolve observations.

Contribution

The authors integrated intrinsic line profiles into SKIRT using multi-Lorentzian parameterization, allowing for direct interpretation of observed line shapes in terms of gas kinematics.

Findings

Intrinsic line profiles match laboratory measurements in optically thin conditions.

Kinematic broadening and shifts are detectable with XRISM/Resolve.

Line profiles directly trace cold-gas kinematics without additional effects.

Abstract

We included the intrinsic line profiles of the strongest fluorescent lines in the X-ray radiative transfer code SKIRT to model the cold-gas structure and kinematics based on high-resolution line observations from XRISM/Resolve and Athena/X-IFU. The intrinsic line profiles of the Ka and Kb lines of Cr, Mn, Fe, Co, Ni, and Cu were implemented based on a multi-Lorentzian parameterisation and line energies are sampled from these Lorentzian components during the radiative transfer routine. In the optically thin regime, the SKIRT results match the intrinsic line profiles as measured in the laboratory. With a more complex 3D model that also includes kinematics, we find that the intrinsic line profiles are broadened and shifted to an extent that will be detectable with XRISM/Resolve; this model also demonstrates the importance of the intrinsic line shapes for constraining kinematics. We find that observed line profiles directly trace the cold-gas kinematics, without any additional radiative transfer effects. With the advent of the first XRISM/Resolve data, this update to the X-ray radiative transfer framework of SKIRT is timely and provides a unique tool for constraining the velocity structure of cold gas from X-ray microcalorimeter spectra.