Letter to the Editor

Intrinsic line profiles for X-ray fluorescent lines in SKIRT

¹ Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium
² Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa 252-5210, Japan
³ Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890-0065, Japan
⁴ Research Center for Space and Cosmic Evolution, Ehime University, Matsuyama 790-8577, Japan
⁵ Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan

Received: 3 July 2024
Accepted: 4 August 2024

Abstract

Context. X-ray microcalorimeter instruments are expected to spectrally resolve the intrinsic line shapes of the strongest fluorescent lines. X-ray models should therefore incorporate these intrinsic line profiles to obtain meaningful constraints from observational data.

Aims. 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.

Methods. The intrinsic line profiles of the Kα and Kβ lines of Cr, Mn, Fe, Co, Ni, and Cu were implemented based on a multi-Lorentzian parameterisation. Line energies are sampled from these Lorentzian components during the radiative transfer routine.

Results. 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.

Conclusions. 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.