2025A&A...700A.263Y

Context. Collisionally ionized plasmas produce X-ray spectra that depend on electron energy and atomic processes, requiring accurate atomic rate coefficients for modeling. While most data are theoretical, experimental measurements - such as those for Fe XXV - are critical for providing important benchmarks and quantifying uncertainties, thereby improving astrophysical spectral analysis, especially with high-resolution observatories like XRISM.
Aims. This study aimed to experimentally measure the electron impact ionization (EII) cross section of Fe XXV, a key ion in astrophysical plasma diagnostics, and to evaluate the impact of these measurements on the interpretation of X-ray spectra from high-temperature plasma environments.
Methods. The EII cross sections were measured using X-ray spectroscopy with an electron beam ion trap (EBIT) at various electron beam energies. The intensity ratios of the w resonance line in Fe XXV and the Lyα_1,2 lines in Fe XXVI were used to derive the cross sections. Level-resolved population calculations were performed using the NOMAD collisional-radiative code to account for processes affecting the emission ratios and ionization balance in the non-Maxwellian EBIT plasma.
Results. The measured EII cross sections show good agreement with relativistic convergent close-coupling calculations. The uncertainties in the measurements, ranging from 8% to 12%, are discussed in terms of their impact on the accuracy of temperature diagnostics for astrophysical plasma environments.