X-ray spectra of the Fe-L complex II: atomic data constraints from EBIT experiment and X-ray grating observations of Capella

TL;DR

This study evaluates atomic data for Fe-L complex lines through laboratory experiments and astrophysical observations, highlighting the importance of accurate atomic models for X-ray spectroscopy and identifying areas needing further refinement.

Contribution

It systematically tests and calibrates atomic data using EBIT experiments and applies these to model Chandra spectra of Capella, improving understanding of atomic processes in X-ray spectra.

Findings

Laboratory measurements validate atomic calculations

Calibrated data improve spectral modeling of Capella

Identified discrepancies guiding future atomic data improvements

Abstract

The Hitomi results for the Perseus cluster have shown that accurate atomic models are essential to the success of X-ray spectroscopic missions, and just as important as knowledge on instrumental calibration and astrophysical modeling. Preparing the models requires a multifaceted approach, including theoretical calculations, laboratory measurements, and calibration using real observations. In a previous paper, we presented a calculation of the electron impact cross sections on the transitions forming the Fe-L complex. In the present work, we systematically test the calculation against cross sections of ions measured in an electron beam ion trap experiment. A two-dimensional analysis in the electron beam energies and X-ray photon energies is utilized to disentangle radiative channels following dielectronic recombination, direct electron-impact excitation, and resonant excitation processes in the experimental data. The data calibrated through laboratory measurements are further fed into global modeling of the Chandra grating spectrum of Capella. We investigate and compare the fit quality, as well as sensitivity of the derived physical parameters to the underlying atomic data and the astrophysical plasma modeling. We further list the potential areas of disagreement between the observation and the present calculations, which in turn calls for renewed efforts in theoretical calculations and targeted laboratory measurements.