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

Gu, Liyi and Shah, Chintan and Mao, Junjie and Raassen, Ton and De Plaa, Jelle and Pinto, Ciro and Akamatsu, Hiroki and Werner, Norbert and Simionescu, Aurora and Mernier, François and Sawada, Makoto and Mohanty, Pranav and Amaro, Pedro and Gu, Ming Feng and Porter, F. Scott and Crespo López-Urrutia, José R. and Kaastra, Jelle S. (2020) X-ray spectra of the Fe-L complex : II. Atomic data constraints from the EBIT experiment and X-ray grating observations of Capella. Astronomy and Astrophysics, 641. A93. ISSN 0004-6361 (https://doi.org/10.1051/0004-6361/202037948)

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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 the store of 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 tested 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 was 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 were further fed into a global modeling of the Chandra grating spectrum of Capella. We investigated and compared the fit quality, as well as the 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 observations and the present calculations, which, in turn, calls for renewed efforts with regard to theoretical calculations and targeted laboratory measurements.