X-Ray Spectroscopy in the Microcalorimeter Era. I. Effects of Fe xxiv Resonant Auger Destruction on Fe xxv Kα Spectra

We discuss the importance of Fe23+ in determining the line intensities of the Fe xxv Kα complex in an optically thick cloud, and investigate resonant auger destruction (RAD) with CLOUDY. Although initially motivated by the Perseus cluster, our calculations are extended to the wide range of column densities encountered in astronomy. A Fe xxv line photon can change/lose its identity upon absorption by three-electron iron as a result of "line interlocking."This may lead to the autoionization of the absorbing ion, ultimately destroying the Fe xxv Kα photon by RAD. Out of the four members in the Fe xxv Kα complex, a significant fraction of the x line photons are absorbed by Fe23+ and destroyed, causing the x line intensity to decrease. For example, at a hydrogen column density of 1025 cm-2, ∼32% of x photons are destroyed due to RAD while w is mostly unaffected. The line intensity of y is slightly (≤2%) reduced. z is not directly affected by RAD, but the contrasting behavior between z and x line intensities points toward the possible conversion of a tiny fraction (∼2%) of x photons into z photons. The change in line intensities due to electron scattering escape off fast thermal electrons is also discussed.