Spectral Signatures Of Charge Exchange In K-shell X-ray Spectra Of Ar, P, And S Measured With The LLNL Electron Beam Ion Trap
Résumé
Charge exchange is an important process in numerous astrophysical contexts, including the interaction of the solar wind with neutral material throughout the solar system, which is hypothesized to contribute a large fraction of the soft X-ray background, and is thus highly relevant to studies of diffuse X-ray emission from the warm-hot phase of the intergalactic medium. It may also be important in supernova remnants, as hot, shocked gas interacts with the surrounding neutral ISM. It will be increasingly important to understand charge exchange in the near future, when the Micro-X rocket mission and the Astro-H SXS become the first imaging high-resolution X-ray spectrometers, allowing observations of highly extended sources with sufficient spectral resolution to easily detect spectral signatures of charge exchange. Charge exchange in the limit of low collision energy is still poorly understood, and measurements benchmarking theoretical predictions of cross-sections and spectra are desirable. We present high resolution K-shell X-ray spectra of highly ionized Ar, P, and S produced by low collision energy charge exchange in the LLNL electron beam ion trap and measured by the NASA/GSFC EBIT calorimeter spectrometer (ECS) and XRS/EBIT instruments. We investigate the scaling of the hardness ratios of the hydrogenic spectra with atomic number, as well as their dependence on the neutral electron donor species. We also find that the He-like triplet line ratios are strongly diagnostic of the neutral electron donor species. Part of this work was prepared by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.