X-Ray-Spectroscopy of Astrophysically-Relevant Photoionized Iron Plasmas at Z

In order to provide benchmark data for models used to interpret X-ray astronomy data from newly-launched orbital telescopes such as Chandra, they have used 120 TW, 180 eV pinch plasmas on the Sandia Z facility to drive iron foils into X-ray photoionized equilibrium. The experiment was designed to achieve photoionization parameters characteristic of accretion-powered objects such as X-ray binaries (neutron stars) and active galactic nuclei (black holes). These objects comprise roughly half of observed X-ray sources, but the interpretation of their spectra is difficult: state-of-the-art models for photoionized iron plasmas do not yet agree on the expected ionization balance. In the initial experiments the foil samples consisted of 200 {angstrom} of iron codeposited with 300 {angstrom} of sodium fluoride and sandwiched between two 1000 {angstrom} layers of Lexan (CH and O). They characterized the pinch spectrum, temperature, power and uniformity and qualified it as a photoionization driver. They obtained time-integrated absorption spectra for the foil from 8 to 18 {angstrom} and identified spectral lines from O VIII, F IX, Na X and XI, and Fe XVII and XVIII, i.e. neon-line and fluorine-like iron. Time-resolved absorption and emission spectra for the foils were also obtained from 12.5 to 16 {angstrom}, and hydrogen-like F and neon-like and fluorine-like Fe were again observed in the 2 ns time window of interest. In subsequent ride along experiments they have developed a density diagnostic and measured the density via foil-expansion imaging at two locations. They conclude by discussing upcoming experiments at Z in which they plan to obtain a full data set of plasma density, temperature, and absorption and emission spectra for multiple photoionization equilibria