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[25.19] Iron photoionization experiments to benchmark models for the spectra of accretion-powered sources

R.F. Heeter, J. Emig, M.E. Foord, D.A. Liedahl, P.T. Springer, R.S. Thoe (Lawrence Livermore Nat'l Lab), J.E. Bailey, M.E. Cuneo (Sandia Nat'l Lab)

Photoionized plasmas are common in astrophysical X-ray sources such as X-ray binaries and active galactic nuclei. Accurate models of such plasmas are essential for interpreting the high-quality X-ray spectra arriving from Chandra and XMM. Confidence in the models' accuracy can be improved by testing their predictions against data from photoionized plasmas produced in fully characterized laboratory experiments, which are now possible.

Here we report two campaigns using 1 \times 10²¹ erg/s X-ray pulses from the Sandia Z pinch facility to drive iron foils into photoionized equilibrium. The pinch radiation heats a thin foil sample which expands, blowing down to <10^-4 of solid density in time for the main X-ray pulse. X-ray fluxes above 3 \times 10¹⁹ \mathrm{erg/s/cm}² and photoionization parameters (\xi \equiv 4\pi flux/density) in the range 10 to 100 erg-cm/s are achieved. The design is optimized so the samples are at the lowest density consistent with achieving a photoionized equilibrium during the X-ray pulse. We characterize the pinch spectrum (mainly blackbody), emission temperature (180 eV), power and spatial uniformity. We measure the X-ray emission and absorption of the photoionized samples using several spectrometers with varying capabilities for time, space, and spectral resolution in the range 8 to 18~{Å}. By imaging the sample's expansion we determine its density. Time-resolved spectra from the photoionization equilibrium period show lines from Fe XVII, XVIII, and XIX, plus low-Z tracer elements in the sample. We will discuss progress in analyzing and interpreting the data, and in developing benchmarks for the astrophysical models.

This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract no. W-7405-Eng-48.

The author(s) of this abstract have provided an email address for comments about the abstract: heeter1@llnl.gov