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[13.10] Measurement of absolute excitation cross-sections for n=3, 4, 5, 6 to n=2 transitions from Fe XXIII and Fe XXIV

H. Chen, P. Beiersdorfer, G.V. Brown (LLNL), K.R. Boyce, K.C. Gendreau, J. Gygax (GSFC), S.M. Kahn (Columbia), R.L. Kelley, F.S. Poter (GSFC), D. Thorn (LLNL)

Observations of the Centaurus cluster by ASCA raised questions about the magnitude of the n=4 to n=2 emissions in Fe XXIII and Fe XXIV, putting the accuracy of the collisional excitation cross-sections used in the spectral modeling packages in doubt. This issue also affects the interpretations of spectra obtained by Chandra and XMM. In most cases the cross-sections used in the spectra fitting packages come from calculations. Recently, with the implementation of the engineering model XRS detector from the Astro-E mission at the Livermore EBIT-2 source, it is now possible for us to provide cross-sections scaled to the absolute intensity of radiative recombination measured by the XRS. We present results from the measurement for Fe XXIII and Fe XXIV line emission for 3 – 2, 4 – 2, 5 – 2 and 6 – 2 transitions at wavelength band from 7 Å to11 Å using both flat-crystal spectrometers and the XRS. 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 and supported by NASA Space Astrophysics Research and Analysis grants to LLNL, GSFC, and Columbia University.