K-Shell Photoabsorption of Magnesium Ions

Abstract

X-ray photoabsorption cross sections have been computed for all magnesium ions using the $R$-matrix method. A comparison with the other available data for Mg II-Mg X shows good qualitative agreement in the resultant resonance shapes. However, for the lower ionization stages, and for singly-ionized Mg II in particular, the previous $R$-matrix results (Witthoeft et al.2009; Witthoeft et al. 2011) overestimate the K-edge position due to the neglect of important orbital relaxation effects, and a global shift downward in photon energy of those cross sections is therefore warranted. We have found that the cross sections for Mg I and Mg II are further complicated by the M-shell ($n=3$) occupancy. As a result, the treatment of spectator Auger decay of $1s\to np$ resonances using a method based on multichannel quantum defect theory and an optical potential becomes problematic, making it necessary to implement an alternative, approximate treatment of Auger decay for neutral Mg. The new cross sections are used to fit the Mg K edge in XMM-Newton spectra of the low-mass X-ray binary GS 1826-238, where most of the interstellar Mg is found to be in ionized form.

49 Pages, 13 Figures, and 22 Tables

References in corpus (7)

• High-Resolution X-ray Spectroscopy of the Interstellar Medium II: Neon and Iron Absorption Edges
• Contemporaneous Chandra HETG and Suzaku X-ray Observations of NGC 4051
• Photoionization modeling of oxygen K absorption in the interstellar medium:the Chandra grating spectra of XTE J1817-330
• A Comprehensive X-ray Absorption Model for Atomic Oxygen
• Elemental Abundances in the Possible Type Ia Supernova Remnant G344.7-0.1
• K-shell photoionization of Na-like to Cl-like ions of Mg, Si, S, Ar, and Ca
• Suzaku Observations of Ejecta-Dominated Galactic Supernova Remnant G346.6-0.2

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