Journal Article

PUBDB-2024-01936

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png High-resolution X-Ray Spectroscopy of Interstellar Iron toward Cygnus X-1 and GX 339-4

Corrales, L. (Corresponding author)Extern* ; Gotthelf, E. V. ; Gatuzz, E. ; Kallman, T. R. ; Lee, J. C. ; Martins, M.Extern*XFEL.EU* ; Paerels, F. ; Psaradaki, I. ; Schippers, S.Extern* ; Savin, D. W.Extern*

2024
Institute of Physics Publ. London

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Please use a persistent id in citations: doi:10.3847/1538-4357/ad2939  doi:10.3204/PUBDB-2024-01936

Abstract: We present a high-resolution spectral study of Fe L-shell extinction by the diffuse interstellar medium (ISM) in the direction of the X-ray binaries Cygnus X-1 and GX 339–4, using the XMM-Newton reflection grating spectrometer. The majority of interstellar Fe is suspected to condense into dust grains in the diffuse ISM, but the compounds formed from this process are unknown. Here, we use the laboratory cross sections from Kortright & Kim (2000) and Lee et al. (2005) to model the absorption and scattering profiles of metallic Fe, and the crystalline compounds fayalite (Fe2SiO4), ferrous sulfate (FeSO4), hematite (α-Fe2O3), and lepidocrocite (γ-FeOOH), which have oxidation states ranging from Fe0 to Fe3+. We find that the observed Fe L-shell features are systematically offset in energy from the laboratory measurements. An examination of over two dozen published measurements of Fe L-shell absorption finds a 1–2 eV scatter in energy positions of the L-shell features. Motivated by this, we fit for the best energy-scale shift simultaneously with the fine structure of the Fe L-shell extinction cross sections. Hematite and lepidocrocite provide the best fits (≈ + 1.1 eV shift), followed by fayalite (≈ + 1.8 eV shift). However, fayalite is disfavored, based on the implied abundances and knowledge of ISM silicates gained by infrared astronomical observations and meteoritic studies. We conclude that iron oxides in the Fe3+ oxidation state are good candidates for Fe-bearing dust. To verify this, new absolute photoabsorption measurements are needed on an energy scale accurate to better than 0.2 eV.

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Contributing Institute(s):

1. DOOR-User (DOOR ; HAS-User)

Research Program(s):

1. 6G3 - PETRA III (DESY) (POF4-6G3) (POF4-6G3)
2. FS-Proposal: I-20170574 (I-20170574) (I-20170574)
3. DFG project 510114039 - Dissoziationsdynamik von rumpfniveauangeregten ionischen, molekularen Radikalen (510114039) (510114039)
4. 05K19GU4 - SFX2: Hochdurchsatz Serielle-Femtosekunden Kristallographie @ EU XFEL. (BMBF-05K19GU4) (BMBF-05K19GU4)

Experiment(s):

1. PETRA Beamline P04 (PETRA III)

Appears in the scientific report 2024

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