Measuring the atomic scattering factors near the iridium L-edges for the Athena silicon pore optics reflector

Hisamitsu Awaki*, Yoshitomo Maeda, Hironori Matsumoto, Sara Svendsen, Marcos Bavdaz, Maximilien Collon, Kazunori Asakura, Finn E. Christensen, Desiree D.M. Ferreira, Matteo Guainazzi, Masato Hoshino, Shuntaro Ide, Kazunori Ishibashi, Wansu Kan, Sonny Massahi, Takuya Miyazawa, Sadayuki Shimizu, Brian Shortt, Yusuke Takehara, Keisuke TamuraKentaro Uesugi, Richard Willingale, Tomokage Yoneyama, Atsushi Yoshida

*Corresponding author for this work

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Athena, a future high-energy mission, is expected to consist of a large aperture x-ray mirror with a focal length of 12 m. The mirror surface is to be coated with iridium and a low Z overcoat. To define the effective area of the x-ray telescope, the atomic scattering factors of iridium with an energy resolution less than that (2.5 eV) of the x-ray integral field unit are needed. We measured the reflectance of the silicon pore optics mirror plate coated with iridium in the energy range of 9 to 15 keV and that near the iridium L-edges in steps of 10 and 1.5 eV, respectively, at the synchrotron beamline SPring-8. The L3, L2, and L1 edges were clearly detected around 11,215, 12,824, and 13,428 eV, respectively. The measured scattering factors were 1/43 % smaller than the corresponding values reported by Henke et al., likely due to the presence of an overlayer on the iridium coating, and were consistent with those measured by Graessle et al. The angular dependence of the reflectivity measured indicates that the iridium surface was extremely smooth, with a surface roughness of 0.3 nm.

Original languageEnglish
Article number014001
JournalJournal of Astronomical Telescopes, Instruments, and Systems
Issue number1
Number of pages19
Publication statusPublished - 2021

Bibliographical note

Funding Information:
The authors would like to thank anonymous referees for their valuable remarks and suggestions, which have helped us improve this paper. The x-ray measurement was performed at BL20B2 in SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) [Proposal No. 2018B1106 (Y. M.)]. We used the MINUIT software package developed by CERN and a part of the library in HEASOFT developed by NASA/GSFC. This work was financially supported by JSPS KAKENHI through Grant Nos. 17K18782 (H. A.), 15H02070 (H. A.), and 20H00175 (H. M.), and Ehime University (research unit). The authors have no relevant financial interests in the manuscript and no other potential conflicts of interest to disclose.

Publisher Copyright:
© The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.


  • Athena
  • Atomic scattering factors
  • Iridium
  • Silicon pore optics
  • X-ray optics


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