Plasma and Fusion Research

Volume 21, 2401002 (2026)

Regular Articles

Fe XVIII–XXIV Kβ Inner-Shell Absorption Lines in the X-Ray Spectra of Neutron Star and Black Hole Binaries with XRISM
Masahiro TSUJIMOTO1,2), Daiki MIURA1,2), Hiroya YAMAGUCHI1,2), Ehud BEHAR3), Chris DONE4), María DÍAZ TRIGO5), Chamani M. GUNASEKERA6), Peter A. M. VAN HOOF7), Stefano BIANCHI8), Maryam DEHGHANIAN9), Gary J. FERLAND9)
1)
JAXA, ISAS, Sagamihara, Kanagawa 252-5210, Japan
2)
The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
3)
Department of Physics, Technion, 3200003 Haifa, Israel
4)
Department of Physics, Durham University, DH1 3LE Durham, UK
5)
ESO, 85748 Garching bei München, Germany
6)
STSci, Baltimore, MD 21218, USA
7)
Royal Observatory of Belgium, 1180 Brussels, Belgium
8)
Università degli Studi Roma Tre, Rome, 00146 Lazio, Italy
9)
University of Kentucky, Lexington, 40506 KY, USA
(Received 9 ugust 2025 / Accepted 13 October 2025 / Published 31 March 2026)

Abstract

The advent of the X-ray microcalorimeter spectrometer Resolve onboard the XRISM space telescope opened a new era for high-resolution X-ray spectroscopy of astrophysical plasmas. Many spectral features were newly detected, including the Kα and Kβ inner-shell transition lines of mildly ionized (F- to Li-like) Fe at 6–8 keV in the spectra of X-ray binaries and active galactic nuclei. The widely used atomic databases contain information on the Kα but not Kβ lines of these ions. We conducted the atomic structure calculation using FAC to derive the Fe Kα and Kβ lines and verified the result against ground experiments and other calculations of the Fe Kα lines. We then implemented the Fe Kβ lines in a radiative transfer code (cloudy) and compared the synthesized and observed spectra with XRISM. A reasonably good agreement was obtained between the observation and the ab initio calculations. This exemplifies the need to expand the atomic databases to interpret astrophysical spectra.

Keywords

atomic structure calculation, radiative transfer calculation, astrophysical plasma, X-ray spectroscopy

DOI: 10.1585/pfr.21.2401002

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