XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- Orbital and Short-Term Variability of Iron Absorption

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Main Authors: Ninoyu, Kaito, Yamada, Shinya, Hell, Natalie, Costantini, Elisa, Adegoke, Oluwashina, Draghis, Paul, Ebisawa, Ken, Garcia, Javier A., Hodges-Kluck, Edmund, Kitamoto, Shunji, Kobayashi, Shogo, Kohmura, Takayoshi, Kubota, Aya, Miller, Jon M., Mizumoto, Misaki, Mizuno, Tsunefumi, Takahashi, Hiromitsu, Uchida, Yuusuke, Yamaoka, Kazutaka, Zhang, Sixuan, Tomaru, Ryota, Ito, Seoru
Format: Preprint
Published: 2026
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author Ninoyu, Kaito
Yamada, Shinya
Hell, Natalie
Costantini, Elisa
Adegoke, Oluwashina
Draghis, Paul
Ebisawa, Ken
Garcia, Javier A.
Hodges-Kluck, Edmund
Kitamoto, Shunji
Kobayashi, Shogo
Kohmura, Takayoshi
Kubota, Aya
Miller, Jon M.
Mizumoto, Misaki
Mizuno, Tsunefumi
Takahashi, Hiromitsu
Uchida, Yuusuke
Yamaoka, Kazutaka
Zhang, Sixuan
Tomaru, Ryota
Ito, Seoru
author_facet Ninoyu, Kaito
Yamada, Shinya
Hell, Natalie
Costantini, Elisa
Adegoke, Oluwashina
Draghis, Paul
Ebisawa, Ken
Garcia, Javier A.
Hodges-Kluck, Edmund
Kitamoto, Shunji
Kobayashi, Shogo
Kohmura, Takayoshi
Kubota, Aya
Miller, Jon M.
Mizumoto, Misaki
Mizuno, Tsunefumi
Takahashi, Hiromitsu
Uchida, Yuusuke
Yamaoka, Kazutaka
Zhang, Sixuan
Tomaru, Ryota
Ito, Seoru
contents We present the first high-resolution spectroscopy of the black hole high-mass X-ray binary Cygnus X-1 with XRISM, including orbital-phase-resolved analyses and tentative evidence of short-term variability in the Fe-K band on second timescales. Using data from the Performance Verification phase in April 2024, we analyzed spectral variability across orbital phases with the Resolve microcalorimeter and the Xtend CCD imager. The unprecedented resolution of Resolve reveals variability in highly ionized Fe absorption lines. The absorption features show orbital-phase-dependent variability in column density, ionization state, and blueshifted velocity, suggesting structural variations in the focused stellar wind along the line of sight. We also find indications of subtle broadening of the neutral Fe emission profile. In addition, intensity-sorted spectroscopy during dip phases suggests possible variability on timescales of a few seconds in the absorption features, consistent with cooler, denser and lower-ionized gas clumps. Although the statistical significance is limited, these results hint that the stellar wind and the X-rays from the accretion disk around the black hole may interact on timescales as short as a few seconds. These XRISM results constrain wind-fed accretion in Cyg X-1 and highlight Resolve's capability to probe plasma environments in high-mass X-ray binaries.
format Preprint
id arxiv_https___arxiv_org_abs_2604_21557
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- Orbital and Short-Term Variability of Iron Absorption
Ninoyu, Kaito
Yamada, Shinya
Hell, Natalie
Costantini, Elisa
Adegoke, Oluwashina
Draghis, Paul
Ebisawa, Ken
Garcia, Javier A.
Hodges-Kluck, Edmund
Kitamoto, Shunji
Kobayashi, Shogo
Kohmura, Takayoshi
Kubota, Aya
Miller, Jon M.
Mizumoto, Misaki
Mizuno, Tsunefumi
Takahashi, Hiromitsu
Uchida, Yuusuke
Yamaoka, Kazutaka
Zhang, Sixuan
Tomaru, Ryota
Ito, Seoru
High Energy Astrophysical Phenomena
We present the first high-resolution spectroscopy of the black hole high-mass X-ray binary Cygnus X-1 with XRISM, including orbital-phase-resolved analyses and tentative evidence of short-term variability in the Fe-K band on second timescales. Using data from the Performance Verification phase in April 2024, we analyzed spectral variability across orbital phases with the Resolve microcalorimeter and the Xtend CCD imager. The unprecedented resolution of Resolve reveals variability in highly ionized Fe absorption lines. The absorption features show orbital-phase-dependent variability in column density, ionization state, and blueshifted velocity, suggesting structural variations in the focused stellar wind along the line of sight. We also find indications of subtle broadening of the neutral Fe emission profile. In addition, intensity-sorted spectroscopy during dip phases suggests possible variability on timescales of a few seconds in the absorption features, consistent with cooler, denser and lower-ionized gas clumps. Although the statistical significance is limited, these results hint that the stellar wind and the X-rays from the accretion disk around the black hole may interact on timescales as short as a few seconds. These XRISM results constrain wind-fed accretion in Cyg X-1 and highlight Resolve's capability to probe plasma environments in high-mass X-ray binaries.
title XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- Orbital and Short-Term Variability of Iron Absorption
topic High Energy Astrophysical Phenomena
url https://arxiv.org/abs/2604.21557