XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- highly ionized Iron absorption structures
Abstract
We present the first high-resolution X-ray spectral analysis of Cygnus X-1 using XRISM. The observation was carried out from April 7 to 10, 2024, covering the orbital phase range 0.65--0.17 during its low/hard state. Taking advantage of the exceptional energy resolution of the Resolve instrument, we examined highly ionized iron absorption lines and characterized the ionization states, column densities, and line-of-sight velocities of the absorbing plasma. Spectral analysis revealed an ionization parameter of approximately 3, column densities of a few times 10^21 cm^-2, and a blueshifted velocity of approximately 100 km s^-1. The observation was divided into two phases: before and after orbital phase phi_orb = 0.9, corresponding to non-dipping and dipping intervals. While only weak absorption features were present before phi_orb = 0.9, strong absorption by He-like and H-like Fe appeared during the dipping phase. We measured equivalent widths of 2.3 eV, 0.4 eV, and 1.2 eV for He-like Fe K-alpha, and H-like Ly-alpha1 and Ly-alpha2, respectively, demonstrating the capability of XRISM Resolve to securely detect narrow absorption features of only a few eV. These measurements trace the motion of the absorbing material and offer insight into the kinematics and spatial distribution of the wind in the vicinity of the black hole. These findings enhance our understanding of wind-fed accretion in Cygnus X-1 and highlight the importance of continued high-resolution X-ray observations to further constrain the physical properties of winds and accretion flows in high-mass X-ray binaries.
Keywords
Cite
@article{arxiv.2604.21497,
title = {XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- highly ionized Iron absorption structures},
author = {Shinya Yamada and Natalie Hell and Elisa Costantini and Oluwashina Adegoke and McKinley Brumback and Paul Draghis and Ken Ebisawa and Javier A. Garcia and Edmund Hodges-Kluck and Shunji Kitamoto and Shogo Kobayashi and Takayoshi Kohmura and Aya Kubota and Jon M. Miller and Misaki Mizumoto and Tsunefumi Mizuno and Kaito Ninoyu and Hiromitsu Takahashi and Yuusuke Uchida and Kazutaka Yamaoka and Sixuan Zhang},
journal= {arXiv preprint arXiv:2604.21497},
year = {2026}
}