Outflowing photoionized plasma in Circinus X-1 using the high-resolution X-ray spectrometer Resolve onboard XRISM and the radiative transfer code cloudy
Year: 2025
Type: preprint
Abstract: High-resolution X-ray spectroscopy is a key to understanding the mass inflow and outflow of compact objects. Spectral lines carry information about the ionization, density, and velocity structures through their intensity ratios and profiles. They are formed in non-local thermodynamic equilibrium conditions under the intense radiation field from the compact objects, thus radiative transfer (RT) calculation is a requisite for proper interpretations. We present such a study for a low-mass X-ray binary, Circinus X-1, from which the P Cygni profile was discovered using the X-ray grating spectrometer onboard Chandra. We observed the source using the X-ray microcalorimeter onboard XRISM at an orbital phase of 0.93-0.97 and revealed many spectral features unidentified before; the higher series transitions (n to 1; n > 2) of highly-ionized (H- and He-like) S, Ca, Ar, and Fe in emission and absorption, the Fe K{\alpha} and K\b{eta} inner-shell excitation absorption of mildly-ionized (O- to Li-like) Fe, and resolved fine-structure level transitions in the Fe Ly{\alpha} and He{\alpha} complexes. They blend with each other at different velocity shifts on top of apparently variable continuum emission that changed its flux by an order of magnitude within a 70 ks telescope time. Despite such complexity in the observed spectra, most of them can be explained by a simple model consisting of the photoionized plasma outflowing at ~300 km s-1 and the variable blocking material in the line of sight of the incident continuum emission from the accretion disk. We demonstrate this with the aid of the RT code cloudy for the line ratio diagnostics and spectral fitting. We further constrain the physical parameters of the outflow and argue that the outflow is launched close to the outer edge of the accretion disk and can be driven radiatively by being assisted by the line force calculated using the RT simulation.
Source: arXiv (Cornell University)
DOI: 10.13016/m2a556-7c7y
Authors: Tsujimoto, Masahiro, Enoto, Teruaki, Trigo, María Díaz, Hell, Natalie, Chakraborty, Priyanka, Leutenegger, Maurice A., Loewenstein, Michael, Pradhan, Pragati, Shidatsu, Megumi, Takahashi, Hiromitsu, Yaqoob, Tahir
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: U.S. Department of Energy, National Aeronautics and Space Administration, Università degli Studi Roma Tre, Space Telescope Science Institute, Ministry of Education, Culture, Sports, Science and Technology, Goddard Space Flight Center, Japan Society for the Promotion of Science, Japan Aerospace Exploration Agency, Lawrence Livermore National Laboratory
Awards: Resolving Launching Mechanism of Disk Winds in Black Hole Binaries via Comparison between X-ray Spectroscopic Observations and Theoretical Predictions, G1356433355, G14554683, G201248631, G2145270357, G2717806384, G3220404094, G3738269475, G6866600364, G7149163316, Revealing the launching mechanism and structure of black hole outflows through high resolution X-ray spectroscopy and multi-wavelength observations, G991281326
OpenAlex ID: W6922182831
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