A hidden quasi-periodic oscillation in Cygnus X-1 revealed by NICER

作者：Federico A. Fogantini, Federico García, Mariano Méndez, Ole König, J. Wilms · 发表于：Astronomy and Astrophysics · 年份：2025 · DOI：10.1051/0004-6361/202453523 · 被引用次数：14 · 研究领域：Particle Accelerators and Free-Electron Lasers、Astrophysics and Cosmic Phenomena、Pulsars and Gravitational Waves Research

Context. Cygnus X-1 is a high-mass black hole binary system that has been extensively studied across multiple wavelengths since its discovery in 1964. Its rapid temporal and spectral variability in X-rays offer critical insights into the physics of accretion and the dynamics around black hole systems. The power spectra of Cygnus X-1 are generally featureless and often modelled with two broad Lorentzian functions without the need for narrow quasi-periodic oscillations, which are prevalent in other black hole X-ray binaries. Aims. We explore this phenomenon in light of the recent proposal that some variability components that are not detected in the power spectra may be significantly detected in the imaginary part of the cross spectra between two different energy bands and the coherence function. Specifically, we study the power, cross, and lag spectra and the coherence function of all available observations of Cygnus X-1 from the NICER mission up to Cycle 6 while looking for the so-called imaginary components. Methods. We simultaneously fitted the power spectra of the source in two energy bands, 0.3−2 keV and 2−12 keV, and the real and imaginary parts of the cross spectrum between the same energy bands with a multi-Lorentzian model. Under the assumption that each Lorentzian is coherent between the two energy bands while the Lorentzians are incoherent with one another, our fits predict the intrinsic coherence and phase lags. Results. The intrinsic coherence shows a narrow dip a...