Modelling the energy dependencies of high-frequency quasi-periodic oscillations in black hole X-ray binaries

• Published in: Monthly notices of the Royal Astronomical Society 2007-07, Vol.379 (1), p.123-129
• Main Authors: Życki, Piotr T., Niedźwiecki, Andrzej, Sobolewska, Małgorzata A.
• Format: Article
• Language: English
• Subjects: accretion; accretion discs; Accretion disks; accretion, accretion discs; Astronomy; Black holes; Double stars; Earth, ocean, space; Exact sciences and technology; relativity; Spectrum analysis; X-ray astronomy; X-rays: binaries; X-rays: individual: GRO J1655−40; X-rays: individual: GRS 1915+105; X-rays: individual: XTE J1550−564
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2007.11917.x

We model energy dependencies of the quasi-periodic oscillations (QPOs) in the model of disc epicyclic motions, with X-ray modulation caused by varying relativistic effects. The model was proposed to explain the high-frequency QPO observed in X-ray binaries. We consider two specific scenarios for the geometry of accretion flow and spectral formation. First, a standard cold accretion disc with an active X-ray emitting corona is assumed to oscillate. Secondly, only a hot X-ray emitting accretion flow oscillates, while the cold disc is absent at the QPO radius. We find that the QPO spectra are generally similar to the spectrum of radiation emitted at the QPO radius, and they are broadened by the relativistic effects. In particular, the QPO spectrum contains the disc component in the oscillating disc with a corona scenario. We also review the available data on energy dependencies of high-frequency QPO, and we point out that they appear to lack the disc component in their energy spectra. This would suggest the hot flow geometry in the spectral states when high-frequency QPOs are observed.