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Kato, Akio

doi:10.4295/audiology.43.559

Cited by 7 publications

(20 citation statements)

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“…This is because the radius where the vertical resonance occurs is sensitive to the vertical structure of disks 2 . In spite of this interesting characteristics of the vertical resonance (Kato 2005), we already showed that the disk oscillations resulting from vertical resonance are damped, not excited, in the case where the disk deformation is one-armed (Kato 2004(Kato , 2008a.…”

Section: Introductionmentioning

confidence: 79%

“…Based on closeness to 3 : 2 of frequencies of twin QPOs, importance of resonant phenomena was emphasized by Abramowicz and Kluźniak (2001). Subsequently, from a different context, Kato (2004Kato ( , 2008a pointed out the importance of resonant processes in a deformed 1 (warped or eccentric) disks as an excitation process of high frequency QPOs. That is, non-linear interaction between disk oscillations and the deformed part of disks resonantly excite or dampen disk oscillations.…”

Section: Introductionmentioning

confidence: 99%

“…is satisfied (Kato 2004(Kato , 2008a, when the one-armed deformation of disks have no precession, where κ(r) is the epicyclic frequency, Ω(r) is the angular velocity of disk rotation and r is the radius from the central source on the disk plane. In the case of Schwarzschild metric, the resonance occurs at 4r g , where r g is the Schwarzschild radius defined by r g = 2GM/c 2 , M being the mass of the central source.…”

Section: Introductionmentioning

confidence: 99%

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Resonant Excitation of Disk Oscillations in Two-Armed-Deformed Disks and Application to High-Frequency QPOs

Katō¹

2009

Publications of the Astronomical Society of Japan

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In previous papers we showed that in a one-armed deformed disks, p-mode and g-mode oscillations are resonantly excited by horizontal resonance, and applied it to high frequency QPOs observed in low mass X-ray binaries. In that model, the observed time variation of kHz QPOs is regarded as a result of a time-dependent precession of the deformation. In this paper we consider another possible cause of time variation of kHz QPOs. That is, we demonstrate that in a two-armed deformed disks, p-mode and g-mode oscillations are excited by vertical resonance, not by horizontal resonance (horizontal resonance dampens them). Furthermore, we show that in the case of vertical resonance, the frequencies of disk oscillations excited can vary with time if vertical disk structure changes with time. A brief application of these results to the time variation of observed kHz QPOs is made.

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Section: Introductionmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Resonant Excitation of Disk Oscillations in Two-Armed-Deformed Disks and Application to High-Frequency QPOs

Katō¹

2009

Publications of the Astronomical Society of Japan

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“…Some kHz QPO models explain the upper kHz QPO with orbital motion of short-lived inhomogeneities at some preferred radius in the accretion flow (van der Klis et al 1996;Strohmayer et al 1996;Miller et al 1998; p.m.bult@uva.nl Stella & Vietri 1999;Kluźniak et al 2004;Alpar & Psaltis 2008), others invoke alternative mechanisms (Lai 1998;Kato 2004;Zhang 2004;Bachetti et al 2010), but for lack of observational clues the correct interpretation has remained elusive.…”

Section: Introductionmentioning

confidence: 99%

PULSE AMPLITUDE DEPENDS ON kHz QPO FREQUENCY IN THE ACCRETING MILLISECOND PULSAR SAX J1808.4-3658

Bult

Klis

2014

ApJ

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We study the relation between the 300-700 Hz upper kHz quasi-periodic oscillation (QPO) and the 401 Hz coherent pulsations across all outbursts of the accreting millisecond X-ray pulsar SAX J1808.4-3658 observed with the Rossi X-ray Timing Explorer. We find that the pulse amplitude systematically changes by a factor of ∼ 2 when the upper kHz QPO frequency passes through 401 Hz: it halves when the QPO moves to above the spin frequency and doubles again on the way back. This establishes for the first time the existence of a direct effect of kHz QPOs on the millisecond pulsations and provides a new clue to the origin of the upper kHz QPO. We discuss several scenarios and conclude that while more complex explanations can not formally be excluded, our result strongly suggests that the QPO is produced by azimuthal motion at the inner edge of the accretion disk, most likely orbital motion. Depending on whether this azimuthal motion is faster or slower than the spin, the plasma then interacts differently with the neutron-star magnetic field. The most straightforward interpretation involves magnetospheric centrifugal inhibition of the accretion flow that sets in when the upper kHz QPO becomes slower than the spin.

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“…Karas 1999; Li & Narayan 2004, and references cited therein). Also in this context, Kato (2004) discussed the resonant interaction between waves propagating in a warped disk, including their rigorous mathematical description. Instead of pursuing a specific model, here we keep the discussion as general as possible, aiming to implement the formalism of multiple scales.…”

Section: Introductionmentioning

confidence: 99%

The autoparametric 3:2 resonance in conservative systems

Horák¹

2005

Astron Nachr

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In the resonance model, high-frequency quasi-periodic oscillations (QPOs) are supposed to be a consequence of nonlinear resonance between modes of oscillations occurring within the innermost parts of an accretion disk. Several models with a prescribed mode--mode interaction were proposed in order to explain the characteristic properties of the resonance in QPO sources. In this paper, we examine nonlinear oscillations of a system having two degrees of freedom and we show that this case could be particularly relevant for QPOs. We present a very convenient way how to study autoparametric resonances of a fully general system using the method of multiple scales. We concentrate to conservative systems and discuss their behavior near the 3:2 parametric resonance.Comment: An update to astro-ph/0408092, 6 pages, 4 figures, Astron. Nachr, in pres

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Cited by 7 publications

References 0 publications

Resonant Excitation of Disk Oscillations in Two-Armed-Deformed Disks and Application to High-Frequency QPOs

Resonant Excitation of Disk Oscillations in Two-Armed-Deformed Disks and Application to High-Frequency QPOs

PULSE AMPLITUDE DEPENDS ON kHz QPO FREQUENCY IN THE ACCRETING MILLISECOND PULSAR SAX J1808.4-3658

The autoparametric 3:2 resonance in conservative systems

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