A Resonance Model of Quasi-Periodic Oscillations of Low-Mass X-Ray Binaries

We try to understand the quasi-periodic oscillations (QPOs) in low-mass neutron-star and black-hole X-ray binaries by a resonance model in warped disks with precession. Our main concern is high-frequency QPOs, hectohertz QPOs, and horizontal-branch QPOs in the z sources and the atoll sources, and the correponding QPOs in black-hole X-ray binaries. Our resonance model can qualitatively, but systematically, explain these QPOs by regarding hectohertz QPOs as a precession of warp.Comment: 4 pages, to be published in PASJ Vol.57, No.

An Attempt to Describe Frequency-Correlations among kHz QPOs and HBOs by Two-Armed Vertical p-mode Oscillations: Case of No Magnetic Field

Trapping of two-armed ($m=2$) vertical p-mode oscillations in relativistic disks are examined. The disks are assumed to be isothermal in the vertical direction, but are truncated at a certain height by the presence of corona. The same issues have been examined in a previous paper (Kato 2012a). In this paper, unlike the previous paper, however, we do not use the approximation that the oscillations are nearly vertical, but limit to a simpler case of no magnetic field. As in the previous paper, the results suggest that the two basic oscillation modes [both are the fundamental ($n=1$) in the vertical direction but in the horizontal direction one is the fundamental ($n_{\rm r}=0$) and the other the first overtone ($n_{\rm r}=1$)] correspond to the twin kHz QPOs. Second, the oscillation mode which is the first overtone $(n=2)$ in the vertical direction and the fundamental in the horizontal direction ($n_{\rm r}=0$) will correspond to the horizontal branch oscillation (HBO) of Z-sources. The latter suggests that the horizontal branch of Z-sources is a sequence of temperature change in disks whose vertical thickness is strongly terminated. The temperature increases leftward along the sequence from the apex between normal and horizontal branches.Comment: 17 pages, 8 figures, to be published in PASJ Vol. 65, No. 1 (2013

Mass and Spin of GRS 1915+105 Based on a Resonance Model of QPOs

We demonstrate that the four high-frequency QPOs observed in GRS 1915+105 can be interpreted as the oscillation modes on disks which non-linearly and resonantly interact with a warp. The warp is assumed to be a low-frequency global pattern on the disk. This identification suggests that the relevant mass, $M$, and spin, $a$, of GRS 1915+105 are, $M=13\sim 14 M_\odot$ and $a=0\sim 0.15$Comment: 4 pages, 5 figures, accepted in PASJ Vol.56(2004) No.5, The English was improved on September

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

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 {\it 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.Comment: 19 pages, 5 figures. To be published in PASJ 61, No.6 (2009

Resonant Excitation of Disk Oscillations in Deformed Disks V: Effects of Dissipative Process

It is suggested that a set of positive- and negative-energy oscillations can be resonantly excited in the inner region of deformed (warped or eccentric) relativistic disks. In this paper we examine how a dissipative process affects on this wave excitation process. The results show that when the resonant condition in frequency is roughly satisfied and thus the oscillations are excited, introduction of a dissipative process works so as to decrease the growth rate of the oscillations. When the frequency difference of the two oscillations deviates more than a certain amount from that required by resonant condition, however, the oscillations are excited by introduction of dissipative process. This excitation by dissipative process can be understood as a special example of the double-diffusive instability.Comment: 14 pages, 2 figures, to be published in PASJ 63, No 2 (2011