Related papers: QPOs in Cataclysmic Variables and in X-ray Binarie…

We compile observations of high-frequency quasi-periodic oscillations (QPOs) around black holes, both stellar and supermassive, and compare their positions in the parameter space of black hole mass, spin, and oscillation frequency. We find…

Twin quasi-periodic millisecond modulations of the X-ray flux (kHz QPOs) have recently been reported from an accreting 2.5 ms X-ray pulsar. We identify modes of disk oscillations whose frequencies are in agreement with the observed ones…

The physical origin of high-frequency QPOs (HFQPOs) in black-hole X-ray binaries remains an enigma despite many years of detailed observational studies. Although there exists a number of models for HFQPOs, many of these are simply "notions"…

We have proposed in previous papers that the high-frequency pair QPOs observed in black-hole binaries with frequency ratio 3:2 are inertial-acoustic oscillations (nearly horizontal oscillations with no node in the vertical direction) or…

On a disk deformed to a non-axisymmetric form, a set of oscillations can be excited by their resonant interaction through the disk deformation (Kato et al. 2011). This resonant instability process has been proposed to suggest a possible…

We suggest a plausible interpretation for the twin kiloHertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries. We identify the upper kHz QPO frequencies to be the rotational frequency and the lower kHz QPOs the…

Low mass x-ray binaries (LMXBs), with either a neutron star (NS) or a black hole, show in their power spectra quasiperiodic oscillations (QPOs). Those at highest frequencies show up in pairs and are named twin peak high frequency QPOs (HF…

We report the discovery of the correlated optical/X-ray low-frequency quasi-periodic oscillations (QPOs) in black hole binary SWIFT J1753.5-0127. The phase lag between two light-curves at the QPO frequency is close to zero. This result puts…

In this work we explore the idea that the high frequency QPOs observed in LMXBs may be explained as a resonant coupling between the neutron star spin and epicyclic modes of accretion disk oscillations. We propose a new model for these QPOs…

Many accreting black holes and neutron stars exhibit rapid variability in their X-ray light curves, termed quasi-periodic oscillations (QPOs). The most commonly observed type is the low-frequency ($\lesssim 10$ Hz), type-C QPO, while only a…

In previous papers, we have proposed a model that the high-frequency quasi-periodic oscillations (HF QPOs) observed in black-hole and neutron-star X-ray binaries are inertial-acoustic oscillations that are resonantly excited on a one-armed…

Low-frequency quasi-periodic oscillations (LFQPOs) are commonly observed in X-ray light curves of black hole X-ray binaries (BHXRBs); however, their origin remains a topic of debate. In order to thoroughly investigate variations in spectral…

We consider the situation where a spin-induced wavy perturbation is present on disks of neutron-star low-mass X-ray binaries. By non-linearly coupling with the perturbation, some modes of disk oscillations resonantly interact with the…

A number of black hole X-ray transients show quasi-periodic oscillations (QPOs) in the optical (ultraviolet) and X-ray bands at the same frequency, which challenge models for production of radiation at these wavelengths. We propose a model…

A new model for the explanation of the high frequency quasi-periodic oscillations (QPOs) in pulsars, black holes and white dwarfs is presented. Three circular tori are assumed to be present around the star: an inner torus with charge $Q_i$,…

X-ray quasi-periodic oscillations (QPOs) are a characteristic feature of low-mass X-ray binaries (LMXBs). These oscillations have been studied for decades and revealed a rich and complex phenomenology that is still not fully understood.…

Using the method of multiple scales, one can derive an analytic solution that describes the behaviour of weakly coupled, non-linear oscillations in nearly Keplerian discs around neutron stars or black holes close to the 3:2 orbital…

We investigate the dynamics of transonic advective accretion flows around spinning black holes in the presence of viscosity. The spacetime of a Kerr black hole is approximated using a pseudo-potential. We study viscously driven shock…

Dwarf nov\ae\ (DNe) and low mass X-ray binaries (LMXBs) are compact binaries showing variability on time scales from years to less than seconds. Here, we focus on explaining part of the rapid fluctuations in DNe, following the framework of…

We find evidence that the two high frequency QPOs in Sco X-1 are, more often than not, approximately in the 2:3 frequency ratio familiar from studies of black hole candidates (e.g., XTE J1550-564, Remillard et al. 2002). This implies that…