Related papers: QPOs in microquasars: the spin problem
We study the dependence of kHz quasi-periodic oscillation (QPO) frequency on accretion-related parameters in the ensemble of neutron star low-mass X-ray binaries. Based on the mass accretion rate, $\dot{M}$, and the magnetic field strength,…
Low-frequency quasi-periodic oscillations (LFQPOs) have been routinely observed in black hole X-ray binaries (BHXRBs). These LFQPOs can be explained by axisymmetric shock oscillation in accretion flow around a rotating black hole. We…
During observations with RXTE we discovered two simultaneous kHz QPOs near 500 Hz and 860 Hz in the Z source Cyg X-2. In the X-ray color-color diagram and hardness-intensity diagram (HID) a clear Z track was traced out. A single kHz QPO…
We expand the relativistic precession model to include nonequatorial and eccentric trajectories and apply it to quasi-periodic oscillations (QPOs) in black hole X-ray binaries (BHXRBs) and associate their frequencies with the fundamental…
Rotating black holes in the brany universe of the Randall-Sundrum type are described by the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b<0 rotating black holes with…
We determine the spin of a supermassive black hole in the context of discseismology by comparing newly detected quasi-periodic oscillations (QPOs) of radio emission in the Galactic centre, Sagittarius A* (Sgr A*), as well as infrared and…
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…
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…
I review recent work that goes beyond our model for the Low-Frequency Quasi-Periodic Oscillation of microquasars, based on the Accretion-Ejection Instability. I show that similar instabilities, which can be viewed as strongly unstable…
Most quasars are known to be radio quiet and according to the ``spin paradigm'', which connects their radio-loudness with the value of the black hole spin, they must harbor very slowly rotating black holes. On the other hand, quasars are…
We investigate the effects of the Gauss-Bonnet (GB) gravitational trace anomaly on the circular motion of test particles around black holes (BHs) and its implications for quasi-periodic oscillations (QPOs) in various theoretical models.…
One of the most dramatic discoveries made with the Rossi X-Ray Timing Explorer is that many accreting neutron stars in low-mass binary systems produce strong, remarkably coherent, high-frequency X-ray brightness oscillations. The 325-1200…
We report the discovery of twin kHz QPOs in the X ray flux of XTE J1807--294, the fourth accreting millisecond pulsar (AMP). This is the second AMP exhibiting twin kHz QPOs. In contrast to the first case, SAX J1808.4--3658, the frequency…
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…
Quasi-periodic oscillations (QPOs) observed in the power spectrum of black holes are unique observational probes to the background spacetime since they can be directly related to the timescales associated with the motion of matter orbiting…
We consider the inner regions of accretion disks surrounding black holes and neutron stars and investigate the nonlinear time dependent evolution of thermal-viscous instabilities. The viscous stress is assumed to be proportional to the gas…
The origin of quasi-periodic oscillations (QPOs) in black hole accretion flow remains uncertain, particularly regarding the role of magnetic field configurations in shaping disk structure and variability signatures. We investigate this…
Based on the interpretation of the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) to the Keplerian and the periastron precession frequencies at the magnetosphere-disk of X-ray…
We present the results of the analysis of a large database of X-ray observations of 22 galactic black-hole transients with the Rossi X-Ray timing explorer throughout its operative life for a total exposure time of ~12 Ms. We excluded…
We have analyzed AstroSat observations of the galactic micro-quasar system GRS 1915+105, when the system exhibited C-type Quasi-periodic Oscillations (QPOs) in the frequency range of 3.4-5.4 Hz. The broad band spectra (1-50 keV) obtained…