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We report the timing results with Insight-HXMT observations of X-ray binary IGR J19294+1816 during its 2019 Type I outburst at the decline phase shortly following its peak. We analyze the light curves and power density spectrum (PDS) of the…
There is strong evidence that the observed kHz Quasi Periodic Oscillations (QPOs) in the X-ray flux of neutron star and black hole sources in LMXRBs are linked to Einstein's General Relativity. Abramowicz&Klu\'zniak (2001) suggested a…
Quasi-periodic oscillations (QPOs) have been discovered in the X-ray emission of many neutron stars and black holes. The QPOs with frequencies greater than about 300 Hz are thought to be produced near the surfaces of neutron stars and the…
I study the behaviour of the maximum rms fractional amplitude, $r_{\rm max}$ and the maximum coherence, $Q_{\rm max}$, of the kilohertz quasi-periodic oscillations (kHz QPOs) in a dozen low-mass X-ray binaries. I find that: (i) The maximum…
Quasi-periodic oscillations (QPOs) in the X-ray lightcurves of accreting neutron star and black hole binaries have been widely interpreted as being due to standing wave modes in accretion disks. These disks are thought to be highly…
We present recent results of 3D magnetohydrodynamic simulations of neutron stars with small misalignment angles, as regards the features in lightcurves produced by regular movements of the hot spots during accretion onto the star. In…
We present an analysis of the energy and frequency dependence of the Fourier time lags of the hectoHertz quasi-periodic oscillations (QPOs) and of the QPOs at the frequency at which the power density spectrum shows a break in the…
Context: The connection between quasi-periodic oscillations (QPOs) and magnetic fields has been investigated across various celestial bodies. Magnetohydrodynamics (MHD) waves have been employed to explain the simultaneous upper and lower…
Twin-peak quasi-periodic oscillations (QPOs) are observed in the X-ray power-density spectra of several accreting low-mass neutron star (NS) binaries. In our previous work we have considered several QPO models. We have identified and…
We report the discovery of Quasi Periodic Oscillations (QPO) at 0.02 Hz in a transient high mass X-ray binary pulsar KS 1947+300 using {\em RXTE}-PCA. The QPOs were detected during May-June 2001, at the end of a long outburst. This is the…
We interpret the correlation over five orders of magnitude between high frequency and low frequency in a quasi-periodic oscillations (QPO) found by Psaltis, Belloni & van der Klis (1999) for black hole (BH), neutron star (NS) systems and…
We present the results from an investigation of the energy dependence of Quasi-Periodic Oscillations (QPOs) exhibited by accreting X-ray pulsars using data from archival \textit{XMM-Newton}, \textit{NuSTAR}, \textit{RXTE}, and…
We suggest an explanation for the twin kilohertz quasi-periodic oscillations (kHz QPOs) in low-mass X-ray binaries (LMXBs) based on magnetohydrodynamics (MHD) oscillation modes in neutron star magnetospheres. Including the effect of the…
I study the behaviour of the maximum rms fractional amplitude, $r_{\rm max}$ and the maximum coherence, $Q_{\rm max}$, of the kilohertz quasi-periodic oscillations (kHz QPOs) in a dozen low-mass X-ray binaries. I find that: (i) The maximum…
We used two XMM-Newton and six Neutron Star Interior Composition Explorer (NICER) observations to investigate the fractional rms amplitude of the millihertz quasi-periodic oscillations (mHz QPOs) in the neutron-star low-mass X-ray binary 4U…
Low-frequency quasi-periodic oscillations (QPOs) are commonly observed in black hole X-ray binaries, and their frequency has been found to correlate with various spectral properties. In this work, we present a detailed timing analysis of…
The frequencies of the highest-frequency kilohertz QPOs recently discovered in some sixteen neutron stars in low-mass X-ray binary systems are most likely orbital frequencies. If so, these QPOs provide tight upper bounds on the masses and…
Quasi-periodic oscillation (QPOs) analysis is important for understanding the dynamical behavior of many astrophysical objects during transient events such as gamma-ray bursts, solar flares, magnetar flares, and fast radio bursts. In this…
Recent observations of the low-mass X-ray binary 4U 1636-53 with the Rossi X-ray Timing Explorer show, for the first time, a kiloHertz quasi-periodic oscillation (kHz QPO) peak separation that exceeds the neutron star spin frequency as…
We report the discovery of kHz fluctuations, including quasi-periodic oscillations (QPO) at ~330 Hz and ~760 Hz and a broadband kHz continuum in the power density spectrum of the high mass X-ray binary pulsar Centaurus X-3. These…