Related papers: QPOs in a highly magnetized ultra-compact X-ray bi…
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…
We investigate the spectral and timing properties of the millihertz quasi-periodic oscillations (mHz QPOs) in neutron-star low-mass X-ray binary 4U 1636-53 using XMM-Newton and Rossi X-ray Timing Explorer (RXTE) observations. The mHz QPOs…
We study in a systematic way the quality factor of the lower and upper kHz QPOs in a sample of low luminosity neutron star X-ray binaries, showing both QPOs varying over a wide frequency range. The sample includes 4U 1636-536, 4U 1608-522,…
We review the pulse profile evolution of the unique accretion powered X-ray pulsar 4U 1626-67 over the last 40 years since its discovery. This pulsar showed two distinct eras of steady spin-up separated by a steady spin-down episode for…
Millihertz quasi-periodic oscillations (mHz QPOs) observed in neutron-star low-mass X-ray binaries (NS LMXBs) are generally explained as marginally stable thermonuclear burning on the neutron star surface. We report the discovery of mHz…
Strong, coherent, quasi-periodic brightness oscillations (QPOs) with frequencies ranging from about 300 Hz to 1200 Hz have been discovered with the Rossi X-ray Timing Explorer in the X-ray emission from some fifteen neutron stars in…
We report the discovery of millihertz quasi-periodic oscillations (mHz QPOs) from the neutron star (NS) low-mass X-ray binary 4U 1730--22 using the Neutron Star Interior Composition Explorer (NICER). After being inactive for almost 50…
We report on the discovery of mHz quasi-periodic oscillations (QPOs) from the high mass X-ray binary (HMXB) IGRJ19140+0951, during a 40 ks XMM-Newton observation performed in 201 5, which caught the source in its faintest state ever…
We report the discovery of a quasi-periodic oscillation (QPO) in data obtained with the Rossi X-ray Timing Explorer of the dipping and eclipsing low-mass X-ray binary EXO 0748-676. The QPO had a frequency between 0.58 and 2.44 Hz changing…
In this paper, we presented a detailed timing analysis of a prominent outburst of 4U 0115+63 detected by \textit{Insight}-HXMT in 2017 August. The spin period of the neutron star was determined to be $3.61398\pm 0.00002$ s at MJD 57978. We…
Before the launch of the Rossi X-ray Timing Explorer (RXTE) it was recognized that neutron star accretion disks could extend inward to very near the neutron star surface, and thus be governed by millisecond timescales. Previous missions…
We present a comprehensive analysis of AstroSat/LAXPC data of the second spin-up and second spin-down phases of the persistent X-ray pulsar 4U 1626-67. Flares followed by a broad dip are detected in the spin-up observations. The pulse…
X-ray radiation from black hole binary (BHB) systems regularly displays quasi-periodic oscillations (QPOs). In principle, a number of suggested physical mechanisms can reproduce their power spectral properties, thus more powerful…
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,…
We analysed the Rossi X-ray Timing Explorer (RXTE) data from a sample of bright accreting neutron star (NS) low-mass X-ray binaries (LMXBs). With the aim of studying the quasi-periodic variability as a function of the accretion regime, we…
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…
Kilohertz quasi-periodic oscillations (kHz QPOs) are believed to originate from the orbital timescales of the inner accretion flow, reflecting the dynamics of the innermost disk regions under strong gravitational forces. Despite numerous…
With a systematic timing investigation of the persistent X-ray binary pulsar Her X-1 based on a large number of Insight-HXMT observations between 2017 to 2019, we confirm the presence of X-ray millihertz quasi-periodic oscillations (mHz…
There have been many efforts to explain the dynamical mechanisms behind the phenomenology of quasi-periodic oscillations (QPOs) seen in the X-ray light curves of low-mass X-ray binaries. Up to now, none of the models can successfully…
The relativistic precession model for quasi periodic oscillations, QPOs, in low mass X-ray binaries is reviewed. The behaviour of three simultaneous types of QPOs is well matched in terms of the fundamental frequencies for geodesic motion…