Related papers: Inclination dependence of QPO phase lags in black …
We suggest that persistent low-frequency quasi-periodic oscillations (QPOs) detected in X-ray, ultraviolet, optical energy ranges the black hole (BH) sources XTE J1118+480, GRO J1655-40 LMC X-1 at ~ 0.1 Hz, and QPOs in HZ Her/Her X-1 at ~…
We analyzed RXTE/PCA and HEXTE data of the transient black hole binary GX 339-4, col- lected over a time span of eight years. We studied the properties and the behavior of low frequency quasi periodic oscillations (QPOs) as a function of…
We report the discovery of quasi-periodic oscillations (QPOs) at roughly 187 Hz and 150 Hz in the X-ray intensity of X-ray nova XTE J1859+226. The source was observed during a recent outburst with RXTE. Besides these high-frequency QPOs, we…
The study of quasi-periodic oscillations (QPOs) of X-ray flux observed in the stellar-mass black hole binaries can provide a powerful tool for testing of the phenomena occurring in strong gravity regime. The high frequency (HF) QPOs usually…
Based on observations from the Insight-Hard X-ray Modulation Telescope (Insight-HXMT), an analysis of Type-C quasi-periodic oscillations (QPOs) observed during the outburst of the new black hole candidate Swift J1727.8-1613 in 2023 was…
Fast time variability is the most prominent characteristic of accreting systems and the presence of quasi periodic oscillations (QPOs) is a constant in all accreting systems, from cataclysmic variables to AGNs, passing through black hole…
We present analysis of fast variability of Very Large Telescope/ISAAC (infra-red), \textit{XMM-Newton}/OM (optical) and EPIC-pn (X-ray), and RXTE/PCA (X-ray) observations of the black hole X-ray binary GX 339-4 in a rising hard state of its…
Swift J1727.8-1613 went into outburst in August 2023 and was one of the brightest black hole X-ray binaries (BHXRBs) in recent years, leading to extensive observing campaigns by NICER and Insight-HXMT. The source exhibited strong X-ray…
We present the results of an extensive timing analysis of the 1999 outburst of the soft X-ray transient and black hole candidate XTE J1859+226 as observed with the Rossi X-Ray Timing Explorer. Three main different types of low frequency…
Black hole and neutron star X-ray binary systems routinely show quasi-periodic oscillations (QPOs) in their X-ray flux. Despite being strong, easily measurable signals, their physical origin has long remained elusive. However, recent…
The shape of the power spectrum of the black hole low-mass X-ray binary evolves systematically over different spectral states during an outburst. Therefore, the power colours (ratio of the variability amplitude at different frequency…
I report the discovery of hard X-ray phase lags associated with the famous 67 Hz quasi-periodic oscillation (QPO) in microquasar GRS 1915+105. The QPO is seen on multiple occasions. For this investigation, I have chosen one particular…
The properties of sub-second time variability of the X-ray emission of the black-hole binary GRS 1915+105 are very complex and strictly connected to its patterns of variability observed on long time scales. A key aspect for determining the…
We have used archival RXTE PCA data to investigate timing and spectral characteristics of the transient XTE J1817-330. The data pertains to 160 PCA pointed observations made during the outburst period 2006, January 27 to August 2. A…
The recently discovered bright transient black hole candidate Swift J1727.8-1613 is studied in a broad energy range ($0.5-79$ keV) using combined NICER and NuSTAR data on 29 August 2023. A promonient type-C Quasi-Periodic Oscillation (QPO)…
Black holes in dense astrophysical environments, such as globular clusters or in the vicinity of other massive objects, may possess accelerations. Such acceleration would modulate the characteristics of the quasi-periodic oscillations…
We measured the phase-lag spectrum of the high-frequency quasi-periodic oscillations (QPO) in the black hole systems (at QPO frequencies) GRS 1915+105 (35 Hz and 67 Hz), GRO J1655-40 (300 Hz and 450 Hz), XTE J1550-564 (180 Hz and 280 Hz),…
The evolution of different types of quasi-periodic oscillations (QPOs) and the coupled radiative/physical changes in the accretion disk are still poorly understood. In a few black hole binaries it was found that fast evolution of QPOs is…
Origin of wide varieties of quasi-periodic oscillation (QPO) observed in compact sources is still not well established. Its frequencies range from mHz to kHz spanning all compact objects. Are different QPOs, with different frequencies,…
We perform a comprehensive wide-band ($3-100$keV) spectro-temporal analysis of 13 outbursting BH-XRBs, using data (quasi)simultaneous with radio observations to unravel the complex disc-jet connection. RXTE observations are analyzed for…