Related papers: X-Ray Variability and the Inner Region in Active G…
The kHz QPOs observed in a neutron star low mass X-ray binary are likely to be produced in the innermost regions of accretion disk around the neutron star. The rotational dynamics of the inner disk can be characterized by the presence of…
We investigate the nature of the inner accretion disk in the neutron star source GX 5-1 by making a detailed study of time lags between X-rays of different energies. Using the cross-correlation analysis, we found anti-correlated hard and…
X-ray spectroscopy offers an opportunity to study the complex mixture of emitting and absorbing components in the circumnuclear regions of active galactic nuclei, and to learn about the accretion process that fuels AGN and the feedback of…
Among the variability behaviour exhibited by neutron star systems are the so-called ``horizontal branch oscillations'' (HBO, with frequencies ~50 Hz), the ``lower-frequency kHz quasi-periodic oscillation'' (QPO) and the ``upper-frequency…
The dramatic discovery with the Rossi X-Ray Timing Explorer satellite of remarkably coherent $\sim$300--1200 Hz oscillations in the X-ray brightness of some sixteen neutron stars in low-mass binary systems has spurred theoretical modeling…
Variability is a fundamental signature for active galactic nuclei (AGN) activity, and serve as an unbiased indicator for rapid instability happened near the center supermassive black hole (BH). Previous studies showed that AGN variability…
We compiled the X-ray and soft gamma-ray observations of the Galactic black hole binary XTE J1859+226 in the 1999--2000 outburst from RXTE, ASCA, BeppoSAX and CGRO. Throughout systematic spectral analysis using a two-component model…
The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of…
Both the broad iron (Fe) line and the frequency of the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (LMXBs) can potentially provide independent measures of the inner radius of the accretion disc.…
Kilohertz quasi-periodic oscillations (kHz QPOs) has been regarded as representing the Keplerian frequency at the inner disk edge in the neutron star X-ray binaries. The so-called ``parallel tracks'' on the plot of the kHz QPO frequency vs.…
Recent X-ray observations have revealed growing evidence of quasi-periodic oscillation (QPO) in the light curve of active galactic nuclei (AGNs), which may serve as a useful probe of black hole physics. In this work, we present a systematic…
We analyze the variability of the parsec-scale jet directions in active galactic nuclei (AGNs). Our analysis involves 317 AGNs at frequencies ranging from 2 to 43 GHz, and is made possible by developing an automatic inner jet direction…
Understanding the radiative and physical structures of inner region of a few 100 pc of AGNs is important to constrain the causes of their activities. Although the X-ray emission from the Comptonization region/corona and the accretion disc…
We use the publicly available XMM-Newton archive to select a sample of 20 active galactic nuclei (AGN) known to exhibit reverberation signatures caused by the reflection of X-rays from the corona off the accretion disc that feeds the…
Variable X-ray absorption has been observed in active galactic nuclei (AGN) on several time scales. Observations allow us to identify the absorber with clouds associated either with the clumpy torus (parsec scales, long timescales) or with…
Significant (marginal) detections of periodic signals have been recently reported in 3 (4) Active Galactic Nuclei. Three of the detections were obtained from long EUVE light curves of moderate-luminosity Seyfert galaxies; the fourth was…
We explain the peak spacing in the power spectra of millisecond variability detected by the Rossi X-ray Timing Explorer (RXTE) in the X-ray emission from the LMXBs (Sco X-1, 4U1728-34, 4U1608-522, 4U1636-536, etc) in terms of the rotational…
We use global magnetohydrodynamic simulations, in a pseudo-Newtonian potential, to investigate the temporal variability of accretion discs around Schwarzschild black holes. We use the vertically-averaged magnetic stress in the simulated…
A number of recent results from X-ray observations of Active Galactic Nuclei involving the Fe K alpha line (reduction of line variability compared to the X-ray continuum variability, the X-ray ``Baldwin effect'') were attributed to a…
We present a general relativistic (GR) model of jet variability in active galactic nuclei due to orbiting blobs in helical motion along a funnel or cone shaped magnetic surface anchored to the accretion disk near the black hole. Considering…