Related papers: Boundary layer, accretion disk and X-ray variabili…

Context. The steep-spectrum radio quasars (SSRQs) are powerful radio sources, with thermal emission from accretion disk and jet nonthermal emission likely both contributing in the Ultraviolet (UV)/optical luminosity, however the former may…

The transient atoll source 4U 1608-52 had been extensively observed by the Rossi X-ray Timing Explorer RXTE during its 1998 outburst. We analyse its X-ray spectra as a function of inferred accretion rate from both the 1998 outburst and from…

It has recently been suggested that gravitomagnetic precession of the inner part of the accretion disk, possibly driven by radiation torques, may be responsible for some of the quasi-periodic X-ray brightness oscillations (QPOs) at 20 - 300…

The X-ray light-curves of the recurring outbursts observed in low-mass X-ray binaries provide strong test beds for constraining (still) poorly understood disc-accretion processes. These light-curves act as a powerful diagnostic to probe the…

I summarize the available RXTE data of the 4 low-mass X-ray binaries (LMXBs) and Atoll sources Aql X-1, 4U 1728-34, 4U 1608-52, and 4U 1636-53. I concentrate on the relation between the frequencies of the quasi-periodic oscillations at…

The Rossi X-Ray Timing Explorer (RXTE) has found that the neutron stars in low-mass X-ray binaries exhibit oscillations in the range 300-1200 Hz. Persistent emission may exhibit one or both of two features. In bursts a nearly coherent…

Over the last years, a number of broadband reverberation mapping campaigns have been conducted to explore the short-term UV and optical variability of nearby AGN. Despite the extensive data collected, the origin of the observed variability…

When a neutron star accretes matter from a companion star in a low-mass X-ray binary, the accreted gas settles onto the stellar surface through a boundary/spreading layer. On rare occasions the accumulated gas undergoes a powerful…

Z sources are bright neutron-star X-ray binaries, accreting at around the Eddington limit. We analyze the 68 RXTE observations (270 ks) of Sco-like Z source GX 17+2 made between 1999 October 3-12, covering a complete Z track. We create and…

Studying the cross-correlation function between the soft and hard X-ray emission in Neutron Star Low Mass X-ray Binaries provides crucial insight into the structure and dynamics of the innermost accretion regions. In this work, we…

We investigated the timing and spectral properties of the millihertz quasi-periodic oscillations (mHz QPOs) in the neutron-star low-mass X-ray binary 4U 1608-52 using NICER observations. Our analysis reveals a correlation between the QPO…

We analyzed the rapid aperiodic X-ray variability of the recently discovered millisecond X-ray pulsar SAX J1808.4-3658. The power density spectrum is dominated by a strong band-limited noise component, which follows a power-law with index…

We present a spectral-timing analysis of two NICER observations of the weakly magnetized neutron star low-mass X-ray binary Cygnus X-2. During these observations, we detect a rapid transition from a narrow 50-Hz horizontal-branch…

Using the X-ray data taken with ASCA, a detailed analysis was made of intensity and spectral variations of three ultra-luminous extra-galactic compact X-ray sources (ULXs); IC 342 source 1, M81 X-6, and NGC 1313 source B, all exhibiting…

The inner regions of accretion disks of weakly magnetized neutron stars are affected by general relativity and stellar magnetic fields. Even for field strengths sufficiently small so that there is no well-defined magnetosphere surrounding…

We calculate self-consistent models of X-ray irradiated accretion discs in close binary systems. We show that a point X-ray source powered by accretion and located in the disc plane cannot modify the disc structure, mainly because of the…

In this paper we propose a new model for quasi-periodic oscillations (QPOs) based on oscillating magnetohydrodynamic modes in neutron star magnetospheres. We argue that the interaction of the accretion disk with the magnetosphere can excite…

We study energy dependencies of quasi-periodic oscillations from a number of black hole X-ray binaries. The selected sources were observed by RXTE at time periods close to state transitions and showed QPO in the 1-10 Hz range. We have…

Short-term variability of X-ray spectra has been reported for several Active Galactic Nuclei. Significant X-ray flux variations are observed within time scales down to 10^4 -- 10^5 seconds. We discuss short variability time scales in the…

Based on previous studies of quasi-periodic oscillations in neutron star LMXBs, mHz quasi-periodic oscillations (QPO) are believed to be related to `marginally stable' burning on the neutron star (NS) surface. Our study of phase resolved…