Related papers: Characterizing X-ray binary long-term variability
In X-ray binaries, rapid variability in X-ray flux of greater than an order of magnitude on time-scales of a day or less appears to be a signature of wind accretion from a supergiant companion. When the variability takes the form of rare,…
We analyzed in a systematic way the public INTEGRAL observations spanning from December 2002 to September 2016, to investigate the hard X-ray properties of about 60 High Mass X-ray Binaries (HMXBs). We considered both persistent and…
The accreting X-ray pulsar Her X-1 shows two types of long-term variations, both with periods of ~35 days: 1) Turn-on cycles, a modulation of the flux}, with a ten-day long Main-On and a five-day long Short-On, separated by two Off-states,…
The detection of pulsations from an X-ray binary is an unambiguous signature of the presence of a neutron star in the system. When the pulsations are missed in the radio band, their detection at other wavelengths, like X-ray or gamma-rays,…
Variation of mass supply rate from the companion can be smeared out by viscous processes inside an accretion disk. By the time the flow reaches the inner edge, the variation in X-rays needs not reflect the true variation of the rate at the…
In this paper we propose and examine a physical mechanism which can lead to the generation of noise in the mass accretion rate of low mass X-ray binaries on time-scales comparable to the orbital period of the system. We consider modulations…
We studied the spectral changes of the high-mass X-ray binary system LMC X-4 to understand the origin and mechanisms beyond its super-orbital modulation (30.4 days). To this aim, we obtained a monitoring campaign with Swift/XRT (0.3-10 keV)…
A comprehensive review of aperiodic rapid X-ray variability (QPO and noise) in X-ray binaries with neutron stars and black holes.
A low mass X-ray binary (LMXB) contains either a neutron star or a black hole accreting materials from its low mass companion star. It is one of the primary astrophysical sources for studying the stellar size compact objects and the…
We review the timing and spectral evolution of black hole X-ray binary systems, with emphasis on the current accretion-ejection paradigm. When in outburst, stellar mass black hole binaries may become the brightest X-ray sources in the sky.…
The search for periodicity in the multi-wavelength high variable emission of blazars is a key feature to understand dynamical processes at work in this class of active galactic nuclei. The blazar PG 1553+113 is an attractive target due to…
We report on optical high-dispersion spectroscopic monitoring observations of the Be/X-ray binary A0535+26/V725 Tau, carried out from November 2005 to March 2009. The main aim of these monitoring observations is to study spectral…
Long-term monitoring of the recently discovered X-ray transient, IGR J17098-3628, by the All Sky Monitor on board the Rossi X-ray Timing Explorer, has shown that it displays a long term (~163d) quasi-periodic modulation in the data spanning…
We present three dimensional smoothed particle hydrodynamics (SPH) calculations of irradiation-driven warping of accretion discs. Initially unwarped planar discs are unstable to the radiation reaction when the disc is illuminated by a…
The X-ray binary 4U 1543$-$624 has been provisionally identified as an ultracompact system with an orbital period of $\simeq$18~min. We have carried out time-resolved optical imaging of the binary to verify the ultra-short orbital period.…
We present the results of a study with the \emph{Swift} Burst Alert Telescope in the 14 -- 195 keV range of the long-term variability of 5 low mass X-ray binaries with reported or suspected super-orbital periods -- 4U 1636-536, 4U 1820-303,…
In this review I briefly describe the latest advances in studies of aperiodic variability of accreting X-ray binaries and outline the model which currently describe the majority of observational appearances of variability of accreting…
The aim of this PhD Thesis is to characterize a representative sample of Supergiant X-ray Binaries (SGXBs) formed by 4 sources: XTE J1855-026, a classical SGXB with long-term stable X-ray flux; AX J1841.0-0535 and AX J1845.0-0433, two…
We analyze 1598 serendipitous Chandra X-ray observations of 462 radio-quiet quasars to constrain the frequency of extreme amplitude X-ray variability that is intrinsic to the quasar corona and innermost accretion flow. The quasars in this…
The X-ray binary pulsar Her X-1 shows a wide variety of long and short term variabilities in the X-ray light curve. The 35 d variability of the source is interpreted as the influence of a warped, inclined, and twisted accretion disk…