X-ray variability of active galactic nuclei - A universal power spectrum with luminosity-dependent amplitude

Lawrence, A.; Papadakis, I. E.

doi:10.1086/187002

Cited by 172 publications

(178 citation statements)

References 0 publications

Supporting

Mentioning

156

Contrasting

Order By: Relevance

“…Marshall et al 1981;Barr & Mushotzky 1986;Lawrence & Papadakis 1993;Green et al 1993;Turner et al 1999;Weaver et al 2001;Manners et al 2002, etc.). X-ray flux variability has long been known to be a common property of active galactic nuclei (AGNs), e.g., Ariel 5 and HEAO 1 first revealed long-term (days to years) variability in AGNs and by uninterrupted observations of EXOSAT rapid (thousands of seconds) variability was also established as common in these sources (see, for example reviews by Mushotzky et al 1993;Ulrich et al 1993, and references therein).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

On the contribution of microlensing to X-ray variability of high-redshifted QSOs

Popovic

Jovanović

2004

A&A

View full text Add to dashboard Cite

Abstract. We consider a contribution of microlensing to the X-ray variability of high-redshifted QSOs. Such an effect could be caused by stellar mass objects (SMO) located in a bulge or/and in a halo of this quasar as well as at cosmological distances between an observer and a quasar. Here, we not consider microlensing caused by deflectors in our Galaxy since it is wellknown from recent MACHO, EROS and OGLE observations that the corresponding optical depth for the Galactic halo and the Galactic bulge is lower than 10 −6 . Cosmologically distributed gravitational microlenses could be localized in galaxies (or even in bulge or halo of gravitational macrolenses) or could be distributed in a uniform way. We have analyzed both cases of such distributions. As a result of our analysis, we obtained that the optical depth for microlensing caused by stellar mass objects is usually small for quasar bulge and quasar halo gravitational microlens distributions (τ ∼ 10 −4 ). On the other hand, the optical depth for gravitational microlensing caused by cosmologically distributed deflectors could be significant and could reach 10 −2 −0.1 at z ∼ 2. This means that cosmologically distributed deflectors may contribute significantlly to the X-ray variability of high-redshifted QSOs (z > 2). Considering that the upper limit of the optical depth (τ ∼ 0.1) corresponds to the case where dark matter forms cosmologically distributed deflectors, observations of the X-ray variations of unlensed QSOs can be used for the estimation of the dark matter fraction of microlenses.

show abstract

Section: Introductionmentioning

confidence: 99%

“…It was first suggested by Barr & Mushotzky (1986) that the flux variation of an AGN is inversely proportional to its luminosity. Lawrence & Papadakis (1993) and Green et al (1993) …”

Section: Introductionmentioning

confidence: 99%

On the contribution of microlensing to X-ray variability of high-redshifted QSOs

Popovic

Jovanović

2004

A&A

View full text Add to dashboard Cite

show abstract

“…Though it may not be feasible with current technology, these basic possibilities are distinguishable. Namely, the difference between short-living flares (which die on the dynamical time-scale) in contrast to the enduring features can be identified in time-resolved spectra (Lawrence & Papadakis 1993;Kawaguchi et al 2000), but in order to resolve it the geometry of the system has to be constrained. This is not an easy task because obscuration e.g.…”

Section: Preliminariesmentioning

confidence: 99%

Theoretical aspects of relativistic spectral features

Karas

2006

Astron Nachr

View full text Add to dashboard Cite

The inner parts of black-hole accretion discs shine in X-rays which can be monitored and the observed spectra can be used to trace strong gravitational fields in the place of emission and along paths of light rays. This paper summarizes several aspects of how the spectral features are influenced by relativistic effects. We focus our attention onto variable and broad emission lines, origin of which can be attributed to the presence of orbiting patterns -spots and spiral waves in the disc. We point out that the observed spectrum can determine parameters of the central black hole provided the intrinsic local emissivity is constrained by theoretical models.

show abstract

“…Although well-known ambiguities are inherent to Fourier power spectra, an ongoing debate is held about the shape of the PSD and the dominant features that could reveal important information about the origin of the variability. The broad-band PSD has been widely employed to examine the fluctuating X-ray light curves, often showing a tendency towards flattening at low frequencies (Lawrence & Papadakis 1993;Mushotzky et al 1993;Uttley et al 2002). PSDs of interest for us are characterized by a power-law form of the Fourier power spectrum ωS (ω), which decays at the high-frequency part proportionally to the first power of ω.…”

Section: Introductionmentioning

confidence: 99%

Hot-spot model for accretion disc variability as random process

Pecháček

Goosmann

Karas

et al. 2013

A&A

View full text Add to dashboard Cite

Context. We study some general properties of accretion disc variability in the context of stationary random processes. In particular, we are interested in mathematical constraints that can be imposed on the functional form of the Fourier power-spectrum density (PSD) that exhibits a multiply broken shape and several local maxima. Aims. We develop a methodology for determining the regions of the model parameter space that can in principle reproduce a PSD shape with a given number and position of local peaks and breaks of the PSD slope. Given the vast space of possible parameters, it is an important requirement that the method is fast in estimating the PSD shape for a given parameter set of the model. Methods. We generated and discuss the theoretical PSD profiles of a shot-noise-type random process with exponentially decaying flares. Then we determined conditions under which one, two, or more breaks or local maxima occur in the PSD. We calculated positions of these features and determined the changing slope of the model PSD. Furthermore, we considered the influence of the modulation by the orbital motion for a variability pattern assumed to result from an orbiting-spot model. Results. We suggest that our general methodology can be useful for describing non-monotonic PSD profiles (such as the trend seen, on different scales, in exemplary cases of the high-mass X-ray binary Cygnus X-1 and the narrow-line Seyfert galaxy Ark 564). We adopt a model where these power spectra are reproduced as a superposition of several Lorentzians with varying amplitudes in the X-ray-band light curve. Our general approach can help in constraining the model parameters and in determining which parts of the parameter space are accessible under various circumstances.

show abstract

X-ray variability of active galactic nuclei - A universal power spectrum with luminosity-dependent amplitude

Cited by 172 publications

References 0 publications

On the contribution of microlensing to X-ray variability of high-redshifted QSOs

On the contribution of microlensing to X-ray variability of high-redshifted QSOs

Theoretical aspects of relativistic spectral features

Hot-spot model for accretion disc variability as random process

Contact Info

Product

Resources

About