Investigating a fluctuating-accretion model for the spectral-timing properties of accreting black hole systems

By P. Arévalo, P. Uttley. 2005

329 citations recorded by the source corpus.

The fluctuating-accretion model of Lyubarskii and its extension by Kotov, Churazov & Gilfanov seek to explain the spectral-timing properties of the X-ray variability of accreting black holes in terms of inward-propagating mass accretion fluctuations produced at a broad range of radii. The fluctuations modulate the X-ray emitting region as they move inwards and can produce temporal-frequency-dependent lags between energy bands, and energy-dependent power spectral densities (PSDs) as a result of the different emissivity profiles, which may be expected at different X-ray energies. Here, we use a simple numerical implementation to investigate in detail the X-ray spectral-timing properties of the model and their relation to several physically interesting parameters, namely the emissivity profile in different energy bands, the geometrical thickness and viscosity parameter of the accretion flow, the strength of damping on the fluctuations and the temporal coherence (measured by the 'quality factor', Q) of the fluctuations introduced at each radius. We find that a geometrically thick flow with large viscosity parameter is favoured, and we confirm that the predicted lags are quite robust to changes in the emissivity profile and physical parameters of the accretion flow, which may help to explain the similarity of the lag spectra in the low/hard and high/soft states of Cyg X-1. We also demonstrate the model regime where the light curves in different energy bands are highly spectrally coherent. We compare model predictions directly to X-ray data from the narrow line Seyfert 1 galaxy NGC 4051 and the black hole X-ray binary (BHXRB) Cyg X -1 in its high/soft state, and we show that this general scheme can reproduce simultaneously the time lags and energy-dependence of the PSD.

Subfields: Astronomy and Astrophysics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/3403bd3f48e3866da7a03a17b180e07d2cb17987

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Statistical and Nonlinear Physics

Citations in the corpus

X-ray reverberation around accreting black holes (2014, background): “A likely alternative is that these lowfrequency hard lags are associated with the propagation of fluctuations through the accretion flow and/or corona (Kotov et al. 2001; Arévalo & Uttley 2006), as may also be the case with the hard lags seen at lower frequencies in the AGN data.”
Intrinsic disc emission and the soft X‐ray excess in active galactic nuclei (2011, background): “This inhomogeneous Comptonisation in BHB is also required to explain the time lags seen in the data (Kotov, Churazov & Gilfanov 2001; Arévalo & Uttley 2006).”
Modelling the behaviour of accretion flows in X-ray binaries (2007, background): “This can match the energy and time dependence of the time lags, as well as the broad band power spectral shape and rms–flux relation (Kotov, Churazov & Gilfanov 2001; Arevalo & Uttley 2006).”
A physical model for the continuum variability and QPO in accreting black holes (2011, background): “A different emissivity for different energy bands gives a way for the model to predict frequency dependent time lags between hard and soft X-ray bands (K01; AU06).”
Broad iron L line and X-ray reverberation in 1H0707-495 (2009, background): “Several models have been suggested to explain the lag, the most successful of which is the propagation of accretion fluctuations (Lyubarskii 1997; Kotov et al. 2001, see also Arévalo & Uttley 2006).”
Active galactic nuclei: what’s in a name? (2017, background): “Rather, it appears that the class of “propagating-fluctuation” models, first introduced by Lyubarskii (1997), are more suitable to explain a vast range of X-ray timing properties, including the rms-flux relation (Arévalo and Uttley 2006; Ingram and Klis 2013).”
A review of quasi-periodic oscillations from black hole X-ray binaries: Observation and theory (2019, background): “1) if the broad band noise is assumed to originate from propagating fluctuations of the mass accretion rate in the inner flow [129, 8, 87].”
A global look at X-ray time lags in seyfert galaxies (2016, background): “Kotov et al. (2001) and later Arévalo & Uttley (2006) extended this idea further to explain the time lags in the X-ray emission.”
Discovery of a relation between black hole mass and soft X-ray time lags in active galactic nuclei (2011, background): “Hard/positive lags (i.e. hard X-ray variations lagging soft X-ray variations) are generally observed in both BHXBs and AGN, and can be interpreted in terms of propagation of mass accretion rate fluctuations in the disc (Kotov, Churazov & Gilfanov 2001; Arévalo & Uttley 2006).”