The power spectra of black hole binaries have been well studied for decades, giving a very detailed phenomenological picture of the variability properties and their correlation with the energy ...spectrum (spectral state) of the source. Here we take the truncated disc/hot inner flow picture which can describe the spectral changes, and show that propagating mass accretion rate fluctuations in the hot flow can match the broad-band power spectral properties seen in black hole binaries, i.e. give an approximately band-limited noise between a low- and a high-frequency break. The low-frequency break marks the viscous time-scale at the outer edge of the hot inner flow, which is the inner edge of the truncated disc. The fluctuations in mass accretion rate propagate towards the central object in a finite time meaning the high-frequency break is more complex than simply the viscous time-scale at the inner edge of the hot flow because fluctuations on time-scales shorter than the propagation time are incoherent. The model also predicts the Lense-Thirring precession time-scale of the hot flow, as this is set by the combination of inner and outer radius of the flow, together with its surface density which is self-consistently calculated from the propagating fluctuations. We show that this naturally gives the observed relation between the low-frequency break and quasi-periodic oscillation (QPO) frequency as the outer radius of the flow moves inwards, and that this model predicts many of the observed QPO properties such as correlation of coherence with frequency, and of the recently discovered correlation of frequency with flux on short time-scales.
We fit this total model of the variability to a sequence of five observed power spectra from the bright black hole binary XTE J1550−564 as the source transitioned from a low/hard to very high state. This is the first time that a power spectrum from a black hole binary has been fit with a physical model for the variability. The data are well fit if the inner radius of the flow remains constant, while the outer radius sweeps inwards from ∼75 to 12 gravitational radii. This range of radii is the same range as required by models of the energy spectral evolution, giving the first self-consistent description of the evolution of both the spectrum and variability of black hole binaries.
Relativistic reflection models of the X-ray spectrum of the ‘complex’ Narrow Line Seyfert 1 (NLS1) 1H 0707−495 require a high-spin, moderate-inclination, low-mass black hole. With these parameters ...fixed, the observed optical/UV emission directly determines the mass accretion rate through the outer disc and hence predicts the bolometric luminosity. This is 140–260 times the Eddington limit. Such a disc should power a strong wind, and winds are generically expected to be clumpy. Changing inclination angle with respect to a clumpy wind structure gives a possible explanation for the otherwise puzzling difference between ‘complex’ NLS1 such as 1H 0707−495 and ‘simple’ ones like PG 1244+026. Lines of sight which intercept the wind show deep absorption features at iron from the hot phase of the wind, together with stochastic dips and complex absorption when the clumps occult the X-ray source (complex NLS1), whereas both these features are absent for more face-on inclination (simple NLS1). This geometry is quite different from the clean view of a flat disc which is assumed for the spin measurements in relativistic reflection models, so it is possible that even 1H 0707−495 has low spin. If so, this re-opens the simplest and hence very attractive possibility that high black hole spin is a necessary and sufficient condition to trigger highly relativistic (bulk Lorentz factor ∼10–15) jets.
ABSTRACT
Accretion disc coronae (ADC) sources are very high inclination neutron star or black hole binaries, where the outer accretion flow blocks a direct view of the central source. The weak ...observed X-ray emission is instead produced mainly by scattering of the intrinsic radiation from highly ionized gas surrounding the source, the ADC. However, the origin of this scattering material is still under debate. We use the ADC source 2S 0921-630 (V395 Car) to test whether it is consistent with a thermal-radiative wind produced by the central X-ray source illuminating and puffing up the outer disc. This wind is clearly visible in blueshifted absorption lines in less highly inclined systems, where the source is seen directly through this material. Using the phenomenological photoionized plasma model, we first characterize the parameter that drives emission lines observed in 2S0921 in XMM–Newton and Chandra data. Following this, we run the Monte Carlo radiation transfer simulation to get scattered/reprocessed emissions in the wind, with the density and velocity structure obtained from the previous work. Our model agrees with all the wind emission lines in the Chandra high and medium energy grating spectra for an intrinsic source luminosity of L > 0.2 LEdd. This result strongly favours thermal-radiative winds as the origin of the ADC. We also show how high-resolution spectra via microcalorimeters can provide a definitive test by detecting blueshifted absorption lines.
We show that the low-frequency quasi-periodic oscillations (QPOs) seen in the power-density spectra of black hole binaries (and neutron stars) can be explained by the Lense–Thirring precession. This ...has been proposed many times in the past, and simple, single-radius models can qualitatively match the observed increase in QPO frequency by decreasing a characteristic radius, as predicted by the truncated disc models. However, this also predicts that the frequency is strongly dependent on spin, and gives a maximum frequency at the last stable orbit which is generally much higher than the remarkably constant maximum frequency at ∼10 Hz observed in all black hole binaries. The key aspect of our model, which makes it match these observations, is the precession of a radially extended region of the hot inner flow. The outer radius is set by the truncation radius of the disc as above, but the inner radius lies well outside of the last stable orbit at the point where numerical simulations show that the density drops off sharply for a misaligned flow. Physically motivated analytic estimates for this inner radius show that it increases with a*, decreasing the expected frequency in a way which almost completely cancels the expected increase with spin, and ties the maximum predicted frequency to around 10 Hz for all a*. This is the first QPO model which explains both frequencies and spectrum in the context of a well-established geometry for the accretion flow.
ABSTRACT
The nature and geometry of the accretion flow in the low/hard state of black hole binaries is currently controversial. While most properties are generally explained in the truncated disc/hot ...inner flow model, the detection of a broad residual around the iron line argues for strong relativistic effects from an untruncated disc. Since spectral fitting alone is somewhat degenerate, we combine it with the additional information in the fast X-ray variability and perform a full spectral-timing analysis for NICER and NuSTAR data on a bright low/hard state of MAXI J1820+070. We model the variability with propagating mass accretion rate fluctuations by combining two separate current insights: that the hot flow is spectrally inhomogeneous, and that there is a discontinuous jump in viscous time-scale between the hot flow and variable disc. Our model naturally gives the double-humped shape of the power spectra, and the increasing high-frequency variability with energy in the second hump. Including reflection and reprocessing from a disc truncated at a few tens of gravitational radii quantitatively reproduces the switch in the lag-frequency spectra, from hard lagging soft at low frequencies (propagation through the variable flow) to the soft lagging hard at the high frequencies (reverberation from the hard X-ray continuum illuminating the disc). The viscous time-scale of the hot flow is derived from the model, and we show how this can be used to observationally test ideas about the origin of the jet.
ABSTRACT
Warm absorbers are present in many active galactic nuclei (AGN), seen as mildly ionized gas outflowing with velocities of a few hundred to a few thousand kilometres per second. These slow ...velocities imply a large launch radius, pointing to the broad-line region and/or torus as the origin of this material. Thermal driving was originally suggested as a plausible mechanism for launching this material but recent work has focused instead on magnetic winds, unifying these slow, mildly ionized winds with the more highly ionized ultrafast outflows. Here we use the recently developed quantitative models for thermal winds in black hole binary systems to predict the column density, velocity, and ionization state from AGN. Thermal winds are sensitive to the spectral energy distribution (SED), so we use realistic models for SEDs which change as a function of mass and mass accretion rate, becoming X-ray weaker (and hence more disc dominated) at higher Eddington ratio. These models allow us to predict the launch radius, velocity, column density, and ionization state of thermal winds as well as the mass-loss rate and energetics. While these match well to some of the observed properties of warm absorbers, the data point to the presence of additional wind material, most likely from dust driving.
Abstract
We present a detailed multiwavelength study of an unobscured, highly super-Eddington Type-1 QSO RX J0439.6-5311. We combine the latest XMM–Newton observation with all archival data from ...infrared to hard X-rays. The optical spectrum is very similar to that of 1H 0707-495 in having extremely weak O iii and strong Fe ii emission lines, although the black hole mass is probably slightly higher at 5-10 × 106 M⊙. The broad-band spectral energy distribution is uniquely well defined due to the extremely low Galactic and intrinsic absorption, so the bolometric luminosity is tightly constrained. The optical/UV accretion disc continuum is seen down to 900 Å, showing that there is a standard thin disc structure down to R ≥ 190–380 R
g and determining the mass accretion rate through the outer disc. This predicts a much higher bolometric luminosity than observed, indicating that there must be strong wind and/or advective energy losses from the inner disc, as expected for a highly super-Eddington accretion flow. Significant outflows are detected in both the narrow-line region (NLR) and broad-line region (BLR) emission lines, confirming the presence of a wind. We propose a global picture for the structure of a super-Eddington accretion flow where the inner disc puffs up, shielding much of the potential NLR material, and show how inclination angle with respect to this and the wind can explain very different X-ray properties of RX J0439.6-5311 and 1H 0707-495. Therefore, this source provides strong supporting evidence that ‘simple’ and ‘complex’ super-Eddington NLS1s can be unified within the same accretion flow scenario but with different inclination angles. We also propose that these extreme NLS1s could be the low-redshift analogues of weak emission-line quasars.
Abstract
In this third paper in a series of three, we present a detailed study of the broad-band spectral energy distribution (SED) of active galactic nuclei (AGNs) based on a nearby unobscured type ...1 AGN sample. We perform a systematic cross-correlation study of several key parameters, i.e. Γ2-10 keV, L
2-10 keV, L
bol/L
Edd = λEdd, L
bol/L
2-10 keV = κ2-10 keV, , FWHMHβ, M
BH, αox, αX and αUV. The well-defined spectral properties of the sample enable us to improve existing relations and to identify new correlations among these parameters. We confirm a break region around FWHMHβ ≃ 4000 km s−1 in the Γ2-10 keV versus FWHMHβ correlation and log(M
BH) ≃ 8.0 in the Γ2-10 keV versus M
BH correlation, where these correlations appear to change form. Beyond the break point, the intrinsic Γ2-10 keV index is dispersed around 1.8. Several new correlations are also reported in this paper, e.g. strong correlations in κ5100 versus λEdd, κ5100 versus κ2-10 keV and κ2-10 keV versus M
BH. The principal component analysis (PCA) is performed on the correlation matrix of the above parameters. This shows that the three physical parameters, i.e. black hole mass, mass accretion rate and Eddington ratio, drive the majority of the correlations. This is consistent with PCA results found from previous optical spectral studies.
For each key parameter, we split the AGNs into three subsamples, binned based on increasing value of that parameter. We co-add the model SEDs for each object in the subsample to see how the SED changes with that parameter. Most parameters, except L
bol, show similar systematic changes in the SED such that the temperature at which the disc peaks is correlated with the ratio of power in the disc versus the Comptonized components and the hard X-ray spectral index. This underlying change in SED shape shows that AGNs do exhibit intrinsically different spectral states. This is superficially similar to the SED differences in black hole binary (BHB) seen as λEdd increases, but the analogy does not hold in detail. Only objects with the highest λEdd appear to correspond to a BHB spectral state (the disc-dominated high/soft state). The AGNs with typical mass accretion rates have spectra which do not match well with any state observed in BHB. We speculate that this could be due to the presence of a powerful ultraviolet line-driven disc wind, which complicates simple mass scaling between stellar and supermassive black holes.
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