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The interband correlations between optical/ultraviolet (UV) and X-ray luminosities of active galactic nuclei (AGNs) are important for understanding the disc–coronal connection, as well as using AGN as standard candles for cosmology. It is conventional to measure the X-ray luminosity at rest-frame 2 keV and compare to the UV luminosity at the rest-frame 2500 Å, but the wavelength dependence was never well explored. In this work, we adopt a well-defined sample of 1169 unobscured quasars in the redshift range 0.13–4.51, and apply the direct-correlation method to explore how the correlation with the 2 keV luminosity changes at different optical/UV wavelengths, from 1280 to 5550 Å where the spectral quality is high. We find that the luminosity at all UV continuum wavelengths correlates with the X-ray luminosity similarly to that at 2500 Å, and that these correlations are better than at the optical wavelengths. Strong self-correlation is also found in the broad-band optical/UV continuum, supporting the scenario that it is dominated by the disc emission. Correlations of various emission lines are also investigated (e.g. C iv, C iii], Mg ii, Hβ, and [O iii]λλ4959/5007), including the Baldwin effect and correlations involving linewidths. We find the forms of these line correlations are different, and they are also different from their underlying continua, suggesting various complexities in the line-generation process. We discuss these results in the disc-wind scenario. Our study confirms that the rest-frame 2500 Å is a good wavelength to represent the optical/UV continual properties of quasars, and shows the advantages of the direct-correlation method.

The ultraviolet (UV) bright accretion disc in active galactic nuclei (AGNs) should give rise to line driving, producing a powerful wind that may play an important role in AGN feedback as well as in producing structures like the broad-line region. However, coupled radiation-hydrodynamic codes are complex and expensive, so we calculate the winds instead using a non-hydrodynamical approach (the qwind framework). The original qwind model assumed the initial conditions in the wind, and had only simple radiation transport. Here, we present an improved version that derives the wind initial conditions and has significantly improved ray tracing to calculate the wind absorption self-consistently, given the extended nature of the UV emission. We also correct the radiation flux for relativistic effects and assess the impact of this on the wind velocity. These changes mean the model is more physical, so its predictions are more robust. We find that, even when accounting for relativistic effects, winds can regularly achieve velocities ≃(0.1−0.5)c, and carry mass-loss rates that can be up to 80 per cent of the accreted mass for black hole masses of 107−9 M⊙, and mass accretion rates of 50 per cent of the Eddington rate. Overall, the ratio of kinetic power carried by the wind to bolometric luminosity increases with mass accretion rate at a given black hole mass, unlike the constant fraction generally assumed in current cosmological simulations that include AGN feedback. The updated code, qwind3, is publicly available in GitHub.1

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.