Multidimensional modelling of X-ray spectra for AGN accretion disc outflows - III. Application to a hydrodynamical simulation

We perform multidimensional radiative transfer simulations to compute spectra for a hydrodynamical simulation of a line-driven accretion disc wind from an active galactic nucleus. The synthetic spectra confirm expectations from parametrized models that a disc wind can imprint a wide variety of spectroscopic signatures including narrow absorption lines, broad emission lines and a Compton hump. The formation of these features is complex with contributions originating from many of the different structures present in the hydrodynamical simulation. In particular, spectral features are shaped both by gas in a successfully launched outflow and in complex flows where material is lifted out of the disc plane but ultimately falls back. We also confirm that the strong Fe Ka line can develop a weak, red-skewed line wing as a result of Compton scattering in the outflow. In addition, we demonstrate that X-ray radiation scattered and reprocessed in the flow has a pivotal part in both the spectrum formation and determining the ionization conditions in the wind. We find that scattered radiation is rather effective in ionizing gas which is shielded from direct irradiation from the central source. This effect likely makes the successful launching of a massive disc wind somewhat more challenging and should be considered in future wind simulations. © 2010 The Authors. Journal compilation © 2010 RAS.

Multidimensional modelling of X-ray spectra for AGN accretion disc outflows

We use a multidimensional Monte Carlo code to compute X-ray spectra for a variety of active galactic nucleus (AGN) disc-wind outflow geometries. We focus on the formation of blueshifted absorption features in the Fe K band and show that line features similar to those which have been reported in observations are often produced for lines of sight through disc-wind geometries. We also discuss the formation of other spectral features in highly ionized outflows. In particular, we show that, for sufficiently high wind densities, moderately strong Fe K emission lines can form and that electron scattering in the flow may cause these lines to develop extended red wings. We illustrate the potential relevance of such models to the interpretation of real X-ray data by comparison with observations of a well-known AGN, Mrk 766. Journal compilation © 2008 RAS.

Multidimensional modelling of X-ray spectra for AGN accretion disc outflows - II

Highly ionized fast accretion disc winds have been suggested as an explanation for a variety of observed absorption and emission features in the X-ray spectra of active galactic nuclei. Simple estimates have suggested that these flows may be massive enough to carry away a significant fraction of the accretion energy and could be involved in creating the link between supermassive black holes and their host galaxies. However, testing these hypotheses, and quantifying the outflow signatures, requires high-quality theoretical spectra for comparison with observations. Here, we describe extensions of our Monte Carlo radiative transfer code that allow us to generate realistic theoretical spectra for a much wider variety of disc wind models than that was possible in our previous work. In particular, we have expanded the range of atomic physics simulated by the code so that L- and M-shell ions can now be included. We have also substantially improved our treatment of both ionization and radiative heating such that we are now able to compute spectra for outflows containing far more diverse plasma conditions. We present example calculations that illustrate the variety of spectral features predicted by parametrized outflow models and demonstrate their applicability to the interpretation of data by comparison with observations of the bright quasar PG1211+143. We find that the major features in the observed 2-10 keV spectrum of this object can be well reproduced by our spectra, confirming that it likely hosts a massive outflow. © 2010 The Authors. Journal compilation © 2010 RAS.

A taxonomy for wavelet neural networks applied to nonlinear modelling

This article presents a novel classification of wavelet neural networks based on the orthogonality/non-orthogonality of neurons and the type of nonlinearity employed. On the basis of this classification different network types are studied and their characteristics illustrated by means of simple one-dimensional nonlinear examples. For multidimensional problems, which are affected by the curse of dimensionality, the idea of spherical wavelet functions is considered. The behaviour of these networks is also studied for modelling of a low-dimension map.

Multidimensional simulations of radiative transfer in Type Ia supernovae

A three-dimensional Monte Carlo code for modelling radiation transport in Type Ia supernovae is described. In addition to tracking Monte Carlo quanta to follow the emission, scattering and deposition of radiative energy, a scheme involving volume-based Monte Carlo estimators is used to allow properties of the emergent radiation field to be extracted for specific viewing angles in a multidimensional structure. This eliminates the need to compute spectra or light curves by angular binning of emergent quanta. The code is applied to two test problems to illustrate consequences of multidimensional structure on the modelling of light curves. First, elliptical models are used to quantify how large-scale asphericity can introduce angular dependence to light curves. Secondly, a model which incorporates complex structural inhomogeneity, as predicted by modern explosion models, is used to investigate how such structure may affect light-curve properties. © 2006 RAS.

Self-consistent modelling of line-driven hot-star winds with Monte Carlo radiation hydrodynamics

Radiative pressure exerted by line interactions is a prominent driver of outflows in astrophysical systems, being at work in the outflows emerging from hot stars or from the accretion discs of cataclysmic variables, massive young stars and active galactic nuclei. In this work, a new radiation hydrodynamical approach to model line-driven hot-star winds is presented. By coupling a Monte Carlo radiative transfer scheme with a finite volume fluid dynamical method, line-driven mass outflows may be modelled self-consistently, benefiting from the advantages of Monte Carlo techniques in treating multiline effects, such as multiple scatterings, and in dealing with arbitrary multidimensional configurations. In this work, we introduce our approach in detail by highlighting the key numerical techniques and verifying their operation in a number of simplified applications, specifically in a series of self-consistent, one-dimensional, Sobolev-type, hot-star wind calculations. The utility and accuracy of our approach are demonstrated by comparing the obtained results with the predictions of various formulations of the so-called CAK theory and by confronting the calculations with modern sophisticated techniques of predicting the wind structure. Using these calculations, we also point out some useful diagnostic capabilities our approach provides. Finally, we discuss some of the current limitations of our method, some possible extensions and potential future applications.