Abstract.We collate the results of recent high resolution X-ray spectroscopic observations of 23 AGN, and use the resulting information to try to provide answers to some of the main open questions about warm absorbers: where do they originate, what effect do they have on their host galaxies, and what is their importance within the energetics and dynamics of the AGN system as a whole? We find that the warm absorbers of nearby Seyferts and certain QSOs are most likely to originate in outflows from the dusty torus, and that the kinetic luminosity of these outflows accounts for well under 1% of the bolometric luminosities of the AGN. Our analysis supports, however, the view that the relativistic outflows recently observed in two PG quasars have their origin in accretion disc winds, although the energetic importance of these outflows is similar to that of the Seyfert warm absorbers. We find that the observed soft X-ray absorbing ionisation phases fill less than 10% of the available volume. Finally, we show that the amount of matter processed through an AGN outflow system, over the lifetime of the AGN, is probably large enough to have a significant influence on the evolution of the host galaxy and of the AGN itself.

Abstract. We present a general formulation for ray-tracing calculations in curved space-time. The formulation takes full account of relativistic effects in the photon transport and the relative motions of the emitters and the light-of-sight absorbing material. We apply the formulation to calculate the emission from accretion disks and tori around rotating black holes. In our model the emission lines and continuum originate from an accretion disk or torus, and the motion of the emitters in the disk/torus is determined by the gravity of the black hole and the space-time structure near the black hole. The line-of-sight absorbing medium is comprised of cold absorbing cloudlets. These cloudlets are kinematically hot, with their velocity dispersion determined by the local virial temperature. The emission from the accretion disk/torus is resonantly absorbed/scattered. Our calculations demonstrate that line-of-sight absorption significantly modifies the profiles of lines from the accretion disks. It is often difficult to disentangle absorption effects from other geometrical and kinematics effects, such as the viewing inclination and the spin of the black hole. Our calculations also show that emission lines from accretion tori and from thin accretion disks differ substantially. Large geometrical obscuration could occur in tori, and as a consequence lines from tori generally have much weaker redshift wings at large viewing inclination angles. Moreover, the blue peak is truncated.

We aim to construct a general relativistic radiative transfer formulation, applicable to particles with or without mass in astrophysical settings, wherein ray-tracing calculations can be performed for arbitrary geodesics for a given space-time geometry. The relativistic radiative transfer formulation is derived from first principles: conserving particle number and phase-space density. The formulation is covariant, and transfer calculations are conducted along particle geodesics connecting the emitters and the observer. The geodesics are determined through the space-time metric, which is specified beforehand. Absorption and emission in the radiative transfer calculations are treated explicitly. The particle-medium interaction is evaluated in the local inertial frame, co-moving with the medium. Relativistic, geometrical and optical depth effects are treated self-consistently within an integral covariant framework. We present a self-consistent general relativistic radiative transfer formulation with explicit treatment of emission and absorption. The formulation is general and is applicable to both particles with mass and without mass. The presence of particles has two major effects: firstly the particle bundle ray is no longer along the null geodesic, and secondly the intensity variation along the particle bundle ray is reduced by an aberration factor. The radiative transfer formulation can handle 3D geometrical settings and structured objects with variations and gradients in the optical depths across the objects and along the line-of-sight. Such scenarios are applicable in calculations of photon emission from complex structured accretion flows around black holes and neutrino emission from remnant neutron tori in neutron-star mergers. We apply the formulation and demonstrate radiation transfer calculations for emission from accretion tori around rotating black holes. We consider two cases: idealised optically thick tori that have a sharply defined emission boundary surface, and structured tori that allow variations in the absorption coefficient and emissivity within the tori. We show intensity images and emission spectra of the tori obtained in our calculations. Our findings in the radiative transfer calculations are summarised as follows. (i) Geometrical effects, such as lensing-induced self-occulation and multiple-image contribution are much more significant in accretion tori than geometrically thin accretion disks. (ii) Optically thin accretion tori show emission line profiles distinguishable from the profiles of lines from optically thick accretion tori and lines from optically thick geometrically thin accretion disks. (iii) The line profiles of the optically thin accretion tori have a weaker dependence on the viewing inclination angle than those of the optically thick accretion tori or accretion disks, especially at high viewing inclination angles. (iv) Limb effects are present in accretion tori with finite optical depths, due to density and temperature stratification within the tori. We note that in accretion ...

We present two covariant radiative transfer formulations, and apply them to calculate emission from relativistic accretion flows around black holes. The first formulation is for situations with only line-of-sight absorption and emission, while the second formulation is for situations where scattering is important. We use the first formulation to calculate emissions from opaque accretion disks and tori around black holes absorbed by high-velocity cloudlets. Our calculations show the importance of effects due to space-time curvature, relativistic motions of the emitters and absorbers, and external line-of-sight absorption. We find that external absorption tends to take away line fluxes at energies red-ward of the line-centre energy. In its presence, emission lines from geometrically thin opaque relativistic accretion disks may not have broad asymmetric double-peak profiles: in some situations the lines may appear to be narrow, sharp and blue-shifted. We also find that geometric effects are important for thick accretion disks (accretion tori). When viewed at high inclination angles, the inner surface of an accretion torus can be self-occulted. As the most highly red-shifted and blueshifted emissions are blocked, emission lines from an opaque accretion torus would suffer less broadening and the line intensities are less boosted. These lines may have single-peak profiles, but their line centres are slightly red-shifted. We apply the radiative transfer formulation to calculate emission lines from optically thin and semi-opaque accretion tori, and generalise it to calculate continua emission, such as the reflection spectra, of accretion disks. The second convariant radiative transfer formulation, which is based on a moment method, is used to calculate the emissions from accretion tori with the opacity being dominated by electron scattering. We demonstrate that the formulation is applicable for a wide range of optical depths appropriate for accretion tori around black holes.

We calculate line emission from relativistic accretion tori around Kerr black holes and investigate how the line profiles depend on the viewing inclination, spin of the central black hole, parameters describing the shape of the tori, and spatial distribution of line emissivity on the torus surface. We also compare the lines with those from thin accretion disks. Our calculations show that lines from tori and lines from thin disks share several common features. In particular, at low and moderate viewing inclination angles they both have asymmetric double-peaked profiles with a tall, sharp blue peak and a shorter red peak which has an extensive red wing. At high viewing inclination angles they both have very broad, asymmetric lines which can be roughly considered as single-peaked. Torus and disk lines may show very different red and blue line wings, but the differences are due to the models for relativistic tori and disks having differing inner boundary radii. Self-eclipse and lensing play some role in shaping the torus lines, but they are effective only at high inclination angles. If inner and outer radii of an accretion torus are the same as those of an accretion disk, their line profiles show substantial differences only when inclination angles are close to 90• , and those differences manifest mostly at the central regions of the lines instead of the wings.

We present simulated results of quasi‐periodic flares generated by the inelastic collisions of a star bound to a supermassive black hole and its attendant accretion disc. We show that the behaviour of the quasi‐periodicity is affected by the mass and spin of the black hole and the orbital elements of the stellar orbit. We also evaluate the possibility of extracting useful information on these parameters and verifying the character of the Kerr metric from such quasi‐periodic signals. Comparisons are made with the observed optical outbursts of OJ 287, infrared flares from the Galactic Centre and X‐ray variability in RE J1034+396.

We have calculated the relativistic reflection component of the X-ray spectra of accretion disks in active galactic nuclei (AGN). Our calculations have shown that the spectra can be significantly modified by the motion of the accretion flow and the gravity and rotation of the central black hole. The absorption edges in the spectra suffer severe energy shifts and smearing, and the degree of distortion depends on the system parameters, in particular, the inner radius of the accretion disk and the disk viewing inclination angles. The effects are significant. Fluorescent X-ray emission lines from the inner accretion disk could be powerful diagnostic of space-time distortion and dynamical relativistic effects near the event horizons of accreting black holes. However, improper treatment of the reflection component in fitting the X-ray continuum could give rise to spurious line-like features. These features mimic the true fluorescent emission lines and may mask their relativistic signatures. Fully relativistic models for reflection continua together with the emission lines are needed in order to extract black-hole parameters from the AGN X-ray spectra.

We investigate jet formation in black-hole systems using 3-D General Relativistic Particle-In-Cell (GRPIC) and 3-D GRMHD simulations. GRPIC simulations, which allow charge separations in a collisionless plasma, do not need to invoke the frozen condition as in GRMHD simulations. 3-D GRPIC simulations show that jets are launched from Kerr black holes as in 3-D GRMHD simulations, but jet formation in the two cases may not be identical. Comparative study of black hole systems with GRPIC and GRMHD simulations with the inclusion of radiate transfer will further clarify the mechanisms that drive the evolution of disk-jet systems.