High Energy Astrophysics: Accretion Disks II 1/59 Accretion Disks II 1 The dynamical equations Astrophysics: Accretion Disks II 2/59 The simplest accretion disc model to construct is that of the thin disc on the azimuthal angle z #12;High Energy ...

Chapitre IV Accretion Disc Outbursts: A New Version of an Old Model Jean�Marie HAMEURY, 1 Kristen inferred. In particular we show that outside�in outbursts are possible when a standard bimodal behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 #12; 86 Accretion ...

We model circumplanetary discs as accretion discs subject to the tidal forces of the central star. The tidal torques remove the disc angular momentum near the disc outer edge and permit the accreting disc gas to lose angular ...

OUTFLOWS FROM DYNAMO-ACTIVE PROTOSTELLAR ACCRETION DISCS BRIGITTA VON REKOWSKI1 , AXEL BRANDENBURG2, Newcastle, UK Abstract. An axisymmetric model of a cool, dynamo-active accretion disc is applied by the disc dynamo driven by the magneto-rotational instability and some ...

Accretion discs are composed of ionized gas in motion around a central object. Sometimes, the disc is the source of powerful bipolar jets along its rotation axis. Theoretical models invoke the existence of a bipolar magnetic field crossing the disc and require two conditions to produce powerful ...

We analyse some properties of circumplanetary discs. Flow through such discs may provide most of the mass to gas giant planets, and such discs are likely sites for the formation of regular satellites. We model these discs as accretion discs subject to ...

Galactic nuclei should contain a cluster of stars and compact objects in the vicinity of the central supermassive black hole due to stellar evolution, minor mergers and gravitational dynamical friction. By analogy with protoplanetary migration, nuclear cluster objects (NCOs) can migrate in the accretion discs that power active galactic nuclei (AGN) by ...

Black holes grow by accreting matter from their surroundings. However, angular momentum provides an efficient natural barrier to accretion and so only the lowest angular momentum material will be available to feed the black holes. The standard subgrid model for black hole accretion in galaxy formation simulations - ...

We construct Super-Eddington Slim discs models around both stellar and supermassive black holes by allowing the formation of a porous layer with a reduced effective opacity. Unlike the standard scenario in which the discs become thick, super-Eddington discs remain slim. In addition, they accelerate a significant ...

The persistent black hole binary LMC X-3 is the best system on which to test theoretical models on the shape of the accretion disc spectrum. This is due to the combination of very low absorbing column density along this line of sight, which allows the shape of the disc emission to be constrained at low energies, ...

I present a model for acceleration of protons by the second-order Fermi process acting on randomly scrambled magnetic flux arches above an accretion disc. The accelerated protons collide with thermal protons in the disc, producing degraded energetic protons, charged and neutral pions, and neutrons. The pions ...

We study the stability of disc accretion in the recurrent nova RS Ophiuchi. We construct a one-dimensional time-dependent model of the binary-disc system, which includes viscous heating and radiative cooling and a self-consistent treatment of the binary potential. We find that the extended ...

We explore the role of X-ray photoevaporation in the evolution and dispersal of viscously evolving T Tauri discs. We show that the X-ray photoevaporation wind rates scale linearly with X-ray luminosity, such that the observed range of X-ray luminosities for solar-type T Tauri stars (1028-1031 erg s-1) gives rise to vigorous disc winds with rates of the ...

The main aim in the current survey is to suggest models of the development of structures, such as vortices and spirals, in accretion white dwarf's binaries. On the base of hydrodynamical analytical considerations it is applied numerical methods and simulations. It is suggested in the theoretical model the perturbation's parameters of ...

An approximation theory of the acceleration of particles in low-density shear flows is developed and is applied to a number of astrophysical flows including accretion disks, radial accretion, and convective turbulence. In the disk application, the theory suggests a mechanism by which the bulk of the accretion power may be converted to ...

TWO�PHASE PAIR CORONA MODEL FOR AGN: PHYSICAL MODELLING AND DIAGNOSTICS Juri Poutanen 1;2 , Roland of the two�phase accretion disc�corona models for active galactic nuclei are compared with ob� servations. We a hemisphere�corona. Keywords: accretion, ...

This study inspects the light and radial-velocity curves of the eclipsing binary AV Del. In comparison with other studies already done, the study shows that the absolute elements, fundamental orbital and physical parameters of the system can be determined using the Wilson-Devinney code. Using these parameters, the configuration of the system is presented. Then, an accretion ...

We consider the specific case of disc accretion for negligibly low viscosity and infinitely high electric conductivity. The key component in this model is the outflowing magnetized wind from the accretion disc, since this wind effectively carries away angular momentum of the ...

In this paper we derive equations describing the dynamics and stationary configurations of a twisted fully relativistic thin accretion disc around a slowly rotating black hole. We assume that the inclination angle of the disc is small and that the standard relativistic generalization of the ? model of ...

Young low-mass stars are characterized by ejection of collimated outflows and by circumstellar discs which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn remove the excess angular momentum from the ...

Young low-mass stars are characterized by ejection of collimated outflows and by circumstellar discs which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn remove the excess angular momentum from the ...

We present time-dependent models of the remnant accretion discs created during compact object mergers, focusing on the energy available from accretion at late times and the composition of the disc and its outflows. We calculate the dynamics near the outer edge of the disc, ...

Highly nonstationary accretion onto a magnetized neutron star from a surrounding accretion disc is considered. Nonstationary accretion has been considered before in terms of droplets or rain or as a necessary consequence of instabilities in the accretion column flow. Here, the extreme of very ...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without magnetic a field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to ...

The dynamics of an axisymmetric stationary disc of accreting magnetofluid with finite conductivity around a rotating compact object is presented here. Along with the Maxwell equations and the generalized Ohm law, the basic equations governing the motion of a finitely conducting plasma in a curved space-time around a slowly rotating compact object are ...

In this paper, we study the structure of the broad emission-line regions (BLRs) of the well-known double-peaked emitter (an active galactic nucleus with broad double-peaked low-ionization emission lines) 3C 390.3. Besides the best-fitting results for the double-peaked broad optical Balmer lines of 3C 390.3 obtained from the theoretical disc model, we also ...

In this paper, we study the structure of the broad emission-line regions (BLRs) of the well-known double-peaked emitter (an active galactic nucleus with broad double-peaked low-ionization emission lines) 3C 390.3. Besides the best-fitting results for the double-peaked broad optical Balmer lines of 3C 390.3 obtained from the theoretical disc model, we also ...

We report a time-lapse eclipse mapping analysis of B-band time-series of the nova-like variable UU Aqr along a typical stunted outburst in 2002 August. Disc asymmetries rotating in the prograde sense in the eclipse maps are interpreted as a precessing elliptical disc with enhanced emission at periastron. From the disc expansion ...

We present a grid of models of accreting brown dwarf systems with circumstellar discs. The calculations involve a self-consistent solution of both vertical hydrostatic and radiative equilibrium along with a sophisticated treatment of dust sublimation. We have simulated observations of the spectral energy distributions and several ...

Context. Interpretation of the X-ray spectra of X-ray binaries during their hard states requires a hot, optically thin medium. There are several accretion disc models that account for this aspect. However, none is designed to simultaneously explain powerful jets detected during these states. Aims: A new quasi-Keplerian hot ...

Context: .Satellite accretion events have been invoked for mimicking the internal secular evolutionary processes of bulge growth. However, N-body simulations of satellite accretions have paid little attention to the evolution of bulge photometric parameters, to the processes driving this evolution, and to the consistency of this evolution with ...

Accreting millisecond pulsars show significant variability of their pulse profiles, especially at low accretion rates. On the other hand, their X-ray spectra are remarkably similar with not much variability over the course of the outbursts. For the first time, we have discovered that during the 2008 outburst of SAX J1808.4-3658 a major pulse profile change ...

We investigate the properties of circumplanetary discs formed in three-dimensional, self-gravitating radiation hydrodynamical models of gas accretion by protoplanets. We determine disc sizes, scaleheights, and density and temperature profiles for different protoplanet masses, in solar nebulae of differing grain ...

We use a combination of a cosmological N-body simulation of the concordance ? cold dark matter paradigm and a semi-analytic model of galaxy formation to investigate the spin development of central supermassive black holes (BHs) and its relation to the BH host galaxy properties. In order to compute BH spins, we use the ? model of Shakura & Sunyaev and ...

It was recently proposed that metal-rich white dwarfs (WDs) accrete their metals from compact discs of debris found to exist around more than a dozen of them. At the same time, elemental abundances measured in atmospheres of some WDs imply vigorous metal accretion at rates up to 1011 g s-1, far in excess of what can be supplied solely ...

It was recently proposed that metal-rich white dwarfs (WDs) accrete their metals from compact discs of debris found to exist around more than a dozen of them. At the same time, elemental abundances measured in atmospheres of some WDs imply vigorous metal accretion at rates up to 1011 g s-1, far in excess of what can be supplied solely ...

We analyse V-band photometry of the aperiodic variability in T CrB. By applying a simple idea of angular momentum transport in the accretion disc, we have developed a method to simulate the statistical distribution of flare durations with the assumption that the aperiodic variability is produced by turbulent elements in the disc. Both ...

In order to explain the main characteristics of the observed population of extrasolar planets and the giant planets in the Solar system, we need to get a clear understanding of which are the initial conditions that allowed their formation. To this end we develop a semi-analytical model for computing planetary systems formation based on the core instability ...

We study the accretion of modified Chaplygin gas upon different types of black holes. Modified Chaplygin gas is one of the best candidates for a combined model of dark matter and dark energy. In addition, from a field theoretical point of view the modified Chaplygin gas model is equivalent to that of a scalar field having a ...

We argue that the quiescent value of the viscosity parameter of the accretion disc in WZ Sge may be ?cold ~ 0.01, in agreement with estimates of ?cold for other dwarf novae. Assuming the white dwarf in WZ Sge to be magnetic, we show that, in quiescence, material close to the white dwarf can be propelled to larger radii, depleting the inner ...

The galactic black hole candidate Cygnus X-1 is observed to be in one of two X-ray spectral states: either the low/hard (low soft X-ray flux and a flat power-law tail) or high/soft (high blackbody-like soft X-ray flux and a steep power-law tail) state. The physical origin of these two states is unclear. We present here a model of an ionized accretion ...

The central engine that drives gamma ray burst (GRB) explosions may derive from the ability of electrons/positrons and nucleons to tap into the momentum and energy from the large neutrino luminosity emitted by an accretion disc surrounding a black hole. This transfer of momentum and energy occurs due to neutrino absorption, scattering and annihilation, and ...

We present a model of an outburst of the soft X-ray transient A0620-003. A two-dimensional time-dependent smoothed particle hydrodynamics scheme is used to simulate the evolution of the accretion disc through a complete outburst. The scheme includes the full tidal potential of the binary and a simple treatment of the thermal-viscous ...

We present results from modelling of quasi-simultaneous broad-band (radio through X-ray) observations of the Galactic stellar black hole (BH) transient X-ray binary (XRB) systems XTE J1118+480 and GX 339-4 using an irradiated disc + compact jet model. In addition to quantifying the physical properties of the jet, we have developed a ...

Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding

May 13, 1999... observations of quiescent discs to determine the local physical properties of their atmospheres, and resolve their spatial dependence. ...

Gas falling quasi-spherically onto a Schwarzschild black hole can form an inner thin accretion disc if its specific angular momentum, $l$, exceeds $\\lmin\\approx 0.75r_gc$, where $r_g$ is the Schwarzschild radius. The standard disc model assumes $l\\gg\\lmin$. We argue that in many black-hole sources the ...

We find long-term evolution of the ? class from the study of X-ray timing and spectral analysis of the Galactic microquasar GRS 1915+105 during two outburst activities, observed by the proportional counter array (PCA) and the High Energy X-ray Timing Experiment on-board Rossi X-ray Timing Explorer. The class is characterized by unusual periodic-like variation in intensity. With the passage of ...

Quasars are the brilliant cores of remote galaxies, at the hearts of which lie supermassive black holes that can generate enough power to outshine the Sun a trillion times. These mighty power sources are fuelled by interstellar gas, thought to be sucked into the hole from a surrounding 'accretion disc'. A paper in this week's issue of the journal Nature, ...

We introduce a prescription for the luminosity from accreting protostars into smoothed particle hydrodynamics simulation and apply the method to simulations of five primordial minihaloes generated from cosmological initial conditions. We find that accretion luminosity delays fragmentation within the haloes but does not prevent it. In haloes that slowly ...

Cataclysmic variables provide the most accessible view of accretion physics. They are the most numerous accretion powered X-ray sources, and there are thus many relatively bright, nearby examples. Known examples include several bright eclipsing systems that allow a quantitative determination of the accretion geometry. Perhaps most ...

We propose four snap-shot observations on the remarkable NLS1 J1633+4718 with the lowest soft X-ray excess temperature of 32eV. Our goals are to test the blackbody nature of this emission and to obtain high quality X-ray and UV data, which are essential for more quantitative testing of accretion disc models in AGN and, hopefully, ...

Two new elements, the Hybrid Accretion Disk (HAD) model and the Rosat survey of resolved X-ray sources and diffuse background, are combined in an attempt to resolve the long standing problem of the cosmic X-Ray Background (XRB), explaining the diffuse XRB...

We perform hydrodynamical simulations of the accretion of pebbles and rocks on to protoplanets of a few hundred kilometres in radius, including two-way drag force coupling between particles and the protoplanetary disc gas. Particle streams interacting with the gas within the Hill sphere of the protoplanet spiral into a prograde circumplanetary ...

We present two-dimensional hydrodynamical simulations of slowly rotating gas that is under the influence of the gravity of a super massive black hole and is irradiated by a thin UV accretion disc and a spherical X-ray corona. We calculate the accretion luminosity of a system based on the accretion rate which is ...

When gas accretes on to a black hole, at a rate either much less than or much greater than the Eddington rate, it is likely to do so in an `adiabatic' or radiatively inefficient manner. Under fluid (as opposed to magnetohydrodynamic) conditions, the disc should become convective and evolve toward a state of marginal instability. We ...

The standard general relativistic model of a razor-thin accretion disc around a black hole, developed by Novikov & Thorne (NT) in 1973, assumes the shear stress vanishes at the radius of the innermost stable circular orbit (ISCO) and that, outside the ISCO, the shear stress is produced by an effective turbulent viscosity. However, ...

We continue our study of weakly ionized protostellar accretion discs that are threaded by a large-scale magnetic field and power a centrifugally driven wind. It has been argued that there is already evidence in several protostellar systems that such a wind transports a significant fraction of the angular momentum from at least some part of the ...

Accretion onto black holes often proceeds via an accretion disc or a temporary disc-like pattern. Variability features, observed in the light curves of such objects, and theoretical models of accretion flows suggest that accretion ...

Millisecond pulsars are believed to be old pulsars spun up by a surrounding accretion disc. Magnetic fields are thought to play a leading role in this, both by determining the location of the inner edge of the disc and by exerting an additional torque on the star (as a result of the interaction between the stellar magnetic field and ...

In response to major changes in the mass accretion rate within the inner accretion flow, black hole binary transients undergo dramatic evolution in their X-ray timing and spectral behaviour during outbursts. In recent years a paradigm has arisen in which `soft' X-ray states are associated with an inner disc radius at, or very close to, ...

The radial-azimuthal instability of a hot two-temperature accretion disc with advection is analyzed. After obtaining the dispersion equation, we find that advection and viscous force have an influence on the stability of acoustic modes, but not on the stability of thermal and viscous modes. We also find azimuthal perturbations to affect the stability of ...

Abstract. Accretion disc turbulence is investigated in the framework of the shearing box approximation. The turbulence is either driven by the magneto-rotational instability or, in the non-magnetic case, by an explicit and artificial forcing term in the momentum equation. Unlike the magnetic case, where most of the dissipation occurs in the ...

We performed hydrodynamical simulations to investigate the formation and evolution of protostars and circumstellar discs from the pre-stellar cloud. As the initial state, we adopted the molecular cloud core with two non-dimensional parameters representing the thermal and rotational energies. With these parameters, we derived 17 models and calculated the ...

We performed hydrodynamical simulations to investigate the formation and evolution of protostars and circumstellar discs from the pre-stellar cloud. As the initial state, we adopted the molecular cloud core with two non-dimensional parameters representing the thermal and rotational energies. With these parameters, we derived 17 models and calculated the ...

The origin of large scale magnetic fields in astrophysical rotators, and the conversion of gravitational energy into radiation near stars and compact objects via accretion have been subjects of active research for a half century. Magnetohydrodynamic turbulence makes both problems highly nonlinear, so both subjects have benefitted from numerical simulations.However, ...

In this letter we show that the observed gamma -ray luminosity can be produced by an accretion disc around a non-magnetic neutron star or low mass black hole in which the dominant dissipative process in the disc is due to magnetic fields. The shearing mot...

The presence of alpha-viscosity in the atmospheres of accretion discs is investigated. It results in the existence of coronae and/or winds. When discs are illuminated by the central X-ray sources, the mass loss may be a significant fraction of the total m...

We have studied the long-term variability of LMC X-3 in optical light curves spanning 6yr, in order to search for optical signatures which could confirm or refute the suggestion that the `modulation' is the result of accretion-rate variability rather than accretion-disc precession. We find that there is no stable period in the optical light curves, that ...

Young close binaries open central gaps in the surrounding circumbinary accretion disc, but the stellar components may still gain mass from gas crossing through the gap. It is not well understood how this process operates and how the stellar components are affected by such inflows. Our main goal is to investigate how gas accretion takes ...

Time-resolved eclipse spectroscopy of the nova-like variable UX UMa obtained with the HST/FOS on 1994 August and November is analysed with eclipse mapping techniques to produce spatially resolved spectra of its accretion disc and gas stream as a function of distance from the disc centre. The inner accretion ...

Dark matter direct detection experiments need to know the local phase space density of dark matter fdm(r,v,t) in order to derive dark matter particle properties. To date, calculations for fdm(r,v,t) have been based on simulations that model the dark matter alone. Here we include the influence of the baryonic matter. We find that a star/gas disc at high ...

We have investigated how envelope pollution by icy planetesimals affects the critical core mass for gas giant formation and the gas accretion time-scales. In the core-accretion model, runaway gas accretion is triggered after a core reaches a critical core mass. All the previous studies on the ...

We have investigated how envelope pollution by icy planetesimals affects the critical core mass for gas giant formation and the gas accretion time-scales. In the core-accretion model, runaway gas accretion is triggered after a core reaches a critical core mass. All the previous studies on the ...

Protostars �0.1 Myr old are heavily obscured, but their circumstellar dust discs can be studied by millimetre interferometry that resolves out the obscuring envelope. Consistent estimates are made for the disc masses of Class 0 protostars, and these range over 7-660 MJup. A simple grain coagulation model reproduces the mass ...

The present study examines the self-similar evolution of advection-dominated accretion flow (ADAF) in the presence of a toroidal magnetic field. In this research, it was assumed that angular momentum transport is due to viscous turbulence and the ?-prescription was used for the kinematic coefficient of viscosity. The flow does not have a good cooling efficiency and so a ...

We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and accretion ...

We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and accretion ...

Accretion disc turbulence is investigated in the framework of the shearing box approximation. The turbulence is either driven by the magneto-rotational instability or, in the non-magnetic case, by an explicit and artificial forcing term in the momentum equation. Unlike the magnetic case, where most of the dissipation occurs in the disc ...

We show that the combination of a weak magnetic propeller and accretion disc resonances can effectively halt accretion in short-period cataclysmic variables (CVs) for large fractions of their lifetimes. This may help to explain the discrepancy between the observed and predicted orbital period distributions of CVs at short periods. ...

A steady-state model of the accretion disk around a white dwarf, including the boundary layer and the hot spot, has been constructed. Calculated distributions of radiation are compared with soft X-ray, ultraviolet, visual, and infrared observations of SS Cyg during outburst as well as with ultraviolet measurements of V 603 Aql and RR Pic. The results ...

General relativistic numerical simulations of magnetized accretion flows around black holes show a disordered electromagnetic structure in the disc and corona and a highly relativistic, Poynting-dominated funnel jet in the polar regions. The polar jet is nearly consistent with the stationary paraboloidal Blandford-Znajek model of an ...

Primordial matter mainly consists of hydrogen and helium with a small amount of lithium. Taking into account contributions to the opacity from hydrogen and helium only has been assumed to be sufficient so far. Lithium, however, influences the opacity indirectly through a change in chemical equilibrium due to absorption of atomic lithium and lithium hydride. The differences reach two orders of ...

We extract all the XMM-Newton European Photon Imaging Camera (EPIC) pn burst mode spectra of GX 339-4, together with simultaneous/contemporaneous RXTE data. These include three disc-dominated and two soft intermediate spectra, and the combination of broad bandpass/moderate spectral resolution gives some of the best data on these bright soft states in black hole binaries. The ...

We extract all the XMM-Newton European Photon Imaging Camera (EPIC) pn burst mode spectra of GX 339-4, together with simultaneous/contemporaneous RXTE data. These include three disc-dominated and two soft intermediate spectra, and the combination of broad bandpass/moderate spectral resolution gives some of the best data on these bright soft states in black hole binaries. The ...

We formulate and solve the equations governing the transonic behaviour of a general relativistic black-hole accretion disc with non-zero advection velocity. We demonstrate that a relativistic Rankine Hugoniot shock may form leading to the formation of accretion powered outflow. We show that the critical points of transonic ...

The accretion disc eclipse mapping method is an astrotomographic inversion technique that makes use of the information contained in eclipse light curves to probe the structure, the spectrum and the time evolution of accretion discs in cataclysmic variables. This paper presents examples of eclipse mapping results ...

We track the coevolution of supermassive black holes (SMBHs) and their host galaxies through cosmic time. The calculation is embedded in the GALFORM semi-analytic model which simulates the formation and evolution of galaxies in a cold dark matter (CDM) universe. The black hole (BH) and galaxy formation models are coupled: during the evolution of the host ...

In the hierarchical galaxy formation model, today's galaxies are the product of frequent galaxy merging, triggering the activity of active galactic nuclei and forming a supermassive black hole binary. A binary may become stalling at the parsec scale and is expected to be detected in nearby normal galaxies, which is inconsistent with observations. In this paper, we investigate ...

The magnetic field of the classical T Tauri star V2129 Oph can be modelled approximately by superposing slightly tilted dipole and octupole moments, with polar magnetic field strengths of 0.35 and 1.2 kG, respectively, as observed by Donati et al. Here we construct a numerical model of V2129 Oph incorporating this result and simulate ...

The X-ray spectra of Galactic binary systems dominated by a quasi-thermal component (disc dominated or high/soft state) are well described by a standard Shakura-Sunyaev disc structure down to the last stable orbit around the black hole. This is not the case in the very high (or steep power-law) state, where the X-ray spectra show both a strong ...

We present the spectral analysis of three Suzaku XIS observations of 3C 111 requested to monitor the predicted variability of its ultra-fast outflow on ~7 days time-scales. We detect an ionized iron emission line in the first observation and a blue-shifted absorption line in the second, when the flux is ~30% higher. The location of the material is constrained at <0.006pc from the variability. ...

We study a combined model of black hole-accretion disc-magnetosphere-jet symbiosis, applicable for supermassive black holes. We quantify the mass and spin evolution and analyse how the limiting value of the spin parameter and the conversion efficiency of accreted mass into radiation depend on the interplay of the ...

We study a combined model of black hole-accretion disc-magnetosphere-jet symbiosis, applicable for supermassive black holes. We quantify the mass and spin evolution and analyse how the limiting value of the spin parameter and the conversion efficiency of accreted mass into radiation depend on the interplay of the ...

The capabilities of XMM-Newton have been fully exploited to detect a broadened iron K? emission line from the 2.5 ms Accreting Millisecond Pulsar, SAX J1808.4-3658. The energy of the transition is compatible with fluorescence from neutral/lowly ionized iron. The observed large width (FWHM more than 1 keV) can be explained through Doppler and relativistic broadening from the ...

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 ...

We analyzed the eclipse light curve of the nova-like star RW Tri in its low luminosity state. During approximately 150 days, RW Tri was about one magnitude fainter than in its usual state. Our eclipse map shows that the brightness temperature in the disc ranges from 19000 K near the white dwarf to 8700 at the disc edge. For the inner parts of ...

We present in this proceeding some aspects of a model that should explain the spectral state changes observed in microquasars. In this model, ejection is assumed to take place only in the innermost disc region where a large scale magnetic field is anchored. Then, in opposite to conventional ADAF models, the ...

The X-ray spectra of accretion discs of eight stellar mass black holes have been analysed to date using the thermal continuum-fitting method, and the spectral fits have been used to estimate the spin parameters of the black holes. However, the underlying model used in this method of estimating spin is the general relativistic ...

Magnetic fields are a distinctive feature of accretion disc plasmas around compact objects (i.e., black holes and neutron stars) and they play a decisive role in their dynamical evolution. A fundamental theoretical question related with this concerns investigation of the so-called gravitational MHD dynamo effect, responsible for the self-generation of ...

FU Orionis (FUOR) outbursts are major optical brightening episodes in low-mass protostars that evidently correspond to rapid mass accretion events in the innermost region of a protostellar disc. The outbursts are accompanied by strong outflows, with the inferred mass outflow rates reaching �10 per cent of the mass inflow rates. Shu et al. proposed that ...

FU Orionis (FUOR) outbursts are major optical brightening episodes in low-mass protostars that evidently correspond to rapid mass accretion events in the innermost region of a protostellar disc. The outbursts are accompanied by strong outflows, with the inferred mass outflow rates reaching �10 per cent of the mass inflow rates. Shu et al. proposed that ...

A small fraction of core-collapse supernovae (SNe) show evidence that the outgoing blast wave has encountered a substantial mass ~1-10Msolar of circumstellar matter (CSM) at radii ~102-103 au, much more than can nominally be explained by pre-explosion stellar winds. In extreme cases, this interaction may power the most luminous, optically energetic SNe yet discovered. Interpretations for the ...

We study the mass flow rate through a disc resulting from a varying mass-supply rate. Variable mass-supply rate occurs, for example, during disc state transitions, and in interacting eccentric binaries. It is, however, damped by the viscosity of the disc. Here, we calculate this damping in detail. We derive an analytical description of ...

We briefly summarise the observational properties of ultra-compact binaries called AM CVn stars. We analyse their outbursts originating from the thermal-viscous instability in helium accretion disc. We present our preliminary results in applying the model of Dwarf Novae outbursts to helium discs. We can calculate ...

Relativistic spectral lines from the accretion disc of a neutron star low-mass X-ray binary can be modelled to infer the disc inner edge radius. A small value of this radius tentatively implies that the disc terminates either at the neutron star hard surface, or at the innermost stable circular ...

Relativistic spectral lines from the accretion disc of a neutron star low-mass X-ray binary can be modelled to infer the disc inner edge radius. A small value of this radius tentatively implies that the disc terminates either at the neutron star hard surface, or at the innermost stable circular ...

The evolution of the magnetic field of an accreting magnetic white dwarf with an initially dipolar field at the surface has been studied for non-spherical accretion under simplifying assumptions. Accretion on to the polar regions tends to advect the field toward the stellar equator which is then buried. This tendency is countered by ...

We present multidimensional non-local thermodynamic equilibrium radiative transfer models of hydrogen and helium line profiles formed in the accretion flows and the outflows near the star-disc interaction regions of classical T Tauri stars (CTTSs). The statistical equilibrium calculations, performed under the assumption of the Sobolev ...

We present multidimensional non-local thermodynamic equilibrium radiative transfer models of hydrogen and helium line profiles formed in the accretion flows and the outflows near the star-disc interaction regions of classical T Tauri stars (CTTSs). The statistical equilibrium calculations, performed under the assumption of the Sobolev ...

We report results from calculations investigating stationary magnetic field configurations in accretion discs around magnetised neutron stars. Our strategy is to start with a very simple model and then progressively improve it, providing complementary insight into results obtained with large numerical simulations. In our first ...

Stellar mass black hole X-ray binaries exhibit X-ray spectral states which also have distinct and characteristic temporal properties. These states are believed to correspond to different accretion disc geometries. We present analysis of two XMM-Newton observations of the ultra-luminous X-ray source (ULX)NGC1313 X-1, which reveal that the system was in two ...

The observations show that less massive the galaxies are, the higher on average is their specific star formation rates (SSFR = SFR/Ms, Ms is the stellar mass). Such a trend, called the 'SSFR downsizing' (SSFR-DS) phenomenon, is seen for local and high-z (back to z~1-2) galaxy samples. We use observational data related only to disc galaxies and explore the average SSFR change ...

We studied the disc emission component hidden in the single-peaked broad emission lines (BELs) of active galactic nuclei using a two-component model. We assumed that the broad lines are formed in an accretion disc plus a surrounding non-disc region, with isotropic cloud velocities. To compare ...

A possible accretion model associated with the ionization instability of quasar disks is proposed to

A model of the accumulation process of a satellite about an accreting planet is proposed in order to

We use a global magnetohydrodynamic simulation of a geometrically thin accretion disc to investigate the locality and detailed structure of turbulence driven by the magnetorotational instability (MRI). The model disc has an aspect ratio H/R? 0.07, and is computed using a higher order Godunov magnetohydrodynamics ...

We use a global magnetohydrodynamic simulation of a geometrically thin accretion disc to investigate the locality and detailed structure of turbulence driven by the magnetorotational instability (MRI). The model disc has an aspect ratio H/R? 0.07, and is computed using a higher order Godunov magnetohydrodynamics ...

We analyse the non-linear, three-dimensional response of a gaseous, viscous protoplanetary disc to the presence of a planet of mass ranging from 1 Earth mass (1 M?) to 1 Jupiter mass (1 MJ) by using the ZEUS hydrodynamics code. We determine the gas flow pattern, and the accretion and migration rates of the planet. The planet is assumed to be in a fixed ...

The discovery of planets around other stars has revealed that planet formation is ubiquitous. However, the mechanisms determining planet formation are not (yet) well-understood. Primordial protoplanetary discs consist 99% out of gas, and only 1% out of dust. With time, those discs are believed to evolve from a flaring geometry into a flat geometry, as the ...

We report results from radiation hydrodynamical simulations of the collapse of molecular cloud cores to form protostars. The calculations follow the formation and evolution of the first hydrostatic core/disc, the collapse to form a stellar core, and effect of stellar core formation on the surrounding disc and envelope. Past barotropic calculations have ...

For more than a decade, the so-called shearing box model has been used to study the fundamental local dynamics of accretion discs. This approach has proved to be very useful because it allows high resolution and long term studies to be carried out, studies that would not be possible for a global disc. Localised ...

Magnetohydrodynamic models of collimated outflows produced by accretion discs around compact objects can be used for interpreting the phenomenology of active astrophysical objects as young stellar objects, microquasars, X-ray binaries, gamma-ray bursts, extended radio galaxies and active galactic nuclei. In the present work, we discuss ...

Context. A large fraction of stars, including young T Tauri stars, are observed to be members of binary or multiple systems. During the early stages of evolution when the individual binary stars are surrounded by a gaseous and dusty disc, the binary orbit plane and disc midplane may be mutually inclined. For the relatively thick protostellar ...

Hyper-accretion discs around black holes emit copious neutrinos and anti-neutrinos. A fraction of the emitted neutrinos convert to electron-positron plasma above the disc through the annihilation reaction $\

thin accretion discs boundary layms are presented for classical '1'l'auri stars, for various values of M* (0.8, l. OMO), R* (1 .6, '2.15, 4.3}~) and M ...

Semi-analytic models of self-gravitating discs often approximate the angular momentum transport generated by the gravitational instability using the phenomenology of viscosity. This allows the employment of the standard viscous evolution equations, and gives promising results. It is, however, still not clear when such an approximation is appropriate. This ...

Young stellar systems are known to undergo outbursts, where the star experiences an increased accretion rate, and the system's luminosity increases accordingly. The archetype is the FU Orionis (FU Ori) outburst, where the accretion rate can increase by three orders of magnitude (and the brightness of the system by five magnitudes). The cause appears to be ...

Angular momentum of an accreting black hole can be determined by careful spectroscopy of the emission and absorption features produced in the inner regions of an accretion disc. We discuss the method employing the relativistic line profiles of iron in the X-ray domain, where the emergent spectrum is blurred by general relativistic ...

The activity of active galaxies may be triggered by the merging of galaxies, and present-day galaxies are probably the product of successive minor mergers. The frequent galactic mergers at high redshift imply that active galaxies harbour supermassive unequal-mass binary black holes at their centre at least once during their lifetime. The secondary black hole interacts and becomes coplanar with the ...

Models of accretion discs and their associated outflows often incorporate assumptions of axisymmetry and symmetry across the disc plane. However, for turbulent discs these symmetries only apply to averaged quantities and do not apply locally. The local asymmetries can induce local imbalances in ...

An outburst of the accreting X-ray millisecond pulsar SAX J1808.4-3658 in 2002 October-November was followed by the Rossi X-ray Timing Explorer for more than a month. A detailed analysis of this unprecedented data set is presented. For the first time, we demonstrate how the area covered by the hotspot at the neutron star surface is decreasing in the course of the outburst ...

In this paper we discuss the spin equilibrium of accreting neutron stars in low-mass X-ray binaries (LMXBs). We demonstrate that, when combined with a naive spin-up torque, the observed data lead to inferred magnetic fields which are at variance with those of Galactic millisecond radio pulsars. This indicates the need for either additional spin-down torques (e.g. gravitational ...

Emission-Line Variability and Implications for Reverberation Mapping: Ballantyne , D. R., .... Impact of reverberation in flared accretion discs on temporal ...

We present high-speed spectroscopic observations of the intermediate polar (IP) DQ Herculis. Doppler tomography of two HeI lines reveals a spiral density structure in the accretion disc around the white dwarf (WD) primary. The spirals look very similar to the spirals seen in dwarf novae during outburst. DQ Her is the first well-established IP in which ...

ESO Very Large Telescope observations revealed on a high confidence level the presence of a variable magnetic field in the optical component (O-supergiant) and in the outer parts of the accreting structure around BH. This result creates observational basis for models of magnetic disc accretion on BH in X-ray ...

Latest observational data provides evidence that the emissions from Sgr A* originate from an accretion disc within ten gravitational radii of the dynamical centre of Milky Way. We investigate the physical processes responsible for the variable observed emissions from the compact radio source Sgr A*. We study the evolution of the variable emission region ...

X-ray observations of Seyfert 1 galaxies offer the unique possibility of observing spectral variability on timescales comparable to the dynamical time of the inner accretion flow. They typically show highly variable lightcurves, with Power Density Spectra characterized by `red noise' and a break at low frequencies. Time resolved spectral analysis have established that spectral ...

We performed a systematic analysis of all INTEGRAL observations from 2003 to 2009 of 14 supergiant fast X-ray transients (SFXTs), implying a net exposure time of about 30 Ms. For each source we obtained light curves and spectra (3-100 keV), discovering several new outbursts. We discuss the X-ray behaviour of SFXTs emerging from our analysis in the framework of the clumpy wind ...

We numerically model fragmentation of a gravitationally unstable gaseous disc under conditions that may be appropriate for the formation of the young massive stars observed in the central parsec of our Galaxy. In this study, we adopt a simple prescription with a locally constant cooling time. We find that, for cooling times just short enough to induce ...

A simple model is employed, which allows analytical study of the effects of toroidal currents in accretion discs around Schwarzschild black holes. These toroidal currents generate poloidal magnetic fields which alter the orbital behavior of magnetized particles in the zone between the horizon and the disc. As a ...

We present high-speed photometry covering one eclipse of the cataclysmic variable system 1RXS J180834.7+101041. The data are modelled as arising from a close binary system containing a low-mass stars filling its Roche lobe plus a white dwarf with an accretion disc. We find an orbital inclination of 77.07 +/- 0.47 degrees and a mass ...

Super-high energy (?1020eV) cosmic rays could be accelerated in current-carrying beams associated with black-hole accretion discs in galactic nuclei. The current system might resemble an electrical circuit with a voltage source (black hole and accretion disc) coupled to a load (cosmic-ray beam) and a low impedance ...

In order to investigate whether massive stars form similarly to their low-mass counterparts, we have used the standard envelope plus disc geometry successfully applied to low-mass protostars to model the near-IR to submillimetre spectral energy distribution (SED) and several mid-IR images of the embedded massive star IRAS 20126+4104. We have used a Monte ...

We study simultaneous X-ray and optical observations of three intermediate polars, EX Hya, V1223 Sgr and TV Col, with the aim of understanding the propagation of matter in their accretion flows. We show that in all cases the power spectra of the flux variability of binary systems in X-ray and optical bands are similar to each other, and the majority of X-ray and optical fluxes ...

T Tauri stars (TTS) are low-mass pre-main-sequence stars that are accreting mass from the surrounding disc. The hotspots detected in some of them are probably heated by the release of gravitational energy in the accretion of the disc material on to the star. In this work we study the UV spectrum of the hotspot ...

The formation of a circumplanetary disc and accretion of angular momentum on to a protoplanetary system are investigated using three-dimensional hydrodynamical simulations. The local region around a protoplanet in a protoplanetary disc is considered with sufficient spatial resolution: the region from outside the Hill sphere to the ...

In this work, the roles of both the inflow kinematic conditions at the inner Lagrangian point L1 as an initial boundary condition and the gas compressibility, physical turbulent viscosity on an accretion disc's dynamics and structure were investigated via simulations of 3D SPH stationary accretion-disc models. ...

Context. The velocity field gradient in the radiative transfer in disc models of cataclysmic variables (CVs) is usually neglected; however, the geometry of the system and the value of Keplerian velocity suggest that it can be important for high inclination angles. Aims: We investigate the influence of the Keplerian velocity gradient on the line formation ...

We report calculations of the evolution, under Reynolds viscosity, of the massive gaseous accretion discs thought to form in the centres of galaxies as a result of major galactic mergers at early epochs. Starting with the formation of such a disc and the postulated existence of a low-mass �seed� black hole, we focus on the mass ...

The spin of a black hole is an important parameter which may be responsible for the properties of the inflow and outflow of the material surrounding the black hole. The broad-band infrared (IR)/optical/ultraviolet (UV) spectrum of the quasar SDSS J094533.99+100950.1 is clearly disc-dominated, with the spectrum peaking in the observed frequency range. Therefore, the ...

We study the eccentricity distribution of a thick-disc sample of stars (defined as those with Vy > 50 km s-1 and 1 < |z|/kpc < 3) observed in the Radial Velocity Experiment (RAVE). We compare this distribution with those obtained in four simulations of galaxy formation taken from the literature as compiled by Sales et al. Each simulation emphasizes different scenarios ...

It is shown that some aspects of the accretion disc physics can be experimentally simulated with the use of an array of properly directed plasma jets created by intense laser beams. For the laser energy of 1 to 3 kJ, one can create a quasi-planar disc with the Reynolds number exceeding 104 and magnetic Reynolds number in the range of ...

Local hydromagnetic simulations of accretion-disc turbulence currently provide the most convincing evidence that the origin of turbulence in discs could be the Balbus-Hawley magnetorotational instability. The main results of such calculations are highlighted with particular emphasis on the generation of large-scale magnetic fields. Comparison with ...

The structure of planetary systems around their host stars depends on their initial formation conditions. Massive planets will likely be formed as a consequence of rapid migration of planetesimals and low-mass cores into specific trapping sites in protoplanetary discs. We present analytical modelling of inhomogeneities in protoplanetary ...

A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed

Accretion in protoplanetary discs is thought to be driven by magnetohydrodynamic (MHD) turbulence via the magnetorotational instability. Recent work has shown that a planetesimal swarm embedded in a fully turbulent disc is subject to strong excitation of the velocity dispersion, leading to collisional destruction of bodies with radii ...

Accretion in protoplanetary discs is thought to be driven by magnetohydrodynamic (MHD) turbulence via the magnetorotational instability. Recent work has shown that a planetesimal swarm embedded in a fully turbulent disc is subject to strong excitation of the velocity dispersion, leading to collisional destruction of bodies with radii ...

One possible scenario for the formation of massive black holes (BHs) in the early Universe is from the direct collapse of primordial gas in atomic-cooling dark matter haloes in which the gas is unable to cool efficiently via molecular transitions. We study the formation of such BHs, as well as the accretion of gas on to these objects and the high energy radiation emitted in ...

The rapid and seemingly random fluctuations in X-ray luminosity of Seyfert galaxies provided early support for the standard model in which Seyferts are powered by a supermassive black hole fed from an accretion disc. However, since EXOSAT there has been little opportunity to advance our understanding of the most rapid X-ray ...

I present work on the accretion onto stellar mass black holes in several scenarios. Due to dynamical friction stellar mass black holes are expected to form high density cusps in the inner parsec of our Galaxy. These compact remnants may be accreting cold dense gas present there, and give rise to potentially observable X-ray emission. I build a simple but ...

We propose a new method to explore the candidate super-Eddington active galactic nuclei (AGNs). We examine the properties of infrared (IR) emission from the inner edge of the dusty torus in AGNs, which are powered by super- or sub-Eddington accretion flows around black holes, by considering the dependence of the polar angle on the radiation flux of ...

It is now established that thermal disc emission and non-thermal jet emission can both play a role at optical/infrared (OIR) wavelengths in X-ray transients. The spectra of the jet and disc components differ, as do their dependence on mass accretion properties. Here we demonstrate that the OIR colour-magnitude diagrams (CMDs) of the ...

It is now established that thermal disc emission and non-thermal jet emission can both play a role at optical/infrared (OIR) wavelengths in X-ray transients. The spectra of the jet and disc components differ, as do their dependence on mass accretion properties. Here we demonstrate that the OIR colour-magnitude diagrams (CMDs) of the ...

The bright ultraluminous X-ray source (ULX), M33 X-8, has been observed several times by XMM-Newton, providing us with a rare opportunity to 'flux bin' the spectral data and search for changes in the average X-ray spectrum with flux level. The aggregated X-ray spectra appear unlike standard sub-Eddington accretion state spectra which, alongside the lack of discernible ...

In order to explain the observed diversity of planetary system architectures and relate this primordial diversity to the initial properties of the discs where they were born, we develop a semi-analytical model for computing planetary system formation. The model is based on the core instability model for the gas ...

We present results from a comprehensive number of relativistic, time-dependent, axisymmetric simulations of the runaway instability of non-constant angular momentum thick discs around black holes. This second paper in the series extends earlier results where only constant angular momentum discs were considered. All relevant aspects of the theory of ...

We present an analysis of high-dispersion and high signal-to-noise ratio spectra of the DAZ white dwarf GALEX J1931+0117. The spectra obtained with the VLT-Kueyen/UV-Visual Echelle Spectrograph show several well-resolved Si II spectral lines enabling a study of pressure effects on line profiles. We observed large Stark shifts in silicon lines in agreement with laboratory measurements. A ...

Jan 29, 2010 ... KY Relativistic Accretion Disk models. A set of models from Dovciak et al. (2004 ) for accretion disk spectra in the strong gravity regime. ...

We consider the basic physical properties of matter forming a thin accretion disc in the static and spherically symmetric space-time metric of the vacuum f(R) modified gravity models. The Lagrangian of the generalized gravity theory is also obtained in a parametric form, and the conditions of the viability of the ...

There is a significant non-linear correlation between the Eddington ratio (Lbol/LEdd) and the Eddington-scaled kinetic power (Lkin/LEdd) of jets in low luminosity active galactic nuclei (AGNs). It is believed that these low luminosity AGNs contain advection-dominated accretion flows (ADAFs). We adopt the ADAF model developed by Li & Cao, in which the ...

We present a systematic analysis of the X-ray spectra of NGC 1313 X-1 and NGC 1313 X-2, using six years of XMM-Newton observations (17 observations). We fitted the continuum with a Comptonization model plus a multicolor blackbody disc, that describes the effects of an accretion disc plus an optically thick corona. ...

Ultraviolet observations of classical T Tauri Stars (cTTSs) have shown that there is a hot (Te? 80 000 K) and dense (ne? 1010 cm-3) component associated with the large-scale jet. This hot component is formed very close to the base of the jet providing fundamental information on the jet formation mechanism. In this series, we have investigated whether this component can be formed in ...

We study the effects of a global magnetic field on viscously rotating and vertically integrated accretion discs around compact objects using a self-similar treatment. We extend Akizuki & Fukue's work by discussing a general magnetic field with three components (r, ?, z) in advection-dominated accretion flows (ADAFs). We also ...

We numerically study the long-term evolution of the accretion disc around the neutron star in a coplanar Be/X-ray binary with a short period and a moderate eccentricity. From three-dimensional smoothed particle hydrodynamics simulations, we find that the disc evolves through three distinct phases, each characterized by different ...

As a formation route for objects such as giant planets and low-mass stars in protostellar discs (as well as stars in AGN discs), theories of self-gravitating disc fragmentation need to be able to predict the initial masses of fragments. We describe a means by which the local Jeans mass inside the spiral structure of a self-gravitating ...

As a formation route for objects such as giant planets and low-mass stars in protostellar discs (as well as stars in AGN discs), theories of self-gravitating disc fragmentation need to be able to predict the initial masses of fragments. We describe a means by which the local Jeans mass inside the spiral structure of a self-gravitating ...

Aims: Bipolarity in proto-planetary and planetary nebulae is associated with events occurring in or around their cores. Past infrared observations have revealed the presence of dusty structures around the cores, many in the form of discs. Characterising those dusty discs provides invaluable constraints on the physical processes that govern the final mass ...

A generic expectation for gas accreted by high-mass haloes is that it is shock-heated to the virial temperature of the halo. In low-mass haloes, or at high redshift, however, the gas cooling rate is sufficiently rapid that an accretion shock is unlikely to form close to the virial radius. Instead, the accretion shock will form at ...

We perform three-dimensional self-gravitating radiative transfer simulations of protoplanet migration in circumstellar discs to explore the impact upon migration of the radial temperature profiles in these discs. We model protoplanets with masses ranging between 10-100 M?, in discs with surface density profiles of ...

We use multiscale smoothed particle hydrodynamic simulations to study the inflow of gas from galactic scales (~10kpc) down to <~ 0.1pc, at which point the gas begins to resemble a traditional, Keplerian accretion disc. The key ingredients of the simulations are gas, stars, black holes (BHs), self-gravity, star formation and stellar feedback (via a ...

Context. In August 2008, the accreting milli-second X-ray pulsar (AMXP), IGR J00291+5934, underwent an outburst lasting ~100 days, the first since its discovery in 2004. Aims: We present data from the 2008 double-peaked outburst of IGR J00291+5934 from Faulkes Telescope North, the Isaac Newton Telescope, the Keck Telescope, PAIRITEL, the Westerbork Synthesis Radio Telescope ...

The spin behaviour of a strongly magnetic star accreting from an internally disrupted disc is considered. The torques are calculated due to the interaction of the star with the disc and the accretion flow, together with the modified structure of the disc. The torques depend on the spin period ...

We model the formation of the Galactic stellar halo via the accretion of satellite galaxies on to a time-dependent semicosmological galactic potential. Our goal is to characterize the substructure left by these accretion events in a close manner to what may be possible with the Gaia mission. We have created a synthetic Gaia solar ...

The collapse of massive stars may result in the formation of accreting black holes in their interiors. The accreting stellar matter may advect substantial magnetic flux on to the black hole and promote the release of its rotational energy via magnetic stresses (the Blandford-Znajek mechanism). In this paper we explore whether this process can explain the ...

Slim accretion discs have a total luminosity of the order L/L(sub E) = m (proportional to) 1, where L(sub E) is the Eddington luminosity and m = M/M(sub c), where M(sub c) is a critical accretion rate, related to the Teddington one. The local stability pr...

We present 3D numerical simulations of the early evolution of long-duration gamma-ray bursts in the collapsar scenario. Starting from the core collapse of a realistic progenitor model, we follow the formation and evolution of a central black hole and centrifugally balanced disc. The dense, hot accretion disc ...

We present a full general relativistic numerical code for estimating the energy-momentum deposition rate (EMDR) from neutrino pair annihilation (?). The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around neutron and quark stars. We calculate the neutrino trajectories by using a ray-tracing algorithm with the general ...

We assess the claim that Ultra-luminous X-ray sources (ULXs) host intermediate-mass black holes (BH) by comparing the cool disc-blackbody model with a range of other models, namelly a more complex physical model based on a power-law component slightly modified at various energies by smeared emission/absorption ...

We present results of angular momentum estimations of two black holes in X-ray novae on the basis of simultaneous fitting of soft X-ray and optical light curves in high/soft state during outbursts. We use the analytic model of viscous evolution of an externally truncated accretion ?-disk. Relativistic effects near Kerr black hole and self-irradiation of ...

We propose to exploit the unique capabilities of it FUSE to monitor variations in the wind-formed spectral lines of 3 luminous, low-inclination, cataclysmic variables (CVs). Our principal goal is to improve our understanding of the dynamics of accretion-disc winds. We have previously used HST to investigate substantial and rapid (sim hours to minutes) variability in our ...

We present optical spectroscopy of the microquasar SS433 covering a significant fraction of a precessional cycle of its jet axis. The components of the prominent stationary H? and H? lines are mainly identified as arising from three emitting regions: (i) a super-Eddington accretion disc wind, in the form of a broad component accounting for most of the mass ...

The stress evolution process is taken into account in the linear stability analysis of standard thin accretion discs. We find that the growth rate of thermally unstable modes can decrease significantly owing to the stress delay, which may help to understand the quasi-periodic variability of GRS 1915+105. We also discuss the possible application of stress ...

An effort to develop a three-dimensional ice accretion modeling method is initiated. This first step

A possible accretion model associated with the ionization instability of quasar disks is proposed to

A common feature of hierarchical galaxy formation models is the process of `inverse' morphological transformation: a bulge dominated galaxy accretes a gas disc, dramatically reducing the system's bulge-to-disc mass ratio. During their formation, present-day galaxies may execute many such cycles across the Hubble ...

It is sometimes suggested that phenomenological power law plus cool disc-blackbody models represent the simplest, most robust interpretation of the X-ray spectra of bright ultraluminous X-ray sources (ULXs); this has been taken as evidence for the presence of intermediate-mass black holes (BHs) (M ~ 103Msolar) in those sources. Here, we assess this claim ...

We have observed with XMM-Newton four radiatively efficient active type 1 galaxies with black hole masses <106Msolar, selected optically from the Sloan Digital Sky Survey and previously detected in the ROSAT All Sky Survey. Their X-ray spectra closely resemble those of more luminous Seyferts and quasars, powered by accretion on to much more massive black holes and none of ...

Exosat observations are used to compare the spectral properties of the persistent emission from a number of X-ray burst sources, high-luminosity low-mass X-ray binaries (LMXRB) and galactic black hole candidates with various models for X-ray emission from an accretion disk surrounding a compact object in a binary system. It is shown that only a ...

The analysis of disc formation in this paper is based on the White & Rees model, in which disc galaxies form by the continuous cooling and accretion of gas within a merging hierarchy of dark matter haloes. A simple Kennicutt law of star formation for discs, based on a single-fluid ...