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

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 ...

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 jets: field lines ...

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 ...

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 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 accreting matter. ...

Young Sun-like stars at the beginning of the pre-main sequence (PMS) evolution are surrounded by accretion discs and remnant protostellar envelopes. Photometric and spectroscopic variations of these stars are driven by interactions of the star with the disc. Time scales and wavelength dependence of the variability ...

Young Sun-like stars at the beginning of the pre-main-sequence (PMS) evolution are surrounded by accretion discs and remnant protostellar envelopes. Photometric and spectroscopic variations of these stars are driven by interactions of the star with the disc. Time-scales and wavelength dependence of the variability ...

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 ...

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 ...

From observations collected with the ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope (CFHT) and with the NARVAL spectropolarimeter at the T�lescope Bernard Lyot (TBL), we report the detection of Zeeman signatures on the prototypical classical T Tauri star AA Tau, both in photospheric lines and accretion-powered emission lines. Using time series of ...

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 ...

A range of important astrophysical systems consist of a strongly magnetic star accreting material from a surrounding disc. These include young stars in T Tauri systems, magnetic neutron stars in X-ray binaries and strongly magnetic white dwarfs in some cataclysmic variables. In all these objects, the stellar magnetic field disrupts the ...

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 ...

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 ...

It has been clear for many years now that the process of accretion on to a compact object is largely dominated by magnetic fields. The magnetic field channels the accretion flow onto strongly magnetized stars such as magnetic white dwarfs (cataclysmic variables), and neutron stars (accreting X-ray pulsars). ...

Many compact sources appear to have a luminosity which is a fair fraction of the Eddington one, implying that slim accretion discs should be used in interpretations of e.g. quasi-periodic variability. Adopting a central mass M~1.4 M_solar, the radial instability structure of slim discs is examined in the ...

In a recent work by the first author, we show that accretion discs in binary systems could retrogradely precess by the same physics that causes the Earth to retrogradely precess [i.e. tidal torques by the Moon and the Sun (or a secondary star) on a tilted, spinning, non-spherical Earth (or e.g. a primary star surrounded by an accretion ...

We use the XMM-Newton EPIC-pn instrument in timing mode to extend spectral time-lag studies of hard state black hole X-ray binaries into the soft X-ray band. We show that variations of the disc blackbody emission substantially lead variations in the power-law emission, by tenths of a second on variability time-scales of seconds or longer. The large lags ...

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 ...

We study the radial ionization structure at the surface of an X-ray illuminated accretion disc. We plot the expected iron K? line energy as a function of the Eddington ratio and of the distance of the emitting matter from the central source, for a non-rotating and a maximally rotating black hole. We compare the predicted disc line ...

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 ...

We assembled a sample of broad-line and narrow-line active galactic nuclei (AGNs) observed by ASCA, the excess variances of which have been determined. The central black hole masses in this sample can be obtained from the reverberation mapping method and the width of the H? emission line. Using the black hole masses and the bolometric luminosity, the Eddington ratio (the ratio of the ionizing ...

Astrophysical jets seem to occur in nearly all types of accreting objects, from supermassive black holes to young stellar objects. On the basis of x-ray binaries, a unified scenario describing the disc/jet coupling has evolved and been extended to many accreting objects. The only major exceptions are thought to be cataclysmic ...

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 ...

Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding

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 ...

We study numerically the interaction of the infalling gas stream and the rim of the accretion disc in cataclysmic variables. The simulations were performed with a smoothed particle hydrodynamics scheme with high spatial resolution. Parameters of the systems AM CVn, OY Car, DQ Her, U Gem and IP Peg were used for the simulations. The ...

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

In Montgomery (2009a), we show that accretion discs in binary systems could retrogradely precess by tidal torques like the Moon and the Sun on a tilted, spinning, non-spherical Earth. In addition, we show that the state of matter and the geometrical shape of the celestial object could significantly affect the precessional value. For example, a Cataclysmic ...

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 ...

Hyper-accreting discs occur in compact-object mergers and in collapsed cores of massive stars. They power the central engine of ?-ray bursts in most scenarios. We calculate the microphysical dissipation (the viscosity and resistivity) of plasma in these discs, and discuss the implications for their global structure and evolution. At ...

XMM-Newton X-ray spectra of the hard state black hole X-ray binaries (BHXRBs) SWIFTJ1753.5-0127 and GX339-4 show evidence for accretion disc blackbody emission, in addition to hard power laws. The soft and hard band power spectral densities (PSDs) of these sources demonstrate variability over a wide range of time-scales. However, on ...

We present simulations of collapsing 100 M&sun; mass cores in the context of massive star formation. The effect of variable initial rotational and magnetic energies on the formation of massive stars is studied in detail. We focus on accretion rates and on the question under which conditions massive Keplerian discs can form in the ...

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 Astrophysics: ...

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 ...

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 ...

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 ...

We have explored spectral line profiles due to spiral patterns in accretion discs around black holes. A parametrization was employed for the shape and emissivity of spiral waves, which can be produced by non-axisymmetric perturbations affecting the disc density and ionization structure. The effects of the light-travel time, energy ...

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 ...

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 Disc Outbursts: A New ...

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 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 ...

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 ...

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 ...

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...

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 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 ...

The properties of accretion discs around stars and brown dwarfs in the ?Ori cluster (age 3Myr) are studied based on near-infrared (IR) time series photometry supported by mid-IR spectral energy distributions (SEDs). We monitor ~30 young low-mass sources over eight nights in the J and K band using the duPont telescope at Las Campanas. We find three objects ...

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 ...

Discoseismic c modes in accretion discs have been invoked to explain low-frequency variabilities observed in black hole X-ray binaries. These modes are trapped in the innermost region of the disc and have frequencies much lower than the rotation frequency at the disc inner radius. We show that ...

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 momentum at the rate ...

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 ...

Wind flows and collimated jets are believed to be a feature of a range of disc accreting systems. These include active galactic nuclei, T Tauri stars, X-ray binaries and cataclysmic variables. The observed collimation implies large-scale magnetic fields and it is known that dipole-symmetry fields of sufficient strength can channel wind ...

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 form of outflow is ...

We propose a ToO observation of a transient black-hole candidate, either known or unknown, during its transition from hard to soft state. This transition, which takes place at high flux levels, encompasses marked changes in the properties of the accretion flow and it includes the time at which the ejection of an accelerating relativistic jet stops abruptly. The study of the ...

break is likely to be variable in time from blue (optical) wavelengths to several microns the transition from optically-thick to thin jet emission; based on previous broad-band photometry, this break to the environments of the primary compact objects, including an optically-thick accretion disc, a diffuse hot coronal

Infrared and optical light curves of the cataclysmic variables UX UMa and U Gem are presented. The curves for Ux UMa can be well fitted by the eclipse of an optically thick steady-state accretion disc. In U Gem the infrared curves are dominated by ellipsoidal variations of the secondary star.

We observed the new X-ray transient and black hole candidate XTE J1652-453 simultaneously with XMM-Newton and the Rossi X-ray Timing Explorer (RXTE). The observation was done during the decay of the 2009 outburst, when XTE J1652-453 was in the hard-intermediate state. The spectrum shows a strong and broad Fe emission line with an equivalent width of �450 eV. The profile is consistent with that ...

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 ...

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 accretion energy can be efficiently converted in ...

Located at the centre of our Galaxy is Sgr A*, a 3 million Msun super-massive black hole (SMBH). Sgr A* is hundreds of times closer than any other known SMBH, and as such it is an ideal object to study accretion physics. Recent observations have revealed the presence of dozens of young mass-losing stars. The winds from these stars provide in principle enough material to ...

We present a time-variability study of the uV resonance lines Nv 1240, Si iv 1397 and C iv 1549 in the dwarf novae AH Her and MU Cen and the nova-like variable QU Car. The main findings are as follows. (i)Virtually no variation can be seen in our data for MU Cen. (ii) AH Her shows velocity shifting of its resonance lines, with semi-amplitudes ranging from ...

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 the tidal forces of ...

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 ...

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 ...

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 ...

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 model ...

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 ...

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) ...

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 ...

DENIS-P J0041353-562112 is a brown dwarf, with a spectral type of M7.5, which may be younger than 20 Myr. On the basis of its H? emission-line asymmetry, it has been suggested that the object is accreting material. If it is accreting, it is expected to rotate slowly. This paper reports on several photometric monitoring runs in the RC and IC bands, designed ...

We present the root mean square (rms)-intensity diagram for black hole transients. Using observations taken with the Rossi X-ray Timing Explorer, we study the relation between the rms amplitude of the variability and the net count rate during the 2002, 2004 and 2007 outbursts of the black hole X-ray binary GX 339-4. We find that the rms-flux relation previously observed during ...

A new Monte Carlo algorithm for calculating time-dependent radiative transfer under the assumption of local thermodynamic equilibrium is presented. Unlike flux-limited diffusion, the method is polychromatic, includes scattering, and is able to treat the optically-thick and free-streaming regimes simultaneously. The algorithm is tested on a variety of 1D and 2D problems, and good agreement with ...

A new Monte Carlo algorithm for calculating time-dependent radiative transfer under the assumption of local thermodynamic equilibrium is presented. Unlike flux-limited diffusion, the method is polychromatic, includes scattering, and is able to treat the optically-thick and free-streaming regimes simultaneously. The algorithm is tested on a variety of 1D and 2D problems, and good agreement with ...

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 - based on the ...

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 ...

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. We checked the ...

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 ...

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 wind with a 'thick ...

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 ...

Exosat observations of Mkn 335 reveal a hard power-law spectrum above about 1 keV, typical for Seyfert 1 galaxies, but with unusually strong variability on time-scales of about 1-2 hr. In addition, an intense soft X-ray component is found to dominate the overall spectrum of Mkn 335 below about 0.6 keV. Both soft and hard components increased in strength by a factor about 6 ...

As a continuation of our previous studies in 2007 and 2008, new photometric observations of the T Tauri star TW Hya obtained by the MOST satellite and the All Sky Automated Survey (ASAS) project over 40 d in 2009 with temporal resolution of 0.2 d are presented. A wavelet analysis of the combined MOST-ASAS data provides a rich picture of coherent, intermittent, variable-period ...

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 ...

We present the preliminary results of two Gemini campaigns to constrain the mass of the black hole in an ultraluminous X-ray source (ULX) via optical spectroscopy. Pilot studies of the optical counterparts of a number of ULXs revealed two candidates for further detailed study, based on the presence of a broad He II 4686 � emission line. A sequence of 10 long-slit spectra were obtained for each ...

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 ...

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 ...

Accreting black holes and neutron stars in their hard (low) state show not only very similar X/?-ray spectra but also that the behavior of their light curves is quite similar which can be quantified as having similar power-density spectra and Fourier-frequency-dependent time/phase lags. Taken together this argues for a common mechanism of the X/?-ray production in these ...

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 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 accretion ...

In this study, a spectral analysis of the dwarf nova WX Hyi (which is a Cataclysmic Variables (CV)) is presented. The system was observed during the normal ourburst with the XMM-Newton observatory. X-ray bolometric flux value (EX<=12 keV) is estimated to be ~2.98�10-12 erg cm-2 s-1 and X-ray luminosity LX = 5�1031 erg/s. Elemental abundance was founded 3 factor of solar ...

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 ...

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 produce gamma-rays by ...

We present the long-term near-IR light curves for two nearby active galactic nuclei (AGN), NGC 3783 and MR 2251-178. The near-IR data are complemented by optical photometry obtained over the same period of time. The light curves in all bands are highly variable and good correlations can be seen between optical and near-IR variations. A cross-correlation analysis for NGC 3783 ...

We study the evolution of gravitationally recoiled supermassive black holes (BHs) in massive gas-rich galaxies by means of high-resolution hydrodynamical simulations. We find that the presence of a massive gaseous disc allows recoiled BHs to return to the centre on a much shorter time-scale than for purely stellar discs. Also, BH ...

Black hole XRB X-ray variability contains information about the accretion and emission mechanisms in strong gravity, but to unlock this information and understand the very rich phenomenology of X-ray timing properties (band-limited noise, QPOs, low-frequency noise), we need to understand the origin of the variations. For many years it has been assumed that ...

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, and its mass ...

We report here results of spectropolarimetric observations of the ?8 Myr classical T Tauri star (cTTS) TW Hya carried out with ESPaDOnS at the Canada-France-Hawaii Telescope in the framework of the 'Magnetic Protostars and Planets' programme, and obtained at two different epochs (2008 March and 2010 March). Obvious Zeeman signatures are detected at all times, both in photospheric lines and in ...

The coupling between accretion processes and ejection mechanisms in accreting black holes in binary systems can be investigated by empirical relations between the X-ray/radio and X-ray/optical-infrared luminosities. These correlations are valid over several orders of magnitude and were initially thought to be universal. However, recently, many black hole ...

Aims.We present a photometric study of the deeply eclipsing SW Sex-type nova-like cataclysmic variable star BH Lyn. Methods: .Time-resolved V-band CCD photometry was obtained for seven nights between 1999 and 2004. Results: .We determined 11 new eclipse timings of BH Lyn and derived a refined orbital ephemeris with an orbital period of 0.155875577(14) �. During the ...

Negative superhumps in cataclysmic variable systems result when the accretion disc is tilted with respect to the orbital plane. The line of nodes of the tilted disc precesses slowly in the retrograde direction, resulting in a photometric signal with a period slightly less than the orbital period. We use the method ...

Optically violent variable quasars and BL Lac objects, which form a subclass of active galactic nuclei are termed as Blazars. Blazars show high degree variation in their flux and polarization in a relatively shorter period of time. They are strong radio sources with a non-stellar continuum. Most of the BL Lac objects do not show any emission lines though in some cases very ...

We extend the existing semi-analytic models of galaxy formation to track atomic and molecular gas in disc galaxies. Simple recipes for processes such as cooling, star formation, supernova feedback and chemical enrichment of the stars and gas are grafted on to dark matter halo merger trees derived from the Millennium Simulation. Each galactic disc is ...

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 ...

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 ...

In this paper we analyze the behavior of the unusual dwarf nova EM Cyg using the data obtained in April-October, 2007, at the Vyhorlat observatory (Slovak Republic) and in September, 2006, at the Crimean Astrophysical Observatory (Ukraine). During our observations, EM Cyg has shown outbursts in every 15-40 days. Because on the light curves of EM Cyg a partial eclipse of the ...

We discuss transportation and redistribution of energy and angular momentum in the magnetic connection (MC) process and Blandford-Payne (BP) process. MC results in readjusting the interior viscous torque, and its effects are operative not only in but also beyond the MC region. The BP process is invoked to transfer the �excessive� angular momentum from an accretion ...

Bounds are placed on the growth rates of dynamical instability in shear flows in accretion discs and tori. Ft is shown that the critical layer lies in the flow even when the boundaries are free for flows in accretion discs, cylinders and isentropic, constant angular momentum tori (for which the relativistic effects ...

Gravitational instability plays an important role in driving gas accretion in massive protostellar discs. Particularly strong is the global gravitational instability which arises when the disc mass is of order 0.1 of the mass of the central star and has a characteristic spatial scale much greater than the disc's ...

The influence of accretion disk instabilities on the UV fluxes of Seyfert 1 galaxies was studied. The observed characteristic timescales of variability are consistent with the interpretation that most of the UV radiation originates in an accretion disk, a...

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 ...

The broadened iron lines observed from accreting compact objects are most easily interpreted in terms of reflection onto the accretion disc of the hard X-ray photons emitted by the central source. In this context, such a broadness is due to the relativistic motion of the reflecting plasma, in the deep gravitational well of the compact ...

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 ...

... Note that the four black discs inside the illusory square appear closer ... motion-related occlusion information as occurs in the accretion and deletion ...

... Additonal cues such as accretion/deletion of texture (not considered here) are ... a perceptually vivid, illusory white square in a field of black discs. ...

May 13, 1999 ... Astro-tomography also has applications over timescales longer or ... optical and IR reprocessing off the accretion disc and companion star. ...

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 ?. This process may drive relativistic jets associated with gamma-ray bursts (GRB) explosions. We calculate the efficiency of energy ...

, Baltimore, MD 21250, USA e-mail: mukai@milkyway.gsfc.nasa.gov Received ???; accepted ??? ABSTRACT Context

turbulent viscocity in accretion discs," Astrophys. Letter & Comm. 34, 383-388 56. Abramowicz, M. A

... onto aluminum or steel discs previously sprayed with silicon oil. A spray mask size of 5 mm ... ...

Radial velocity studies using optical emission lines (from the accretion discs) have been performed for a few TOADs. However, when mass determinations ...

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, which contains the ...

String theory predicts the existence of extremely compact objects spinning faster than Kerr black holes. The spacetime exterior to such superspinars is described by Kerr naked singularity geometry breaking the black-hole limit on the internal angular momentum. We demonstrate that the conversion of Kerr superspinars into a near-extreme black hole due to an accretion ...

We study conditions for magnetocentrifugal jet launching from accretion discs around black holes, whereby large-scale magnetic field lines anchored in the disc may fling tenuous coronal gas outwards. We find that a disc around a critically spinning black hole may centrifugally launch a jet along the rotation axis.

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 ...

Cosmological models predict that large galaxies like the Milky Way formed from the accretion of smaller stellar systems. The most spectacular of these merger events are stellar tidal streams, rivers of stars and dark matter that envelop the discs of spiral galaxies. We present a research project for a collaboration with amateur astronomers in the study of ...

We use quasi-simultaneous near-infrared (near-IR) and optical spectroscopy from four observing runs to study the continuum around 1 micron in 23 well-known broad-emission line active galactic nuclei (AGN). We show that, after correcting the optical spectra for host galaxy light, the AGN continuum around this wavelength can be approximated by the sum of mainly two emission components, a hot dust ...

We use quasi-simultaneous near-infrared (near-IR) and optical spectroscopy from four observing runs to study the continuum around 1 ?m in 23 well-known broad emission line active galactic nuclei (AGN). We show that, after correcting the optical spectra for host galaxy light, the AGN continuum around this wavelength can be approximated by the sum of mainly two emission components, a hot dust ...

We present the frequency-resolved energy spectra (FRS) of the low-mass X-ray binary dipper XB1323-619 during persistent emission in four different frequency bands using an archival XMM-Newton observation. FRS method helps to probe the inner zones of an accretion disc. XB1323-619 is an Atoll source and a type-I burster. We find that the FRS is well ...

The interest in X/ ?-ray Astronomy has grown enormously in the last decades thanks to the ability to send X-ray space missions above the Earth�s atmosphere. There are more than half a million X-ray sources detected and over a hundred missions (past and currently operational) devoted to the study of cosmic X/ ? rays. With the improved sensibilities of the currently active missions new detections ...

We investigate the evolution of a thin viscous disc surrounding a magnetic star, including the spin-down of the star by the magnetic torques it exerts on the disc. The transition from an accreting to a non-accreting state, and the change of the magnetic torque across the corotation radius rc are included in a ...

We investigate the evolution of a thin viscous disc surrounding a magnetic star, including the spin-down of the star by the magnetic torques it exerts on the disc. The transition from an accreting to a non-accreting state, and the change of the magnetic torque across the corotation radius rc are included in a ...

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 the accretion flow, ...

We investigate the influence of the Doppler shift on the radiative transfer through the discs of cataclysmic variables. All the disc structure, the radial and latitude dependence, is included in the radiative transfer. The matter distribution as well as the opacity and emissivity are calculated using the AcDc non-LTE code.

Context: Variability is a common characteristic of pre-main-sequence stars (PMS). Near-IR variability surveys of young stellar objects (YSOs) can probe stellar and circumstellar environments and provide information about the dynamics of the ongoing magnetic and accretion processes. Furthermore, variability can be ...

In this paper we describe the application of the Smoothed Particle Hydrodynamics (SPH) method to the dynamics of protostellar discs, and in particular to the problem of characterising gravitational instabilities in such discs. Initially, we briefly describe the basic features of SPH, a Lagrangian mesh-free method of solving the equations of fluid dynamics ...

High-resolution two-dimensional magnetohydrodynamical simulations have been carried out to investigate the role of continuing infall of clumpy gas as a driver of turbulence in extended H I galactic discs. We have compared the responses of isothermal gas discs with sound speeds 4 and 8 km/s to infalling, condensed clouds. For mass ...

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 relatively small charge separation is required ...

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright ...

SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright ...

The global nonlinear time-dependent evolution of the inertial-acoustic mode instability in accretion

We study spectral variability of 11 ultraluminous X-ray sources (ULX) using archived XMM-Newton and Chandra observations. We use three models to describe the observed spectra: a power law, a multicolour disc (MCD) and a combination of these two models. We find that seven ULXs show a correlation between the luminosity LX and the photon index ?. Furthermore, ...

The observed properties of wind-formed resonance lines in the spectra of nova-like variables and dwarf novae in outburst, are discussed. A method is then presented of calculating inclination- and orbital-phase-dependent resonance line profiles formed in a constant-ionization wind flowing from an accretion disc centre. The particular ...

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 try to find another ...

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 try to find another ...

The X-ray transient source XTE J1818-245 went through an outburst in 2005 that was observed during a multi-wavelength campaign from radio to soft ?-rays. We performed new optical observations with the ESO/NTT telescope at La Silla. The broad-band spectral energy distribution revealed that the outer parts of the accretion disc had to be irradiated by its ...

Dynamo�generated Turbulence and Outflows from Accretion Discs B y Axel Brandenburg Department scale magnetic fields. Comparison with mean�field dynamo theory is made. This theory is then used, in the case of the sun there is turbulent convection which leads to dynamo action. However, the strong shear

... STANDARD SPRAY DRYING WAS USED TO PELLETIZE THE POWDERS FOR THE PRODUCTION OF CERAMIC DISCS BY DOUBLE ACTION ...

We present the results from a monitoring campaign of the Narrow-Line Seyfert 1 galaxy PG 1211+143. The object was monitored with ground-based facilities (UBVRI photometry; from 2007 February to July) and with Swift [X-ray photometry/spectroscopy and ultraviolet (UV)/optical photometry; between 2007 March and May]. We found PG 1211+143 in a historical low X-ray flux state at the beginning of the ...

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 accretion ...

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 broad-band photometric ...

We present Hubble Space Telescope STIS (1160-1700 �) echelle spectra of the cataclysmic variable (CV) star QU Car, at three epochs. In catalogues this binary is classified as a nova-like variable. QU Car was observed three times in time-tag mode for 2300, 2600 and 2600 s, allowing us to study the spectral time evolution on time-scales down to ~10 s. We ...

Magnetic interactions between a protostar and its accretion disc can induce warping in the disc and produce secular changes in the stellar spin direction, so that the spin axis may not always be perpendicular to the disc. This may help to explain the 7� misalignment between the ecliptic plane of the Solar system ...

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 ...

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, accretion discs; galaxies: ...

A newborn star is encircled by a remnant disc of gas and dust. A fraction of the disc coalesces into planets. Another fraction spirals inward and accretes onto the star. Accreting gas not only produces observed ultraviolet radiation, but also drags along embedded planets, helping to explain otherwise mysterious ...

Bursty transport phenomena associated with convective motion present universal statistical characteristics among different physical systems. In this Letter, a stochastic univariate model and the associated probability distribution function for the description of bursty transport in plasma turbulence is presented. The proposed stochastic process recovers the universal distribution of density ...

Bursty transport phenomena associated with convective motion present universal statistical characteristics among different physical systems. In this Letter, a stochastic univariate model and the associated probability distribution function for the description of bursty transport in plasma turbulence is presented. The proposed stochastic process recovers the universal distribution of density ...

We briefly review a few open questions on the interpretation of the X-ray spectra of unobscured Active Galactic Nuclei and their rapid variability. We discuss the so-called soft excess problem, and we present a few recent results which point out the importance of relativistic X-ray reflection from the inner accretion disc in shaping ...

Using the exceptional monitoring capabilities of the MACHO project, the authors present the optical history of the LMC supersoft source RX J0513.9-6951, for a continuous 3-year period. Recurring low states, in which the optical brightness drops by up to a magnitude, are observed at quasi-regular intervals. This provides a crucial insight into the nature of the supersoft sources and, in particular, ...

Bursty transport phenomena associated with convective motion present universal statistical characteristics among different physical systems. In this Letter, a stochastic univariate model and the associated probability distribution function for the description of bursty transport in plasma turbulence is presented. The proposed stochastic process recovers the universal distribution of density ...

We present optical spectroscopy and multicolor photometry of the old nova V 840 Oph. As part of a long-term project to investigate novae with large outburst amplitudes, we identified this nova via its color characteristics and confirmed it spectroscopically. We find V840 Oph to be one of very few cataclysmic variables showing C IV emission at 580/1 nm. The study of the carbon ...

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 ...

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 opacities. We find that ...

We investigate the behaviour of the accretion discs in the outbursts of the low-mass black hole X-ray binaries (BHXRBs), an overview of which we have presented previously. Almost all of the systems in which there are sufficient observations in the most-disc-dominated states show a variation in the disc luminosity ...

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 ...

May 27, 2010 ... The Earth Sciences Division is committed to advancing science and ... Modeling Biomass Consumption Variability in Forest Fires (2007) ...

Mar 14, 2011 ... In many regions, total TWS variability can be approximated as the sum of changes in snow, soil moisture, and ground water. All GLDAS LSMs ...

We present high-resolution 3D smoothed particle hydrodynamics simulations of the formation and evolution of protostellar discs in a turbulent molecular cloud. Using a piecewise polytropic equation of state, we perform two sets of simulations. In both cases, we find that isolated systems undergo a fundamentally different evolution than members of binary or multiple systems. ...

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 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 ...

The spectral energy distribution (SED) of the TT Ari system, which is well known from published IUE and optical photometric observations, was modeled by a steady-state accretion ?-disc around a white dwarf. Parameters of the system were derived from time-resolved optical spectral observations in the bright state that we obtained in Sep. 1998. The radial ...

We present VLT spectroscopy and NTT photometry of the faint cataclysmic binary SDSS J003941.06+005427.5. This object shows triple-peaked H? emission with all three peaks variable in both strength and velocity. We measure an orbital period of 91.395 � 0.093 min from the velocity variations of the wings of the H? emission line. Using the GALEX and SDSS photometry of this ...

Strong magnetic fields modify particle motion in the curved space-time of spinning black holes and change the stability conditions of circular orbits. We study conditions for magnetocentrifugal jet launching from accretion discs around black holes, whereby large-scale black hole lines anchored in the disc may fling tenuous coronal gas ...

The accretion of matter on to intermediate polar white dwarfs (IPWDs) seems to provide attractive conditions for acceleration of particles to high energies in a strongly magnetized turbulent region at the accretion disc inner radius. We consider possible acceleration of electrons and hadrons in such region and investigate their ...

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 ...

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 accretion ...

I calculate the specific angular momentum of mass accreted by a binary system embedded in the dense wind of a mass-losing asymptotic giant branch star. The accretion flow is of the Bondi-Hoyle-Lyttleton type. For most of the space of the relevant parameters the flow is basically an isothermal high Mach number accretion flow. I find ...

The report is a limited research study in order to provide a quick evaluation of the flip-disc variable message board as built by the ADDCO Manufacturing Corporation. The sign was compared to the commonly used bulb-matrix type variable message board for l...

The narrow line Seyfert 1 galaxy REJ 1034+396 is so far unique amongst active galaxies (AGN) in showing a quasi-periodic oscillation (QPO) in its variability power spectrum. There are multiple types of QPO seen in black hole binary (BHB) systems, so we need to identify which BHB QPO corresponds to the one seen in the AGN. A key hint is the `hot disc ...

Over the last few years, several models have been proposed to interpret the widespread soft excess observed in the X-ray spectra of type 1 active galactic nuclei (AGN). In particular, reflection from the photoionized accretion disc blurred by relativistic effects has proven to be successful in reproducing both the spectral shape and the ...

We present a new keplerian accretion disc solution, the so-called Jet Emitting Disc (JED hereafter), which is part of global self-consistent disc-jet MHD structure. In our framework, a large scale, organized vertical magnetic field is threading the JED giving birth, when conditions are met, to stationnary ...

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 disc, ...

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 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 consider the King et al. warped ...

Context: It is known that for solar-mass stars planet formation begins in a circumstellar disc. The study of transitional objects exhibiting clear signs of evolution in their discs, such as the growth of dust particles and beginning of disc dispersal, is fundamental to understanding the processes governing dust-grain coagulation and ...

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 self-interacting potential. We formulate the ...

The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best evidence to date for the existence of supermassive black holes in active galactic nuclei. Observations with ASCA revealed an X-ray iron line profile shaped by strong Doppler and gravitational effects. In this paper the shape of the iron line, its variability characteristics and the robustness of this ...

We investigate the nature of OGLE05155332-6925581, one of the brightest members of the enigmatic group of double periodic variables (DPVs) recently found in the Magellanic Clouds. The modelling of archival orbital light curves (LCs), along with the analysis of the radial velocities (RVs) suggest that this object is a semidetached binary with the less massive star transferring ...

We present a detailed model atmosphere analysis of high-dispersion and high signal-to-noise ratio spectra of the heavily polluted DAZ white dwarf GALEX J1931+0117. The spectra obtained with the Very Large Telescope (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 ...

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 model for the gas ...

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 ...