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The formation of supermassive black holes is not fully understood. The proposed mechanisms predict the formation of these at late times. We study a new scenario where black holes form in a CDM cosmology. While the baryons are smoothly distributed until after the recombination era, cold dark matter decouples early from background expansion, allowing the dark matter inhomogeneities to grow long before recombination. After recombination baryonic matter decouples from photons and falls into the deep gravitational potential wells of the dark component. [ABSTRACT FROM AUTHOR]

When the iron core of a (non-rotating) massive star collapses to a neutron star there are three possible outcomes. First, if a neutrino powered explosion of sufficient intensity develops, almost all the material outside the neutron star is ejected and a typical supernova of about 1051erg produced. If the neutrino powered explosion does not develop, then a black hole forms in the time it takes for the proto-neutron star to accrete a few tenths of a solar mass - a second or so. But there is a third intermediate possibility that we explored in some detail here. A shock is be launched initially, but lacks adequate energy to eject all the overlying matter. Then, after a time that is highly sensitive to the initial shock energy, mass falls back to the origin, accretes, and possibly produce a black hole. In SN 1987A, an explosion of roughly $1.2\cdot10^{51}$erg in a 20 M$_\odot$ blue supergiant, it was previously estimated that roughly 0.1 M$_\odot$ re-imploded in this way (Chevalier 1989). [ABSTRACT FROM AUTHOR]

The measured radial velocities, and the recently derived tangential velocities based on Hipparcos observations, have demonstrated that several high-mass X-ray binaries (HMXBs) with OB-supergiant companion travel through interstellar space with velocities on the order of 50 km s-1. On theoretical grounds it is expected that all HMXBs are runaway systems, since the loss of mass from the system during the supernova explosion of the compact star's progenitor results in a kick to the remaining (bound) binary system. When a massive star is running through space with a supersonic velocity, the interaction of its stellar wind with the interstellar medium will result in the formation of a bow shock. The detection of a wind bow shock around a high-mass X-ray binary would be an indication that the system is moving with a high space velocity, and from its shape the direction of motion could be derived. Especially for systems at larger distances, for which no Hipparcos measurements are available, the detection of a bow shock would be a valuable diagnostic. We searched for the presence of bow shocks around high-mass X-ray binaries using infrared observations. Up to now, we have only one firm detection out of 12 candidates, while for (apparently single) OB runaway stars the detection rate is about 30% [5]. A new hypothesis to explain this difference is put forward. [ABSTRACT FROM AUTHOR]

We present a detailed evolutionary sequence for Cygnus X-2, and calculate possible dynamical orbits of the system in a realistic Galactic potential. [ABSTRACT FROM AUTHOR]

Both the recently observed high runaway velocities of Cyg X-1 ($\sim 50$ km s-1) and X-ray Nova Sco 1994 ($\ge 100$ km s-1) and the relatively low radial velocities of the black hole X-ray binaries with low mass donor stars, can be explained by symmetric mass ejection in the supernovae (SNe) which formed the black holes in these systems. We find that at least $2.6M_\odot$ and $4.1M_\odot$ must have been ejected in the formation of Cyg X-1 and Nova Sco, respectively. A possible kick at the formation of the black hole is not needed to explain their space velocities. [ABSTRACT FROM AUTHOR]

We are carrying out a programme of non-linear, time-dependent calculations to study non-stationary accretion onto black holes. We plan to use this study as a basis for considering whole populations of accreting objects. Some of the most interesting results are presented. [ABSTRACT FROM AUTHOR]

Luminosity functions are a standard tool of observational astrophysics. Here I explore the interrelation between luminosity and mass functions for Active Galactic Nuclei. The formal relation relating BH mass and bolometric luminosity is $L_{bol} = \epsilon M_{BH} c^2/t_E$ with the ‘Eddington ratio' $\epsilon \equiv L/L_E$. Using a semi-empirical M(L) relation for AGN, we can (statistically) convert luminosity functions into mass spectra of radiatively accreting black holes. [ABSTRACT FROM AUTHOR]

Hubble Space Telescope observations revealed that the central surface brightness profiles of early type galaxies show either cuspy cores or featureless power law profiles. I find that there is a clear dichotomy also in the X-ray properties: cuspy core galaxies span the whole observed range of Lx values (roughly two orders of magnitude in Lx), while power law ones are confined to log Lx (erg s-1) < 41. So, a global property, such as Lx, that measures the hot gas content on a galactic scale, turns out to be well linked to a nuclear one. This could indicate that a central massive black hole (MBH) plays an important role in determining Lx (i.e., the hot gas content of early type galaxies). [ABSTRACT FROM AUTHOR]

Because of their closeness, the galaxies of the Local Group are an interesting sample for finding weak manifestations of nuclear activity (as is known for M31 and the Milky Way). Archival ROSAT PSPC and HRI observations have been examined for X-ray sources associated with the centres of several Local Group members. Detections will be considered candidate massive Black Holes. Besides four relatively luminous systems (mostly known already), two smaller galaxies contain candidate central cores. These are however in Irregular systems without well-defined nuclei. So far, and also given observational results in other wavebands, only those four present good candidates for massive nuclear Black Holes within the Local Group. [ABSTRACT FROM AUTHOR]

We find that the formation of clouds capable of producing the broad emission lines seen in the spectra of most active galactic nuclei (AGNs) is possible within an unsteady, turbulent accretion flow. The resulting clouds display the correct range in densities and velocities to produce the observed line shape. We also find that the modeled broad line region (BLR) size and differential line response, with the blue and red wings responding fastest to continuum changes, are consistent with the results of reverberation studies. [ABSTRACT FROM AUTHOR]

We discuss the role of the coronal outflow perpendicular to the disc surface and study the problem of its influence on spectral shape and on the amplitude of reflected component in hard X-ray spectrum. We compare our results with the predictions of model of X-ray emission from the central spherical source, surrounded by the cold disc which inner part is disrupted. [ABSTRACT FROM AUTHOR]

It was previously shown that our gravitation equations [1] lead to the existence of supermassive stable compact configurations of degenerated electronic gas [2],[3] without an event horizon. In the present paper the simplest model of such objects in a gas environment has been considered. It is shown that for spherically symmetric accretion onto the object the luminosity is about 1031erg/s for a mass accretion rate of the order of $\dot M = 10^{-6}M_\odot /year$. The wavelength of the radiation maximum is 400-500 Å. There is an ionization zone around the central objects. [ABSTRACT FROM AUTHOR]

We calculate the temporal response of the iron fluorescent line to the illuminating flux from orbiting flares above a black hole accretion disc. We take into account all relevant general relativistic effects. We suggest that the complex temporal behaviour of Fe line profiles seen in future data from XMM or Constellation-X may not necessarily imply a complicated model but could be explained for example in the framework of the orbiting flare model. [ABSTRACT FROM AUTHOR]

Accretion onto compact objects is a prominent astrophysical problem involving dissipative fluid flow in strong gravitational fields. The generic approach for modeling is by the relativistic Navier-Stokes-Fourier equations, which are of non-hyperbolic type. Consequently, fluctuations in the dissipative variables (shear stress and beat flux) propagate at causality violating infinite speeds, and thermodynamic equilibrium states are unstable. This description is problematic in particular for systems that undergo variability on timescales shorter than or comparable to the dissipative relaxation times. To overcome these difficulties we proposed (Peitz & Appl [3]) to model relativistic accretion flows using extended causal fluid theories. Here we review such a theory and the corresponding 3+1 representation appropriate for numerical implementation. [ABSTRACT FROM AUTHOR]

Diffuse plasma existing above an accretion disc can affect the X-ray spectrum by iron K$\alpha$ resonance absorption. We embark on a fully relativistic computation of this effect and calculate the iron line profile in the framework of a specific model in which rotating, highly ionized and resonantly-absorbing plasma occurs close to the black hole. This can explain the features seen in the iron K$\alpha$ line profile recently obtained by Nandra et al. (1999) for the Seyfert 1 galaxy NGC 3516. We show that the redshift of this feature can be mainly gravitational in origin and accounted for without the need to invoke fast accretion of the matter onto the black hole. [ABSTRACT FROM AUTHOR]

A hot disk corona forms due to the dynamo amplification of the magnetic field in the differentially rotating, turbulent disk and buoyancy instability of the magnetic field tubes. The resulting configuration of the magnetic field in the disk corona is explained in terms of Z-pinch. The energy release in Z-pinch leads to the formation of relativistic particle beams and collimated plasma outflows. [ABSTRACT FROM AUTHOR]

We present a summary of several recent papers on the simulation of relativistic jet formation in the vicinity of rotating and non-rotating black holes. We find that the strongest and fastest jets ($\Gamma \sim 3$) occur when the hole is rotating and the disk plunges rapidly into the ergosphere. [ABSTRACT FROM AUTHOR]

We present an improved approach to derive the observed evolution of a typical synchrotron outburst in 3C 273. The method consists in a simultaneous decomposition of 13 long-term light curves - spanning 20 years of observations from 2.7 GHz to 0.35 mm - into a series of 15 self-similar synchrotron outbursts. The spectral evolution of the outbursts is found to be in remarkable agreement with the evolution expected by the shock model of Marscher & Gear (1985). [ABSTRACT FROM AUTHOR]

We present the results of a 2.5-year multiwavelength monitoring programme of Cygnus X-1, making use of hard and soft X-ray data, optical spectroscopy, UBVJHK photometry and radio data. In particular we confirm that the 5.6-day orbital period is apparent in all wavebands and note the existence of a wavelength-dependence to the modulation, in the sense that higher energies reach minimum first. We also find a strong modulation at aperiod of $142 \pm 7$ days, which we suggest is due to precession and/or radiative warping of the accretion disc. We present the basic components required for more detailed future modelling of the system - including a partially optically truck jet, quasi-continuous in the low state. In addition, we choose two periods of flaring to study in further detail and find that the hard and soft X-rays are well-correlated in the first and that the soft X-rays and radio are correlated in the second. [ABSTRACT FROM AUTHOR]

The black hole binary 4U 1543-47 has been observed extensively (using B, V, and I) during the 1998 and 1999 seasons by the YALO (Yale - AURA - Lisbon - Ohio State) 1 meter telescope at Cerro Tololo. The folded light curves show clean amplitudes of 0.05 mag in B, 0.03 mag in V, and < 0.02 mag in I. We discuss models of the light curves and present updated and refined system parameters. [ABSTRACT FROM AUTHOR]

The X-ray spectrum of the famous starburst galaxy M82 consists of three components: soft, medium, and hard (Tsuru et al. 1997). We conducted a monitoring observation with ASCA in 1996. Although the X-ray flux of the soft and medium components remained constant, a significant time variability of the hard component was found between 3 x 1040 erg s-1 and 1 x 1041 erg s-1 at various time scales from 3 ks to one month. The spectrum of the variable source obtained by subtracting the spectrum of the lowest state from the highest state suggests strong absorption of $N_H \sim 10^{22}$ cm2, which means a variable source is embedded in the center of M82. These observations suggest existence of a LLAGN in M82. [ABSTRACT FROM AUTHOR]

We present simulated microlensing light curves of a quasar accretion disk using two canonical accretion disk models. Furthermore, we investigate the method to reconstruct the accretion disk structure from observed microlensing light curves. Additionally, we also show a new method to limit the size of the origin of quasar variabilities from macrolens effects. [ABSTRACT FROM AUTHOR]

There have been many suggestions about the existence of supermassive binary black hole systems in the nuclei of Active Galactic Nuclei (AGN). One of the best candidates has been a blazar called OJ287 where we have found a possible periodicity of about 12 year in the optical major outbursts. However, there has been a confusion if the periodicity is exactly strict or not. In this new work we will show clear evidence that the periodicity is really amazingly strict and this gives strang support to the binary black-hole model developed for OJ287. [ABSTRACT FROM AUTHOR]

We discuss the detection of a giant X-ray flare ( $L_x\gtrsim 10^{44}$ erg/s) from the direction of the previously unknown, optically inactive galaxy pair RXJ1242.6-1119 and investigate outburst scenarios. The most likely one is an accretion event onto a supermassive black hole in the center of one of the two galaxies, e.g., by a tidal disruption event. [ABSTRACT FROM AUTHOR]

We review our work on, and extent the discussion of, the giant X-ray flare from the HII-type galaxy NGC 5905 (Bade et al. 1996, Komossa & Bade 1999), which we consider to be presently the best candidate for a tidal disruption or tidal stripping event at the center of an otherwise non-active galaxy. [ABSTRACT FROM AUTHOR]

The main X-ray and optical properties of a very luminous X-ray outburst source are summarized. The results are: large variability in X-ray emission (count rate rise of a factor of 10 within 7 days), soft X-ray spectrum (photon index = -3.8), giant peak X-ray luminosity (1044 erg/s), previously unknown non-active optical counterpart (redshift = 0.05). [ABSTRACT FROM AUTHOR]

Several black hole X-ray transients have a very long recurrence time, decades of years [2]. We interpret this as a marginal occurrence of a dwarf nova type disk instability in the cool outer accretion disk. We compute how the recurrence time varies with the mass overflow rate from the companion star. Evaporation of the inner accretion disk is an essential feature of disk evolution which depends on the black hole mass. For accretion rates only slightly lower than those in the known black hole X-ray transients the disk does not reach the instability. We argue that many of those stationary, optically faint black hole X-ray binaries exist. [ABSTRACT FROM AUTHOR]

We present mid-infrared photometric results obtained with ISOCAM and ISOPHOT on 3 millisecond pulsars and 3 ordinary radio pulsars. No detections have been obtained for the three ms pulsars nor the two more distant radio pulsars. A faint enhancement in the brightness map at $90 \mu$m is seen at about 5 arcsec from the radio position of PSR J0108-1431, the nearest radio pulsar (Tauris et al, 1994), located at 85 pc from us. We conclude that this $90 \mu$m emission, amounting to about 12 mJy, originates either from material orbiting the pulsar or from cirrus on the line of sight. We deduce the upper limits on mass of dust orbiting this pulsar and on the mean temperature of grains. [ABSTRACT FROM AUTHOR]

We present mid-infrared spectrophotometric and imaging photometric results obtained with ISO on the peculiar X-ray binary Cygnus X-3. The observations covered the orbital phases 0.83 to 1.04, during quiescence. The flux observed with ISOCAM at $11.5\mu$m is $3.51\pm 0.73$ mJy, in good agreement with that observed in the K and mm ranges, during quiescence (Fender et al, 1999; Ogley et al, 1999). Spectrophotometry with ISOPHOT-S in the range $2.4 - 12 \mu$m shows an unresolved line at about $4 \mu$m, peaking at $61\pm 10$ mJy above a mean flux in the $3.5 - 4.5 \mu$m range of $9.0 \pm 3.2$ mJy; it is interpreted as the expected HeII(10-8) line at $4.05 \mu$m. [ABSTRACT FROM AUTHOR]

We have observed in the Galactic X-ray source GRS 1915+105 some of the brightest 20-min quasi-periodic oscillations yet seen, simultaneously at $2.2\mu$m (with UKIRT) and at 1.3 mm (with JCMT). These oscillations are associated with the disappearance and probable ejection of substantial parts of the inner accretion disc. The emission shows remarkable similarities at the two wavebands, both in timing and intensity. The mechanism for the emission is still unclear. [ABSTRACT FROM AUTHOR]

We present first results from an RXTE monitoring campaign of the black hole candidate Cygnus X-1 in 1999. The spectral and temporal properties of this hard state black hole show considerable variability, even though the state does not change. We find that a shortening of the time lags is accompanied by a hardening of the X-ray spectrum, as well as by an increase of the characteristic "shot time scale". We briefly discuss possible physical/geometrical reasons for this variability of the hard state properties. [ABSTRACT FROM AUTHOR]

We present results from an RXTE monitoring campaign of the black hole candidate LMC X-3 since 1996 December. The spectral properties of this canonical soft state source show considerable variability on timescales of $\sim 100$ d. We report on these changes, including on two or possibly three instances where we found that the soft spectral component vanishes and where the X-ray spectrum of LMC X-3 resembles that of a hard state source such as Cyg X-I. [ABSTRACT FROM AUTHOR]

New subarcsecond data on NGC 3227 and NGC 1068 obtained with the Plateau de Bure millimeter interferometry indicate large enclosed masses and the possibility of warped molecular gas disks. [ABSTRACT FROM AUTHOR]

All observations were made using the Double-Beam Spectrograph on the 2.3m telescope at Siding Spring. See Table 1 for a log of observations. Both the red and blue sides were utilised together with the D1 dichroic mirror. All spectra were reduced using the standard reduction techniques in IRAF. [ABSTRACT FROM AUTHOR]

Soft X-ray Transients (SXTs) are binary systems that are believed to consist of a black hole and a normal late type dwarf star which fills its Roche Lobe. We have used GRIM II on the ARC 3.5 meter telescope at Apache Point Observatory to obtain infrared photometry of GS2000+25 (QZ Vul). By modeling the SXT ellipsoidal variations with WD98, we can determine the orbital period and inclination of the system. The inclination for a best fit circular orbit is $75^\circ$, and when combined with the observed mass function, corresponds to a primary mass of $6.55M_\odot$. More data is needed to better define the minima, fill in the small gaps in the light curve, and explore the possibility of an eccentric orbit. [ABSTRACT FROM AUTHOR]