| Monday 21 August 2006 |
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Session I - Stellar-mass black holes
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| Chair |
P. Charles |
| 14:00 |
J. Casares
Observational evidence for stellar-mass black holes
Radial velocity studies of X-ray binaries still provide the most solid
evidence for the existence of stellar-mass black holes. We currently have 20 confirmed cases, with dynamical masses in excess of 3 Msun. Accurate masses have been obtained for a subset of systems which give us a hint on the mass spectrum of the black hole population.
These cases will be summarized and the most recent results presented. (Invited Review)
|
| 14:36-14:54 | P. T. Zycki
X-ray energy spectra of low and high-frequency QPO in accreting black holes
We have analyzed energy spectra of low-frequency QPO in a number of transient X-ray binaries, around the time periods of state transitions. The QPO spectra show an interesting anti-correlation with the time averaged X-ray spectra: the QPO spectra are harder than the time averaged spectra when the latter are soft, while they are softer than the time averaged spectra when the latter are hard. We then model and interpret these results with models of spectral variability of Comptonized emission. We point out that the QPO in the soft state appear to be driven by modulations in the hot plasma, while most of the QPO models assumes that the modulations are driven by instabilities in the accretion disks. We have also considered the model for high-frequency QPO in accreting black holes, involving epicyclic motions of the accretion disk. Assuming that X-ray modulation comes solely from relativistic effects, we have constructed theoretical energy spectra of the QPO. These could be compared with good quality data. |
| 14:54-15:12 | F. Mirabel
Microquasars: disk-jet coupling in stellar-mass black holes
I will review the observation of microquasars that provide a basic understanding of the physics in accreting black holes. Particular emphasis will be on: 1) the accretion-jet relation, 2) the origin of stellar-mass black holes and their connection to GRBs, and 3) the General Relativity applications. |
| 15:12-15:30 | A. Kubota
Suzaku observation of the black hole transient 4U1630-472
An outburst of the black hole transient 4U1630-472 was reported by the RXTE All Sky Monitor on 2005 December. From 2006 February 8 to March 23, we observed this source six times with each exposure of 21-23ks as part of the initial performance verification of Suzaku. Suzaku carries 4 sets of X-ray telescopes each with a focal-plane X-ray CCD camera (XIS, X-ray Imaging Spectrometer), together with a non-imaging Hard X-ray Detector (HXD) which covers the 10--600 keV energy band with the Si PIN photo-diodes and the GSO scintillation counters. During the observations in 2 months, the source signal was clearly detected up to 40keV with PIN, and its spectrum was found to be the typical high/soft state with the dominant disk component and very weak hard tail of photon index ~2.5. Based on the XIS spectra, the disk temperature was found to be 1.4keV at the first observation and gradually decreased to 1.2keV by keeping disk inner radius constant at ˜25km (distance and inclination are assumed to be 10kpc and 70 degree). Thus the bolometric disk luminosity changed from 2.8E38 erg/s to 1.6E38 erg/s. Importantly, with this Suzaku observation, we discovered narrow absorption lines at 6.7 keV and 7.0 keV, which correspond to H- and He-like iron K alpha, respectively. Through six observations, H-like iron K alpha was found to show almost constant equivalent width of 30eV, while the equivalent width of He-like iron K alpha increased from 8eV to 20 eV. The values of equivalent width correspond to iron column density of 1-4E17 /cm2 and 1E18/cm2 for He- and H-like iron, respectively, with an assumption of velocity dispersion of 500km/s. We run xstar to have ratio of He- like to H-like iron for the disk spectra, and found that the xi-parameters should change from 5-7E4 to 3-4E4 from the first to the sixth observation. Based on these results, we will discuss geometry and origin of the absorption lines together with change of the accretion disk parameters. |
| 15:30-16:00 | Coffee |
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Session II - Stellar-mass black holes
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| Chair |
R. Narayan |
| 16:00-16:36 | A. R. King
Matter accretion and ejection in black-hole systems
Many systems are known to accrete at rates near or above the Eddington limit, in both stellar-mass and supermassive cases. I discuss how such systems may appear in practice, the efficiency of the accretion process, and how such holes grow over time. |
| 16:36-16:54 | P. C. Joss
Formation of Rapidly Rotating Black Holes in Massive Binary Stellar Systems
A hypernova, along with an observable “long” gamma-ray burst, may result from the formation of a microquasar - a rapidly rotating stellar mass black hole surrounded by a massive disk - following core collapse in a high-mass star. If long gamma-ray bursts are in fact produced by hypernovae, a problem that must be confronted is how the core of the hypernova progenitor retains or acquires sufficient angular momentum to produce the requisite axisymmetric collapse. Physical processes during the evolution of an isolated massive star will tend to extract any initial angular momentum from the stellar core, rendering it difficult for such a star to become a hypernova. However, a substantial fraction of massive stars are members of binary systems. Tidal locking, mass transfer, or stellar merger in an evolved massive binary may lead to the transfer of orbital angular momentum to the core of one of the stars (or the merged star), sufficient to produce the progenitor of a hypernova. We have developed a new binary stellar evolution code that includes the effects of mass and angular momentum transfer between the component stars and the subsequent transport of angular momentum through one of the stars. This transport is effected by dynamical and secular shear instabilities, convective motions, the critical layer instability, and gravity waves. Our code treats in a self-consistent way the dynamical distortion of the star resulting from the induced rapid differential rotation. Our numerical results indicate that late main-sequence or early post-main-sequence accretion from a binary companion onto a star with an initial mass greater than ~20 solar masses may produce a stellar core that is rotating sufficiently rapidly when it collapses to provide the initial conditions necessary for a the formation of a rapidly rotating black hole and a microsquasar that generates a long gamma-ray burst. Our results also indicate that the merger of a late post-main-sequence star with its binary companion may also lead to the formation of a microquasar but is unlikely to produce an observable gamma-ray burst. |
| 16:54-17:12 | R. Matsumoto
Sawtooth-like Oscillations of Black Hole Accretion Disks
Black hole candidates sometimes show high frequency quasi-periodic oscillations (QPOs) whose frequency is about 100Hz when the mass of the black hole is 10 solar mass. High frequency QPOs are accompanied by low frequency QPOs. We studied the excitation mechanism of these QPOs by three-dimensional resistive magnetohydrodynamic (MHD) simulations of optically thin black hole accretion disks. Initial state is a rotating disk threaded by weak toroidal magnetic fields. General relativistic effects are simulated by using the pseudo-Newtonian potential. As the magneto-rotational instability (MRI) grows, the disk matter accretes to the black hole. When the temperature of the disk is not too high, the accreting matter accumulates into a torus formed around 10 Schwarzschild radius. We found that the torus sometimes shows sawtooth-like large amplitude oscillations with frequency 10/(M/10)Hz where M is the mass of the black hole in unit of the solar mass. Sawtooth-like oscillation is triggered by the growth of non-axisymmetric m=1 mode (m is the azimuthal mode number), which deforms the inner torus into a crescent shape. During this stage, magnetic fields inside the torus are amplified until magnetic energy becomes comparable to the thermal energy. Subsequently, magnetic reconnection suddenly releases the accumulated magnetic energy and recovers the circular shape of the torus. A new cycle of the oscillation starts when non-axisymmetric m=1 mode begins to grow inside the torus. We found that when large-amplitude sawtooth-like oscillations appear, high frequency QPOs are excited. |
| 17:12-17:30 | J. I. Gonzalez Hernandez
On the origin of the black hole in the X-ray binary XTE J1118+480
The high-velocity black hole in the low mass X-ray binary XTE J1118+480 could be the remnant of an massive star formed in the early stages of the evolution of the Galaxy (Mirabel et al. 2001). Alternatively, it could have been ejected from the Galactic plane as a result of a `kick' received during a supernova explosion (Gualandris et al. 2005). The chemical composition of the secondary star may provide unique clues on the origin of this black hole. Here, we present a medium-resolution optical spectra of the companion and determine the atmospheric abundances of Fe, Ca, Mg, Ni and Al. We find supersolar abundances for all these elements, rejecting the black hole was originated from the direct collapse of an ancient massive halo star. The compact object probably formed in a supernova event whose nucleosynthetic products polluted the secondary star. The observed element abundances and their ratios have been compared with a variety of supernova models for different metallicities and progenitor masses. Although we cannot definitely discard a supernova origin in the Galactic halo, the abundance pattern of the secondary star clearly suggest that black hole formed in the supernova explosion of a metal-rich massive progenitor and was violently `kicked out' from its birth place in the Galactic disc. |
| 17:30-18:15 | Poster viewing |
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Invited Discourse
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| 18:15 | Shuang Nan Zhang
Similar phenomena at different scales: Black Holes, Sun, Supernovae, Galaxies and Galaxy Clusters
Many similar phenomena occur in astrophysical systems with spatial and mass scales different by many orders of magnitudes. In this talk I will summarize briefly these phenomena and possible physical mechanisms responsible for them. I will emphasize the importance of using the Sun as an astrophysical laboratory in studying some of these physical processes, especially the roles magnetic field plays in them; it is quite likely that magnetic reconnections dominate the fundamental energy release processes in all these systems. As a case study, I will show that X-ray light curves from solar flares, black hole binaries and gamma-ray bursts exhibit a common scaling law of non-linear dynamical property, over a dynamical range of many orders of magnitudes in intensities, in support of self-organized criticality mechanisms operating in their energy release processes. |
| Tuesday 22 August 2006 |
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Session III - Formation and evolution of massive black holes
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| Chair |
K. Pounds |
| 9:00-09:36 |
M. J. Rees
Massive black holes
This talk will review recent progress on two distinct issues. (i) The origin and growth of massive holes in the context of galaxy formation and evolution: Why is there such a close correlation between hole masses and the properties of host galaxies? What is the the role of galactic mergers? How rapidly can holes grow? How can we account for powerful QSOs at the highest redshift? Are Population III remnants the 'seeds' for massive holes? (ii) Probes of the 'strong-field' domain: X-ray spectroscopy, jet physics, variability and precession effects, gravitational waves, etc. (Invited Review) |
| 09:36-09:54 | G. Hasinger
The cosmic evolution of Black Hole acretion
Different feeding modes have been identified for growing black holes, starting from small flares occurring almost daily in our Galactic Center. In several other galaxies we discovered major flares, in which an otherwise dormant black hole tidally disrupts and swallows a normal star. Major mergers between two galaxies seem to play an important role in the feeding of black holes. In the nearby merger NGC 6240 we identified a double supermassive black hole in a single galaxy for the first time, which will merge in the future. The X-ray sky is dominated by a diffuse extragalactic background radiation, which our team, together with others, was able to resolve almost completely into discrete sources using the X-ray satellites ROSAT, Chandra and XMM-Newton - we observe the growth phase of the population of supermassive black holes throughout the history of the Universe. Indeed, the mass distribution of black holes in local galaxies is well traced by the evolution of the accreting black hole luminosity function. However, the maximum of high-luminosity objects occurs significantly earlier in the history of the universe (at redshifts 2-3), than that of low-luminosity objects, which have a peak at redshifts below unity. This anti-hierarchical evolution is similar to the down-sizing effect observed in the optical galaxy population and still awaits a theoretical explanation. At the end I will advertise a new X-ray survey satellite: SRG, carrying eROSITA and Lobster as prime instruments. |
| 09:54-10:30 | S. Mateos
X-ray emission properties of the broad-line AGN in the XMM-2dF Wide Angle Survey
The 2dF-XMM Wide Angle Survey includes one of the largest samples of spectroscopically identified AGN assembled so far. This sample contains more than 700 objects identified as type-1 AGN and for which medium resolution optical spectra are available. The large number of type-1 AGN with 2dF optical spectra available in our sample has allowed us to start a statistical analysis of the optical broad emission line properties of the objects with optical spectra with the best signal to noise ratio. Our large sample of sources, extending to redshifts up to ~3, allows us to study the dependence of the optical emission line properties of type-1 AGN over a broad range of intrinsic X-ray luminosities. A significant fraction of our type-1 AGN cover the redshift interval with spectroscopic coverage to the [OIII] 5007 emission line which is believed to originate in the narrow line region (NLR) and therefore it is considered to be a good indicator of the intrinsic luminosity of AGN. The [OIII] 5007 observed emission line properties, such as its luminosity distribution for our X-ray selected type-1 AGN will be presented. |
| 10:30-11:00 | Coffee |
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Session IV - Formation and evolution of massive black holes
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| Chair |
F. Macchetto |
| 11:00-11:36 | P. Madau
Formation and evolution of supermassive black holes, black-hole binary merging
I review scenarios for the assembly of massive black holes (MBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark halo merger tree. The first active galactic nuclei likely formed 150 Myr after the big bang in 1e6 Msun minihaloes. X-ray photons from such miniquasars may have permeated the universe more uniformly than EUV radiation, made the low-density diffuse intergalactic medium shine at 21-cm prior to the epoch of reionization, and changed the chemistry of primordial gas. I'll discuss the conditions under which massive black holes become incorporated through a series of mergers into larger and larger halos, sink to the center owing to dynamical friction, accrete a fraction of the gas in the merger remnant to become supermassive, form a binary system, and eventually coalesce. The spin distribution of MBHs is determined by gas accretion, and is predicted to be heavily skewed towards fast-rotating Kerr holes, already in place at early epochs, and not to change significantly below redshift 5. Decaying MBH binaries may shape the innermost central regions of galaxies and should be detected in significant numbers by LISA. (Invited) |
| 11:36-11:54 | D. Dultzin-Hacyan
Quasar Evolution: Black Hole Mass and Accretion Rate Determination
Accurate measurements of line properties are crucial to understand the physics of the BLR (Broad Line Region) in quasars. This region consists of clouds that are the closest to the central engine and cannot possibly be spatialy resolved (they are at distances of only a few light days). The only way to study them is with high S/N spectra. We present here a compilation of our optical and IR data for a large sample of quasars, and their analysis within the framework of the E1 parameter space, which could be viewed as a surrogate H-R diagram for quasars. The physical parameters underlying evolution most likely involved are: Black Hole mass and accretion rate (which we determine from line and continuum measurements). We briefly discuss the caveats of these determinations |
| 11:54-12:12 | G. Chartas
X-ray Spectral Evolution of Quasars
Evidence of a possible correlation of the X-ray spectral slope Gamma of radio-quiet quasars (RQQs) at z > 1.5 with X-ray luminosity L_x was recently reported by Dai et al. (2004). That result was based on the analysis of a sample of z > 1.5 gravitationally lensed quasars. If this correlation is confirmed by large samples of RQQs it will have very important implications for quasar evolution. Such a correlation between Gamma and L_x is not found in nearby z < 0.1 RQQs suggesting that quasars at redshifts near the peak of their number density may have different accretion properties than lower redshift quasars. In order to significantly increase the sample size and place tighter constraints on the significance of the Gamma - L_x correlation we have analyzed additional high redshift RQQs with moderate-to-high signal-to-noise (S/N) ratio spectra available in archived deep-field observations performed with Chandra. We report on the detection of a correlation between Gamma and L_x at the > 99.99% significance level based on the Chandra deep field sample of ˜40 RQQs with redshifts in the range of 1.5 < z < 2.3. The strength of the Gamma - L_x correlation is found to be strongly dependent on redshift. In particular, the Gamma - L_x correlation is not as significant for RQQs outside the redshift range of 1.5 < z < 2.3. We performed a variety of tests that rule out possible effects that might drive the correlation such as Compton reflection from the disk, soft X-ray excess and intrinsic absorption. We present various interpretations for the origin and redshift dependence of the Gamma - L_x correlation. We acknowledge financial support from NASA grant NAS8-03060. |
| 12:12-12:30 | J. E. Greene
Black Hole Growth in the Local Universe
While black holes (BHs) are apparently a ubiquitous component of the nuclei of local spheroids, their role in galaxy evolution remains largely unknown. The tight correlations between galaxy spheroid properties and BH mass provide important boundary conditions for models of the coevolution of BHs and galaxies. Here we consider another important boundary condition: the local mass function of broad-line active galaxies. We use standard virial mass estimation techniques to examine the distribution of BH masses and accretion rates for active galaxies in the local universe. Comparisons with local galaxy luminosity functions and star-formation rate distributions allow us to compare average current growth rates of galaxies and BHs as a function of mass. We also compare the distribution of BH masses in local broad and narrow-line objects, and find that both populations have a characteristic mass of ~10^7 M_sun[.] Most importantly, this is the first BH mass function to consider BH with masses below 10^6 M_sun. The space density of this important population allows us to place constraints on potential mechanisms for the creation of seed BHs in the early universe. |
| 12:30-14:00 | Lunch |
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Session V - Active galactic nuclei
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| Chair |
A. Celotti |
| 14:00-14:36 |
M. C. Begelman
Supermassive black holes: accretion and outflows
Black holes tend to be fussy eaters, returning a significant fraction of the binding energy released during accretion in the form of jets and winds. I will discuss some of the mechanisms that may be responsible for these outflows and outline their effects on the environments of supermassive black holes. (Invited Review) |
| 14:36-14:54 | H. Kunieda
Hard X-ray spectra of AGN observed with Suzaku
Suzaku satellite is characterized by two performance; soft X-ray response below 1 keV and hard X-ray response above 10 keV. Since the sensitivity at 6-7keV is as good as Newton, Suzaku is the best mission to explore the AGN, whose broad band spectra consist of soft X-ray excess, variable power law, iron K lines, reflection component, and sometimes with strong absorption. In this paper, combined spectra of XIS(CCD camera) and HXD(Si PIN + GSO) will be used to examine the power law component with absorption and/or reflection components. Iron line feature should be taken into account to model the broad band spectra. Finally the time variability is another important key element to distinguish these multiple components. |
| 14:54-15:12 | K. R. W. Tristram
Mapping The Circumnuclear Dust In Nearby AGN With The Mid Infrared Interferometric Instrument MIDI
According to the unified scheme of AGN, the central engine, a supermassive black hole surrounded by an accretion disc, is embedded in a toroidal dusty structure. Orientation effects lead to the Seyfert 1 / Seyfert 2 dichotomy. Single dish telescopes fail to provide the necessary resolution to resolve the circumnuclear dusty torus, the key component in this picture. We have observed four nearby AGN with the mid infrared interferometric instrument MIDI located at the VLTI to investigate the mid infrared emission with the goal to resolve the dust emission. With our measurements we resolve the dusty structure around the nucleus of the Circinus galaxy, a nearby prototype Seyfert 2 galaxy. We find an elongated structure of 0.5 * 0.7 parsec at 9 µm and 0.7 × 1.0 parsec at 12 µm. We interpret the emission to be originating in a geometrically thick dusty torus heated by the nucleus. We find this torus to be oriented perpendicular to the ionisation cone and outflow in this galaxy. It has the same size and position angle as a rotating maser disc surrounding the nucleus. Our finding hence confirms the unified picture nicely. We have also observed the nucleus of the well known radio galaxy Centaurus A and find that 70% of the mid infrared flux originates from an unresolved source with a size of less than 0.2 parsec. In this case the majority of the emission does not originate from dust but comes from a synchrotron source at the base of the radio jet. Two further galaxies, Mrk 1239 (Seyfert 1) and MCG -05-16-023 (Seyfert 2) also show unresolved mid infrared sources limiting the size of the dust distribution to less than 5 and 2 parsec respectively. |
| 15:12-15:30 | R. W. Goosmann
X-ray Variability in Active Galactic Nuclei: Implications of Magnetic Flares
The last generation of X-ray satellites continues to reveal a complex nature of the X-ray variability in Active Galactic Nuclei (AGN) in the energy band of the iron Kalpha line. Simple expectations of radiation reprocessing by the disk do not explain the data. We address this issue in the frame work of the magnetic flare model. We model the observed energy-dependent fractional variability amplitude in the Seyfert galaxy MCG-6-30-15 using Monte-Carlo simulations of large flare distributions co-rotating with the accretion disk. Our modeling includes detailed radiative transfer computations for an accretion disk in hydrostatic equilibrium, which is locally illuminated by a point source, and a full-relativistic treatment of the reprocessed radiation. It turns out that the relative lack of variability at the rest frame position of the iron Kalpha line and the enhanced variability in its red wing can be reproduced if the effective energy dissipation by the flares is large in the central region of the disk. We also address the issue of the time delays between the hard and soft X-rays by considering in detail an individual strong flare event. The model considers an intrinsic delay between the primary radiation, which is thought to be emitted by an elevated source above the disk, and the reprocessed radiation coming from the disk surface. Both spectral components are simulated by time-modulated power-laws. The model reproduces the observed time lags well and enables to put constraints on the height of the primary flare source above the accretion disk. |
| 15:30-16:00 | Coffee |
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Session VI - Active galactic nuclei
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| Chair |
G. Matt |
| 16:00-16:18 | K. A. Pounds
Cumulative Effects of Outflows on the X-Ray Spectra of AGN
High quality broad-band X-ray spectra are being obtained with the XMM-Newton Observatory for an increasingly large sample of AGN. These data contain unique information on the X-ray emission mechanism(s) and on re-processing that takes place in both accreting and non-accreting matter. In this presentation we focus on the short and longer term effects of large scale outflows that can carry away a major fraction of the accreting mass and bolometric luminosity. We discuss several individual cases in detail to demonstrate the potential of X-ray observations for exploring the 'central engine' of AGN and its influence on the larger scale galactic environment. |
| 16:18-16:36 | S. Collin
Uncertainties on the black hole masses in AGN and consequences on the Eddington ratios
Black hole (BH) masses in Active Galactic Nuclei (AGN) are determined in ~ 40 objects through reverberation mapping of the emission line region. Scatter around the relationship between BH masses obtained by this method and host-galaxy bulge velocity dispersion, indicates that the masses are uncertain typically by a factor of about three. Systematic errors seem to be linked to the Eddington luminosity ratio and to the inclination of the line emission region. When BH masses are not known via reverberation mapping but estimated using empirical relations, the uncertainties can be larger, especially when the relations are extrapolated to high and low masses and/or luminosities. In particular they lead to small masses and consequently to Eddington ratios of the order of or larger than unity in samples of Narrow Line Seyfert 1. If these masses are correct, the optical luminosities imply sometimes accretion rates at ~1000 R_G larger than the critical rate by one or two orders of magnitude. Either accretion onto BHs is also performed at super-critical rate, resulting in rapid growth of the BH, or strong winds produced close to the BHs evacuate a large fraction of the accretion flow. |
| 16:36-16:54 | A. Lawrence
Warped disks and the Unified Scheme
The standard Unified Scheme for AGN involves obscuration by a geometrically thick "molecular torus" with an opening angle of around 30 degrees. This simple picture seems physically implausible, fails to explain several facts about Type I and Type II AGN, and leaves key features such as the height of the torus or the spectrum of the dust as arbitrary details. Warped disks have been suggested in the past as a more physically plausible alternative for making a geometrically thick obscuring structure. I will show that a simple variant of this idea quite naturally explains the ratio of Type II to Type I AGN, their different OIII strengths, the average size of the IR bump compared to the the UV bump, and the typical temperature of the radiating dust. A physical model which corresponds to this simple recipe is likely to involve a strongly magnetised disc over a large scale range. |
| 16:54-17:12 | T. Yaqoob
An Accretion Disk Laboratory In The Seyfert Galaxy NGC 2992
The Seyfert 1.9 galaxy NGC 2992 has been observed by all X-ray astronomy missions since HEAO-1 for over a quarter of a century, including a one-year RXTE monitoring campaign in 2005/ 2006 and three Suzaku observations in 2005. The source exhibited over a factor of 20 variability in the hard X-ray luminosity over the ˜25 year period and over an order-of-magnitude variability in the luminosity during the RXTE monitoring period. The luminosity changes are accompanied by spectral variability. In particular there is complex variability in the Fe K emission-line profile which consists of an accretion-disk component and a distant-matter component. The relativistic disk line component shows variability that likely corresponds to changes in the spatial illumination of the disk and the Suzaku data are able to decouple the disk line component from the distant-matter component. In one of the historical BeppoSAX observations an emission-line component from highly ionized Fe was also apparent. In this contribution we illustrate how the unique X-ray properties of NGC 2992 make it one of best supermassive black-hole candidates for testing accretion disk theories since any model must be able to satisfy all of the short and long timescale observational constraints. Future observations need to be planned to exploit the rich behavior to provide even more stringent constraints. NGC 2992 is also a good candidate for constraining AGN unification models. |
| 17:12-17:30 | Y. Ueda
Cosmological Evolution of Active Galactic Nuclei X-ray Luminosity Function
The X-ray background (XRB) is the integration of emission from all accreting black holes in the universe, and hence carries key information on the growth history of supermassive black holes in galactic centers. To solve the XRB origin is equivalent to revealing the cosmological evolution of Active Galactic Nuclei (AGNs) that constitute the XRB. Here we present our latest results of AGN X-ray luminosity function (XLF) over the redshift range from 0 to 5, by utilizing the largest sample ever available, obtained from surveys of various depth and area performed with ROSAT, HEAO1, ASCA, Chandra, and XMM. The combined sample detected in the soft (0.5-2 keV) and/ or hard (2-10 keV) bands consists of more than 1400 sources in total. We utilize a maximum likelihood method to reproduce the count-rate versus redshift distribution for each survey, taking account of all the selection biases. This enables us to determine the intrinsic XLF and the absorption distribution function of type-I plus type-II AGNs with an unprecedented accuracy, establishing the population synthesis model of the XRB. |
| 17:30-18:15 | Poster viewing |
|
Invited Discourse
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| 18:15 | Reinhard Genzel
The power of new experimental techniques in astronomy: Zooming in on the Black Hole in the Center of the Milky Way
Evidence has been accumulating for several decades that quasars, the most luminous objects in the Universe, are powered by accretion of matter onto massive black holes. I will discuss recent observations, employing adaptive optics imaging and spectroscopy on large ground-based telescopes that prove the existence of such a massive black hole in the center of our Milky Way, beyond any reasonable doubt. These observations also indicate that the Galactic Center black hole may be rotating rapidly. The central black hole is surrounded by a cluster of young massive stars, partly arranged in two, rotating disks. I discuss possible explanations for this 'paradox of youth'. |
| Wednesday 23 August 2006 |
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Session VII - Physical processes near black holes
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| Chair |
V. Karas |
| 09:00-09:36 | A. C. Fabian
Strong-gravity effects: X-ray spectra, timing, polarimetry
The radiation emitted from close to a black hole undergoes strong doppler shifts, redshift and light bending. I review the observations of such effects in the data from active galactic nuclei and Galactic Black Hole Binaries. X-ray reflection within the innermost regions of the accretion flow produces observable features in spectra, timing and polarimetry. The potential for measuring black hole spin will be discussed. (Invited Review) |
| 09:36-09:54 | R. Narayan
GRS 1915+105: A Near-Extreme Kerr Black Hole
Based on a spectral analysis of the X-ray continuum of the microquaqsar GRS 1915+105, we conclude that the compact primary in this binary X-ray source is a rapidly-rotating Kerr black hole. We estimate a dimensionless spin parameter a* in the range 0.98-1.0. Our result is robust in the sense that it is independent of the details of the data analysis and insensitive to uncertainties in the mass and distance of the black hole. Furthermore, the result is based on a fully relativistic accretion-disk model, which includes an advanced treatment of spectral hardening. In addition, it is based on a rigorous and quantitative definition of the thermal state of black hole binaries and makes use of all of the available RXTE and ASCA data for the thermal state of GRS 1915+105. We also give an update on published results on the relatively moderate spins that have been reported for three other stellar-mass black holes, GRO J1655-40, 4U 1543-47 and LMC X-3. We discuss the significance of the results for models of quasi-periodic oscillations, relativistic jets and core-collapse, and discuss implications for the detection of gravitational waves from coalescing black hole binaries. |
| 09:54-10:12 | J. Bicak
Black holes and magnetic fields
The exact mechanism of formation of highly relativistic jets from galactic nuclei and microquasars remains unknown but most accepted models involve a central black hole and a strong external magnetic field. This idea is based on assumption that the black hole rotates and the magnetic field threads its horizon. Magnetic torques provide a link between the hole and the surrounding plasma which then becomes accelerated. We first review our work on black holes immersed in external stationary vacuum (electro)magnetic fields in both test-field approximation and within exact general-relativistic solutions. A special attention will be paid to the Meissner-type effect of the expulsion of the flux of external axisymmetric stationary fields across rotating (or charged) black holes when they approach extremal states. This is a potential threat to any electromagnetic mechanism launching the jets at the account of black-hole rotation because it inhibits the extraction of black-hole rotational energy. We show that the otherwise very useful "membrane viewpoint of black holes" advocated by Thorne, Price and Macdonald does not represent an adequate formalism in the context of the field expulsion from extreme black holes. After briefly summarizing the results for black holes in magnetic fields in higher dimensions - the expulsion of stationary axisymmetric fields was demonstrated to occur also for extremal black-hole solutions in string theory and Kaluza-Klein theory - we shall review astrophysically relevant axisymmetric numerical simulations reported recently by Gammie, Komissarov, Krolik and others. Although the field expulsion has not yet been observed in these time-dependent simulations, they may still be too far away from the extreme limit at which the black-hole Meissner effect should show up. We mention some open problems which, according to our view, deserve further investigation. |
| 10:12-10:30 | S. B. Markoff
Constraining Jet Physics in Weakly Accreting Black Holes
Outflowing jets are observed in a variety of astronomical objects such as accreting compact objects from X-ray binaries (XRBs) to active galactic nuclei (AGN), as well as at stellar birth and death. Yet we still do not know exactly what they are comprised of, why and how they form, or their exact relationship with the accretion flow. In this talk I will focus on jets in black hole systems, which provide the ideal test population for studying the relationship between inflow and outflow over an extreme range in mass and accretion rate. I will present several recent results from coordinated multi-wavelength studies of low-luminosity sources. These results not only support similar trends in weakly accreting black hole behavior across the mass scale, but also suggest that the same underlying physical model can explain their broadband spectra. I will discuss how comparisons between small- and large-scale systems are revealing new information about the regions nearest the black hole, providing clues about the creation of these weakest of jets. Furthermore, comparisons between our Galactic center nucleus Sgr A* and other sources at slightly higher accretion rates can illucidate the processes which drive central activity, and pave the way for new tests with upcoming instruments. |
| 10:30-11:00 | Coffee |
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Session VIII - Physical processes near black holes/The Galactic Center
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| Chair |
Z. Stuchlik |
| 11:00-11:18 | D. Heinzeller
Black Hole Accretion: Theoretical Limits And Observational Implications
Introduction: Recently, the issue of the role of the Eddington limit in accretion discs became a matter of debate. While the classical (spherical) Eddington limit is certainly an over-simplification, it is not really clear how to treat it in a flattened (though not necessarily geometrically very thin) structure like an accretion disc. Methods: We calculate the critical accretion rates and resulting disc luminosities for various disc models corresponding to the classical Eddington limit by equating the attractive and repulsive forces locally. We also discuss the observational appearance of such highly accreting systems by analysing their spectral energy distributions. Results: Our calculations indicate that the allowed mass accretion rates differ considerably from what one expects by applying the Eddington limit in its classical form, while the luminosities only weakly exceed their classical equivalent. Depending on the orientation of the disc relative to the observer, mild relativistic beaming turns out to be an important effect which has to be considered for a proper interpretation of disc spectra. Discussion: Possible "Super-Eddington" accretion, combined with mild relativistic beaming, supports the idea that ultraluminous X-ray sources (ULXs) host stellar mass black holes and accounts partially for the observed high temperatures of these objects. |
| 11:18-11:36 | G. Beskin
Search for the event horizon evidences by means of optical observations with high temporal resolution
The essential property of the black hole is the presence of the event horizon instead of the surface. It may be detected only by means of the detailed study of the emission features (temporal, spectral, polarimetric) of its surroundings. The temporal resolution of such observations has to be better than r[g]/c and lays in the 10^-6 - 10 s range depending on the black hole mass. In SAO RAS we have developed the MANIA hardware and software complex based on the panoramic photon counter and use it in observations on 6-m telescope for the search and investigation of the optical variability on the time scales of 10^-6 - 10^3 s of various astronomical objects. We present the hardware and methods used for these photometrical, spectroscopic and polarimetrical observations, the principles and criteria of the object selection, first of all - probable isolated black holes. The list of the latter includes objects with featureless optical spectra (DC white dwarfs, blazars), unidentified gamma-ray sources and long microlensing events. We present the results of the timing observations of the location of the MACHO-1999-BLG-22 object. The limits on the power of variable emission component are derived on the level of 20% to 1% of the background brightness on the time scales from 10 us up to 1000 s, and compared with the results of the optical and IR (Hubble, REM) and x-ray (Chandra, ROSAT), and with the theoretical predictions. The general conclusion is that the lens in this object is the black hole with mass of 20-30 M [sun], located in the bulge. Also, we'll present the results of the observations on the 6-m telescope in June-July 2006. |
| 11:36-11:54 | D. Proga
Dynamics of radiatively inefficient flows accreting onto
I present results from recent modelling of gas dynamics outside luminous accretion disks in active galactic nuclei. The gas gravitationally captured by a super massive black hole can be affected by the radiation energy and momentum output from an accretion disk located at the very center of the system. Using multidimensional, time-dependent numerical simulations, I study how the mass accretion and outflow rates, and the flow dynamics respond to thermal effects and effects of radiation pressure due to continuum and line opacities. The focus of these simulations is to gain insights into the problem of the growth of black hole masses. |
| 11:54-12:30 | R. Genzel
The Galactic Center
In the past decade high resolution measurements in the infrared employing adaptive optics imaging on 10m telescopes have allowed determining the three dimensional orbits stars within ten light hours of the compact radio source SgrA* at the Center of the Milky Way. These observations show that SgrA* is a three million solar mass black hole, beyond any reasonable doubt. The Galactic Center thus constitutes the best astrophysical evidence for the existence of black holes which have long been postulated, and is also an ideal 'lab' for studying the physics in the vicinity of such an object. Remarkably, young massive stars are present there and probably have formed in the innermost stellar cusp. Variable infrared and X-ray emission from SgrA* are a new probe of the physics and space time just outside the event horizon. |
| 12:30-14:00 | Lunch |
|
Session IX - The Galactic Center
|
| Chair |
T. Yaqoob |
| 14:00-14:18 |
A. Eckart
The simultaneous radio to X-ray observations
The compact source SgrA* that can be associated with the massive black hole at the center of the Milky Way shown a strong variability from the radio to the X-ray wavelength domain. Here report on the latest simultaneous NIR/ sub-millimeter/X-ray observations using the NACO adaptive optics (AO) instrument at the European Southern Observatory's Very Large Telescope. In the X-ray and radio domain we used the ACIS-I instrument aboard the Chandra X-ray Observatory and the Submillimeter Array on Mauna Kea, Hawaii, as well as the Very Large Array in New Mexico, respectively. We also summarize the most recent results from a VLT NACO observations of polarized NIR flare emission of SgrA*. We interpret the results using a model in which spots are on relativistic orbits around SgrA* and discus the possibility of a jet or outflow from such a disk. |
| 14:18-14:36 | R. Schoedel
The Structure of the Nuclear Stellar Cluster of the Milky Way
We used AO assisted high-resolution near-infrared (NIR) imaging observations of the stellar cluster within 20" (about 0.75 pc) of Sgr A*, the massive black hole at the centre of the Milky Way to derive the structure of the nuclear star cluster via stellar number counts. Our findings are: (a) We demonstrate that an analysis of the stellar surface brightness is not the adequate tool for determining the density of the cluster because the NIR flux is dominated by a minority of very bright stars and does not reflect the structure of the underlying cluster. Therefore stellar number counts must be used. (b) Several significant density clumps are detected, at least one of them is probably a co-moving dense cluster, similar to the well-known IRS~13E complex. (c) A detailed map of the variation of interstellar extinction in the central ~0.5 pc of the Milky Way is presented. The extinction map in combination with possible shock structures in an L'-band map provides support for the assumption of an outflow from the central arc seconds. (d) The overall structure of the GC nuclear cluster can be described well by a broken power-law. The break radius is located between 8"-12" (0.30-0.44 pc). (e) In agreement with previous observations, a density excess, the 'cusp', around Sgr A* is detected with a high significance. Such a structure is the expected signature that a massive black hole imprints on a surrounding dense stellar cluster. (f) Effects of mass segregation can be seen in the surface density of the horizontal branch/red clump stars. Their distribution shows a significantly flatter power-law index than that of the other, heavier stars. |
| 14:36-14:54 | J. Cuadra
Variable Accretion of Stellar Winds onto Sgr A*
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 make Sgr A* radiate as an AGN. However, its observed luminosity is orders of magnitude smaller than what is expected from simple accretion theories. This seems to be caused, at least partially, by a low accretion rate onto the SMBH. Here we report a 3-dimensional numerical study of the accretion of stellar winds onto Sgr A*. Compared with previous investigations, we allow the stars to be on realistic orbits, include the recently discovered slow wind sources and allow for optically thin radiative cooling. Our study highlights the importance of source distribution geometry and net angular momentum in the problem. We find that for wind sources distributed in a disc, the accretion rate is a few times 10^-6 Msun/yr, an order of magnitude lower than the one reported by previous studies, and much more in line with Chandra observations. In addition, introducing the slow winds, we find these to shock and rapidly cool, forming cold gas blobs and filaments. The accretion rate in this case consists of two components: the hot quasi steady-state one, and the cold one that is highly time variable in time-scales of tens to hundreds of years. Because of the non-linear nature of the accretion processes, the variability in the accretion rate would result in an even more variable luminosity. This result suggests that, on time-scales of hundreds of years, Sgr A* may be a much more important energy source for the inner Galaxy than what is inferred from its current low luminosity. |
| 14:54-15:12 | M. R. Morris
The Character of the Short-term Variability of Sagittarius A* from the Radio to the Near-Infrared
Observations of Sgr A* over the past 4 years with the Keck Telescope in the near-infrared, coupled with millimeter and submillimeter observations, show that the 3.7 x 10^6 M[8] Galactic Black Hole, Sagittarius A*, displays continuous variability at all these wavelengths, with the variability power concentrated on characteristic time scales of ˜2 hours, and with a variability fraction that increases with wavelength. Interpreted as a dynamical time, the few-hour variability time scale corresponds to a radial distance of 2 AU, or 25 Schwarzchild radii. Searches for quasi-periodicities in the near-infrared data from the Keck Telescope have so far been negative. One implication of the character of these variations is that they most likely result from a recurring disk instability, rather than from variations in the mass accretion rate flowing through the outer boundary of the emission region. Other implications for activity in and near the presumed accretion disk, including processes giving rise to X-ray flares, will be discussed. |
| 15:12-15:30 | L. Subr
Stellar dynamics with Kozai's resonance in Sagittarius A*
By numerical simulations we further examine the motion of stars and the resulting structure of a central stellar cluster around a supermassive black hole. In our computations we include a gradual decay of stellar orbits via dissipative interaction with an accretion disc. We discuss a steady-state model of the central cluster and we estimate the rate at which stars migrate to the centre. Combination of an axisymmetric gravitational field and the dissipative environment can provide a mechanism explaining the origin of stars on highly eccentric orbits near the central black hole. |
| 15:30-16:00 | Coffee |
|
Session X - Ultraluminous X-ray sources
|
| Chair |
M. Abramowicz |
| 16:00-16:36 | K. Makishima
Observational Evidence for Intermediate-Mass Black Holes: Ultra-Luminous X-ray Sources
Ultra-luminous compact X-ray sources (ULXs; Makishima et al. 2000) are promising candidates for intermediate-mass black holes. This candidacy comes in the first place from their high X-ray luminosities reaching 10^39.5-40.5 erg/s, corresponding to the Eddington limits for 20-200 M[sun] black holes. Although ULXs could be normal stellar-mass black holes with highly super-Eddington and/or anisotropic X-ray emission (e.g., King 2002), this possibility is considered rather low because of the absence of such abnormally luminous states among known Galactic and Magellanic black-hole binaries (BHB). Although ULXs exhibit rather complex spectral behavior, they are typically found in either multi-color-disk type spectral state, or in power-law type one. The former state of ULXs may be distinguished from the standard-disk state of Galactic/ Magellanic BHBs, by the rather high disk temperature (Makishima et al. 200) of ULXs and apparent non-constancy of their inner-disk radii (Mizuno et al. 2001). Observations with the CCD camera (XIS) onboard Suzaku launched in 2005 July, as well as the XMM-Newton EPIC (e.g., Foschini et al. 2005; Tsunoda et al. 2006), suggest that the multi-color-disk type spectra are in reality emitted by slim disks (Watarai et al. 2001), which may form around black holes under super-critical accretion rate (but the luminosity remaining only slightly super-Eddington; Kubota and Makishima 2004; Abe et al. 2005). The Hard X-ray Detector onboard Suzaku is providing useful upper limits on the 15-50 keV emission from a few ULXs. It is intriguing that a fair fraction of ULXs are surrounded by optical line-emitting nebulae (Pakull 2004). In X-rays as well, some ULXs may be accompanied by thin-thermal spectral components (e.g., Miyaji et al. 2001). This possibility is reinforced by the Suzaku XIS data, and archival XMM-Newton data. These optical and X-ray results suggest that each ULX is surrounded by a gigantic hot plasma bubble, which could be interpreted as a remnant of the explosion which produced the IMBH. (Invited Review) |
| 16:36-16:54 | P. A. Charles
SS433-type X-ray Binaries and the Nature of ULXs
The nature of the ultra-luminous X-ray sources (ULXs) discovered in significant numbers in nearby galaxies by XMM and CXO continues to be a controversial topic. Interpreted simply as Eddington-limited accreting binaries implies compact object masses substantially in excess of those derived for typical galactic black-hole X-ray binaries. Whilst this could be alleviated by the effects of relativistic beaming, no ULXs have been observed in our own Galaxy. However, the best example of relativistic jets in our Galaxy is the prototypical microquasar SS433, an apparently very weak X-ray source, yet its jet power is enormous. Nevertheless there continues to be great argument over the nature of the compact object in SS433 and I will review the most recent studies, showing why super-Eddington limited accretion can lead to extremely dense outflowing winds that make dynamical studies next to impossible. Of potential significance to the nature of SS433 is the discovery by INTEGRAL of a new class of highly obscured high-mass X-ray binaries, one of which we have discovered to exhibit a long-term modulation on a timescale similar to that of SS433's precessing jets. |
| 16:54-17:00 | S. N. Fabrika
The Supercritical Accretion Disk in SS433 and Ultraluminous X-ray Sources
SS433 is the only known persistent supercritical accretor, it may be very important for understanding ultraluminous X-ray sources (ULXs) located in external galaxies. We describe main properties of the SS433 supercritical accretion disk and jets. Basing on observational data of SS433 and published 2D-simulations of supercritical accretion disks we estimate parameters of the funnel in the disk/wind of SS433 and discuss formation of the jets. We argue that the UV radiation of the SS433 disk (˜50000 K, ˜10E40 erg/s) is roughly isotropical, but X-ray radiation (~10E7 K, ˜10E40 erg/s) of the funnel is middle anisotropical. A face-on SS433 star has to be ultraluminous in X-rays (10E(40-41) erg/s). Expected typical time-scales of the funnel flux variability are 10-100 sec. Shallow, very broad (0.1-0.3c) and blue-shifted absorption lines (O, Fe, Ni) are expected in the funnel X-ray spectrum. |
| 17:00-17:12 | T. Preibisch
Sequentially triggered SF in OB associations (Invited) |
| 17:12-17:30 | P. Abolmasov
The Optical Counterpart of an Ultraluminous X-ray Source NGC6946X-1
We present a study of a peculiar nebula MF16 associated with an Ultraluminous X-ray Source NGC6946 X-1. We use integral-field and long-slit spectral data obtained with the 6-m telescope (Russia). The nebula is found to be very dense (n[e] ˜ 10^3 cm^ -3), highly asymmetric and expanding with about 100 km/s. A velocity gradient was detected in the integral-field data. The expansion velocity is similar to that of a Supernova Remnant (SNR) of a comparable size. The total power of the emission-line source, however, exceeds by about an order of magnitude that of brightest SNRs, that points to an existence of an additional source of excitation and ionization. Using CLOUDY96.01 photoionization code we derive the properties of the photoionizing source. Its total UV/EUV luminosity must be about 10^40 erg/s. Such an ultraviolet luminosity is too high for a standard accretion disk around an Intermediate Mass Black Hole, but could be produced by a Supercritical Accretion disk like that in SS433. The observed velocity gradient can be understood as an impact of a collimated wind or jets. |
| 17:30-20:00 | Poster viewing |
| 20:00 | Farewell reception of the General Assembly |
| Thursday 24 August 2006 |
|
Session XI - Ultraluminous X-ray sources
|
| Chair |
B. Czerny |
| 09:00-09:18 | R. Soria
Recipes for ULX formation: necessary ingredients and garnishments
There is growing evidence that ultraluminous X-ray sources (ULXs) are the upper end of, or an extension to the high-mass X-ray binary (HMXB) population. Their higher luminosities, longer duration of the high state, and X-ray spectra dominated by a power law rather than a disk component, may be explained by higher masses of the accreting black holes (up to about 100 solar masses) as well as higher accretion rates from the OB companions. How and where can those massive black holes be formed? The association of many of the brightest ULXs (L_x >˜ 1E40 erg/ s) with collisional environments gives an important hint. We suggest that galaxy-galaxy or cloud-galaxy collisions may produce two parallel, independent effects. Firstly, they often trigger starbursts or enhance the global star formation rate. This increases the normalization of the HMXB luminosity function but it should not increase the upper luminosity cut-off, i.e., it does not help producing the brightest ULXs. Secondly, more importantly, collisions may trigger a qualitatively different process of star formation, inducing the dynamical collapse of molecular clumps and the formation of very massive progenitor stars (at least 200 solar masses). If the metal abundance is sufficiently low (of order 1/10 of the solar abundance), those massive stars may evolve into rather massive black holes, impossible to produce at solar metallicity. In summary, we argue that the necessary conditions for the formation of the brightest ULXs are: local star formation triggered by fast cloud collisions, and low metal abundance. A high star formation rate in the host galaxy is neither a necessary nor a sufficient condition. Other processes such as core collapse in super star-clusters might occasionally create ULXs but are not the main formation channel. |
| 09:18-09:36 | S. Tsuruta
Explosion of Very Massive Stars and the Origin of Intermediate Mass Black Holes
We calculate the evolution, explosion, collapse, and nucleosynthesis of Population III very-massive stars with 500 solar mass and 1000 solar mass. The evolution is calculated in spherical symmetry, while the explosion, collapse and nucleosynthesis are calculated by a two-dimensional code, based on the bipolar jet models. We compare the results of nucleosynthesis with the abundance patterns of intercluster matter, hot gases in M82, and extremely metal-poor stars in the Galactic halo. It was found that both 500 solar mass and 1000 solar mass models enter the stage of iron-core collapse, not pair-instability supernovae. Our results suggest that the explosions of Population III very-massive stars contribute significantly to the chemical evolution of gases in clusters of galaxies. The final black hole masses are about 500 solar mass for our most massive 1000 solar mass models. This result may support the view that Population III very massive stars are responsible for the origin of intermediate mass black holes which were recently reported to be discovered. |
| 09:36-09:54 | Z. Kuncic
Ultra-Luminous X-ray Sources: X-ray Binaries in a High/Hard State?
We calculate the broadband radio-to-X-ray spectra predicted by micro-blazar/quasar models for Ultra-Luminous X-ray sources (ULXs), exploring the possibility that their dominant power-law component is produced by a relativistic jet, even at near-Eddington mass accretion rates. We do this by first constructing a generalized disk-jet theoretical framework in which some fraction of the total accretion power is efficiently removed from the accretion disk by a magnetic torque responsible for jet formation. Thus, for different black hole masses, mass accretion rates and magnetic coupling strength, we self-consistently calculate the relative importance of the modified disk spectrum, as well as the overall jet emission due to synchrotron and Compton processes. In general, transferring accretion power to a jet makes the disk fainter and cooler than a standard disk at the same mass accretion rate; this may explain why the soft spectral component appears less prominent than the dominant power-law component in most bright ULXs. We show that the apparent X-ray luminosity and spectrum produced by relativistic beaming are consistent with the observed properties of most ULXs. We predict that the radio synchrotron jet emission is too faint to be detected at the typical threshold of radio surveys to date. This is consistent with the high rate of non-detections over detections in radio counterpart searches. Conversely, we conclude that the observed radio emission found associated with a few ULXs cannot be due to beamed synchrotron emission from a relativistic jet. |
| 09:54-10:12 | M. Cropper
On the Nature of Ultra-Luminous X-ray Sources from Optical/IR Measurements
Ultra-luminous X-ray sources (ULX) are at the extreme of the luminosity function (log(E)>40 ergs/sec) of stellar X-ray sources in nearby galaxies. They achieve their high luminosity through high rates of accretion onto at least moderately massive black holes. Most of the X-ray emission is from regions close to the black hole where complicated physical effects have to be accommodated. Our current understanding of ULX is mostly based on these X-ray observations, but with the identification of their optical/IR counterparts, we have additional constraints on their nature. Here we present a model for the optical/IR signature of ULX, which takes into account the effects of intense X-ray irradiation on the accretion disk and mass-donor secondary star. We also include the secondary star evolution for consistency in the calculations of both the intrinsic and mass-transfer induced emission from the system. We compare our model predictions with HST and ground-based photometric observations. Using our model and the observational data, we constrain the masses, radii and ages of the ULX mass-donor stars, and provide limits on the black hole masses. |
| 10:12-10:30 | A. Wolter
Variability of UltraLuminous X-ray Sources in the Cartwheel Ring
The Cartwheel galaxy is one of the most outstanding examples of star formation occurring in a peculiar ring structure. We have detected 16 Ultra Luminous X-ray sources in the ring with Chandra. Their LF is consistent with them being High Mass X-ray Binaries. The brightest source, detected by Chandra at Lx=1.e41 cgs, can be considered an Hyperluminous source, and is one of the brightest non nuclear sources in external galaxies. We have observed the Cartwheel with XMM-Newton in two epochs. The HLX flux of the first epoch is consistent with the Chandra observation, but the source has dimmed by at least a factor of two 6 months later, in the second observation. This fact implies that the source might harbour an Intermediate Mass Black Hole. Other sources in the ring vary in flux between the different datasets. We will discuss our findings in the context of ULX and HLX models. |
| 10:30-11:00 | Coffee |
|
Session XII - Supermassive black holes and their galaxies
|
| Chair |
G. Hasinger |
| 11:00-11:36 | L. Ferrarese
The Inner Workings of Early-Type Galaxies: Supermassive Black Holes and Stellar Nuclei
Stellar and gas dynamical studies in an ever-increasing number of galaxies have established that many --- and perhaps all --- luminous galaxies contain central supermassive black holes (SBHs). Following the discovery that the SBH masses correlate with various properties of the host galaxy --- such as bulge luminosity, mass, velocity dispersion, light concentration, and halo circular velocity --- it has become widely accepted that SBH and galaxy formation are closely entwined. Most recently, imaging surveys with the Hubble Space Telescope have shown that 50 to 80% of low- and intermediate-luminosity galaxies contain a compact stellar nucleus at their center, regardless of host galaxy morphological type. This contribution explores the connection between stellar nuclei, SBHs and host galaxies. Using data for a large, representative sample of early-type galaxies in the Virgo cluster , obtained as part of the ACS Virgo cluster Survey (ACSVCS), the masses of compact stellar nuclei are shown to obey a tight correlation with the masses of the host galaxies. The same correlation is obeyed by SBHs found in predominantly massive galaxies. One possibile interpretation of these results is that a generic by-product of galaxy formation is the creation of a "central massive object" (CMO) --- either a SBH or a compact stellar nucleus --- that contains a mean fraction, ˜0.2%, of the total galactic mass. In galaxies with masses greater than a few tens of billion of solar masses, SBHs might be the dominant mode of CMO formation. (Invited) |
| 11:36-11:54 | G. B. Taylor
Imaging Compact Binary Black Holes with VLBI
Given that most galaxies harbor supermassive black holes at their centers, and that galaxy mergers are common, binary black holes should likewise be common. Yet very few systems have been found, perhaps because they proceed rapidly to parsec-scale separations which cannot be resolved by current X-ray or optical telescopes. Fortunately, in the case where both black holes are radio loud, they can be imaged using Very Long Baseline Interferometry. An understanding of the evolution and formation of these systems is important for an understanding of the evolution and formation of galaxies in general. We report on the discovery of a supermassive binary black-hole (SBBH) system in the radio galaxy 0402+379, with a projected separation between the two black holes of just 7.3 pc. This is the most compact SBBH pair yet found by more than two orders of magnitude. These results are based upon multi-frequency imaging using the Very Long Baseline Array (VLBA) which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of 0402+379. Multi-epoch observations from the VLBA also provide constraints on the total mass and dynamics of the system. The two nuclei appear stationary while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hot spots. The discovery of this system has implications for the number of compact binary black holes that might be sources of gravitational radiation. The VLBI Imaging and Polarimetry Survey (VIPS) currently underway should discover several more SBBHs. |
| 11:54-12:12 | F. D. Macchetto
Radiatively Inefficient Accretion Disks in Low-Luminosity AGN.
Low luminosity AGN (LLAGN) are an important class of sources, since they represent a laboratory to study accretion of matter onto supermassive black holes at the lowest level of activity. Unfortunately, emission from radiatively inefficient accretion flows, (RIAFs), is often swamped by other radiation processes. With the HST, we have studied a local sample of LLAGN, which extends from the least luminous LINERs up to low power radio galaxies. With HST's resolution we can disentangle the faint nuclear sources associated with either the accretion process or with ejection of matter from the vicinity of the black holes. Our results give us a powerful tool to find objects in which RIAFs can be detected. We discuss the SED of some LLAGN, and in particular NGC 4565, a Seyfert galaxy that shows clear evidence for the existence of RIAFs. |
| 12:12-12:30 | H. A. Dottori
THE CENTRAL 80x200 PARSECS OF M83, HOW MANY BH AND HOW MASSIVE ARE THEY?
GEMINI-S+CIRPASS configuration has been used to obtain 490 spectra with a spectral resolving power of 3200, centered at 1.3 microns, oriented NW-SE and covering 110x280 pc of the central region of M83. We determine the kinematics of this region with 0.36 arcsec sampling and sub-arcsec resolution. Disk-like motions are detected in Pbeta at parsecs scales around: a) the optical nucleus b) center of the external K-band isophotes (Thatte et al, 2003) coincident with the CO velocity map (Sakamoto et al. 2004) both also tracing the center of the bulge (Jensen et al 1981). (c) a hidden condensation (Mast et al 2006), now more precisely located at (R,theta)=(158pc, 301deg). The present resolution allows to detect another whirl near the position of the blue-shifted lobe of the hidden condensation, coincident with a bright knot in the HST image. The disk around (a) has a radius of 12-18 pc and the two around (b) and (c) can be traced approximately up to 50-60 pc from their kinematical centers. The rotation curves can be fitted by Satoh like spheroids indicating masses of 2-4 E6 Msun, 10-15 E6 Msun and 15-20 E6 Msun respectively. Limit to the masses of central BHs can be set by supposing that the kinematics inside the r=9 pc central is dominated by the BH but outwards it have to respond to the BH+Satoh potential. The models were smoothed with 9 pc gaussian. The upper mass limit derived for the BH is for (a) ˜10^6/seni Msun, and for (b) and (c) 2-6E5/seni Msun. Many questions arise from this interesting nucleus: 1- Are we witnessing a unique phenomenon or simply a barred galaxy with ongoing strong SF in our backyard? Does each one of the condensations host a BH? or there is only one at the bulge or kinematical center? N-body simulations show that nuclei (a), (b) and (c) will merge in 10-50 Myrs. What would happens with the putative BHs after the merge? |
| 12:30-13:00 | R. Mushotzky
Black Holes Across The Mass Spectrum- From Stellar Mass BHs To Ulxs And AGN
I will discuss the observational characteristics of black holes and how they compare across the 10^8 range in mass and as a function of luminosity and apparent Eddington ratio. I will concentrate on the broad band spectrum, the timing signatures and the energy budget of these objects. In particular I will compare and contrast the similarities and differences in the x-ray spectra and power density spectra of AGN, ultraluminous x-ray sources and galactic black holes as a function of 'state'. I will also discuss the nature of the Fe K line in these 3 classes of objects and other diagnostics of the regions near the event horizon. (Invited Review) |
| 13:00 | Lunch |
| Friday 25 August 2006 |
|
Session XIII - Supermassive black holes and their galaxies
|
| Chair |
S. Collin |
| 09:00-09:18 |
T. Storchi-Bergmann
Inward Bound: Following the Gas Flow from Nuclear Spirals to the Accretion Disk
One of the possible processes by which gas from galactic scales reaches an active nucleus to feed the supermassive black hole inside is through streaming motions along nuclear gaseous spirals. I present an analysis of HST images of a sample of 50 nearby active galaxies as compared with a control sample of inactive galaxies which indeed shows a clear excess of nuclear dusty spirals in the active galaxies when compared with the control sample. In the case of the LINER/Seyfert 1 galaxy NGC1097, I show also kinematic evidence of streaming motions along a nuclear spiral down to 30 pc from the nucleus, obtained through H alpha Integral Field spectroscopy of the nuclear region using the Gemini South Telescope. I then use the accretion disk parameters derived from the fit of the nuclear X-ray and UV continuum as well as from the fit of the double-peaked Halpha profile to relate the accretion rate of the disk to the large scale streaming motions along the nuclear spiral. In this way, I derive constraints to the total mass rate reaching the accretion disk and on the geometry of the flow in the region between the innermost resolvable radius of the nuclear spiral (30 pc) and the outer radius of the accretion disk. |
| 09:18-09:36 | C. Y. Peng
Probing the Coevolution of Supermassive Black Holes and Galaxies Out to z˜4.5 Using Gravitational Lensing
In the local universe, supermassive black holes (BH) appear to be closely related to their host galaxy's mass, luminosity, and stellar velocity dispersion. These correlations are clues that may help understand how galaxies grow and evolve. Quasar host galaxies are currently the best way to study the BH-bulge correlations because only in quasars may both quantities be reliably estimated out to significant look-back times. But the experiment is non-trivial because of the high contrast between the quasars and their host. Gravitational lensing is a powerful tool for this purpose because lensing can magnify the host galaxy's size relative to the quasar, allowing for easier host detection and separation from the central AGN. We have extend the study of the BH/bulge scaling relations out to redshift 4.5. We find that the ratio of the BH-to-bulge mass is on average a factor of 4 higher at z˜2 than today (G(z), see Figure), which at face value suggests that galaxies would also grow by the same factor since the peak of the quasar epoch. This can be reconciled with observations of nearby BH-bulge relations through a combination of star formation and galaxy merging. We discuss several other projects underway to improve on the results. |
| 09:36-09:54 | A. J. Barth
The smallest black holes in nearby AGNs
The well-known correlations between black hole mass and host galaxy bulge properties are now firmly established for galaxies with velocity dispersions between about 70 and 400 km/sec, and black holes with masses from a few million to a few bililon solar masses. However, extending the black hole census to smaller masses is challenging because we cannot generally resolve the gravitational sphere of influence of black holes with masses below a few million solar masses, at distances greater than a few Mpc. Currently, the best way to find evidence for smaller black holes is through AGN surveys. We will describe recent work aimed at identification of the smallest and least massive AGN host galaxies. New Keck observations have been used to determine the stellar velocity dispersions in the least luminous and least massive Seyfert 2 host galaxies in the Sloan Digital Sky Survey. We have identified a sample of Seyfert 2 host galaxies having central stellar velocity dispersions smaller than 60 km/sec (the lowest being 25 km/sec), which are likely candidates for having black hole masses of ˜10^6 solar masses or less. We will describe the properties of these AGNs and their host galaxies, and their implications for the demographics of low-mass black holes. We will also describe new XMM-Newton observations of the dwarf Seyfert 1 galaxy POX 52, which has a black hole mass of order 10^5 solar masses. |
| 09:54-10:12 | C. D. Impey
The Evolution of Supermassive Black Holes and Galaxies in the COSMOS Survey
COSMOS is an HST imaging survey of 2 square degrees that is coupled to a large galaxy redshift survey and extensive multi-wavelength (X-ray to radio) data. The combination of breadth and depth surpasses any other deep survey, allowing the co-evolution of galaxies and black holes to be followed with unprecedented statistics in a single contiguous volume. Spectroscopy with the Magellan telescope will yield a sample of ˜1000 confirmed AGN. This interim report on the survey summarizes the host morphologies and galactic environments of AGN in the range 0.5 < z < 2.5, and the relationship of the energy distribution and emission line properties to large scale environment. The coupled evolution of black holes and their surrounding galaxies means that surveys like this are required to disentangle the fueling of AGN and the effect of AGN activity on the surrounding galaxy. |
| 10:12-10:30 | J. Woo
Cosmic Evolution of Black Holes and Galaxies to z=0.4
Investigating the nature of the black hole-galaxy connection is essential in understanding black hole growth and galaxy evolution. We test the evolution of the correlation between black hole mass and bulge velocity dispersion (M[BH]- ) using a carefully selected sample of 14 Seyfert 1 galaxies at z=0.36±0.01. We measure velocity dispersion from stellar absorption lines around Mgb (5175A) and Fe (5270A) using high S/N Keck spectra, and estimate black hole mass from the H line width and the optical luminosity at 5100A, based on the empirically calibrated photo-ionization method. We find a significant offset from the local relation, in the sense that velocity dispersions were smaller for given black hole masses at z=0.36 than locally. The measured offset is log M[BH] = 0.62±0.10 ±0.25, i.e. log =0.15 ±0.03 ± 0.06, where the error bars include a random component and an upper limit to the systematics. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M [BH]- relation is the universal evolutionary end-point. Along with two samples of active galaxies with consistently determined black hole mass and stellar velocity dispersion taken from the literature, we quantify the observed evolution± with the best fit linear relation, log M[BH] = (1.66±0.43)z + (0.04±0.09) with respect to the local relationship of Tremaine et al. (2002), and log M[BH] = (1.55±0.46)z + (0.01±0.12) with respect to that of Ferrarese (2002). This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales (< > =170 km s^-1). |
| 10:30-11:00 | Coffee |
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Session XIV - Black holes across the mass spectrum
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| Chair |
F. Mirabel |
| 11:00-11:18 |
J. M. Hameury
The Disc Instability Model for Dwarf Novae in the AGN Context
Accretion discs in AGN should be subject to the same type of instability as in cataclysmic variables (CVs) or in LMXBs, which leads to dwarf novae outbursts and soft X-ray transients. It has been suggested that this thermal/viscous instability can account for long term variability of AGNs. Using our adaptative grid numerical code developed in the context of CVs, we show that, because the Mach number is very large in AGNs, the width of the heating and cooling fronts is so small that they cannot be resolved by standard codes, and that they propagate on time scales much smaller than the viscous time. As a result, a sequence of heating and cooling fronts propagate back and forth in the disc, leading to small variations of the accretion rate onto the black hole. Truncation of the inner part of the disc by e.g. an ADAF does not alter this result. We finally discuss on the possible effects of irradiation by the central X-ray source. |
| 11:18-11:36 | K. Ohsuga
Radiation Hydrodynamic Simulations of Super-Eddington Accretion Flows
We study the global structure of super-Eddington accretion flows around black holes by performing the two-dimensional radiation-hydrodynamic simulations. Super-Eddington accretion is one of the plausible mechanisms for formation of the Super-massive black holes in the early universe. It is also thought to exist in some quasars and NLS1s. Our numerical simulations show that the super-Eddington accretion flow is composed of two parts: the radiation pressure-supported disk and the radiation pressure-driven outflow above the disk. It is found that the mass-accretion rate onto the BH considerably exceeds the critical value. It implies that the black hole can rapidly grow. Its timescale is about 10^6 yr. Apparent luminosity is much larger than the Eddington luminosity. Thus, the large luminosity in ULXs can be explained without IMBHs. In addition, we study the limit-cycle oscillations, which are induced by the disk instability. Our simulations succeed in reproducing the recurrent outbursts in microquasar, GRS 1915+105. |
| 11:36-11:54 | M. Tuerler
Synchrotron Outbursts in Galactic and Extra-galactic Jets, Any Difference?
We discuss differences and similarities between jets powered by super-massive black holes in quasars and by stellar-mass black holes in micro-quasars. The comparison is based on multi-wavelength radio-to-infrared observations of the two active galactic nuclei 3C 273 and 3C 279, as well as the two galactic binaries GRS 1915+105 and Cyg X-3. The physical properties of the jet are derived by fitting the parameters of a shock-in-jet model simultaneously to all available observations. We show that the variable jet emission of galactic sources is, at least during some epochs, very similar to that of extra-galactic jets. As for quasars, their observed variability pattern can be well reproduced by the emission of a series of self-similar shock waves propagating down the jet and producing synchrotron outbursts. This suggests that the physical properties of relativistic jets is independent of the mass of the black hole. For more information on this work, including animated images and figures, visit: http://isdc.unige.ch/˜turler/jets/ |
| 11:54 | Closing: Present status and future developments of black holes across the range of masses; F. Mirabel |
