有吸积盘时径向运动云的谱线轮廓

在活动星系核的黑洞模型中,黑洞附近运动的电离云所发出的光线将要受到多普勒频移、引力红移和光线偏折等效应的影响,如果黑洞周围还有吸积盘存在,电离云的辐射还可能被吸积盘遮挡。本文全面地考虑了这些效应,利用光子输运方程方法,给出了在Schwarzchild度规中径向运动电离云发出的谱线轮廓的精确解,并发现在某些情况下将出现不对称的双峰结构。     

Line emission from accretion discs around black holes: the analytic approach

The broad X-ray iron line observed in many active galactic nuclei spectra is thought to originate from the accretion disc surrounding the putative supermassive black hole. We show here how to perform the analytical integration of the geodesic equations that describe the photon trajectories in the general case of a rotating black hole (Kerr metric), in order to write a fast and efficient numerical code for modelling emission line profiles from accretion discs.     

Line Shape Variability in a Sample of AGN with Broad Lines

The spectral variability of active galactic nuclei (AGN) is one of the key features that enables us to study in more detail, the structure of AGN emitting regions. Especially, the broad line profiles that vary both in flux and shape, give us invaluable information about the kinematics and geometry of the broad line region (BLR) where these lines are originating from. We give here a comparative review of the line shape variability in a sample of five type 1 AGNs, those with broad emission lines in their spectra, of the data obtained from the international long-term optical monitoring campaign coordinated by the Special Astrophysical Observatory of the Russian Academy of Science. The main aim of this campaign is to study the physics and kinematics of the BLR on a uniform data set, focusing on the problems of the photoionization heating of the BLR and its geometry, where, in this paper, we give for a first time, a comparative analysis of the variabilty of five type 1 AGNs, discussing their complex BLR physics and geometry in the framework of the estimates of the supermassive black hole mass in AGN.     

The effect of a central supermassive black hole on gas fuelling

When a supermassive black hole exists in the centre of a galaxy, an additional inner Lindblad resonance (ILR) exists inside the usual ILRs. We study gas dynamics in a weakly barred potential with a central supermassive black hole by using 2D numerical simulations, and we investigate the effect of the additional ILR on the fuelling of gas into nuclear starburst regions or active galactic nuclei (AGNs). Our numerical results show that strong trailing spiral shocks are formed at the resonance region, and that the gas in the shock region is rapidly fuelled into a central region and makes a nuclear gas ring. As a result, a large amount of gas is concentrated in the nuclear region beyond the ILR in a dynamical time-scale.     

Compact jets as probes for sub-parsec scale regions in AGN

Compact relativistic jets in active galactic nuclei offer an effective tool for investigating the physics of nuclear regions in galaxies. The emission properties, dynamics, and evolution of jets in AGN are closely connected to the characteristics of the central supermassive black hole, accretion disk and broad-line region in active galaxies. Recent results from studies of the nuclear regions in several active galaxies with prominent outflows are reviewed in this contribution.     

Effects of inflationary bubbles on the polarization and temperature anisotropies of the cosmic microwave background

The broad X-ray iron line, detected in many active galactic nuclei, is likely to be produced by fluorescence from the X-ray-illuminated central parts of an accretion disc close to a supermassive black hole. The time-averaged shape of the line can be explained most naturally by a combination of special and general relativistic effects. Such line profiles contain information about the black hole spin and the accretion disc, as well as the geometry of the emitting region, and may help to test general relativity in the strong gravity regime. In this paper we embark on the computation of the temporal response of the line to the illuminating flux. Previous studies concentrated on the calculation of reverberation signatures from static sources illuminating the disc. In this paper we focus on the more physically justified case of flares located above the accretion disc and corotating with it. We compute the time-dependent iron line, taking into account all general relativistic effects, and show that its shape is of a very complex nature, and we also present light curves accompanying the iron line variability. We suggest that present and future X-ray satellites like XMM or Constellation-X may be capable of detecting features present in the computed reverberation maps.     

Determination of Supermassive Black Hole Spins Based on the Standard Shakura–Sunyaev Accretion Disk Model and Polarimetric Observations

Based on spectropolarimetry for 47 type 1 active galactic nuclei observed with the 6-m BTA telescope, we have estimated the spins of the supermassive black holes at the centers of these galaxies. We have determined the spins based on the standard Shakura–Sunyaev accretion disk model. About 70% of the investigated active galactic nuclei are shown to have Kerr supermassive black holes with a dimensionless spin greater than 0.9.     

X-rays from cusps of compact remnants near galactic centres

Compact remnants – stellar mass black holes and neutron stars formed in the inner few parsec of galactic centres are predicted to sink into the central parsec due to dynamical friction on low-mass stars, forming a high concentration cusp. Same physical region may also contain very high-density molecular clouds and accretion discs that are needed to fuel supermassive black hole (SMBH) activity. Here we estimate gas capture rates on to the cusp of stellar remnants, and the resulting X-ray luminosity, as a function of the accretion disc mass. At low disc masses, most compact objects are too dim to be observable, whereas in the high disc case most of them are accreting at their Eddington rates. We find that for low accretion disc masses, compact remnant cusps may be more luminous than the central SMBHs. This 'diffuse' emission may be of importance for local moderately bright active galactic nuclei (AGNs), especially low-luminosity AGNs. We also briefly discuss how this expected emission can be used to put constraints on the black hole cusp near our Galactic Centre.     

The active galaxy NGC 4151: Archetype or exception?

Summary. The Seyfert galaxy NGC 4151 harbors in its nucleus the most intensively studied AGN (Active Galactic Nucleus). Among the brightest AGN (in apparent luminosity) it is the most widely variable and the variations of its ultraviolet and X-ray spectrum have been studied on time scales ranging from hours to decades. These observations have formed the basis of methods and models which have been found to generally apply to broad emission line AGN: the rich and complex relation between the X-ray and UV variations, the comptonization model of the X-ray spectrum from medium X-ray to -rays, the reverberation mapping, the stratification in velocity and physical conditions of the gas in the broad line region, and a method to estimate the black hole mass from emission line variability. The large barred spiral which hosts this nucleus has been extensively studied especially in the central region. Inflow of gas along the and possibly also the orbits have been detected, but since the accretion disk is not in the galactic plane (as evidenced by the significant angle separating the radio axis and the rotation axis of the galaxy) the incoming gas seen on kpcs scale must, as it flows further inward, move out of the galactic plane, along trajectories which are entirely unknown. There is more to learn on NGC 4151. In fact, the best is yet to come. Three avenues of investigation appear particularly promising: 1) The variations in flux and spectral shape of the X-ray continuum and its relationship with the UV variations are the key to understanding the specifics of the Comptonization model. Progress on this point will come from repeated simultaneous observations of the UV spectrum and of the entire X-ray and -ray spectrum. This will also give insights on the structure of the disk in the last stable orbits, the formation and structure of the corona and in the end, the process of energy production. Exciting results on these topics are expected in the near future from Chandra-AXAF, XMM and INTEGRAL. The Chandra and XMM (which have short energy range) main contributions will, however, be line diagnostics and for Chandra, imaging of the soft diffuse emission. 2) The search for the gas inflow which merges into and/or forms the torus could finally be successful. Several powerful approaches are possible: observing molecular lines in emission with millimeter arrays of increasing baseline and collecting area; using the nuclear radio structure as background source to observe free-free and atomic or molecular lines in absorption. 3) The observations of NGC 4151 during a state of deep minimum will provide a unique oportunity to observe the X-ray spectrum of a Seyfert 1 nucleus at epochs of very low accretion rate, to identify the nature of the narrow variable lines, to determine the stellar population of a currently active nucleus, and measure the mass of the black hole from the stellar lines. NGC 4151 at minimum states should be a target of opportunity for all space missions. In addition, observations on time scales of 10 years or more, especially following a deep minimum, will allow one to map emitting regions of size up to 1pc, thereby overlapping with the linear scale directly mapped with large radio telescopes. Received 30 October 1999 / Published online: 24 March 2000     

Ultra high energy cosmic ray generation in black hole magnetosphere: testing by polarimetric observations

We develop the method that allows to estimate ultra high energy cosmic ray (UHECR) production in active galactic nuclei (AGNs). We used the model developed by Neronov et al. (New J. Phys. 11:065015, 2009) and estimated the magnetic field strength near the innermost stable orbit in an accretion disk and at the horizon radius of a supermassive black hole (SMBH) using the data of polarimetric observations of broad lines emission. It allows to estimate the kinetic power of the relativistic jet at the base of Blandford–Znajek mechanism. In a result we estimated the cosmic ray power for a number of AGNs with known values of SMBH spins.     

Supermassive black holes, star formation and downsizing of elliptical galaxies

The overabundance of Mg relative to Fe, observed in the nuclei of bright ellipticals, and its increase with galactic mass, poses a serious problem for all current models of galaxy formation. Here, we improve on the one-zone chemical evolution models for elliptical galaxies by taking into account positive feedback produced in the early stages of supermassive central black hole growth. We can account for both the observed correlation and the scatter if the observed anti-hierarchical behaviour of the AGN population couples to galaxy assembly and results in an enhancement of the star formation efficiency which is proportional to galactic mass. At low and intermediate galactic masses, however, a slower mode for star formation suffices to account for the observational properties.     

X-ray reverberation around accreting black holes

Luminous accreting stellar mass and supermassive black holes produce power–law continuum X-ray emission from a compact central corona. Reverberation time lags occur due to light travel time delays between changes in the direct coronal emission and corresponding variations in its reflection from the accretion flow. Reverberation is detectable using light curves made in different X-ray energy bands, since the direct and reflected components have different spectral shapes. Larger, lower frequency, lags are also seen and are identified with propagation of fluctuations through the accretion flow and associated corona. We review the evidence for X-ray reverberation in active galactic nuclei and black hole X-ray binaries, showing how it can be best measured and how it may be modelled. The timescales and energy dependence of the high-frequency reverberation lags show that much of the signal is originating from very close to the black hole in some objects, within a few gravitational radii of the event horizon. We consider how these signals can be studied in the future to carry out X-ray reverberation mapping of the regions closest to black holes.     

Super-massive binary black holes and emission lines in active galactic nuclei

It is now agreed that mergers play an essential role in the evolution of galaxies and therefore that mergers of supermassive black holes (SMBHs) must have been common. We see the consequences of past supermassive binary black holes (SMBs) in the light profiles of so-called ‘core ellipticals’ and a small number of SMBs have been detected. However, the evolution of SMBs is poorly understood. Theory predicts that SMBs should spend a substantial amount of time orbiting at velocities of a few thousand kilometers per second. If the SMBs are surrounded by gas observational effects might be expected from accretion onto one or both of the SMBHs. This could result in a binary Active Galactic Nucleus (AGN) system. Like a single AGN, such a system would emit a broad band electromagnetic spectrum and broad and narrow emission lines.The broad emission spectral lines emitted from AGNs are our main probe of the geometry and physics of the broad line region (BLR) close to the SMBH. There is a group of AGNs that emit very broad and complex line profiles, showing two displaced peaks, one blueshifted and one redshifted from the systemic velocity defined by the narrow lines, or a single such peak. It has been proposed that such line shapes could indicate an SMB system. We discuss here how the presence of an SMB will affect the BLRs of AGNs and what the observational consequences might be.We review previous claims of SMBs based on broad line profiles and find that they may have non-SMB explanations as a consequence of a complex BLR structure. Because of these effects it is very hard to put limits on the number of SMBs from broad line profiles. It is still possible, however, that unusual broad line profiles in combination with other observational effects (line ratios, quasi-periodical oscillations, spectropolarimetry, etc.) could be used for SMBs detection.Some narrow lines (e.g., [O III]) in some AGNs show a double-peaked profile. Such profiles can be caused by streams in the Narrow Line Region (NLR), but may also indicate the presence of a kilo-parsec scale mergers. A few objects indicated as double-peaked narrow line emitters are confirmed as kpc-scale margers, but double-peaked narrow line profiles are mostly caused by the complex NLR geometry.We briefly discuss the expected line profile of broad Fe Kα that probably originated in the accretion disk(s) around SMBs. This line may also be very complex and indicate the complex disk geometry or/and an SMB presence.Finally we consider rare configurations where a SMB system might be gravitationally lensed by a foreground galaxy, and discuss the expected line profiles in these systems.     

Shaping the relation between the mass of supermassive black holes and the velocity dispersion of galactic bulges

I use the fact that the radiation emitted by the accretion disk of supermassive black hole can heat up the surrounding gas in the protogalaxy to achieve hydrostatic equilibrium during the galaxy formation. The correlation between the black hole mass M _BH and velocity dispersion σ thus naturally arises. The result generally agrees with empirical fittings from observational data, even with M _BH ≤10⁶ M _⊙. This model provides a clear picture on how the properties of the galactic supermassive black holes are connected with the kinetic properties of the galactic bulges.     

Acceleration of particles in the vicinity of a massive black hole

Recent results of the gamma-ray Cherenkov astronomy definitely prove the existence of fast variability in the very high energy (V.H.E.) gamma-ray flux of some active galactic nuclei. The BL Lac PKS 2155-304 for instance showed variations down to a few minutes time scale. From standard light travel time argument, these variations put extremely strong constraints on the size of the TeV emitting zone, which has to be of the order of a few Schwarzschild radius, even for high values of the relativistic Doppler factor of the emitting jets. Such discovery is a challenge for particle acceleration scenarios, which have to imagine efficient acceleration processes at work in a very compact zone. Eventually, the immediate vicinity of the central black hole appears as the most conservative choice for the location of the TeV emission region of active galactic nuclei. In this paper, we propose a two-step mechanism for charged particle acceleration in the magnetosphere of a massive black hole surrounded by an accretion disk. Particles first gain energy by a stochastic process during the accretion phase. It is shown that effective proton acceleration up to energies 10¹⁷–10¹⁹ eV is possible in a low-luminosity magnetized accretion disk with 2D turbulent motion. The distribution function of energetic protons over energies is a power law function with typical index ≃−1. Here electrons are not very efficiently accelerated because of their drastic losses by synchrotron radiation. In a second time, part of the fast particles escape from the disk and are then entrained by the magnetic structure above the disk, in the rotating black hole magnetosphere. They thus gain additional energy by direct centrifugal mechanism, up to about 10²⁰ eV for the protons and to 10–100 TeV for the electrons when they cross the light cylinder surface. Such energetic particles can further radiate in the TeV spectral range observed by Cherenkov experiments as HESS, MAGIC and VERITAS. Energetic protons can produce γ-radiation in the energy band 1 GeV–100 TeV and above mainly by nuclei collisions with the disk matter, clouds, or ambient low energy photons. Energetic electrons can also reach the required spectral range by inverse Compton emission. However their acceleration is less efficient due to heavy radiation losses, and only gained by centrifugal process during the second phase of the whole mechanism we describe. Our present analysis would therefore favor hadronic scenarios for TeV emission of active galactic nuclei. It is tempting to relate long term variability over years of TeV active galactic nuclei to the first stochastic acceleration phase, which also provides the needed power law particle distributions, while short term variability over minutes is more likely due to perturbations of the second fast direct acceleration phase.     

The problem of few black holes

The problem of few black holes becomes important in multiple mergers of galaxies. If supermassive black holes in centres of galaxies are common, then interaction of three or four supermassive black holes should also be common. The merger of two galaxies with one black hole each produces a semi-stable black hole binary system. Subsequent mergers of galaxies with their own central black holes produces dynamical few-body evolution in which mergers of black holes occur. According to our numerical simulations this evolution typically ends when only one or two black holes remain and, in the latter case, they are ejected in opposite directions from the center of the galaxy. Even when we pick the initial black hole masses at random from a wide distribution, the two black hole ejections happen rather symmetrically. Sometimes the final masses differ considerably in which case only the lighter black hole is ejected. This is caused by the potential barrier of the galaxy itself which prevents the heavy slowly moving black hole flying out of the galaxy. We discuss OJ287 as a possible example of a multiple black hole system.     

The interaction of the stars with accretion disk around the massive black hole in the nuclei of active galaxies and quasars

We consider a passage of the stars through the accretion disk near the supermassive black hole in the nuclei of active galaxies and quasars. When a star penetrates the disk, a hydrodynamical track is formed behind it. The boundary of the track is a cylindric shock-wave. The region of the track is optically thick with respect to the true absorption. The transfer of the energy dissipated by the passage of the star with a radius ≈10¹² cm (the typical dimensions of a star in a galactic nucleus) across the disk provided by the radiative heat conduction. Each star passage through the intermediate region of the disk results in the appearance of a bright spot on its surface. The energy emitted by the spots lies inside the frequency range from visible to UV, exceeding the disk luminosity due to accretion in the range considered.     

Feedback of Active Galactic Nuclei in Seyfert 2 Galaxies

It is well accepted that feedback from active galactic nuclei (AGNs) plays an important role in the coevolution of the supermassive black hole (SMBH) and its host galaxy,but the concrete mechanism of feedback remains unclear.A considerable body of evidence suggests that AGN feedback suppresses star formation in the host galaxy.We assemble a sample of Seyfert 2 galaxies with recent observational data of compact nuclear starbursts and estimate the gas surface density as a function of column density to illuminate the relation between feedback and AGN properties.Although there are some uncertainties,our data still imply the deviation from the star formation law (Kennicutt-Schmidt law).Further,they indicate that:(1) Feedback correlates with the Eddington ratio,rather than with the mass of SMBH,as a result of decreasing star formation efficiency.(2) The SMBH and the torus are probably undergoing coevolution.Conclusions presented here can be refined through future high resolution CO or HCN observations.     

Broad reprocessed Balmer emission from warped accretion discs

Double-peaked broad emission lines in active galactic nuclei are generally considered to be formed in an accretion disc. In this paper, we compute the profiles of reprocessing emission lines from a relativistic, warped accretion disc around a black hole in order to explore the possibility that certain asymmetries in the double-peaked emission-line profile which cannot be explained by a circular Keplerian disc may be induced by disc warping. The disc warping also provides a solution for the energy budget in the emission-line region because it increases the solid angle of the outer disc portion subtended to the inner portion of the disc. We adopted a parametrized disc geometry and a central point-like source of ionizing radiation to capture the main characteristics of the emission-line profile from such discs. We find that the ratio between the blue and red peaks of the line profiles becoming less than unity can be naturally predicted by a twisted warped disc, and a third peak can be produced in some cases. We show that disc warping can reproduce the main features of multipeaked line profiles of four active galactic nuclei from the Sloan Digital Sky Survey.