Indicators of black-hole mass and Eddington accretion ratio from QSO X-ray and UV spectra

The evolution of luminous QSOs is linked to the evolution of massive galaxies. We know this because the relic black-holes found locally have masses dependent on the properties of the host galaxy’s bulge. An important way to explore this evolution would be to measure dependences of black-hole masses and Eddington accretion ratios over a range of redshifts, i.e., with cosmological age. For low redshift QSOs (and their lower luminosity Seyfert galaxy counterparts) it has been possible to infer black-hole masses from the luminosities and velocity dispersions of their host-galaxy bulges. These masses agree with those virial black-hole masses calculated from the Doppler widths of the broad Hβ emission lines. The latter method can then be extended to more distant and luminous QSOs, up to redshifts of 0.6 with ground-based optical observations. We discuss ways to extend these explorations to higher redshifts – up to 3 using the widths of QSOs’ broad UV emission lines, and in principle, and to redshifts near 4 from ground-based infrared observations of rest-frame Hβ at 2.5 μm. We discuss the possibility of investigating the accretion history of the higher redshift QSOs using measures of Eddington accretion ratio – the soft X-ray spectral index and the eigenvectors of Principal Components Analyses of QSOs’ UV emission-line spectra.     

Principal components in the PG-X-ray QSO sample

We have performed a spectral principal component analysis for a complete sample of 22 low redshift QSOs with spectra from Ly to H, and found three significant principal components, which account for 78% of the spectrum-to-spectrum variance. We present strong arguments that the first principal component represents the Baldwin effect, relating equivalent widths to the luminosity (i.e. accretion rate). The second component represents continuum variations, probably dominated by intrinsic reddening. The third principal component is directly related to broad emission-line width and X-ray spectral index, and therefore probably driven by Eddington accretion ratio, L/L_Edd. The third set of relationships tie directly to the optical Principal Component 1 found by Boroson and Green [Boroson, T., Green, R.F., Astrophys. J. Suppl. 80, 109, 1992 (BG92)], and are the primary cause of scatter in the Baldwin relationships.     

Composite profile of the Fe Kα spectral line emitted from a binary system of supermassive black holes

We used a model of a relativistic accretion disk around a supermassive black hole (SMBH), based on ray-tracing method in the Kerr metric, to study the variations of the composite Fe Kα line emitted from two accretion disks around SMBHs in a binary system. We assumed that the orbit of such a binary is approximately Keplerian, and simulated the composite line shapes for different orbital elements, accretion disk parameters and mass ratios of the components. The obtained results show that, if observed in the spectra of some SMBH binaries during their different orbital phases, such composite Fe Kα line profiles could be used to constrain the orbits and several properties of such SMBH binaries.     

Observational appearances of isolated stellar-mass black hole accretion – Theory and observations

General properties of accretion onto isolated stellar-mass black holes in the Galaxy are discussed. An analysis of plasma internal energy growth during the infall is performed. Adiabatic heating of collisionless accretion flow due to magnetic adiabatic invariant conservation is 25% more efficient than in the standard non-magnetized gas case. It is shown that magnetic field line reconnections in discrete current sheets lead to significant nonthermal electron component formation, which leads to a formation of a hard (UV, X-ray, up to gamma), highly variable spectral component in addition to the standard synchrotron optical component first derived by Shvartsman generated by thermal electrons in the magnetic field of the accretion flow. Properties of accretion flow emission variability are discussed. Observation results of two single black hole candidates – gravitational lens MACHO-1999-BLG-22 and radio-loud X-ray source with featureless optical spectrum J1942+10 – in optical band with high temporal resolution are presented and interpreted in the framework of the proposed model.     

The case for massive,evolving winds in black hole X-ray binaries

In the last decade, high-resolution X-ray spectroscopy has revolutionized our understanding of the role of accretion disk winds in black hole X-ray binaries. Here I present a brief review of the state of wind studies in black hole X-ray binaries, focusing on recent arguments that disk winds are not only extremely massive, but also highly variable. I show how new and archival observations at high timing and spectral resolution continue to highlight the intricate links between the inner accretion flow, relativistic jets, and accretion disk winds. Finally, I discuss methods to infer the driving mechanisms of observed disk winds and their implications for connections between mass accretion and ejection processes.     

Obscured QSOs and the X-ray Background

The question of whether there exists a large population of dust obscured QSOs is currently very controversial. In favour of this hypothesis are models for the origin of the X-ray Background (XRB) and also the Unified Model of AGN which both invoke large populations of obscured QSOs. For example, Madau et al. (1994) suggest a population of QSOs with N_H ∼ 10²⁴ cm⁻² or A_V = 1000^m to improve the fit to the XRB between 1 < E < 100 keV. Arguments contradicting this theory include those of Boyle & di Matteo (1995) who claim that the tight X-ray/optical flux ratio relation for QSOs precludes the existence of a large population of objects obscured by significant amounts of intrinsic dust. Here, we follow Madau et al. (1994) and Comastri et al. (1995) to make fits to the XRB using obscured QSO populations and investigate whether selection effects may allow a tight distribution of X-ray/optical ratios to be maintained. We find that even for a flat distribution of absorbing columns, reasonable fits to the XRB can be obtained while both optical and X-ray absorption combine to produce the tight observed X-ray/optical correlation.     

The demography of massive galactic black holes

This review describes dynamical evidence for massive black holes (BHs) at the centers of galaxies. BHs appear to be a common if not ubiquitous feature of local galactic spheroids, with a mean mass that is roughly 0.5% of the parent stellar spheroid mass. This mass is large enough that the formation and evolution of central BHs has had a significant influence on the inner stellar density profile. For example, low-density, core-type profiles may have been created by the scouring action of binary BH pairs, whose orbital decay ejects stars from the center of the galaxy. Or, BHs may have grown substantially by gas accretion, pulling in surrounding stars and creating the cuspy cores and power laws that are seen in spheroids. If BHs are ubiquitous in galactic spheroids at the above mass ratio, their total local mass density is comparable to that implied by the energy density of QSO photons, suggesting that these local BHs are the long-sought fossil BHs of QSO central engines. However, QSOs are much rarer per unit co-moving volume than local BHs, unless one equates them to just the massive BHs found in rare and massive local spheroids. The resultant BH masses exceed typical QSO BH mass estimates by nearly a factor of 10, suggesting that BHs have grown in mass by roughly that factor since the QSO era. At least some of that growth might have occurred as protogalaxies grew in mass by mergers, and their BHs also merged and grew apace.     

Polarization effects in radiation from compact X-ray sources

The theory of polarization effects in radiation from compact X-ray sources is presented. The following four problems are considered: 1) the polarization of X-rays from the magnetized neutron stars; 2) the polarization of X-rays from the accretion disk around a black hole; 3) the optical polarization from X-ray binaries, and 4) the results of X-ray polarimetric observations.     

Evolution of the temporal and the spectral properties in 2010 and 2011 outbursts of H 1743-322

The Galactic black hole candidate H 1743-322 exhibited two X-ray outbursts in rapid succession: one in August 2010 and the other in April 2011. We analyze archival data of this object from the PCA instrument on board RXTE (2–25 keV energy band) to study the evolution of its temporal and spectral characteristics during both the outbursts, and hence to understand the behavioral change of the accretion flow dynamics associated with the evolution of the various X-ray features. We study the evolution of QPO frequencies during the rising and the declining phases of both the outbursts. We successfully fit the variation of QPO frequency using the Propagating Oscillatory Shock (POS) model in each of the outbursts and obtain the accretion flow parameters such as the instantaneous shock locations, the shock velocity and the shock strength. Based on the degree of importance of the thermal (disk black body) and the non-thermal (power-law) components of the spectral fit and properties of the QPO (if present), the entire profiles of the 2010 and 2011 outbursts are subdivided into four different spectral states: hard, hard-intermediate, soft-intermediate and soft. We attempt to explain the nature of the outburst profile (i.e., hardness-intensity diagram) with two different types of mass accretion flow.     

Radiation of accretion disks in quasars and galactic nuclei

The continuum spectra of accretion disks around supermassive Schvarzshild black hole are calculated for a set of accretion disk parameters. In every point of the disk surface the atmosphere is considered to be similar to the atmosphere of the star with the same values of the surface gravity and effective temperature. All important effects of general relativity affected the spectrum shape are taken into account.     

Black hole spectral states and physical connections

The dramatic changes seen in the X-ray spectral and timing properties of accreting black hole candidates (BHCs) provide important clues about the accretion and jet formation processes that occur in these systems. Dividing the different source behaviors into spectral states provides a framework for studying BHCs. To date, there have been three main classification schemes with Luminosity-based, Component-based, or Transition-based criteria. The canonical, Luminosity-based criteria and physical models that are based on this concept do not provide clear explanations for several phenomena, including hysteresis of spectral states and the presence of jets. I discuss the re-definitions of states, focusing on an application of the Component-based states to more than 400 RXTE observations of the recurrent BHC 4U 1630–47. We compare the X-ray properties for the recent 2002–2004 outburst to those of an earlier (1998) outburst, during which radio jets were observed. The results suggest a connection between hysteresis of states and major jet ejections, and it is possible that both of these are related to the evolution of the inner radius of the optically thick accretion disk.     

The relevance of the Eddington limit to thick accretion disks

Thick accretion disks with narrow funnels around massive black holes are considered promising models for active galactic nuclei. These models assume a supercritical accretion rate and emit collimated beams with super-Eddington luminosities. We have made approximate calculations of the interaction between the emerging radiation and the walls for an optically thin funnel. The results are sensitive to the sound velocity and to the viscosity parameter α. They suggest that a significant particle luminosity can accompany the radiation in the super-Eddington case. By applying an Eddington type limit based on mechanical equilibrium to a suitably chosen interior surface in the disk, we find that energy transport, if radiative, can strongly limit the efficiency of these models.     

X射线选择类星体的一些性质

本文对109个X射线选择的类星体和114个射电及光学选择的类星体进行统计分析.发现在它们的红移、光学光度以及平均光学-X射线谱指数的直方分布图上, X射线选择类星体统计上都分布在这些参数图的低端.在所有样品的单色X射线光度l_X与单色光学光度l_O的关系图上, X射线选择类星体绝大部分处在光学暗的低光度区域.若以lglo=31.2erg/s·Hz为分界点, 可把光学光度划分为光学亮和暗两个区域, 则发现射电及光学选择类星体在图中光学亮区内的斜率b=0.64, 在光学暗区内的斜率b=0.95, 而X射线选择类星体的b仅为0.78, 因而暗示出它们可能是类星体现象中的一个次型.      

Probing the origin of the iron Kα line around stellar and supermassive black holes using X-ray polarimetry

Asymmetric, broad iron lines are a common feature in the X-ray spectra of both X-ray binaries (XRBs) and type-1 Active Galactic Nuclei (AGN). It was suggested that the distortion of the Fe Kα emission results from Doppler and relativistic effects affecting the radiative transfer close to the strong gravitational well of the central compact object: a stellar mass black hole (BH) or neutron star (NS) in the case of XRBs, or a super massive black hole (SMBH) in the case of AGN. However, alternative approaches based on reprocessing and transmission of radiation through surrounding media also attempt to explain the line broadening. So far, spectroscopic and timing analyzes have not yet convinced the whole community to discriminate between the two scenarios. Here we study to which extent X-ray polarimetric measurements of black hole X-ray binaries (BHXRBs) and type-1 AGN could help to identify the possible origin of the line distortion. To do so, we report on recent simulations obtained for the two BH flavors and show that the proposed scenarios are found to behave differently in polarization degree and polarization angle. A relativistic origin for the distortion is found to be more probable in the context of BHXRBs, supporting the idea that the same mechanism should lead the way also for AGN. We show that the discriminating polarization signal could have been detectable by several X-ray polarimetry missions proposed in the past.     

A study of a complete soft X-ray selected sample of AGN

We present preliminary results from analyses of hard X-ray and optical observations of a soft X-ray selected sample. We created a small but complete sample with 20 of the softest and brightest objects with low Galactic absorption from the ROSAT bright soft X-ray selected radio-quiet AGN sample. This sample consists of 10 narrow-line Seyfert 1 galaxies and 10 broad-line Seyfert galaxies. We analyze ASCA data in the 0.6–10 keV band and optical spectra from ground-based telescopes. We investigate the photon indices in the hard X-ray band, soft excesses in the ASCA band, and optical emission line properties. The photon indices in the 2–10 keV band are nominal for both narrow-line Seyfert 1 galaxies and broad-line Seyfert 1 galaxies in each class compared with other heterogeneous samples. All of the narrow-line Seyfert 1 galaxies show soft excesses, but this component seems to be less significant for broad-line Seyfert 1 galaxies. There seems to be a trend of steeper X-ray spectra to be accompanied by narrower Hβ for narrow-line Seyfert 1 galaxies, but this is not extended to the larger velocity width regime of broad-line Seyfert 1 galaxies, and no clear trend is seen among them.     

The iron Kα-line diagnostics of the rotating black hole metric in Seyfert galaxies

Observations of Seyfert galaxies in X-ray region reveal the wide emissive lines in their spectra, which can arise in inner parts of accretion disks, where the effects of General Relativity (GR) must be taken into account. A spectrum of a solitary emission line of a hot spot in Kerr accretion disk is simulated depending on the radial coordinate r and the angular momentum a = J/M of a black hole, under the assumption of equatorial circular motion of a hot spot. It is shown that the characteristic two-peak line profile with the sharp edges arises at a large distance (about r ≈ (3–10) r_g). The inner regions emit the line, which is observed with one maximum and extremely wide red wing. We present results of simulations for the isothermal and Shakura–Sunayev disks.     

The optical to X-ray spectrum of the broad-line ultrasoft AGN RE J2248-511

We present a series of monitoring observations of the ultrasoft broad-line Seyfert galaxy RE J2248-511 with XMM-Newton. Previous X-ray observations showed a transition from a very soft state to a harder state five years later. We find that the ultrasoft X-ray excess has re-emerged, yet there is no change in the hard power-law. Reflection models with a reflection fraction of 15, and Comptonisation models with two components of different temperatures and optical depths (kT₁ = 83 keV, T₁ = 30 eV, τ₁ = 0.8; KT₂ = 3.5 keV, T₂ = 60 eV, τ₂ = 2.8) can be fit to the spectrum, but cannot be constrained. The best representation of the spectrum is a model consisting of two blackbodies (kT₁ = 0.09 ± 0.01 keV, kT₂ = 0.21 ± 0.03 keV) plus a power-law (Γ = 1.8 ± 0.08). We also present simultaneous optical and infrared data showing that the optical spectral slope also changes dramatically on timescales of years. If the optical to X-ray flux comes primarily from a Comptonised accretion disk we obtain estimates for the black hole mass , accretion rate and inclination cos(i)  0.8 of the disk.     

类星体的X射线辐射研究

由爱因斯坦天文台最近观测到的273个类星体、Ⅰ型Seyfeft星系的软X射线光度(L_x为0.5—4.5keV)资料,与它们的红移z值构成一个连续序列(图1)。利用球对称吸积模型计算得到:高红移的类星体,由于其较大的吸积率,在这个序列上停留的时间较短(～106年);而低红移类星体及Ⅰ型Seyfert星系停留的时间较长(～108年)。利用现有的107个类星体的射电单色光度l_r,光学单色光度l_o以及X射线单色光度l_x的资料,讨论了类星体大尺度谱的硬度,发现类星体的光学光度有两个不同的演化阶段;文中还定性地讨论了类星体射电辐射机制不同于光学和射电辐射的机制之处。      

SIGMA observations of hard X-ray and soft gamma-ray emission from X-ray binaries

After more than two years of operation, the imaging γ-ray SIGMA telescope has accumulated several days of observation toward well known X-ray binaries. Four bright sources falling in this category have been detected so far: The pulsar GX 1+4 near the center of our galaxy, the stellar wind accreting system 4U 1700-377, and the black hole candidates Cygnus X-1 and GX 339-4. Moreover, SIGMA have observed three transients sources, which turned out to be also hard X-ray sources : The burster KS 1731-260, Tra X-1, and the Musca Nova. The properties of these systems in the SIGMA domain will be reviewed and a spectral distinction between black holes and neutron stars will be sketched.     

Spherical accretion of massive black holes: A model for galactic nuclei

The possibility of explaining the continuous emission of active galactic nuclei in the frame of a model of spherical accretion onto a massive black hole is discussed. Cool inhomogeneities (T 10⁴°K) within the accretion flow could be responsible for the broad line emission if half of the accreting matter is in the dense phase. A crucial test of this hypothesis is the expected correlation between the ratio of the luminosity in lines to the total luminosity and the hardness of the continuous spectrum.