Accretion Disk Wind Research Articles

CHANDRAHIGH-RESOLUTION SPECTROSCOPY OF THE CIRCUMNUCLEAR MATTER IN THE BROAD-LINE RADIO GALAXY 3C 445

We present evidence for X-ray line emitting and absorbing gas in the nucleus of the Broad-Line Radio Galaxy (BLRG), 3C 445. A 200ks Chandra LETG observation of 3C 445 reveals the presence of several highly ionized emission lines in the soft X-ray spectrum, primarily from the He and H-like ions of O, Ne, Mg and Si. Radiative recombination emission is detected from O VII and O VIII, indicating that the emitting gas is photoionized. The He-like emission appears to be resolved into forbidden and intercombination line components, which implies a high density of >10^{10} cm^{-3}, while the Oxygen lines are velocity broadened with a mean width of ~2600 km s^{-1} (FWHM). The density and widths of the ionized lines indicate an origin of the gas on sub-parsec scales in the Broad Line Region (BLR).The X-ray continuum of 3C 445 is heavily obscured either by a partial coverer or by a photoionized absorber of column density N_{H}=2x10^{23} cm^{-2} and ionization parameter log(xi)=1.4 erg cm s^{-1}. However the view of the X-ray line emission is unobscured, which requires the absorber to be located at radii well within any parsec scale molecular torus. Instead, we suggest that the X-ray absorber in 3C 445 may be associated with an outflowing, but clumpy, accretion disk wind with an observed outflow velocity of ~10000 km/s.

Line profile variations in selected Seyfert galaxies

Continua as well as the broad emission lines in Seyfert 1 galaxies vary in different galaxies with different amplitudes on typical timescales of days to years. We present the results of two independent variability campaigns taken with the Hobby-Eberly Telescope. We studied in detail the integrated line and continuum variations in the optical spectra of the narrow-line Seyfert galaxy Mrk 110 and the very broad-line Seyfert galaxy Mrk 926. The broad-line emitting region in Mrk 110 has radii of four to 33 light-days as a function of the ionization degree of the emission lines. The line-profile variations are matched by Keplerian disk models with some accretion disk wind. The broad-line region in Mrk 926 is very small showing an extension of two to three light-days only. We could detect a structure in the rms line-profiles as well as in the response of the line profile segments of Mrk 926 indicating the BLR is structured.

MODELING HIGH-VELOCITY QSO ABSORBERS WITH PHOTOIONIZED MAGNETOHYDRODYNAMIC DISK WINDS

We extend our modeling of the ionization structure of magnetohydrodynamic (MHD) accretion-disk winds, previously applied to Seyfert galaxies, to a population of quasi-stellar-objects (QSOs) of much lower X-ray-to-UV flux ratios, i.e. smaller $\alpha_{\rm ox}$ index, motivated by UV/X-ray ionized absorbers with extremely high outflow velocities in UV-luminous QSOs. We demonstrate that magnetically-driven winds ionized by a spectrum with $\alpha_{\rm ox} \simeq -2$ can produce the charge states responsible for \civ ~and \fexxv/\fexxvi ~absorption in wind regions with corresponding maximum velocities of $v$(\civ) $\lsim 0.1c$ and $v({\rm \fexxv}) \lsim 0.6 c$ (where $c$ is the speed of light) and column densities $N_H \sim 10^{23}-10^{24}$ cm$^{-2}$, in general agreement with observations. In contrast to the conventional radiation-driven wind models, {\it high-velocity flows are always present in our MHD-driven winds} but manifest in the absorption spectra only for $\alpha_{\rm ox} \lsim -2$, as larger $\alpha_{\rm ox}$ values ionize the wind completely out to radii too large to demonstrate the presence of these high velocities. We thus predict increasing velocities of these ionized absorbers with decreasing (steeper) $\alpha_{\rm ox}$, a quantity that emerges as the defining parameter in the kinematics of the AGN UV/X-ray absorbers.

SS 433's circumbinary ring and accretion disc viewed through its attenuating disc wind

We present optical spectroscopy of the microquasar SS 433 covering a significant fraction of a precessional cycle of its jet axis. The components of the prominent stationary Hα and Hβ lines are mainly identified as arising from three emitting regions: (i) a super-Eddington accretion disc wind, in the form of a broad component accounting for most of the mass loss from the system; (ii) a circumbinary disc of material that we presume is being excreted through the binary's L2 point and (iii) the accretion disc itself as two remarkably persistent components. The accretion disc components move with a Keplerian velocity of ≳600 km s ―1 in the outer region of the disc. A direct result of this decomposition is the determination of the accretion disc size, whose outer radius attains ∼8 R ⊙ in the case of Keplerian orbits around a black hole mass of 10 M ⊙ . We determine an upper limit for the accretion disc inner to outer radius ratio in SS 433, R in /R out ∼ 0.2, independent of the mass of the compact object. The Balmer decrements, Hα/Hβ, are extracted from the appropriate stationary emission lines for each component of the system. The physical parameters of the gaseous components are derived. The circumbinary ring decrement seems to be quite constant throughout precessional phase, implying a constant electron density of log N e (cm ―3 ) ≃ 11.5 for the circumbinary disc. The accretion disc wind shows a larger change in its decrements exhibiting a clear dependence on precessional phase, implying a sinusoid variation in its electron density log N e (cm ―3 ) along our line of sight between 10 and 13. This dependence of density on direction suggests that the accretion disc wind is polloidal in nature.

Broad-line region physical conditions along the quasar eigenvector 1 sequence

[Abridged] We compare broad emission line profiles and estimate line ratios for all major emission lines between Ly-alpha and H-beta in a sample of six quasars. The sources were chosen with two criteria in mind: the existence of high quality optical and UV spectra as well as the possibility to sample the spectroscopic diversity in the 4D Eigenvector 1 context . In the latter sense each source occupies a region (bin) in the FWHM(H-beta) vs. optical FeII strength plane that is significantly different from the others. High S/N H-beta emission line profiles are used as templates for modeling the other lines (Ly-alpha, CIV 1549, HeII 1640, Al III 1860, Si III] 1892, and Mg II 2800). We can adequately model all broad lines assuming the existence of three components distinguished by blueshifted, unshifted and redshifted centroids (indicated as blue, broad and very broad component respectively). The broad component (high electron density, low ionization parameter; high column density) is present in almost all type-1 quasars and therefore corresponds most closely to the classical broad line emitting region (the reverberating component). The blue component emission (lower electron density; high ionization; low column density) arises in less optically thick gas; it is often thought to arise in an accretion disk wind. The least understood component involves the very broad component (high ionization and large column density). It is perhaps the most distinguishing characteristic of quasars with FWHM H-beta > 4000 km/s that belong to the so-called Population B of our 4DE1 space. Population A quasars (FWHM H-beta < 4000 km/s) are dominated by broad component emission in H-beta and blue component emission in CIV 1549 and other high ionization lines. 4DE1 appears to be the most useful current context for revealing and unifying spectral diversity in type-1 quasars.

The physics of disk winds, jets, and X-ray variability in GRS 1915+105

AbstractWe present new insights about accretion and ejection physics based on joint RXTE/Chandra HETGS studies of rapid X-ray variability in GRS 1915+105. For the first time, with fast phase-resolved spectroscopy of the ρ state, we are able to show that changes in the broadband X-ray spectrum (RXTE) on timescales of seconds are associated with measurable changes in absorption lines (Chandra HETGS) from the accretion disk wind. Additionally, we make a direct detection of material evaporating from the radiation-pressure-dominated inner disk. Our X-ray data thus reveal the black hole as it ejects a portion of the inner accretion flow and then drives a wind from the outer disk, all in a bizarre cycle that lasts fewer than 60 seconds but can repeat for weeks. We find that the accretion disk wind may be sufficiently massive to play an active role in GRS 1915+105, not only in quenching the jet on long timescales, but also in possibly producing or facilitating transitions between classes of X-ray variability.

X-ray radiation of the jets and the supercritical accretion disk in SS 433

AbstractThe observed X-ray luminosity of SS 433 is ~1036 erg/s, it is known that all the radiation is formed in the famous SS 433 jets. The bolometric luminosity of SS 433 is ~1040 erg/s, and originally the luminosity must be realized in X-rays. The original radiation is probably thermalized in the supercritical accretion disk wind, however the missing more than four orders of magnitude is surprising. We have analysed the XMM-Newton spectra of SS 433 using a model of adiabatically and radiatively cooling X-ray jets. The multi-temperature thermal jet model reproduces very well the strongest observed emission lines, but it can not reproduce the continuum radiation and some spectral features. We have found a notable contribution of ionized reflection to the spectrum in the energy range from ~3 to 12 keV. The reflected spectrum is an evidence of the supercritical disk funnel, where the illuminating radiation comes from deeper funnel regions, to be further reflected in the outer visible funnel walls (r ≥ 2 ⋅ 1011 cm). The illuminating spectrum is similar to that observed in ULXs, its luminosity has to be no less than ~1039 erg/s. A soft excess has been detected, that does not depend on the thermal jet model details. It may be represented as a BB with a temperature of Tbb ≈ 0.1 keV and luminosity of Lbb~3 ⋅ 1037 erg/s. The soft spectral component has about the same parameters as those found in ULXs.

THE GEOMETRY AND IONIZATION STRUCTURE OF THE WIND IN THE ECLIPSING NOVA-LIKE VARIABLES RW TRI AND UX UMa

The UV spectra of nova-like variables are dominated by emission from the accretion disk, modified by scattering in a wind emanating from the disk. Here we model the spectra of RW Tri and UX UMa, the only two eclipsing nova-likes which have been observed with the Hubble Space Telescope in the far-ultraviolet, in an attempt to constrain the geometry and the ionization structure of their winds. Using our Monte Carlo radiative transfer code we computed spectra for simply-parameterized axisymmetric biconical outflow models and were able to find plausible models for both systems. These reproduce the primary UV resonance lines - N V, Si IV, and C IV - in the observed spectra in and out of eclipse. The distribution of these ions in the wind models is similar in both cases as is the extent of the primary scattering regions in which these lines are formed. The inferred mass loss rates are 6% to 8% of the mass accretion rates for the systems. We discuss the implication of our point models for our understanding of accretion disk winds in cataclysmic variables.

ORIGIN OF THE COMPLEX RADIO STRUCTURE IN BAL QSO 1045+352

We present new more sensitive high-resolution radio observations of a compact broad absorption line (BAL) quasar, 1045+352, made with the EVN+MERLIN at 5 GHz. They allowed us to trace the connection between the arcsecond structure and the radio core of the quasar. The radio morphology of 1045+352 is dominated by a knotty jet showing several bends. We discuss possible scenarios that could explain such a complex morphology: galaxy merger, accretion disk instability, precession of the jet and jet-cloud interactions. It is possible that we are witnessing an ongoing jet precession in this source due to internal instabilities within the jet flow, however, a dense environment detected in the submillimeter band and an outflowing material suggested by the X-ray absorption could strongly interact with the jet. It is difficult to establish the orientation between the jet axis and the observer in 1045+352 because of the complex structure. Nevertheless taking into account the most recent inner radio structure we conclude that the radio jet is oriented close to the line of sight which can mean that the opening angle of the accretion disk wind can be large in this source. We also suggest that there is no direct correlation between the jet-observer orientation and the possibility of observing BALs.

Multidimensional modelling of X-ray spectra for AGN accretion disc outflows - II

Highly-ionized fast accretion-disk winds have been suggested as an explanation for a variety of observed absorption and emission features in the X-ray spectra of Active Galactic Nuclei. Simple estimates have suggested that these flows may be massive enough to carry away a significant fraction of the accretion energy and could be involved in creating the link between supermassive black holes and their host galaxies. However, testing these hypotheses, and quantifying the outflow signatures, requires high-quality theoretical spectra for comparison with observations. Here we describe extensions of our Monte Carlo radiative transfer code that allow us to generate realistic theoretical spectra for a much wider variety of disk wind models than possible in our previous work. In particular, we have expanded the range of atomic physics simulated by the code so that L- and M-shell ions can now be included. We have also substantially improved our treatment of both ionization and radiative heating such that we are now able to compute spectra for outflows containing far more diverse plasma conditions. We present example calculations that illustrate the variety of spectral features predicted by parametrized outflow models and demonstrate their applicability to the interpretation of data by comparison with observations of the bright quasar PG1211+143. We find that the major features in the observed 2 - 10 keV spectrum of this object can be well-reproduced by our spectra, confirming that it likely hosts a massive outflow.

LARGE-SCALE CAVITIES SURROUNDING MICROQUASARS INFERRED FROM EVOLUTION OF THEIR RELATIVISTIC JETS

The black hole X-ray transient XTE J1550-564 has undergone a strong outburst in 1998 and two relativistic X-ray jets have been detected years later with the $\it Chandra$ X-ray observatory; the eastern jet was found previously to have decelerated after its first detection. Here we report a full analysis of the evolution of the western jet; significant deceleration is also detected in the western side. Our analysis indicates that there is a cavity outside the central source and the jets first traveled with constant velocity and then were slowed down by the interactions between the jets and the interstellar medium (ISM). The best fitted radius of the cavity is $\sim$0.31 pc on the eastern side and $\sim$0.44 pc on the western side, and the densities also show asymmetry, of $\sim$0.034 cm$^{-3}$ on the east to $\sim$0.12 cm$^{-3}$ on the west. The best fitted magnetic fields on both sides are $\sim$0.5 mG. Similar analysis is also applied to another microquasar system, H 1743-322, and a large scale low density region is also found. Based on these results and the comparison with other microquasar systems, we suggest a generic scenario for microquasar jets, classifying the observed jets into three main categories, with different jet morphologies (and sizes) corresponding to different scales of vacuous environments surrounding them. We also suggest that either continuous jets or accretion disk winds, or both may be responsible for creating these cavities. Therefore X-ray jets from microquasars provide us with a promising method of probing the environment of accreting black holes.

Inflows and Outflows in Nearby AGN from Integral Field Spectroscopy

AbstractI report recent results on the kinematics of the inner few hundred parsecs (pc) around nearby active galactic nuclei (AGN) at a sampling of a few pc to a few tens of pc, using optical and near-infrared (near-IR) integral field spectroscopy obtained with the Gemini telescopes. The stellar kinematics of the hosts — comprised mostly of spiral galaxies — are dominated by circular rotation in the plane of the galaxy. Inflows with velocities of ~50 km s−1 have been observed along nuclear spiral arms in (optical) ionized gas emission for low-luminosity AGN and in (near-IR) molecular gas emission for higher-luminosity AGN. We have also observed gas rotating in the galaxy plane, sometimes in compact (few tens of pc) disks which may be fuelling the AGN. Outflows have been observed mostly in ionized gas emission from the narrow-line region, whose flux distributions and kinematics frequently correlate with radio flux distributions. Channel maps along the emission-line profiles reveal velocities as high as ~ 600 km s−1. Mass outflow rates in ionized gas range from 10−2 to 10−3M⊙ yr−1 and are 10–100 times larger than the mass accretion rates on to the AGN, supporting an origin for the bulk of the outflow in gas from the galaxy plane entrained by a nuclear jet or accretion disk wind.

Inflow and outflow from the accretion disc of the microquasar SS 433: UKIRT spectroscopy

A succession of near-IR spectroscopic observations, taken nightly throughout an entire cycle of SS433's orbit, reveal (i) the persistent signature of SS433's accretion disc, having a rotation speed of ~500 km/s, (ii) the presence of the circumbinary disc recently discovered at optical wavelengths by Blundell, Bowler and Schmidtobreick (2008) and (iii) a much faster outflow than has previously been measured for the disc wind. From these, we find a much faster accretion disc wind than has noted before, with a terminal velocity of ~1500 km/s. The increased wind terminal velocity results in a mass-loss rate of ~10e-4 M_sun/yr. These, together with the newly (upwardly) determined masses for the components of the SS433 system, result in an accurate diagnosis of the extent to which SS433 has super-Eddington flows. Our observations imply that the size of the companion star is comparable with the semi-minor axis of the orbit which is given by (1-e^2)^(1/2) 40 R_sun, where e is the eccentricity. Our relatively high spectral resolution at these near-IR wavelengths has enabled us to deconstruct the different components that comprise the Brackett-gamma line in this binary system, and their physical origins. With this line dominated throughout our series of observations by the disc wind, and the accretion disc itself being only a minority (~15 per cent) contribution, we caution against use of the unresolved Brackett-gamma line intensity as an "accretion signature" in X-ray binaries or microquasars in any quantitative way.

Double-peaked emission lines as a probe of the broad-line regions of active galactic nuclei

Broad, double-peaked, Balmer emission lines are found in the optical spectra of a relatively small fraction of active galactic nuclei. They can be an extremely useful diagnostic for the structure and dynamics of the “broad-line region” (the medium that emits the broad emission lines). In general terms the rarity and shapes of their profiles provide strong constraints on universal models of the broad-line region. A series of observational tests and basic physical considerations suggest that these lines are emitted from a flat, rotating disk, very likely the outer parts of the accretion disk that fuels the black hole. In the context of models for accretion disk winds, double-peaked emission lines originate in disks with feeble winds of low optical depth. Therefore, they provide evidence that the outer accretion disk and its associated wind are the source of the broad emission lines. Within this framework, double-peaked Balmer emission lines and corresponding high-ionization lines in the near-ultraviolet allow us to study the conditions under which the winds become dense and the onset of significant outflows. Moreover, double-peaked emission lines give us a direct view of the dense material of the disk proper and allow us to study dynamical perturbations and other transient behavior though the long-term variability of their profiles.

ORIGIN AND DYNAMICAL SUPPORT OF IONIZED GAS IN GALAXY BULGES

We combine ionized gas ([N II] 6583) and stellar central velocity dispersions for a sample of 345 galaxies, with and without active galactic nuclei (AGNs), to study the dynamical state of the nuclear gas and its physical origin. The gas dispersions strongly correlate with the stellar dispersions over the velocity range of 30-350 km/s such that sigma_g/sigma_* ~ 0.6-1.4, with an average value of 0.80. These results are independent of Hubble type (for galaxies from E to Sbc), presence or absence of a bar, or local galaxy environment. For galaxies of type Sc and later and that have sigma_* < 40 km/s, the gas seems to have a minimum threshold of sigma_g ~ 30 km/s, such that sigma_g/sigma_* always exceeds 1. Within the sample of AGNs, sigma_g/sigma_* increases with nuclear luminosity or Eddington ratio, a possible manifestation of AGN feedback associated with accretion disk winds or outflows. This extra source of nongravitational line broadening should be removed when trying to use sigma_g to estimate sigma_*. We show that the mass budget of the narrow-line region can be accounted for by mass loss from evolved stars. The kinematics of the gas, dominated by random motions, largely reflect the velocity field of the hot gas in the bulge. Lastly, we offer a simple explanation for the correlation between line width and line luminosity observed in the narrow-line region of AGNs.

THE IMPACT OF ACCRETION DISK WINDS ON THE X-RAY SPECTRA OF ACTIVE GALACTIC NUCLEI. II. XSCORT + HYDRODYNAMIC SIMULATIONS

abridged: We use XSCORT, together with the hydrodynamic accretion disc wind simulation from Proga & Kallman (2004), to calculate the impact that the accretion disk wind has on the X-ray spectrum from a 1E8 solar mass black hole Active Galactic Nuclei (AGN) accreting at 0.5 L/L_Edd. The properties of the resulting spectra depend on viewing angle and clearly reflect the distinct regions apparent in the original hydrodynamic simulation. Very equatorial lines-of-sight (l.o.s) are dominated by Compton scattering and nearly-neutral absorption. Polar l.o.s result in largely featureless spectra. Finally, l.o.s that intersect the transition region between these extremes have a wide range of absorption features imprinted on the spectrum. Both polar and transition region l.o.s produce spectra that show highly-ionized, blue-shifted, Fe absorption features that are qualitatively similar to features observed in the X-ray spectra of a growing number of AGN. The spectra presented here clearly demonstrate that current simulations of line driven AGN accretion disk winds cannot reproduce the smooth soft X-ray excess. Furthermore, they predict that high accretion rate (L/L_Edd) AGN are likely to be strongly affected by obscuration, in sharp contrast to the clean picture that is generally assumed, based on the observed relation between the opening angle of the molecular torus and AGN luminosity.

Accretion disk winds as the jet suppression mechanism in the microquasar GRS 1915+105

Stellar-mass black holes with relativistic jets, also known as microquasars, mimic the behaviour of quasars and active galactic nuclei. Because timescales around stellar-mass black holes are orders of magnitude smaller than those around more distant supermassive black holes, microquasars are ideal nearby 'laboratories' for studying the evolution of accretion disks and jet formation in black-hole systems. Whereas studies of black holes have revealed a complex array of accretion activity, the mechanisms that trigger and suppress jet formation remain a mystery. Here we report the presence of a broad emission line in the faint, hard states and narrow absorption lines in the bright, soft states of the microquasar GRS 1915+105. ('Hard' and 'soft' denote the character of the emitted X-rays.) Because the hard states exhibit prominent radio jets, we argue that the broad emission line arises when the jet illuminates the inner accretion disk. The jet is weak or absent during the soft states, and we show that the absorption lines originate when the powerful radiation field around the black hole drives a hot wind off the accretion disk. Our analysis shows that this wind carries enough mass away from the disk to halt the flow of matter into the radio jet.

On the absorption of X-ray bright broad absorption line quasars

Context. Most X-ray studies of broad absorption line quasars (BALQSOs) found significant (NH ∼ 10 22−24 cm −2 ) intrinsic column densities of gas absorbing an underlying typical power-law continuum emission, in agreement with expectations from radiatively driven accretion disk wind models. However, direct spectral analysis was performed only on a limited number of bright sources. Aims. We investigate the X-ray emission of a large number of BALQSOs at medium to high redshift (0.8 < z < 3.7) with the best data available to date. Methods. We drew a large BALQSO sample from the cross-correlation of SDSS DR5 and 2XMM catalogs to perform moderatequality X-ray spectral and hardness ratio analysis and X-ray/optical photometry. We compare our results with previous studies of BALQSOs and theoretical disk wind model expectations. Results. No or little intrinsic X-ray neutral absorption is found for one third of the spectroscopically analyzed BALQSO sample (NH < 4 × 10 21 cm −2 at 90% confidence level), and lower than typical X-ray absorption is found in the remaining sources (� NH �∼ 5 × 10 22 cm −2 ) even including the faintest sources analyzed through hardness ratio analysis. The mean photon index is Γ ∼ 1.9, with no significant evolution with redshift. The optical/X-ray spectral indices αox are typical of radio-quiet broad line AGN, in contrast with the known (from previous X-ray studies) “soft X-ray weakness” of BALQSOs and in agreement with the lack of X-ray absorption. We found the low-absorption index (AI) subsample to host the lowest X-ray absorbing column densities of the entire sample. Conclusions. X-ray selected BALQSOs show lower X-ray absorption than purely optically selected ones, and soft X-ray weakness does not hold for any of them. Their outflows may be launched by different mechanisms than classical soft X-ray weak BALQSOs or they may be the tail of the already known population seen along a different line of sight, in both cases expanding the observational parameter space for their search and investigation.

Milne–Eddington Solutions for Relativistic Plane-Parallel Flows

Abstract Radiative transfer in a relativistic plane-parallel flow, e.g., an accretion-disk wind, has been examined using a fully special-relativistic treatment. Under the assumption of a constant flow speed, for a relativistically moving atmosphere, we analytically obtained generalized Milne–Eddington solutions of radiative moment equations: the radiation energy density, the radiative flux, and the radiation pressure. In the static limit these solutions reduce to the traditional Milne–Eddington ones for a plane-parallel static atmosphere, whereas the source function nearly becomes constant as the flow speed increases. Using the analytical solutions, we analytically integrated the relativistic transfer equation to obtain the specific intensity. This specific intensity also reduces to the Milne–Eddington case in the static limit, while the emergent intensity is strongly enhanced toward the flow direction due to Doppler and aberration effects as the flow speed increases (relativistic peaking).

Funnel wall jets and the nature of the soft X-ray excess

Abstract The smooth soft X-ray excess seen in many type 1 active galactic nuclei can be well described by models of absorption in partially ionized material with a large velocity dispersion, often physically interpreted as a radiatively driven accretion disc wind. However, the state-of-the-art xscort code, which calculates the photoionized radiative transfer through a differentially outflowing absorber, shows that terminal velocities of the order of ∼0.9c are required in order to reproduce the soft X-ray excess. Such a high outflow velocity rules out ultraviolet line driving, continuum radiation driving and thermal driving as mechanisms for producing the wind. Entrainment of material by the magnetically driven jet is the only plausible origin of such a high-velocity flow, but numerical simulations of jets and associated outflows do not currently show sufficient material at high enough velocities to reproduce the soft X-ray excess. If the soft excess is produced by absorption then it seems more likely that the material is clumpy and/or only partially covers the source rather than forming a continuous outflow.