Torus Component Research Articles

The effect of stellar feedback on the formation and evolution of gas and dust tori in AGN

Recently, the existence of geometrically thick dust structures in active galactic nuclei (AGN) has been directly proven with the help of interferometric methods in the mid-infrared. The observations are consistent with a two-component model made up of a geometrically thin and warm central disc, surrounded by a colder, fluffy torus component. Within the framework of an exploratory study, we investigate one possible physical mechanism, which could produce such a structure, namely the effect of stellar feedback from a young nuclear star cluster on the interstellar medium in centres of AGN. The model is realized by numerical simulations with the help of the hydrodynamics code tramp. We follow the evolution of the interstellar medium by taking discrete mass-loss and energy ejection due to stellar processes, as well as optically thin radiative cooling into account. In a post-processing step, we calculate observable quantities like spectral energy distributions (SEDs) and surface brightness distributions with the help of the radiative transfer code mc3d. The interplay between injection of mass, supernova explosions and radiative cooling leads to a two-component structure made up of a cold geometrically thin, but optically thick and very turbulent disc residing in the vicinity of the angular momentum barrier, surrounded by a filamentary structure. The latter consists of cold long radial filaments flowing towards the disc and a hot tenuous medium in between, which shows both inwards and outwards directed motions. With the help of this modelling, we are able to reproduce the range of observed neutral hydrogen column densities of a sample of Seyfert galaxies as well as the relation between them and the strength of the silicate 10 μm spectral feature. Despite being quite crude, our mean Seyfert galaxy model is even able to describe the SEDs of two intermediate type Seyfert galaxies observed with the Spitzer Space Telescope.

Resolving the complex structure of the dust torus in the active nucleus of the Circinus galaxy

To test the dust torus model for active galactic nuclei directly, we study the extent and morphology of the nuclear dust distribution in the Circinus galaxy using high resolution interferometric observations in the mid-infrared with the MIDI instrument at the Very Large Telescope Interferometer. We find that the dust distribution in the nucleus of Circinus can be explained by two components, a dense and warm disk-like component of 0.4 pc size and a slightly cooler, geometrically thick torus component with a size of 2.0 pc. The disk component is oriented perpendicular to the ionisation cone and outflow and seems to show the silicate feature at 10 micron in emission. It coincides with a nuclear maser disk in orientation and size. From the energy needed to heat the dust, we infer a luminosity of the accretion disk corresponding to 20% of the Eddington luminosity of the nuclear black hole. We find that the interferometric data are inconsistent with a simple, smooth and axisymmetric dust emission. The irregular behaviour of the visibilities and the shallow decrease of the dust temperature with radius provide strong evidence for a clumpy or filamentary dust structure. We see no evidence for dust reprocessing, as the silicate absorption profile is consistent with that of standard galactic dust. We argue that the collimation of the ionising radiation must originate in the geometrically thick torus component. Our findings confirm the presence of a geometrically thick, torus-like dust distribution in the nucleus of Circinus, as required in unified schemes of Seyfert galaxies. Several aspects of our data require that this torus is irregular, or clumpy.

On hyperbolic 3–manifolds realizing the maximal distance between toroidal Dehn fillings

For a hyperbolic 3-manifold M with a torus boundary component, all but finitely many Dehn fillings on the torus component yield hyperbolic 3-manifolds. In this paper, we will focus on the situation where M has two exceptional Dehn fillings, both of which yield toroidal manifolds. For such situation, Gordon gave an upper bound for the distance between two slopes of Dehn fillings. In particular, if M is large, then the distance is at most 5. We show that this upper bound can be improved by 1 for a broad class of large manifolds.

Fusion Engineering and Plasma Science Conditions of Spherical Torus Component Test Facility

A broadly based study of the fusion engineering and plasma science conditions of a Component Test Facility (CTF), using the Spherical Torus or Spherical Tokamak (ST) configuration, have been carried out. The chamber systems testing conditions in a CTF are characterized by high fusion neutron fluxes Γn > 4.4 × 1013 n/s/cm2, over size scales > 105 cm2 and depth scales > 50 cm, delivering > 3 accumulated displacement per atom (dpa) per year. The desired chamber conditions can be provided by a CTF with R0 = 1.2 m, A = 1.5, elongation ~ 3, Ip ~ 9 MA, BT ~ 2.5 T, producing a driven fusion burn using 36 MW of combined neutral beam and RF power. Relatively robust ST plasma conditions are adequate, which have been shown achievable4 without active feedback manipulation of the MHD modes. The ST CTF will test the single-turn, copper alloy center leg for the toroidal field coil without an induction solenoid and neutron shielding, and require physics data on solenoid-free plasma current initiation, ramp-up, and sustainment to multiple MA level. A new systems code that combines the key required plasma and engineering science conditions of CTF has been prepared and utilized as part of this study. The results show high potential for a family of lower-cost CTF devices to suit a variety of fusion engineering science test missions.

X-ray spectral variability of the Seyfert galaxy NGC 4051

We report on the X-ray spectral variability of the Seyfert 1 galaxy NGC 4051 observed with the Rossi X-ray Timing Explorer (RXTE) during a 1000 day period between May 1996 and March 1999. The spectra were obtained as part of monitoring observations and from two long observations using the RXTE Proportional Counter Array (PCA). During the monitoring period the 2-10 keV flux of NGC 4051 varied between 10E-12 and 7x 10E11 (cgs). We re-analysed RXTE PCA observations from a distinct low state in May 1998 using the latest background and detector response models. The RXTE and BeppoSAX observations of NGC 4051 during the low state show a very hard spectrum with a strong unresolved fluorescence line. This emission, probably due to reflection from a molecular torus, is likely to be constant over long time-scales and is therefore assumed as an underlying component at all flux states. By subtracting the torus component we are able to determine the spectral variability of the primary continuum. In the variable component we observe a strong anti-correlation of X-ray flux and spectral hardness in the PCA energy band. We show that the changes in hardness are caused by slope variability of the primary power law spectrum rather than by changing reflection or variable photoelectric absorption. The primary spectral index varies between Gamma=1.6 for the faintest states and Gamma=2.3 during the brightest states, at which level the spectral index approaches an asympotic value. We find that the response of the flux of the 6.4 keV iron fluorescence line to changes in the continuum flux depends on the timescale of the observation. The profile of the line is very broad and indicates an origin in the innermost regions of the accretion disk.

Observations of hyperluminous infrared galaxies with theInfrared Space Observatory: implications for the origin of their extreme luminosities

We present 7–180 μm photometry of a sample of hyperluminous infrared galaxies (HyLIGs) obtained with the photometer and camera mounted on the Infrared Space Observatory. We have used radiative transfer models of obscured starbursts and dusty torii to model their spectral energy distributions (SEDs). We find that IRAS F00235+1024, IRAS F14218+3845 and IRAS F15307+3252 require a combination of starburst and active galactic nuclei (AGN) components to explain their mid- to far-infrared (FIR) emission, while for TXS 0052+471 a dust torus AGN model alone is sufficient. For IRAS F00235+1024 and IRAS F14218+3845 the starburst component is the predominant contributor, whereas for IRAS F15307+3252 the dust torus component dominates. The implied star formation rates (SFRs) for these three sources estimated from their infrared luminosities are yr−1h50−2 and are amongst the highest SFRs estimated to date. We also demonstrate that the well-known radio–FIR correlation extends into both higher radio and infrared power than previously investigated. The relation for HyLIGs has a mean q value of 1.94. The results of this study imply that better sampling of the infrared spectral energy distributions of HyLIGs may reveal that both AGN and starburst components are required to explain all the emission from the near-infrared to the submillimetre.

A Hiker's Guide to K3.¶Aspects of N= (4,4) Superconformal Field Theory¶with Central Charge c= 6

We study the moduli space ${\cal M}$ of N=(4,4) superconformal field theories with central charge c=6. After a slight emendation of its global description we find the locations of various known models in the component of ${\cal M}$ associated to K3 surfaces. Among them are the Z_2 and Z_4 orbifold theories obtained from the torus component of ${\cal M}$. Here, SO(4,4) triality is found to play a dominant role. We obtain the B-field values in direction of the exceptional divisors which arise from orbifolding. We prove T-duality for the Z_2 orbifolds and use it to derive the form of ${\cal M}$ purely within conformal field theory. For the Gepner model (2)^4 and some of its orbifolds we find the locations in ${\cal M}$ and prove isomorphisms to nonlinear sigma models. In particular we prove that the Gepner model (2)^4 has a geometric interpretation with Fermat quartic target space.

Observations and a model for the infrared continuum of Centaurus A

We present ISOSWS, ISOPHOT_S and 8–13 μm observations of Centaurus A which show prominent PAH and silicate features. These and other data are used to construct a model for the infrared continuum. We find that, in a small nuclear aperture (∼ 4 arcsec, ∼ 60 pc), the spectral energy distribution is characteristic of emission from a starburst and dusty AGN torus; in larger apertures, additional components of cirrus and starburst emission are required. The model components are based on the radiative transfer models of Efstathiou et al. which include multiple scattering and the radiative effects of a dust-embedded source with a distribution of grain species and sizes. The torus component is modelled in terms of a tapered dusty disc centrally illuminated by a quasar-like source. The cirrus and starburst components are, respectively, modelled in terms of diffuse dust illuminated by the interstellar medium and an ensemble of optically thick molecular clouds centrally illuminated by hot stars. These latter components additionally include emission from small graphite particles and PAHs. Based on our overall model, the torus diameter is estimated to be 3.6 pc and the best inclination angle of the torus is 45°. We present independent observational evidence for this structure. This result has implications for the detectability of tori in low-power AGN and for the use of the IRAS 60/25-μm flux ratio as an indicator of the torus inclination.

Leak detection system in ITER

This article describes the current design status of a leak detection system in International Thermonuclear Experimental Reactor (ITER). The ITER leak detection system is comprised of residual gas analyzers (RGAs) and mass spectrometer leak detectors (MSLDs) with different specifications, and targets leaks in the torus, cryostat and other miscellaneous components. For fine leak testing in the torus and cryostat, a 4He background gassing rate ( Q back) will be a dominant factor in determining an actual time response of the leak detection system. The Q back should be reduced to less than 10 −12 Pa m 3 s −1, in order to achieve a reasonable time response of ∼90 s for a 10 −8 Pa m 3 s −1 4He leakage. To eliminate the drain and dry out scheme of the leak checking procedure for the torus in-vessel water cooling circuits, a spiking method, which adds some soluble tracers to circulating waters, has been proposed although further R&D is required.

Effect of Shielding Design Margin on the Quantity of Fusion Reactor Material

In traditional shielding design, thicknesses of shieldings have been determined so that calculated shielding properties multiplied by safety factors do not exceed design limits. A shielding design margin is defined for the safety factors that are included in the estimated shielding thicknesses in the design process. Sensitivities of the shielding design margin to the fusion reactor scale and amount of material are examined for a typical fusion experimental reactor such as the International Thermonuclear Experimental Reactor (ITER). From these investigations, supposing the shielding design margin can be made smaller by up to half the typical value of 3 used in a reactor, the amount of toroidal coil, transformer coil, and other torus component materials can be reduced by 1.5, 0.7, and 0.7%, respectively. If one includes a reactor building and accessory facilities that are not affected by the shielding design margin, the whole reactor material reduction becomes 0.55%. Since reactor cost is assumed to be proportional to the amount of material, the 0.55% reduction may be worth $55 million when the estimated price of the reactor is assumed to be $10 billion.

Temporal and spectral variability of AGN with RXTE

We present RXTE PCA observations of temporal and spectral variability of the four X-ray bright Seyfert galaxies NGC 4051, NGC 5506, NGC 5548 and MGC-6-30-15 covering a period of 18 months from February 1996. We find evidence of a knee in the long timescale power spectrum of NGC 4051 at a frequency of 5×10 −5 Hz. There is possible evidence of a knee at a slightly lower frequency in the higher luminosity source MCG-6-30-15 but no knees have been found in the still higher luminosity sources NGC 5506 and NGC 5548. If the knee frequency scales inversely with the central black hole mass then, by comparison with galactic black hole X-ray binaries, we deduce a mass of approximately 10 5 M ⊙ in NGC 4051. Strong continuum reflection components and iron fluorescent lines are seen in all four galaxies and we find evidence of strong X-ray spectral variability in all four galaxies. Here we discuss the spectra of NGC 5506 and MCG-6-30-15 as NGC 4051 is discussed elsewhere in these proceedings [1] and a possibly confusing BL Lac lies within the PCA field of view of NGC 5548. In both NGC 5506 and MCG-6-30-15 we find strong evidence for a steeping of the continuum spectral slope as the intensity increases. In MCG-6-30-15 the iron line flux increases only weakly as the continuum flux rises and, indeed, the iron line flux is consistent with being constant. In NGC 5506, however, there is an approximately linear relationship between the iron line flux and continuum flux with only weak evidence for an additional steady component. One explanation, although by no means confirmed, of the spectral index variability and relative quiescence of the iron line flux is that, in addition to rapidly varying steep spectrum continuum emission, there is also a harder reflected component from the surrounding torus. The torus component would not vary on the timescales of our observations and would dominates at very low flux levels. The difference between the variability of NGC 5506 and MCG-6-30-15 may be a lesser contribution from the torus in NGC 5506.

Investigation of an ITER Advanced Technology Phase

AbstractThe ultimate performance of ITER has the potential to exceed the nominal levels needed to meet the objectives of the Physics and Technology phases, as outlined in the ITER Terms of Reference. Higher power levels, even with the existing set of physics design rules, may be achievable with modifications to torus components and appropriate additions to the balance of plant. It may also be possible to generate net electric power from a machine the same size as the current ITER baseline, but with a slightly different design. Because of the large investment in ITER and the value of the information gained from its operation to the progress of fusion research, it is important that the operation and performance of the machine be maximized. The greater value of information that could be obtained with more ambitious performance levels must be weighed against the additional costs, technological risks, and safety implications. This study examines the feasibility and implications of a potential third phase, or A...

Incompressible planar surfaces in 3-manifolds

Let M be an orientable 3-manifold and T a torus component of ∂ M. We show that the boundary-slopes of incompressible, boundary-incompressible planar surfaces ( P,∂ P)⊂( M, T) are pairwise within distance 4; in particular, there are at most six such boundary-slopes. A corollary is that, for any knot K in S 3, at most six Dehn surgeries on K can yield a reducible 3-manifold.

The Jovian Nebula: A Post-Voyager Perspective

Voyager 1 carried a diverse collection of magnetospheric probes through the inner Jovian magnetosphere in March 1979. The ensuing data analysis and theoretical investigation provided a comprehensive description of the Jovian nebula, a luminous torus populated with newly released heavy ions drawn from Io's surface. Recent refinements in Earth-based imaging instrumentation are used to extend the Voyager in situ picture in temporal and spatial coverage. An analysis of [SIII] and [SII] optical emissions observed during the Jovian apparitions of 1981 through 1983 reveals three distinct torus components. Regularities have been identified in the ion partitioning and ion densities in the hot outer and inner tori, sharply defined radial structure is found in the plasma near Io, and the relative permanence of the cool inner torus is inferred. An extended cloud of neutral material is required as a source of fresh ions in the nebula.

Materials selection for the U.S. INTOR divertor collector plate

The divertor collector plate in the INTOR reactor will be subjected to high heat, particle, and neutron fluxes, making it the most severely damaged torus component. The collector plate is composed of a protection plate, which is directly exposed to the particle flux, and a heat sink which provides support for the protection plate and carries the water coolant. The high-Z refractory metals have been considered for use as the protection plate material and austenitic stainless steels and copper alloys have been considered as the heat sink material. Tungsten and Type 316 stainless steels have been selected for the protection plate and heat sink, respectively. The protection plate has a sputtering lifetime of 1.75 y at a 50% duty factor, while the heat sink is expected to last the lifetime of the reactor.

Tritium-related surface effects in tokamaks

The effects of tritium adsorbed on internal torus and near-torus components in tokamaks are discussed. For in-torus locations, which normally experience plasma particle fluxes, the effects of adsorbed tritium are entirely negligible because of the weakness of the tritium β-decay. Tritium adsorbed on surfaces, however, can dramatically degrade diagnostic devices by causing particle counting backgrounds due to the decay electrons. Experimental data on channel electron multipliers (CEMs) which have been tritium-exposed illustrate this degradation and point out the necessity of determining tritium effects for all particle detector types which will be exposed to tritium in tokamaks.

Gparity and the breaking of exchange degeneracy

Exact exchange degeneracy, a property of the planar $S$ matrix, is not a feature of the physical world. $G$ parity, an exact symmetry of strong interactions, fails to be maintained by the discontinuities of the planar $S$ matrix. This paper examines the connection between these two conflicting concepts and shows how calculations of exchange-degeneracy breaking may be based on $G$ parity. The relation of $G$ parity to the cylinder and torus components of the topological expansion is a central feature. We apply our arguments to $\ensuremath{\rho}\ensuremath{-}{A}_{2}$ splitting and justify the use of an unsubtracted dispersion relation for ${\ensuremath{\alpha}}_{A2}\ensuremath{-}{\ensuremath{\alpha}}_{\ensuremath{\rho}}$. Our analysis of the dispersion relation reveals a dominant role for the $\ensuremath{\pi}\ensuremath{\pi}$ channel.