12781236
The lower boundary of the accretion column in magnetic cataclysmic variables
Using a parametrized function for the mass loss at the base of the post-shock region, we have constructed a formulation for magnetically confined accretion flows which avoids singularities, such as the infinity in density, at the base associated with all previous formulations. With the further inclusion of a term allowing for the heat input into the base from the accreting white dwarf, we are also able to obtain the hydrodynamic variables to match the conditions in the stellar atmosphere. (We do not, however, carry out a mutually consistent analysis for the match.) Changes to the emitted X-ray spectra are negligible unless the thickness of mass leakage region at the base approaches or exceeds one per cent of the height of the post-shock region. In this case the predicted spectra from higher-mass white dwarfs will be harder, and fits to X-ray data will predict lower white dwarf masses than previous formulations.
13854637
Ionization structure in accretion shocks with a composite cooling function
ABSTRA C T We have investigated the ionization structure of the post-shock regions of magnetic cataclysmic variables, using an analytic density and temperature structure model in which effects caused by bremsstrahlung and cyclotron cooling are considered. We find that in the majority of the shock-heated region where H- and He-like lines of the heavy elements are emitted, the collisional-ionization and corona-condition approximations are justified. We have calculated the line emissivity and ionization profiles for iron as a function of height within the post-shock flow. For low-mass white dwarfs, line emission takes place near the shock. For high-mass white dwarfs, most of the line emission takes place in regions well below the shock and hence it is less sensitive to the shock temperature. Thus, the line ratios are useful to determine the white dwarf masses for the low-mass white dwarfs, but the method is less reliable when the white dwarfs are massive. Line spectra can, however, be used to map the hydrodynamic structure of the post-shock accretion flow.
119332271
Low and High Angular Momentum Accretion Flows in BHCs: Case Study of XTE J1550-564
The 1998 outburst of XTE J1550-564 started with a hard X-ray spike, rising in less than a day and declining after 3-4 days; at the same time, the soft X-ray flux was rising with a longer timescale (~ 10 days). We suggest that the soft and the initial hard X-ray emission are produced by two different components of the accretion flow: a higher angular momentum flow, which forms the disk, and a lower angular momentum flow feeding the hot inner region. Thus, we argue that the onset of the outburst is determined by an increased mass transfer rate from the companion star, but the outburst morphology is also determined by the distribution of specific angular momentum in the accreting matter. In XTE J1550-564, we attribute the initial, impulsive low angular momentum accretion to the breaking down of magnetic confinement by the magnetically active secondary star. We show that a hard X-ray spike is seen at the onset of an outburst in other BHCs.
18756154
Formation of optical lines in black-hole binaries
The HI Balmer emission lines of black-hole binaries show double-peaked profiles during the high-soft state and the quiescent state. In the high-soft state the profiles are asymmetric with a stronger red peak, but the profiles are symmetric in the quiescent state. We suggest that in the high-soft state the emission lines originate from the temperature-inversion layer caused by irradiative heating of an optically thick accretion disk. Irradiative heating also causes the formation of a disk wind, which mildly absorbs the blue peak of the lines. The double-peaked lines seen in the quiescent state arise from an optically thin disk. In the absence of a disk wind, the lines are unabsorbed and so the symmetry of the line profiles is preserved.
14186187
Accretion Flow along a Dipolar Field: Application to Intermediate Polars
A hydrodynamic formulation for accretion flow channeled by a dipolar magnetic field is constructed using a curvi-linear coordinate system natural to the field structure. We solve the hydrodynamic equations and determine the velocity, density and temperature profiles of the post-shock accretion flow. The results are applied to accretion flows in intermediate polars. We have found that for systems with massive white dwarfs (~ 1 M ⊙ ) the temperature profiles in the flow can differ significantly to those obtained from models in which the accretion column is assumed to be cylindrical.
1734663
Line emission from optically thick relativistic accretion tori
We calculate line emission from relativistic accretion tori around Kerr black holes and investigate how the line profiles depend on the viewing inclination, spin of the central black hole, parameters describing the shape of the tori, and spatial distribution of line emissivity on the torus surface. We also compare the lines with those from thin accretion disks. Our calculations show that lines from tori and lines from thin disks share several common features. In particular, at low and moderate viewing inclination angles they both have asymmetric double-peaked profiles with a tall, sharp blue peak and a shorter red peak which has an extensive red wing. At high viewing inclination angles they both have very broad, asymmetric lines which can be roughly considered as single-peaked. Torus and disk lines may show very different red and blue line wings, but the differences are due to the models for relativistic tori and disks having differing inner boundary radii. Self-eclipse and lensing play some role in shaping the torus lines, but they are effective only at high inclination angles. If inner and outer radii of an accretion torus are the same as those of an accretion disk, their line profiles show substantial differences only when inclination angles are close to 90°, and those differences manifest mostly at the central regions of the lines instead of the wings.
14150373
Axial anomaly in lattice abelian gauge theory in arbitrary dimensions
Abstract The axial anomaly of lattice abelian gauge theory on a hyper-cubic regular lattice in arbitrary even dimensions is investigated by applying the method of exterior differential calculus. The topological invariance, gauge invariance and locality of the axial anomaly determine the explicit form of the topological part. The anomaly is obtained up to a multiplicative constant for finite lattice spacing and can be interpreted as the Chern character of the abelian lattice gauge theory.
120439571
New BRST quantization of the bosonic string and string field theory
Abstract A new BRST quantization for the open bosonic string is carried out. The new BRST charge and anti-BRST charge obtained are identical with the generators J − α proposed by Siegel and Zwiebach, justifying their postulate. A light-cone like action is written and casted into its manifest OSp (1, 1 2 ) invariant form in the physical sector. By integrating over the unphysical coordinates, we obtain the gauge invariant action of the string field.
119450282
Brans-Dicke Theory and Discrete Symmetry
We derive exactly the Brans-Dicke theory on the manifold M(4)xZ(2), where M(4) is the four-dimensional space-time and Z(2) is a discrete internal space with two points. We use the extended affine connection formalism, which is simpler than the vielbein formalism of the previous work and one can see more directly the effect of the Z(2) symmetry. A new formulation is given for the non-commutative differential calculus, which is proper in our discussion.
960106
Non-commutative differential calculus and the axial anomaly in Abelian lattice gauge theories
Abstract The axial anomaly in lattice gauge theories has a topological nature when the Dirac operator satisfies the Ginsparg–Wilson relation. We study the axial anomaly in Abelian gauge theories on an infinite hypercubic lattice by utilizing cohomological arguments. The crucial tool in our approach is the non-commutative differential calculus (NCDC) which makes the Leibniz rule of exterior derivatives valid on the lattice. The topological nature of the “Chern character” on the lattice becomes manifest in the context of NCDC. Our result provides an algebraic proof of Luscher's theorem for a four-dimensional lattice and its generalization to arbitrary dimensions.
18113451
Symplectic, multisymplectic structures and Euler-Lagrange cohomology
We study the Euler-Lagrange cohomology and explore the symplectic or multisymplectic geometry and their preserving properties in classical mechanism and classical field theory in Lagrangian and Hamiltonian formalism in each case respectively. By virtue of the Euler-Lagrange cohomology that is nontrivial in the configuration space, we show that the symplectic or multisymplectic geometry and related preserving property can be established not only in the solution space but also in the function space if and only if the relevant closed Euler-Lagrange cohomological condition is satisfied in each case. We also apply the cohomological approach directly to Hamiltonian-like ODEs and Hamiltonian-like PDEs no matter whether there exist known Lagrangian and/or Hamiltonian associated with them.