15481267
A Chandra search for coronal X-rays from the cool white dwarf GD 356
We report observations with the Chandra X-ray Observatory of the single, cool, magnetic white dwarf GD 356. For consistent comparison with other X-ray observations of single white dwarfs, we also re-analyzed archival ROSAT dataforGD356(GJ1205),G99-47(GR290=V1201Ori),GD90,G195-19(EG250=GJ339.1),andWD2316+123, andarchivalChandradataforLHS1038(GJ1004)andGD358(V777Her).OurChandraobservationdetectedno X-rays from GD 356, setting the most restrictive upper limit to the X-ray luminosity from any cool white dwarf: LX < 6:0 ; 10 25 ergs s � 1 , at 99.7% confidence, for a 1 keV thermal bremsstrahlung spectrum. The corresponding limit to the electron density is n0 < 4:4 ; 10 11 cm � 3 . Our re-analysis of the archival data confirmed the nondetections reported by the original investigators. We discuss the implications of our and prior observations for models of coronal emission from white dwarfs. For magnetic white dwarfs, we emphasize the more stringent constraints imposed by cyclotron radiation. In addition, we describe (in an Appendix) a statistical methodology for detecting asource and for constraining the strength of a source, which applies even when the number of source or background events is small. Subject headingg methods: statistical — radiation mechanisms: thermal — stars: coronae — white dwarfs — X-rays: individual (GD 356)
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.
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.
14603217
Topological obstruction in block-spin transformations
Abstract Block-spin transformations from a fine lattice to a coarse one are shown to give rise to a one-to-one correspondence between the zero-modes of the Ginsparg-Wilson Dirac operator on the fine lattice and those on the coarse lattice. The index is then preserved under the blocking process. Such a one-to-one correspondence is violated and the block-spin transformation becomes necessarily ill-defined when the absolute value of the index is larger than 2 rN , where N is the number of the sites on the coarse lattice and r is the dimension of the gauge group representation of the fermion variables.
117147252
THE STANDARD MODEL WITH HIGGS AS GAUGE FIELD ON FOURTH HOMOTOPY GROUP
Based upon a fundamental principle, the generalized gauge principle, we construct a general model with G(L) x G(R)' x Z(2) gauge symmetry, where Z(2) = pi(4)(G(L)) is the fourth homotopy group of the gauge group G(L), by means of the non-commutative differential geometry and reformulating the standard model with the Higgs field being a gauge field on the fourth homotopy group of their gauge groups. We show that in this approach not only the Higgs held is automatically introduced on an equal footing with ordinary Yang-Mills gauge potentials and there are no extra constraints among the parameters at the tree level but also most importantly the models survive quantum corrections.
119041621
Total variation in Hamiltonian formalism and symplectic energy integrators
We present a discrete total variation calculus in Hamiltonian formalism in this paper. Using this discrete variation calculus and generating functions for the flows of Hamiltonian systems, we derive symplectic-energy integrators of any finite order for Hamiltonian systems from a variational perspective. The relationship between the symplectic integrators derived directly from the Hamiltonian systems and the variationally derived symplectic-energy integrators is explored.
121721377
Vertex operator and BRST charges on higher genus Riemann surfaces
Abstract By using the Krichever and Novikov formalism on a higher-genus Riemann surface Γ we introduce the tachyon vertex operator and also the “interacting” BRST charges onto Γ. The tachyon mass is shown to be independent of the genus. This result suggests that the usual divergence of the loop integral over modular variable should be removed by appropriate regularizations. We also discuss the BRST-invariance of the total hamiltonian including the vertex.
18532275
On variations in discrete mechanics and field theory
In this paper, we propose the difference variational approach with variable step-length for discrete mechanics and field theory. Based upon the Hamilton's principle for the vertical variations and the horizontal variations, we get the equation of motion and the relevant relations between the equation of motion and conservation law of the energy/energy-momentum tensor for continuous as well as for the discrete systems, respectively. For those discrete cases, these relations determine the variable step-length of the differences. In addition, by taking the double operation of vertical exterior differential on action, we show that there should exist the Euler-Lagrange cohomology for both continuous and variable step-length difference cases in general. This indicates that the necessary and sufficient condition for symplectic/multisymplectic structure preserving properties is the relevant Euler-Lagrange one-form being closed in each case. Our approach can be applied to both the Lagrangian formalism and the Hamiltonian formalism, via discrete Legendre transformation, for the difference discrete mechanics and field theory. (C) 2003 American Institute of Physics.