arXiv subjects

Maurice H. P. M. van Putten

Publications and source records attributed to Maurice H. P. M. van Putten.

102 records · Page 6Linked to original sources

arXiv2000

Electron-positron outflow from black holes and the formation of winds

The collapse of young massive stars or the coalescence of a black hole-neutron star binary is expected to give rise to a black hole-torus system. When the torus is strongly magnetized, the black hole produces electron-positron outflow along open magnetic field-lines. Through curvature radiation in gaps, this outflow rapidly develops into a $e^\pmγ$-wind, which is ultra-relativistic and of low comoving density, proposed here as a possible input to GRB fireball models.

astro-ph↗

arXiv2000

An $\dot{f}(f)$-frequency dynamics algorithm for gravitational waves

Coalescence of low mass compact binaries of neutron stars and black holes are primary burst sources for LIGO and VIRGO.Of importance in the early stages of observations will be the classification of candidate detections by source-type. The diversity in source parameters and serendipity in any new window of observations suggest to consider model-independent detection algorithms. Here a frequency dynamics algorithm is described which extracts a trajectory in the $\dot{f}(f)$-plane from the noisy signal. The algorithm is studied in simulated binary coalescence. Robust results are obtained with experimental noise data. Experiments show the method to be superior to matched filtering in the presence of model imperfections.

astro-ph↗

arXiv1999

Electron-positron outflow from black holes

Gamma-ray bursts (GRBs) appear as the brightest transient phenomena in the Universe. The nature of the central engine in GRBs is a missing link in the theory of fireballs to their stellar mass progenitors. Here it is shown that rotating black holes produce electron-positron outflow when brought into contact with a strong magnetic field. The outflow is produced by a coupling of the spin of the black hole to the orbit of the particles. For a nearly extreme Kerr black hole, particle outflow from an initial state of electrostatic equilibrium has a normalized isotropic emission of $\sim 5\times10^{48}(B/B_c)^2(M/7M_\odot)^2\sin^2θ$ erg/s, where B is the external magnetic field strength, B_c=4.4 x 10^{13}G, and M is the mass of the black hole. This initial outflow has a half-opening angle $θ\ge\sqrt{B_c/3B}$. A connection with fireballs in $γ$-ray bursts is given.

astro-ph↗

arXiv1998

Approximate black holes from a variable cosmological constant

The small or zero cosmological constant, $Λ$, probably results from a macroscopic cancellation mechanism of the zero-point energies. However, nearby horizon surfaces any macroscopic mechanism is expected to result in imperfect cancellations. A phenomenological description is given for the residual variable cosmological constant. In the static, spherically symmetric case it produces approximate black holes. The model describes the case of exponential decay by $\Box\lnΛ=-3a$, were $a$ is a positive constant.

gr-qc↗

arXiv1997

Nonlinear wave equations for numerical relativity: towards the computation of gravitational wave forms of black hole binaries

The prime candidate of LIGO/VIRGO sources of gravitational waves is the spiral in of black holes and neutron stars in compact binaries. While the early stages of the evolution of compact binaries is computable from post-Newtonian calculations, prediction of their late stages requires large scale numerical simulation. A fully covariant and strictly hyperbolic formulation for numerical relativity is described, and illustrated in a one-dimensional computation of a Gowdy-wave on the three-torus. This formulation allows foliations in full generality, in particular it poses no restriction on the lapse function.

gr-qc↗

arXiv1997

Formation, Evolution, and the Structure of Fronts Produced By Unsteady Injection of Highly Magnetized, Relativistic Flows

We study the formation, evolution and structure of dissipative fronts produced by overtaking collisions of relativistic streams, with emphasis on strongly magnetized flows. The evolution of the system is followed using analytical approach in the simple wave regime and numerical simulations in the non-simple wave regime, until a steady-state is reached. The steady-state structure of the front is then examined by solving the appropriate jump conditions. The conversion of magnetic energy into kinetic energy is parametrized in terms of the Alfvén 4-velocity inside the front. The implications for gamma-ray jets are briefly discussed.

astro-ph↗

arXiv1997

A Riemann sum upper bound in the Riemann-Lebesque theorem

The Riemann-Lebesque Theorem is commonly proved in a few strokes using the theory of Lebesque integration. Here, the upper bound $2π|c_k(f)|\le S_k(f)-s_k(f)$ for the Fourier coefficients $c_k$ is proved in terms of majoring and minoring Riemann sums $S_k(f)$ and $s_f(k)$, respectively, for Riemann integrable functions $f(x)$. This proof has been used in a course on methods of applied mathematics.

funct-an↗

arXiv1997

Numerical Integration of Nonlinear Wave Equations for General Relativity

A second-order numerical implementation is given for recently derived nonlinear wave equations for general relativity. The Gowdy T$^3$ cosmology is used as a test bed for studying the accuracy and convergence of simulations of one-dimensional nonlinear waves. The complete freedom in space-time slicing in the present formulation is exploited to compute in the Gowdy line-element. Second-order convergence is found by direct comparison of the results with either analytical solutions for polarized waves, or solutions obtained from Gowdy's reduced wave equations for the more general unpolarized waves. Some directions for extensions are discussed.

gr-qc↗

arXiv1996

Approximate Black Holes for Numerical Relativity

Spherically symmetric solutions in Brans-Dicke theory of relativity with zero coupling constant, $ω=0$, are derived in the Schwarzschild line-element. The solutions are obtained from a cubic transition equation with one small parameter. The exterior space-time of one family of solutions is arbitrarily close to the exterior Schwarzschild space-time. These nontopological solitons have some similarity with soliton stars, and are proposed as candidates for {\em approximate black holes} for the use in numerical relativity, in particular for treatment of horizon boundary conditions.

gr-qc↗

arXiv1995

Knots in Magnetized Relativistic Jets and Their Simulations

Bright features (`knots') in extragalactic jets are commonly associated with reheating of charged particles in regions with shocks or strong compression. We find a natural appearance of nozzles in simulations of toroidally magnetized jets, and propose this as a generic mechanism of knotted structures such as in the jet of 0800+608. Nozzles provide correlated enhancement of emission in radio and optical, such as discovered in HST observations of 3C273. The simulations reveal a rich structure of knots, including a nose cone with a propagating knotted structure and a hot-spot as the most extended brightness feature. Unexpected is the observed separation of the hot-spot from a composite Mach disk closer to the source.

astro-ph↗

arXiv1995

NONLINEAR WAVE EQUATIONS FOR RELATIVITY

Graviational radiation is described by canonical Yang-Mills wave equations on the curved space-time manifold, together with evolution equations for the metric in the tangent bundle. The initial data problem is described in Yang-Mills scalar and vector potentials, resulting in Lie-constraints in addition to the familiar Gauss-Codacci relations.

gr-qc↗

arXiv1993

The Theory Of Ideal Yang-Mills Fluids In Symmetric Hyperbolic Form

The theory of ideal Yang-Mills fluids (IYMF; a Yang-Mills field coupled to a fluid in the limit of infinite conductivity) is embedded in symmetric hyperbolic form. This yields both causality and well-posedness of initial value problems in this theory. The embedding is based on a covariant, constraint-free divergence formulation of IYMF, developped by the author previously for magneto-hydrodynamics. Expressions for the small amplitude wave structure are also derived, showing that in general Alfven waves do not persist in the presence of colored magnetic fields.

hep-ph↗