2,415 research outputs found
Gravitational Waves from the Merger of Binary Neutron Stars in a Fully General Relativistic Simulation
We performed 3D numerical simulations of the merger of equal-mass binary
neutron stars in full general relativity using a new large scale supercomputer.
We take the typical grid size as (505,505,253) for (x,y,z) and the maximum grid
size as (633,633,317). These grid numbers enable us to put the outer boundaries
of the computational domain near the local wave zone and hence to calculate
gravitational waveforms of good accuracy (within error) for the
first time. To model neutron stars, we adopt a -law equation of state
in the form , where P, , \varep and
are the pressure, rest mass density, specific internal energy, and adiabatic
constant. It is found that gravitational waves in the merger stage have
characteristic features that reflect the formed objects. In the case that a
massive, transient neutron star is formed, its quasi-periodic oscillations are
excited for a long duration, and this property is reflected clearly by the
quasi-periodic nature of waveforms and the energy luminosity. In the case of
black hole formation, the waveform and energy luminosity are likely damped
after a short merger stage. However, a quasi-periodic oscillation can still be
seen for a certain duration, because an oscillating transient massive object is
formed during the merger. This duration depends strongly on the initial
compactness of neutron stars and is reflected in the Fourier spectrum of
gravitational waves. To confirm our results and to calibrate the accuracy of
gravitational waveforms, we carried out a wide variety of test simulations,
changing the resolution and size of the computational domain.Comment: 40 pages; pubslihed in Prog. Theor. Phys. 107 (2002), 26
Stellar Forensics II: Millisecond Pulsar Binaries
We use the grid of models described in paper~I to analyse those millisecond
pulsar binaries whose secondaries have been studied optically. In particular,
we find cooling ages for these binary systems that range from to
. Comparison of cooling ages and characteristic spin down ages
allows us to constrain the initial spin periods and spin-up histories for
individual systems, showing that at least some millisecond pulsars had
sub-Eddington accretion rates and long magnetic field decay times.Comment: Latex, 14 pages, and 15 postscript figures. Accepted by Monthly
Notice
The Pulsar Kick Velocity Distribution
We analyse the sample of pulsar proper motions, taking detailed account of
the selection effects of the original surveys. We treat censored data using
survival statistics. From a comparison of our results with Monte Carlo
simulations, we find that the mean birth speed of a pulsar is 250-300 km/s,
rather than the 450 km/s foundby Lyne & Lorimer (1994). The resultant
distribution is consistent with a maxwellian with dispersion . Despite the large birth velocities, we find that the pulsars with long
characteristic ages show the asymmetric drift, indicating that they are
dynamically old. These pulsars may result from the low velocity tail of the
younger population, although modified by their origin in binaries and by
evolution in the galactic potential.Comment: Latex, 10 pages, and 11 postscript figures. Accepted by Monthly
Notice
Evaluation of LACIE phase 3 yield models, detailed data
There are no author-identified significant results in this report
Alien Registration- Phinney, Lawrence M. (Eastport, Washington County)
https://digitalmaine.com/alien_docs/1380/thumbnail.jp
Alien Registration- Stuart, Lena M. (Eastport, Washington County)
https://digitalmaine.com/alien_docs/1233/thumbnail.jp
Laser interferometry for the Big Bang Observer
The Big Bang Observer is a proposed space-based gravitational-wave detector intended as a follow on mission to the Laser Interferometer Space Antenna (LISA). It is designed to detect the stochastic background of gravitational waves from the early universe. We discuss how the interferometry can be arranged between three spacecraft for this mission and what research and development on key technologies are necessary to realize this scheme
Relativistic Winds from Compact Gamma-Ray Sources: II. Pair Loading and Radiative Acceleration in Gamma-ray Bursts
We consider the effects of rapid pair creation by an intense pulse of
gamma-rays propagating ahead of a relativistic shock. Side-scattered photons
colliding with the main gamma-ray beam amplify the density of scattering
charges. The acceleration rate of the pair-loaded medium is calculated, and its
limiting bulk Lorentz factor related to the spectrum and compactness of the
photon source. One obtains, as a result, a definite prediction for the relative
inertia in baryons and pairs. The deceleration of a relativistic shock in the
moving medium, and the resulting synchrotron emissivity, are compared with
existing calculations for a static medium. The radiative efficiency is
increased dramatically by pair loading. When the initial ambient density
exceeds a critical value, the scattering depth traversed by the main gamma-ray
pulse rises above unity, and the pulse is broadened. These considerations place
significant constraints on burst progenitors: a pre-burst mass loss rate
exceeding 10^{-5} M_\odot per year is difficult to reconcile with individual
pulses narrower than 10 s, unless the radiative efficiency is low. An
anisotropic gamma-ray flux (on an angular scale \Gamma^{-1} or larger) drives a
large velocity shear that greatly increases the energy in the seed magnetic
field forward of the propagating shock.Comment: 19 pp., LaTeX (aaspp4.sty), revised 12/23/99, Ap. J. in press;
summary section added and several minor improvements in presentatio
Relativistic Winds from Compact Gamma-ray Sources: I. Radiative Acceleration in the Klein-Nishina Regime
We consider the radiative acceleration to relativistic bulk velocities of a
cold, optically thin plasma which is exposed to an external source of
gamma-rays. The flow is driven by radiative momentum input to the gas, the
accelerating force being due to Compton scattering in the relativistic
Klein-Nishina limit. The bulk Lorentz factor of the plasma, Gamma, derived as a
function of distance from the radiating source, is compared with the
corresponding result in the Thomson limit. Depending on the geometry and
spectrum of the radiation field, we find that particles are accelerated to the
asymptotic Lorentz factor at infinity much more rapidly in the relativistic
regime; and the radiation drag is reduced as blueshifted, aberrated photons
experience a decreased relativistic cross section and scatter preferentially in
the forward direction. The random energy imparted to the plasma by gamma-rays
can be converted into bulk motion if the hot particles execute many Larmor
orbits before cooling. This `Compton afterburn' may be a supplementary source
of momentum if energetic leptons are injected by pair creation, but can be
neglected in the case of pure Klein-Nishina scattering. Compton drag by
side-scattered radiation is shown to be more important in limiting the bulk
Lorentz factor than the finite inertia of the accelerating medium. The
processes discussed here may be relevant to a variety of astrophysical
situations where luminous compact sources of hard X- and gamma-ray photons are
observed, including active galactic nuclei, galactic black hole candidates, and
gamma-ray bursts.Comment: LateX, 20 pages, 5 figures, revised version accepted for publication
in the Ap
- …