572 research outputs found
A timing formula for main-sequence star binary pulsars
In binary radio pulsars with a main-sequence star companion, the spin-induced
quadrupole moment of the companion gives rise to a precession of the binary
orbit. As a first approximation one can model the secular evolution caused by
this classical spin-orbit coupling by linear-in-time changes of the longitude
of periastron and the projected semi-major axis of the pulsar orbit. This
simple representation of the precession of the orbit neglects two important
aspects of the orbital dynamics of a binary pulsar with an oblate companion.
First, the quasiperiodic effects along the orbit, due to the anisotropic
nature of the quadrupole potential. Secondly, the long-term secular
evolution of the binary orbit which leads to an evolution of the longitude of
periastron and the projected semi-major axis which is non-linear in time.
In this paper a simple timing formula for binary radio pulsars with a
main-sequence star companion is presented which models the short-term secular
and most of the short-term periodic effects caused by the classical spin-orbit
coupling. I also give extensions of the timing formula which account for
long-term secular changes in the binary pulsar motion. It is shown that the
short-term periodic effects are important for the timing observations of the
binary pulsar PSR B1259--63. The long-term secular effects are likely to become
important in the next few years of timing observations of the binary pulsar PSR
J0045--7319. They could help to restrict or even determine the moments of
inertia of the companion star and thus probe its internal structure.
Finally, I reinvestigate the spin-orbit precession of the binary pulsar PSR
J0045--7319 since the analysis given in the literature is based on an incorrect
expression for the precession of the longitude of periastron.Comment: 12 pages (LaTeX), 20 Postscript figures; replaced by accepted versio
Geodetic Precession and the Binary Pulsar B1913+16
A change of the component separation in the profiles of the binary pulsar PSR
B1913+16 has been observed for the first time (Kramer 1998) as expected by
geodetic precession. In this work we extend the previous work by accounting for
recent data from the Effelsberg 100-m telescope and Arecibo Observatory and
testing model predictions. We demonstrate how the new information will provide
additional information on the solutions of the system geometry.Comment: 2 pages, 1 figure, IAU 177 Colloquium: Pulsar Astronomy - 2000 and
Beyon
Pulsar-black hole binaries: prospects for new gravity tests with future radio telescopes
The anticipated discovery of a pulsar in orbit with a black hole is expected
to provide a unique laboratory for black hole physics and gravity. In this
context, the next generation of radio telescopes, like the Five-hundred-metre
Aperture Spherical radio Telescope (FAST) and the Square Kilometre Array (SKA),
with their unprecedented sensitivity, will play a key role. In this paper, we
investigate the capability of future radio telescopes to probe the spacetime of
a black hole and test gravity theories, by timing a pulsar orbiting a
stellar-mass-black-hole (SBH). Based on mock data simulations, we show that a
few years of timing observations of a sufficiently compact pulsar-SBH (PSR-SBH)
system with future radio telescopes would allow precise measurements of the
black hole mass and spin. A measurement precision of one per cent can be
expected for the spin. Measuring the quadrupole moment of the black hole,
needed to test GR's no-hair theorem, requires extreme system configurations
with compact orbits and a large SBH mass. Additionally, we show that a PSR-SBH
system can lead to greatly improved constraints on alternative gravity theories
even if they predict black holes (practically) identical to GR's. This is
demonstrated for a specific class of scalar-tensor theories. Finally, we
investigate the requirements for searching for PSR-SBH systems. It is shown
that the high sensitivity of the next generation of radio telescopes is key for
discovering compact PSR-SBH systems, as it will allow for sufficiently short
survey integration times.Comment: 20 pages, 11 figures, 1 table, accepted for publication in MNRA
Gravitational waveforms from unequal-mass binaries with arbitrary spins under leading order spin-orbit coupling
The paper generalizes the structure of gravitational waves from orbiting
spinning binaries under leading order spin-orbit coupling, as given in the work
by K\"onigsd\"orffer and Gopakumar [PRD 71, 024039 (2005)] for single-spin and
equal-mass binaries, to unequal-mass binaries and arbitrary spin
configurations. The orbital motion is taken to be quasi-circular and the
fractional mass difference is assumed to be small against one. The emitted
gravitational waveforms are given in analytic form.Comment: 13 pages, 2 figures, submitted to PRD on 11 Sep. 200
Timing models for the long-orbital period binary pulsar PSR B1259-63
The pulsar PSR B1259-63 is in a highly eccentric 3.4-yr orbit with the Be
star SS 2883. Timing observations of this pulsar, made over a 7-yr period using
the Parkes 64-m radio telescope, cover two periastron passages, in 1990 August
and 1994 January. The timing data cannot be fitted by the normal pulsar and
Keplerian binary parameters. A timing solution including a (non-precessing)
Keplerian orbit and timing noise (represented as a polynomial of fifth order in
time) provide a satisfactory fit to the data. However, because the Be star
probably has a significant quadrupole moment, we prefer to interpret the data
by a combination of timing noise, dominated by a cubic phase term, and
and terms. We show that the and are
likely to be a result of a precessing orbit caused by the quadrupole moment of
the tilted companion star. We further rule out a number of possible physical
effects which could contribute to the timing data of PSR B1259-63 on a
measurable level.Comment: LaTeX, 9 pages, 8 figures, accepted for publication in MNRA
A new test of conservation laws and Lorentz invariance in relativistic gravity
General relativity predicts that energy and momentum conservation laws hold
and that preferred frames do not exist. The parametrised post-Newtonian
formalism (PPN) phenomenologically quantifies possible deviations from general
relativity. The PPN parameter alpha_3 (which identically vanishes in general
relativity) plays a dual role in that it is associated both with a violation of
the momentum conservation law, and with the existence of a preferred frame. By
considering the effects of alpha_3 neq 0 in certain binary pulsar systems, it
is shown that alpha_3 < 2.2 x 10^-20 (90% CL). This limit improves on previous
results by several orders of magnitude, and shows that pulsar tests of alpha_3
rank (together with Hughes-Drever-type tests of local Lorentz invariance) among
the most precise null experiments of physics.Comment: Submitted to Classical Quantum Gravity, LaTeX, requires ioplppt.sty,
no figure
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