292 research outputs found
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
Prospects for probing strong gravity with a pulsar-black hole system
The discovery of a pulsar (PSR) in orbit around a black hole (BH) is expected
to provide a superb new probe of relativistic gravity and BH properties. Apart
from a precise mass measurement for the BH, one could expect a clean
verification of the dragging of space-time caused by the BH spin. In order to
measure the quadrupole moment of the BH for testing the no-hair theorem of
general relativity (GR), one has to hope for a sufficiently massive BH. In this
respect, a PSR orbiting the super-massive BH in the center of our Galaxy would
be the ultimate laboratory for gravity tests with PSRs. But even for gravity
theories that predict the same properties for BHs as GR, a PSR-BH system would
constitute an excellent test system, due to the high grade of asymmetry in the
strong field properties of these two components. Here we highlight some of the
potential gravity tests that one could expect from different PSR-BH systems,
utilizing present and future radio telescopes, like FAST and SKA.Comment: Proceedings of IAUS 291 "Neutron Stars and Pulsars: Challenges and
Opportunities after 80 years", J. van Leeuwen (ed.); 6 pages, 3 figure
Prospects for Probing the Spacetime of Sgr A* with Pulsars
The discovery of radio pulsars in compact orbits around Sgr A* would allow an
unprecedented and detailed investigation of the spacetime of the supermassive
black hole. This paper shows that pulsar timing, including that of a single
pulsar, has the potential to provide novel tests of general relativity, in
particular its cosmic censorship conjecture and no-hair theorem for rotating
black holes. These experiments can be performed by timing observations with 100
micro-second precision, achievable with the Square Kilometre Array for a normal
pulsar at frequency above 15 GHz. Based on the standard pulsar timing
technique, we develop a method that allows the determination of the mass, spin,
and quadrupole moment of Sgr A*, and provides a consistent covariance analysis
of the measurement errors. Furthermore, we test this method in detailed mock
data simulations. It seems likely that only for orbital periods below ~0.3 yr
is there the possibility of having negligible external perturbations. For such
orbits we expect a ~10^-3 test of the frame dragging and a ~10^-2 test of the
no-hair theorem within 5 years, if Sgr A* is spinning rapidly. Our method is
also capable of identifying perturbations caused by distributed mass around Sgr
A*, thus providing high confidence in these gravity tests. Our analysis is not
affected by uncertainties in our knowledge of the distance to the Galactic
center, R0. A combination of pulsar timing with the astrometric results of
stellar orbits would greatly improve the measurement precision of R0.Comment: 12 pages, 10 Figures, accepted for publication in Ap
Prospects for accurate distance measurements of pulsars with the SKA: enabling fundamental physics
Parallax measurements of pulsars allow for accurate measurements of the
interstellar electron density and contribute to accurate tests of general
relativity using binary systems. The Square Kilometre Array (SKA) will be an
ideal instrument for measuring the parallax of pulsars, because it has a very
high sensitivity, as well as baselines extending up to several thousands of
kilometres. We performed simulations to estimate the number of pulsars for
which the parallax can be measured with the SKA and the distance to which a
parallax can be measured. We compare two different methods. The first method
measures the parallax directly by utilising the long baselines of the SKA to
form high angular resolution images. The second method uses the arrival times
of the radio signals of pulsars to fit a transformation between time
coordinates in the terrestrial frame and the comoving pulsar frame directly
yielding the parallax. We find that with the first method a parallax with an
accuracy of 20% or less can be measured up to a maximum distance of 13 kpc,
which would include 9,000 pulsars. By timing pulsars with the most stable
arrival times for the radio emission, parallaxes can be measured for about
3,600 millisecond pulsars up to a distance of 9 kpc with an accuracy of 20%.Comment: 9 pages, 8 figures, accepted for publication in A&A, table format has
been modified, language edite
A characteristic observable signature of preferred frame effects in relativistic binary pulsars
In this paper we develop a consistent, phenomenological methodology to
measure preferred-frame effects (PFEs) in binary pulsars that exhibit a high
rate of periastron advance. We show that in these systems the existence of a
preferred frame for gravity leads to an observable characteristic `signature'
in the timing data, which uniquely identifies this effect. We expand the
standard Damour-Deruelle timing formula to incorporate this `signature' and
show how this new PFE timing model can be used to either measure or constrain
the parameters related to a violation of the local Lorentz invariance of
gravity in the strong internal fields of neutron stars. In particular, we
demonstrate that in the presence of PFEs we expect a set of the new timing
parameters to have a unique relationship that can be measured and tested
incontrovertibly. This new methodology is applied to the Double Pulsar, which
turns out to be the ideal test system for this kind of experiments.The
currently available dataset allows us only to study the impact of PFEs on the
orbital precession rate, d omega/dt, providing limits that are, at the moment,
clearly less stringent than existing limits on PFE strong-field parameters.
However, simulations show that the constraints improve fast in the coming
years, allowing us to study all new PFE timing parameters and to check for the
unique relationship between them. Finally, we show how a combination of several
suitable systems in a "PFE antenna array", expected to be availabe for instance
with the Square-Kilometre-Array (SKA), provides full sensitivity to possible
violations of local Lorentz invariance in strong gravitational fields in all
directions of the sky. This PFE antenna array may eventually allow us to
determine the direction of a preferred frame should it exist.Comment: Accepted for publication in MNRAS, 12 pages, 5 figures, figures 3 and
5 in reduced quality due to size limitation
Can we see pulsars around Sgr A*? - The latest searches with the Effelsberg telescope
Radio pulsars in relativistic binary systems are unique tools to study the
curved space-time around massive compact objects. The discovery of a pulsar
closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr
A*, would provide a superb test-bed for gravitational physics. To date, the
absence of any radio pulsar discoveries within a few arc minutes of Sgr A* has
been explained by one principal factor: extreme scattering of radio waves
caused by inhomogeneities in the ionized component of the interstellar medium
in the central 100 pc around Sgr A*. Scattering, which causes temporal
broadening of pulses, can only be mitigated by observing at higher frequencies.
Here we describe recent searches of the Galactic centre region performed at a
frequency of 18.95 GHz with the Effelsberg radio telescope.Comment: 3 pages, 2 figures, Proceedings of IAUS 291 "Neutron Stars and
Pulsars: Challenges and Opportunities after 80 years", 201
Observing Radio Pulsars in the Galactic Centre with the Square Kilometre Array
The discovery and timing of radio pulsars within the Galactic centre is a
fundamental aspect of the SKA Science Case, responding to the topic of "Strong
Field Tests of Gravity with Pulsars and Black Holes" (Kramer et al. 2004;
Cordes et al. 2004). Pulsars have in many ways proven to be excellent tools for
testing the General theory of Relativity and alternative gravity theories (see
Wex (2014) for a recent review). Timing a pulsar in orbit around a companion,
provides a unique way of probing the relativistic dynamics and spacetime of
such a system. The strictest tests of gravity, in strong field conditions, are
expected to come from a pulsar orbiting a black hole. In this sense, a pulsar
in a close orbit ( < 1 yr) around our nearest supermassive black
hole candidate, Sagittarius A* - at a distance of ~8.3 kpc in the Galactic
centre (Gillessen et al. 2009a) - would be the ideal tool. Given the size of
the orbit and the relativistic effects associated with it, even a slowly
spinning pulsar would allow the black hole spacetime to be explored in great
detail (Liu et al. 2012). For example, measurement of the frame dragging caused
by the rotation of the supermassive black hole, would allow a test of the
"cosmic censorship conjecture." The "no-hair theorem" can be tested by
measuring the quadrupole moment of the black hole. These are two of the prime
examples for the fundamental studies of gravity one could do with a pulsar
around Sagittarius A*. As will be shown here, SKA1-MID and ultimately the SKA
will provide the opportunity to begin to find and time the pulsars in this
extreme environment.Comment: 14 pages, 5 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
The relativistic pulsar-white dwarf binary PSR J1738+0333 I. Mass determination and evolutionary history
PSR J1738+0333 is one of the four millisecond pulsars known to be orbited by
a white dwarf companion bright enough for optical spectroscopy. Of these, it
has the shortest orbital period, making it especially interesting for a range
of astrophysical and gravity related questions. We present a spectroscopic and
photometric study of the white dwarf companion and infer its radial velocity
curve, effective temperature, surface gravity and luminosity. We find that the
white dwarf has properties consistent with those of low-mass white dwarfs with
thick hydrogen envelopes, and use the corresponding mass-radius relation to
infer its mass; M_WD = 0.181 +/- +0.007/-0.005 solar masses. Combined with the
mass ratio q=8.1 +/- 0.2 inferred from the radial velocities and the precise
pulsar timing ephemeris, the neutron star mass is constrained to M_PSR = 1.47
+/- +0.07/-0.06 solar masses. Contrary to expectations, the latter is only
slightly above the Chandrasekhar limit. We find that, even if the birth mass of
the neutron star was only 1.20 solar masses, more than 60% of the matter that
left the surface of the white dwarf progenitor escaped the system. The accurate
determination of the component masses transforms this system in a laboratory
for fundamental physics by constraining the orbital decay predicted by general
relativity. Currently, the agreement is within 1 sigma of the observed decay.
Further radio timing observations will allow precise tests of white dwarf
models, assuming the validity of general relativity.Comment: Article published in Monthly Notices of the Royal Astronomical
Society v.3: Updated reference
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