608 research outputs found
Status Update of the Parkes Pulsar Timing Array
The Parkes Pulsar Timing Array project aims to make a direct detection of a
gravitational-wave background through timing of millisecond pulsars. In this
article, the main requirements for that endeavour are described and recent and
ongoing progress is outlined. We demonstrate that the timing properties of
millisecond pulsars are adequate and that technological progress is timely to
expect a successful detection of gravitational waves within a decade, or
alternatively to rule out all current predictions for gravitational wave
backgrounds formed by supermassive black-hole mergers.Comment: 10 pages, 3 figures, Amaldi 8 conference proceedings, accepted by
Classical & Quantum Gravit
The PULSE@Parkes project: A new observing technique for long-term pulsar monitoring
The PULSE@Parkes project has been designed to monitor the rotation of radio
pulsars over time spans of days to years. The observations are obtained using
the Parkes 64-m and 12-m radio telescopes by Australian and international high
school students. These students learn the basis of radio astronomy and
undertake small projects with their observations. The data are fully calibrated
and obtained with the state-of-the-art pulsar hardware available at Parkes. The
final data sets are archived and are currently being used to carry out studies
of 1) pulsar glitches, 2) timing noise, 3) pulse profile stability over long
time scales and 4) the extreme nulling phenomenon. The data are also included
in other projects such as gamma-ray observatory support and for the Parkes
Pulsar Timing Array project. In this paper we describe the current status of
the project and present the first scientific results from the Parkes 12-m radio
telescope. We emphasise that this project offers a straightforward means to
enthuse high school students and the general public about radio astronomy while
obtaining scientifically valuable data sets.Comment: accepted for publication by PAS
Development of a pulsar-based timescale
Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA)
project we develop the first pulsar-based timescale that has a precision
comparable to the uncertainties in international atomic timescales. Our
ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the
free atomic timescale Echelle Atomique Libre (EAL). The EPS can be used to
detect fluctuations in atomic timescales and therefore can lead to a new
realisation of Terrestrial Time, TT(PPTA11). We successfully follow features
known to affect the frequency of the International Atomic Timescale (TAI) and
we find marginally significant differences between TT(PPTA11) and TT(BIPM11).
We discuss the various phenomena that lead to a correlated signal in the pulsar
timing residuals and therefore limit the stability of the pulsar timescale.Comment: Accepted for publication in MNRA
Constraining the coalescence rate of supermassive black-hole binaries using pulsar timing
Pulsar timing observations are used to place constraints on the rate of
coalescence of supermassive black-hole (SMBH) binaries as a function of mass
and redshift. In contrast to the indirect constraints obtained from other
techniques, pulsar timing observations provide a direct constraint on the
black-hole merger rate. This is possible since pulsar timing is sensitive to
the gravitational waves (GWs) emitted by these sources in the final stages of
their evolution. We find that upper bounds calculated from the recently
published Parkes Pulsar Timing Array data are just above theoretical
predictions for redshifts below 10. In the future, with improved timing
precision and longer data spans, we show that a non-detection of GWs will rule
out some of the available parameter space in a particular class of SMBH binary
merger models. We also show that if we can time a set of pulsars to 10ns timing
accuracy, for example, using the proposed Square Kilometre Array, it should be
possible to detect one or more individual SMBH binary systems
On detection of the stochastic gravitational-wave background using the Parkes pulsar timing array
We search for the signature of an isotropic stochastic gravitational-wave
background in pulsar timing observations using a frequency-domain correlation
technique. These observations, which span roughly 12 yr, were obtained with the
64-m Parkes radio telescope augmented by public domain observations from the
Arecibo Observatory. A wide range of signal processing issues unique to pulsar
timing and not previously presented in the literature are discussed. These
include the effects of quadratic removal, irregular sampling, and variable
errors which exacerbate the spectral leakage inherent in estimating the steep
red spectrum of the gravitational-wave background. These observations are found
to be consistent with the null hypothesis, that no gravitational-wave
background is present, with 76 percent confidence. We show that the detection
statistic is dominated by the contributions of only a few pulsars because of
the inhomogeneity of this data set. The issues of detecting the signature of a
gravitational-wave background with future observations are discussed.Comment: 12 pages, 8 figures, 7 tables, accepted for publication in MNRA
Measurement and correction of variations in interstellar dispersion in high-precision pulsar timing
Signals from radio pulsars show a wavelength-dependent delay due to dispersion in the interstellar plasma. At a typical observing wavelength, this delay can vary by tens of microseconds on 5-yr time-scales, far in excess of signals of interest to pulsar timing arrays, such as that induced by a gravitational wave background. Measurement of these delay variations is not only crucial for the detection of such signals, but also provides an unparalleled measurement of the turbulent interstellar plasma at astronomical unit (au) scales.
In this paper we demonstrate that without consideration of wavelength-independent red noise, ‘simple’ algorithms to correct for interstellar dispersion can attenuate signals of interest to pulsar timing arrays. We present a robust method for this correction, which we validate through simulations, and apply it to observations from the Parkes Pulsar Timing Array. Correction for dispersion variations comes at a cost of increased band-limited white noise. We discuss scheduling to minimize this additional noise, and factors, such as scintillation, that can exacerbate the problem.
Comparison with scintillation measurements confirms previous results that the spectral exponent of electron density variations in the interstellar medium often appears steeper than expected. We also find a discrete change in dispersion measure of PSR J1603−7202 of ∼2 × 10^(−3) cm^(−3) pc for about 250 d. We speculate that this has a similar origin to the ‘extreme scattering events’ seen in other sources. In addition, we find that four pulsars show a wavelength-dependent annual variation, indicating a persistent gradient of electron density on an au spatial scale, which has not been reported previously
Does a "stochastic" background of gravitational waves exist in the pulsar timing band?
We investigate the effects of gravitational waves (GWs) from a simulated population of binary supermassive black holes (SMBHs) on pulsar timing array data sets. We construct a distribution describing the binary SMBH population from an existing semi-analytic galaxy formation model. Using realizations of the binary SMBH population generated from this distribution, we simulate pulsar timing data sets with GW-induced variations. We find that the statistics of these variations do not correspond to an isotropic, stochastic GW background. The "Hellings & Downs" correlations between simulated data sets for different pulsars are recovered on average, though the scatter of the correlation estimates is greater than expected for an isotropic, stochastic GW background. These results are attributable to the fact that just a few GW sources dominate the GW-induced variations in every Fourier frequency bin of a five-year data set. Current constraints on the amplitude of the GW signal from binary SMBHs will be biased. Individual binary systems are likely to be detectable in five-year pulsar timing array data sets where the noise is dominated by GW-induced variations. Searches for GWs in pulsar timing array data therefore need to account for the effects of individual sources of GWs
The Sensitivity of the Parkes Pulsar Timing Array to Individual Sources of Gravitational Waves
We present the sensitivity of the Parkes Pulsar Timing Array to gravitational
waves emitted by individual super-massive black-hole binary systems in the
early phases of coalescing at the cores of merged galaxies. Our analysis
includes a detailed study of the effects of fitting a pulsar timing model to
non-white timing residuals. Pulsar timing is sensitive at nanoHertz frequencies
and hence complementary to LIGO and LISA. We place a sky-averaged constraint on
the merger rate of nearby () black-hole binaries in the early phases
of coalescence with a chirp mass of 10^{10}\,\rmn{M}_\odot of less than one
merger every seven years. The prospects for future gravitational-wave astronomy
of this type with the proposed Square Kilometre Array telescope are discussed.Comment: fixed error in equation (4). [13 pages, 6 figures, 1 table, published
in MNRAS
The international pulsar timing array project: using pulsars as a gravitational wave detector
The International Pulsar Timing Array project combines observations of
pulsars from both Northern and Southern hemisphere observatories with the main
aim of detecting ultra-low frequency (~10^-9 to 10^-8 Hz) gravitational waves.
Here we introduce the project, review the methods used to search for
gravitational waves emitted from coalescing supermassive binary black-hole
systems in the centres of merging galaxies and discuss the status of the
project.Comment: accepted by Classical and Quantum Gravity. Review talk for the
Amaldi8 conference serie
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