Mon.Not.Roy.Astron.Soc.378:493-506,2007 We present an analysis of the variations seen in the dispersion measures
(DMs) of 20 millisecond pulsars observed as part of the Parkes Pulsar Timing
Array ...project. We carry out a statistically rigorous structure function
analysis for each pulsar and show that the variations seen for most pulsars are
consistent with those expected for an interstellar medium characterised by a
Kolmogorov turbulence spectrum. The structure functions for PSRs J1045-4509 and
J1909-3744 provide the first clear evidence for a large inner scale, possibly
due to ion-neutral damping. We also show the effect of the solar wind on the
DMs and show that the simple models presently implemented into pulsar timing
packages cannot reliably correct for this effect. For the first time we clearly
show how DM variations affect pulsar timing residuals and how they can be
corrected in order to obtain the highest possible timing precision. Even with
our presently limited data span, the residuals (and all parameters derived from
the timing) for six of our pulsars have been significantly improved by
correcting for the DM variations.
The first direct detection of gravitational waves may be made through observations of pulsars. The principal aim of pulsar timing array projects being carried out worldwide is to detect ultra-low ...frequency gravitational waves (f ~ 10^-9 to 10^-8 Hz). Such waves are expected to be caused by coalescing supermassive binary black holes in the cores of merged galaxies. It is also possible that a detectable signal could have been produced in the inflationary era or by cosmic strings. In this paper we review the current status of the Parkes Pulsar Timing Array project (the only such project in the Southern hemisphere) and compare the pulsar timing technique with other forms of gravitational-wave detection such as ground- and space-based interferometer systems.
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.
We present an analysis of the variations seen in the dispersion measures (DMs) of 20 millisecond pulsars observed as part of the Parkes Pulsar Timing Array project. We carry out a statistically ...rigorous structure function analysis for each pulsar and show that the variations seen for most pulsars are consistent with those expected for an interstellar medium characterised by a Kolmogorov turbulence spectrum. The structure functions for PSRs J1045-4509 and J1909-3744 provide the first clear evidence for a large inner scale, possibly due to ion-neutral damping. We also show the effect of the solar wind on the DMs and show that the simple models presently implemented into pulsar timing packages cannot reliably correct for this effect. For the first time we clearly show how DM variations affect pulsar timing residuals and how they can be corrected in order to obtain the highest possible timing precision. Even with our presently limited data span, the residuals (and all parameters derived from the timing) for six of our pulsars have been significantly improved by correcting for the DM variations.
