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Abstract

We present an analysis of the variations seen in the dispersion measures (DMs) of 20-ms 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 characterized 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.

Item Type:	Article
Authors/Creators:	You, XP and Hotan, AW and Ord, SM and Jenet, F and Bhat, NDR and Teoh, A and Hobbs, G and Coles, WA and Manchester, RN and Edwards, R and Bailes, M and Sarkissian, J and Verbiest, JPW and van Straten, W
Keywords:	pulsars: general – ISM: general.
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Blackwell Publishing
ISSN:	0035-8711
DOI / ID Number:	https://doi.org/10.1111/j.1365-2966.2007.11617.x
Additional Information:	The definitive version is available at www.blackwell-synergy.com
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