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Measurement and correction of variations in interstellar dispersion in high-precision pulsar timing

Keith, M. J. and Coles, W. and Shannon, R. M. and Hobbs, G. B. and Manchester, R. N. and Bailes, M. and Bhat, N. D. R. and Burke-Spolaor, S. and Champion, D. J. and Chaudhary, A. and Hotan, A. W. and Khoo, J. and Kocz, J. and Osłowski, S. and Ravi, V. and Reynolds, J. E. and Sarkissian, J. and van Straten, W. and Yardley, D. R. B. (2013) Measurement and correction of variations in interstellar dispersion in high-precision pulsar timing. Monthly Notices of the Royal Astronomical Society, 429 (3). pp. 2161-2174. ISSN 0035-8711.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Bailes, M.0000-0003-3294-3081
Burke-Spolaor, S.0000-0003-4052-7838
Kocz, J.0000-0003-0249-7586
Osłowski, S.0000-0003-0289-0732
Ravi, V.0000-0002-7252-5485
Additional Information:© 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2012 November 23. Received 2012 November 22; in original form 2012 June 14. Published: 22 December 2012. This work has been carried out as part of the Parkes Pulsar Timing Array project. GBH is the recipient of an Australian Research Council QEII Fellowship (project DP0878388), the PPTA project was initiated with support from RNM’s Federation Fellowship (FF0348478). The Parkes radio telescope is part of the Australia Telescope which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.
Funding AgencyGrant Number
Australian Research CouncilDP0878388
Australian Research CouncilFF0348478
Commonwealth of AustraliaUNSPECIFIED
Subject Keywords:methods: data analysis – pulsars: general – ISM: structure
Issue or Number:3
Record Number:CaltechAUTHORS:20130214-090229819
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Official Citation:M. J. Keith, W. Coles, R. M. Shannon, G. B. Hobbs, R. N. Manchester, M. Bailes, N. D. R. Bhat, S. Burke-Spolaor, D. J. Champion, A. Chaudhary, A. W. Hotan, J. Khoo, J. Kocz, S. Osłowski, V. Ravi, J. E. Reynolds, J. Sarkissian, W. van Straten, D. R. B. Yardley; Measurement and correction of variations in interstellar dispersion in high-precision pulsar timing, Monthly Notices of the Royal Astronomical Society, Volume 429, Issue 3, 1 March 2013, Pages 2161–2174,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36911
Deposited By: JoAnn Boyd
Deposited On:19 Feb 2013 19:13
Last Modified:24 Oct 2019 22:26

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