Temporal variations in scattering and dispersion measure in the Crab Pulsar and their effect on timing precision

McKee, J. W.; Lyne, A. G.; Stappers, B. W.; Bassa, C. G.; Jordan, C. A.

Abstract

We have measured variations in scattering time-scales in the Crab Pulsar over a 30-yr period, using observations made at 610 MHz with the 42-ft telescope at Jodrell Bank Observatory. Over more recent years, where regular Lovell Telescope observations at frequencies around 1400 MHz were available, we have also determined the dispersion measure variations, after disentangling the scattering delay from the dispersive delay. We demonstrate a relationship between scattering and dispersion measure variations, with a correlation coefficient of 0.56 ± 0.01. The short time-scales over which these quantities vary, the size of the variations, and the close correlation between scattering and dispersion measure all suggest that the effects are due to discrete structures within the Crab Nebula, with size scales of ~6 au (corresponding to an angular size of ~2 mas at an assumed distance of 2200 pc). We mitigate the effects of scattering on the observed pulse shape by using the measured scattering information to modify the template used for generating the pulse arrival times, thus improving the precision to which the pulsar can be timed. We test this on timing data taken during periods of high scattering, and obtain a factor of two improvements in the root mean square of the timing residuals.

Citation

McKee, J. W., Lyne, A. G., Stappers, B. W., Bassa, C. G., & Jordan, C. A. (2018). Temporal variations in scattering and dispersion measure in the Crab Pulsar and their effect on timing precision. Monthly notices of the Royal Astronomical Society, 479(3), 4216-4224. https://doi.org/10.1093/mnras/sty1727

• Journal Article Type: Article
• Acceptance Date: Jun 22, 2018
• Online Publication Date: Jul 4, 2018
• Publication Date: Sep 21, 2018
• Deposit Date: Nov 29, 2022
• Publicly Available Date: Jan 19, 2023
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 479
• Issue: 3
• Pages: 4216-4224
• DOI: https://doi.org/10.1093/mnras/sty1727
• Public URL: https://hull-repository.worktribe.com/output/4134736