Abstract
Pulsars are rotating neutron stars that produce lighthouse-like beams of radio emission from their magnetic poles. The observed pulse of emission enables their rotation rates to be measured with great precision. For some young pulsars, this provides a means of studying the interior structure of neutron stars. Most pulsars have stable pulse shapes, and slow down steadily (for example, see ref. 20). Here we report the discovery of long-term, highly periodic and correlated variations in both the pulse shape and the rate of slow-down of the pulsar PSR B1828-11. The variations are best described as harmonically related sinusoids, with periods of approximately 1,000, 500 and 250 days, probably resulting from precession of the spin axis caused by an asymmetry in the shape of the pulsar. This is difficult to understand theoretically, because torque-free precession of a solitary pulsar should be damped out by the vortices in its superfluid interior1,2.
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Acknowledgements
We thank D. J. Nice for providing the two-standard-profile frequency-domain fitting routine, M. Goss for obtaining the interferometric pulsar position, F. Graham Smith for reading of the manuscript and F. Camilo for discussions. I.H.S. received support from a Natural Sciences and Engineering Research Council of Canada postdoctoral fellowship.
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Stairs, I., Lyne, A. & Shemar, S. Evidence for free precession in a pulsar. Nature 406, 484–486 (2000). https://doi.org/10.1038/35020010
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DOI: https://doi.org/10.1038/35020010
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