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A millisecond pulsar in an X-ray binary system

Nature volume 394, pages 344–346 (1998)Cite this article

Abstract

Ordinary radio pulsars1 are neutron stars with magnetic fields of ∼1012 gauss and spin periods in the range 0.1 to 3 seconds. In contrast, millisecond radio pulsars2 have much weaker fields (∼109 gauss) and faster, millisecond spin rates. For both types of pulsar, the energy driving the radio pulsations is thought to be derived from the rotation of the neutron star. The star gradually ‘spins down’ as energy is radiated away. Millisecond radio pulsars are often located in binary systems3. In a widely accepted theoretical model4,5, they started as ordinary pulsars which lost most of their magnetic field and were ‘spun up’ to millisecond periods by the accretion of matter from a companion star in an X-ray binary system. Evidence6,7,8,9,10,11 for this model has gradually mounted, but direct proof—in the form of the predicted coherent millisecond X-ray pulsations in the persistent flux of an X-ray binary has been lacking, despite many searches12,13,14,15. Here we report the discovery16 of such a pulsar, confirming theoretical expectations. The source will probably become a millisecond radio pulsar when the accretion turns off completely.

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Figure 1: Leahy12 normalized power-density spectrum of the 1998 April 11 20:38–21:21 UTpersistent emission of XTE J1808−369.
Figure 2: The 2–60 keV light curve folded at the 249-ms period.

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Acknowledgements

We thank L. Bildsten, J. van Paradijs, R. Fender and R. Ramachandran for comments on versions of this manuscript, the aforementioned, J. Arons and F. Verbunt for discussions, and the RXTE team for promptly makng the data available online. M.K. was supported by the Visiting Miller Professor Program of the Miller Institute for Basic Research in Science (UCB). This work was supported by the Netherlands Organization for Research in Astronomy ASTRON.

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Authors and Affiliations

  1. Astronomical Institute Anton Pannekoek, University of Amsterdam, and Center for High Energy Astrophysics, Kruislaan 403, Amsterdam, 1098, SJ, The Netherlands

    Rudy Wijnands & Michiel van der Klis

  2. Department of Astronomy, University of California, Berkeley, Berkeley, 94720, California, USA

    Michiel van der Klis

Authors
  1. Rudy Wijnands
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  2. Michiel van der Klis
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Correspondence to Michiel van der Klis.

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Wijnands, R., van der Klis, M. A millisecond pulsar in an X-ray binary system. Nature 394, 344–346 (1998). https://doi.org/10.1038/28557

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