Spin-down episode of the X-ray pulsar Vela X-1

Article metrics


Since the discovery1 of a 283-s pulsation of an X-ray binary Vela X-1, several observations2–8 between 1975 and 1978 have revealed that its pulse period P was decreasing with an average value of /P −1.5 × 10−4 yr−1. The long-term spin-up which is considered to be caused by the angular torque of accreting matter, is a common feature of X-ray pulsars. The pulse periods of Vela X-1 were measured by the Japanese satellite Hakucho in March 1979 and March 1980, and the period in the latter was found to be significantly greater than in the earlier period despite the general spin-up between early 1976 and early 1979. Moreover, we have measured for the first time the spin-down rate /P = (2.6 ± 0.2)× 10−3 yr−1 in March 1980. This spin-down phenomenon is of great importance, as it is considered to be a manifestation of the dynamical behaviour caused by the internal structure of a neutron star.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    McClintock, J. E. et al. Astrophys. J. Let. 206, L99 (1976).

  2. 2

    Rappaport, S., Joss, P. C. & McClintock, J. E. Astrophys. J. Lett. 206, L103 (1976).

  3. 3

    Ögelman, H. et al. Astr. Astrophys. 58, 385 (1977).

  4. 4

    Rappaport, S. & Joss, P. C. Nature 266, 683 (1977).

  5. 5

    Becker, R. H. et al. Astrophys. J. 221, 912 (1978).

  6. 6

    Charles, P. A. et al. Mon. Nat. R. astr. Soc. 183, 813 (1978).

  7. 7

    Rappaport, S., Joss, P. C. & Stothers, R. Astrophys. J. 235, 570 (1980).

  8. 8

    Staubert, R. et al. Astrophys. J. 239, 1010 (1980).

  9. 9

    Watson, M. G. & Griffiths, R. E. Mon. Not. R. astr. Soc. 178, 513 (1977).

  10. 10

    Tsunemi, H. et al. Publ. astr. Soc. Jap. (in the press).

  11. 11

    Ghosh, P. & Lamb, F. K. Astrophys. J. Lett. 223, L83 (1978).

  12. 12

    Ghosh, P. & Lamb, F. K. Astrophys. J. 234, 296 (1979).

  13. 13

    Baym, G., Lamb, D. Q. & Lamb, F. K. Astrophys. J. 208, 829 (1976).

Download references

Author information

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Nagase, F., Hayakawa, S., Kunieda, H. et al. Spin-down episode of the X-ray pulsar Vela X-1. Nature 290, 572–573 (1981) doi:10.1038/290572a0

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.