Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Measurement of circular polarisation in the Crab Nebula at 1,415 MHz


RECENTLY Rees and Gunn1 suggested that the 30-Hz wave power probably emerging from the Crab Nebula Pulsar NP0532 does not propagate further than a small region around the pulsar with a radius of about 10% of the nebular radius. Beyond this, in the main body of the nebula, the magnetic field is built up in toroidal form to equipartition strength so that the continuum emission from the bulk of the nebula is entirely synchrotron radiation. The axis of this toroid is aligned with the rotational axis of the pulsar which is assumed to be lying in the plane of the sky along the major axis of the nebula (NW/SE). A test of this proposal is the measurement of a characteristic sign change in the distribution of Faraday rotation or circular polarisation over the nebula. If the nebula is divided into quadrants along its major and minor axes, then adjacent quadrants should have the opposite sign and opposite quadrants the same sign. Since any measured Faraday rotation does not necessarily arise within the body of the nebula, the critical test becomes a detection of the characteristic sign distribution in the small amount of circular polarisation (0.1 %) expected at radio frequencies from ordinary synchrotron radiation2. The theoretical frequency dependence of ν−1/2 for the fraction of circular polarisation would then explain the null result of Landstreet and Angel3 (see also ref. 4) at optical frequencies. Here I report a measurement of the distribution of circular polarisation (Stokes parameter V) in the Crab Nebula at 1,415 MHz obtained during a series of high accuracy full polarisation measurements with the Westerbork Synthesis Radio Telescope in November 1971.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Get just this article for as long as you need it


Prices may be subject to local taxes which are calculated during checkout


  1. Rees, M. J., and Gunn, J. E., Mon. Not. R. astr. Soc., 167, 1 (1974).

    Article  ADS  Google Scholar 

  2. Legg, M. P. C., and Westfold, K. C., Astrophys. J., 154, 499 (1968).

    Article  ADS  Google Scholar 

  3. Landstreet, J. D., and Angel, J. R. P., Nature, 230, 103 (1971).

    Article  ADS  Google Scholar 

  4. Martin, P. G., Illing, R., and Angel, J. R. P., Mon. Not. R. astr. Soc., 159, 191 (1972).

    Article  ADS  Google Scholar 

  5. Weiler, K. W., Astr. Astrophys., 26, 403 (1973).

    ADS  Google Scholar 

  6. Conway, R. G., Gilbert, J. A., Raimond, E., and Weiler, K. W., Mon. Not. R. astr. Soc., 152, 1p (1971).

    Article  ADS  Google Scholar 

  7. Berge, G. L., and Seielstad, G. A., Astr. J., 77, 810 (1972).

    Article  ADS  Google Scholar 

  8. Duin, R. M., and Laan, H. van der, Astrophys. Lett., 12, 177 (1972).

    ADS  Google Scholar 

  9. Weiler, K. W., and Seielstad, G. A., Astr. Astrophys., 21, 393 (1972).

    ADS  Google Scholar 

  10. Seielstad, G. A., and Weiler, K. W., Astrophys. J., 154, 817 (1968).

    Article  ADS  Google Scholar 

  11. Ekers, R. D., Allen, R. J., and Luyten, J. R., Astr. Astrophys., 27, 77 (1973).

    ADS  Google Scholar 

Download references

Author information

Authors and Affiliations


Rights and permissions

Reprints and Permissions

About this article

Cite this article

WEILER, K. Measurement of circular polarisation in the Crab Nebula at 1,415 MHz. Nature 253, 24–25 (1975).

Download citation

  • Received:

  • Issue Date:

  • DOI:


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.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing