Skip to main content

Thank you for visiting nature.com. 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.

Polarimetric evidence of a white dwarf pulsar in the binary system AR Scorpii

Abstract

The variable star AR Scorpii (AR Sco) was recently discovered to pulse in brightness every 1.97 min from ultraviolet wavelengths into the radio regime. The system is composed of a cool, low-mass star in a tight, 3.55-hour orbit with a more massive white dwarf. Here we report new optical observations of AR Sco that show strong linear polarization (up to 40%) that varies strongly and periodically on both the spin period of the white dwarf and the beat period between the spin and orbital period, as well as low-level (up to a few per cent) circular polarization. These observations support the notion that, similar to neutron-star pulsars, the pulsed luminosity of AR Sco is powered by the spin-down of the rapidly rotating white dwarf that is highly magnetized (up to 500 MG). The morphology of the modulated linear polarization is similar to that seen in the Crab pulsar, albeit with a more complex waveform owing to the presence of two periodic signals of similar frequency. Magnetic interactions between the two component stars, coupled with synchrotron radiation from the white dwarf, power the observed polarized and non-polarized emission. AR Sco is therefore the first example of a white dwarf pulsar.

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

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

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

Figure 1: Time-series polarimetry.
Figure 2: Polarimetry periodograms.
Figure 3: Spin-modulated polarization.
Figure 4: Stokes parameters Q, U and polarized flux variations over spin period.

References

  1. Gold, T. Rotating neutron stars as the origin of the pulsating radio sources. Nature 218, 731–732 (1968).

    Article  ADS  Google Scholar 

  2. Marsh, T. R. et al. A radio-pulsing white dwarf binary star. Nature 537, 374–377 (2016).

    Article  ADS  Google Scholar 

  3. Wynn, G. A., King, A. R. & Horne, K. A magnetic propeller in the cataclysmic variable AE Aquarii. Mon. Not. R. Astron. Soc. 286, 436–446 (1997).

    Article  ADS  Google Scholar 

  4. Ikhsanov, N. R. The pulsar-like white dwarf in AE Aqarii. Astron. Astrophys. 338, 521–526 (1998).

    ADS  Google Scholar 

  5. Meintjes, P. J. & Venter, L. A. The diamagnetic blob propeller in AE Aquarii and non-thermal radio to mid-infrared emission. Mon. Not. R. Astron. Soc. 360, 573–582 (2005).

    Article  ADS  Google Scholar 

  6. Oruru, B. & Meintjes, P. J. X-ray characteristics and the spectral energy distribution of AE Aquarii. Mon. Not. R. Astron. Soc. 421, 1557–1586 (2012).

    Article  ADS  Google Scholar 

  7. Potter, S. B. et al. Polarized QPOs from the INTEGRAL polar IGRJ14536-5522 (=Swift J1453.4-5524). Mon. Not. R. Astron. Soc. 402, 1161–1170 (2010).

    Article  ADS  Google Scholar 

  8. Słowikowski, A., Kanbach, G., Kramer, M. & Stefanescu, A. Optical polarization of the Crab pulsar: Precision measurements and comparison to the radio emission. Mon. Not. R. Astron. Soc. 397, 103–123 (2009).

    Article  ADS  Google Scholar 

  9. Karastergiou, A. & Johnston, S. Absolute polarization position angle profiles of southern pulsars at 1.4 and 3.1 GHz. Mon. Not. R. Astron. Soc. 365, 353–366 (2006).

    Article  ADS  Google Scholar 

  10. Radhakrishnan, V. & Cooke, D. J. Magnetic poles and the polarization structure of pulsar radiation. Astrophys. J. Lett. 3, 225–229 (1969).

    Google Scholar 

  11. Landolfi, M., Landi Degl’Innocenti, E., Landi Degl’Innocenti, M. & Leroy, J. L. Linear polarimetry of Ap stars. I. A simple canonical model. Astron. Astrophys. 272, 285–298 (1993).

    ADS  Google Scholar 

  12. Butters, O. W. et al. Circular polarization survey of intermediate polars. I. Northern targets in the range 17 h < RA < 23. Astron. Astrophys. 496, 891–902 (2009).

    Article  ADS  Google Scholar 

  13. Potter, S. B. et al. On the spin modulated circular polarization from the intermediate polars NY Lup and IGR J150946649. Mon. Not. R. Astron. Soc. 420, 2596–2602 (2012).

    Article  ADS  Google Scholar 

  14. de Búrca, D. & Shearer, A. Circular polarization of synchrotron radiation in high magnetic fields. Mon. Not. R. Astron. Soc. 450, 533–540 (2015).

    Article  ADS  Google Scholar 

  15. Ferrario, L., de Martino, D. & Gänsicke, B. T. Magnetic white dwarfs. Space Sci. Rev. 191, 111–169 (2015).

    Article  ADS  Google Scholar 

  16. Katz, J. I. AR Sco: A white dwarf synchronar. Astrophys. J. Preprint at https://arxiv.org/abs/1609.07172 (2017).

  17. Meintjes, P. J. & Jurua, E. Secondary star magnetic fields in close binaries. Mon. Not. R. Astron. Soc. 372, 1279–1288 (2006).

    Article  ADS  Google Scholar 

  18. Becker, W. & Trìmpher, J. The X-ray luminosity of rotation-powered pulsars. Astron. Astrophys. 326, 682–691 (1997).

    ADS  Google Scholar 

  19. Becker, W. in Neutron Stars and Pulsars (ed. Becker, W. ) 91–140 (Springer, 2009).

    Chapter  Google Scholar 

  20. Abdo, A. A. et al. The first Fermi Large Area Telescope catalog of gamma-ray pulsars. Astrophys. J. Suppl. Ser. 187, 460–494 (2010).

    Article  ADS  Google Scholar 

  21. Geng, J.-J., Zhang, B. & Huang, Y.-F. A model of white dwarf pulsar AR Scorpii. Astrophys. J. 831, L10 (2016).

    Article  ADS  Google Scholar 

  22. Donati, J.-F. & Landstreet, J. D. Magnetic fields of nondegenerate stars. Annu. Rev. Astron. Astrophys. 47, 333–370 (2009).

    Article  ADS  Google Scholar 

  23. Mestel, L. Magnetic braking by a stellar wind I. Mon. Not. R. Astron. Soc. 138, 359–391 (1968).

    Article  ADS  Google Scholar 

  24. Mestel, L. & Spruit, H. C. On magnetic braking of late-type stars. Mon. Not. R. Astron. Soc. 226, 57–66 (1987).

    Article  ADS  Google Scholar 

  25. Haerendel, G. Acceleration from field-aligned potential drops. Astrophys. J. Suppl. S. 90, 765–774 (1994).

    Article  ADS  Google Scholar 

  26. Venter, L. A. & Meintjes, P. J. The tenuous X-ray corona enveloping AE Aquarii. Mon. Not. R. Astron. Soc. 378, 681–690 (2007).

    Article  ADS  Google Scholar 

  27. van der Laan, H. A model for variable extragalactic radio sources. Nature 211, 1131–1133 (1966).

    Article  ADS  Google Scholar 

  28. Bastian, T. S., Dulk, G. A. & Chanmugam, G. Radio flares from AE Aquarii: A low-power analog to Cygnus X-3? Astrophys. J. 324, 431–440 (1988).

    Article  ADS  Google Scholar 

  29. Arons, J. & Scharlemann, E. T. Pair formation above polar caps — structure of the low altitude acceleration zone. Astrophys. J. 231, 854–879 (1979).

    Article  ADS  Google Scholar 

  30. Michel, F. C. Coherent neutral sheet radiation from pulsars. Comments Astrophys. Space Phys. 3, 80–86 (1971).

    ADS  Google Scholar 

  31. Coroniti, F. V. Magnetically striped relativistic magnetohydrodynamic winds: The Crab nebula revisited Astrophys. J. 349, 538–545 (1990).

    Article  ADS  Google Scholar 

  32. Kirk, J. G., Lyubarsky, Y. & Pétri, J. in Neutron Stars and Pulsars (ed. Becker, W. ) 421–450 (Springer, 2009).

    Book  Google Scholar 

  33. Patterson, J. The DQ Herculis stars. Publ. Astron. Soc. Pacif. 106, 209–238 (1994).

    Article  ADS  Google Scholar 

  34. Meintjes, P. J. On the evolution of the nova-like variable AE Aquarii. Mon. Not. R. Astron. Soc. 336, 265–275 (2002).

    Article  ADS  Google Scholar 

  35. Schenker, K., King, A. R., Kolb, U., Wynn, G. A. & Zhang, Z. AE Aquarii: How cataclysmic variables descend from supersoft binaries. Mon. Not. R. Astron. Soc. 337, 1105–1112 (2002).

    Article  ADS  Google Scholar 

  36. Potter, S. B. et al. Polarized QPOs from the INTEGRAL polar IGRJ14536-5522 (=Swift J1453.4-5524). Mon. Not. R. Astron. Soc. 402, 1161–1170 (2010).

    Article  ADS  Google Scholar 

  37. Hsu, J.-C. & Breger, M. On standard polarized stars. Astrophys. J. 262, 732–738 (1982).

    Article  ADS  Google Scholar 

  38. Eastman, J., Siverd, R. & Gaudi, S. Achieving better than 1 minute accuracy in the heliocentric and barycentric Julian dates. Publ. Astron. Soc. Pacif. 122, 935–946 (2010).

    Article  ADS  Google Scholar 

  39. Paczynski, B. Evolution of single stars. VI. Model nuclei of planetary nebulae. Acta Astron. 21, 417–435 (1971).

    ADS  Google Scholar 

  40. Plavec, M. & Kratochvil, P. Tables for the Roche model of close binaries. Bull. Astr. Czech. 15, 165–170 (1964).

    ADS  Google Scholar 

  41. Joss, P. C., Katz, J. I. & Rappaport, S. A. Synchronous rotation in magnetic X-ray binaries. Astrophys. J. 230, 176–183 (1979).

    Article  ADS  Google Scholar 

  42. Papaloizou, J. & Pringle, J. E. A model for VW Hydri. Astron. Astrophys. 70, L65–67 (1978).

    ADS  Google Scholar 

  43. Campbell, C. G. in Magnetohydrodynamics in Binary Stars 88–89 (Kluwer, 1997).

    Book  Google Scholar 

  44. Ghosh, P & Lamb, F. K. in Neutron Stars: Theory and Observation (eds Ventura, J. E. & Pines, D. ) 363–444 (Kluwer, 1991).

    Book  Google Scholar 

  45. Meintjes, P. J. & de Jager, O. C. Propeller spin-down and non-thermal emission from AE Aquarii. Mon. Not. R. Astron. Soc. 311, 611–620 (2000).

    Article  ADS  Google Scholar 

  46. Goldreich, P. & Julian, W. H. Pulsar electrodynamics. Astrophys. J. 157, 869–880 (1969).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

For D.A.H.B., P.J.M. and S.B.P., this work was supported by the National Research Foundation of South Africa. T.R.M. was supported by the Science and Technology Facilities Council (STFC) under grant ST/L000733. B.T.G. is supported through European Research Council grant 320964. This work is based on observations obtained at the SAAO.

Author information

Authors and Affiliations

Authors

Contributions

D.A.H.B. conceived the HIPPO observing programme, organized and undertook the observations, assisted in the analysis and interpretation of the polarimetry, participated in the modelling and was primary author of the paper. P.J.M. undertook the modelling and led most of the interpretation. S.B.P. undertook the reductions of the HIPPO data, produced most of the figures and assisted in interpretation of the results. T.R.M. and B.T.G. provided information on AR Sco, including pre-publication material, and assisted in the interpretation of the results and models.

Corresponding author

Correspondence to D. A. H. Buckley.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Table 1, Supplementary Figures 1–8. (PDF 1209 kb)

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Buckley, D., Meintjes, P., Potter, S. et al. Polarimetric evidence of a white dwarf pulsar in the binary system AR Scorpii. Nat Astron 1, 0029 (2017). https://doi.org/10.1038/s41550-016-0029

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s41550-016-0029

This article is cited by

Search

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