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.

  • Letter
  • Published:

Re-detection and a possible time variation of soft X-ray polarization from the Crab

An Author Correction to this article was published on 30 June 2020

This article has been updated

Abstract

The Crab nebula is so far the only celestial object with a statistically significant detection in soft X-ray polarimetry1,2,3,4, a window that has not been explored in astronomy since the 1970s. However, soft X-ray polarimetry is expected to be a sensitive probe of magnetic fields in high-energy astrophysical objects, including rotation-powered pulsars5,6,7 and pulsar wind nebulae8. Here we report the re-detection of soft X-ray polarization after 40 years from the Crab nebula and pulsar with PolarLight9, a miniature polarimeter utilizing a novel technique10,11 onboard a CubeSat. The polarization fraction of the Crab in the on-pulse phases was observed to decrease after a glitch of the Crab pulsar on 23 July 2019, while that of the pure nebular emission remained constant within uncertainty. The phenomenon may have lasted about 100 days. If the association between the glitch and polarization change can be confirmed with future observations, it will place strong constraints on the physical mechanism of the high-energy emission12,13,14 and glitch15,16,17 of pulsars.

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

Fig. 1: Polarization measurements of the Crab with PolarLight.
Fig. 2: Time dependent polarization of the Crab.
Fig. 3: Significance test for a polarization variation associated with the glitch.

Similar content being viewed by others

Data availability

The datasets generated and analysed in this study are available from the corresponding author on reasonable request.

Change history

References

  1. Novick, R., Weisskopf, M. C., Berthelsdorf, R., Linke, R. & Wolff, R. S. Detection of X-ray polarization of the Crab nebula. Astrophys. J. 174, L1 (1972).

    Article  ADS  Google Scholar 

  2. Weisskopf, M. C. et al. Measurement of the X-ray polarization of the Crab nebula. Astrophys. J. 208, L125–L128 (1976).

    Article  ADS  Google Scholar 

  3. Weisskopf, M. C., Silver, E. H., Kestenbaum, H. L., Long, K. S. & Novick, R. A precision measurement of the X-ray polarization of the Crab nebula without pulsar contamination. Astrophys. J. 220, L117–L121 (1978).

    Article  ADS  Google Scholar 

  4. Silver, E. H. et al. Search for X-ray polarization in the Crab pulsar. Astrophys. J. 225, 221–225 (1978).

    Article  ADS  Google Scholar 

  5. Dyks, J., Harding, A. K. & Rudak, B. Relativistic effects and polarization in three high-energy pulsar models. Astrophys. J. 606, 1125–1142 (2004).

    Article  ADS  Google Scholar 

  6. Takata, J. & Chang, H. K. et al. Pulse profiles, spectra, and polarization characteristics of nonthermal emissions from the Crab-like pulsars. Astrophys. J. 670, 677–692 (2007).

    Article  ADS  Google Scholar 

  7. Harding, A. K. & Kalapotharakos, C. Multiwavelength polarization of rotation-powered pulsars. Astrophys. J. 840, 73 (2017).

    Article  ADS  Google Scholar 

  8. Bucciantini, N., Bandiera, R., Olmi, B. & Del Zanna, L. Modeling the effect of small-scale magnetic turbulence on the X-ray properties of pulsar wind nebulae. Mon. Not. R. Astron. Soc. 470, 4066–4074 (2017).

    Article  ADS  Google Scholar 

  9. Feng, H. et al. PolarLight: a CubeSat X-ray polarimeter based on the gas pixel detector. Exp. Astron. 47, 225–243 (2019).

    Article  ADS  Google Scholar 

  10. Costa, E. et al. An efficient photoelectric X-ray polarimeter for the study of black holes and neutron stars. Nature 411, 662–665 (2001).

    Article  ADS  Google Scholar 

  11. Bellazzini, R. et al. A photoelectric polarimeter based on a micropattern gas detector for X-ray astronomy. Nucl. Instrum. Methods Phys. Res. A 510, 176–184 (2003).

    Article  ADS  Google Scholar 

  12. Cheng, K. S., Ho, C. & Ruderman, M. Energetic radiation from rapidly spinning pulsars. II. Vela and Crab. Astrophys. J. 300, 522–539 (1986).

    Article  ADS  Google Scholar 

  13. Muslimov, A. G. & A. K., Harding High-altitude particle acceleration and radiation in pulsar slot gaps. Astrophys. J. 606, 1143–1153 (2004).

    Article  ADS  Google Scholar 

  14. Kalapotharakos, C., Kazanas, D., Harding, A. & Contopoulos, I. Toward a realistic pulsar magnetosphere. Astrophys. J. 749, 2 (2012).

    Article  ADS  Google Scholar 

  15. Baym, G., Pethick, C. & Pines, D. Superfluidity in neutron stars. Nature 224, 673–674 (1969).

    Article  ADS  Google Scholar 

  16. Anderson, P. W. & Itoh, N. Pulsar glitches and restlessness as a hard superfluidity phenomenon. Nature 256, 25–27 (1975).

    Article  ADS  Google Scholar 

  17. Alpar, M. A., Chau, H. F., Cheng, K. S. & Pines, D. Postglitch relaxation of the Vela pulsar after its first eight large glitches: a reevaluation with the vortex creep model. Astrophys. J. 409, 345–359 (1993).

    Article  ADS  Google Scholar 

  18. Kallman, T. Astrophysical motivation for X-ray polarimetry. Adv. Space Res. 34, 2673–2677 (2004).

    Article  ADS  Google Scholar 

  19. Soffitta, P. et al. XIPE: the X-ray imaging polarimetry explorer. Exp. Astron. 36, 523–567 (2013).

    Article  ADS  Google Scholar 

  20. Bellazzini, R. et al. Photoelectric X-ray polarimetry with gas pixel detectors. Nucl. Instrum. Methods Phys. Res. A 720, 173–177 (2013).

    Article  ADS  Google Scholar 

  21. Kislat, F., Clark, B., Beilicke, M. & Krawczynski, H. Analyzing the data from X-ray polarimeters with Stokes parameters. Astropart. Phys. 68, 45–51 (2015).

    Article  ADS  Google Scholar 

  22. Shaw, B. et al. A glitch in the Crab pulsar (PSR B0531+21). Astronomer’s Telegram 12957, 1 (2019).

    ADS  Google Scholar 

  23. Thomas, R. M. & Fenton, K. B. The pulsed fraction of X-rays from the Crab nebula. In International Cosmic Ray Conference Vol. 1 (ed. Pinkau, K.) 188–193 (Max Planck Institute for Extraterrestrial Physics, 1975).

  24. Ruderman, M., Zhu, T. & Chen, K. Neutron star magnetic field evolution, crust movement, and glitches. Astrophys. J. 492, 267–280 (1998).

    Article  ADS  Google Scholar 

  25. Palfreyman, J., Dickey, J. M., Hotan, A., Ellingsen, S. & van Straten, W. Alteration of the magnetosphere of the Vela pulsar during a glitch. Nature 556, 219–222 (2018).

    Article  ADS  Google Scholar 

  26. Wong, T., Backer, D. C. & Lyne, A. G. Observations of a series of six recent glitches in the Crab pulsar. Astrophys. J. 548, 447–459 (2001).

    Article  ADS  Google Scholar 

  27. Alpar, M. A., Chau, H. F., Cheng, K. S. & Pines, D. Postglitch relaxation of the Crab pulsar after its first four major glitches: the combined effects of crust cracking, formation of vortex depletion region and vortex creep. Astrophys. J. 459, 706–716 (1996).

    Article  ADS  Google Scholar 

  28. Weisskopf, M. C. et al. The Imaging X-ray Polarimetry Explorer (IXPE). In Society of Photo-Optical Instrumentation Engineers Conference Series Vol. 9905 (eds den Herder, J.-W. A. et al.) 990517 (SPIE, 2016).

  29. Zhang, S. et al. The enhanced X-ray timing and polarimetry mission—eXTP. Sci. China Phys. Mech. Astron. 62, 29502 (2019).

    Article  ADS  Google Scholar 

  30. Jeffreys, H. The Theory of Probability 3rd edn (Oxford Classic Texts in the Physical Sciences, Oxford Univ. Press, 1961).

  31. Kirsch, M. G. et al. Crab: the standard X-ray candle with all (modern) X-ray satellites. In Society of Photo-Optical Instrumentation Engineers Conference Series Vol. 5898 (Siegmund, O. H. W.) 589803 (SPIE, 2005).

  32. Muleri, F. et al. Spectral and polarimetric characterization of the gas pixel detector filled with dimethyl ether. Nucl. Instrum. Methods Phys. Res. Sect. A 620, 285–293 (2010).

    Article  ADS  Google Scholar 

  33. Folkner, W. M., Williams, J. G., Boggs, J. G., Park, R. S. & Kuchynka, P. The planetary and lunar ephemerides DE430 and DE431. Interplanet. Netw. Prog. Rep. 42, 196 (2014).

    Google Scholar 

  34. Lyne, A. G., Pritchard, R. S. & Graham Smith, F. 23 years of Crab pulsar rotational history. Mon. Not. R. Astron. Soc. 265, 1003–1012 (1993).

    Article  ADS  Google Scholar 

  35. Mikhalev, V. Pitfalls of statistics-limited X-ray polarization analysis. Astron. Astrophys. 615, A54 (2018).

    Article  ADS  Google Scholar 

  36. Maier, D., Tenzer, C. & Santangelo, A. Point and interval estimation on the degree and the angle of polarization: a Bayesian approach. Publ. Astron. Soc. Pac. 126, 459–468 (2014).

    Article  ADS  Google Scholar 

  37. Chauvin, M. et al. The PoGO+ view on Crab off-pulse hard X-ray polarization. Mon. Not. R. Astron. Soc. 477, L45–L49 (2018).

    Article  ADS  Google Scholar 

  38. Li, H. et al. Assembly and test of the gas pixel detector for X-ray polarimetry. Nucl. Instrum. Methods Phys. Res. A 804, 155–162 (2015).

    Article  ADS  Google Scholar 

Download references

Acknowledgements

We thank H.-K. Chang, J. Takata, M. Ge and J. Heyl for helpful discussions. H.F. acknowledges funding support from the National Natural Science Foundation of China under the grant numbers 11633003 and 11821303, and the National Key R&D Project (grants numbers 2018YFA0404502 and 2016YFA040080X).

Author information

Authors and Affiliations

Authors

Contributions

H.F. is the principal investigator of PolarLight and led the project. H.L. and X.L. conducted the daily operation of the CubeSat and had a major contribution to the data analysis. R.B. led the development of the GPD. E.C., P.S. and F.M. participated in the discussion, and E.C. made a special contribution to the initiation of the project. J.H. performed the simulation and modelling of the in-orbit background. Q.W., W.J., M.M., D.Y., L.B., S.C., H.N., A.J., J.Y., G.J., M.Z., P.A., A.B., L.L., C.S., G.S. and M.P. contributed to the development of the payload instrument. W.W. and R.X. participated in the interpretation of the results.

Corresponding author

Correspondence to Hua Feng.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature Astronomy thanks Mozsi Kiss, Andrea Santangelo and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Energy spectra measured with PolarLight.

The solid curves are for the Crab and the dotted are for the background. The background spectra are obtained by observing source-free regions. The red spectra are constructed using all x-ray events passing from particle discrimination and the blue ones consist of events used for polarimetry (with one more criterion on the number of fired pixels). Errors of 1σ are shown on the two Crab spectra. We note that the background events shown in the plot are mainly due to charged particles but can not be distinguished by particle discrimination. A discussion on the time variation and modulation of the background can be found in Methods.

Extended Data Fig. 2 Quality factor as a function of energy.

Polarization quality factor of PolarLight when observing the Crab.

Extended Data Fig. 3 Pulse profile of the Crab pulsar.

Folded pulse profile of the Crab pulsar measured with PolarLight in the energy band of 3.0-4.5 keV. The on-pulse phase interval is indicated by the horizontal bar.

Extended Data Fig. 4 Posterior distributions.

Top: posterior distributions of PF and PA with data before the glitch (red) or data within 100 days after the glitch (blue). Bottom: posterior distribution of PF (marginalized over PA). Each measurement is not consistent with the other at a 3σ level, and this conclusion is valid if one chooses any date from 30 days to 100 days after the glitch.

Extended Data Fig. 5 Lightcurves for the Crab and background.

3.0–4.5 keV lightcurves measured with PolarLight when observing the Crab and background regions. The bars show typical errors. Each point is the count rate averaged in a continuous exposure, which varies and has a typical duration of 15 minutes. The gap in the Crab data from MJD 58620 to 58670 (early May to early July, 2019) is due to a small angular separation to the Sun, which precludes observations in this period.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Feng, H., Li, H., Long, X. et al. Re-detection and a possible time variation of soft X-ray polarization from the Crab. Nat Astron 4, 511–516 (2020). https://doi.org/10.1038/s41550-020-1088-1

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41550-020-1088-1

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