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.
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The datasets generated and analysed in this study are available from the corresponding author on reasonable request.
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).
Weisskopf, M. C. et al. Measurement of the X-ray polarization of the Crab nebula. Astrophys. J. 208, L125–L128 (1976).
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).
Silver, E. H. et al. Search for X-ray polarization in the Crab pulsar. Astrophys. J. 225, 221–225 (1978).
Dyks, J., Harding, A. K. & Rudak, B. Relativistic effects and polarization in three high-energy pulsar models. Astrophys. J. 606, 1125–1142 (2004).
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).
Harding, A. K. & Kalapotharakos, C. Multiwavelength polarization of rotation-powered pulsars. Astrophys. J. 840, 73 (2017).
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).
Feng, H. et al. PolarLight: a CubeSat X-ray polarimeter based on the gas pixel detector. Exp. Astron. 47, 225–243 (2019).
Costa, E. et al. An efficient photoelectric X-ray polarimeter for the study of black holes and neutron stars. Nature 411, 662–665 (2001).
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).
Cheng, K. S., Ho, C. & Ruderman, M. Energetic radiation from rapidly spinning pulsars. II. Vela and Crab. Astrophys. J. 300, 522–539 (1986).
Muslimov, A. G. & A. K., Harding High-altitude particle acceleration and radiation in pulsar slot gaps. Astrophys. J. 606, 1143–1153 (2004).
Kalapotharakos, C., Kazanas, D., Harding, A. & Contopoulos, I. Toward a realistic pulsar magnetosphere. Astrophys. J. 749, 2 (2012).
Baym, G., Pethick, C. & Pines, D. Superfluidity in neutron stars. Nature 224, 673–674 (1969).
Anderson, P. W. & Itoh, N. Pulsar glitches and restlessness as a hard superfluidity phenomenon. Nature 256, 25–27 (1975).
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).
Kallman, T. Astrophysical motivation for X-ray polarimetry. Adv. Space Res. 34, 2673–2677 (2004).
Soffitta, P. et al. XIPE: the X-ray imaging polarimetry explorer. Exp. Astron. 36, 523–567 (2013).
Bellazzini, R. et al. Photoelectric X-ray polarimetry with gas pixel detectors. Nucl. Instrum. Methods Phys. Res. A 720, 173–177 (2013).
Kislat, F., Clark, B., Beilicke, M. & Krawczynski, H. Analyzing the data from X-ray polarimeters with Stokes parameters. Astropart. Phys. 68, 45–51 (2015).
Shaw, B. et al. A glitch in the Crab pulsar (PSR B0531+21). Astronomer’s Telegram 12957, 1 (2019).
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).
Ruderman, M., Zhu, T. & Chen, K. Neutron star magnetic field evolution, crust movement, and glitches. Astrophys. J. 492, 267–280 (1998).
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).
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).
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).
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).
Zhang, S. et al. The enhanced X-ray timing and polarimetry mission—eXTP. Sci. China Phys. Mech. Astron. 62, 29502 (2019).
Jeffreys, H. The Theory of Probability 3rd edn (Oxford Classic Texts in the Physical Sciences, Oxford Univ. Press, 1961).
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).
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).
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).
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).
Mikhalev, V. Pitfalls of statistics-limited X-ray polarization analysis. Astron. Astrophys. 615, A54 (2018).
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).
Chauvin, M. et al. The PoGO+ view on Crab off-pulse hard X-ray polarization. Mon. Not. R. Astron. Soc. 477, L45–L49 (2018).
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).
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).
The authors declare no competing interests.
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.
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.
Polarization quality factor of PolarLight when observing the Crab.
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.
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.
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.
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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
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