Abstract
The Crab pulsar and its nebula are among the most studied astrophysical systems, and constitute one of the most promising environments where high-energy processes and particle acceleration can be investigated. They are the only objects for which significant X-ray polarization was detected in the past. Here we present the Imaging X-ray Polarimetry Explorer (IXPE) observation of the Crab pulsar and nebula. The total pulsar pulsed emission in the [2–8] keV energy range is unpolarized. Significant polarization up to 15% is detected in the core of the main peak. The nebula has a total space integrated polarized degree of 20% and polarization angle of 145°. The polarized maps show a large variation in the local polarization, and regions with a polarized degree up to 45–50%. The polarization pattern suggests a predominantly toroidal magnetic field. Our findings for the pulsar are inconsistent with most inner magnetospheric models, and suggest emission is more likely to come from the wind region. For the nebula, the polarization map suggests a patchy distribution of turbulence, uncorrelated with the intensity, in contrast with simple expectations from numerical models.
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Data availability
Data from the Crab PSR and nebula observation are available in the HEASARC IXPE Data Archive (https://heasarc.gsfc.nasa.gov/docs/ixpe/archive/). Additional data are available in the Supplementary Information and from figshare at https://doi.org/10.6084/m9.figshare.22203163. Source data are provided with this paper.
Code availability
The ixpeobssim software and documentation can be downloaded at https://github.com/lucabaldini/ixpeobssim. Other information supporting the findings of this study, and specific data-reduction pipelines, are available from the corresponding author upon request.
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Acknowledgements
The IXPE is a joint US and Italian mission. The US contribution is supported by NASA and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract no. NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) through contract no. ASI-OHBI-2017-12-I.0, agreement nos. ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) with agreement nos. ASI-INAF-2022-14-HH.0 and ASI-INFN 2021-43-HH.0, and by the Istituto Nazionale di Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. This research used data products provided by the IXPE Team (MSFC, SSDC, INAF and INFN) and distributed with additional software tools by the High-Energy Astrophysics Science Archive Research Center (HEASARC), at NASA Goddard Space Flight Center (GSFC). The research at Boston University was supported in part by National Science Foundation grant no. AST-2108622. Part of the French contributions is supported by the Scientific Research National Center (CNRS) and the French spatial agency (CNES). I.A. acknowledges financial support from the Spanish ‘Ministerio de Ciencia e Innovación’ (grant no. MCIN/AEI/ 10.13039/501100011033) through the Center of Excellence Severo Ochoa award for the Instituto de Astrofísica de Andalucía-CSIC (grant no. CEX2021-001131-S), and through grant nos. PID2019-107847RB-C44 and PID2022-139117NB-C44. C.-Y.N. is supported by a GRF grant from the Hong Kong Government under no. HKU 17305419. N.B. was supported by the INAF MiniGrant ‘PWNnumpol - Numerical Studies of Pulsar Wind Nebulae in The Light of IXPE’. J.H. acknowledges support from the Natural Sciences and Engineering Research Council of Canada through a Discovery Grant, the Canadian Space Agency through the co-investigator grant programme, and computational resources and services provided by Compute Canada, Advanced Research Computing at the University of British Columbia, and the SciServer science platform. S.G. and E.W. were supported by grant nos. JSPS KAKENHI JP 19H00696 and 22K14068.
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Contributions
N.B. led the data analysis and the writing of the paper. R.F., M.B., J.R., L.P. and F.M. contributed to data analysis and data calibration. N.D.L., C.S., N.O., T.K., T.M., S.G. and E.W. contributed to data analysis and results interpretation. M.C.W., M.N., S.S., E.D.O.W., F.X., J.H., R.W.R., P.T., A.P. and H.L.M. contributed to text revision and data interpretation. L.B. and M.P.-R. contributed to software development. The remaining members of the IXPE collaboration contributed to the design of the mission, to the calibration of the instrument, to defining its science case and to the planning of the observations. All authors provided inputs and comments on the paper.
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Nature Astronomy thanks Santosh Vadawale and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary information
Supplementary Information
Supplementary Figs. 1–5 and Tables 1 and 2.
Supplementary Data 1
Chandra count map (Fig. 2).
Supplementary Data 2
IXPE count map (Fig. 2).
Supplementary Data 3
IXPE OP count map (Fig. 2).
Supplementary Data 4
IXPE PD (Fig. 4).
Supplementary Data 5
IXPE intensity (Fig. 4).
Supplementary Data 6
IXPE significance (Supplementary Fig. 3).
Supplementary Data 7
IXPE Q/I (Supplementary Fig. 4).
Supplementary Data 8
IXPE U/I (Supplementary Fig. 4).
Supplementary Data 9
Data of Supplementary Fig. 1.
Supplementary Data 10
Data of Supplementary Fig. 5.
Source data
Source Data Fig. 1
Data already reported in Table 1 of the main text.
Source Data Fig. 2
Images as data tables. Fits file images also provided as Supplementary Data and/or figshare.
Source Data Fig. 3
Polarization data already reported in Supplementary Table 2. We provide also the ASCII table for the light-curve and optical data.
Source Data Fig. 4
Images as data tables (polarization directions as list). Fits file images also provided as Supplementary Data and/or figshare.
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Bucciantini, N., Ferrazzoli, R., Bachetti, M. et al. Simultaneous space and phase resolved X-ray polarimetry of the Crab pulsar and nebula. Nat Astron 7, 602–610 (2023). https://doi.org/10.1038/s41550-023-01936-8
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DOI: https://doi.org/10.1038/s41550-023-01936-8
