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Vacuum birefringence and the polarized X-ray emission from a radio magnetar

Nature作者：Rachael E. Stewart2026年8月5日正文已收录本站

Data availability

NICER observations (ObsIDs: 8020300101, 8020300102, 8020300103 and 8020300104) and IXPE observations (04003801) are readily accessible in the HEASARC data archive: https://heasarc.gsfc.nasa.gov/W3Browse (https://doi.org/10.25504/FAIRsharing.979d22). Radio observations made by Murriyang/Parkes (ObsIDs: r070819_124237, uwl_250326_173709, uwl_250330_171906 and uwl_250331_131207; doi10.4225/08/52292AE9B2D80, doi10.25919/rzdr-pw25 and doi10.25919/v5hn-4v34) are publicly available from the CSIRO Data Access Portal (https://data.csiro.au/) following an 18-month proprietary period starting on the observation date.

Code availability

Data reduction and analysis of X-ray products were performed using publicly available software HEAsoft v.6.35.0 (https://heasarc.gsfc.nasa.gov/docs/software/lheasoft/) from the High Energy Astrophysics Science Archive Research Center (HEASARC), particularly FTOOLs v.6.35.1, SAOImage DS9 v.8.4b1 and Xspec v.12.15.0. Generation and calibration of the NICER event lists was also performed by NICERDAS v.12 of HEASoft. The simulation and analysis framework ixpeobssim v.31.1.0 was used to generate high-level IXPE data products (https://ixpeobssim.readthedocs.io/en/latest/). Moreover, the software filterbackground.py was used for the treatment of the IXPE background, found at GitHub (https://github.com/aledimarco/IXPE-background). Timing analysis was performed using tempo2 (https://github.com/mattpitkin/tempo2), PINT (https://github.com/nanograv/PINT) and CRIMP (https://github.com/georgeyounes/CRIMP/tree/main). PyXspecCorner (https://github.com/garciafederico/pyXspecCorner) and corner.py (https://corner.readthedocs.io/en/latest/) were used to generate the X-ray spectro-polarimetric and radio RVM corner plots, respectively. Additional custom code for generating figures and performing analysis is available at GitHub (https://github.com/rae-stewart/Polarimetric-Analysis-of-1E-1547.0-5408). Custom code for the MAGTHOMSCATT Monte Carlo simulation is available upon reasonable request.

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Acknowledgements

This work reports observations obtained with the IXPE, a joint US (NASA) and Italian (ASI) mission, led by Marshall Space Flight Center (MSFC). The research uses data products provided by the IXPE Science Operations Center (MSFC), using algorithms developed by the IXPE Collaboration (MSFC, Istituto Nazionale di Astrofisica (INAF), Istituto Nazionale di Fisica Nucleare (INFN) and ASI Space Science Data Center (SSDC)) and distributed by the High-Energy Astrophysics Science Archive Research Center (HEASARC). Murriyang, the Parkes radio telescope of CSIRO, is part of the Australia Telescope National Facility (https://ror.org/05qajvd42), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Wiradjuri people as the Traditional Owners of the Observatory site. This project was supported by resources and expertise provided by CSIRO IMT Scientific Computing and made use of the Ngarrgu Tindebeek supercomputer at the OzSTAR National Facility at Swinburne University of Technology. The OzSTAR programme receives funding in part from the Astronomy National Collaborative Research Infrastructure Strategy (NCRIS) allocation provided by the Australian Government, and from the Victorian Higher Education State Investment Fund (VHESIF) provided by the Victorian Government. G.Y. acknowledges constructive discussion with A. Philippov on radio emission from magnetars and P. Ray on radio/X-ray timing analysis.

Funding

The material is based on work supported by NASA under award no. 80GSFC24M0006. G.Y. acknowledges NASA support under grant nos. 80NSSC25K7257 and 80NSSC25K0283, through which R.E.S. and A.V.K. are partially supported. M.E.L. is supported by an Australian Research Council Discovery Early Career Research Award DE250100508. M.G.B. thanks NASA for generous support under grant nos. 80NSSC24K0589, 80NSSC25K7257 and 80NSSC25K0079. W.C.G.H. acknowledges support through grant no. 80NSSC23K0078 from NASA. J.B.C. acknowledges support under NASA award no. 80GSFC21M0006. F.C., A.K.H., T.E., C.P.H., P.K., M.N., P.S. and Z.W. do not declare relevant funding.

Author information

Author notes

  1. These authors contributed equally: Rachael E. Stewart, Hoa Dinh Thi

Authors and Affiliations

  1. Department of Physics, George Washington University, Washington, DC, USA

    Rachael E. Stewart & Alex Van Kooten

  2. Department of Physics and Astronomy, Rice University, Houston, TX, USA

    Hoa Dinh Thi & Matthew G. Baring

  3. Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    George Younes & Zorawar Wadiasingh

  4. Center for Space Sciences and Technology, University of Maryland Baltimore County, Baltimore County, MD, USA

    George Younes

  5. Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria, Australia

    Marcus E. Lower

  6. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA

    Michela Negro

  7. South African Radio Astronomy Observatory, Cape Town, South Africa

    Fernando Camilo

  8. Department of Physics and Astronomy, Howard University, Washington, DC, USA

    Joel B. Coley

  9. CRESST/Mail Code 661, Astroparticle Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA

    Joel B. Coley

  10. Department of Physics, Kyoto University, Kyoto, Japan

    Teruaki Enoto

  11. Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM, USA

    Alice K. Harding

  12. Department of Physics and Astronomy, Haverford College, Haverford, PA, USA

    Wynn C. G. Ho

  13. Department of Physics, National Changhua University of Education, Changhua, Taiwan

    Chin-Ping Hu

  14. NASA Marshall Space Flight Center, Huntsville, AL, USA

    Philip Kaaret

  15. Department of Physics and Astronomy, York University, Toronto, Ontario, Canada

    Paul Scholz

  16. Department of Astronomy, University of Maryland, College Park, MD, USA

    Zorawar Wadiasingh

Authors

  1. Rachael E. Stewart
  2. Hoa Dinh Thi
  3. George Younes
  4. Marcus E. Lower
  5. Matthew G. Baring
  6. Michela Negro
  7. Fernando Camilo
  8. Joel B. Coley
  9. Teruaki Enoto
  10. Alice K. Harding
  11. Wynn C. G. Ho
  12. Chin-Ping Hu
  13. Philip Kaaret
  14. Paul Scholz
  15. Alex Van Kooten
  16. Zorawar Wadiasingh

Contributions

R.E.S. performed the X-ray polarization and spectral data analysis and contributed to writing the paper. H.D.T. and M.G.B. led the simulation analysis and theoretical interpretations and contributed to writing the paper. G.Y. is the principal investigator of the IXPE observation presented in this work, which was obtained through the NASA IXPE Guest Observer cycle 2 program. G.Y. performed the X-ray timing analysis and contributed to writing the paper. M.E.L. performed the radio observations and analysis, and contributed to writing the paper. M.N. provided support with the X-ray polarization analysis and contributed to writing the paper. F.C., J.B.C., T.E., A.K.H., W.C.G.H., C.-P.H, P.K., P.S., A.V.K. and Z.W. provided comments and contributed to the writing of the paper. F.C. is the principal investigator of the Parkes P885 project.

Corresponding authors

Correspondence to Rachael E. Stewart, Hoa Dinh Thi, George Younes, Marcus E. Lower or Matthew G. Baring.

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Competing interests

The authors declare no competing interests.

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Extended data figures and tables

Extended Data Fig. 1 Model-dependent and model-independent polarization characteristics comparison.

A comparative study between model-independent Stokes Q and U polarization characteristics obtained through using IXPEOBSSIM (Panel a) and through applying a polconst*bbodyrad spectral model in Xspec (Panel b) at four energy bins: 2–3 keV, 3–4 keV, 4–5 keV, and 2–8 keV. The resulting PD and PA for the two methods are comparable to each other. Notably, both show a non-linear trend in the energy-dependence of the PD as the 4–5 keV band approaches the value of the 2–3 keV band at  ~ 1σ level. Future observations with higher count statistics are needed to complement this study to more directly probe the nature of the high-energy polarization.

Extended Data Fig. 2 Phase-averaged IXPE spectra.

The simultaneous spectral νFν models of the NICER+IXPE observations. Panel a displays the best fit model, a single absorbed blackbody with a linear polarization component: constant*tbabs(pollin*bbodyrad). NB: Only the IXPE spectra are displayed here for the sake of visual clarity. Panel b shows the data divided by the folded model for the absorbed BB model. The right-hand panels show the normalized Stokes Q/I (Panel c) and U/I (Panel d) spectra in linear space for the three IXPE DUs with the solid lines showing the best fit of the linear polarization component. The quasi-thermal BB is accompanied by a strong polarization signal that decreases as a function of energy.

Extended Data Fig. 3 Phase-averaged NICER spectra.

Simultaneous spectral modeling of the NICER+IXPE observations in the νFν representation (see also Extended Data Fig. 2). The top panel shows the best-fit model to the NICER spectra, described by a single absorbed blackbody. For visual clarity, we do not display the SCORPEON background model components. The bottom panel shows the ratio of the NICER data to the folded model.

Extended Data Fig. 4 X-ray spectro-polarimetric posterior distributions.

Corner plots of the one- and two-dimensional posterior distributions of the X-ray spectro-polarimetric parameters from the best-fit model shown in Table 1 produced by an MCMC chain (Panels a-u). The contours denote the 11.8%, 39.3%, 67.5%, 86.4% credible regions (corresponding to 0.5, 1, 1.5, and 2σ).

Extended Data Fig. 5 Radio RVM posterior distributions.

Corner plots of the one- and two-dimensional posterior distributions of the radio RVM fit parameters (Panels a-n). The contours denote the 39%, 87%, and 99% credible regions (corresponding to 1, 2, and 3σ).

Extended Data Fig. 6 Phase-resolved polarization characteristics in three X-ray bands.

Complementary plot to Fig. 2, with IXPE intensity, PD, and PA (shown in the lower three panels, respectively) binned according to 2–3 keV (a–e), 3–4 keV (f–j), and 4–8 keV (k–o).

Extended Data Fig. 7 RVM fit to the phase-resolved X-ray PA.

Panels a-n: Black contours represent the one- and two-dimensional posterior distributions for the RVM parameters α, ζ, β, ψ0, and ϕ0, obtained from a Bayesian fit to the 2-4 keV phase-resolved polarization angle profile using the55 wrapped-angle likelihood. Contours denote the 39%, 87%, and 99% credible regions (corresponding to 1, 2, and 3σ). The blue contours are those derived from the radio RVM fit overlaid for ease of comparison. Panel o: Phase-resolved X-ray PA measurements (black points) overlaid with the maximum-posterior RVM model (solid black line). Light gray curves show random posterior draws, illustrating the range of model realizations consistent with the data.

Extended Data Fig. 8 Stokes Q/I, U/I, and I modeling.

Simulated Stokes Q/I (panel a), U/I (panel b), and intensity (panel c) pulse profiles from MAGTHOMSCATT for a single hotspot wedge offset from the magnetic pole as a function of rotational phase (solid lines). The black dots represent the Stokes Q/I (panel a), U/I (panel b), and intensity (panel c) data extracted from IXPE in the 2–3 keV energy range. The case with the best statistical fit (lowest combined total χ2; see Methods) incorporates vacuum birefringence, and corresponds to a magnetic colatitude of θm = [0°, 17°] and longitude ϕm = [0°, 120°] (zero longitude contains the rotation and magnetic axes); it is displayed in blue. The orange solid curves on the center and right panel show the corresponding polarization profiles wherein VB is turned off - these fits are statistically worse than those with VB on (see Methods). Panel (d) displays the comparison in the Stokes Q-U space between the observed data (black dots) and the simulated results obtained with the best-fit wedge-shaped hotspot with (blue line) and without (orange line) including magnetospheric VB, plotted for one rotational cycle. The red solid line represents the best result among the VB-off cases (see Methods), corresponding to a pole-centered circular hotspot with a magnetic inclination of α = 2° and a viewing angle of ζ = 20. 5°.

Extended Data Table 1 Timing and Pulsar Parameters

Full size table

Extended Data Table 2 Observations

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Supplementary information

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Stewart, R.E., Dinh Thi, H., Younes, G. et al. Vacuum birefringence and the polarized X-ray emission from a radio magnetar. Nature (2026). https://doi.org/10.1038/s41586-026-10859-z

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