CaltechAUTHORS
Published December 2022 | Version public
Journal Article Metadata-only

Determination of X-ray pulsar geometry with IXPE polarimetry

Creators

  • 1. ROR icon University of Tübingen
  • 2. ROR icon University of Turku
  • 3. ROR icon Space Research Institute
  • 4. ROR icon California Institute of Technology
  • 5. ROR icon Institute for Space Astrophysics and Planetology
  • 6. ROR icon University of British Columbia
  • 7. ROR icon University of Oxford
  • 8. ROR icon Leiden University
  • 9. ROR icon Pennsylvania State University
  • 10. ROR icon Marshall Space Flight Center
  • 11. ROR icon University College London
  • 12. ROR icon Instituto de Astrofísica de Andalucía
  • 13. ROR icon Astronomical Observatory of Rome
  • 14. ROR icon Agenzia Spaziale Italiana
  • 15. ROR icon INFN Sezione di Pisa
  • 16. ROR icon University of Pisa
  • 17. ROR icon Roma Tre University
  • 18. ROR icon INFN Sezione di Torino
  • 19. ROR icon University of Turin
  • 20. ROR icon Arcetri Astrophysical Observatory
  • 21. ROR icon University of Florence
  • 22. ROR icon National Institute for Nuclear Physics
  • 23. ROR icon INFN Sezione di Roma II
  • 24. ROR icon Stanford University
  • 25. ROR icon Astronomical Institute
  • 26. ROR icon RIKEN
  • 27. ROR icon Yamagata University
  • 28. ROR icon Osaka University
  • 29. ROR icon Chuo University
  • 30. ROR icon Boston University
  • 31. ROR icon St Petersburg University
  • 32. ROR icon Washington University in St. Louis
  • 33. ROR icon Observatory of Strasbourg
  • 34. ROR icon Massachusetts Institute of Technology
  • 35. ROR icon Nagoya University
  • 36. ROR icon Hiroshima University
  • 37. ROR icon University of Hong Kong
  • 38. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 39. ROR icon Max Planck Institute for Astrophysics
  • 40. ROR icon Brera Astronomical Observatory
  • 41. ROR icon University of Padua
  • 42. ROR icon University of Rome Tor Vergata
  • 43. ROR icon University of Maryland, College Park
  • 44. ROR icon University of Amsterdam
  • 45. ROR icon Guangxi University

Abstract

Using observations of X-ray pulsar Hercules X-1 by the Imaging X-ray Polarimetry Explorer we report a highly significant (>17σ) detection of the polarization signal from an accreting neutron star. The observed degree of linear polarization of ~10% is far below theoretical expectations for this object, and stays low throughout the spin cycle of the pulsar. Both the degree and angle of polarization exhibit variability with the pulse phase, allowing us to measure the pulsar spin position angle 57(2) deg and the magnetic obliquity 12(4) deg, which is an essential step towards detailed modelling of the intrinsic emission of X-ray pulsars. Combining our results with the optical polarimetric data, we find that the spin axis of the neutron star and the angular momentum of the binary orbit are misaligned by at least ~20 deg, which is a strong argument in support of the models explaining the stability of the observed superorbital variability with the precession of the neutron star.

Additional Information

This Article is based on observations made by IXPE, a joint US and Italian mission. 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 the NASA Goddard Space Flight Center (GSFC). The US contribution is supported by NASA and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract number NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) through contract number ASI-OHBI-2017-12-I.0, agreement numbers ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) and by the Istituto Nazionale di Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. V.D. and V.F.S. acknowledge support from the German Academic Exchange Service (DAAD) under travel grant number 57525212. J.P. and S.S.T. thank the Russian Science Foundation for support under grant number 20-12-00364 and the Academy of Finland for support under grant numbers 333112, 349144, 349373 and 349906. V.F.S. thanks the German Research Foundation (DFG) for grant number WE 1312/53-1. I.C. is a Sherman Fairchild Fellow at Caltech and thanks the Burke Institute at Caltech for supporting her research. A.A.M. acknowledges support from the Netherlands Organization for Scientific Research Veni Fellowship.

Additional details

Identifiers

Eprint ID
117757
Resolver ID
CaltechAUTHORS:20221107-999291600.31

Funding

Istituto Nazionale di Astrofisica (INAF)
Deutscher Akademischer Austauschdienst (DAAD)
57525212
Russian Science Foundation
20-12-00364
Istituto Nazionale di Fisica Nucleare (INFN)
Academy of Finland
349144
Academy of Finland
349373
Academy of Finland
333112
Agenzia Spaziale Italiana (ASI)
ASI-OHBI-2017-12-I.0
Agenzia Spaziale Italiana (ASI)
ASI-INAF-2017-12-H0
Academy of Finland
349906
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)
Deutsche Forschungsgemeinschaft (DFG)
WE 1312/53-1
Sherman Fairchild Foundation
Walter Burke Institute for Theoretical Physics, Caltech

Dates

Created
2022-11-18
Created from EPrint's datestamp field
Updated
2023-03-16
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Space Radiation Laboratory, TAPIR, Walter Burke Institute for Theoretical Physics