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Published October 10, 2022 | Version Published
Journal Article Open

The X-Ray Polarization View of Mrk 421 in an Average Flux State as Observed by the Imaging X-Ray Polarimetry Explorer

Creators

  • 1. ROR icon Agenzia Spaziale Italiana
  • 2. ROR icon Brera Astronomical Observatory
  • 3. ROR icon Instituto de Astrofísica de Andalucía
  • 4. ROR icon Observatory of Strasbourg
  • 5. ROR icon University of Turin
  • 6. ROR icon INFN Sezione di Torino
  • 7. ROR icon Stanford University
  • 8. ROR icon National Institute for Astrophysics
  • 9. ROR icon Washington University in St. Louis
  • 10. ROR icon Boston University
  • 11. ROR icon St Petersburg University
  • 12. ROR icon Sapienza University of Rome
  • 13. ROR icon University of Rome Tor Vergata
  • 14. ROR icon University of Turku
  • 15. ROR icon Massachusetts Institute of Technology
  • 16. ROR icon Astronomical Observatory of Rome
  • 17. Institut de Radioastronomie Millimétrique, Avenida Divina Pastora, 7, Local 20, E-18012 Granada, Spain
  • 18. ROR icon University of Maryland, Baltimore County
  • 19. ROR icon Goddard Space Flight Center
  • 20. ROR icon Osservatorio Astronomico di Cagliari
  • 21. ROR icon INFN Sezione di Pisa
  • 22. ROR icon University of Pisa
  • 23. ROR icon Marshall Space Flight Center
  • 24. ROR icon Roma Tre University
  • 25. ROR icon Arcetri Astrophysical Observatory
  • 26. ROR icon University of Florence
  • 27. ROR icon INFN Sezione di Firenze
  • 28. ROR icon INFN Sezione di Roma II
  • 29. ROR icon University of Tübingen
  • 30. ROR icon Space Research Institute
  • 31. ROR icon Astronomical Institute
  • 32. ROR icon RIKEN
  • 33. ROR icon California Institute of Technology
  • 34. ROR icon Yamagata University
  • 35. ROR icon Osaka University
  • 36. ROR icon University of British Columbia
  • 37. ROR icon Chuo University
  • 38. ROR icon Nagoya University
  • 39. ROR icon Hiroshima University
  • 40. ROR icon University of Hong Kong
  • 41. ROR icon Pennsylvania State University
  • 42. ROR icon Institut de Planétologie et d'Astrophysique de Grenoble
  • 43. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 44. ROR icon University of Padua
  • 45. ROR icon University of Maryland, College Park
  • 46. ROR icon University College London
  • 47. ROR icon University of Amsterdam
  • 48. ROR icon Guangxi University

Abstract

Particle acceleration mechanisms in supermassive black hole jets, such as shock acceleration, magnetic reconnection, and turbulence, are expected to have observable signatures in the multiwavelength polarization properties of blazars. The recent launch of the Imaging X-Ray Polarimetry Explorer (IXPE) enables us, for the first time, to use polarization in the X-ray band (2–8 keV) to probe the properties of the jet synchrotron emission in high-synchrotron-peaked BL Lac objects (HSPs). We report the discovery of X-ray linear polarization (degree Πx = 15% ± 2% and electric vector position angle ψ x = 35° ± 4°) from the jet of the HSP Mrk 421 in an average X-ray flux state. At the same time, the degree of polarization at optical, infrared, and millimeter wavelengths was found to be lower by at least a factor of 3. During the IXPE pointing, the X-ray flux of the source increased by a factor of 2.2, while the polarization behavior was consistent with no variability. The higher level of Πx compared to longer wavelengths, and the absence of significant polarization variability, suggest a shock is the most likely X-ray emission site in the jet of Mrk 421 during the observation. The multiwavelength polarization properties are consistent with an energy-stratified electron population, where the particles emitting at longer wavelengths are located farther from the acceleration site, where they experience a more disordered magnetic field.

Copyright and License

© 2022. The Author(s). Published by the American Astronomical Society.

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

IXPE is a joint US and Italian mission. The US contribution is supported by the National Aeronautics and Space Administration (NASA) and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana, ASI), through contract ASI-OHBI-2017-12-I.0, agreements ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) with agreements ASI-INAF-2022-14-HH.0 and ASI-INFN 2021-43-HH.0, and by Istituto Nazionale di Astrofisica (INAF) and 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's Goddard Space Flight Center (GSFC). The Instituto de Astrofisica de Andalucia (IAA)-CSIC group acknowledges financial support from the Spanish "Ministerio de Ciencia e Innovación" (MCINN) through the "Center of Excellence Severo Ochoa" award for IAA-CSIC (SEV-2017-0709) and through grants AYA2016-80889-P and PID2019-107847RB-C44. The Polarimetric Monitoring of AGN at Millimeter Wavelengths (POLAMI) observations were carried out at the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). Some of the data reported here are based on observations made with the NOT, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku, and the University of Oslo, representing Denmark, Finland, and Norway; the University of Iceland; and Stockholm University at Observatorio del Roque de los Muchachos, La Palma, Spain, of Instituto de Astrofisica de Canarias. E.L. was supported by Academy of Finland projects 317636 and 320045. The data presented here were obtained (in part) with the Alhambra Faint Object Spectrograph and Camera (ALFOSC), which is provided by IAA under a joint agreement with the University of Copenhagen and NOT. Part of the French contribution is supported by the Scientific Research National Center (CNRS) and the French space agency (CNES). The research at Boston University was supported in part by National Science Foundation (NSF) grant AST-2108622, NASA Fermi Guest Investigator grant 80NSSC21K1917, and NASA Swift Guest Investigator grant 80NSSC22K0537. This research was conducted in part using the Mimir instrument, jointly developed at Boston University and Lowell Observatory and supported by NASA, NSF, and the W. M. Keck Foundation. We thank D. Clemens for guidance in the analysis of the Mimir data.

Facilities

Facilities: IXPE - , NOT - , NuSTAR, Swift - , XMM - , Perkins, IRAM:30m. -

Software References

Software: Xspec version 12.12.1.

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Additional details

Funding

National Aeronautics and Space Administration
NNM15AA18C
Agenzia Spaziale Italiana
ASI-OHBI-2017-12-I.0
Agenzia Spaziale Italiana
ASI-INAF-2017-12-H0
Agenzia Spaziale Italiana
ASI-INFN-2017.13-H0
Agenzia Spaziale Italiana
ASI-INAF-2022-14-HH.0
Agenzia Spaziale Italiana
ASI-INFN 2021-43-HH.0
Istituto Nazionale di Fisica Nucleare
Fundación Severo Ochoa
SEV-2017-0709
Ministerio de Ciencia, Innovación y Universidades
AYA2016-80889-P
Ministerio de Ciencia, Innovación y Universidades
PID2019-107847RB-C44
Research Council of Finland
317636
Research Council of Finland
320045
Centre National de la Recherche Scientifique
Centre National d'Études Spatiales
National Science Foundation
AST-2108622
National Aeronautics and Space Administration
80NSSC21K1917
National Aeronautics and Space Administration
80NSSC22K0537
W. M. Keck Foundation

Dates

Accepted
2022-09-12
Accepted
Available
2022-10-13
Published online

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Published