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

Creators: Di Gesu, Laura¹; Donnarumma, Immacolata¹; Tavecchio, Fabrizio²; Agudo, Iván³; Barnounin, Thibault⁴; Cibrario, Nicolò^{5, 6}; Di Lalla, Niccolò⁷; Di Marco, Alessandro⁸; Escudero, Juan³; Errando, Manel⁹; Jorstad, Svetlana G.^{10, 11}; Kim, Dawoon E.^{8, 12, 13}; Kouch, Pouya M.¹⁴; Liodakis, Ioannis¹⁴; Lindfors, Elina¹⁴; Madejski, Grzegorz⁷; Marshall, Herman L.¹⁵; Marscher, Alan P.¹⁰; Middei, Riccardo^{1, 16}; Muleri, Fabio⁸; Myserlis, Ioannis¹⁷; Negro, Michela^{18, 19}; Omodei, Nicola⁷; Pacciani, Luigi⁸; Paggi, Alessandro⁵; Perri, Matteo^{1, 16}; Puccetti, Simonetta¹; Antonelli, Lucio A.^{1, 16}; Bachetti, Matteo²⁰; Baldini, Luca^{21, 22}; Baumgartner, Wayne H.²³; Bellazzini, Ronaldo²¹; Bianchi, Stefano²⁴; Bongiorno, Stephen D.²³; Bonino, Raffaella^{5, 6}; Brez, Alessandro²¹; Bucciantini, Niccolò^{25, 26, 27}; Capitanio, Fiamma⁸; Castellano, Simone²¹; Cavazzuti, Elisabetta¹; Ciprini, Stefano^{1, 28}; Costa, Enrico⁸; De Rosa, Alessandra⁸; Del Monte, Ettore⁸; Doroshenko, Victor^{29, 30}; Dovčiak, Michal³¹; Ehlert, Steven R.²³; Enoto, Teruaki³²; Evangelista, Yuri⁸; Fabiani, Sergio⁸; Ferrazzoli, Riccardo⁸; Garcia, Javier A.³³; Gunji, Shuichi³⁴; Hayashida, Kiyoshi³⁵; Heyl, Jeremy³⁶; Iwakiri, Wataru³⁷; Karas, Vladimir³¹; Kitaguchi, Takao³²; Kolodziejczak, Jeffery J.²³; Krawczynski, Henric⁹; La Monaca, Fabio⁸; Latronico, Luca⁶; Maldera, Simone⁶; Manfreda, Alberto²¹; Marin, Frédéric⁴; Marinucci, Andrea¹; Massaro, Francesco^{5, 6}; Matt, Giorgio²⁴; Mitsuishi, Ikuyuki³⁸; Mizuno, Tsunefumi³⁹; Ng, C.-Y.⁴⁰; O'Dell, Stephen L.²³; Oppedisano, Chiara⁶; Papitto, Alessandro¹⁶; Pavlov, George G.⁴¹; Peirson, Abel L.⁷; Pesce-Rollins, Melissa²¹; Petrucci, Pierre-Olivier⁴²; Pilia, Maura²⁰; Possenti, Andrea²⁰; Poutanen, Juri^{14, 30}; Ramsey, Brian D.²³; Rankin, John⁸; Ratheesh, Ajay⁸; Romani, Roger W.⁷; Sgrò, Carmelo²¹; Slane, Patrick⁴³; Soffitta, Paolo⁸; Spandre, Gloria²¹; Tamagawa, Toru³²; Taverna, Roberto⁴⁴; Tawara, Yuzuru³⁸; Tennant, Allyn F.²³; Thomas, Nicolas E.²³; Tombesi, Francesco^{13, 28, 45}; Trois, Alessio²⁰; Tsygankov, Sergey^{14, 30}; Turolla, Roberto^{44, 46}; Vink, Jacco⁴⁷; Weisskopf, Martin C.²³; Wu, Kinwah⁴⁶; Xie, Fei^{8, 48}; Zane, Silvia⁴⁶

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

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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