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Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE | Nature Astronomy

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The accretion of matter by compact objects can be inhibited by radiation pressure if the luminosity exceeds a critical value known as the Eddington limit. The discovery of ultraluminous X-ray sources has shown that accretion can proceed even when the apparent luminosity considerably exceeds this limit. A high apparent luminosity might be produced due to the geometric beaming of radiation by an outflow. The outflow half-opening angle, which determines the amplification due to beaming, has never been robustly constrained. Using the Imaging X-ray Polarimetry Explorer, we measured the X-ray polarization in the Galactic X-ray binary Cygnus X-3 (Cyg X-3). We found high, >20%, nearly energy-independent linear polarization orthogonal to the direction of the radio ejections. These properties unambiguously indicate the presence of a collimating outflow from the X-ray binary Cyg X-3 and constrain its half-opening angle to ≲ 15°. Thus, the source can be used as a laboratory for studying the supercritical accretion regime. This finding underscores the importance of X-ray polarimetry in advancing our understanding of accreting sources.

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The IXPE, NuSTAR, NICER, INTEGRAL and Fermi data are freely available in the HEASARC Data Archive (https://heasarc.gsfc.nasa.gov). The SRG ART-XC data are available via ftp://hea.iki.rssi.ru/public/SRG/ART-XC/data/Cyg_X-3/artxc_cygx3_04-20keV_lcurve.qdp. The multiwavelength raw data are available on request from the individual observatories.

The analysis and simulation software IXPEOBSSIM developed by the IXPE Collaboration and its documentation is available publicly through the web-page https://ixpeobssim.readthedocs.io/en/latest/?badge=latest.494. XSPEC is distributed and maintained under the aegis of the HEASARC and can be downloaded as part of HEAsoft from http://heasarc.gsfc.nasa.gov/docs/software/lheasoft/download.html. The MIR software package for the SMA data is available at https://lweb.cfa.harvard.edu/~cqi/mircook.html. Models of the polarized emission from the funnel are available via Zenodo at https://zenodo.org/records/10889892 (ref. 106). The STOKES code v.2.07 is available upon reasonable request from the authors.

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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, with industry partner Ball Aerospace (Contract NNM15AA18C). The Italian contribution is supported by ASI (Contract ASI-OHBI-2017-12-I.0 and Agreements ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0) and its Space Science Data Center and by the Italian National Institute for Astrophysics and the Italian National Institute for Nuclear Physics. For the AMI observations, we thank the staff of the Mullard Radio Astronomy Observatory, University of Cambridge, for their support in the maintenance and operation of the telescope, and we acknowledge support from the European Research Council (Grant No. ERC-2012-StG-307215 LODESTONE). The SMA is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. SMA is on Maunakea, which is a culturally important site for the indigenous Hawaiian people; we are privileged to study the cosmos from its summit. This work is partly based on observations with the 100-m telescope of the Max Planck Institute for Radio Astronomy at Effelsberg. The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 101004719; ORP). The AGILE Mission is funded by ASI with scientific and programmatic participation by the Italian National Institute for Astrophysics and the Italian National Institute for Nuclear Physics. This investigation was supported by the ASI (Grant No. I/028/12/7-2022). We thank H. Feng for providing the data on the representative ULX models. F. Muleri, A.D.M., F.L.M., E. Costa, P. Soffitta, S.F. and R.F. are partially supported by the Italian Ministry of Foreign Affairs (Grant No. CN24GR08, GRBAXP: Guangxi-Rome Bilateral Agreement for X-ray Polarimetry in Astrophysics). A.V., J. Poutanen and S.S.T. acknowledge support from the Academy of Finland (Grant Nos. 333112, 347003, 349144, 349373, 349906 and 355672). A.A.M. is supported by the Stephen Hawking fellowship from UK Research and Innovation. H.K. and N.R.C. acknowledge NASA support (Grant Nos. 80NSSC18K0264, 80NSSC22K1291, 80NSSC21K1817 and NNX16AC42G). V.D. thanks the German Academic Exchange Service (Travel Grant No. 57525212). A.I. acknowledges support from the Royal Society. J. Podgorný, M.D., J.S. and V.K. give thanks for support from the Czech Science Foundation (Project 21-06825X) and institutional support from the Astronomical Institute of the Czech Academy of Sciences (Project RVO:67985815). We thank the staff of the GMRT who made these observations possible. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. R.K. acknowledges the support of the Department of Atomic Energy, Government of India (Project No. 12-R&D-TFR-5.02-0700). M.M. is supported by NASA (Contract NAS8-03060). S.A.T. is supported by the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2022-262; 13.MNPMU.21.0003). A.A.Z. acknowledges support from the Polish National Science Center (Grant No. 2019/35/B/ST9/03944).

Unaffiliated: Alexander A. Lutovinov, Sergey V. Molkov, Ilya A. Mereminskiy.

Department of Physics and Astronomy, University of Turku, Turku, Finland

Alexandra Veledina, Juri Poutanen, Sofia V. Forsblom, Vladislav Loktev, Sergey S. Tsygankov & Jari J. E. Kajava

Nordita, KTH Royal Institute of Technology and Stockholm University, Stockholm, Sweden

INAF Institute of Space Astrophysics and Planetology, Rome, Italy

Fabio Muleri, Fiamma Capitanio, Alessandra De Rosa, Alessandro Di Marco, Fabio La Monaca, Ajay Ratheesh, Enrico Costa, Giovanni Piano, Paolo Soffitta, Ettore Del Monte, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, John Rankin & Fei Xie

University of Strasbourg, CNRS, Strasbourg Astronomical Observatory, Strasbourg, France

Jakub Podgorný & Frédéric Marin

Astronomical Institute of the Czech Academy of Sciences, Prague, Czech Republic

Jakub Podgorný, Michal Dovčiak, Jiri Svoboda & Vladimir Karas

Astronomical Institute, Charles University, Prague, Czech Republic

Max Planck Institute for Astrophysics, Garching, Germany

Eugene Churazov & Rashid A. Sunyaev

NASA Marshall Space Flight Center, Huntsville, AL, USA

Philip Kaaret, Martin C. Weisskopf, Wayne H. Baumgartner, Stephen D. Bongiorno, Steven R. Ehlert, Jeffery J. Kolodziejczak, Stephen L. O’Dell, Brian D. Ramsey, Allyn F. Tennant & Nicholas E. Thomas

Physics Department and McDonnell Center for the Space Sciences, Washington University in St Louis, St Louis, MO, USA

Henric Krawczynski & Nicole Rodriguez Cavero

Department of Physics, University of Rome 'Tor Vergata', Rome, Italy

Fabio La Monaca & Francesco Tombesi

Department of Physics, University of Rome 'La Sapienza', Rome, Italy

Astrophysics, Department of Physics, University of Oxford, Oxford, UK

Alexander A. Mushtukov & Joe S. Bright

Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

James F. Steiner, Mark Gurwell, Michael McCollough, Ramprasad Rao & Patrick Slane

Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw, Poland

Department of Mathematics and Physics, Roma Tre University, Rome, Italy

Stefano Bianchi, Giorgio Matt & Francesco Ursini

Special Astrophysical Observatory of the Russian Academy of Sciences, Nizhnij Arkhyz, Russia

Nikolaj Bursov, Nikolaj Nizhelsky, Anton Shevchenko, Sergei A. Trushkin & Peter Tsybulev

INAF Astronomical Observatory of Cagliari, Selargius, Italy

Elise Egron, Maura Pilia, Matteo Bachetti, Andrea Possenti & Alessio Trois

NASA Goddard Space Flight Center, Greenbelt, MD, USA

Javier A. Garcia & Michela Negro

California Institute of Technology, Pasadena, CA, USA

Cavendish Laboratory, University of Cambridge, Cambridge, UK

School of Mathematics, Statistics, and Physics, Newcastle University, Newcastle upon Tyne, UK

Serco for the European Space Agency (ESA), European Space Astronomy Centre, Madrid, Spain

National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India

Max Planck Institute for Radio Astronomy, Bonn, Germany

Institute for Astronomy and Astrophysics, University of Tübingen, Tübingen, Germany

Denys Malyshev & Victor Doroshenko

Space Science Data Center, Italian Space Agency, Rome, Italy

Carlotta Pittori, Lucio A. Antonelli, Stefano Ciprini, Matteo Perri & Simonetta Puccetti

INAF Astronomical Observatory of Rome, Rome, Italy

Carlotta Pittori, Lucio A. Antonelli, Alessandro Papitto & Matteo Perri

INAF Institute of Radio Astronomy, Bologna, Italy

National Institute of Nuclear Physics, Rome Section 'Tor Vergata', Rome, Italy

Francesco Tombesi & Stefano Ciprini

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

Kazan Federal University, Kazan, Russia

Mullard Space Science Laboratory, University College London, Dorking, UK

Kinwah Wu, Roberto Turolla & Silvia Zane

Institute of Astrophysics of Andalusia–CSIC, Granada, Spain

Iván Agudo & Alessandro Brez

National Institute of Nuclear Physics, Pisa Section, Pisa, Italy

Luca Baldini, Ronaldo Bellazzini, Simone Castellano, Alberto Manfreda, Melissa Pesce-Rollins, Carmelo Sgrò & Gloria Spandre

Department of Physics, University of Pisa, Pisa, Italy

National Institute of Nuclear Physics, Turin Section, Turin, Italy

Raffaella Bonino, Luca Latronico, Simone Maldera, Francesco Massaro & Chiara Oppedisano

Department of Physics, University of Turin, Turin, Italy

Raffaella Bonino & Francesco Massaro

INAF Arcetri Astrophysical Observatory, Florence, Italy

Department of Physics and Astronomy, University of Florence, Florence, Italy

National Institute of Nuclear Physics, Florence Section, Florence, Italy

Italian Space Agency, Rome, Italy

Elisabetta Cavazzuti, Laura Di Gesu, Immacolata Donnarumma & Andrea Marinucci

Science and Technology Institute, Universities Space Research Association, Huntsville, AL, USA

Chien-Ting Chen, Oliver Roberts & Doug Swartz

Department of Physics and Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA, USA

Niccolò Di Lalla, Nicola Omodei, Abel L. Peirson & Roger W. Romani

RIKEN Cluster for Pioneering Research, Wako, Japan

Teruaki Enoto, Takao Kitaguchi & Toru Tamagawa

University of British Columbia, Vancouver, British Columbia, Canada

International Center for Hadron Astrophysics, Chiba University, Chiba, Japan

Institute for Astrophysical Research, Boston University, Boston, MA, USA

Svetlana G. Jorstad & Alan P. Marscher

Department of Astrophysics, St Petersburg State University, St Petersburg, Russia

Department of Physics and Astronomy and Space Science Center, University of New Hampshire, Durham, NH, USA

Finnish Centre for Astronomy with ESO, University of Turku, Turku, Finland

MIT Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA

Graduate School of Science, Division of Particle and Astrophysical Science, Nagoya University, Nagoya, Japan

Ikuyuki Mitsuishi & Yuzuru Tawara

Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Japan

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

Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD, USA

Department of Physics, The University of Hong Kong, Hong Kong, China

Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA, USA

Grenoble Alpes University, CNRS, IPAG, Grenoble, France

INAF Brera Astronomical Observatory, Merate, Italy

Department of Physics and Astronomy, University of Padua, Padua, Italy

Roberto Taverna & Roberto Turolla

Anton Pannekoek Institute for Astronomy & GRAPPA, University of Amsterdam, Amsterdam, The Netherlands

Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning, China

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