Authors
James F. Steiner, Harvard & Smithsonian
Edward Nathan, California Institute of Technology
Kun Hu, Washington University in St. Louis
Henric Krawczynski, Washington University in St. Louis
Michal Dovčiak, Czech Academy of Sciences
Alexandra Veledina, University of Turku
Fabio Muleri, INAF Istituto di Astrofisica e Planetologia Spaziali
Jiri Svoboda, Czech Academy of Sciences
Kevin Alabarta, New York University Abu Dhabi
Maxime Parra, Universitá degli Studi Roma Tre
Yash Bhargava, Tata Institute of Fundamental Research
Giorgio Matt, Universitá degli Studi Roma Tre
Juri Poutanen, University of Turku
Pierre-Olivier Petrucci, Université Grenoble Alpes
Allyn F. Tennant, NASA Marshall Space Flight Center
M Cristina Baglio, INAF-Osservatorio Astronomico di Brera
Luca Baldini, Istituto Nazionale di Fisica Nucleare
Samuel Barnier, Université Grenoble Alpes
Sudip Bhattacharyya, Tata Institute of Fundamental Research
Stefano Bianchi, Universitá degli Studi Roma Tre
Maimouna Brigitte, Czech Academy of Sciences
Mauricio Cabezas, Czech Academy of Sciences
Floriane Cangemi, Université Paris-Cité
Fiamma Capitanio, INAF Istituto di Astrofisica e Planetologia Spaziali
Jacob Casey, University of New Hampshire, Durham
Nicole Rodriguez Cavero, Washington University in St. Louis
Simone Castellano, Istituto Nazionale di Fisica Nucleare
Elisabetta Cavazzuti, Agenzia Spaziale Italiana
Sohee Chun, Washington University in St. Louis
Eugene Churazov, Max Planck Institute for Astrophysics
Enrico Costa, INAF Istituto di Astrofisica e Planetologia Spaziali
Niccolò Di Lalla, Stanford University
Alessandro Di Marco, INAF Istituto di Astrofisica e Planetologia Spaziali
Elise Egron, INAF-Osservatorio Astronomico di Cagliari
Elise Egron, INAF-Osservatorio Astronomico di Cagliari
Melissa Ewing, Newcastle University
Sergio Fabiani, INAF Istituto di Astrofisica e Planetologia Spaziali
Javier A. García, NASA Goddard Space Flight Center
David A. Green, University of Cambridge
Victoria Grinberg, European Space Agency
Petr Hadrava, Czech Academy of Sciences
Adam Ingram, Newcastle University
Philip Kaaret, NASA Marshall Space Flight Center
Fabian Kislat, University of New Hampshire, DurhamFollow
Takao Kitaguchi, RIKEN Cluster for Pioneering Research
Vadim Kravtsov, University of Turku
Brankica Kubátová, Czech Academy of Sciences
Fabio La Monaca, INAF Istituto di Astrofisica e Planetologia Spaziali
Luca Latronico, Istituto Nazionale di Fisica Nucleare
Vladislav Loktev, University of Turku
Christian Malacaria, International Space Science Institute
Frédéric Marin, Université de Strasbourg
Andrea Marinucci, Agenzia Spaziale Italiana
Olga Maryeva, Czech Academy of Sciences
Guglielmo Mastroserio, INAF-Osservatorio Astronomico di Cagliari
Tsunefumi Mizuno, Hiroshima University
Michela Negro, Louisiana State University at Baton Rouge
Nicola Omodei, Stanford University
Jakub Podgorný, Czech Academy of Sciences
John Rankin, INAF Istituto di Astrofisica e Planetologia Spaziali
Ajay Ratheesh, INAF Istituto di Astrofisica e Planetologia Spaziali
Lauren Rhodes, University of Oxford
David M. Russell, New York University Abu Dhabi
Miroslav Šlechta, Czech Academy of Sciences
Paolo Soffitta, INAF Istituto di Astrofisica e Planetologia Spaziali
Sean Spooner, University of New Hampshire, DurhamFollow
Valery Suleimanov, Universität Tübingen
Francesco Tombesi, Università degli Studi di Roma "Tor Vergata"
Sergei A. Trushkin, Russian Academy of Sciences
Martin C. Weisskopf, NASA Marshall Space Flight Center
Silvia Zane, University College London
Andrzej A. Zdziarski, Polish Academy of Sciences
Sixuan Zhang, Hiroshima University
Wenda Zhang, Chinese Academy of Sciences
Menglei Zhou, Universität Tübingen
Iván Agudo, Instituto de Astrofísica de Andalucía
Lucio A. Antonelli, INAF Osservatorio Astronomico di Roma
Matteo Bachetti, INAF Osservatorio Astronomico di Cagliari
Wayne H. Baumgartner, NASA Marshall Space Flight Center
Ronaldo Bellazzini, Istituto Nazionale di Fisica Nucleare
Stephen D. Bongiorno, NASA Marshall Space Flight Center
Raffaella Bonino, Istituto Nazionale di Fisica Nucleare
Alessandro Brez, Istituto Nazionale di Fisica Nucleare
Niccolò Bucciantini, INAF Osservatorio Astrofisico di Arcetri
Chien-Ting Chen, Universities Space Research Association
Stefano Ciprini, Istituto Nazionale di Fisica Nucleare
Alessandra De Rosa, INAF Istituto di Astrofisica e Planetologia Spaziali
Ettore Del Monte, INAF Istituto di Astrofisica e Planetologia Spaziali
Laura Di Gesu, Agenzia Spaziale Italiana
Immacolata Donnarumma, Agenzia Spaziale Italiana
Victor Doroshenko, Universität Tübingen
Steven R. Ehlert, NASA Marshall Space Flight Center
Teruaki Enoto, RIKEN Cluster for Pioneering Research
Yuri Evangelista, INAF Istituto di Astrofisica e Planetologia Spaziali
Riccardo Ferrazzoli, INAF Istituto di Astrofisica e Planetologia Spaziali
Shuichi Gunji, Yamagata University
Kiyoshi Hayashida, Osaka University
Jeremy Heyl, University of British Columbia
Wataru Iwakiri, Chiba University
Svetlana G. Jorstad, Boston University
Vladimir Karas, Astronomical Institute of the Czech Academy of Sciences
Jeffery J. Kolodziejczak, NASA Marshall Space Flight Center
Ioannis Liodakis, NASA Marshall Space Flight Center
Simone Maldera, Istituto Nazionale di Fisica Nucleare
Alberto Manfreda, Istituto Nazionale di Fisica Nucleare
Alan P. Marscher, Boston University
Herman L. Marshall, Massachusetts Institute of Technology
Francesco Massaro, Istituto Nazionale di Fisica Nucleare
Ikuyuki Mitsuishi, Nagoya University
Chi-Yung Ng, The University of Hong Kong
Stephen L. O'Dell, NASA Marshall Space Flight Center
Chiara Oppedisano, Istituto Nazionale di Fisica Nucleare
Alessandro Papitto, INAF Osservatorio Astronomico di Roma
George G. Pavlov, The Pennsylvania State University
Abel L. Peirson, Stanford University
Matteo Perri, INAF Osservatorio Astronomico di Roma
Melissa Pesce-Rollins, Istituto Nazionale di Fisica Nucleare
Maura Pilia, INAF Osservatorio Astronomico di Cagliari
Andrea Possenti, INAF Osservatorio Astronomico di Cagliari
Simonetta Puccetti, Agenzia Spaziale Italiana
Brian D. Ramsey, NASA Marshall Space Flight Center
Oliver J. Roberts, Universities Space Research Association
Roger W. Romani, Stanford University
Carmelo Sgrò, Istituto Nazionale di Fisica Nucleare
Patrick Slane, Harvard & Smithsonian
Gloria Spandre, Istituto Nazionale di Fisica Nucleare
Douglas A. Swartz, Universities Space Research Association
Toru Tamagawa, RIKEN Cluster for Pioneering Research
Fabrizio Tavecchio, INAF Osservatorio Astronomico di Brera
Roberto Taverna, Università degli Studi di Padova
Yuzuru Tawara, Nagoya University
Nicholas E. Thomas, NASA Marshall Space Flight Center
Alessio Trois, INAF Osservatorio Astronomico di Cagliari
Sergey S. Tsygankov, University of Turku
Roberto Turolla, University College London
Jacco Vink, University of Amsterdam
Kinwah Wu, University College London
Fei Xie, INAF Istituto di Astrofisica e Planetologia Spaziali
Abstract
We present the first X-ray spectropolarimetric results for Cygnus X-1 in its soft state from a campaign of five IXPE observations conducted during 2023 May–June. Companion multiwavelength data during the campaign are likewise shown. The 2–8 keV X-rays exhibit a net polarization degree PD = 1.99% ± 0.13% (68% confidence). The polarization signal is found to increase with energy across the Imaging X-ray Polarimetry Explorer’s (IXPE) 2–8 keV bandpass. The polarized X-rays exhibit an energy-independent polarization angle of PA = −25.°7 ± 1.°8 east of north (68% confidence). This is consistent with being aligned to Cyg X-1’s au-scale compact radio jet and its parsec-scale radio lobes. In comparison to earlier hard-state observations, the soft state exhibits a factor of 2 lower polarization degree but a similar trend with energy and a similar (also energy-independent) position angle. When scaling by the natural unit of the disk temperature, we find the appearance of a consistent trend line in the polarization degree between the soft and hard states. Our favored polarimetric model indicates that Cyg X-1’s spin is likely high (a * ≳ 0.96). The substantial X-ray polarization in Cyg X-1's soft state is most readily explained as resulting from a large portion of X-rays emitted from the disk returning and reflecting off the disk surface, generating a high polarization degree and a polarization direction parallel to the black hole spin axis and radio jet. In IXPE’s bandpass, the polarization signal is dominated by the returning reflection emission. This constitutes polarimetric evidence for strong gravitational lensing of X-rays close to the black hole.
Department
Physics; Space Science Center
Publication Date
7-1-2024
Journal Title
The Astrophysical Journal Letters
Publisher
American Astronomical Society
Recommended Citation
James F. Steiner et al 2024 ApJL 969 L30
Rights
© 2024. The Author(s). Published by the American Astronomical Society.
Comments
This is an open access article published by American Astronomical Society in The Astrophysical Journal Letters in 2024, available online: https://dx.doi.org/10.3847/2041-8213/ad58e4