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arXiv · 2311.04632

X-Ray Polarized View on the Accretion Geometry in the X-Ray Binary Circinus X-1

John Rankin·Fabio La Monaca·Alessandro Di Marco·Juri Poutanen·Anna Bobrikova·Vadim Kravtsov·Fabio Muleri·Maura Pilia·Alexandra Veledina·Rob Fender·Philip Kaaret·Dawoon E. Kim·Andrea Marinucci·Herman L. Marshall·Alessandro Papitto·Allyn F. Tennant·Sergey S. Tsygankov·Martin C. Weisskopf·Kinwah Wu·Silvia Zane·Filippo Ambrosino·Ruben Farinelli·Andrea Gnarini·Iván Agudo·Lucio A. Antonelli·Matteo Bachetti·Luca Baldini·Wayne H. Baumgartner·Ronaldo Bellazzini·Stefano Bianchi·Stephen D. Bongiorno·Raffaella Bonino·Alessandro Brez·Niccolò Bucciantini·Fiamma Capitanio·Simone Castellano·Elisabetta Cavazzuti·Chien-Ting Chen·Stefano Ciprini·Enrico Costa·Alessandra De Rosa·Ettore Del Monte·Laura Di Gesu·Niccolò di Lalla·Immacolata Donnarumma·Victor Doroshenko·Michal Dovčiak·Steven R. Ehlert·Teruaki Enoto·Yuri Evangelista·Sergio Fabiani·Riccardo Ferrazzoli·Javier A. Garcia·Shuichi Gunji·Kiyoshi Hayashida·Jeremy Heyl·Wataru Iwakiri·Svetlana G. Jorstad·Vladimir Karas·Fabian Kislat·Takao Kitaguchi·Jeffery J. Kolodziejczak·Henric Krawczynski·Luca Latronico·Ioannis Liodakis·Simone Maldera·Alberto Manfreda·Frédéric Marin·Alan P. Marscher·Francesco Massaro·Giorgio Matt·Ikuyuki Mitsuishi·Tsunefumi Mizuno·Michela Negro·Chi-Yung Ng·Stephen L. O'Dell·Nicola Omodei·Chiara Oppedisano·George G. Pavlov·Abel L. Peirson·Matteo Perri·Melissa Pesce-Rollins·Pierre-Olivier Petrucci·Andrea Possenti·Simonetta Puccetti·Brian D. Ramsey·Ajay Ratheesh·Oliver J. Roberts·Roger W. Romani·Carmelo Sgrò·Patrick Slane·Paolo Soffitta·Gloria Spandre·Douglas A. Swartz·Toru Tamagawa·Fabrizio Tavecchio·Roberto Taverna·Yuzuru Tawara·Nicholas E. Thomas·Francesco Tombesi
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Abstract

Cir X-1 is a neutron star X-ray binary characterized by strong variations in flux during its eccentric $\sim$16.6 days orbit. There are also strong variations in the spectral state, and historically it has shown both atoll and Z state properties. We observed the source with the Imaging X-ray Polarimetry Explorer during two orbital segments, 6 days apart, for a total of 263~ks. We find an X-ray polarization degree in these segments of $1.6\%\pm0.3\%$ and $1.4\%\pm0.3\%$ at polarization angles of $37^\circ\pm5^\circ$ and $-12^\circ\pm7^\circ$, respectively. Thus we observed a rotation of the polarization angle by $49^\circ\pm8^\circ$ along the orbit. Because variations of accretion flow, and then of the hardness ratio, are expected during the orbit, we also studied the polarization binned in hardness ratio, and found the polarization angle differing by $67^\circ\pm11^\circ$ between the lowest and highest values of the hardness ratio. We discuss possible interpretations of this result that could indicate a possible misalignment between the symmetry axes of the accretion disk and the Comptonizing region caused by the misalignment of the neutron star's angular momentum with respect to the orbital one.

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John Rankin, Fabio La Monaca, Alessandro Di Marco, Juri Poutanen, Anna Bobrikova, Vadim Kravtsov, Fabio Muleri, Maura Pilia, Alexandra Veledina, Rob Fender, Philip Kaaret, Dawoon E. Kim, Andrea Marinucci, Herman L. Marshall, Alessandro Papitto, Allyn F. Tennant, Sergey S. Tsygankov, Martin C. Weisskopf, Kinwah Wu, Silvia Zane, Filippo Ambrosino, Ruben Farinelli, Andrea Gnarini, Iván Agudo, Lucio A. Antonelli, Matteo Bachetti, Luca Baldini, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolò Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chien-Ting Chen, Stefano Ciprini, Enrico Costa, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Niccolò di Lalla, Immacolata Donnarumma, Victor Doroshenko, Michal Dovčiak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, Wataru Iwakiri, Svetlana G. Jorstad, Vladimir Karas, Fabian Kislat, Takao Kitaguchi, Jeffery J. Kolodziejczak, Henric Krawczynski, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Frédéric Marin, Alan P. Marscher, Francesco Massaro, Giorgio Matt, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Michela Negro, Chi-Yung Ng, Stephen L. O'Dell, Nicola Omodei, Chiara Oppedisano, George G. Pavlov, Abel L. Peirson, Matteo Perri, Melissa Pesce-Rollins, Pierre-Olivier Petrucci, Andrea Possenti, Simonetta Puccetti, Brian D. Ramsey, Ajay Ratheesh, Oliver J. Roberts, Roger W. Romani, Carmelo Sgrò, Patrick Slane, Paolo Soffitta, Gloria Spandre, Douglas A. Swartz, Toru Tamagawa, Fabrizio Tavecchio, Roberto Taverna, Yuzuru Tawara, Nicholas E. Thomas, Francesco Tombesi. 2023-12-22. X-Ray Polarized View on the Accretion Geometry in the X-Ray Binary Circinus X-1. https://doi.org/10.3847/2041-8213%2Fad1832

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