TY - JOUR Y1 - 2024/08// N2 - 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. ID - discovery10196156 UR - https://doi.org/10.1038/s41550-024-02294-9 VL - 8 SP - 1031 JF - Nature Astronomy A1 - Veledina, Alexandra A1 - Muleri, Fabio A1 - Poutanen, Juri A1 - Podgorný, Jakub A1 - Dov?iak, Michal A1 - Capitanio, Fiamma A1 - Churazov, Eugene A1 - De Rosa, Alessandra A1 - Di Marco, Alessandro A1 - Forsblom, Sofia V A1 - Kaaret, Philip A1 - Krawczynski, Henric A1 - La Monaca, Fabio A1 - Loktev, Vladislav A1 - Lutovinov, Alexander A A1 - Molkov, Sergey V A1 - Mushtukov, Alexander A A1 - Ratheesh, Ajay A1 - Rodriguez Cavero, Nicole A1 - Steiner, James F A1 - Sunyaev, Rashid A A1 - Tsygankov, Sergey S A1 - Weisskopf, Martin C A1 - Zdziarski, Andrzej A A1 - Bianchi, Stefano A1 - Bright, Joe S A1 - Bursov, Nikolaj A1 - Costa, Enrico A1 - Egron, Elise A1 - Garcia, Javier A A1 - Green, David A A1 - Gurwell, Mark A1 - Ingram, Adam A1 - Kajava, Jari JE A1 - Kale, Ruta A1 - Kraus, Alex A1 - Malyshev, Denys A1 - Marin, Frédéric A1 - Matt, Giorgio A1 - McCollough, Michael A1 - Mereminskiy, Ilya A A1 - Nizhelsky, Nikolaj A1 - Piano, Giovanni A1 - Pilia, Maura A1 - Pittori, Carlotta A1 - Rao, Ramprasad A1 - Righini, Simona A1 - Soffitta, Paolo A1 - Shevchenko, Anton A1 - Svoboda, Jiri A1 - Tombesi, Francesco A1 - Trushkin, Sergei A A1 - Tsybulev, Peter A1 - Ursini, Francesco A1 - Wu, Kinwah A1 - Agudo, Iván A1 - Antonelli, Lucio A A1 - Bachetti, Matteo A1 - Baldini, Luca A1 - Baumgartner, Wayne H A1 - Bellazzini, Ronaldo A1 - Bongiorno, Stephen D A1 - Bonino, Raffaella A1 - Brez, Alessandro A1 - Bucciantini, Niccolò A1 - Castellano, Simone A1 - Cavazzuti, Elisabetta A1 - Chen, Chien-Ting A1 - Ciprini, Stefano A1 - Del Monte, Ettore A1 - Di Gesu, Laura A1 - Di Lalla, Niccolò A1 - Donnarumma, Immacolata A1 - Doroshenko, Victor A1 - Ehlert, Steven R A1 - Enoto, Teruaki A1 - Evangelista, Yuri A1 - Fabiani, Sergio A1 - Ferrazzoli, Riccardo A1 - Gunji, Shuichi A1 - Hayashida, Kiyoshi A1 - Heyl, Jeremy A1 - Iwakiri, Wataru A1 - Jorstad, Svetlana G A1 - Karas, Vladimir A1 - Kislat, Fabian A1 - Kitaguchi, Takao A1 - Kolodziejczak, Jeffery J A1 - Latronico, Luca A1 - Liodakis, Ioannis A1 - Maldera, Simone A1 - Manfreda, Alberto A1 - Marinucci, Andrea A1 - Marscher, Alan P A1 - Marshall, Herman L A1 - Massaro, Francesco A1 - Mitsuishi, Ikuyuki A1 - Mizuno, Tsunefumi A1 - Negro, Michela A1 - Ng, Chi-Yung A1 - O?Dell, Stephen L A1 - Omodei, Nicola A1 - Oppedisano, Chiara A1 - Papitto, Alessandro A1 - Pavlov, George G A1 - Peirson, Abel L A1 - Perri, Matteo A1 - Pesce-Rollins, Melissa A1 - Petrucci, Pierre-Olivier A1 - Possenti, Andrea A1 - Puccetti, Simonetta A1 - Ramsey, Brian D A1 - Rankin, John A1 - Roberts, Oliver A1 - Romani, Roger W A1 - Sgrò, Carmelo A1 - Slane, Patrick A1 - Spandre, Gloria A1 - Swartz, Doug A1 - Tamagawa, Toru A1 - Tavecchio, Fabrizio A1 - Taverna, Roberto A1 - Tawara, Yuzuru A1 - Tennant, Allyn F A1 - Thomas, Nicholas E A1 - Trois, Alessio A1 - Turolla, Roberto A1 - Vink, Jacco A1 - Xie, Fei A1 - Zane, Silvia PB - Springer Science and Business Media LLC SN - 2397-3366 TI - Cygnus X-3 revealed as a Galactic ultraluminous X-ray source by IXPE AV - public EP - 1046 N1 - This version is the author accepted manuscript. For information on re-use, please refer to the publisher?s terms and conditions. KW - Compact astrophysical objects KW - High-energy astrophysics ER -