First X-Ray Polarization Measurement Confirms the Low Black Hole Spin in LMC X-3
Jiří Svoboda, Michal Dovčiak, James F. Steiner, Fabio Muleri, Adam Ingram, Anastasiya Yilmaz, Nicole Rodriguez Cavero, Lorenzo Marra, Juri Poutanen, Alexandra Veledina, Mehrnoosh Rahbardar Mojaver, S. Bianchi, Javier A. García, P. Kaaret, H. Krawczynski, G. Matt, Jakub Podgorný, Martin C. Weisskopf, Fabian Kislat, Pierre-Olivier Petrucci, M. Brigitte, Michal Bursa, Sergio Fabiani, Kun Hu, Sohee Chun, Guglielmo Mastroserio, Romana Mikušincová, Ajay Ratheesh, Roger W. Romani, P. Soffitta, F. Ursini, Silvia Zane, I. Agudo, L. A. Antonelli, Matteo Bachetti, L. Baldini, W. H. Baumgartner, R. Bellazzini, Stephen D. Bongiorno, R. Bonino, A. Brez, N. Bucciantini, Fiamma Capitanio, Simone Castellano, E. Cavazzuti, Chien‐Ting Chen, S. Ciprini, E. Costa, Alessandra De Rosa, E. Del Monte, Laura Di Gesu, Niccolò Di Lalla, Alessandro Di Marco, I. Donnarumma, Victor Doroshenko, Steven R. Ehlert, Teruaki Enoto, Y. Evangelista, Riccardo Ferrazzoli, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, W. Iwakiri, Svetlana G. Jorstad, V. Karas, Takao Kitaguchi, Jeffery J. Kolodziejczak, Fabio La Monaca, L. Latronico, Ioannis Liodakis, S. Maldera, Alberto Manfreda, Frédéric Marin, Andrea Marinucci, Alan P. Marscher, Herman L. Marshall, F. Massaro, Ikuyuki Mitsuishi, Tsunefumi Mizuno, Michela Negro, C.‐Y. Ng, Stephen L. O’Dell, N. Omodei, C. Oppedisano, Alessandro Papitto, George G. Pavlov, Abel L. Peirson, M. Perri, M. Pesce-Rollins, M. Pilia, Andrea Possenti, Simonetta Puccetti, Brian D. Ramsey, John Rankin, O. J. Roberts, C. Sgró, Patrick Slane, G. Spandre, Douglas A. Swartz, Toru Tamagawa
Abstract
Abstract X-ray polarization is a powerful tool to investigate the geometry of accreting material around black holes, allowing independent measurements of the black hole spin and orientation of the innermost parts of the accretion disk. We perform X-ray spectropolarimetric analysis of an X-ray binary system in the Large Magellanic Cloud, LMC X-3, that hosts a stellar-mass black hole, known to be persistently accreting since its discovery. We report the first detection of the X-ray polarization in LMC X-3 with the Imaging X-ray Polarimetry Explorer, and find the average polarization degree (PD) of 3.2% ± 0.6% and a constant polarization angle of −42° ± 6° over the 2–8 keV range. Using accompanying spectroscopic observations by NICER, NuSTAR, and the Neil Gehrels Swift observatories, we confirm previous measurements of the black hole spin via the X-ray continuum method, a ≈ 0.2. From polarization analysis only, we found consistent results with low black hole spin, with an upper limit of a < 0.7 at a 90% confidence level. A slight increase in the PD with energy, similar to other black hole X-ray binaries in the soft state, is suggested from the data but with a low statistical significance.