The First X-Ray Polarization Observation of the Black Hole X-Ray Binary 4U 1630–47 in the Steep Power-law State
Nicole Rodriguez Cavero, Lorenzo Marra, H. Krawczynski, Michal Dovčiak, S. Bianchi, James F. Steiner, Jiří Svoboda, Fiamma Capitanio, G. Matt, Michela Negro, Adam Ingram, Alexandra Veledina, Roberto Taverna, V. Karas, F. Ursini, Jakub Podgorný, Ajay Ratheesh, В. Ф. Сулейманов, Romana Mikušincová, Silvia Zane, P. Kaaret, Fabio Muleri, Juri Poutanen, Christian Malacaria, Pierre-Olivier Petrucci, Ephraim Gau, Kun Hu, Sohee Chun, I. Agudo, L. A. Antonelli, Matteo Bachetti, L. Baldini, W. H. Baumgartner, R. Bellazzini, Stephen D. Bongiorno, R. Bonino, A. Brez, N. Bucciantini, 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, Sergio Fabiani, Riccardo Ferrazzoli, Javier A. García, Shuichi Gunji, Kiyoshi Hayashida, Jeremy Heyl, W. Iwakiri, Svetlana G. Jorstad, Fabian Kislat, 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, 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, Roger W. Romani, C. Sgró, Patrick Slane, G. Spandre, P. Soffitta, Douglas A. Swartz, Toru Tamagawa, F. Tavecchio, Yuzuru Tawara
Abstract
Abstract The Imaging X-ray Polarimetry Explorer (IXPE) observed the black hole X-ray binary 4U 1630–47 in the steep power-law (or very high) state. The observations reveal a linear polarization degree of the 2–8 keV X-rays of 6.8% ± 0.2% at a position angle of 21.°3 ± 0.°9 east of north (all errors at 1 σ confidence level). Whereas the polarization degree increases with energy, the polarization angle stays constant within the accuracy of our measurements. We compare the polarization of the source in the steep power-law state with the previous IXPE measurement of the source in the high soft state. We find that, even though the source flux and spectral shape are significantly different between the high soft state and the steep power-law state, their polarization signatures are similar. Assuming that the polarization of both the thermal and power-law emission components are constant over time, we estimate the power-law component polarization to be 6.8%–7.0% and note that the polarization angle of the thermal and power-law components must be approximately aligned. We discuss the implications for the origin of the power-law component and the properties of the emitting plasma.