arXiv · 2301.12919
A strong X-ray polarization signal from the magnetar 1RXS J170849.0-400910
Abstract
Magnetars are the most strongly magnetized neutron stars, and one of the most promising targets for X-ray polarimetric measurements. We present here the first Imaging X-ray Polarimetry Explorer (IXPE) observation of the magnetar 1RXS J170849.0-400910, jointly analysed with a new Swift observation and archival NICER data. The total (energy and phase integrated) emission in the 2-8 keV energy range is linerarly polarized, at a ~35% level. The phase-averaged polarization signal shows a marked increase with energy, ranging from ~20% at 2-3 keV up to ~80% at 6-8 keV, while the polarization angle remain constant. This indicates that radiation is mostly polarized in a single direction. The spectrum is well reproduced by a combination of either two thermal (blackbody) components or a blackbody and a power law. Both the polarization degree and angle also show a variation with the spin phase, and the former is almost anti-correlated with the source counts in the 2-8 keV and 2-4 keV bands. We discuss the possible implications and interpretations, based on a joint analysis of the spectral, polarization and pulsation properties of the source. A scenario in which the surface temperature is not homogeneous, with a hotter cap covered by a gaseous atmosphere and a warmer region in a condensed state, provides a satisfactory description of both the phase- and energy-dependent spectro-polarimetric data. The (comparatively) small size of the two emitting regions, required to explain the observed pulsations, does not allow to reach a robust conclusion about the presence of vacuum birefringence effects.
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Silvia Zane, Roberto Taverna, Denis Gonzalez Caniulef, Fabio Muleri, Roberto Turolla, Jeremy Heyl, Keisuke Uchiyama, Mason Ng, Toru Tamagawa, Ilaria Caiazzo, Niccolo' Di Lalla, Herman L. Marshall, Matteo Bachetti, Fabio La Monaca, Ephraim Gau, Alessandro Di Marco, Luca Baldini, Michela Negro, Nicola Omodei, John Rankin, Giorgio Matt, George G. Pavlov, Takao Kitaguchi, Henric Krawczynski, Fabian Kislat, Ruth Kelly, Ivan Agudo, Lucio A. Antonelli, Wayne H. Baumgartner, Ronaldo Bellazzini, Stefano Bianchi, Stephen D. Bongiorno, Raffaella Bonino, Alessandro Brez, Niccolo' Bucciantini, Fiamma Capitanio, Simone Castellano, Elisabetta Cavazzuti, Chieng Ting Chen, Stefano Ciprini, Enrico Costa, Alessandra De Rosa, Ettore Del Monte, Laura Di Gesu, Immacolata Donnarumma, Victor Doroshenko, Michal Dovciak, Steven R. Ehlert, Teruaki Enoto, Yuri Evangelista, Sergio Fabiani, Riccardo Ferrazzoli, Javier A. Garcia, Shuichi Gunji, Kiyoshi Hayashida, Wataru Iwakiri, Svetlana G. Jorstad, Philip Kaaret, Vladimir Karas, Jeffery J. Kolodziejczak, Luca Latronico, Ioannis Liodakis, Simone Maldera, Alberto Manfreda, Frederic Marin, Andrea Marinucci, Alan P. Marscher, Francesco Massaro, Ikuyuki Mitsuishi, Tsunefumi Mizuno, C. Y. Ng, Stephen L. O'Dell, Chiara Oppedisano, Alessandro Papitto, Abel L. Peirson, Matteo Perri, Melissa Pesce Rollins, Pierre Olivier Petrucci, Maura Pilia, Andrea Possenti, Juri Poutanen, Simonetta Puccetti, Brian D. Ramsey, Ajay Ratheesh, Oliver J. Roberts, Roger W. Romani, Carmelo Sgro', Patrick Slane, Paolo Soffitta, Gloria Spandre, Douglas A. Swartz, Fabrizio Tavecchio, Yuzuru Tawara, Allyn F. Tennant, Nicholas E. Thomas, Francesco Tombesi, Alessio Trois, Sergey S. Tsygankov, Jacco Vink, Martin C. Weisskopf. 2023-01-30. A strong X-ray polarization signal from the magnetar 1RXS J170849.0-400910. https://doi.org/10.3847/2041-8213%2Facb703
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