학술논문
A strong X-ray polarization signal from the magnetar 1RXS J170849.0-400910
Document Type
Working Paper
Author
Zane, Silvia; Taverna, Roberto; Caniulef, Denis Gonzalez; Muleri, Fabio; Turolla, Roberto; Heyl, Jeremy; Uchiyama, Keisuke; Ng, Mason; Tamagawa, Toru; Caiazzo, Ilaria; Di Lalla, Niccolo'; Marshall, Herman L.; Bachetti, Matteo; La Monaca, Fabio; Gau, Ephraim; Di Marco, Alessandro; Baldini, Luca; Negro, Michela; Omodei, Nicola; Rankin, John; Matt, Giorgio; Pavlov, George G.; Kitaguchi, Takao; Krawczynski, Henric; Kislat, Fabian; Kelly, Ruth; Agudo, Ivan; Antonelli, Lucio A.; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bianchi, Stefano; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolo'; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, Elisabetta; Chen, Chieng Ting; Ciprini, Stefano; Costa, Enrico; De Rosa, Alessandra; Del Monte, Ettore; Di Gesu, Laura; Donnarumma, Immacolata; Doroshenko, Victor; Dovciak, Michal; Ehlert, Steven R.; Enoto, Teruaki; Evangelista, Yuri; Fabiani, Sergio; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Iwakiri, Wataru; Jorstad, Svetlana G.; Kaaret, Philip; Karas, Vladimir; Kolodziejczak, Jeffery J.; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marin, Frederic; Marinucci, Andrea; Marscher, Alan P.; Massaro, Francesco; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Ng, C. Y.; O'Dell, Stephen L.; Oppedisano, Chiara; Papitto, Alessandro; Peirson, Abel L.; Perri, Matteo; Rollins, Melissa Pesce; Petrucci, Pierre Olivier; Pilia, Maura; Possenti, Andrea; Poutanen, Juri; Puccetti, Simonetta; Ramsey, Brian D.; Ratheesh, Ajay; Roberts, Oliver J.; Romani, Roger W.; Sgro', Carmelo; Slane, Patrick; Soffitta, Paolo; Spandre, Gloria; Swartz, Douglas A.; Tavecchio, Fabrizio; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, Nicholas E.; Tombesi, Francesco; Trois, Alessio; Tsygankov, Sergey S.; Vink, Jacco; Weisskopf, Martin C.; Wu, Kinwah; Xie, Fei
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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.
Comment: 14 pages, 5 Figures, accepted for publication on ApJL
Comment: 14 pages, 5 Figures, accepted for publication on ApJL