A strong X-ray polarization signal from the magnetar 1RXS J170849.0-400910
Creators: name: Zane, Silvia
name: Taverna, Roberto
name: Caniulef, Denis Gonzalez
name: Muleri, Fabio
name: Turolla, Roberto
name: Heyl, Jeremy
name: Uchiyama, Keisuke
name: Ng, Mason
name: Tamagawa, Toru
name: Caiazzo, Ilaria
name: Di Lalla, Niccolo'
name: Marshall, Herman L.
name: Bachetti, Matteo
name: La Monaca, Fabio
name: Gau, Ephraim
name: Di Marco, Alessandro
name: Baldini, Luca
name: Negro, Michela
name: Omodei, Nicola
name: Rankin, John
name: Matt, Giorgio
name: Pavlov, George G.
name: Kitaguchi, Takao
name: Krawczynski, Henric
name: Kislat, Fabian
name: Kelly, Ruth
name: Agudo, Ivan
name: Antonelli, Lucio A.
name: Baumgartner, Wayne H.
name: Bellazzini, Ronaldo
name: Bianchi, Stefano
name: Bongiorno, Stephen D.
name: Bonino, Raffaella
name: Brez, Alessandro
name: Bucciantini, Niccolo'
name: Capitanio, Fiamma
name: Castellano, Simone
name: Cavazzuti, Elisabetta
name: Chen, Chieng Ting
name: Ciprini, Stefano
name: Costa, Enrico
name: De Rosa, Alessandra
name: Del Monte, Ettore
name: Di Gesu, Laura
name: Donnarumma, Immacolata
name: Doroshenko, Victor
name: Dovciak, Michal
name: Ehlert, Steven R.
name: Enoto, Teruaki
name: Evangelista, Yuri
name: Fabiani, Sergio
name: Ferrazzoli, Riccardo
name: Garcia, Javier A.
name: Gunji, Shuichi
name: Hayashida, Kiyoshi
name: Iwakiri, Wataru
name: Jorstad, Svetlana G.
name: Kaaret, Philip
name: Karas, Vladimir
name: Kolodziejczak, Jeffery J.
name: Latronico, Luca
name: Liodakis, Ioannis
name: Maldera, Simone
name: Manfreda, Alberto
name: Marin, Frederic
name: Marinucci, Andrea
name: Marscher, Alan P.
name: Massaro, Francesco
name: Mitsuishi, Ikuyuki
name: Mizuno, Tsunefumi
name: Ng, C. Y.
name: O'Dell, Stephen L.
name: Oppedisano, Chiara
name: Papitto, Alessandro
name: Peirson, Abel L.
name: Perri, Matteo
name: Rollins, Melissa Pesce
name: Petrucci, Pierre Olivier
name: Pilia, Maura
name: Possenti, Andrea
name: Poutanen, Juri
name: Puccetti, Simonetta
name: Ramsey, Brian D.
name: Ratheesh, Ajay
name: Roberts, Oliver J.
name: Romani, Roger W.
name: Sgro', Carmelo
name: Slane, Patrick
name: Soffitta, Paolo
name: Spandre, Gloria
name: Swartz, Douglas A.
name: Tavecchio, Fabrizio
name: Tawara, Yuzuru
name: Tennant, Allyn F.
name: Thomas, Nicholas E.
name: Tombesi, Francesco
name: Trois, Alessio
name: Tsygankov, Sergey S.
name: Vink, Jacco
name: Weisskopf, Martin C.
name: Wu, Kinwah
name: Xie, Fei
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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.
description: 14 pages, 5 Figures, accepted for publication on ApJL