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Published February 20, 2023 | Published
Journal Article Open

A Strong X-Ray Polarization Signal from the Magnetar 1RXS J170849.0-400910

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


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 observation of the magnetar 1RXS J170849.0-400910, jointly analyzed 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 remains 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 anticorrelated with the source counts in the 2–8 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.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. The Imaging X-ray Polarimetry Explorer (IXPE) is a joint US and Italian mission. The US contribution is supported by the National Aeronautics and Space Administration (NASA) and led and managed by its Marshall Space Flight Center (MSFC), with industry partner Ball Aerospace (contract NNM15AA18C). The Italian contribution is supported by the Italian Space Agency (Agenzia Spaziale Italiana; ASI) through contract ASI-OHBI-2017-12-I.0, agreements ASI-INAF-2017-12-H0 and ASI-INFN-2017.13-H0, and its Space Science Data Center (SSDC) with agreements ASI-INAF-2022-14-HH.0 and ASI-INFN 2021-43-HH.0, and by the Istituto Nazionale di Astrofisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) in Italy. This research used data products provided by the IXPE Team (MSFC, SSDC, INAF, and INFN). We thank K. C. Gendreau and Z. Arzoumanian for their help in scheduling NICER observations of the source. We acknowledge the use of public data from the Swift data archive, and we thank the Swift team for promptly scheduling a target of opportunity (ToO) observation. R.T. and R.T. acknowledge financial support from the Italian Ministry of University and Research (MUR) through grant PRIN 2017LJ39LM. D.G.-C., J.H., and I.C. acknowledge support from the Natural Sciences and Engineer Council of Canada and the Canadian Space Agency. M.N. acknowledges the support by NASA under award number 80GSFC21M0002. T.T. was supported by grant JSPS KAKENHI JP19H05609. H.K. and E.G. acknowledge NASA support under grants 80NSSC18K0264, 80NSSC22K1291, 80NSSC21K1817, and NNX16AC42G. We thank an anonymous referee for a careful reading of the paper. Facilities: IXPE - , Swift (XRT) - , NICER. -

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August 22, 2023
October 18, 2023