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Published February 1, 2023 | Published
Journal Article Open

Polarization Properties of the Weakly Magnetized Neutron Star X-Ray Binary GS 1826-238 in the High Soft State

Capitanio, Fiamma ORCID icon
Fabiani, Sergio ORCID icon
Gnarini, Andrea ORCID icon
Ursini, Francesco ORCID icon
Ferrigno, Carlo ORCID icon
Matt, Giorgio ORCID icon
Poutanen, Juri ORCID icon
Cocchi, Massimo ORCID icon
Mikusincova, Romana ORCID icon
Farinelli, Ruben ORCID icon
Bianchi, Stefano ORCID icon
Kajava, Jari J. E. ORCID icon
Muleri, Fabio ORCID icon
Sanchez-Fernandez, Celia ORCID icon
Soffitta, Paolo ORCID icon
Wu, Kinwah ORCID icon
Agudo, Iván ORCID icon
Antonelli, Lucio A. ORCID icon
Bachetti, Matteo ORCID icon
Baldini, Luca ORCID icon
Baumgartner, Wayne H. ORCID icon
Bellazzini, Ronaldo ORCID icon
Bongiorno, Stephen D. ORCID icon
Bonino, Raffaella ORCID icon
Brez, Alessandro ORCID icon
Bucciantini, Niccolò ORCID icon
Castellano, Simone ORCID icon
Cavazzuti, Elisabetta 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
Di Lalla, Niccolò ORCID icon
Di Marco, Alessandro 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
Ferrazzoli, Riccardo ORCID icon
García, Javier A. ORCID icon
Gunji, Shuichi ORCID icon
Hayashida, Kiyoshi ORCID icon
Heyl, Jeremy ORCID icon
Iwakiri, Wataru ORCID icon
Jorstad, Svetlana G. ORCID icon
Karas, Vladimir ORCID icon
Kitaguchi, Takao
Kolodziejczak, Jeffery J. ORCID icon
Krawczynski, Henric ORCID icon
La Monaca, Fabio 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
Marshall, Herman L. ORCID icon
Mitsuishi, Ikuyuki
Mizuno, Tsunefumi ORCID icon
Ng, C.-Y. ORCID icon
O'Dell, Stephen L. ORCID icon
Omodei, Nicola ORCID icon
Oppedisano, Chiara ORCID icon
Papitto, Alessandro ORCID icon
Pavlov, George G. 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
Puccetti, Simonetta ORCID icon
Ramsey, Brian D. ORCID icon
Rankin, John ORCID icon
Ratheesh, Ajay ORCID icon
Romani, Roger W. ORCID icon
Sgrò, Carmelo ORCID icon
Slane, Patrick ORCID icon
Spandre, Gloria ORCID icon
Tamagawa, Toru ORCID icon
Tavecchio, Fabrizio ORCID icon
Taverna, Roberto 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
Turolla, Roberto ORCID icon
Vink, Jacco ORCID icon
Weisskopf, Martin C. ORCID icon
Xie, Fei ORCID icon
Zane, Silvia ORCID icon


The launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in X-ray astronomy. We report here the results of the first IXPE observation of a weakly magnetized neutron star, GS 1826−238, performed on 2022 March 29–31 when the source was in a high soft state. An upper limit (99.73% confidence level) of 1.3% for the linear polarization degree is obtained over the IXPE 2–8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. The spectral parameters obtained from the fits to the broadband spectrum were used as inputs for Monte Carlo simulations considering different possible geometries of the X-ray emitting region. Comparing the IXPE upper limit with these simulations, we can put constraints on the geometry and inclination angle of GS 1826–238.

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) and distributed with additional software tools by the High-Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC). This work made use of the MAXI light curves, publicly available at http://maxi.riken.jp/top/slist.html. INTEGRAL is an ESA project with instruments and a science data center funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, and Spain) and with the participation of Russia and the USA. We thank Keith Gendreau, Craig Markwardt, and the NICER SOC for granting and performing the NICER observations of the source and helping with data reduction. J.P. and S.S.T. acknowledge support from Russian Science Foundation grant 20-12-00364 and Academy of Finland travel grants 349144, 349373, and 349906. J.P. and J.J.E.K. were supported by Academy of Finland grant 333112. Facilities: IXPE - , Swift (XRT and UVOT) - , INTEGRAL. - Software: Stingray (Huppenkothen et al. 2019a, 2019b), xspec (Arnaud 1996), ixpeobssim (Baldini et al. 2022), monk (Zhang et al. 2019).

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August 22, 2023
October 25, 2023