Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1

Journal
Date Issued
2024
Author(s)
Bobrikova, Anna
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Forsblom, Sofia V.
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Poutanen, Juri
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Ng, Mason
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Ravi, Swati
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Loktev, Vladislav
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Kajava, Jari J. E.
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Veledina, Alexandra
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Thomas, Nicholas E.
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Tsygankov, Sergey S.
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Turolla, Roberto
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Vink, Jacco
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Wu, Kinwah
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Zane, Silvia
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Rogantini, Daniele
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Salmi, Tuomo
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Bianchi, Stefano
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Done, Chris
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Gnarini, Andrea
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Heyl, Jeremy
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Kaaret, Philip
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Nitindala, Anagha P.
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Weisskopf, Martin C.
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Agudo, Iván
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Baldini, Luca
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Baumgartner, Wayne H.
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Bellazzini, Ronaldo
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Bongiorno, Stephen D.
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Bonino, Raffaella
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Brez, Alessandro
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Castellano, Simone
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Cavazzuti, Elisabetta
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Chen, Chien-Ting
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Ciprini, Stefano
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Di Gesu, Laura
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Di Lalla, Niccolò
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Donnarumma, Immacolata
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Doroshenko, Victor
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Dovčiak, Michal
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Ehlert, Steven R.
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Enoto, Teruaki
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García, Javier A.
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Gunji, Shuichi
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Hayashida, Kiyoshi
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Iwakiri, Wataru
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Jorstad, Svetlana G.
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Karas, Vladimir
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Kislat, Fabian
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Kitaguchi, Takao
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Kolodziejczak, Jeffery J.
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Krawczynski, Henric
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Latronico, Luca
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Liodakis, Ioannis
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Maldera, Simone
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Manfreda, Alberto
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Marin, Frédéric
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Marinucci, Andrea
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Marscher, Alan P.
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Marshall, Herman L.
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Mitsuishi, Ikuyuki
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Mizuno, Tsunefumi
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Negro, Michela
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Ng, Chi-Yung
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O'Dell, Stephen L.
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Omodei, Nicola
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Oppedisano, Chiara
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Pavlov, George G.
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Peirson, Abel L.
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Pesce-Rollins, Melissa
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Petrucci, Pierre-Olivier
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Puccetti, Simonetta
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Ramsey, Brian D.
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Roberts, Oliver J.
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Romani, Roger W.
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Sgrò, Carmelo
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Slane, Patrick
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Spandre, Gloria
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Swartz, Douglas A.
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Tamagawa, Toru
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Taverna, Roberto
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Tawara, Yuzuru
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Tennant, Allyn F.
DOI
Abstract
Weakly magnetized neutron stars in X-ray binaries show a complex phenomenology with several spectral components that can be associated with the accretion disk, the boundary, and/or a spreading layer, a corona, and a wind. Spectroscopic information alone, however, is not enough to distinguish these components. The analysis of the timing data revealed that most of the variability, and in particular, kilohertz quasi-period oscillations, are associated with the high-energy component that corresponds to the boundary and/or spreading layer. Additional information about the nature of the spectral components, and in particular, about the geometry of the emission region, can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster GX 13+1, was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the XMM-Newton. Using the XMM-Newton data, we obtained the best-fit values for the continuum spectral parameters and detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2-8 keV energy band, with an overall polarization degree (PD) of 1.4%±0.3% at a polarization angle (PA) of −2° ±6° (errors at the 68% confidence level). During the two-day long observation, we detected rotation of the PA by about 70° with the corresponding changes in the PD from 2% to nondetectable and then up to 5%. These variations in polarization properties are not accompanied by visible spectral state changes of the source. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest a constant polarization component, strong wind scattering, or a different polarization of the two main spectral components with an individually peculiar behavior. The rotation of the PA suggests a misalignment of the neutron star spin from the orbital axis.
Volume
688
Start page
A170
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2024A&A...688A.170B
Rights
open.access
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