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Ultrasoft state of microquasar Cygnus X-3: X-ray polarimetry reveals the geometry of the astronomical puzzle
Tekijät: Veledina, Alexandra; Poutanen, Juri; Bocharova, Anastasiia; Di Marco, Alessandro; Forsblom, Sofia V.; La Monaca, Fabio; Podgorný, Jakub; Tsygankov, Sergey S.; Zdziarski, Andrzej A.; Ahlberg, Varpu; Green, David A.; Muleri, Fabio; Rhodes, Lauren; Bianchi, Stefano; Costa, Enrico; Dovčiak, Michal; Loktev, Vladislav; McCollough, Michael; Soffitta, Paolo; Sunyaev, Rashid
Kustantaja: EDP Sciences
Julkaisuvuosi: 2024
Journal: Astronomy and Astrophysics
Tietokannassa oleva lehden nimi: Astronomy & Astrophysics
Artikkelin numero: L27
Vuosikerta: 688
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202451356
Verkko-osoite: http://dx.doi.org/10.1051/0004-6361/202451356
Rinnakkaistallenteen osoite: https://research.utu.fi/converis/portal/detail/Publication/457594616
Preprintin osoite: https://arxiv.org/abs/2407.02655
Cygnus X-3 is an enigmatic X-ray binary that is both an exceptional accreting system and a cornerstone for population synthesis studies. Prominent X-ray and radio properties follow a well-defined pattern, and yet the physical reasons for the state changes observed in this system are not known. Recently, the presence of an optically thick envelope around the central source in the hard state was revealed using the X-ray polarization data obtained with the Imaging X-ray Polarimetry Explorer (IXPE). In this work we analyse IXPE data obtained in the ultrasoft (radio quenched) state of the source. The average polarization degree (PD) of 11.9 ± 0.5% at a polarization angle (PA) of 94° ±1° is inconsistent with the simple geometry of the accretion disc viewed at an intermediate inclination. The high PD, the blackbody-like spectrum, and the weakness of fluorescent iron line imply that the central source is hidden behind the optically thick outflow, similar to the hard-state geometry, and its beamed radiation is scattered, by the matter located along the funnel axis, towards our line of sight. In this picture the observed PD is directly related to the source inclination, which we conservatively determine to lie in the range 26° < i < 28°. Using the new polarimetric properties, we propose a scenario that can be responsible for the cyclic behaviour of the state changes in the binary.
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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-2022-13-I.0, agreements ASI-INAF-2022-19-HH.0 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 research has been supported by the Academy of Finland grant 355672 (AV, VA) and the Vilho, Yrjö, and Kalle Väisälä foundation (SVF). ADM, FLM, EC, FM and PS are partially supported by MAECI with grant CN24GR08 “GRBAXP: Guangxi-Rome Bilateral Agreement for X-ray Polarimetry in Astrophysics”. AAZ acknowledges support from the Polish National Science Center grants 2019/35/B/ST9/03944, 2023/48/Q/ST9/00138, and from the Copernicus Academy grant CBMK/01/24. JPod and MD acknowledge the support from the Czech Science Foundation project GACR 21–06825X and the institutional support from the Astronomical Institute RVO:6798581.
