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IXPE view of the Sco-like source GX 349+2 in the normal branch
INAF–Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere 100, 00133 Roma, Italy; Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Roma, Italy.
Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland.
Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland.
Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Barcelona, Spain, Campus UAB, Carrer de Can Magrans s/n; Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castelldefels (Barcelona), Spain, Barcelona; INAF–Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate (LC), Italy.
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2025 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 702, article id A40Article in journal (Refereed) Published
Abstract [en]

We present a detailed spectropolarimetric study of the Sco-like Z-source GX 349+2, simultaneously observed with the Imaging X-ray Polarimetry Explorer (IXPE) and Nuclear Spectroscopic Telescope Array (NuSTAR). During the observations, GX 349+2 was mainly found in the normal branch. A model-independent polarimetric analysis yields a polarisation degree of 1.1%±0.3% at a polarisation angle of 29° ±7° in the 2–8 keV band, with a ∼4.1σ confidence level significance. No variability of polarisation in time and flux has been observed, while an energy-resolved analysis shows a complex dependence of polarisation on energy, as confirmed by a spectropolarimetric analysis. Spectral modelling reveals a dominant disc blackbody component and a Comptonising emitting region, with evidence of a broad iron line associated with a reflection component. Spectropolarimetric fits suggest differing polarisation properties for the disc and Comptonised components, and slightly favour a spreading layer geometry. The polarisation of the Comptonised component exceeds the theoretical expectations but is in line with the results for other Z-sources with similar inclinations. A study of the reflection’s polarisation is also reported, with the polarisation degree ranging around 10% depending on the assumptions. Despite GX 349+2’s classification as a Sco-like source, these polarimetric results align more closely with the Cyg-like system GX 340+0 of similar inclination. This indicates that polarisation is primarily governed by accretion state and orbital inclination, rather than by the subclass to which the source belongs.

Place, publisher, year, edition, pages
EDP Sciences , 2025. Vol. 702, article id A40
Keywords [en]
accretion, accretion disks, polarization, stars: individual: GX 349+2, X-rays: binaries
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-372452DOI: 10.1051/0004-6361/202555647ISI: 001586589200001Scopus ID: 2-s2.0-105018484333OAI: oai:DiVA.org:kth-372452DiVA, id: diva2:2012146
Note

QC 20251107

Available from: 2025-11-07 Created: 2025-11-07 Last updated: 2025-11-07Bibliographically approved

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Veledina, Alexandra

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