A1 Vertaisarvioitu alkuperäisartikkeli tieteellisessä lehdessä
X-ray spectro-polarimetry analysis of the weakly magnetized neutron star X-ray binary GX 9+1
Tekijät: Tarana, A.; Capitanio, F.; Gnarini, A.; Fabiani, S.; Ursini, F.; Bianchi, S.; Ferrigno, C.; Parra, M.; Cocchi, M.; Farinelli, R.; Matt, G.; Soffitta, P.; Bobrikova, A.; Kaaret, P.; Ng, M.; Poutanen, J.; Ravi, S.
Kustantaja: EDP Sciences
Julkaisuvuosi: 2025
Journal: Astronomy and Astrophysics
Tietokannassa oleva lehden nimi: Astronomy & Astrophysics
Artikkelin numero: A245
Vuosikerta: 698
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202554083
Verkko-osoite: https://doi.org/10.1051/0004-6361/202554083
Rinnakkaistallenteen osoite: https://research.utu.fi/converis/portal/detail/Publication/499270234
We present an X-ray spectro-polarimetric study of the weakly magnetized neutron star low-mass X-ray binary GX 9+1, utilizing data from the Imaging X-ray Polarimetry Explorer (IXPE), alongside simultaneous NuSTAR, NICER, and INTEGRAL observations. GX 9+1, located in the Galactic bulge, is a persistently bright atoll source known for its spectral variability along the color–color diagram. Our spectral analysis during the soft state confirms that the emission is dominated by a soft blackbody and thermal Comptonization components, with no evidence of a hard X-ray tail. Moreover, these observations suggest a relatively low-inclination system (23° < i < 46°) with a weak reflection component, consistent with emission from the accretion disk and neutron star boundary layer. Spectro-polarimetric analysis reveals no significant polarization in the 2–8 keV range, with a 3σ level upper limit on the polarization degree of 1.9%. However, marginal evidence of polarization is detected in the 2–3 keV band at the 95.5% confidence level (2σ), suggesting potential contributions from scattering effects in the individual spectral components (disk, reflection, and Comptonization) that may cancel each other out due to the different orientations of their polarization angles. This behavior aligns with other atoll sources observed by IXPE, which typically exhibit lower and less variable polarization degrees compared to Z–class sources.
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Julkaisussa olevat rahoitustiedot:
This work reports observations obtained with the Imaging X-ray Polarimetry Explorer (IXPE), a joint US (NASA) and Italian (ASI) mission, led by Marshall Space Flight Center (MSFC). The research uses data products provided by the IXPE Science Operations Center (MSFC), using algorithms developed by the IXPE Collaboration, and distributed by the High-Energy Astrophysics Science Archive Research Center (HEASARC). AT, FC, and SF acknowledge financial support by the Istituto Nazionale di Astrofisica (INAF) grant 1.05.23.05.06: Spin and Geometry in accreting X-ray binaries: The first multi frequency spectro-polarimetric campaign. AG, FC, SB, SF, GM, PF and FU acknowledge financial support by the Italian Space Agency (Agenzia Spaziale Italiana, ASI) through the contract ASI-INAF-2022-19-HH.0. SF, PS have been also supported by the project PRIN 2022 - 2022LWPEXW - An X-ray view of compact objects in polarized light, CUP C53D23001180006. MN is a Fonds de Recherche du Quebec - Nature et Technologies (FRQNT) postdoctoral fellow. JP thanks the Academy of Finland grant 333112 for support. This research used data products and software provided by the IXPE, the NICER, and NuSTAR teams and distributed with additional software tools by the High-Energy Astrophysics Science Archive Research Center (HEASARC), at NASA Goddard Space Flight Center.
