Evidence fora slim accretion disc in GX 17+2: a polarimetric study of super-Eddington flows
accretion, accretion discs; polarization; stars: neutron; X-rays: binaries; X-rays: individual: GX 17+2
This study presents a time-resolved spectro-polarimetric analysis of GX 17+2 using IXPE, NICER, and NuSTAR observations. Spectral modelling with (Formula presented) (Formula presented) (Formula presented) (Formula presented) (Formula presented) (Formula presented) (Formula presented) (Formula presented) (Formula presented) ) indicates that the source was in a soft spectral state, and accreting at super-Eddington luminosity. Time-resolved PCUBE analysis shows that the polarization degree (PD) and polarization angle (PA) remain nearly constant across the 2.0(Formula presented) 8.0?keV energy range, suggesting an aligned geometry between the spin and the binary orbital axes of the neutron star. Energy-resolved PCUBE analysis further indicates that the blackbody emission component most likely originates from the boundary layer. The spectro-polarimetric analysis confirms that the reflected emission contributes a PD <20per?cent, consistent with theoretical expectations. In contrast, the Comptonizing medium exhibits a PD of (Formula presented) 1.4per?cent, while the accretion disc shows a PD of (Formula presented) 3.2per?cent in the 2.0(Formula presented) 8.0?keV energy range, exceeding theoretical predictions. Energy-resolved spectro-polarimetric analysis hints at excess disc polarization, possibly associated with the formation of a slim disc and the presence of disc wind under super-Eddington accretion conditions. Both time- and energy-resolved polarization measurements reveal a rotation of the PA for the (Formula presented) and (Formula presented) components in the 3.5(Formula presented) 8.0?keV energy range, suggesting a coupling between the soft and hard polarized emission components. Our results indicate that while the geometry of GX 17+2 is aligned, the emergent hard X-ray emission is significantly influenced by inner disc outflows. The nearly constant PD across energy and time further points to a complex interplay among the accretion disc, Comptonization, and reflection components. The Author(s) 2026. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Lavanya, S.; Thomas, Neal Titus; Gudennavar, S.B.; Bubbly, S.G.
Monthly Notices of the Royal Astronomical Society;Volume;549;Issue;2;Article No.;stag900;
https://doi.org/10.1093/mnras/stag900 https://www.scopus.com/pages/publications/105039995953?origin=resultslist
Lavanya S., Department of Physics and Electronics, CHRIST University, Karnataka, Bengaluru, 560029, India; Thomas N.T., Department of Physics and Electronics, CHRIST University, Karnataka, Bengaluru, 560029, India; Gudennavar S.B., Department of Physics and Electronics, CHRIST University, Karnataka, Bengaluru, 560029, India; Bubbly S.G., Department of Physics and Electronics, CHRIST University, Karnataka, Bengaluru, 560029, India