X-ray polarimetry and spectroscopy of the neutron star low-mass X-ray binary GX 9+9: An in-depth study with IXPE and NuSTAR

0574442 - ASÚ 2024 RIV FR eng J - Journal Article
Ursini, F. - Farinelli, R. - Gnarini, A. - Dovčiak, Michal - Karas, Vladimír … Total 105 authors
X-ray polarimetry and spectroscopy of the neutron star low-mass X-ray binary GX 9+9: An in-depth study with IXPE and NuSTAR.
Astronomy & Astrophysics. Roč. 676, August (2023), č. článku A20. ISSN 0004-6361. E-ISSN 1432-0746
Institutional support: RVO:67985815
Keywords : accretion disks * neutron stars * polarization
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 6.5, year: 2022
Method of publishing: Open access

We report on a comprehensive analysis of simultaneous X-ray polarimetric and spectral data of the bright atoll source GX 9+9 with the Imaging X-ray Polarimetry Explorer (IXPE) and NuSTAR. The source is significantly polarized in the 4-8 keV band, with a degree of 2.2% , & PLUSMN,  , 0.5% (uncertainty at the 68% confidence level). The NuSTAR broad-band spectrum clearly shows an iron line, and is well described by a model including thermal disc emission, a Comptonized component, and reflection. From a spectro-polarimetric fit, we obtain an upper limit to the polarization degree of the disc of 4% (at the 99% confidence level), while the contribution of Comptonized and reflected radiation cannot be conclusively separated. However, the polarization is consistent with resulting from a combination of Comptonization in a boundary or spreading layer, plus reflection off the disc, which significantly contributes in any realistic scenario.
Permanent Link: https://hdl.handle.net/11104/0345569