First Detection of X-Ray Polarization from the Accreting Neutron Star 4U 1820-303

0576952 - ASÚ 2024 RIV US eng J - Journal Article
Di Marco, A. - La Monaca, F. - Poutanen, J. - Dovčiak, Michal - Karas, Vladimír … Total 120 authors
First Detection of X-Ray Polarization from the Accreting Neutron Star 4U 1820-303.
Astrophysical Journal Letters. Roč. 953, č. 2 (2023), č. článku L22. ISSN 2041-8205. E-ISSN 2041-8213
Institutional support: RVO:67985815
Keywords : low-mass x-ray binary stars * neutron stars * polarimetry
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 7.9, year: 2022
Method of publishing: Open access

This paper reports the first detection of polarization in the X-rays for atoll-source 4U 1820-303, obtained with the Imaging X-ray Polarimetry Explorer (IXPE) at 99.999% confidence level (CL). Simultaneous polarimetric measurements were also performed in the radio with the Australia Telescope Compact Array. The IXPE observations of 4U 1820-303 were coordinated with Swift X-ray Telescope, Neutron Star Interior Composition Explorer, and Nuclear Spectroscopic Telescope Array aiming to obtain an accurate X-ray spectral model covering a broad energy interval. The source shows a significant polarization above 4 keV, with a polarization degree of 2.0% & PLUSMN, 0.5% and a polarization angle of 55 & DEG, & PLUSMN, 7 & DEG, in the 4-7 keV energy range, and a polarization degree of 10% & PLUSMN, 2% and a polarization angle of67 & DEG, & PLUSMN, 7 & DEG, in the 7-8 keV energy bin. This polarization also shows a clear energy trend with polarization degree increasing with energy and a hint for a position-angle change of & SIME, 90 & DEG, at 96% CL around 4 keV. The spectro-polarimetric fit indicates that the accretion disk is polarized orthogonally to the hard spectral component, which is presumably produced in the boundary/spreading layer. We do not detect linear polarization from the radio counterpart, with a 3 & sigma, upper limit of 50% at 7.25 GHz.
Permanent Link: https://hdl.handle.net/11104/0347226