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

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2306.02740.pdf (777.93 KB)

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https://arxiv.org/abs/2306.02740

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https://doi.org/10.48550/arXiv.2306.02740
 http://hdl.handle.net/11603/28264

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
UMBC Faculty Collection

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Author/Creator ORCID

https://orcid.org/0000-0002-6548-5622

Date

2023-06-05

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journal articles
preprints
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Citation of Original Publication

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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
Public Domain Mark 1.0

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Abstract

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% ± 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 disk emission, a Comptonized component, and reflection. From a spectro-polarimetric fit, we obtain an upper limit to the polarization degree of the disk of 4% (at 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 gives a significant contribution in any realistic scenario.