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arXiv · 2410.00972

X-ray spectro-polarimetric characterization of GX 340+0 in the horizontal branch: a highly inclined source?

Fabio La Monaca·Alessandro Di Marco·Renee M. Ludlam·Anna Bobrikova·Juri Poutanen·Songwei Li·Fei Xie
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Abstract

We report the first detection of X-ray polarization in the horizontal branch for GX 340+0 as obtained by Imaging X-ray Polarimetry Explorer (IXPE). A polarization degree of 4.3%$\pm$0.3% is obtained. This value is in agreement with the previous polarization measurements of Z-sources in the horizontal branch. Spectro-polarimetric analysis, performed using a broad-band spectral model obtained by NICER and NuSTAR quasi-simultaneous observations, allowed us to constrain the polarization for the soft and hard spectral components typical to these sources. The polarization angle for the two components differs by ${\sim}40{\deg}$. This result could be explained by a misalignment of the NS rotations axis with respect to the accretion disk axis. We provide a comparison of the results with polarization expected in different models. Theoretical expectations for the polarization of the disk and the Comptonization components favor an orbital inclination for GX 340+0 higher than 60{\deg}, as expected for Cyg-like sources, in contrast with results we report for the reflection component using broad-band spectrum.

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Fabio La Monaca, Alessandro Di Marco, Renee M. Ludlam, Anna Bobrikova, Juri Poutanen, Songwei Li, Fei Xie. 2024-10-01. X-ray spectro-polarimetric characterization of GX 340+0 in the horizontal branch: a highly inclined source?. https://doi.org/10.1051/0004-6361%2F202451966

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