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arXiv · 2401.02658

Correlated spectro-polarimetric study along the Z track in XTE J1701-462 puts constraints on its coronal geometry

Wei Yu·Qingcui Bu·Victor Doroshenko·Lorenzo Ducci·Long Ji·Wenda Zhang·Andrea Santangelo·Shuangnan Zhang·Anand Waghmare·Mingyu Ge·Yue Huang·Hexin Liu·Lian Tao·Zixu Yang·Liang Zhang·Jinlu Qu
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Abstract

Context. In September 2022, the transient neutron star low-mass X-ray binary XTE J1701-462 went into a new outburst. Aims. The objective of this work is to examine the evolution of the accretion geometry of XTE J1701-462 by studying the spectro-polarimetric properties along the Z track of this source. The simultaneous observations archived by the Insight-Hard X-ray Modulation Telescope (HXMT) and the Imaging X-ray Polarimetry Explorer (IXPE) give us the opportunity. Methods. We present a comprehensive X-ray spectro-polarimetric analysis of XTE J1701-462, using simultaneous observations from IXPE, Insight-HXMT and NuSTAR. For IXPE observations, two methods are employed to measure the polarization: a model-independent measurement with PCUBE and a model-dependent polarization-spectral analysis with XSPEC. The corresponding spectra from Insight-HXMT and NuSTAR are studied with two configurations that correspond to a slab-like corona and a spherical shell-like corona, respectively. Results. Significant polarization characteristics are detected in XTE J1701-462. The polarization degree shows a decreasing trend along the Z track, reducing from (4.84 $\pm$ 0.37)% to (3.76 $\pm$ 0.43)% on the horizontal branch and jumping to less than 1% on the normal branch. The simultaneous spectral analysis from Insight-HXMT and NuSTAR suggests that the evolution of the PD is closely linked to changes in the flux of the Comptonized component and its covering factor along the Z track, supporting a shrinking corona.

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Wei Yu, Qingcui Bu, Victor Doroshenko, Lorenzo Ducci, Long Ji, Wenda Zhang, Andrea Santangelo, Shuangnan Zhang, Anand Waghmare, Mingyu Ge, Yue Huang, Hexin Liu, Lian Tao, Zixu Yang, Liang Zhang, Jinlu Qu. 2025-02-13. Correlated spectro-polarimetric study along the Z track in XTE J1701-462 puts constraints on its coronal geometry. https://doi.org/10.1051/0004-6361%2F202349041

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