Fabiani, S;
Capitanio, F;
Iaria, R;
Gnarini, A;
Ursini, F;
Farinelli, R;
Bobrikova, A;
... Slane, P; + view all
(2024)
Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5−1.
Astronomy and Astrophysics
, 684
, Article A137. 10.1051/0004-6361/202347374.
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Abstract
We report on the coordinated observations of the neutron star low-mass X-ray binary (NS-LMXB) GX 5-1 in X-rays (IXPE, NICER, NuSTAR, and INTEGRAL), optical (REM and LCO), near-infrared (REM), mid-infrared (VLT VISIR), and radio (ATCA). This Z-source was observed by IXPE twice in March-April 2023 (Obs. 1 and 2). In the radio band the source was detected, but only upper limits to the linear polarization were obtained at a 3σ level of 6.1% at 5.5 GHz and 5.9% at 9 GHz in Obs. 1 and 12.5% at 5.5 GHz and 20% at 9 GHz in Obs. 2. The mid-IR, near-IR, and optical observations suggest the presence of a compact jet that peaks in the mid-or far-IR. The X-ray polarization degree was found to be 3:7% ± 0:4% (at 90% confidence level) during Obs. 1 when the source was in the horizontal branch of the Z-Track and 1:8% ± 0:4% during Obs. 2 when the source was in the normal-flaring branch. These results confirm the variation in polarization degree as a function of the position of the source in the color-color diagram, as for previously observed Z-Track sources (Cyg X-2 and XTE 1701-462). Evidence of a variation in the polarization angle of ∼20° with energy is found in both observations, likely related to the different, nonorthogonal polarization angles of the disk and Comptonization components, which peak at different energies.
| Type: | Article |
|---|---|
| Title: | Discovery of a variable energy-dependent X-ray polarization in the accreting neutron star GX 5−1 |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1051/0004-6361/202347374 |
| Publisher version: | http://dx.doi.org/10.1051/0004-6361/202347374 |
| Language: | English |
| Additional information: | Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication. |
| Keywords: | Accretion, accretion disks – stars: neutron – X-rays: binaries – X-rays: general – X-rays: individuals: GX 5−1 |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10191914 |
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