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arXiv · 2401.15367

AstroSat and NICER timing view of the Z-type Neutron Star X-ray binary GX 340+0

Mayukh Pahari·Shree Suman·Yash Bhargava·Alexander Weston·Liang Zhang·Sudip Bhattacharyya·Ranjeev Misra·Ian McHardy
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Abstract

The timing properties of the Z-type low-mass X-ray binaries provide insights into the emission components involved in producing the unique Z-shaped track in the hardness-intensity diagrams of these sources. In this work, we investigate the AstroSat and NICER observations of the GX 340+0 covering the complete 'Z'-track from the horizontal branch (HB) to the extended flaring branch (EFB). For the first time, we present the Z-track as seen in soft X-rays using the AstroSat/SXT and NICER (the soft colour is defined as a ratio of 3-6 keV to 0.5-3 keV). The shape of the track is distinctly different in soft X-rays, strongly suggesting the presence of additional components active in soft X-rays. The detailed timing analysis revealed significant quasi-periodic oscillation throughout the HB and the normal branch (NB) using LAXPC and the first NICER detection of 33.1 +/- 1.1 Hz horizontal branch oscillation (HBO) in 3-6 keV. The oscillations at the HB/NB vertex are observed to have higher frequencies (41-52 Hz) than the HB oscillations (16-31 Hz) and NB oscillations (6.2-8 Hz) but significantly lower rms (~1.6%). The HB oscillation is also limited to the energy range of 3-20 keV, indicating an association of HBO origin with the non-thermal component. It is also supported by earlier studies that found the strongest X-ray polarisation during HB.

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Mayukh Pahari, Shree Suman, Yash Bhargava, Alexander Weston, Liang Zhang, Sudip Bhattacharyya, Ranjeev Misra, Ian McHardy. 2024-01-27. AstroSat and NICER timing view of the Z-type Neutron Star X-ray binary GX 340+0. https://arxiv.org/abs/2401.15367

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