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arXiv · 2307.13979

AstroSat view of the neutron star low-mass X-ray binary GX 340+0

Yash Bhargava·Sudip Bhattacharyya·Jeroen Homan·Mayukh Pahari
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Abstract

Understanding the spectral evolution along the `Z'-shaped track in the hardness-intensity diagram of Z-sources, which are a class of luminous neutron star low-mass X-ray binaries, is crucial to probe accretion processes close to the neutron star. Here, we study the horizontal branch (HB) and the normal branch (NB) of the Z source GX 340+0 using $AstroSat$ data. We find that the HB and the NB appear as two different types of X-ray intensity dips, which can appear in any sequence and with various depths. Our $0.8-25$ ~keV spectra of dips and the hard apex can be modeled by the emissions from an accretion disk, a Comptonizing corona covering the inner disk, and the neutron star surface. We find, as the source moves onto the HB the corona is replenished and energized by the disk and a reduced amount of disk matter reaches the neutron star surface. We also conclude that quasi-periodic oscillations during HB/NB are strongly associated with the corona, and explain the evolution of strength and hard-lag of this timing feature using the estimated coronal optical depth evolution.

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Yash Bhargava, Sudip Bhattacharyya, Jeroen Homan, Mayukh Pahari. 2023-07-26. AstroSat view of the neutron star low-mass X-ray binary GX 340+0. https://doi.org/10.3847/1538-4357%2Facee7a

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