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arXiv · 2409.11875

Modelling the Energy-dependent broadband variability in the black-hole transient GX 339-4 using Astrosat and NICER

Hitesh Tanenia·Akash Garg·Ranjeev Misra·Somasri Sen
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Abstract

We present a spectro-timing analysis of the black hole X-ray transient GX 339-4 using simultaneous observations from Astrosat and NICER during the 2021 outburst period. The combined spectrum obtained from NICER, LAXPC, and SXT data is effectively described by a model comprising a thermal disk component, hard Comptonization component, and reflection component with an edge. Our analysis of the Astrosat and NICER spectra indicates the source to be in a low/hard state, with a photon index of ~1.64. The Power Density Spectra (PDS) obtained from both Astrosat and NICER observations exhibit two prominent broad features at 0.22 Hz and 2.94 Hz. We generated energy-dependent time lag and fractional root mean square (frms) at both frequencies in a broad energy range of 0.5-30 keV and found the presence of hard lags along with a decrease in variability at higher energy levels. Additionally, we discovered that the correlated variations in accretion rate, inner disc radius, coronal heating rate, and the scattering fraction, along with a delay between them, can explain the observed frms and lag spectra for both features.

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Hitesh Tanenia, Akash Garg, Ranjeev Misra, Somasri Sen. 2024-09-18. Modelling the Energy-dependent broadband variability in the black-hole transient GX 339-4 using Astrosat and NICER. https://arxiv.org/abs/2409.11875

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