Spectral evolution of NS binary system GX 349+2 using AstroSat observations
Abstract
We present a broadband spectral study of the Sco-like Z source GX 349+2 using AstroSat LAXPC and SXT observations obtained during 2019 and 2024. The X-ray light curves exhibit large variability, and the hardness-intensity diagram traces the characteristic Z-shaped track. Using hardness ratio and intensity, the Z-track is segmented into six regions comprising normal branch, soft apex, and an extended flaring branch. We perform simultaneous broadband spectral fitting in the energy range 0.7-25.0 keV using two model configurations, tbabs*(thcomp*bbodyrad+diskbb) and tbabs*(bbodyrad+thcomp*diskbb), to study the evolution of emission from the neutron-star boundary layer, accretion disk, and Comptonizing corona along the Z-track. The comparative analysis reveals that, irrespective of the adopted Comptonization geometry, the inferred inner disk radius remains large (~100 km) and exhibits no systematic inward motion as the source luminosity increases. This suggests that the accretion disk remains truncated and the disk luminosity tends to saturate, consistent with a radiation pressure influenced inner disk. The relatively small variation in the inferred mass accretion rate across the branches indicates that changes in Ṁ alone cannot account for the observed Z-track evolution. Instead, the boundary-layer component becomes progressively dominant toward the flaring branch, with both its temperature and flux increasing with total luminosity, while the relative contribution from the disk decreases. These results indicate a redistribution of accretion power toward the boundary layer and the associated Comptonizing region, suggesting that the primary energy dissipation in GX 349+2 occurs within the boundary layer region of the neutron star.
Related
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- JWST observations of the planetary nebula NGC 6302 IV: PAH spectral characteristics, formation and evolution
BibTeX
@misc{tyagi2026spectral,
title = {{Spectral evolution of NS binary system GX 349+2 using AstroSat observations}},
author = {Garima Tyagi and Suchismito Chattopadhyay and Sree Bhattacherjee and Akash Garg and Ranjeev Misra and Somasri Sen},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11787},
eprint = {2609.11787},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11787},
}
RIS
TY - UNPB
TI - Spectral evolution of NS binary system GX 349+2 using AstroSat observations
AU - Garima Tyagi
AU - Suchismito Chattopadhyay
AU - Sree Bhattacherjee
AU - Akash Garg
AU - Ranjeev Misra
AU - Somasri Sen
PY - 2026
DA - 2026/09/10
PB - arXiv
DO - 10.48550/arxiv.2609.11787
UR - https://arxiv.org/abs/2609.11787
AB - We present a broadband spectral study of the Sco-like Z source GX 349+2 using AstroSat LAXPC and SXT observations obtained during 2019 and 2024. The X-ray light curves exhibit large variability, and the hardness-intensity diagram traces the characteristic Z-shaped track. Using hardness ratio and intensity, the Z-track is segmented into six regions comprising normal branch, soft apex, and an extended flaring branch. We perform simultaneous broadband spectral fitting in the energy range 0.7-25.0 keV using two model configurations, tbabs*(thcomp*bbodyrad+diskbb) and tbabs*(bbodyrad+thcomp*diskbb), to study the evolution of emission from the neutron-star boundary layer, accretion disk, and Comptonizing corona along the Z-track. The comparative analysis reveals that, irrespective of the adopted Comptonization geometry, the inferred inner disk radius remains large (~100 km) and exhibits no systematic inward motion as the source luminosity increases. This suggests that the accretion disk remains truncated and the disk luminosity tends to saturate, consistent with a radiation pressure influenced inner disk. The relatively small variation in the inferred mass accretion rate across the branches indicates that changes in Ṁ alone cannot account for the observed Z-track evolution. Instead, the boundary-layer component becomes progressively dominant toward the flaring branch, with both its temperature and flux increasing with total luminosity, while the relative contribution from the disk decreases. These results indicate a redistribution of accretion power toward the boundary layer and the associated Comptonizing region, suggesting that the primary energy dissipation in GX 349+2 occurs within the boundary layer region of the neutron star.
ER -