Work

Spectral evolution of NS binary system GX 349+2 using AstroSat observations

Year: 2026

Type: article

Abstract: 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 disc, and Comptonizing corona along the Z-track. The comparative analysis reveals that, irrespective of the adopted Comptonization geometry, the inferred inner disc radius remains large ($\sim$100 km) and exhibits no systematic inward motion as the source luminosity increases. This suggests that the accretion disc remains truncated and the disc luminosity tends to saturate, consistent with a radiation pressure-influenced inner disc. The relatively small variation in the inferred mass accretion rate across the branches indicates that changes in $\dot{M}$ alone cannot account for the observed Z-track evolution. Instead, the boundary-layer component becomes progressively dominant towards the flaring branch, with both its temperature and flux increasing with total luminosity, while the relative contribution from the disc decreases. These results indicate a redistribution of accretion power towards 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.

Source: Monthly Notices of the Royal Astronomical Society

DOI: 10.1093/mnras/stag1735

Authors: Garima Tyagi, Suchismito Chattopadhyay, Sree Bhattacherjee, Akash Garg, Ranjeev Misra, Somasri Sen

Institutions: Jamia Millia Islamia, Inter-University Centre for Astronomy and Astrophysics, Tezpur University

Language: English

Topic: Astrophysical Phenomena and Observations

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $3,046

Funders: Inspire Foundation, Tata Institute of Fundamental Research, Department of Science and Technology, Ministry of Science and Technology, India, Department of Science and Technology, Government of Kerala