Probing the soft state evolution of 4U 1543-47 during its 2021 outburst using AstroSat

• DOI: 10.1093/mnras/stad2204
• Publication Date: 2023-07-25T21:40:48Z
• Authors: Nazma Husain; Yash Bhargava; Akash Garg; Sneha Prakash Mud...; Ranjeev Misra; Somasri Sen
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); 13. Climate action; FOS: Physical sciences; Astrophysics - High Energy Astrophysical Phenomena

ABSTRACT 4U 1543-47 underwent its brightest outburst in 2021 after two decades of inactivity. During its decay phase, AstroSat conducted nine observations of the source spanning from 2021 July 1 to September 26. The first three observations were performed with an offset of 40 arcmin with AstroSat/LAXPC, while the remaining six were on-axis observations. In this report, we present a comprehensive spectral analysis of the source as it was in the High/Soft state during the entire observation period. The source exhibited a disc-dominated spectra with a weak high-energy tail (power-law index ≥2.5) and a high inner disc temperature (∼0.84 keV). Modelling the disc continuum with non-relativistic and relativistic models, we find inner radius to be significantly truncated at >10 Rg. Alternatively, to model the spectral evolution with the assumption that the inner disc is at the innermost stable circular orbit, it is necessary to introduce variation in the spectral hardening in the range ∼1.5–1.9.