| Abstract : | We report a detailed broadband timing and spectral study of the black hole low mass X-ray binary (LMXB) 4U 1543-475 using the data from SXT (Soft X-ray Telescope) and LAXPC (Large Area X-ray Proportional Counters) instruments on board AstroSat during its 2021 outburst. AstroSat observed the source over seven epochs during the decaying phase of the outburst. The hardness intensity diagram of LAXPC and MAXI exhibits the evolution of the spectral state during this outburst. For most of the AstroSat observations, the source was observed to be in softer states. We performed the spectral analysis of the AstroSat observations and found the source spectra to be best described by a combination of a thermal multicolored disk model and a non-thermal power-law model. We observed a decrease in inner disk temperature (1.02 keV to 0.95 keV) with decreasing flux. The source moved towards a non-thermally dominated state with increasing Comptonization efficiency during final epochs. We conducted power spectral analysis for all seven observations to estimate the variability of the disk and corona. The integrated RMS changed drastically for the first three observations, followed by the lowest variability in the 4th and 5th observations, and finally, it again increased for the last two observations. The increase of non-thermal flux at the 6th observation, along with the sudden change in RMS variability, implies that the corona is the major contributor to the variability in this epoch. We examined the energy dependence of the variability components to probe their correlation with the radiative counterparts. The variation of the temporal and spectral parameters indicates a spectral state transition between the sixth and seventh epochs, possibly from a soft intermediate state. This work sheds light on the evolution of disk and corona components during the decaying outburst phase of black hole LMXBs. |
