Spectro-temporal investigation of the black hole X-ray transient 4U 1543-475 during the 2021 outburst

TL;DR

This study provides a detailed spectro-temporal analysis of the 2021 outburst of black hole binary 4U 1543-475, revealing state transitions, variability components, and disk-corona interactions through AstroSat observations.

Contribution

It offers new insights into the variability evolution and flip-flop phenomena in black hole X-ray binaries during outbursts, emphasizing the roles of disk and coronal changes.

Findings

Emergence of band-limited noise during state transition

Correlation between low-frequency variability and non-thermal component

Detection of flip-flop phenomenon with rapid flux and RMS variation

Abstract

We report a detailed spectro-temporal analysis of the black hole (BH) low mass X-ray binary (LMXB) 4U 1543-475 during its 2021 outburst using the data from LAXPC (Large Area X-ray Proportional Counters) and SXT (Soft X-ray Telescope) instrument on board AstroSat. We investigate the energy and frequency dependency of the source variability to probe the origin of the disc/coronal fluctuations. Following the state transition (from soft to intermediate state), the emergence of a band-limited noise (BLN) component is observed along with the power law noise (PLN) when the disk is recovering from a sudden decrease in the inner disk radius. A possible correlation between the low-frequency variability amplitude (RMS) and the covering fraction of the non-thermal component is detected. During the final AstroSat observation, a flip-flop phenomenon is reported, where rapid variation in RMS occurs in concurrence with sudden flux transition. An indication of the evolution of inner disk temperature along with a significant change in thermal flux was observed during the flip-flop phase, arguing for a disk instability-driven origin for this phenomenon. Our results suggest that the long-term variability evolution is primarily affected by the coronal changes, whereas the disk behavior governs the short-term variability evolution.