Wideband study of the brightest black hole X-ray binary 4U 1543−47 in the 2021 outburst: signature of disc-wind regulated accretion

ABSTRACT A comprehensive wideband spectral analysis of the brightest black hole X-ray binary 4U 1543−47 during its 2021 outburst is carried out for the first time using NICER, NuSTAR, and AstroSat observations by phenomenological and reflection modelling. The source attains a super-Eddington peak luminosity and remains in the soft state, with a small fraction (3{\ per\ cent}) of the inverse-Comptonized photons. The spectral modelling reveals a steep photon index (Γ ∼ 2–2. 6) and relatively high inner disc temperature (Tin ∼ 0. 9–1. 27 keV). The line-of-sight column density varies between (0. 45–0. 54) × 1022 cm−2. Reflection modelling using the RELXILL model suggests that 4U 1543−47 is a low-inclination system (θ ∼ 32°–40°). The accretion disc is highly ionized (log ξ 3) and has super solar abundance (3. 6–10 AFe, ⊙) over the entire period of study. We detected a prominent dynamic absorption feature between ∼8 and 11 keV in the spectra throughout the outburst. This detection is the first of its kind for X-ray binaries. We infer that the absorption of the primary X-ray photons by the highly ionized, fast-moving disc winds can produce the observed absorption feature. The phenomenological spectral modelling also shows the presence of a neutral absorption feature ∼7. 1–7. 4 keV, and both ionized and neutral absorption components follow each other with a delay of a typical viscous time-scale of 10–15 d.