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The black hole X-ray binary source 4U 1543--47 experienced a super-Eddingtonoutburst in 2021, reaching a peak flux of up to $\sim1.96\times10^{-7}\rm erg\\rm cm^{-2}\ \rm s^{-1}$ ($\sim 8.2$ Crab) in the 2--10\,keV band. Soon afterthe outburst began, it rapidly transitioned into the soft state. Our goal is tounderstand how the accretion disk structure deviates from a standard thin diskwhen the accretion rate is near Eddington. To do so, we analyzed spectraobtained from quasi-simultaneous observations conducted by the Hard X-rayModulation Telescope (Insight-HXMT), the Nuclear Spectroscopic Telescope Array(NuSTAR), and the Neil Gehrels Swift Observatory (Swift). These spectra arewell-fitted by a model comprising a disk, a weak corona, and a reflectioncomponent. We suggest that the reflection component is caused by diskself-irradiation, that is by photons emitted from the inner disk which returnto the accretion disk surface, as their trajectories are bent by the stronggravity field. In this scenario, the best-fitting parameters imply that thereflected flux represents more than half of the total flux. Using generalrelativistic ray-tracing simulations, we show that this scenario is viable whenthe disk becomes geometrically thick, with a funnel-like shape, as theaccretion rate is near or above the Eddington limit. In the specific case of 4U1543--47, an angle $\gtrsim$ 45 deg between the disk surface and the equatorialplane can explain the required amount of self-irradiation.

The bright black hole X-ray binary 4U 1543--47 during 2021 outburst: a thick accretion disk inflated by high luminosity