Evolution of the 0.5−10 keV flux, hardness, and main spectral parameters over the course of the 2021 outburst. The left panel shows the evolution over time and the right panel shows how these parameters depend on luminosity. The orange data points in the left panel represent the light curve over the course of the outburst. The hardness is defined as (H − S)/(H + S) where H is the count rate in the 0.5−2 keV band and where S is the count rate in the 2−10 keV band. Each point corresponds to one observation.