Presentation #107.33 in the session Stellar/Compact Objects - Poster Session.
The Black Hole X-ray Binary (BHXRB) GX 339-4 went into a full outburst in 2021 that lasted for several months. This lead to a massive coordinated multi-wavelength observing campaign that caught the source at different Epochs during the duration of the outburst. Using the numerous data from the broadband NICER+NuSTAR coverage of the campaign, we followed the evolution of important spectral parameters as the source transitions from one state to another. These include the photon index, the temperature of the inner disk, the broad component of the Fe K α line and most importantly the disk inner radius - allowing us to probe the possible presence of a truncated disk especially in the hard state. The observations show strong relativistic reflection features that tend to evolve in relation to the illuminating X-ray flux over the course of the outburst.