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@ARTICLE{Stiele:1008421,
      author       = {Stiele, H. and Kong, A. K. H.},
      title        = {{A} journey from the hard to the soft state: {H}ow do
                      {QPO}s evolve in the 2021 outburst of {GX} 339–4?},
      journal      = {Monthly notices of the Royal Astronomical Society},
      volume       = {522},
      number       = {1},
      issn         = {0035-8711},
      address      = {Oxford},
      publisher    = {Oxford Univ. Press},
      reportid     = {FZJ-2023-02333},
      pages        = {268 - 274},
      year         = {2023},
      abstract     = {We investigated the snapshots of five NICER observations of
                      the black hole transient GX 339–4 when the source
                      transited from the hard state into the soft state during its
                      outburst in 2021. In this paper, we focused our study on the
                      evolution of quasi-periodic oscillations (QPOs) and noise
                      components using power-density spectra. In addition, we
                      derived hardness ratios by comparing count rates above and
                      below 2 keV. The evolution from the hard to the soft state
                      was a somewhat erratic process, showing several transitions
                      between states that are dominated by top-flat noise and can
                      show type-C QPOs; those that are dominated by red noise and
                      can show type-B QPOs. From the parameters that we studied,
                      we only found a strong correlation between the hardness
                      ratio and the type of QPO observed. This implies that the
                      appearance of type-B QPOs is related to a change in the
                      accretion geometry of the system that also reflects in
                      altered spectral properties. We also observed that the
                      type-B QPO forms from or disintegrates into a broad peaked
                      feature when the source comes out of or goes to the hard
                      intermediate state, respectively. This implies some strong
                      decoherence in the process that creates this feature.},
      cin          = {JSC},
      ddc          = {520},
      cid          = {I:(DE-Juel1)JSC-20090406},
      pnm          = {5111 - Domain-Specific Simulation $\&$ Data Life Cycle Labs
                      (SDLs) and Research Groups (POF4-511)},
      pid          = {G:(DE-HGF)POF4-5111},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000991993800005},
      doi          = {10.1093/mnras/stad969},
      url          = {https://juser.fz-juelich.de/record/1008421},
}