tokens: to test its significance and simulating 500 CPSDs from the best-fit model, scattered around within the uncertainties of the measured CPSD, we find that a similar improvement in can occur by chance with probability. We therefore conclude that this feature is not significantly detected. 4. DISCUSSION We have presented time-resolved spectral and timing analysis of NuSTAR data of GX 339−4 , taken during a HIMS in early 2015. The time-resolved approach was necessary as the source was softening significantly over the course of the observation and at the same time the prominent type-C QPO increased in frequency. From the energy spectra we concluded that the accretion disk is truncated around 9 r g , independent of the assumed geometry. This value is larger than the ISCO for a spin of () or (), as measured by Parker et al. ( 2016 ) and Miller et al. ( 2008 ), respectively. We note that using the relativistic effects to constrain the inner radius of the accretion disk still has systematic uncertainties, as all available geometries are simple approximations, as discussed in F15 . Independent of these assumptions, the data show that within the uncertainties, the inner radius is not changing over the course of the observation, despite the observed changes in spectral hardness (Figure 5 (e)). Our best-fit model assumes that the power-law continuum incident on the reflector is harder than that observed as the underlying continuum. This configuration was invoked in F15 for the hard state and later confirmed by Parker et al. ( 2016 ) in a soft state observation, and indicates a complex geometry of the corona. Using this geometry, F15 found that the iron abundance is significantly reduced compared to other models. This is not the case in the observation presented here, and all models require an iron abundance around 4–5 solar, similar to the values found by Parker et al. ( 2016 ) and García et al. ( 2015 ), using NuSTAR and RXTE data, respectively. 4.1. Truncation of the Inner Accretion Disk Using relativistic reflection models, we find that the inner radius of the accretion disk is truncated significantly outside the ISCO, at around 9 r g . This result is independent of the assumed geometry, either a standard disk emissivity profile with an index of q = 3, or a lamppost geometry. This amount of truncation is similar to the one found by Tamura et al. ( 2012 ), assuming a black hole. This result indicates that the accretion disk does not move all the way to the ISCO before the source has entered the soft state. This seems to be at odds with results finding the accretion disk to be at the ISCO in bright hard states (e.g., Miller et al. 2015 ). On the other hand, it might simply show that different outbursts behave differently. It is in theory also possible that the truncation is not a strict function of luminosity, and truncation appears again during the HIMS, given its slightly different radiation balance at the accretion disk/corona boundary (e.g., a
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