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We present spectral analysis of five NuSTAR and Swift observations of GX339-4 taken during a failed outburst in summer 2013. These observations coverEddington luminosity fractions in the range ~0.9-6%. Throughout this outburst,GX 339-4 stayed in the hard state, and all five observations show similar X-rayspectra with a hard power-law with a photon index near 1.6 and significantcontribution from reflection. Using simple reflection models we findunrealistically high iron abundances. Allowing for different photon indices forthe continuum incident on the reflector relative to the underlying observedcontinuum results in a statistically better fit and reduced iron abundances.With a photon index around 1.3, the input power-law on the reflector issignificantly harder than that which is directly observed. We study theinfluence of different emissivity profiles and geometries and consistently findan improvement when using separate photon indices. The inferred inner accretiondisk radius is strongly model dependent, but we do not find evidence for atruncation radius larger than 100 r_g in any model. The data do not allowindependent spin constraints but the results are consistent with the literature(i.e., a>0). Our best-fit models indicate an inclination angle in the range40-60 degrees, consistent with limits on the orbital inclination but higherthan reported in the literature using standard reflection models. The iron linearound 6.4 keV is clearly broadened, and we detect a superimposed narrow coreas well. This core originates from a fluorescence region outside the influenceof the strong gravity of the black hole and we discuss possible geometries.

The complex accretion geometry of GX 339-4 as seen by NuSTAR and Swift