NuSTAR (blue circles: module A; red triangles: module B) spectra of J17407 during the high luminosity state (i.e., flares; red triangles in Fig. 3). Top panel: spectra are fitted with two power law, both absorbed, one of them with a high-energy cutoff. Middle panel: residuals of the same fit of the top panel. Bottom panel: residuals of the fit of the spectra with an absorbed power law. The purpose of this panel is to highlight the presence of a feature in the residuals at ∼8.6 keV, which requires the use of a more complex model, as described in Sect. 3.2. See Table 2 for the best-fit parameters, also with other spectral models.