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tokens: spectrum, using tbnew with the spectral fit parameters. Plainly this severely limits the sensitivity of these data, but we note that lower absorption columns for other objects may make this more visible [e.g. MAXI J1820 + 070 in Kara et al. ( 2019 ), where the column is only 1.5 × 10 21 cm −2 ]. Figure 11. The effect upon the overall thermal spectrum of considering the additional emission produced by the turbulent disc region. The red solid line denotes the xspec diskbb spectrum using parameters of Table 1 . The blue solid line denotes a bbodyrad spectrum with the same temperature as the diskbb component, but with of the power, inferred from the fit parameter of . The black solid line denotes the sum of these two components. The black dashed line denotes the absorbed total spectrum. We see that, when absorption is accounted for, the difference in shape arising from the bbodyrad component is inconsequential for the observable energy range. Placing our resultant truncation radius in the context of other studies, the same NuSTAR data set is fit by Wang-Ji et al. ( 2018 ) as ‘Obs 1 2015’, though they use the simultaneous Swift XRT data to extend this down to lower energies rather than the higher signal-to-noise ratio (but possibly worse cross-calibrated) XMM–Newton data. They fit the time-averaged spectrum with a simpler continuum model, with only a single-Compton component (rather than two as used here). Their derived relativistic smearing requires a disc with extreme iron overabundance that extends down to around 2.5 R g , an order of magnitude smaller than the radius derived here. If we remove one of our Compton continua, we find a similar fit from our XMM–Newton data, which also requires an extreme iron overabundance of A Fe = 8.67, and a small innermost disc radius of 2.69 R g (for details see Appendix B ). This fit is considerably worse (combined Δχ 2 > 300) than the two-Compton continuum model used in our spectral fits, where the reflection spectrum is solar abundance, and arises from a disc with an inner radius of 30 R g . This shows that the inferred relativistic smearing is highly sensitive to the assumed continuum shape. Here, we model only the first observation of this observing run (O1), and we set the spectral components in the timing section from fitting to the time-averaged spectral data alone. In future work, we will extend the modelling framework to fit to the later observations in this run (O2, O3, O4 of DM17 , with ObsIDs 0760646301, 0760646401, 0760646501, respectively), where the source has declined further into the hard state. To this end, we aim to develop a fully integrated fitting procedure, in which the spectral data are fit iteratively with the cross-spectrum, in order to close the loop when determining the shape of the underlying spectral components of the timing model. 11 CONCLUSIONS In MD18a / b , we developed a model for the spectral-timing properties of accreting hard-state black hole binaries, whereby