We present an analysis of the first observation of the iconic High Mass X-ray Binary so with the chandra High Energy Transmission Gratings during an X-ray eclipse. The goal of the observation was to study the structure/physical conditions in the clumpy stellar wind through high resolution spectroscopy. We find that: a) emission line brightness from K shell transitions, corresponding to near neutral species, directly correlates with continuum illumination. However, these lines do not greatly diminish during eclipse. This is readily explained if fluorescence K$alpha$ emission comes from the bulk of the wind. b) The highly ionised Fexxv and Fexxvi Ly$alpha$ diminish during eclipse. Thus, they must be produced in the vicinity of the compact object where $log xi >3$. c) to describe the emission line spectrum, the sum of two self consistent photo ionisation models with low ionisation ($log xisim -1$) and high ionisation ($log xisim 2.4$) is required. From their emission measures, the clump-to-interclump density ratio can be estimated to be $n_c/n_isim 300$. To fit the complex He-like ion{Si}{xiii}{} profile, the plasma requires a broadening with $v_{rm bulk}sim 840$ km s$^{-1}$. Reproducing the observed $rapprox f$ line fluxes requires the addition of a third collisionally ionised plasma. d) Emission lines widths appear unresolved at the textsc{hetg} gratings resolution with exception of Silicon. There is no clear radial segregation between (quasi)neutral and ionised species, consistent with cold wind clumps interspersed in a hot rarefied interclump medium.
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