Time-resolved SALT spectra of the short-period , dipping X-ray transient , Swift J1357.2-0933 , during its 2017 outburst has revealed broad Balmer and HeII \lambda 4686 absorption features , blue-shifted by \sim 600 km s ^ { -1 } .
Remarkably these features are also variable on the \sim 500s dipping period , indicating their likely association with structure in the inner accretion disc .
We interpret this as arising in a dense , hot ( \gtrsim 30 , 000 K ) outflowing wind seen at very high inclination , and draw comparisons with other accretion disc corona sources .
We argue against previous distance estimates of 1.5 kpc and favour a value \gtrsim 6 kpc , implying an X-ray luminosity L _ { X } \gtrsim 4 \times 10 ^ { 36 } erg s ^ { -1 } .
Hence it is not a very faint X-ray transient .
Our preliminary 1D Monte-Carlo radiative transfer and photoionization calculations support this interpretation , as they imply a high intrinsic L _ { X } , a column density N _ { H } \gtrsim 10 ^ { 24 } cm ^ { -2 } and a low covering factor for the wind .
Our study shows that Swift J1357.2-0933 is truly remarkable amongst the cohort of luminous , galactic X-ray binaries , showing the first example of HeII \lambda 4686 absorption , the first ( and only ) variable dip period and is possibly the first black hole ‘ accretion disc corona ’ candidate .