  We analysed data from five XMM-Newton observations of GX 13+1 to investigate
the variability of the photo-ionised absorber present in this source. We fitted
EPIC and RGS spectra obtained from the "least-variable" intervals with a model
consisting of disc-blackbody and blackbody components together with a Gaussian
emission feature at ~6.55-6.7 keV modified by absorption due to cold and
photo-ionised material. We found a significant correlation between the hard,
~6-10 keV, flux, the ionisation and column density of the absorber and the
equivalent width of the broad iron line. We interpret the correlation in a
scenario in which a disc wind is thermally driven at large, ~10^{10} cm, radii
and the broad line results from reprocessed emission in the wind and/or hot
atmosphere. The breadth of the emission line is naturally explained by a
combination of scattering, recombination and fluorescence processes. We
attribute the variations in the absorption and emission along the orbital
period to the view of different parts of the wind, possibly located at slightly
different inclination angles. We constrain the inclination of GX 13+1 to be
between 60 and 80 degrees from the presence of strong absorption in the line of
sight, that obscures up to 80% of the total emission in one observation, and
the absence of eclipses. We conclude that the presence of a disc wind and/or a
hot atmosphere can explain the current observations of narrow absorption and
broad iron emission features in neutron star low mass X-ray binaries as a
class.
