The variable, fast soft X-ray wind in PG 1211+143
  The analysis of a series of seven observations of the nearby ($z=0.0809$)
QSO, PG 1211+143, taken with the Reflection Grating Spectrometer (RGS) on-board
XMM-Newton in 2014, are presented. The high resolution soft X-ray spectrum,
with a total exposure exceeding 600 ks, shows a series of blue-shifted
absorption lines, from the He and H-like transitions of N, O and Ne, as well as
from L-shell Fe. The strongest absorption lines are all systematically
blue-shifted by $-0.06c$, originating in two absorption zones, from low and
high ionization gas. Both zones are variable on timescales of days, with the
variations in absorber opacity effectively explained by either column density
changes or by the absorber ionization responding directly to the continuum
flux. We find that the soft X-ray absorbers probably exist in a two-phase wind,
at a radial distance of $10^{17}-10^{18}$ cm from the black hole, with the
lower ionization gas as denser clumps embedded within a higher ionization
outflow. The overall mass outflow rate of the soft X-ray wind may be as high as
$2{\rm M}_{\odot}$ yr$^{-1}$, close to the Eddington rate for PG 1211+143 and
similar to that previously deduced from the Fe K absorption.
