Resolving the X-ray obscuration in a low flux observation of the quasar
  PDS 456
  Simultaneous XMM-Newton, NuSTAR and HST observations, performed in March
2017, of the nearby ($z=0.184$) luminous quasar PDS 456 are presented. PDS 456
had a low X-ray flux compared to past observations, where the first of the two
new XMM-Newton observations occurred during a pronounced dip in the X-ray
lightcurve. The broad-band X-ray spectrum is highly absorbed, attenuated by a
soft X-ray absorber of column density $N_{\rm H}=6\times10^{22}$ cm$^{-2}$. An
increase in obscuration occurs during the dip, which may be due to an X-ray
eclipse. In addition, the persistent, fast Fe K outflow is present, with
velocity components of $-0.25c$ and $-0.4c$. The soft absorber is less ionized
($\log\xi=3$) compared to the iron K outflow ($\log\xi=5$) and is outflowing
with a velocity of approximately $-0.2c$. A soft X-ray excess is present below
1 keV against the highly absorbed continuum and can be attributed to the
re-emission from a wide angle wind. The complex X-ray absorption present in PDS
456 suggests that the wind is inhomogeneous, whereby the soft X-ray absorber
originates from denser clumps or filaments which may form further out along the
outflow. In contrast to the X-ray observations, the simultaneous UV spectrum of
PDS 456 is largely unabsorbed, where only a very weak broad absorption trough
is present bluewards of Ly$\alpha$, compared to a past observation in 2000 when
the trough was significantly stronger. The relative weakness of the UV
absorption may be due to the soft X-ray absorber being too highly ionized and
almost transparent in the UV band.
