Variability of the High Velocity Outflow in the Quasar PDS 456

We present a comparison of two Suzaku X-ray observations of the nearby (z=0.184), luminous ($L_{bol} \sim 10^{47}$ erg s$^{-1}$) type I quasar, PDS456. A new 125ks Suzaku observation in 2011 caught the quasar during a period of low X-ray flux and with a hard X-ray spectrum, in contrast to a previous 190ks Suzaku observation in 2007 when the quasar appeared brighter and had a steep ($\Gamma>2$) X-ray spectrum. The 2011 X-ray spectrum contains a pronounced trough near 9\,keV in the quasar rest frame, which can be modeled with blue-shifted iron K-shell absorption, most likely from the He and H-like transitions of iron. The absorption trough is observed at a similar rest-frame energy as in the earlier 2007 observation, which appears to confirm the existence of a persistent high velocity wind in PDS 456, at an outflow velocity of $0.25-0.30$c. The spectral variability between 2007 and 2011 can be accounted for by variations in a partial covering absorber, increasing in covering fraction from the brighter 2007 observation to the hard and faint 2011 observation. Overall the low flux 2011 observation can be explained if PDS 456 is observed at relatively low inclination angles through a Compton thick wind, originating from the accretion disk, which significantly attenuates the X-ray flux from the quasar.