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We present a spectral-variability analysis of the low-redshift quasar PDS 456using principal component analysis. In the XMM-Newton data, we find a strongpeak in the first principal component at the energy of the Fe absorption linefrom the highly blueshifted outflow. This indicates that the absorption featureis more variable than the continuum, and that it is responding to thecontinuum. We find qualitatively different behaviour in the Suzaku data, whichis dominated by changes in the column density of neutral absorption. In thiscase, we find no evidence of the absorption produced by the highly ionized gasbeing correlated with this variability. Additionally, we perform simulations ofthe source variability, and demonstrate that PCA can trivially distinguishbetween outflow variability correlated, anti-correlated, and un-correlated withthe continuum flux. Here, the observed anti-correlation between the absorptionline equivalent width and the continuum flux may be due to the ionization ofthe wind responding to the continuum. Finally, we compare our results withthose found in the narrow-line Seyfert 1 IRAS 13224-3809. We find that the Fe KUFO feature is sharper and more prominent in PDS 456, but that it lacks thelower energy features from lighter elements found in IRAS 13224-3809,presumably due to differences in ionization.

Using principal component analysis to understand the variability of PDS 456