A Massive X-ray Outflow from the Quasar PDS 456

We report on XMM-Newton spectroscopic observations of the luminous radio-quiet quasar PDS 456. The hard X-ray spectrum of PDS 456 shows a deep absorption trough (constituting 50% of the continuum) at energies above 7 keV in the quasar rest frame, which can be attributed to a series of blueshifted K-shell absorption edges due to highly ionized iron. The higher resolution soft X-ray Reflection Grating Spectrometer spectrum exhibits a broad absorption line feature near 1 keV, which can be modeled by a blend of L-shell transitions from highly ionized iron (Fe XVII-Fe XXIV). An extreme outflow velocity of ~50,000 km s-1 is required to model the K- and L-shell iron absorption present in the XMM-Newton data. Overall, a large column density (NH = 5 × 1023 cm-2) of highly ionized gas (log ξ = 2.5) is required in PDS 456. A high-mass outflow rate of ~10 M☉ yr-1 (assuming a conservative outflow covering factor of 0.1 sr) is derived, which is of the same order as the overall mass accretion rate in PDS 456. The kinetic energy of the outflow represents a substantial fraction (~10%) of the quasar energy budget, while the large column and outflow velocity place PDS 456 toward the extreme end of the broad absorption line quasar population.