A New Relativistic Component of the Accretion Disk Wind in PDS 456

Abstract

Past X-ray observations of the nearby luminous quasar PDS 456 (at z = 0.184) have revealed a wide angle accretion disk wind, with an outflow velocity of ∼-0.25c. Here, we unveil a new, relativistic component of the wind through hard X-ray observations with NuSTAR and XMM-Newton, obtained in 2017 March when the quasar was in a low-flux state. This very fast wind component, with an outflow velocity of -0.46 ± 0.02c, is detected in the iron K band, in addition to the -0.25c wind zone. The relativistic component may arise from the innermost disk wind, launched from close to the black hole at a radius of ∼10 gravitational radii. The opacity of the fast wind also increases during a possible obscuration event lasting for 50 ks. We suggest that the very fast wind may only be apparent during the lowest X-ray flux states of PDS 456, becoming overly ionized as the luminosity increases. Overall, the total wind power may even approach the Eddington value.