Evidence for a radiatively driven disc-wind in PDS 456?

TL;DR

This study reveals a correlation between wind outflow velocity and X-ray luminosity in quasar PDS 456, supporting the idea that the wind is driven by radiation pressure, especially given its high Eddington ratio.

Contribution

It provides the first evidence of a direct correlation between wind velocity and X-ray luminosity in PDS 456, indicating a radiatively driven disc wind.

Findings

Wind outflow velocity increases with X-ray luminosity.

Correlation follows a power-law with index 0.22.

Supports radiative driving mechanism for the wind.

Abstract

We present a newly discovered correlation between the wind outflow velocity and the X-ray luminosity in the luminous ($L_{\rm bol}\sim10^{47}\,\rm erg\,s^{-1}$) nearby ($z=0.184$) quasar PDS\,456. All the contemporary XMM-Newton, NuSTAR and Suzaku observations from 2001--2014 were revisited and we find that the centroid energy of the blueshifted Fe\,K absorption profile increases with luminosity. This translates into a correlation between the wind outflow velocity and the hard X-ray luminosity (between 7--30\,keV) where we find that $v_{\rm w}/c \propto L_{7-30}^{\gamma}$ where $\gamma=0.22\pm0.04$. We also show that this is consistent with a wind that is predominately radiatively driven, possibly resulting from the high Eddington ratio of PDS\,456.