Revisiting the extremely fast disc wind in a gravitationally lensed quasar APM 08279+5255

TL;DR

Reanalysis of the quasar APM 08279+5255's X-ray spectra suggests its wind velocity is lower than previously claimed, likely driven by radiation, especially UV line driving, rather than magnetic forces, altering our understanding of its outflow mechanisms.

Contribution

The study introduces a 3D Monte Carlo radiative transfer model to reinterpret the quasar's wind, challenging prior claims of ultra-fast velocities and supporting radiation-driven outflows.

Findings

Wind velocity likely below 0.2c, compatible with radiation driving.

UV line driving is a plausible acceleration mechanism given the spectral energy distribution.

No need for magnetic acceleration to explain the observed features.

Abstract

The gravitationally lensed quasar APM 08279+5255 has the fastest claimed wind from any AGN, with velocities of 0.6-0.7c, requiring magnetic acceleration as special relativisitic effects limit all radiatively driven winds to v<0.3-0.5c. However, this extreme velocity derives from interpreting both the narrow and broad absorption features in the X-ray spectrum as iron absorption lines. The classic ultrafast outflow source PDS 456 also shows similar absorption systems, but here the higher energy, broader feature is generally interpreted as an absorption edge. We reanalyse all the spectra from APM 08279+5255 using a full 3-dimensional Monte Carlo radiative transfer disc wind model for the ionised wind at 0.1-0.2c, together with complex absorption from lower ionisation material, and find that this is a better description of the data. Thus there is no strong requirement for outflow velocities beyond 0.2c, which can be powered by radiation driving. We show that UV line driving is especially likely given the spectral energy distribution of this source which is intrinsically UV bright and X-ray weak. While the peak of this emission is unobservable, it must be luminous enough to power the observed hot dust, favouring at least moderate black hole spin.