Remarkable Spectral Variability of PDS 456

TL;DR

This study presents the highest quality X-ray spectrum of quasar PDS 456, revealing significant spectral variability over time, with reflection dominating in 2007 and previous spectra showing strong outflow absorption.

Contribution

The paper introduces a unified model explaining spectral variability in PDS 456 through variable outflow partial covering and reflection effects.

Findings

2007 spectrum dominated by reflection, minimal outflow absorption

Previous spectra show absorption from ultra-high-velocity outflows

Reflection medium may be outflowing at v/c = -0.06 ± 0.02

Abstract

We report on the highest to date signal-to-noise-ratio X-ray spectrum of the luminous quasar PDS 456, as obtained during two XMM-Newton orbits in September 2007. The present spectrum is considerably different from several previous X-ray spectra recorded for PDS 456 since 1998. The ultra-high-velocity outflow seen as recently as February 2007 is not detected in absorption. Conversely, a significant reflection component is detected. The reflection model suggests the reflecting medium may be outflowing at a velocity v/c = -0.06 +/- 0.02. The present spectrum is analyzed in the context of the previous ones in an attempt to understand all spectra within the framework of a single model. We examine whether an outflow with variable partial covering of the X-ray source along the line of sight that also reflects the source from other lines of sight can explain the dramatic variations in the broad-band spectral curvature of PDS 456. It is established that absorption plays a major role in shaping the spectrum of other epochs, while the 2007 XMM-Newton spectrum is dominated by reflection, and the coverage of the source by the putative outflow is small (< 20%).