REMARKABLE SPECTRAL VARIABILITY OF PDS 456

摘要

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 2007 September. 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 2007 February is not detected in absorption. Conversely, a significant reflection component is detected (Δχ2 = 313 compared to a simple absorbed power law). The reflection model suggests that the reflecting medium may be outflowing at a velocity v/c = –0.06 ± 0.02 (Δχ2 = 28 compared to v/c = 0). 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 broadband 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%).