Variability of the High-Velocity Outflow in the Quasar PDS 456

Abstract

We present a comparison of two Suzaku X-ray observations of the nearby (z=0.184), luminous (L bol ∼ 10 47 erg s −1 ) type I quasar, PDS 456. A new 125 ks Suzaku observation in 2011 caught the quasar during a period of low X-ray flux and with a hard X-ray spectrum, in contrast to a previous 190 ks Suzakuobservation in 2007 when the quasar appeared brighter and had a steep (Γ > 2) X-ray spectrum. The 2011 X-ray spectrum contains a pronounced trough near 9 keV in the quasar rest frame, which can be modeled with blue-shifted iron K-shell absorption, most likely from the He and H-like transitions of iron. The absorption trough is observed at a similar rest-frame energy as in the earlier 2007 observation, which appears to confirm the existence of a persistent high velocity wind in PDS 456, at an outflow velocity of 0.25 − 0.30 c. The spectral variability between 2007 and 2011 can be accounted for by variations in a partial covering absorber, increasing in covering fraction from the brighter 2007 observation to the hard and faint 2011 observation. Overall the low flux 2011 observation can be explained if PDS 456 is observed at relatively low inclination angles through a Compton thick wind, originating from the accretion disk, which significantly attenuates the X-ray flux from the quasar.

Ultrafast outflows disappear in high-radiation fields

“…Some models include variable column density or covering fraction (e.g. Reeves et al 2014, Hagino et al 2016.…”

Revealing the X-ray variability of AGN with principal component analysis

“…The second component appears to be a good match for the third or fourth order components described in § 4.1 (although more redshifted), which are attributed to relativistic reflection variability. PDS 456 is rapidly variable and shows a strong absorption edge at ∼ 8 keV (Reeves et al 2000), and there is strong evidence of high-velocity outflowing material (O'Brien et al 2005;Reeves et al 2014). The broad band spectrum has been successfully modelled using a standard relativistic model by Walton et al (2010).…”

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

“…Ohsuga et al 2009;Kazanas et al 2012). Most outflow studies so far mainly concentrated on radiatively driven winds (e.g., Sim et al 2010;Reeves et al 2014;Hagino et al 2015;Nomura & Ohsuga 2017). However, recently Fukumura et al (2017) successfully applied an MHD wind model to the microquasar GRO J1655-40 suggesting that a similar mechanism applies across the black hole mass and luminosity scales.…”

“…Since the first XMM-Newton (40 ks) observation carried out in 2001 (Reeves, O'Brien & Ward 2003), PDS 456 has showed the presence of a persistent deep absorption trough in the Fe K band above 7 keV. This can be associated to highly ionized Fe K-shell absorption with a corresponding outflow velocity of vw ∼ 0.25-0.3c (Reeves et al 2009(Reeves et al , 2014Gofford et al 2014;N15;Matzeu et al 2016, hereafter M16), which originates from an accretion disk wind. In this letter we present a new correlation between the discwind velocity derived from the Fe K profile and the intrinsic X-ray luminosity, which we interpret in the framework of a radiatively driven wind.…”