Detection of Absorption Features in the X-Ray Spectrum of the Narrow-Line Quasar PG 1404+226: Possible Evidence of Accretion Disk Winds

Abstract

We present the results of an analysis of data from XMM-Newton and Chandra observations of the high-luminosity narrow-line quasar PG 1404+226. We confirm a strong soft X-ray excess in the X-ray spectrum, and we find rapid variability (a factor of 2 in about 5000 s). When the X-ray spectrum is fitted with a two-component model that includes a power-law and a blackbody component, we find that low-energy absorption lines are required to fit the data. If we interpret these lines as due to highly ionized species of heavy elements in an outflowing accretion disk wind, an outflow velocity of ~26,000 km s-1 could be derived. One interesting feature of the present observation is the possible detection of variability in the absorption features: the absorption lines are visible only when the source is bright. From the upper limits of the equivalent widths of the absorption lines during the low-flux states and also from the model-independent pulse-height ratios, we argue that the strength of absorption is lower during the low-flux states. This constrains the physical size of the absorbing medium within 100 Schwarzschild radius (RS) of the putative supermassive black hole. We also find a marginal evidence of a correlation between the strength of the absorption line and the X-ray luminosity.