XMM-Newton OBSERVATIONS OF THE NARROW-LINE QSO PHL 1092: DETECTION OF A HIGH AND VARIABLE SOFT COMPONENT

We present results based on an XMM-Newton observation of the high luminosity narrow-line QSO PHL 1092 performed in 2003 January. The 0.3 − 10 keV spectrum is well described by a model which includes a power-law (Γ ∼ 2.1) and two blackbody components (kT ∼ 130 eV and kT ∼ 50 eV). The soft X-ray excess emission is featureless and contributes ∼ 80% to the total X-ray emission in the 0.3−10 keV band. The most remarkable feature of the present observation is the detection of X-ray variability at very short time scales: the X-ray emission varied by 35% in about 5000 s. We find that this variability can be explained by assuming that the overall normalisation varied during the observation. This indicates that the X-ray emission arises from very close to the putative black hole: within a few Schwarzschild radius. Considering the high intrinsic luminosity (∼ 2 × 10 erg s) and the large inferred mass of the putative black hole (∼ 1.6 × 10 M⊙), the observed time scale of variability indicates emission at close to Eddington luminosity arising from very close to the black hole. We suggest that PHL 1092 in particular (and narrow line Seyfert galaxies in general) is a fast rotating black hole emitting close to its Eddington luminosity and the X-ray emission corresponds to the high-soft state seen in Galactic black hole sources. Subject headings: galaxies: active – galaxies: individual: PHL 1092 – galaxies: QSO – X-rays: galaxies