XMM-Newton observation of the narrow-line QSO PHL 1092: detection of a high and variable soft component

Dasgupta, Surajit ; Rao, A. R. ; Dewangan, G. C. (2004) XMM-Newton observation of the narrow-line QSO PHL 1092: detection of a high and variable soft component The Astrophysical Journal, 614 (2). pp. 626-633. ISSN 0004-637X

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Official URL: http://iopscience.iop.org/0004-637X/614/2/626

Related URL: http://dx.doi.org/10.1086/423837

Abstract

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 that 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 a very short timescale; the X-ray emission varied by 35% in about 5000 s. We find that this variability can be explained by assuming that only the overall normalization varied during the observation. There was no evidence for any short-term spectral variability, and the spectral shape was similar even during the ASCA observation carried out in 1997. Considering the high intrinsic luminosity (~2 x 1045 ergs s-1) and the large inferred mass of the putative black hole (~1.6 x 108 M), the observed timescale of variability indicates emission at close to the 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.

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