# X-Ray Properties of Narrow-Line Seyfert 1 Galaxies with Very Small Broad-Line Widths

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Narrow-line Seyfert\,1 galaxies NLS1s with very small broad-line widths say, FWHM\hb $\la$ 1200\,\kms represent the extreme type of Seyfert\,1 galaxies that have small black hole masses \mbh and-or high Eddington ratios edd. Here we study the X-ray properties of a homogeneously and optically selected sample of 13 such objects, termed as very narrow line Seyfert\,1 galaxies VNLS1s, using archival \xmm\ data. It is found that the Fe K$\alpha$ emission line is at most weak in these objects. A soft X-ray excess is ubiquitous, with the thermal temperatures falling within a strict range of 0.1-0.2\,keV. Our result highlights the puzzling independence of the thermal temperature by extending the relations to even smaller FWHM\hb, i.e., smaller \mbh\ $\sim 10^6$ \msun and-or higher edd. The excess emission can be modeled by a range of viable models, though the disk reflection and Comptonization models generally give somewhat better fits over the smeared absorption and the $p$-free models. At the Eddington ratios around unity and above, the X-ray spectral slopes in the 2-10\,keV band are systematically flatter than the Risaliti et al.s predictions of the relationship with edd\ suggested previously. Short timescale 1-2 hours X-ray variability is common, which, together with the variability amplitude computed for some of the objects, are supportive of the scenario that NLS1s are indeed AGN with relatively small \mbh.

Autor: Y. L. Ai; W. Yuan; H. Y. Zhou; T. G. Wang; S. H. Zhang

Fuente: https://archive.org/