X-Ray Properties of Narrow-Line Seyfert 1 Galaxies With Very Small Broadline Widths

Narrow-line Seyfert\,1 galaxies (NLS1s) with very small broad-line widths (say, FWHM() 1200\,) represent the extreme type of Seyfert\,1 galaxies that have small black hole masses () and/or high Eddington ratios (). 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 \ data. It is found that the Fe Kα 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(), i.e., smaller \ (~ 10⁶ ) and/or higher . 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 \ 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 .