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 (redd). 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 redd. 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 redd 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.
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