An XMM-Newton Study of Narrow-Line Seyfert 1 Galaxies at 𝑧 = 0.35−0.92

We report a detailed analysis of the XMM-Newton spectra of six Narrow-Line Seyfert 1 (NLS1) galaxies at redshift z = 0.35−0.92. Their spectra all show soft X-ray excess emission below 2 keV with respect to the extrapolation of the 2−10 keV continuum. We compare our sources with a sample of NLS1s and BLS1s at lower redshifts in the literature. Our measurements show that our sample has a softer hard X-ray continuum than the lower-redshift sources at similar Eddington ratios. However, the quantified soft excess strength does not show an obvious discrepancy from previous studies of the lower-redshift sample. The systematic effect mainly lies in the bolometric correction factor. We further fit the spectra assuming two more physical models for the soft excess: warm Comptonization and relativistic reflection from the inner accretion disk. In the first scenario, we confirm the ubiquity of a warm (𝑘𝑇_e,w ≈ 0.1−1 keV) and optically thick (τ ≈ 5−20) corona. In the second scenario, we find that a significant fraction of the energy of the accretion disk is released to the hot corona in order to explain the best-fit electron density parameter. These two models provide similarly good fits to the data. Due to the low signal-to-noise ratio in the iron emission band, we could not obtain good constraints on some of the parameters in the reflection model. Future X-ray missions like the Athena and self-consistent hybrid models for the soft excess emission might provide new insights about our NLS1 sample.