2020ApJ...896...95O

We present a detailed comparative systematic study using a sample of 221 narrow-line Seyfert 1 (NLSy1) galaxies in comparison to a redshift-matched sample of 154 broad-line Seyfert 1 (BLSy1) galaxies based on their observations using ROSAT and/or XMM-Newton in soft X-ray band (0.1-2.0 keV). A homogeneous analysis is carried out to estimate their soft X-ray photon indices (Γ_X^s) and its correlations with other parameters of nuclear activities such as Eddington ratios (R_Edd), bolometric luminosities (L_bol), black hole masses (M_BH), and the widths of the broad component of Hβ lines (FWHM(Hβ)). In our analysis, we found clear evidence of the difference in the Γ_X^s and R_Edd distributions among NLSy1 and BLSy1 galaxies, with steeper Γ_X^s and higher R_Edd for the former. Such a difference also exists in the spectral index distribution in hard X-ray (Γ_X^h), based on the analysis of 53 NLSy1 and 46 BLSy1 galaxies in the 2-10 keV energy band. The difference in R_Edd distributions does exist even after applying the average correction for the difference in the inclination angle of NLSy1 and BLSy1 galaxies. We also estimated R_Edd, based on SED fitting of 34 NLSy1 and 30 BLSy1 galaxies over the 0.3-10 keV energy band, and found that results are still consistent with R_Edd estimates based on the optical bolometric luminosity. Our analysis suggests that the higher R_Edd in NLSy1 is responsible for its steeper X-ray spectral slope compared to the BLSy1, consistent with the disk-corona model as proposed for the luminous AGNs.