A Comparison of X-Ray Photon Indices among the Narrow- and Broad-line Seyfert 1 Galaxies

Abstract

Abstract 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 ( ) 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 and R Edd distributions among NLSy1 and BLSy1 galaxies, with steeper and higher R Edd for the former. Such a difference also exists in the spectral index distribution in hard X-ray ( ), 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.