A Comparison of X-Ray Photon Indices among the Narrow- and Broad-line Seyfert 1 Galaxies
Vineet Ojha, Hum Chand, Gulab Chand Dewangan, Suvendu Rakshit
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 H β lines (FWHM(H β )). 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.