A comparison of X-ray photon indices among the narrow and broad-line Seyfert 1 galaxies

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 telescopes in soft X-ray band (0.1-2.0 keV). A homogeneous analysis is carried out to estimate their soft X-ray photon indices (${\Gamma }_X^s$) and its correlations with other parameters of nuclear activities such as Eddington ratios (R${}_{\mathrm{Edd}}$), bolometric luminosities (L${}_{\mathrm{bol}}$), black hole masses (M${}_{\mathrm{BH}}$) and the widths of the broad component of H$\beta$ lines (FWHM(H$\beta$)). In our analysis, we found clear evidence of the difference in the ${\Gamma }_X^s$ and R${}_{\mathrm{Edd}}$ distributions among NLSy1 and BLSy1 galaxies, with steeper ${\Gamma }_X^s$ and higher R${}_{\mathrm{Edd}}$ for the former. Such a difference also exists in the spectral indices distribution in hard X-ray (${\Gamma }_X^h$), based on the analysis of 53 NLSy1 and 46 BLSy1 galaxies in the 2-10 keV energy band. The difference in R${}_{\mathrm{Edd}}$ 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${}_{\mathrm{Edd}}$, 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${}_{\mathrm{Edd}}$ estimates based on the optical bolometric luminosity. Our analysis suggests that the higher R${}_{\mathrm{Edd}}$ in NLSy1 is responsible for its steeper X-ray spectral slope compared to the BLSy1, consistent with the disc-corona model as proposed for the luminous AGNs.

arXiv comment21 pages, 12 figures, Accepted for publication in ApJ

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