A comparison of hard X-ray photon indices and iron \ka emission lines in X-ray luminous narrow- and broad-line Seyfert 1 galaxies

TL;DR

This study systematically compares X-ray spectral properties of narrow- and broad-line Seyfert 1 galaxies using XMM-Newton data, revealing differences in photon indices and iron line strengths that relate to AGN structure.

Contribution

It provides a comprehensive comparison of X-ray spectral features between NLS1 and BLS1 galaxies, highlighting differences in photon indices and iron line properties with implications for AGN models.

Findings

NLS1s and BLS1s have similar luminosity distributions.

NLS1s tend to have steeper X-ray photon indices (>2.0).

NLS1s exhibit weaker narrow iron Kα lines than BLS1s.

Abstract

We use publicly available XMM-Newton data to systematically compare the hard X-ray photon indices, $\Gamma_{\rm 2-10\ keV}$ and the iron K$\alpha$ emission lines of narrow-line (NL) and broad-line Seyfert 1 (BLS1) galaxies. We compile a flux-limited ($f_{\rm 2-10\ keV} \geq 1 \times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$) sample including 114 radio-quiet objects, with the 2-10 keV luminosity ranging from 10$^{41}$ to 10$^{45}$ erg s$^{-1}$. Our main results are: 1) NLS1s and BLS1s show similar luminosity distributions; 2) The weighted mean of $\Gamma_{\rm 2-10\ keV}$ of NLS1s, BLS1s and the total sample is $2.04\pm0.04$, $1.74\pm0.02$, $1.84\pm0.02$, respectively; a significant anti-correlation between \ga and FWHMH$\beta$ suggests that $\Gamma_{\rm 2-10\ keV} > 2.0$ may be taken to indicate X-ray luminous NLS1 type; 3) The 6.4 keV narrow iron K$\alpha$ lines from NLS1s are generally weaker than that from BLS1s; this would indicate a smaller covering factor of the dusty tori in NLS1s, if the line emission originates from the inner boundary region of the dusty torus in an AGN; 4) all the broadened iron K$\alpha$ lines with intrinsic width $\sigma>0.5$ keV correspond to FWHM\hb $\leq 4000 ~\kms$.