A Suzaku sample of unabsorbed narrow-line and broad-line Seyfert 1 galaxies: I. X-ray spectral properties

TL;DR

This study analyzes Suzaku X-ray observations of 69 Seyfert 1 galaxies, revealing that NLS1s have steeper spectra, higher Eddington ratios, and stronger soft/hard excesses, with correlations suggesting a common origin.

Contribution

It provides the first comprehensive Suzaku-based analysis comparing X-ray spectral properties of NLS1 and BLS1 galaxies, highlighting differences and correlations in their soft and hard excesses.

Findings

NLS1s have steeper photon indices than BLS1s.

NLS1s exhibit higher X-ray Eddington ratios.

Soft and hard excesses are correlated in NLS1s.

Abstract

A sample of narrow-line (NLS1) and broad-line Seyfert 1 (BLS1) galaxies observed with Suzaku is presented. The final sample consists of 22 NLS1s and 47 BLS1s, for a total of 69 AGN that are all at low redshift (z<0.5) and exhibit low host galaxy column densities (<10^22 cm^-2). The average spectrum for each object is fit with a toy model to characterise important parameters, including the photon index, soft excess, Compton hump (or hard excess), narrow iron line strength, luminosity and X-ray Eddington ratio (L_x/L_Edd). We confirm previous findings that NLS1s have steeper power laws and higher X-ray Eddington ratios, but also find that NLS1 galaxies have stronger soft and hard excesses than their BLS1 counterparts. Studying the correlations between parameters shows that the soft and hard excesses are correlated for NLS1 galaxies, while no such correlation is observed for BLS1s. Performing a principal component analysis (PCA) on the measured X-ray parameters shows that while the X-ray Eddington ratio is the main source of variations within our sample (PC1), variations in the soft and hard excesses form the second principal component (PC2) and it is dominated by the NLS1s. The correlation between the soft and hard excess in NLS1 galaxies may suggest a common origin for the two components, such as a blurred reflection model. The presented Suzaku sample of Seyfert 1 galaxies is a useful tool for analysis of the X-ray properties of AGN, and for the study of the soft and hard excesses observed in AGN.