Investigating the nature of narrow-line Seyfert 1 galaxies with high-energy spectral complexity

Abstract

(abridged) With the commissioning of XMM came the discovery of 2.5-10 keV spectral complexity in some narrow-line Seyfert 1 galaxies (NLS1). In this work, we define two samples of NLS1: a complex sample whose members exhibit high-energy complexity (C-sample), and a general sample of NLS1 whose 2.5-10 keV spectra do not strongly deviate from a simple power law (S-sample). Considering historical light curves of each object we find that the C-sample is representative of NLS1 in a low X-ray flux state, whereas the members of the S-sample appear to be in a typical flux state. Moreover, from measurements of alpha_ox with contemporaneous UV/X-ray data, we find that the C-sample of NLS1 appear X-ray weaker at the time of the observation. For two NLS1 in the C-sample multi-epoch measurements of alpha_ox are available and suggest that alpha_ox approaches more normal values as the complexity between 2.5-10 keV diminishes. This implies that a source could transit from one sample to the other as its X-ray flux varies. Secondly, there are indications that the C-sample sources, on average, exhibit stronger optical FeII emission, with the three most extreme (FeII/H_beta > 1.8) FeII emitters all displaying complexity in the 2.5-10 keV band. However, it is not clear if the possible connection between FeII strength and spectral complexity is due to the FeII producing mechanism or because strong FeII emitters may exhibit the greatest variability and consequently more likely to be caught in an extreme (low) flux state. Based on the current analysis it we can not straightforwardly dismiss absorption or reflection as the cause of the X-ray complexity.