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

With the commissioning of XMM-Newton came the discovery of 2.5-10keV spectral complexity in some narrow-line Seyfert 1 galaxies (NLS1). This high-energy complexity can be manifested as sharp, spectral drops or gradual curvature in the spectrum. Models which are normally considered are ionized reflection and partial covering. 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 2.5-10keV spectra do not strongly deviate from a simple power law (S sample). We than compare multiwavelength parameters of these two samples to determine if there are any distinguishing characteristics in the complex NLS1. 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 α_ox with contemporaneous ultraviolet (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 α_ox are available and suggest that α_ox approaches more normal values as the complexity between 2.5 and 10keV 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/Hβ > 1.8) FeII emitters all displaying complexity in the 2.5-10keV band. It is an intriguing possibility that we may be able to identify X-ray complex NLS1 based on the extreme strength of the more easily observable optical FeII emission. 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, we cannot straightforwardly dismiss absorption or reflection as the cause of the X-ray complexity; by considering the multiple UV/X-ray observations of 1H 0707-495 (a C sample member), we discuss a possible method of distinguishing the two models provided further UV/X-ray observations.