Ultrasoft Narrow-Line Seyfert 1 Galaxies and X-ray Surveys

Abstract

We describe how recent X-ray surveys have led to advances in the understanding of ultrasoft narrow-line Seyfert 1 galaxies. The number of known ultrasoft narrow-line Seyfert 1s has increased greatly in recent years due to X-ray surveys, and it is now possible to obtain high quality 0.1--10 keV spectral and variability measurements for a large number of these galaxies. We generalize some of the correlations between X-ray properties and optical emission line properties, focusing on how the ROSAT band spectral slope appears to be directly connected to the Boroson & Green (1992) primary eigenvector. We discuss how ultrasoft narrow-line Seyfert 1s may well have extremal values of a primary physical parameter, and we describe new projects that should further improve our understanding of these extreme representatives of Seyfert activity.