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K. Leighly (The University of Oklahoma), J. Halpern (Columbia University)
Narrow-line Seyfert 1 galaxies (NLS1s) are known for their distinctive X-ray properties, including high-amplitude X-ray variability, steep X-ray spectra, and strong soft X-ray excesses. The theory that NLS1s are characterized by a high accretion rate relative to Eddington has been advanced. The wide range of behavior among NLS1s and correlations between their properties can be used to test this theory. In particular, NLS1s with the strongest strong soft X-ray excesses also show the highest amplitude X-ray variability, exhibiting light curves characterized by flares.
We have recently discovered that NLS1s with these extreme X-ray properties have unusual UV spectroscopic properties as well. The high-ionization lines in their UV spectra are strongly blueshifted, and are much broader than the narrow, symmetric low-ionization lines. These facts are most simply explained if the high-ionization lines are emitted by a wind, while the low-ionization lines are emitted from an accretion disk or from the base of the wind. A strong wind may be expected when the accretion rate approaches the Eddington value. These HST\/ spectra provide the first strong evidence favoring a disk-wind model for AGN emission lines over all other models.
In these extreme NLS1s, the high-ionization lines are apparently dominated by the emission from the high-velocity wind. That is not true for all NLS1s however: many also appear to have a low-velocity symmetric component in their high-ionization lines that we think originates in the accretion disk or low-velocity base of the wind. We postulate that the low-velocity component is absent in the extreme NLS1s because the wind is so thick that it absorbs most of the ionizing flux before it can reach the low-velocity material. We conclude that the NLS1s with the most extreme properties, including high amplitude X-ray variability, strong soft X-ray excesses, and highly blueshifted emission lines, are the ones that have the highest Eddington ratio (\propto L/M\rm BH).