ASCA Observations of NLS1s
  The study of NLS1s using ASCA has many advantages. A representative sample can be studied; to date, observations of more than 30 NLS1s have been made. ASCA observations are conducted contiguously, so their X-ray variability properties can be studied systematically. ASCA detectors have a broad band pass and moderate energy resolution, properties which allow their complex X-ray spectrum to be deconvolved. ASCA observations have revealed that a soft excess extending up to 1 keV is frequently found in the X-ray spectra from NLS1s. The hard X-ray photon index has been shown to be systematically steeper than in Seyfert 1 galaxies with broad optical lines. NLS1s also exhibit larger amplitude variability than broad-line Seyferts of similar hard X-ray luminosity. On occasion, features in the soft X-ray band have been detected that appear to be specific to NLS1s; ionized iron lines have also been observed. These results have been fundamental for building our current picture of the X-ray emission from NLS1s. Many of the properties can be explained if the specific accretion rate is larger in NLS1s than in Seyfert 1 galaxies with broad optical lines. NLS1s may exemplify an extreme state of an intrinsic physical parameter and therefore their study may lead to an enhanced understanding of AGN in general. This proceedings contribution has two parts. First I describe and discuss some of the results obtained from a study of the X-ray variability in NLS1s using ASCA data (Leighly 1999ab). Then, I discuss the results from our HST observations of NLS1s that were first presented during this meeting (Leighly & Halpern 2000). 
Karen M. Leighly (Columbia University, New York, USA)