A Study of a Complete Soft X-ray Selected Sample of AGN

Soft X-ray selection picks out unabsorbed objects with strong "soft excess". This energetically important component, likely to be the high energy tail of the accretion disk spectrum, plays an important role in production of optical emission lines and hard X-ray spectra. One reason that the soft excess is strong in some AGN could be that the accretion rate is large and/or the black hole mass is small. This scenario generally describes the Narrow-line Seyfert 1 galaxies (NLS1); however, several examples show that it may not be appropriate for all soft X-ray selected AGN. Aiming to understand the origin and the role of the soft excess, we will perform statistical tests on multiwavelength properties of an unbiased sample. We chose a complete subsample of the 20 brightest, softest and least absorbed objects in the ROSAT sample and conducted observations. Half of them are NLS1s and the others are broad line Seyferts. Now we have ASCA and optical spectra for all of them, and EUVE data for most. Resulting trends will allow us to advance our understanding of the relationships between the soft excess, multiwavelength SED, emission line and hard X-ray properties.