AN X-RAY SPECTRAL STUDY OF 24 TYPE-1 ACTIVE GALACTIC NUCLEI

I present a study of the X-ray spectral properties of a sample contain ing 24 type 1 active galactic nuclei using the medium spectral resolut ion of ASCA. The sample consists of 20 radio-quiet objects (18 Seyfert 1 galaxies and two radio-quiet quasars) and four radio-loud objects ( three broad-line radio galaxies and one radio-loud quasar). A simple p ower-law continuum absorbed by Galactic material provides a very poor description of the spectra of most objects. Deviations from the power- law form are interpreted in terms of X-ray reprocessing/absorption pro cesses. In particular, at least half of the objects show K-shell absor ption edges of warm oxygen (O VII and O VIII) characteristic of optica lly thin, photoionized material along the line of sight to the central engine, the so-called warm absorber. The amount and presence of this absorption are found to depend on either the luminosity or radio prope rties of the objects: luminous and/or radio-loud objects are found to possess less ionized absorption. This ambiguity exists because the rad io-loud objects are also amongst the most luminous of the sample. It i s also found that objects with significant optical reddening display d eep O VII edges. The converse is true with two possible exceptions (NG C 3783 and NGC 3516). Coupled with other evidence resulting from detai led study of particular objects, this Suggests the existence of dusty warm plasma. A radiatively driven outflow originating from the molecul ar torus is probably the source of this plasma. Rapid variability of t he warm absorber also points to there being another component closer t o the central source and probably situated within the broadline region (BLR). Independent evidence for such an optically thin, highly. ioniz ed BLR component comes from detailed optical/UV studies. Spectral feat ures at energies characteristic of cold iron K alpha emission are comm on. Such emission is expected to arise from the fluorescence of cold i ron in optically thick material when illuminated by the primary X-ray continuum. Radio-quiet objects have iron emission well, described as o riginating either from the inner regions of an accretion disc or, in a small number of cases, from the molecular torus. Two of the radio-lou d objects (3C 120 and 3C 382) have a much broader feature which presen ts problems for the relativistic disc model. The presence of radio jet s may be important in forming this spectral feature.