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Title:
An X-ray spectral study of 24 type 1 active galactic nuclei
Authors:
Reynolds, C. S.
Affiliation:
AA(Institute of Astronomy, Madingley Road, Cambridge CB3 0HA)
Publication:
Monthly Notices of the Royal Astronomical Society, Volume 286, Issue 3, pp. 513-537. (MNRAS Homepage)
Publication Date:
04/1997
Origin:
MNRAS
MNRAS Keywords:
ACCRETION, ACCRETION DISCS, PLASMAS, GALAXIES: ACTIVE, GALAXIES: SEYFERT, X-RAYS: GALAXIES
Bibliographic Code:
1997MNRAS.286..513R

Abstract

I present a study of the X-ray spectral properties of a sample containing 24 type 1 active galactic nuclei using the medium spectral resolution 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 power-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 processes. In particular, at least half of the objects show K-shell absorption edges of warm oxygen (Ovii and Oviii) characteristic of optically 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 properties of the objects: luminous and/or radio-loud objects are found to possess less ionized absorption. This ambiguity exists because the radio-loud objects are also amongst the most luminous of the sample. It is also found that objects with significant optical reddening display deep Ovii edges. The converse is true with two possible exceptions (NGC 3783 and NGC 3516). Coupled with other evidence resulting from detailed study of particular objects, this suggests the existence of dusty warm plasma. A radiatively driven outflow originating from the molecular torus is probably the source of this plasma. Rapid variability of the warm absorber also points to there being another component closer to the central source and probably situated within the broad-line region (BLR). Independent evidence for such an optically thin, highly ionized BLR component comes from detailed optical/UV studies. Spectral features at energies characteristic of cold iron Kalpha emission are common. Such emission is expected to arise from the fluorescence of cold iron in optically thick material when illuminated by the primary X-ray continuum. Radio-quiet objects have iron emission well described as originating either from the inner regions of an accretion disc or, in a small number of cases, from the molecular torus. Two of the radio-loud objects (3C 120 and 3C 382) have a much broader feature which presents problems for the relativistic disc model. The presence of radio jets may be important in forming this spectral feature.

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