Puchnarewicz, Elizabeth Maria; (1992) Multiwavelength studies of ultra-soft X-ray AGN. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

I investigate the X-ray, optical and infra-red properties of the 53 AGN identified as part of the Einstein Ultra-Soft Survey (USS). Of all sources in the IPC database, these have the strongest, distinct soft X-ray excesses at 0.25 keV. The IPC data are modelled using two separate components, the 'soft' and 'hard' X-ray components. Continuum and line parameters are measured from optical spectra while CCD images provide accurate magnitudes and information on the AGN morphology and environment. Infra-red fluxes of the nucleus and the underlying galaxy are measured from UKIRT images. Multiwavelength spectra, combining IR, optical, UV and X-ray data, are presented for thirteen AGN. I find that approximately one third of USS AGN are hard X-ray quiet; the remaining hard X-ray fluxes are typical of other X-ray selected AGN. All optical and IR continuum luminosities are 'normal'. A striking characteristic of the sample is the high proportion of narrow-line objects it contains; I also find that the permitted lines are weak. Optical Fell emission is strong where hard X-rays are weak, contradicting hard X-ray dependent models for their production. All results are considered in the context of two models for the production of a strong soft X-ray flux, accretion disks and the cool clouds model of Guilbert and Rees. The narrow lines suggest that we may be seeing a flattened BLR face-on - alternatively, the BLR may lie further from the black hole than for other AGN. An association of a face-on BLR with an accretion disk would strongly favour geometrically thick disks over thin. The overall spectral distribution can also be well reproduced by the cool clouds model.

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