Weak Soft X-Ray Excesses Need Not Result from the High-Frequency Tail of the Optical/Ultraviolet Bump in Active Galactic Nuclei
Abstract
The broad-band ROSAT/EXOSAT X-ray spectra of six Seyfert 1 galaxies are fitted by a model consisting of a direct power law and a component due to reflection/reprocessing from a partially ionized, optically thick medium. The reflected spectrum contains emission features from various elements in the soft X-ray range. In all objects but one (Mrk 335), the fit is satisfactory, and no additional soft X-ray excess is required by the data. This means that in most sources there is no need for the thermal "big blue bumps" to extend into soft X-rays, and the soft X-ray excesses reported previously can be explained by reflection/reprocessing. Satisfactory fits are obtained for a medium ionized by a source radiating at <~ 15% of the Eddington rate. The fits require that the reflection is enhanced relative to an isotropically emitting source above a flat disk. The necessary high effectiveness of reflection in the soft X-ray band requires strong soft thermal flux dominating over hard X-rays.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 1994
- DOI:
- 10.1086/187459
- Bibcode:
- 1994ApJ...431L...5C
- Keywords:
-
- Accretion Disks;
- Active Galactic Nuclei;
- Black Holes (Astronomy);
- Seyfert Galaxies;
- Ultraviolet Astronomy;
- X Ray Astronomy;
- X Rays;
- Dispersions;
- Exosat Satellite;
- Ginga Satellite;
- Photoionization;
- Rosat Mission;
- Stellar Luminosity;
- Space Radiation;
- ACCRETION;
- ACCRETION DISKS;
- ATOMIC PROCESSES;
- GALAXIES: ACTIVE;
- X-RAYS: GALAXIES