The origin of soft X-rays in luminous AGN.
Abstract
We examine the effects of a nuclear jet expelled from an accretion disk on the UV-to-X-ray spectra of quasars. The base of the jet is immersed in the UV radiation field from the disk and heats up to the Compton-temperature scattering the UV photons from the disk into the soft X-ray range. Unsaturated comptonization leads to a power law extension of the UV bump spectrum to higher frequencies with spectral index α_s_>~1.7 (Snu_ {prop.to} ν^-α_s_^). In the keV range, a nonthermal hard X-ray component with flatter spectral index shows up. This emission component is assumed to be associated with nonthermal processes in the jet. In radio-louds, where the jet is highly collimated and relativistic, particle acceleration occurs at a large distance from the disk, producing a boosted α_h_~0.5 hard X-ray spectrum at a low radiation compactness. In radio-quiets, the jet is slow and highly dissipative a few scale heights above the disk, producing hard X-rays with spectral index α_h_~1 by pair cascades at a moderate radiation compactness. The jet provides the energetical link between the disk and the hard X-ray source. Modeling the broad-band spectra of several quasars, we find that soft X-ray excesses in the keV range occur when the kinetic power of the jet is of the same order as the UV luminosity.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 1995
- DOI:
- 10.48550/arXiv.astro-ph/9509048
- arXiv:
- arXiv:astro-ph/9509048
- Bibcode:
- 1995A&A...303L..41M
- Keywords:
-
- ACCRETION DISKS;
- GALAXIES: ACTIVE;
- JETS;
- QUASARS: GENERAL;
- X-RAYS: GALAXIES;
- Astrophysics
- E-Print:
- 4 pages, uuencoded and compressed Postscript file, also available at http://www.uni-sw.gwdg.de/preprints/preprints.html