Observable Properties of X-Ray--heated Winds in Active Galactic Nuclei: Warm Reflectors and Warm Absorbers
Abstract
First discovered by spectropolarimetry, the warm reflecting gas near active galactic nuclei (AGNs) may be observed in many ways. When the nucleus itself is obscured and instrumental angular resolution is fine enough to exclude radiation from the host galaxy, this gas can be seen in the soft X-ray band by a combination of bremsstrahlung, intrinsic line emission, and reflection of the nuclear continuum, both by electron scattering and by resonance line scattering. Strong blended line features can be expected in the spectrum. We show that the strong emission-line features seen in the keV region in the X-ray spectra of obscured AGNs may be due to this gas, partly due to intrinsic emission (as suggested by some previous studies), and partly due to resonance scattering. In the ultraviolet, intrinsic emission is very weak. Reflection, principally by electron scattering but also with some contribution from resonance lines, is the main signature in the UV.
When our line of sight to the nucleus is not obscured, the dominant effect is absorption. In the soft X-ray band, ionization edges of highly ionized species and resonance lines contribute comparably to the opacity; in the ultraviolet, the gas is almost transparent except for a small number of resonance lines. We identify the "warm absorbers" seen in many AGN X-ray spectra with this gas but argue that most of the UV absorption lines seen must be due to a small amount of more weakly ionized gas that is embedded in the main body of the warm, reflecting gas. Because the ionization equilibration timescales of some ions may be as long as the variability timescales in AGNs, the ionic abundances indicated by the transmission spectra may not be well described by ionization equilibrium.- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1995
- DOI:
- 10.1086/175896
- arXiv:
- arXiv:astro-ph/9501089
- Bibcode:
- 1995ApJ...447..512K
- Keywords:
-
- GALAXIES: ACTIVE;
- GALAXIES: NUCLEI;
- RADIATION MECHANISMS: NONTHERMAL;
- X-RAYS: GALAXIES;
- Astrophysics
- E-Print:
- 24 pages, AASLaTeX, to appear in July 10 1995 Ap.J.