Ionization structure of the warm wind in NGC 5548: discrete or continuous?
Abstract
We present the results from a 540 ks Chandra LETGS/HETGS observation of NGC 5548. The spectrum of the warm outflow is well fitted by a continuous ionization distribution, indicating that the traditional idea of clouds in pressure equilibrium with a hot outflowing medium does not apply. There is further evidence against the cloud model as the lowly ionized UV absorber cannot be in pressure equilibrium with the hot X-ray absorber. Comparing the present Chandra spectra with archival spectra, which were obtained when the source had a different X-ray luminosity, we detect no variability in the warm absorber, with the exception of O V. This is inconsistent with the picture of clouds in pressure equilibrium, as the individual ionization parameters should have changed with changing X-ray luminosities. We propose that the outflow occurs in the form of narrow streamers, with a continuous ionization distribution. This ionization gradient is due to the density gradient in this stream. This proposition is supported by the calculated upper limit to the opening angle, which is smaller than 0.7 sr for highly ionized ions (low density) and smaller than 0.0007 sr for lowly ionized ions (high density), such as O V.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35..281S