
Up: Ultraviolet variability of
The analysis of the ultraviolet variability of the AGN in the Seyfert
I galaxy Fairall-9 (continuum
and emission lines) has been made using IUE spectra of this AGN
between 1978 and 1991 (4903 days) with a mean sampling interval of
96 days. These data have been combined with those available at other
wavelength domains to derive the SED of F-9. This instantaneous SED
has been used as input for the ionizing continuum in
photoionization models. The line profile variability has allowed
the decomposition of the strongest lines in several components. The
comparison between the line ratios in these components for
,
,
and
combined with the photoionization model calculations and
the results of reverberation analysis has allowed to
derive a consistent model for the structure and dynamics of the BLR.
- The UV continuum shows a dominant variation with
and a characteristic time of 182 days. Also faster
variability on time scales of the order of 56 days appears present, but this has
not been adequately sampled in the available data. The intrinsic spectral index
UV-optical is
and the optical variations
don't lag behind the UV ones. In the NIR, The J band flux shows as
an extension of the UV-optical continuum with
. On the contrary, the H, K, and L
bands variations lag behind the UV ones (Clavel et al. 1989).
The
flux is proportional to the UV continuum at low flux
levels, while at higher UV flux levels this proportionality breaks down.
- The SED of the F-9 nucleus shows two important flux excesses,
extending over the FIR-NIR range and from the J-band to the X-rays.
The FIR-NIR excess,
together with the delays of the H, K and L bands fluxes with respect
to the UV continuum, is consistent with reradiation from dust heated
directly by the ionizing continuum, as already suggested by Clavel
et al.\
(1989) and Barvainis (1992). The deduced hot dust
mass is
at a distance of
of the UV ionizing source (Clavel et al.\
1989).
The problems for a simple disk model to explain the big
blue bump (J-soft X-rays) of F-9 (Clavel et al. 1989 and
Courvoisier & Clavel 1991) and the
strong correlation observed in the X-rays-UV variations at low UV
flux levels for Fairall-9, are similar to those reported for NGC 5548
(Clavel et al. 1992) and NGC 4151 (Perola et al.\
1986). In these AGN the partial solution includes reprocessing on
an accretion disk of the hard X-rays emitted from a region above the
disk. The presence of strong Fe K
line centered at
in the Ginga spectra of F-9 supports this model.
However, the equivalent width of this line,
, could
indicate that the Fe abundance is
larger than the cosmic
one (Zdziarski 1990; Bai 1979). Wills et
al. (1985) similarly obtained this Fe overabundance in their
Seyfert 1 galaxies sample from the high ratio FeII
. This is consistent with the ratio obtained by us (see
Table
8 (click here)).
- The line profile variability for
,
,
and
\
has allowed us to isolate the same four components (represented by
gaussians) in all lines and at all levels of brightness: one narrow
(i.e. unresolved at the IUE resolution), and three broad components:
a central (FWHM=3600
, velocity same as the narrow
line), a red shifted (FWHM=5800
,
) and
a blue shifted (FWHM=5900
,
) one. The
strong correlations obtained between the three broad components and
the UV continuum indicates that photoionization is the dominant
mechanism in the BLR. The delays between these components and the
UV continuum are
,
and
for
the central, red and blue one, respectively.
- Photoionization models (CLOUDY) with a UV-optical cut-off
of 3.5 ryd, derived from the observed instantaneous SED, have been applied to
the observed lines ratios of the
broad components, and indicate that the BLR is situated at
from the ionizing source, with an hydrogen
density of
, a column density of
and a covering factor of
, with an
ionization parameter between 0.003 and 0.089. However, all these
optically thick models underestimate the
ratio and
overestimate the
one. The solution to this discrepancy
could be associated with the co-existence of optically thick and optically
thin material in the BLR, as suggested by Shield (1995).
- From all the results we have propose a model for the structure
and dynamics of the BLR: the mass of the central compact
object is
. Around this exist two
distinct gas zones within the BLR: the gas producing the central component at
and
the one emitting the red and the blue fluxes at
moving inward to a central source. These results require
that both gas zones be localized along the line-of-sight or,
alternatively, that the continuum emission must
be strongly anisotropic. Besides, the gas emitting the central component is most
likely
mixed with the dust and the central gas
to dust mass ratio is Mass
.
Acknowledgements
Part of this work was supported by a Comunidad de Madrid FPI
grant between 1990-1994. M.C. Recondo-González thanks all the
VILSPA personal for their kindness and Antonio
De la Fuente for his help.

Up: Ultraviolet variability of
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