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A&A Supplement series, Vol. 121, March 1997, 461-487

Received February 29; accepted June 20, 1996

Ultraviolet variability of the Seyfert 1 galaxy Fairall 9

M.C. Recondo-Gonzáleztex2html_wrap4411, W. Wamstekertex2html_wrap4413, J. Claveltex2html_wrap4415, P.M. Rodríguez-Pascualtex2html_wrap4417, R. Viotex2html_wrap4419, Wang Ting-guitex2html_wrap4421, M. Santos-Lleótex2html_wrap4423, and F. Makinotex2html_wrap4425

Send offprint request: G. Wuchterl

tex2html_wrap4427  ESA IUE Observatory, Apartado 50727, 28080-Madrid, Spain
tex2html_wrap4429  ISO Observatory, Astrophysics Division of ESA, Apartado 50727, 28080-Madrid, Spain
tex2html_wrap4431  Astronomy department, University of Padua, Vicolo del Osservatorio 5, 35122 Padva, Italy
tex2html_wrap4433  LAEFF, Apartado 50727, 28080-Madrid, Spain
tex2html_wrap4435  Center for Astrophysics, University of Science and Technology of China, Hefei, 230026-Anhui, P.R. China
tex2html_wrap4437  Affiliated to the Astrophysics Division, Space Science Department, Noordwijk, The Netherlands
tex2html_wrap4439  Institute of Space and Astronautical Science, 3-1-1,Yoshinda, Sagamihara-shi, Kanagawa 229, Japan


The large amplitude of the variations of the Seyfert I Galaxy Fairall-9 between 1978 and 1991 make this Active Galaxy especially suitable for a combined study in terms of reverberation analysis and photoionization modeling over the velocity field of the broad lines of its ultraviolet spectrum. We have combined our ultraviolet data with those available at other wavelengths to derive the intrinsic ionizing continuum and to compare the predictions of the photoionization models with the observations. The UV continuum varies with a factor of tex2html_wrap_inline4347 on a characteristic time scale of 182 days. The intrinsic spectral index UV-optical is tex2html_wrap_inline4349 and the optical variations do not lag behind the UV variations at the mean sampling interval of 96 days. In the near IR, the J band flux presents a direct extension of the UV-optical continuum (tex2html_wrap_inline4353). Only at low flux levels is the tex2html_wrap_inline4355 flux proportional to the UV continuum, at higher UV flux levels proportionality between the X-rays and the UV brightness breaks down. The continuum spectral energy distribution (SED) of the nucleus supports the previously reported FIR-NIR excess associated with 0.02 tex2html_wrap_inline4357 dust at a distance of some tex2html_wrap_inline4359, as well as a soft X-ray excess, possibly associated with the reprocessing on an accretion disk of the hard X-rays emitted from a region above the disk. The presence of strong Fe Ktex2html_wrap_inline4361 line in the GINGA spectra of this galaxy does lend support to this model. Line profile variability has been used to isolate four gaussian line components, which are sufficient to describe all lines at all levels of brightness in a consistent way: one narrow (i.e. unresolved at the IUE resolution), and three broad components: a central (velocity same as the narrow line), a red shifted (tex2html_wrap_inline4363) and a blue shifted (tex2html_wrap_inline4365) one. The three broad components are strongly correlated with the UV continuum, indicating that photoionization is the dominant mechanism in the BLR. Correlation analysis shows different delays between the broad components and the UV continuum: respectively, tex2html_wrap_inline4367, tex2html_wrap_inline4369 and tex2html_wrap_inline4371 for the central, red and blue one. Only the red component of tex2html_wrap_inline4373 and tex2html_wrap_inline4375 appear to vary linearly with the continuum and give significant transfer functions. The resulting transfer functions are peaked at zero days delay and are unresolved at the average time resolution (96 days) of our data. The photoionization models (CLOUDY) applied to the line ratios in these components, indicate that the Broad-Line-Region (BLR) is situated between tex2html_wrap_inline4377 from the ionizing source, with an hydrogen density of tex2html_wrap_inline4379, a column density of tex2html_wrap_inline4381 and a covering factor of tex2html_wrap_inline4383, with an ionization parameter between 0.003 and 0.089. However, no optically thick model reproduces the tex2html_wrap_inline4385/CIV and tex2html_wrap_inline4387/NV ratios. From these results we propose a model for the structure and dynamics of the BLR: the mass of the central compact object is M tex2html_wrap_inline4391. Around this exist two distinct gas zones within the BLR: the gas producing the central component at tex2html_wrap_inline4393 light-days and gas, emitting the red and the blue components, at tex2html_wrap_inline4395 light-days moving inward to a central source. These results require that both these 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 (central gas)/mass(dust) = 100 - 750.

keywords: galaxies: individual (Fairall 9) -- galaxies: Seyfert -- ultraviolet: spectra

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