ULTRAVIOLET VARIABILITY OF THE SEYFERT-1 GALAXY FAIRALL-9

The large amplitude of the variations of the Seyfert I Galaxy Fairall- 9 between 1978 and 1991 make this Active Galaxy especially suitable fo r a combined study in terms of reverberation analysis and photoionizat ion modeling over the velocity field of the broad lines of its ultravi olet spectrum. We have combined our ultraviolet data with those availa ble at other wavelengths to derive the intrinsic ionizing continuum an d to compare the predictions of the photoionization models with the ob servations. The UV continuum varies with a factor of 33 +/- 4 on a cha racteristic time scale of 182 days. The intrinsic spectral index UV-op tical is alpha = -0.07 +/- 0.02 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-opt ical continuum (alpha(J-UV) = -0.07 +/- 0.05). Only at low flux levels is the 2-10 keV flux proportional to the UV continuum, at higher UV f lux levels proportionality between the X-rays and the UV brightness br eaks down. The continuum spectral energy distribution (SED) of the nuc leus supports the previously reported FIR-NIR excess associated with 0 .02 M(circle dot) dust at a distance of some 400 +/- 100 light-days, a s well as a soft X-ray excess: possibly associated with the reprocessi ng on an accretion disk of the hard X-rays emitted from a region above the disk. The presence of strong Fe K alpha line in the GINGA spectra of this galaxy does lend support to this model. Line profile variabil ity has been used to isolate four gaussian line components, which are sufficient to describe all lines at all levels of brightness in a cons istent way: one narrow (i.e. unresolved at the IUE resolution), and th ree broad components: a central (velocity same as the narrow line), a red shifted (upsilon = 3300 km s(-1)) and a blue shifted (upsilon = -3 600 km s(-1)) 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 bet ween the broad components and the UV continuum: respectively, 400 +/- 100, -4 +/- 70 and 230 +/- 95 days for the central, red and blue one. Only the red component of Ly alpha lambda 1216 and CIV lambda 1549 app ear to vary linearly with the continuum and give significant transfer functions. The resulting transfer functions are peaked at zero days de lay 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 situ ated between 50 - 250 light-days from the ionizing source, with an hyd rogen density of 10(12-10) cm(-3), a column density of 10(23-26) cm(-2 ) and a covering factor of 12 - 2%, with an ionization parameter betwe en 0.003 and 0.089. However, no optically thick model reproduces the L y alpha/CIV and Ly alpha/NV ratios. From these results we propose a mo del for the structure and dynamics of the BLR: the mass of the central compact object is M approximate to 2 10(8) M(circle dot). Around this exist two distinct gas zones within the BLR: the gas producing the ce ntral component at approximate to 200 light-days and gas, emitting the red and the blue components, at approximate to 80 light-days moving i nward to a central source. These results require that both these gas z ones be localized along the line-of-sight or, alternatively, that the continuum emission must be strongly anisotropic. Besides, the gas emit ting 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.