Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. IX. Ultraviolet Observations of Fairall 9

TLDR: In this article, an 8-month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with the International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN).

Abstract: An 8 month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with the International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN). While the results of this campaign are more ambiguous than those of previous monitoring campaigns on lower luminosity sources, we find general agreement with the earlier results: (1) there is no measurable lag between ultraviolet continuum bands, and (2) the measured emission-line time lags are very short. It is especially notable that the Ly? + N V emission-line lag is about 1 order of magnitude smaller than determined from a previous campaign by Clavel, Wamsteker, & Glass (1989) when Fairall 9 was in a more luminous state. In other well-monitored sources, specifically NGC 5548 and NGC 3783, the highest ionization lines are found to respond to continuum variations more rapidly than the lower ionization lines, which suggests a radially ionization-stratified broad-line region. In this case, the results are less certain, since none of the emission-line lags are very well determined. The best-determined emission line lag is Ly? + N V, for which we find that the centroid of the continuum-emission-line cross-correlation function is ?cent ? 14-20 days. We measure a lag ?cent 4 days for He II ?1640; this result is consistent with the ionization-stratification pattern seen in lower luminosity sources, but the relatively large uncertainties in the emission-line lags measured here cannot rule out similar lags for Ly? + N V and He II ?1640 at a high level of significance. We are unable to determine a reliable lag for C IV ?1550, but we note that the profiles of the variable parts of Ly? and C IV ?1550 are not the same, which does not support the hypothesis that the strongest variations in these two lines arise in the same region.

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FIG. 1.ÈMean (top) and rms (bottom) SWP spectra of Fairall 9. The bands in which the continuum has been measured are marked above the spectrum, and the dotted lines show power-law Ðts to the Ñuxes in these bands in both the mean and rms spectra. The Lya ] N V, C IV j1550, and He II j1640 integration ranges are marked below the mean spectrum.

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FIG. 2.ÈLight curves of the continuum Ñuxes at 1390 1510 1795A , A , and 1880 (observed wavelengths).A , A

FIG. 7.ÈThe average proÐles at high (thick lines) and low (thin lines) states (top) and their di†erences (bottom) are shown for Lya (left), C IV j1550 (middle), and He II j1640 (right). Note that the overlap in the proÐles of C IV j1550 and He II j1640 is not present in their di†erence proÐles. The thick lines in the bottom panels show the Gaussian Ðts to the di†erence proÐles.