Steps toward Determination of the Size and Structure of the Broad-line Region in Active Galactic Nuclei. X. Variability of Fairall

The results of an optical monitoring campaign on the active nucleus in the luminous Seyfert 1 galaxy Fairall 9 are presented. This campaign was undertaken in parallel with ultraviolet spectroscopic monitoring with the IUE satellite which is described in a separate paper. The primary purpose of this program is to measure the response times (or ““ lags ÏÏ) of the emission lines to continuum variations and thus to extend the range in luminosity of active galactic nuclei (AGNs) for which such measurements have been made. The main conclusions of this work are as follows : 1. Continuum (at 5340 variations of amplitude D12% are detected on timescales as short as D20 AŽ ) days. These variations are much larger than the typical uncertainties in the measurements, which are of order D2%. Over D94 days, a factor of 2 change in the nuclear continuum was observed. 2. The optical continuum light curve resembles that of the UV continuum, showing two ““ events ÏÏ of low-amplitude variations with a duration of D70 days and with no measurable lag between the UV and optical continuum light curves. The UV data show a third larger amplitude event that occurred after the optical monitoring had terminated and unfortunately went unobserved in the optical. 3. The Hb emission-line Ñux also underwent signiÐcant, low-amplitude (o20%) variations. Crosscorrelation analysis reveals that Hb lags behind the UV continuum by about 23 days, a value much smaller than what was previously suggested by earlier variability studies. However, this small lag is consistent with the lags for the UV lines during this campaign in the sense that the Hb lag is approximately 50% larger than that of Lya j1216, as it has been found for lower luminosity AGNs. 4. The Hb di†erence proÐle produced by subtracting the low-state from the high-state data can be described as a two-component structure with blue and red components of similar width (D2500 km s~1) and that appear to vary in phase. Subject headings : galaxies : active È galaxies : individual (Fairall 9) È galaxies : nuclei È galaxies : Seyfert 1 Partly based on observations collected at the European Southern Observatory, La Silla, Chile and at the Observato rio do Pico dos Dias, Minas Gerais, Brazil. 2 Laboratorio AstroЍ sica Espacial y Fi sica Fundamental, LAEFF-INTA, Apartado 50727, Madrid, Spain. 3 Sterrewacht Leiden, Postbus 9513, 2300 R.A. Leiden, Netherlands. 4 Universidade de Sa8 o Paulo, C.P. 9638, 01065-970 Sa8 o Paulo, Brazil. 5 Departamento de Astronomia, Instituto de Fi sica, Universidade Federal do Rio Grande do Sul, Avenida Bento 9500, CP15051, CEP 91500, GoncÓ alves, Porto Alegre, RS, Brazil. 6 CNPq Fellow. 7 URA CNRS D2052, Service dÏAstrophysique, CE Saclay, 91191 Gif sur Yvette, France. 8 Department of Astronomy, Ohio State University, 174 West 18th Avenue, Columbus, OH 43210. 9 ESA IUE Observatory, P.O. Box 50727, 28080 Madrid, Spain. 10 Osservatorio Astronomico di Bologna, Via Zamboni 33, I-40126, Bologna, Italy. 11 Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, 12 Institut dÏAstrophysique, Universite de Liège, Av. de Cointe 5, B-4000 Liège, Belgium. 13 Astronomisches Institut, Universitaet Basel, Venusstrase 7, CH-4102 Binningen, Switzerland. 14 Dipartamento di Astronomia, Universita degli Studi di Bologna, Via Zamboni 33, I-40126, Bologna, Italy. 15 ESO, Casilla 19001, Santiago 19, Chile. 16 Royal Greenwich Observatory, Madingley Road, Cambridge CB3 0HA, United Kingdom. 17 Departament dÏAstronomia i Meteorologia, Universitat de Barcelona, Avenida Diagonal 647, Barcelona, Spain. 18 Lund Observatory, BOX 43, S-22100 Lund, Sweden. 19 McDonald Observatory, RLM 15.308, University of Texas, Austin, TX 78712. 20 Institut fuŽ r Astronomie, UniversitaŽ t Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria. 21 UniversitaŽ ts-Sternwarte GoŽ ttingen, Geismarlandstrasse 11, D-37083 GoŽ ttingen, Germany. 22 Observatorio Astrono mico de Co rdoba, Laprida 854, 5000 Co rdoba, Argentina. 23 Departamento de Astronomia, Observato rio Nacional, Rua Gal. Jose Cristino 77, CEP 20921-030 Rio de Janeiro, RJ, Brazil. 24 Landessternwarte Heidelberg, KoŽ nigstuhl, D-69117 Heidelberg, Germany. 25 Divisa8 o de AstroЍ sica, Instituto Nacional de Pesquisas Espaciais, C.P. 515, CEP 12201-970, Sa8 o Jose dos Campos, SP, Brazil. 26 Vainu Bappu Observatory, Indian Institute of Astrophysics, Kavalur, Alangayam 635701, Tamil Nadu, India. 27 Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218.