Steps Toward Determinaton of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. V. Variability of the Ultraviolet Continuum and Emission Lines of NGC 3783

We report on the results of intensive ultraviolet spectral monitoring of the Seyfert 1 galaxy NGC 3783. The nucleus of NGC 3783 was observed with the International Ultraviolet Explorer satellite on a regular basis for a total of 7 months, once every 4 days for the first 172 days and once every other day for the final 50 days. Significant variability was observed in both continuum and emission-line fluxes. The light curves for the continuum fluxes exhibited two well-defined local minima or "dips," the first lasting 5 2 0 days and the second 5 4 days, with additional episodes of relatively rapid flickering of approximately the same amplitude. As in the case of NGC 5548 (the only other Seyfert galaxy that has been the subject of such an intensive, sustained monitoring effort), the largest continuum variations were seen at the shortest wavelengths, so that the continuum became "harder" when brighter. The variations in the continuum occurred simultaneously at all waveUniversities Space Research Association, NASA Goddard Space Flight Center, Code 668, Greenbelt, MD 20771; I: [email protected]. ' Guest Observer with the International Ultraviolet Explorer satellite. ESA IUE Observatory, P.O. Box 50727,28080 Madrid, Spain. Observatoire de Paris. URA173 CNRS. Universite Paris 7. 92195 Meudon, France. I S 0 Observatorv. Astro~hvsics Division of ESA, ESTEC, Postbus 299, 2200-AG ~ o o r d w i j k l ~ h e ~ ihdrlands. Astronomy Program, Computer Sciences Corporation, NASA Goddard Space Flight Center, Code 681, Greenbelt, MD 20771. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218. Department of Astronomy, University of California at Los Angeles, MathScience Building, Los Angeles, CA 90024. School of Physics and Astronomy and Wise Observatory, Tel-Aviv University, Tel Aviv 69978, Israel. l o Department of Astronomy, Ohio State University, 174 West 18th Avenue, Columbus, OH 43210. Istituto Astronomico dell'universita, Via Lancisi 29,I-00161 Rome, Italy. l 2 European Southern Observatory, La Silla, Casilla 19001, Santiago, Chile. l 3 Department of Astronomy, New Mexico State University, Box 30001, Department 4500, Las Cruces, NM 88003. l 4 Space Sciences Laboratory, University of California at Berkeley, Berkeley, CA 94720. " Universitatssternwarte, Geismarlandstrasse 11, D-3400 Gottingen, Germany. l 6 Computer Sciences Corporation, NASA Goddard Space Flight Center, Code 684.9, Greenbelt, MD 20771. l 7 S ~ a c e Telesco~e Science Institute. 3700 San Martin Drive. Baltimore. MD 21'218. l 8 Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720. l 9 Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588-0111. 20 Department of Physics and Astronomy, University College London, Gower Street, London WClE 6BT, UK. Astrophysics Group, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX1 1 OQX, UK. Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Code 665, Greenbelt, MD 20771. 2 3 Department of Astronomy, University of Michigan, Dennison Building, Ann Arbor, MI 48109-1090. 24 Institute for Advanced Study, Princeton, NJ 08540. 2 5 NASA, Code SZB, Washington, DC 20546, and Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303. 26 Department of Astronomy, University of British Columbia, Vancouver, BC, Canada V6T 1W5. '' Departamento de Astronomia, Instituto de Fisica, Universidade Federal do Rio Grande do Sul, Avenido Bento Gonqalves 9500, CP15051, CEP 91500, Porto Alegre, RS, Brazil. Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Spain. 29 Department of Physics and Astronomy, Bowling Green State University, Bowling Green, OH 43403. 30 Center for Astrophysics and Space Science, University of California at San Diego, MC C-011, La Jolla, CA 92093. 3 1 Department of Physics and Astronomy and Bradley Observatory, Agnes Scott College, Decatur, GA 30030. " Computer Sciences Corporation, NASA Goddard Space Flight Center, Code 668.1, Greenbelt, MD 20771. 3 3 Joint Institute for Laboratory Astrophysics and National Institute of Standards and Technology, University of Colorado, Campus Box 440,