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

Authors

G. A. Reichert, NASA Goddard Space Flight Center
P. M. Rodriguez-Pascual, ESA IUE Observatory
D. Alloin, Universite Paris
J. Clavel, Astro~hvsics Division of ESA
D. Michael Crenshaw, NASA Goddard Space Flight CenterFollow
Gerard A. Kriss, Johns Hopkins UniversityFollow
Julian Henry Krolik, Johns Hopkins UniversityFollow
Matthew A. Malkan, University of California at Los AngelesFollow
Hagai Netzer, Tel-Aviv UniversityFollow
Bradley M. Peterson, Ohio State UniversityFollow
W. Wamsteker, ESA IUE Observatory
A. Altamore, Instituto Astronomico dell'universita
B. Altieri, European Southern Observatory, La Silla
K. S.J. Anderson, New Mexico State UniversityFollow
J. H. Blackwell Jr,, NASA Goddard Space Flight Center
C. Boisson, Universite ParisFollow
N. Brosch, Tel-Aviv UniversityFollow
T. E. Carone, University of California at Berkeley
M. Dietrich, Universitatssternwarte
M. N. England, NASA Goddard Space Flight Center
I. N. Evans, S ~ a c eT elesco~eS cience Institute
A. V. Filippenko, University of California at BerkeleyFollow
C. Martin Gaskell, University of Nebraska-LincolnFollow
M. Goad, University College LondonFollow
P. M. Gondhalekar., Rutherford Appleton Laboratory
K. Horne, S ~ a c eT elesco~eS cience Institute
D. Kazanas, NASA Goddard Space Flight Center
W. Kol Latschny, Universitatssternwarte,
A. P. Koratkar, S ~ a c eT elesco~eS cience Institute
Kirk T. Koristag, S ~ a c eT elesco~eS cience InstituteFollow
G. M. Macalpine, University of Michigan
D. Maoz, Princeton
T. Mazeh, Tel-Aviv University
B. Mccollum, NASA Goddard Space Flight Center
H. Richard Miller, Georgia State UniversityFollow
C. Mendes De Oliveira, University of British Columbia
Paul T. O'brien, University College LondonFollow
M. G. Pastoriza, Instituto de FisicaFollow
D. Pelat, Universite Paris
E. Perez, Instituto de Astrofisica de Canarias
G. C. Perola, Istituto Astronomico dell'universita
Richard William Pogge, Ohio State UniversityFollow
R. L. Ptak, Bowling Green State University
M. C. Recondo-Gonzalez, ESA IUE Observatory,
J. Rodriguez-Espinosa, Instituto de Astrofisica de Canarias
E. I. Rosenblatt, University of California at San Diego
A. C. Sadun, Agnes Scott College
M . Santos-Lleo, Universite Paris
J. C. Shields, Ohio State University
C. R. Shrader, NASA Goddard Space Flight Center
J. M. Shull, University of Colorado
S. M. Simkin, Michigan State University
M. L. Sitko, University of Cincinnati
M. A.J Snuders, Universitat Tiibingen
L. S. Sparke, University of Wisconsin
G. M. Stirpe, Osservatorio Astronomico di Bologna
R. Stoner, Bowling Green State University
T. . Storchi-Bergm, Universidade Federal do Rio Grande do Sul
W. H. Sun, National Central University
T. F. Wang, University of Science and Technology
W. F. Welsh, S ~ a c eT elesco~eS cience Institute
R. J. White, Ohio State University
C. Winge, Universidade Federal do Rio Grande do Sul
W. Zhen, Johns Hopkins University

Date of this Version

1994

Comments

Published in THE ASTROPHYSICAL JOURNAL 42, 5: 582-608,1994 April 20 Copyright 1994. The American Astronomical Society. All rights reserved. Printed in U.S.A. Used by permission.

Abstract

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 ≤20 days and the second ≤ 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 wave-lengths (Δt < 2 days). Generally, the amplitude of variability of the emission lines was lower than (or comparable to) that of the continuum. Apart from Mg II (which varied little) and N v (which is relatively weak and badly blended with Ly∝), the light curves of the emission lines are very similar to the continuum light curves, in each case with a small systematic delay or "lag." As for NGC 5548, the highest ionization lines seem to respond with shorter lags than the lower ionization lines. The lags found for NGC 3783 are considerably shorter than those obtained for NGC 5548, with values of (formally) ~0 days for He II + O III] , and ~4 days for Ly∝ and C IV. The data further suggest lags of ~4 days for Si IV + O IV] and 8-30 days for Si III] + C III]. Mg II lagged the 1460 Å continuum by ~9 days, although this result depends on the method of measuring the line flux and may in fact be due to variability of the underlying Fe II lines. Correlation analysis further shows that the power density spectrum contains substantial unresolved power over timescales of ≤ 2 days, and that the character of the continuum variability may change with time.