Reichert, G. A.; Rodriguez-Pascual, P. M.; Alloin, D.; Clavel, J.; Crenshaw, D. M.; Kriss, G. A.; Krolik, J. H.; Malkan, M. A.; Netzer, H.; Peterson, B. M.; Wamsteker, W.; Altamore, A.; Altieri, B.; Anderson, K. S.; Blackwell, J. H., Jr.; Boisson, C.; Brosch, N.; Carone, T. E.; Dietrich, M.; England, M. N.; Evans, I. N.; Filippenko, A. V.; Gaskell, C. M.; Goad, M.; Gondhalekar, P. M.; Horne, K.; Kazanas, D.; Kollatschny, W.; Koratkar, A. P.; Korista, K. T.; MacAlpine, G. M.; Maoz, D.; Mazeh, T.; McCollum, B.; Miller, H. R.; Mendes de Oliveira, C.; O'Brien, P. T.; Pastoriza, M. G.; Pelat, D.; Perez, E.; Perola, G. C.; Pogge, R. W.; Ptak, R. L.; Recondo-Gonzalez, M. C.; Rodriguez-Espinosa, J. M.; Rosenblatt, E. I.; Sadun, A. C.; Santos-Lleo, M.; Shields, J. C.; Shrader, C. R.; Shull, J. M.; Simkin, S. M.; Sitko, M. L.; Snijders, M. A. J.; Sparke, L. S.; Stirpe, G. M.; Stoner, R.; Storchi-Bergmann, T.; Sun, W.-H.; Wang, T.; Welsh, W. F.; White, R. J.; Winge, C.; Zheng, W.
Bibliographical reference
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 425, no. 2, p. 582-608
Advertised on:
4
1994
Journal
Citations
166
Refereed citations
142
Description
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 is less than or approximately 20 days and the
second is less than or approximately 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 wavelengths (delta(t) is less than 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(alpha), 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) approximately 0 days for He II + O
III), and approximately 4 days for Ly(alpha) and C IV. The data further
suggest lags of approximately 4 days for Si IV + O IV) and 8-30 days for
Si III + C III). Mg II lagged the 1460 A continuum by approximately 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 is
less than or approximately 2 days, and that the character of the
continuum variability may change with time.