Bibcode
DOI
Wills, D.; Wills, B. J.; Wilkes, B. J.; Wagner, R. M.; Veilleux, S.; Thiele, U.; Sun, W.-H.; Smith, P. S.; Smith, H. A.; Shields, J. C.; Shapovalova, A. I.; Rosenblatt, E. I.; Richmond, M. W.; Pogge, R. W.; Perez, E.; Penston, M. V.; Penfold, J.; Malkan, M. A.; Mendes de Oliveira, C.; Netzer, H.; Laor, A.; MacAlpine, G. M.; Koratkar, A. P.; Korista, K. T.; Lame, N. J.; Huchra, J. P.; Hutchings, J. B.; Filippenko, A. V.; Gaskell, C. M.; Elvis, M.; Carone, T. E.; Boroson, T. A.; Dietrich, M.; Kollatschny, W.; Peterson, B. M.; Bechtold, J.; Bertram, R.; Bochkarev, N. G.
Bibliographical reference
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 408, no. 2, p. 416-427.
Advertised on:
5
1993
Journal
Citations
94
Refereed citations
82
Description
Measurements of optical emission-line flux variations based on spectra
of the Seyfert galaxy NGC 5548 obtained between December 1988 and
October 1989 are reported. All of the measured optical emission lines,
H-alpha, H-beta, H-gamma, He I 5876, and He II 4686, exhibit the same
qualitative behavior as the UV and optical continua, but with short time
delays, or lags, which are different for the various lines.
Cross-correlation analysis is applied to measure the lags between the
various lines and the continuum. Similar lags are found with respect to
the UV continuum for H-alpha and H-beta, 17 and 19 d, respectively. The
lag for H-gamma is shorter (13 d), only somewhat larger than the lag
measured for Ly-alpha (about 10 d). The helium lines respond to
continuum variations more rapidly than the hydrogen lines, with lags of
about 7 d for He II 4686 and 11 d for He I 5876.