Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. IV - Intensity variations of the optical emission lines of NGC 5548

Dietrich, M.Kollatschny, W.Peterson, B. M.Bechtold, J.Bertram, R.Bochkarev, N. G.Boroson, T. A.Carone, T. E.Elvis, MartinFilippenko, A. V.Gaskell, C. M.Huchra, JohnHutchings, J. B.Koratkar, A. P.Korista, K. T.Lame, N. J.Laor, A.MacAlpine, G. M.Malkan, M. A.Mendes de Oliveira, C.Netzer, H.Penfold, J.Penston, M. V.Perez, E.Pogge, R. W.Richmond, M. W.Rosenblatt, E. I.Shapovalova, A. I.Shields, J. C.Smith, H. A.Smith, P. S.Sun, W.-H.Thiele, U.Veilleux, S.Wagner, R. M.Wilkes, BelindaWills, B. J.Wills, D.2017-02-131993Dietrich, M., W. Kollatschny, B. M. Peterson, J. Bechtold, R. Bertram, N. G. Bochkarev, T. A. Boroson, et al. 1993. “Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. IV - Intensity Variations of the Optical Emission Lines of NGC 5548.” The Astrophysical Journal 408 (May): 416. doi:10.1086/172599.0004-637Xhttp://nrs.harvard.edu/urn-3:HUL.InstRepos:30212181Measurements 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.en-USActive Galactic NucleiEmission SpectraGalactic StructureLuminous IntensityOptical Emission SpectroscopySeyfert GalaxiesH Alpha LineH Beta LineH Gamma LineLight CurveLyman SpectraTime Series AnalysisUltraviolet SpectraSteps toward determination of the size and structure of the broad-line region in active galactic nuclei. IV - Intensity variations of the optical emission lines of NGC 5548Journal Article2017-02-1310.1086/172599