# Steps toward Determination of the Size and Structure of the Broad‐Line Region in Active Galactic Nuclei. XV. Long‐Term Optical Monitoring of NGC 5548

 Title: Steps toward Determination of the Size and Structure of the Broad‐Line Region in Active Galactic Nuclei. XV. Long‐Term Optical Monitoring of NGC 5548 Author: Peterson, B. M.; Barth, A. J.; Berlind, P.; Bertram, R.; Bischoff, K.; Bochkarev, N. G.; Burenkov, A. N.; Cheng, F.‐Z.; Dietrich, M.; Filippenko, A. V.; Giannuzzo, E.; Ho, L. C.; Huchra, J; Hunley, J.; Kaspi, S.; Kollatschny, W.; Leonard, D. C.; Malkov, Yu. F.; Matheson, T.; Mignoli, M.; Nelson, B.; Papaderos, P.; Peters, J.; Pogge, R. W.; Pronik, V. I.; Sergeev, S. G.; Sergeeva, E. A.; Shapovalova, A. I.; Stirpe, G. M.; Tokarz, S.; Wagner, R. M.; Wanders, I.; Wei, J.‐Y.; Wilkes, Belinda Jane; Wu, H.; Xue, S.‐J.; Zou, Z.‐L. Note: Order does not necessarily reflect citation order of authors. Citation: Peterson, B. M., A. J. Barth, P. Berlind, R. Bertram, K. Bischoff, N. G. Bochkarev, A. N. Burenkov, et al. 1999. “Steps Toward Determination of the Size and Structure of the Broad‐Line Region in Active Galactic Nuclei. XV. Long‐Term Optical Monitoring of NGC 5548.” The Astrophysical Journal 510 (2) (January 10): 659–668. doi:10.1086/306604. Full Text & Related Files: stepstowarddeter.pdf (333.2Kb; PDF) Abstract: We present the results of 3 yr of ground-based observations of the Seyfert 1 galaxy NGC 5548, which, combined with previously reported data, yield optical continuum and broad-line Hβ light curves for a total of 8 yr. The light curves consist of over 800 points, with a typical spacing of a few days between observations. During this 8 yr period, the nuclear continuum has varied by more than a factor of 7, and the Hβ emission line has varied by a factor of nearly 6. The Hβ emission line responds to continuum variations with a time delay or lag of ~10-20 days, the precise value varying somewhat from year to year. We find some indications that the lag varies with continuum flux in the sense that the lag is larger when the source is brighter. Published Version: doi:10.1086/306604 Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:30248642 Downloads of this work: