A spectroscopic and photometric study of short-timescale variability in NGC 5548

Authors

M. Dietrich, University of Florida
C. F. Bender, University of Nebraska-Lincoln
D. J. Bergmann, University of Nebraska-Lincoln
T. E. Bills, University of Nebraska-Lincoln
N. G. Bochkarev, Sternberg Astronomical Institute, Moscow
A. Burenkov, Special Astrophysical Observatory, Russian Academy of Science
C. Martin Gaskell, University of Nebraska-LincolnFollow
D. D. Gutzmer, University of Nebraska-Lincoln
R. Grove, University of Nebraska-Lincoln
M. E. Hiller, University of Nebraska-Lincoln
J. P. Huchra, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA
Elizabeth S. Klimek, University of Nebraska-LincolnFollow
C. Lund, University of Nebraska - Lincoln
Nelly I. Merkulova, Crimean Astrophysical ObservatoryFollow
S. Pebley, University of Nebraska - Lincoln
Matt Poulsen, University of Nebraska-LincolnFollow
V. I. Pronik, Crimean Astrophysical Observatory, Ukraine, & Isaac Newton Institute of Chile
S. G. Sergeev, Crimean Astrophysical Observatory, Ukraine, & Isaac Newton Institute of Chile
E. A. Sergeeva, Crimean Astrophysical Observatory, Ukraine, & Isaac Newton Institute of Chile
A. I. Shapovalova, Sternberg Astronomical Institute, Moscow
V. V. Vlasyuk, Special Astrophysical Observatory, Russian Academy of Science
Belinda J. Wilkes, Harvard-Smithsonian Center for AstrophysicsFollow

Document Type

Article

Date of this Version

2-1-2001

Comments

Published in Astronomy & Astrophysics 371, 79-92 (2001). DOI: 10.1051/0004-6361:20010330. Published by EDP Sciences; copyright ESO 2001. Online at http://www.edpsciences.org/articles/aa/abs/2001/19/aa10482/aa10482.html

Abstract

Results of a ground-based optical monitoring campaign on NGC 5548 in June 1998 are presented. The broad-band fluxes (U, B, V), and the spectrophotometric optical continuum flux F_λ (5100 Å) monotonically decreased in flux while the broad-band R and I fluxes and the integrated emission-line fluxes of Hα and Hβ remained constant to within 5% . On June 22, a short continuum flare was detected in the broad band fluxes. It had an amplitude of about ~18% and it lasted only ≈90 min. The broad band fluxes and the optical continuum F_λ (5100 Å) appear to vary simultaneously with the EUV variations. No reliable delay was detected for the broad optical emission lines in response to the EUVE variations. Narrow Hβ emission features predicted as a signature of an accretion disk were not detected during this campaign. However, there is marginal evidence for a faint feature at λ ≃ 4962 Å with FWHM ≃ 6 Å redshifted by Δv ≃ 1100 km s^–1 with respect to Hβ_narrow.