Free Access
Volume 371, Number 1, May III 2001
Page(s) 79 - 92
Section Extragalactic astronomy
Published online 15 May 2001

A&A 371, 79-92 (2001)
DOI: 10.1051/0004-6361:20010330

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

M. Dietrich1, 2, C. F. Bender3, D. J. Bergmann3, T. E. Bills3, N. G. Bochkarev4, A. Burenkov5, C. M. Gaskell3, D. D. Gutzmer3, R. Grove3, M. E. Hiller3, J. P. Huchra6, E. S. Klimek3, C. Lund3, N. Merkulova7, 8, S. Pebley3, M. A. Poulsen3, V. I. Pronik7, 8, S. G. Sergeev7, 8, E. A. Sergeeva7, 8, A. I. Shapovalova4, V. V. Vlasyuk5 and B. Wilkes6

1  Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055, USA
2  Landessternwarte Heidelberg, Königstuhl, 69117 Heidelberg, Germany
3  University of Nebraska, Lincoln, Department of Physics and Astronomy, Lincoln, NE 68588-0111, USA
4  Sternberg Astronomical Institute, Universitetskij Prospect, 13, 119899 Moscow, Russia
5  Special Astrophysical Observatory, Russian Academy of Science, Nyzknij Arkhyz, Karachaj-Cherkess Republic, 369167, Russia
6  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
7  Crimean Astrophysical Observatory, p/o Nauchny, 98409 Crimea, Ukraine
8  Isaac Newton Institute of Chile, Crimean Branch, Chile

(Received 17 November 2000 / Accepted 6 February 2001)

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 $F_\lambda$ (5100 Å) monotonically decreased in flux while the broad-band R and I fluxes and the integrated emission-line fluxes of H$\alpha$ and H$\beta$ 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 $\approx$90 min. The broad band fluxes and the optical continuum $F_\lambda$ (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 H$\beta$ 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 $\lambda \simeq 4962$ Åwith $FWHM\simeq 6$ Åredshifted by $\Delta v\simeq 1100$ km s-1 with respect to H $\beta _{\rm narrow}$.

Key words: galaxies: active -- galaxies: Seyfert galaxies -- galaxies: individual (NGC 5548)

Offprint request: M. Dietrich,

SIMBAD Objects
Tables at the CDS

© ESO 2001

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.