A Spectroscopic and Photometric Study of Short-Timescale Variability in NGC5548

Abstract

Results of a ground-based optical monitoring campaign on NGC5548 in June 1998 are presented. The broad-band fluxes (U,B,V), and the spectrophotometric optical continuum flux F_lambda(5100 A) monotonically decreased in flux while the broad-band R and I fluxes and the integrated emission-line fluxes of Halpha and Hbeta 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_lambda(5100 A) 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 Hbeta 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 = 4962 A with FWHM=~6 A redshifted by Delta v = 1100 km/s with respect to Hbeta_narrow.

arXiv comment12 pages, 7 figures, accepted for publishing in A&A

References in corpus (20)

• Reverberation Measurements for 17 Quasars and the Size-Mass-Luminosity Relations in Active Galactic Nuclei
• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei: I. Comparing the Photoionization and Reverberation Techniques
• On Uncertainties in Cross-Correlation Lags and the Reality of Wavelength-Dependent Continuum Lags in Active Galactic Nuclei
• ASCA Observations of Seyfert 1 galaxies: III. The Evidence for Absorption & Emission due to Photoionized Gas
• X-Ray and Optical Variability in NGC 4051 and the Nature of Narrow-Line Seyfert 1 Galaxies
• On the Reliability of Cross Correlation Function Lag Determinations in Active Galactic Nuclei
• Multiwavelength observations of short time-scale variability in NGC 4151. IV. Analysis of multiwavelength continuum variability
• Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei. III. Integrated Spectra for Hydrogen-Helium Disks
• Simultaneous EUVE/ASCA/RXTE Observations of NGC 5548
• Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XII. Ground-Based Monitoring of 3C 390.3
• New constraints on the continuum-emission mechanism of AGN: Intensive monitoring of NGC 7469 in the X-ray and ultraviolet
• Multiwavelength observations of short time-scale variability in NGC 4151. II. Optical observations
• Reverberation Mapping and the Physics of Active Galactic Nuclei
• 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
• Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. VI. Variability of NGC 3783 from ground-based data
• Intensive HST, RXTE and ASCA Monitoring of NGC 3516: Evidence Against Thermal Reprocessing
• Multiwavelength observations of short time-scale variability in NGC 4151. I. Ultraviolet observations
• Multiwavelength observations of short time-scale variability in NGC 4151. III. X-ray and Gamma-ray observations
• X-ray Observations of the Broad-Line Radio Galaxy 3C 390.3
• The X-ray Spectral Variability of the Seyfert Galaxy NGC 3227

Cited by in corpus (5)

• Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A Thirteen-Year Study of Spectral Variability in NGC 5548
• Evidence for periodicity in 43 year-long monitoring of NGC 5548
• Profile variability of the H-alpha and H-beta broad emission lines in NGC5548
• Using Multiwavelength Observations to Determine the Black Hole Mass and Accretion Rate in the Type 1 Seyfert Galaxy NGC 5548
• Simultaneous X-ray and Ultraviolet spectroscopy of the Seyfert galaxy NGC 5548. III. X-ray time variability