Ultraviolet and optical variations in active galactic nuclei - The Seyfert 1 galaxy NGC 5548

Wamsteker, W.; Rodríguez-Pascual, P.; Wills, Beverley J.; Netzer, H.; Wills, D.; Gilmozzi, R.; Barylak, M.; Talavera, A.; Maoz, Dan; Barr, P.; Heck, André

doi:10.1086/168707

Cited by 57 publications

(66 citation statements)

References 3 publications

(14 reference statements)

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“…Fe II emission is relatively weak in NGC5548 (e.g., Wamsteker et al 1990;Vestergaard & Peterson 2005;Denney et al 2009;Mehdipour et al 2015). Vestergaard & Peterson (2005) selected 73 spectra of NGC5548 spanning 13 yr of the AGN Watch project and quantitatively showed that, on average, the flux ratio of optical Fe II over the range 4250-5710 Å (rest-frame) to broad Hβ line is 0.66.…”

Section: Spectral Measurementsmentioning

confidence: 99%

Spectroscopic Indication of a Centi-Parsec Supermassive Black Hole Binary in the Galactic Center of Ngc 5548

Wang

et al. 2016

ApJ

111

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As a natural consequence of cosmological hierarchical structure formation, sub-parsec supermassive black hole binaries (SMBHBs) should be common in galaxies but thus far have eluded spectroscopic identification. Based on four decades of optical spectroscopic monitoring, we report that the nucleus of NGC5548, a nearby Seyfert galaxy long suspected to have experienced a major merger about 1 billion yr ago, exhibits long-term variability with a period of ∼14 yr in the optical continuum and broad Hβ emission line. Remarkably, the double-peaked profile of Hβ shows systematic velocity changes with a similar period. These pieces of observations plausibly indicate that an SMBHB resides in the center of NGC5548. The complex, secular variations in the line profiles can be explained by orbital motion of a binary with equal mass and a semimajor axis of ∼22 light-days (corresponding to ∼18 milli-parsec). At a distance of 75Mpc, NGC5548 is one of the nearest sub-parsec SMBHB candidates that offers an ideal laboratory for gravitational wave detection.

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Section: Spectral Measurementsmentioning

confidence: 99%

Spectroscopic Indication of a Centi-Parsec Supermassive Black Hole Binary in the Galactic Center of Ngc 5548

Wang

et al. 2016

ApJ

111

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“…Especially the large amplitude of the variability offers a good opportunity to evaluate the possible existence of different response characteristics over the extent of the broad lines. The line analysis has been done in three stages following the same procedures as applied by Wamsteker et al (1990) for NGC 5548: first we have removed the various continuum contributions, since especially the small blue bump, mainly composed of Balmer continuum and the many blended FeII lines, form a semicontinuum, which could affect the final results of the line analysis. After the continuum has been properly allowed Fig.…”

Section: Analysis Of the Emission Linesmentioning

confidence: 99%

“…This allows us furthermore to measure strongly blended lines such as Lyαλ1216 and NVλ1240. We have used the error measure of Rodríguez-Pascual (1989) and Wamsteker et al (1990). This method assumes that the component errors are perfectly correlated, and thus gives an upper limit for the error.…”

Section: Line Variability: Total Intensitymentioning

confidence: 99%

“…This method has been first applied by Wamsteker et al (1990) to the UV and optical spectra of NGC 5548 and has here been used for Lyαλ1216, CIVλ1549, SiIVλ1397 and MgIIλ2798. With only four components, all line profiles of F-9 could be described over the whole brightness range.…”

Section: Profile Decompositionmentioning

confidence: 99%

“…These are introduced as input parameters in the total profile fit. Similarly to Wamsteker et al (1990), we represent the components as gaussians. This procedure makes it also possible to measure some of the highly blended lines by introducing the blends as individual components in an overall line fit.…”

Section: Profile Decompositionmentioning

confidence: 99%

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Ultraviolet variability of the Seyfert 1 galaxy Fairall 9

Recondo¹,

Wamsteker²,

Clavel³

et al. 1997

Astron. Astrophys. Suppl. Ser.

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Abstract. The large amplitude of the variations of the Seyfert I Galaxy Fairall-9 between 1978 and 1991 make this Active Galaxy especially suitable for a combined study in terms of reverberation analysis and photoionization modeling over the velocity field of the broad lines of its ultraviolet spectrum. We have combined our ultraviolet data with those available at other wavelengths to derive the intrinsic ionizing continuum and to compare the predictions of the photoionization models with the observations. The UV continuum varies with a factor of 33 ± 4 on a characteristic time scale of 182 days. The intrinsic spectral index UV-optical is α = −0.07 ± 0.02 and the optical variations do not lag behind the UV variations at the mean sampling interval of 96 days. In the near IR, the J band flux presents a direct extension of the UV-optical continuum (α J−UV = −0.07 ± 0.05). Only at low flux levels is the 2−10 keV flux proportional to the UV continuum, at higher UV flux levels proportionality between the X-rays and the UV brightness breaks down. The continuum spectral energy distribution (SED) of the nucleus supports the previously reported FIR-NIR excess associated with 0.02 M dust at a distance of some 400 ± 100 light-days, as well as a soft X-ray excess, possibly associated with the reprocessing on an accretion disk of the hard X-rays emitted from a region above the disk. The presence of strong Fe Kα line in the GINGA spectra of this galaxy does lend support to this model. Line profile variability has been used to isolate four gaussian line components, which are sufficient to describe all lines at all levels of brightness in a consistent way: one narrow (i.e. unresolved at the IUE resolution), and three broad components: a central (velocity same as the narSend offprint requests to: G. Wuchterl Tables 1, 10, 11, 12, 13 only available in electronic form at CDS via anonymous ftp to CDSARC.U-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html row line), a red shifted (v = 3300 km s −1 ) and a blue shifted (v = −3600 km s −1 ) one. The three broad components are strongly correlated with the UV continuum, indicating that photoionization is the dominant mechanism in the BLR. Correlation analysis shows different delays between the broad components and the UV continuum: respectively, 400 ± 100, −4 ± 70 and 230 ± 95 days for the central, red and blue one. Only the red component of Lyαλ1216 and CIVλ1549 appear to vary linearly with the continuum and give significant transfer functions. The resulting transfer functions are peaked at zero days delay and are unresolved at the average time resolution (96 days) of our data. The photoionization models (CLOUDY) applied to the line ratios in these components, indicate that the Broad-Line-Region (BLR) is situated between 50 − 250 light-days from the ionizing source, with an hydrogen density of 10 12−10 cm −3 , a column density of 10 23−26 cm −2 and a covering factor of 12 − 2%, with an ionization parameter between 0.003 and 0.089. However, no optically thick mode...

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Ultraviolet and optical variations in active galactic nuclei - The Seyfert 1 galaxy NGC 5548

Cited by 57 publications

References 3 publications

Spectroscopic Indication of a Centi-Parsec Supermassive Black Hole Binary in the Galactic Center of Ngc 5548

Spectroscopic Indication of a Centi-Parsec Supermassive Black Hole Binary in the Galactic Center of Ngc 5548

Ultraviolet variability of the Seyfert 1 galaxy Fairall 9

AGN Emission Lines

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