Rapid variability of active galactic nuclei: The 160min periodicity in NGC 3516, NGC 4151 and Quasar 3C 273

ABSTRACT We present a multifractal analysis of the long-term light curves of a small sample of type 1 active galactic nuclei: NGC 4151, Arp 102B, 3C 390.3, E1821+643 and NGC 7469. We aim to investigate how the degrees of multifractality of the continuum and Hβ line vary among the five different objects and to check whether the multifractal behaviours of the continuum and the Hβ line correlate with standard accretion parameters. The backward (θ = 0) one-dimensional multifractal detrended moving average procedure was applied to light curves covering the full observation period and partial observation periods containing an equal number of epochs for each object. We detected multifractal signatures for the continua of NGC 4151, Arp 102B and 3C 390.3 and for the Hβ lines of NGC 4151 and 3C 390.3. However, we found nearly monofractal signatures for the continua of E1821+643 and NGC 7469, as well as for the Hβ lines of Arp 102B, E1821+643 and NGC 7469. In addition, we did not find any correlations between the degree of multifractality of the Hβ line and accretion parameters, while the degree of multifractality of the continuum seems to correlate with the Eddington ratio (i.e. the smaller the ratio is, the stronger the degree of multifractality). The given method is not robust, and these results should be taken with caution. Future analysis of the sampling rate and other properties of the light curves should help with better constraining and understanding these results.

Download Full-text

Infrared Line Shapes in Active Galactic Nuclei

Symposium - International Astronomical Union ◽

10.1017/s0074180900176430 ◽

1994 ◽

Vol 159 ◽

pp. 462-462

Author(s):

Rodger I. Thompson

Keyword(s):

Active Galactic Nuclei ◽

Electron Density ◽

Galactic Nuclei ◽

Complete Spectrum ◽

Line Shapes ◽

Ngc 4151

This paper presents the complete spectrum of NGC 4151 from 0.87 to 2.5 μm as well as detail of the Paschen α profile in 3C273 at a resolution of about 5000. Analysis of the several observed Fe II lines yields a most probable electron density of 104 and a most likely temperature of 104. The Fe II to H ratio is 2+/− 1 × 10−6 which is 5–7% of the available iron if the Fe/H ratio is solar.

Download Full-text

Fluorescence in the Active Galactic Nuclei NGC 4151

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313004997 ◽

2012 ◽

Vol 8 (S295) ◽

pp. 266-266

Author(s):

Mattias Eriksson ◽

Hans Veenhuizen

Keyword(s):

Active Galactic Nuclei ◽

Wavelength Region ◽

Galactic Nuclei ◽

Collisional Excitation ◽

Ngc 4151 ◽

Uv Emission

AbstractThe possibility of UV lines from Fe II formed in the BLR of NGC 4151 has been examined. As a result Fe II emission has been shown to play an important role for the topology of the 2000 to 3000 Å wavelength region of the NGC 4151 spectra. The Fe II UV emission originates from two processes, collisional excitation and PAR (photoexcitation by accidental resonance).

Download Full-text

Rapid X-ray variability in active galactic nuclei

Symposium - International Astronomical Union ◽

10.1017/s0074180900152842 ◽

1986 ◽

Vol 119 ◽

pp. 269-271 ◽

Cited By ~ 1

Author(s):

P. Barr ◽

R. Mushotzky ◽

P. Giommi ◽

J. Clavel ◽

W. Wamsteker

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Seyfert Galaxies ◽

Low Earth Orbit ◽

Earth Orbit ◽

Rapid Variability ◽

X Ray ◽

Electron Positron ◽

Eddington Limit

SummaryRecent EXOSAT observations of active galactic nuclei are presented. Unlike earlier X-ray satellites (all of which flew in low earth orbit), the deep orbit of EXOSAT allows long continuous observations of celestial X-ray sources, uninterrupted by earth occultation etc. We present the results of EXOSAT observations of several AGN which have been seen to vary rapidly (timescale 0.2–6 hours). We also consider the implications of rapid variability in AGN. For Seyfert galaxies and quasars, we find a highly significant correlation between the timescale of variability and their X-ray luminosity. They are not, howwever, bounded either by the (classical) Eddington limit nor by efficiency arguments. We sugest, rather, that the emitting plasma is dominated by electron-positron pairs.

Download Full-text

X-Ray Properties of Galactic Nuclei

Highlights of Astronomy ◽

10.1017/s1539299600004512 ◽

1980 ◽

Vol 5 ◽

pp. 623-630

Author(s):

Daniel W. Weedman

Keyword(s):

Emission Line ◽

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Seyfert Galaxy ◽

Seyfert Galaxies ◽

Strong Emission ◽

X Ray ◽

Ngc 4151 ◽

Survey Results ◽

Emission Line Galaxies

Preparing this review was my just punishment for stating only two years ago - in another review (Weedman 1977) - that Seyfert galaxies are not strong X-ray sources. I said that because, as recently as three years ago, NGC 4151 was the only Seyfert galaxy known as an X-ray source. Now we have 36 Seyfert 1 galaxies, along with 12 other galaxies with strong emission-line nuclei, that are X-ray sources. And this is all without even having HEAO-2 data at our disposal yet. The study of active galactic nuclei with X-ray astronomy is progressing so rapidly that a reviewer feels almost hopeless. The best I can do is summarize what is known as of the summer of 1979 and give a simple overview of how X-ray and other properties relate.Some excellent reviews of the X-ray properties of Seyfert and other emission-line galaxies already exist. I especially recommend that by Andrew Wilson (1979). He provides very complete references as of a year ago, but X-ray astronomy is progressing so rapidly that he then had only somewhat more than half the active nuclei now in Tables 1 and 2. It was the group working with the Ariel V SSI that made the initial comprehensive X-ray studies of Seyfert galaxies (Ward et al. 1977, Elvis et al. 1978). The UHURU results for Seyfert galaxies followed soon after and are summarized by Tananbaum et al. (1978); the HEAO-A-2 survey results are now in press (Marshall et al. 1979) I have tried to incorporate these and other recent results in Tables 1 and 2.

Download Full-text

1–3-Day Variations of the Broad Emission Lines of Seyfert Nuclei

Symposium - International Astronomical Union ◽

10.1017/s0074180900155172 ◽

1987 ◽

Vol 121 ◽

pp. 219-222

Author(s):

Nikolay G. Bochkarev

Keyword(s):

Active Galactic Nuclei ◽

Angular Size ◽

Galactic Nuclei ◽

Photometric Data ◽

Emission Lines ◽

Line Profiles ◽

Physical Processes ◽

Ngc 4151 ◽

Broad Emission ◽

Broad Emission Line

One of the principal problems of investigation of AGNs is to understand the nature of the central objects and the physical processes which yield their gigantic luminosities. This requires us to consider the innermost parts of AGNs (3–30 gravitational radii, i.e. ≲ 1016 cm: angular size less than 1 milliarcsecond).1–3d variations of the relative shape of broad emission line profiles of active galactic nuclei (AGN) are perhaps the most informative probe of the innermost parts of AGNs (r = 1015–16 cm from the centre). Optimal objects for these observations are Sy 1.5 with strong variations of the non-thermal continuum (e.g. NGC 4151). The expected amplitude of the variations ranges from a few percent to 10–20%. The optimal spectral resolution is 0.5–5 Å. It is very desirable to complement spectral observations with photometric data. The results of the first set of such observations with the 6-meter telescope are reported.

Download Full-text

Analyzing temporal variations of AGN emission line profiles in the context of (dusty) cloud structure formation in the broad line region

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834291 ◽

2019 ◽

Vol 621 ◽

pp. A46 ◽

Cited By ~ 2

Author(s):

J. Esser ◽

J.-U. Pott ◽

H. Landt ◽

W. D. Vacca

Keyword(s):

Active Galactic Nuclei ◽

Accretion Disk ◽

Galactic Nuclei ◽

Temporal Variations ◽

Cloud Formation ◽

Broad Line ◽

Ngc 4151 ◽

Broad Line Region ◽

The Past ◽

Line Region

The formation processes and the exact appearance of the dust torus and broad line region (BLR) of active galactic nuclei (AGN) are under debate. Theoretical studies show a possible connection between the dust torus and BLR through a common origin in the accretion disk. However observationally the dust torus and BLR are typically studied separately. NGC 4151 is possibly one of the best suited Seyfert 1 galaxies for simultaneous examinations because of its high number of both photometric and spectroscopic observations in the past. Here we compare changes of the dust radius to shape variations of broad emission lines (BEL). While the radius of the dust torus decreased by almost a factor of two from 2004 to 2006 shape variations can be seen in the red wing of BELs of NGC 4151. These simultaneous changes are discussed in a dust and BEL formation scheme. We also use the BEL shape variations to assess possible cloud distributions, especially in azimuthal direction, which could be responsible for the observed variations. Our findings can best be explained in the framework of a dust inflated accretion disk. The changes in the BELs suggest that this dusty cloud formation does not happen continuously, and over the whole accretion disk, but on the contrary in spatially confined areas over rather short amount of times. We derive limits to the azimuthal extension of the observed localized BEL flux enhancement event.

Download Full-text

The EXOSAT Spectral Survey of Emission Line AGN

Symposium - International Astronomical Union ◽

10.1017/s0074180900140689 ◽

1989 ◽

Vol 134 ◽

pp. 155-160

Author(s):

K. A. Pounds ◽

T. J. Turner

Keyword(s):

Emission Line ◽

Active Galactic Nuclei ◽

Spectral Component ◽

Broad Band ◽

Galactic Nuclei ◽

Rapid Variability ◽

X Ray ◽

Disc Model ◽

Spectral Survey ◽

Seyfert Type

Results are presented from EXOSAT observations of Seyfert type active galactic nuclei (AGN). The sample chosen for study are 48 hard X-ray selected Seyfert type AGN, including all 30 of the emission line AGN in the Piccinotti sample. Combining EXOSAT LE and ME data has allowed us to obtain broad band X-ray spectra over the range 0.1–10 keV. Spectra in the ∼ 2–10 keV range are found to be well described by a simple power-law. The distribution of spectral indices across the sample can be approximated by a Gaussian distribution of mean energy index ∝ = 0.70 with σ∝ = 0.17 although not all individual spectra are consistent with this mean at the 90% confidence level. EXOSAT has also revealed a substantial number of sources with complex soft X-ray spectra. These include spectra with a second spectral component at soft X-ray energies and sources with “leaky” absorbing columns. Evidence that soft excess components occur in at least 50% of Seyfert type AGN together with detection of rapid variability in the soft component provides quantitative support for an accretion disc model for AGN.

Download Full-text

FEEDBACK FROM MASS OUTFLOWS IN NEARBY ACTIVE GALACTIC NUCLEI. II. OUTFLOWS IN THE NARROW-LINE REGION OF NGC 4151

The Astrophysical Journal ◽

10.1088/0004-637x/799/1/83 ◽

2015 ◽

Vol 799 (1) ◽

pp. 83 ◽

Cited By ~ 25

Author(s):

D. Michael Crenshaw ◽

Travis C. Fischer ◽

Steven B. Kraemer ◽

Henrique R. Schmitt

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Narrow Line ◽

Ngc 4151 ◽

Line Region ◽

Narrow Line Region

Download Full-text

Possible mechanism for multiple changing-look phenomena in active galactic nuclei

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038575 ◽

2020 ◽

Vol 641 ◽

pp. A167 ◽

Cited By ~ 2

Author(s):

M. Sniegowska ◽

B. Czerny ◽

E. Bon ◽

N. Bon

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Active Galaxies ◽

Simple Explanation ◽

Ngc 4151 ◽

Outer Disk ◽

Accretion Process ◽

Further Development ◽

Eddington Limit ◽

Standard Gas

Context. The changing-look phenomenon observed in a growing number of active galaxies challenges our understanding of the accretion process close to a black hole. Aims. We propose a simple explanation for the sources where multiple semi-periodic outbursts are observed, and the sources are operating close to the Eddington limit. Methods. The outburst are caused by the radiation pressure instability operating in the narrow ring between the standard gas-dominated outer disk and the hot optically thin inner advection-dominated accretion flow. The corresponding limit cycle is responsible for periodic outbursts, and the timescales are much shorter than the standard viscous timescale due to the narrowness of the unstable radial zone. Results. Our toy model gives quantitative predictions and works well for multiple outbursts like those observed in NGC 1566, NGC 4151, NGC 5548, and GSN 069, although the shapes of the outbursts are not yet well modeled, and further development of the model is necessary.

Download Full-text