scholarly journals Optical Variability in Active Galactic Nuclei: Starbursts or Disk Instabilities?

1998 ◽  
Vol 504 (2) ◽  
pp. 671-679 ◽  
Author(s):  
T. Kawaguchi ◽  
S. Mineshige ◽  
M. Umemura ◽  
Edwin L. Turner
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Optical Variability

scholarly journals Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. X. Optical Variability Characteristics

2019 ◽  
Vol 877 (1) ◽  
pp. 23 ◽  
Author(s):  
Kai-Xing Lu ◽  
Ying-Ke Huang ◽  
Zhi-Xiang Zhang ◽  
Kai Wang ◽  
Pu Du ◽  
...  
Keyword(s):  
Black Holes ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Optical Variability ◽  
Accretion Rates

scholarly journals Using AGN Variability Surveys to explore the AGN-Galaxy Connection

2013 ◽  
Vol 9 (S304) ◽  
pp. 385-390
Author(s):  
Vicki L. Sarajedini
Keyword(s):  
Conference Proceedings ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Optical Variability ◽  
Host Galaxies ◽  
X Ray ◽  
Galaxy Surveys ◽  
Successful Technique

AbstractVariability is a successful technique used to identify active galactic nuclei in both ground and space-based galaxy surveys. Optical variability surveys using HST have uncovered a number of AGN in deep extragalactic fields extending to z ~ 3 and probing intrinsically faint sources. Mid-IR variability surveys using Spitzer have identified a significant number of AGN and are particularly sensitive to obscured sources. Many variability-detected AGN are not strong X-ray sources or lack the characteristic colors of AGN and would thus be unidentified using other selection techniques. In this conference proceedings, I discuss the nature of the variable sources and their host galaxies identified in deep extragalactic optical and mid-IR surveys.

scholarly journals AGN in the GOODS Fields: Variability and Multiwavelength Detection

2009 ◽  
Vol 5 (S267) ◽  
pp. 139-139
Author(s):  
Vicki L. Sarajedini ◽  
David C. Koo ◽  
Alison J. Klesman
Keyword(s):  
Active Galactic Nuclei ◽  
Selection Criteria ◽  
Galactic Nuclei ◽  
Optical Variability ◽  
Complete Sample ◽  
X Ray

AbstractActive galactic nuclei can be identified in deep HST surveys using different selection techniques and multiwavelength data. We aim to produce a complete sample of AGN in the GOODS South and North fields by combining X-ray, optical and mid-IR selection criteria, including galaxies displaying nuclear optical variability.

scholarly journals Optical Variability in AGNs; Disk Instability or Starbursts?

1998 ◽  
Vol 188 ◽  
pp. 451-452
Author(s):  
T. Kawaguchi ◽  
S. Mineshige ◽  
M. Umemura ◽  
E. L. Turner
Keyword(s):  
Structure Function ◽  
Active Galactic Nuclei ◽  
Common Property ◽  
Function Analysis ◽  
Galactic Nuclei ◽  
Light Curves ◽  
Optical Variability ◽  
Physical Origin

Aperiodic optical variability is a common property of Active Galactic Nuclei (AGN), though its physical origin is still open to question. We have compared light curves among the following two models and observation of quasar 0957+561A,B (Kundić et al. 1997) in terms of structure function analysis (§2).

scholarly journals Optically variable AGN in the three-year VST survey of the COSMOS field

2019 ◽  
Vol 627 ◽  
pp. A33 ◽  
Author(s):  
D. De Cicco ◽  
M. Paolillo ◽  
S. Falocco ◽  
M. Poulain ◽  
W. N. Brandt ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Automated Analysis ◽  
Optical Variability ◽  
Wide Field ◽  
Field Surveys ◽  
Dense Sampling ◽  
A Current ◽  
Field Of Inquiry ◽  
Selection Of

Context. The analysis of the variability of active galactic nuclei (AGN) at different wavelengths and the study of possible correlations of different spectral windows are a current main field of inquiry. Optical variability has been largely used to identify AGN in multivisit surveys. The strength of a selection based on optical variability lies in the opportunity of analyzing data from surveys of large sky areas by ground-based telescopes. However, the effectiveness of optical variability selection with respect to other multiwavelength techniques has been poorly studied down to the depth that is expected from next-generation surveys. Aims. Here we present the results of our r-band analysis of a sample of 299 optically variable AGN candidates in the VST survey of the COSMOS field, counting 54 visits spread over three observing seasons spanning more than three years. This dataset is more than three times larger than the dataset presented in our previous analysis, and the observing baseline is about eight times longer. Methods. We push toward deeper magnitudes (r(AB) ∼ 23.5 mag) than were reached in past studies. We made wide use of ancillary multiwavelength catalogs in order to confirm the nature of our AGN candidates, and constrained the accuracy of the method based on spectroscopic and photometric diagnostics. We also performed tests aimed at assessing the relevance of dense sampling in view of future wide-field surveys. Results. We demonstrate that the method allows the selection of high-purity (> 86%) samples. We take advantage of the longer observing baseline to achieve great improvement in the completeness of our sample with respect to X-ray and spectroscopically confirmed samples of AGN (59% vs. ∼15% in our previous work), as well as in the completeness of unobscured and obscured AGN. The effectiveness of the method confirms the importance of developing future more refined techniques for the automated analysis of larger datasets.

scholarly journals On the Time Scales of Optical Variability of AGN and the Shape of Their Optical Emission Line Profiles

Atoms ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 26
Author(s):  
Edi Bon ◽  
Paola Marziani ◽  
Predrag Jovanović ◽  
Nataša Bon
Keyword(s):  
Emission Line ◽  
Active Galactic Nuclei ◽  
Time Scales ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
Optical Emission ◽  
Light Curves ◽  
Optical Variability ◽  
Line Profiles ◽  
Line Shapes

The mechanism of the optical variability of active galactic nuclei (AGN) is still very puzzling. It is now widely accepted that the optical variability of AGN is stochastic, producing red noise-like light curves. In case they were to be periodic or quasi-periodic, one should expect that the time scales of optical AGN variability should relate to orbiting time scales of regions inside the accretion disks with temperatures mainly emitting the light in this wavelength range. Knowing the reverberation scales and masses of AGN, expected orbiting time scales are in the order of decades. Unfortunately, most of monitored AGN light curves are not long enough to investigate such time scales of periodicity. Here we investigate the AGN optical variability time scales and their possible connections with the broad emission line shapes.

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