Astronomía

Líneas de Investigación en el análisis y estudio de variabiliad en AGN.

Complex Variability of Kepler AGN Revealed by Recurrence Analysis

The advent of new time domain surveys and the imminent increase in astronomical data expose the shortcomings in traditional time series analysis (such as power spectra analysis) in characterising ...

'Recent applications of novel methods from non-linear dynamics have shown promise in characterising higher modes of variability and time-scales in AGN. Recurrence analysis in particular can provide complementary information about characteristic time-scales revealed by other methods, as well as probe the nature of the underlying physics in these objects. Recurrence analysis was developed to study the recurrences of dynamical trajectories in phase space, which can be constructed from one-dimensional time series such as light curves. We apply the methods of recurrence analysis to two optical light curves of Kepler-monitored AGN'.

A Forward Modeling Approach to AGN Variability--Method Description and Early Applications

and Ce Zhang 6 * The Astrophysical Journal , Volume 883 , Number 2 Citation Lia F. Sartori et al 2019 ApJ 883 139 1 Institute for Particle Physics and Astrophysics, ETH Zürich ...

https://iopscience.iop.org/article/10.3847/1538-4357/ab3c55/meta

'We present a numerical framework for the variability of active galactic nuclei (AGNs), which links the variability of AGNs over a broad range of timescales and luminosities to the observed properties of the AGN population as a whole, and particularly the Eddington ratio distribution function'.

Ann E. Wehrle Michael Carini Paul J. Wiita 1, 2, and 3 * The Astrophysical Journal , Volume 877 , Number 2 Citation Ann E. Wehrle et al 2019 ApJ 877 151 1 Space Science Institute, 4750 Walnut St ...

https://iopscience.iop.org/article/10.3847/1538-4357/ab1b2d/meta

'We characterize the variability in nearly continuous optical observations of nine active galactic nuclei (AGNs) detected with the Fermi Gamma Ray Space Telescope Large Area Telescope (Fermi-LAT), obtained during the K2 mission with the Kepler spacecraft with 1-minute or 30-minute cadences'.

Extreme AGN variability: evidence of magnetically elevated accretion?

Rapid, large amplitude variability at optical to X-ray wavelengths is now seen in an increasing number of Seyfert galaxies and luminous quasars. The variations imply a global change in accretion ...

'The variations imply a global change in accretion power, but are too rapid to be communicated by inflow through a standard thin accretion disc. Such discs are long known to have difficulty explaining the observed optical/UV emission from active galactic nuclei'.

The Kepler Light Curves of AGN: A Detailed Analysis

and * The Astrophysical Journal , Volume 857 , Number 2 Citation Krista Lynne Smith et al 2018 ApJ 857 141 1 Kavli Institute for Particle Astrophysics and Cosmology, Stanford University ...

https://iopscience.iop.org/article/10.3847/1538-4357/aab88d/meta

'We present a comprehensive analysis of 21 light curves of Type 1 active galactic nuclei (AGN) from the Kepler spacecraft. First, we describe the necessity and development of a customized pipeline for treating Kepler data of stochastically variable sources like AGN. We then present the light curves, power spectral density functions (PSDs), and flux histograms. The light curves display an astonishing variety of behaviors, many of which would not be detected in ground-based studies, including switching between distinct flux levels. Six objects exhibit PSD flattening at characteristic timescales that roughly correlate with black hole mass. These timescales are consistent with orbital timescales or free-fall accretion timescales. We check for correlations of variability and high-frequency PSD slope with accretion rate, black hole mass, redshift, and luminosity. We find that bolometric luminosity is anticorrelated with both variability and steepness of the PSD slope'.

A model for AGN variability on multiple timescales

We present a framework to link and describe AGN variability on a wide range of timescales, from days to billions of years. In particular, we concentrate on the AGN variability features related to ...

'We propose a model to simulate the evolution of AGN light curves with time based on the probability density function (PDF) and power spectral density (PSD) of the Eddington ratio (L/LEdd) distribution. Motivated by general galaxy population properties, we propose that the PDF may be inspired by the L/LEdd distribution function (ERDF), and that a single (or limited number of) ERDF+PSD set may explain all observed variability features. After outlining the framework and the model, we compile a set of variability measurements in terms of structure function (SF) and magnitude difference. We then combine the variability measurements on a SF plot ranging from days to Gyr. The proposed framework enables constraints on the underlying PSD and the ability to link AGN variability on different timescales, therefore providing new insights into AGN variability and black hole growth phenomena'.

Extracting Information from AGN Variability

AGN exhibit rapid, high amplitude stochastic flux variations across the entire electromagnetic spectrum on timescales ranging from hours to years. The cause of this variability is poorly understood

'We present a Green's Function-based method for using variability to (1) measure the time-scales on which flux perturbations evolve and (2) characterize the driving flux perturbations. We model the observed light curve of an AGN as a linear differential equation driven by stochastic impulses. We analyze the light curve of the Kepler AGN Zw 229-15 and find that the observed variability behavior can be modeled as a damped harmonic oscillator perturbed by a colored noise process. The model powerspectrum turns over on time-scale 385~d. On shorter time-scales, the log-powerspectrum slope varies between 2 and 4, explaining the behavior noted by previous studies'.

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