Download or read book The Optical Variability of Active Galactic Nuclei written by Jackeline Moreno and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active Galactic Nuclei (AGN) exhibit strong, rapid optical luminosity fluctuations that are often described as stochastic (exhibiting intrinsic randomness). The physical mechanisms that produce stochastic fluctuations may be studied by characterizing the correlation structure of such data in both the time domain and the frequency domain. We find evidence that AGN do not exhibit a universal optical PSD; the PSD shape (or light curve correlation structure) may be a function of fundamental AGN properties. In this work, we develop an application of continuous-time autoregressive moving average models (CARMA) to AGN optical light curves, and we discuss their relationships to more traditional techniques such as the structure function (SF) and the power spectral density (PSD). We present a study of AGN variability using the Damped Harmonic Oscillator (DHO) or CARMA(2,1) model. We estimate DHO timescales and optical variability amplitudes for 7492 objects with both SDSS (Stripe 82) r-band and CRTS V-band light curves. We employ clustering methods (t-distributed stochastic neighbor embedding) in this work to test the non-universality of AGN variability (deviations from the damped random walk; DRW or CARMA(1,0)). This approach groups together light curves with similar correlation structure as described by DHO timescales. We identify three classes of AGN variability. We find a "long memory" variability class characterized by milder variability amplitudes ($\sim12\%$) and steeper SFs than DRWs. We also detect a variability class characterized by an excess of short timescale variability ($

Download or read book A Statistical Study of the Optical Variability of Active Galactic Nuclei written by Malav Mahendra Shah and published by . This book was released on 1984 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Active Galactic Nuclei written by Volker Beckmann and published by John Wiley & Sons. This book was released on 2013-08-29 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active Galactic Nuclei This AGN textbook gives an overview on the current knowledge of the Active Galacitc Nuclei phenomenon. The spectral energy distribution will be discussed, pointing out what can be observed in different wavebands. The different physical models are presented together with formula important for the understanding of AGN physics. Furthermore, the authors discuss the AGN with respect to its environment, host galaxy, feedback in galaxies and in clusters of galaxies, variability, etc. and finally the cosmological evolution of the AGN phenomenon. This book includes phenomena based on new results in the X-Ray and gamma-ray domain from new telescopes such as Chandra, XMM-Newton, the Fermi Gamma-Ray Space Telescope, and the VHE regime not mentioned so far in AGN books. Those and other new developments as well as simulations of AGN merging events and formations, enabled through latest super-computing capabilities. From the contents: The observational picture of AGN Radiative processes The central engine AGN types and unification AGN through the electromagnetic spectrum AGN variability Environment Quasars and cosmology Formation, evolution and the ultimate fate of AGN What we do not know (yet)

Download or read book Variability of Active Galactic Nuclei written by Hugh Richard Miller and published by . This book was released on 1991 with total page 387 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active galactic nuclei (AGN), the most powerful objects in the universe, continue to receive a great deal of attention from observational astronomers & theorists. This book collects the results presented at a meeting held at Georgia State University in May 1990 on the topic of variability in active galactic nuclei. It is clear that careful analysis of variability over many wave bands is likely to give clues to the nature of the central engine in AGN. The contributions are grouped in themes: multifrequency variability, UV-optical-IR variability, radio variability, & X-ray variability. One of the most exciting results reported here is that many blazars exhibit micro-variability. There is an important group of papers on NGC 5548 & other Seyfert galaxies. The meeting in Atlanta provided the first opportunity for discussion for those who participated in the worldwide campaign to observe NGC 5548, & new results are also announced for many quasars, Seyfert galaxies, BL Lacertae objects, & radio galaxies. The observational data are interspersed with theoretical insights that enable us to better understand the physical conditions & processes in galactic nuclei, including giant black holes thought to lurk in their cores.

Download or read book A Search for Rapid Optical Variability in Four Active Galactic Nuclei written by Gareth Power and published by . This book was released on 2000 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advanced Lectures on the Starburst AGN Connection written by D. Kunth and published by World Scientific. This book was released on 2001 with total page 396 pages. Available in PDF, EPUB and Kindle. Book excerpt: A group of leading experts in the field of starbursts and active galactic nuclei have joined hands to produce this review volume which covers the starburst-AGN connection, and the tests to be carried out with the upcoming new astronomical facilities to ascertain the relevance of both components to the formation and evolution of galaxies.The book is addressed to advanced graduate students and researchers in the fields of active galactic nuclei and young galaxies.

Download or read book The Long term X ray UV and Optical Variability of Active Galactic Nuclei written by Samuel Dominic Connolly and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book An Introduction to Active Galactic Nuclei written by Bradley M. Peterson and published by Cambridge University Press. This book was released on 1997-02-13 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: How can we test if a supermassive black hole lies at the heart of every active galactic nucleus? What are LINERS, BL Lacs, N galaxies, broad-line radio galaxies and radio-quiet quasars and how do they compare? This timely textbook answers these questions in a clear, comprehensive and self-contained introduction to active galactic nuclei - for graduate students in astronomy and physics. The study of AGN is one of the most dynamic areas of contemporary astronomy, involving one fifth of all research astronomers. This textbook provides a systematic review of the observed properties of AGN across the entire electromagnetic spectrum, examines the underlying physics, and shows how the brightest AGN, quasars, can be used to probe the farthest reaches of the Universe. This book serves as both an entry point to the research literature and as a valuable reference for researchers in the field.

Download or read book Quasars and Active Galactic Nuclei written by Ajit K. Kembhavi and published by Cambridge University Press. This book was released on 1999-03-11 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: The latest observations and theoretical models are combined in this clear, pedagogic textbook for advanced undergraduates and graduate students.

Download or read book The Physics and Evolution of Active Galactic Nuclei written by Hagai Netzer and published by Cambridge University Press. This book was released on 2013-09-16 with total page 369 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive introduction to the theory underpinning our study of active galactic nuclei and the ways we observe them.

Download or read book The Relationship Between UV and Optical Variability and X ray Variability in Active Galactic Nuclei written by Duncan Cameron and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The X ray Background written by Xavier Barcons and published by Cambridge University Press. This book was released on 1992-07-31 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt: A review of the current observational knowledge and understanding of the cosmic X-ray background.

Download or read book Active Galactic Nuclei written by Julian H. Krolik and published by Princeton University Press. This book was released on 2021-03-09 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the first comprehensive treatment of active galactic nuclei--the cosmic powerhouses at the core of many distant galaxies. The term active galactic nuclei refers to quasars, radio galaxies, Seyfert galaxies, blazars, and related objects, all of which are believed to share a similar central engine--a supermassive black hole many times the mass of the Sun. Astrophysicists have studied these phenomena for the past several decades and have begun to develop a consensus about many of their properties and internal mechanisms. Julian Krolik, one of the world's leading authorities on the subject, sums up leading ideas from across the entire range of research, making this book an invaluable resource for astronomers, physicists interested in applications of the theory of gravitation, and graduate students. Krolik begins by addressing basic questions about active galactic nuclei: What are they? How can they be found? How do they evolve? He assesses the evidence for massive black holes and considers how they generate power by accretion. He discusses X-ray and g-ray emission, radio emission and jets, emission and absorption lines, anisotropic appearance, and the relationship between an active nucleus and its host galaxy. He explores the mysteries of what ignites, fuels, and extinguishes active galactic nuclei, and concludes with a general review of where the field now stands. The book is unique in paying careful attention to relevant physics as well as astronomy, reflecting in part the importance of general relativity to understanding active galactic nuclei. Clear, authoritative, and detailed, this is crucial reading for anyone interested in one of the most dynamic areas of astrophysics today.

Download or read book Variability of Blazars written by E. VALTAOJA (Ed) and published by Cambridge University Press. This book was released on 1992 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt: Blazars (also known as BL Lac objects), first discovered in 1978, are unusually energetic objects in the extragalactic universe. About 200 are known or suspected. They are radio sources with highly variable optical and radio emission, as well as high polarisation, and their optical spectra normally have no distinguishable features. It is generally accepted that they belong to that class of galaxies with active galactic nuclei, which are presumed to be driven by infall of matter to a supermassive black hole. In this book researchers give a complete summary of the observations of blazars and the theoretical interpretation. A comprehensive listing of confirmed and candidate objects is included. Mechanisms in which the variability can arise from shocks and relativistic jets are discussed. There are at least four different answers given to the question: what is a blazar? This book is a complete overview of the violent activity observed in these extreme active galactic nuclei.

Download or read book Investigation of Fundamental Black Hole Properties of AGN Through Optical Variability written by Wesley Thomas Ryle and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Active galactic nuclei (AGN) are known to vary in brightness in all regions of the electromagnetic spectrum and over a wide range of timescales. Many methods have been utilized to transform this observed variability into meaningful information about the central engines of AGN. One such technique, adapted from time series analysis of galactic x-ray binary systems, has been used to detect a characteristic break timescale in the power density spectra of x-ray variability in Seyfert galaxies. This timescale, thought to be related to instabilities in the accretion disk, appears to scale with black hole mass over many orders of magnitude. This dissertation performs similar time series analyses with the optical data of eight blazars. The majority of these objects also display a characteristic break timescale. In cases where a black hole estimate is known, the timescales are in good agreement with the relationship observed for galactic x-ray binary systems and Seyfert galaxies. For objects of unknown mass, this relationship can be used to provide a mass estimate of the super massive black hole. Comparisons are made between the structure function and power density spectrum for each object, and the implications for the connection between the accretion disk and the relativistic jet in AGN are discussed.

Download or read book Active Galactic Nuclei written by Ian Robson and published by Wiley-Blackwell. This book was released on 1996 with total page 420 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the energy source and physical processes within active galaxies are the most challenging areas of current research. Using a logical format and easy-to-follow explanations, Robson demonstrates the crucial connections between observation and theory, illustrating how diverse classes of active galaxies fit into the contemporary perspective. Summary sections explain the physical concepts behind the mathematics.

Download or read book The Astrophysics of Active Galactic Nuclei Variability in Large Scale Spectroscopic Surveys written by John J. Ruan and published by . This book was released on 2017 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: More than 50 years after the initial discovery of the extragalactic nature of quasi-stellar objects (quasars) by Schmidt (1963), studies of luminous active galactic nuclei (AGN) have revolutionized our understanding of black hole growth across cosmic time, accretion and jet physics, as well as galaxy evolution and cosmology. In the coming decade, these studies will be further fueled by large (a few x10^6) samples of quasars from massive optical spectroscopic surveys (e.g., from eBOSS and DESI). These spectra will be accompanied by well-sampled photometric light curves from time-domain imaging surveys (e.g., from Pan-STARRS and LSST), enabling discovery of rare objects and new time-domain phenomena. Current spectroscopic and imaging surveys have well-established that nearly all Type 1 quasars are optically variable, although the origin of this variability is still unknown. The primary goal of this thesis is to investigate various AGN variability phenomena in the UV/optical, to understanding their origin. In particular, I investigate the origin of 10-20% flux variability ubiquitously observed in quasars, the apparent change in accretion states observed in ‘transition blazars’, as well as the rapid fading observed in the recently-discovered ‘changing-look quasars’ phenomenon. I also prepare for the science enabled by the large samples of AGN that will be discovered in future time-domain imaging surveys, by characterizing the unique properties of variability-selected AGN. The primary technique I use in this dissertation to probe AGN variability is repeat optical spectroscopy. AGN optical spectra contain a wealth of information about the central engine, encoded in the properties of the emission lines, absorption lines, and continuum emission. Repeat optical spectroscopy can further probe the time-variable nature of these emission components, but this has previously been little explored in comparison to single-epoch spectroscopy. One notable exception in repeat AGN spectroscopy is the well-established reverberation mapping technique of mapping the size of AGN broad line regions; this has lead to the development of black hole mass estimates based on broad Balmer emission line widths in single-epoch spectroscopy. However, these and other studies based on repeat AGN spectroscopy are only available for small samples of a few dozen AGN at low redshifts, due to the expensive nature of repeat spectroscopy for large samples of faint quasars at higher redshifts. The development of multi-object spectrographs now have the ability to do repeat spectroscopy for large numbers of quasars, opening new windows into AGN astrophysics in the time-domain. Surveys dedicated to repeat quasar spectroscopy, including currently in SDSS-IV and in the future in SDSS-V, will fuel the early science results from this dissertation. In this dissertation, I first use SDSS repeat spectroscopy of quasars to quantify the bluer-when-brighter trend of wavelength-dependent quasar spectral variability, and use it to con- strain simple models of quasar variability. In particular, I test whether the observed spectral variability is consistent with recent toy models of inhomogeneous accretion disks with large temperature fluctuations. These models provide a natural explanation for quasar UV/optical variability, and the first to be consistent with measurements of quasar accretion disk sizes and characteristic timescales of variability. I show that the observed spectral variability can be reproduced by strongly inhomogeneous disks with large temperature fluctuations. I then use SDSS repeat spectroscopy to investigate the origin of the ‘transition blazars’ phenomenon, which is observed in a handful of AGN with relativistic jets aligned with the line of sight. In transition blazars, the blazars appear to switch between BL Lac objects and Flat-Spectrum Radio Quasars (FSRQs) classifications, which correspond to low- and high- accretion rate states, respectively. I show that transition blazars are FSRQs with especially strong beaming, such that the strongly-beamed continuum swamps the broad emission lines. This occasionally causes the broad emission lines to disappear and reappear, producing the transitional behavior. Furthermore, I mine SDSS repeat spectroscopy to uncover the origin of the recently-discovered ‘changing-look quasars’ phenomenon. Repeat optical spectroscopy of this new class of objects show dramatic transitions from luminous broad line quasars into quiescent galaxies or low-luminosity AGN. Surprisingly, these changes occur over timescales of just a few years, a factor of >10^4 faster than both theoretical expectations and scaling spectral state transition timescales in X-ray binaries to 10^8 M_sun supermassive black holes (SMBHs). To understand this phenomenon, I perform the first large systematic search for CL quasars and I show that the fading of the continuum and broad emission lines in CL quasars is consistent with rapidly decreasing accretion rates, while disfavoring alternative interpretations including changes in intrinsic dust extinction and transient tidal disruption events or supernovae. Finally, future time-domain imaging surveys such as the ZTF and LSST will discover a few x10^7 variable objects, and AGN will constitute the majority of variable objects discovered. To understand the science enabled by these massive variability-selected samples of AGN, I utilized spectra from the Time-Domain Spectroscopic Survey (TDSS) to understand the unique properties of variability-selected quasars. TDSS is the first systematic spectroscopic survey of variable objects, and I show that variability-selected quasars complement color-based selection by selecting additional redder quasars, resulting in a smooth redshift distribution. Furthermore, I show that variability selection yields higher fractions of peculiar AGN such as broad absorption line quasars and blazars.