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Periodic Variability in Active Galactic Nuclei

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Periodic Variability in Active Galactic Nuclei Periodic variability in Active Galactic Nuclei INAUGURAL-DISSERTATION zur Erlangung des Doktorgrades der Matematisch-Naturwissenschaftlichen FakultÄat der UniversitÄatzu KÄoln vorgelegt von Nadezhda Kudryavtseva aus Riga, Lettland KÄoln2008 2 Berichterstatter: Prof. Dr. J. Anton Zensus Prof. Dr. Andreas Eckart Tag der mÄundlichen PrÄufung:15.10.2008 0.1. ABSTRACT 3 0.1 Abstract In this doctoral thesis, multi-frequency very long baseline interferometry ob- servations together with multi-frequency total flux-density variability data of compact relativistic jets in active galactic nuclei are presented and analyzed. The main goal of the thesis is to investigate the physical mechanisms in rel- ativistic jets responsible for such phenomena as the co-existence of moving and stationary jet components, jet wiggling and precession. We also aim to study the connection between the structural changes in the relativistic jets and flares in the total flux-density light curves and to ¯nd observational ev- idences for the appearance of a primary perturbation in the base of the jet and its further propagation. In this thesis we also investigate which physical mechanisms are responsible for periodical total flux-density variability and to search for periodicities as a sign of jet precession. In order to study the jet physics we used the multi-frequency very long baseline interferometry technique which gives the highest possible in astron- omy resolution. We also compared jet structural changes with single-dish multi-frequency observations spanning more than 30 years together with op- tical and γ-ray data. In particular, analysis of the long-term kinematics of two active galactic nuclei S5 1803+784 and 0605-085 shows evidence for jet precession. The jet is precessing with a timescale similar to a period in the total flux-density light curves. Moreover, I show that jet structural changes are correlated with the total flux-density variability. Analyzing the long-term kinematics of S5 1803+784 I found for the ¯rst time that its jet consists of seven \oscillating" jet features which were observed for more than 20 years. We found ¯ve blazars and quasars (3C 454.3, 3C 446, CTA 102, 0133+476, and 0605-085) which show clear periodical total flux-density radio variabil- ity. Moreover, in the case of 3C 454.3 and 3C 446 the predicted flares were meanwhile observed. In this thesis I propose a new physical approach for searching periodicities and calculating flaring activity cycles in radio total flux-density variability. I use the separation of the flares into "core" and "jet" outbursts. I found that for the sources 3C 454.3 and 3C 446 optically thick "core" outbursts appear periodically. 4 0.2 Zusammenfassung In dieser Doktorarbeit werden Multi-Frequenz-Beobachtungen mit Hilfe der Interferometrie mit langen Basislinien (Very Long baseline Interferome- try - VLBI) zusammen mit Multi-Frequenz-Flussdichte-VariabilitÄatsdaten kompakter relativistischer Jets prÄasentiert und analysiert. Das Hauptziel der Arbeit ist die Erforschung physikalischer Mechnismen in relativistis- chen Jets, die verantwortlich sind fÄurPhÄanomenewie die Koexistenz von beweglichen und stationaeren Jet-Komponenten, Jet-"SchlÄangeln" und - PrÄazession.Wir sind ebenfalls bestrebt, den Zusammenhangs zwischen struk- turellen VerÄanderungender relativistischen Jets und sogenannten "Flares" in den Lichtkurven der totalen Flussdichte zu untersuchen sowie Beobach- tungsnachweise fÄurdas Auftreten einer primaeren StÄorungin der Basis des Jets und ihrer weiteren Ausbreitung zu ¯nden. In dieser Arbeit prÄufenwir weiterhin, welche physikalischen Mechanismen fÄureine periodische Vari- abilitÄatder totalen Flussdichte verantwortlich zeichnen und wir suchen nach PeriodizitÄatenals Anzeichen einer Jet-PrÄazession. Um die Jet-Physik zu untersuchen, verwendeten wir die Tech- nik der Multi-Frequenz-Interferometrie mit langen Basislinien, die die hÄochstmÄogliche astronomische Aufl¨osung bietet. Ferner haben wir strukturelle VerÄanderungen des Jets mit Multi-Frequenz-Einzelteleskop- Beobachtungen aus mehr als 30 Jahren zusammen mit optischen und Gamma-Daten verglichen. Insbesondere die Analyse der Langzeit-Kinematik der beiden Aktiven Galaxienkerne S5 1803+784 und 0605-085 zeigt Anhalt- spunkte fÄureine PrÄazessiondes Jets. Der Jet prÄazediertauf einer Zeitskala vergleichbar mit einer Periode in den Lichtkurven der totalen Flussdichte. UberdiesÄ zeige ich, dass strukturelle AnderungenÄ im Jet mit der VariabilitÄat der totalen Flussdichte korrelieren. Bei der Analyse der Langzeit-Kinematik von 1802+784 gelang mir zum ersten Mal der Nachweis, dass der Jet aus sieben "oszillierenden" Jet-Merkmalen besteht, die Äuber mehr als 20 Jahre beobachtet wurden. Wir konnten fÄunf Blazare ausmachen (3C454.3, 3C446, CTA102, 0133+476 und 0605-085), die deutlich eine periodische VariabilitÄatder to- talen Radioflussdichte aufweisen. Zudem wurden die im Fall von 3C454.3 und 3C446 vorhergesagten Flares zwischenzeitlich beobachtet. Im Zuge der Doktorarbeit stelle ich einen neuen physikalischen Ansatz zur Suche nach PeriodizitÄatenund zur Berechnung von AktivitÄatszyklenin der VariabilitÄat der totalen Radioflussdichte vor. Dazu verwende ich die Einteilung der Flares 0.2. ZUSAMMENFASSUNG 5 in "Kern-" und "Jet-"AusbrÄuche. Ich habe festgestellt, dass fÄurdie Quellen 3C454.3 und 3C446 optisch dichte "Kern-"AusbrÄuche periodisch auftreten. 6 0.3 The structure of the thesis In the ¯rst chapter di®erent types of active galaxies and the main topics I want to study will be presented. In the second chapter, the analysis of the variability of four sources 3C 454.3, 3C 446, CTA 102, and 0133+476 is discussed. The periodicities, the spectral energy distribution, and the opac- ity will be analysed. In the third chapter, I will discuss the analysis of the jet structure of S5 1803+784. The source shows unusual jet structure and evidence for jet precession. In the fourth chapter, jet kinematics and total flux-density variability of the highly periodic quasar 0605-085 will be pre- sented. There is evidence for jet precession in 0605-085. In the last chapter I will summarize the results of this thesis and will list the main conclusions. Contents 0.1 Abstract . 3 0.2 Zusammenfassung . 4 0.3 The structure of the thesis . 6 1 Introduction 11 1.1 Questions we want to discuss in the thesis . 22 2 Periodicities in blazars 23 2.1 Introduction . 23 2.2 Observations and Methods . 24 2.2.1 Time series analysis . 25 2.2.2 Autocorrelation method . 26 2.2.3 Jurkevich method . 26 2.2.4 Frequency-dependent time delays . 28 2.3 Results { 3C 454.3 (2251+158) . 31 2.3.1 Introduction . 31 2.3.2 Search for periodicity . 32 2.3.3 Jet components ejections . 34 2.3.4 Frequency-dependent time delays . 35 2.3.5 Binary black hole in 3C 454.3 . 40 2.3.6 Summary . 42 2.4 Results { 3C 446 (2223-052) . 47 2.4.1 Introduction . 47 2.4.2 Search for periodicity . 47 2.4.3 Jet components ejections . 50 2.4.4 Predicted flare . 51 2.4.5 Frequency-dependent time delays . 52 2.4.6 Summary . 56 2.5 Results { CTA 102 (2230+114) . 59 7 8 CONTENTS 2.5.1 Introduction . 59 2.5.2 Search for periodicity . 59 2.5.3 Jet components ejections . 62 2.5.4 Frequency-dependent time delays . 63 2.5.5 Summary . 67 2.6 Results { 0133+476 . 71 2.6.1 Introduction . 71 2.6.2 Search for periodicity . 71 2.6.3 Frequency-dependent time delays . 73 2.6.4 Jet components ejections . 75 2.6.5 Summary . 76 2.7 Shapes of the flares . 80 2.8 Frequency-dependent core shifts . 82 3 Kinematics of S5 1803+784 87 3.1 Introduction . 87 3.2 Observations and data reduction . 88 3.2.1 Component Identi¯cation . 90 3.3 Oscillating jet components . 101 3.3.1 Comparison with literature data . 102 3.3.2 Comparison with geodetic VLBI data . 105 3.3.3 Flux-density evolution along the jet . 106 3.3.4 Displacement of Ca . 107 3.4 The "fast" component B3 . 107 3.5 Signi¯cant position angle changes . 108 3.6 Evolution of the mean jet ridge line . 108 3.7 Evolution of the jet width . 109 3.8 Summary: kinematic results . 116 3.9 Opacity of 1803+784 . 117 3.10 Correlations & Anti correlations . 121 3.10.1 Correlation between core separation, position angle and the flux for each particular jet component: . 122 3.10.2 Correlations between the core flux and the core sepa- ration, position angle and the flux for each particular jet component: . 123 3.10.3 Correlation between the core separation, position angle and the flux for di®erent jet components: . 125 CONTENTS 9 3.10.4 Correlation between the core separation, position angle and the total flux-density variability: . 128 3.11 Periodicity analysis . 133 3.12 Binary black holes . 141 3.13 Discussion . 141 4 Kinematics of 0605-085 145 4.1 Introduction . 145 4.2 Total flux-density light curves . 146 4.3 Periodicity analysis . 149 4.4 Frequency-dependent time delays . 151 4.5 Spectral evolution . 152 4.6 Kinematics of 0605-085 . 155 4.6.1 Component ejections . 156 4.6.2 Stationary component C1 . 157 4.6.3 Comparison of the trajectories . 159 4.7 Precession model . 165 4.8 Summary of the results . 167 4.9 Discussion . 168 5 Summary 171 6 Abbreviations 177 7 Acknowledgements 197 8 ErklÄarung 199 8.1 Curriculum Vitae . 201 10 CONTENTS Chapter 1 Introduction The main idea of this thesis is to study the physics of Active Galactic Nuclei (AGN), in particular phenomena related to the flux-density and structural variability of the parsec-scale jet. In general the term \active galactic nu- cleus", or AGN, refers to the existence of energetic phenomena in the nuclei, or central regions of galaxies, which cannot be attributed clearly and directly to stars. The common picture of an AGN is that the material, pulled by the super- massive (» 106 ¡ 1010 solar masses) black hole's gravity in the center of a galaxy, streams toward the black hole in the center.
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