Fakultät Physik – Experimentelle Physik 5 Long-term observations of the TeV blazar 1ES 1959+650 Temporal and spectral behavior in the multi-wavelength context Dissertation zur Erlangung des akademischen Grades eines Doktors der Naturwissenschaften (Dr. rer. nat.) vorgelegt von Dipl.-Phys. Michael Backes Dezember 2011 Contents 1 Introduction 1 2 Brief Introduction to Astroparticle Physics 3 2.1 ChargedCosmicRays .............................. 4 2.1.1 CompositionofCosmicRays . 4 2.1.2 EnergySpectrumofCosmicRays. 5 2.1.3 Sources of Cosmic Rays up to 1018 eV................ 6 ∼ 2.1.4 Sources of Cosmic Rays above 1018 eV................ 8 ∼ 2.2 AstrophysicalNeutrinos . ... 12 2.3 PhotonsfromOuterSpace. 13 2.3.1 Leptonic Processes: Connecting Low and High Energy Photons . 13 2.3.2 Hadronic Processes: Connecting Photons, Protons, and Neutrinos . 16 2.4 ActiveGalacticNuclei . 16 2.4.1 Blazars .................................. 17 2.4.2 EmissionModels ............................. 19 2.4.3 BinaryBlackHolesinAGN . 20 3 Instruments for Multi-Wavelength Astronomy 25 3.1 RadioandMicrowave .............................. 25 3.1.1 Single-DishInstruments . 25 3.1.2 Interferometers .............................. 26 3.1.3 Satellites ................................. 27 3.2 Infrared ...................................... 27 3.3 Optical ...................................... 28 3.3.1 Satellite-Born............................... 28 3.3.2 Ground-Based .............................. 28 3.4 Ultraviolet..................................... 29 3.5 X-Rays ...................................... 29 3.6 Gamma-Rays ................................... 31 4 Cherenkov Telescopes 33 4.1 Imaging Atmospheric Cherenkov Technique . ...... 33 4.2 HistoricalInstruments . ... 34 4.2.1 HEGRACT1............................... 34 4.2.2 HEGRACTSystem ........................... 36 iii iv Contents 4.3 Latest Generation Instruments and General Limitations ........... 36 4.3.1 MAGICTelescope(s). 38 4.4 ImprovementsonDataAnalysis. ... 42 5 FACT – The First G-APD Cherenkov Telescope 45 5.1 Geiger-Mode Avalanche Photodiodes . .... 46 5.2 36-PixelTestCameraM0 ............................ 46 5.3 FACTCamera .................................. 48 5.4 DriveSystem ................................... 48 5.5 Mirrors ...................................... 50 5.5.1 Re-Working and Spectral Reflectivities . .... 50 5.5.2 Focal Lengths and Point Spread Functions . .... 53 5.6 StatusandOutlook................................ 57 6 VHE Gamma-Ray Monitoring of Blazars 63 6.1 AGNMonitoringwithMAGIC . 64 6.1.1 ResultsonMkn421 ........................... 64 6.1.2 ResultsonMkn501 ........................... 65 6.2 ConclusionandOutlook . 65 7 The Blazar 1ES1959+650 67 7.1 BasicPropertiesof1ES1959+650. .... 67 7.1.1 HostGalaxy ............................... 67 7.1.2 CentralBlackHole. 68 7.1.3 RadioMorphology ............................ 69 7.2 TemporalBehaviorof1ES1959+650 . ... 70 7.2.1 RadioObservations . 70 7.2.2 OpticalObservations. 70 7.2.3 X-RayObservations . 73 7.2.4 Gamma-RayObservations. 75 7.2.5 VHE Gamma-Ray Observations . 77 7.2.6 NeutrinoObservations . 78 7.2.7 CosmicRayObservations . 79 7.2.8 Fractional Variability Fvar ........................ 79 7.2.9 Periodicities................................ 80 7.3 VHE Energy Spectrum of the Steady State of 1 ES 1959+650 . ...... 83 7.3.1 VHEEnergySpectra. 83 7.3.2 Steady State VHE Energy Spectrum . 88 7.4 Spectral Energy Distribution of 1ES 1959+650 . ....... 93 7.4.1 RadioObservations . 93 7.4.2 OpticalObservations. 93 7.4.3 X-RayObservations . 93 7.4.4 Estimation of the Synchrotron Peak . 97 7.4.5 Gamma-RayObservations. 97 7.4.6 ModelingtheSEDof1ES1959+650 . 101 7.5 ConclusionandOutlook . 103 Contents v 8 The DWARF Network 109 8.1 FACT – The First G-APD Cherenkov Telescope . 109 8.2 Whipple10mTelescope ............................. 110 8.3 TACTIC...................................... 111 8.4 OMEGA...................................... 112 8.5 RomanianCT................................... 113 8.6 StarBaseUtah .................................. 114 8.7 FeasibilityandConclusions . .... 114 9 Final Conclusions and Outlook 117 A Energy Ranges 121 B Data for Lightcurves 123 B.1 RadioObservations............................... 123 B.2 OpticalObservations. 126 B.3 X-RayObservations ............................... 145 B.4 HEGamma-RayObservations. 154 B.5 VHEGamma-RayObservations. 155 C Figures for the Combined VHE Spectrum 157 D Data for SED Modeling 165 D.1 RadioObservations............................... 165 D.2 InfraredObservations . 168 D.3 OpticalandUVObservations . 178 D.4 X-RayObservations ............................... 180 D.5 LE and ME Gamma-Ray Observations . 187 D.6 HEGamma-RayObservations. 189 D.7 VHEGamma-RayObservations. 191 D.8 VHE Gamma-Ray Flare Observations . 194 Glossary of Abbreviations I List of Figures V List of Tables IX Bibliography XIII Author’s Publications LIII Acknowledgments / Danksagung LV Chapter 1 Introduction Astroparticle physics bridges the research fields of astrophysics and particle physics, study- ing the highest energetic phenomena in the Universe. The central question of this research field is the origin of ultra high energetic charged particles, dubbed cosmic rays, stemming from astrophysical objects and arriving at Earth isotropically. Due to deflection in in- tergalactic magnetic fields, these particles cannot be traced back to their origins by their arrival directions. Hence, their sources can only be identified indirectly through electri- cally neutral particles as neutrinos and high energetic photons, stemming from the same sources. Blazars, a subclass of Active Galactic Nuclei with highly relativistic plasma outflows pointing towards the Earth, are for several reasons good candidates for being the origin of cosmic rays. In this context, the spectral and temporal long-term behav- ior of the blazar 1ES 1959+650 is studied throughout this thesis. Having shown strong hints of hadronic emission processes in the past, this blazar is a primary candidate for a source of cosmic rays and thus it was monitored with the MAGIC telescope since 2004. The temporal variability for different wavelength bands, which should be connected in the case of non-hadronic emission processes is examined in this thesis. Furthermore, the time-integrated spectral energy distribution is compiled from radio to very high energy gamma-rays and modeled for hadronic and leptonic emission scenarios to unveil the char- acter of the emitting particles. Additionally, the idea of long-term monitoring of blazars at very high energy gamma-rays is pursued further. The characterization of the mirrors for setting-up the FACT telescope for blazar monitoring and the coordination of DWARF, a worldwide network of Cherenkov telescopes are presented. The contents of this thesis is structured as follows. Chapter 2 gives a short overview of astroparticle physics, introducing the three messenger particles of cosmic radiation, their acceleration and emission processes and their inter-connections. Having introduced Active Galactic Nuclei as possible sources for cosmic rays, their properties are outlined in the second part of that chapter, focusing on the subclass of blazars and possible emission models of their non-thermal radiation. 1 2 Chapter 1 Introduction Chapter 3 briefly reviews the nearly forty instruments used throughout this thesis for the compilation of the multi-wavelength data from radio to high energy gamma-rays. Chapter 4 even enlarges the covered energy range to very high energy gamma-rays. The working principle of imaging atmospheric Cherenkov telescopes is illustrated and the HEGRA and MAGIC telescopes, from which data have been retrieved, are in- troduced. Additionally, general limitations of the latest generation telescopes are discussed. Two methods to improve both the quality and the computing perfor- mance of multivariate classification algorithms, developed in the peripherals of this thesis and used for the analysis of Cherenkov telescope data, are outlined here. Chapter 5 is devoted to the FACT telescope. This is a completely refurbished former HEGRA telescope and the very first Cherenkov telescope whose camera is entirely based on semi-conductor devices for photon detection, called G-APDs. In the course of this thesis the mirror facets for FACT have been reworked and characterized, measuring the focal lengths and the spot sizes of each facet. Furthermore, the thickness of the protective quartz coating has been estimated from the measured spectral reflectivity. Chapter 6 outlines the ways, in which long-term gamma-ray monitoring of known, bright blazars can deepen our knowledge about these sources. The blazar monitoring pro- gram of MAGIC is introduced and results on two of the tree sources monitored by MAGIC are briefly summarized. Chapter 7 highlights the third source of the MAGIC monitoring program, 1ES 1959+650. The observational history of this blazar is reviewed, and both the spectral and the temporal behavior is presented. Together with the new results from the monitoring observations with MAGIC and recent observations with Fermi–LAT, this enables for the first time the compilation of the complete spectral energy distribution of this blazar. The presented measurements of the non-thermal emission from this blazar span over 20 orders of magnitude in energy with essentially no gaps. Although not being simultaneously recorded, the compilation of these data allows to study the underlying emission processes and particle populations. Chapter