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Numerical Treatment of Radiation Processes in the Internal Shocks of Magnetized Relativistic Outflows

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Numerical Treatment of Radiation Processes in the Internal Shocks of Magnetized Relativistic Outflows Departament d’Astronom´ıa i Astrof´ısica Programa de Doctorat en F´ısica Numerical treatment of radiation processes in the internal shocks of magnetized relativistic outflows Tesi Doctoral feta per Jesus´ Misrayim´ Rueda Becerril dirigida per Dr. Miguel Angel´ Aloy Toras´ Dr. Petar Mimica Juliol de 2017 Miguel A´ ngel Aloy Toras´ , Profesor Titular del Departamento de Astronom´ıa y Astrof´ısica de la Universitat de Valencia` y Petar Mimica, Investigador Asociado al Departamento de Astronom´ıa y Astrof´ısica de la Universitat de Valencia` CERTIFICAN: Que la presente memoria, titulada: Numerical treatment of radiation processes in the internal shocks of magnetized relativistic outflows, ha sido realizada bajo su direccion´ en el Departamento de Astronom´ıa y Astrof´ısica de la Universitat de Valencia` por Jesus´ Misrayim´ Rueda Becerril, y constituye su Tesis Doctoral para optar al grado de Doctor en F´ısica. Y para que conste firman el presente certificado en Burjassot, a 29 de mayo de 2017 Fdo: Miguel Angel´ Aloy Toras´ Fdo: Petar Mimica Abstract Blazars are a type of active galactic nuclei (AGNs) which are among the most en- ergetic and violent astrophysical objects, alongside γ-ray bursts (GRBs). The phys- ical processes, and, in particular, the relativistic jet itself in which the high energy radiation detected by the terrestrial and space observatories is generated, has been attracting the attention and interest of astronomers and astrophysicists since their dis- covery. In the present thesis, we investigate the internal shock (IS) model in which two magnetized shells of plasma, with cylindrical geometry, collide forming shock waves, which propagate throughout the plasma accelerating electrons (thermal and nonthermal) in their wake. Those electrons interact with the magnetic field of the jet producing magnetobremsstrahlung emission, which is detected by observations. In this model we also consider that the surroundings of the jet in which this collision takes place are filled with a monochromatic photon field, which emulates the more complex broad line region (BLR) of the AGN. Both photons from the external field and those produced in situ are Compton upscattered by the accelerated electrons. The main work of the present thesis has been the search of signatures imprinted on the double bump spectral energy distribution (SED) of blazars that may uncover the degree of the shell magnetization and the profile of the electrons energy distribu- tion (EED) injected at the shock front. We have approached the problem numerically, so that a fair fraction of the work has consisted on improving already existing sophis- ticated numerical tools or developing new ones from scratch. We have used these numerical tools to simulate the IS model and reproduce broadband SEDs of blazars. i Abstract To validate our methodology and put bounds on the parameters of our model, ob- servational data has been analyzed so that the generated SEDs are able to reproduce generic observational data and inferred physical trends. From the Compton dominance and the spectral index of γ-ray photons obtained in our models, we infer that a fair fraction of the blazar sequence could be explained by the shells magnetization; the negligibly magnetized models describing the Flat Spectrum Radio Quasars (FSRQs) region, whereas moderately magnetized shells fall into the BL Lacertae object (BL Lac) region. On the other hand, by including thermal electrons into the population of injected particles and using a numerical tool which reproduces the low energy region of the magnetobremsstrahlung (MBS) emission, we have found that the valley which separates the synchrotron and inverse-Compton (IC) components grows deeper when thermal dominated distributions are injected at the shock front. A slightly varying synchrotron peak between 1011–1013 Hz, in contrast with a parameters dependent IC component. These effects induce a scattering in the vertical direction of the Compton dominance-synchrotron peak plane. From this clear fact, we cautiously suggest that the proportions of the thermal/nonthermal electrons have a prominent role explaining the location of blazars in that plane. ii Preface This thesis aims to reveal the physics underlying the phenomenology observed in blazars. The reasons why blazars find themselves among the most appealing Astro- physical objects known and why they are fascinating objects that have stimulated the creativity of several generations of astronomers and astrophysicists will be addressed in Chapter 1. In Chapter 2 we will elaborate on the physical background on which the MBS and the blazars IS model resides. We will start with the dynamics and electrodynamics of a charged particle immersed in a homogeneous magnetic field. We will continue with the description of the dynamics of colliding shells in the IS model, based on Mimica & Aloy (2012). The last part of this chapter gives an overview of the different types of distributions of particles, the model employed for the injection of particles at a shock front and the evolution of particles in a shocked region in two regimes: with and without including a radiative cooling term active over a finite period of time. In Chapter 3 we will enclose a detailed description of the numerical techniques and methods developed and used during my stay in the Computer Aided Modeling of Astrophysical Plasma (CAMAP) research group with Prof. Miguel Angel´ Aloy and Dr. Petar Mimica. The first part of that chapter is focused on the Internal Shocks code developed by Mimica & Aloy (2012), which is the cornerstone of the present work. In the second part we present a detailed description of the code CHAMBA: a new computational tool which intends to reproduce the emissivity out of single charged particles moving with arbitrary speed, and also of distributions of particles of arbi- iii Preface trary profile in a magnetic field. Our published works (Rueda-Becerril et al. 2014b, 2017) are results out of a systematic and consistent use of these tools. Chapter 4 is based on research performed in the CAMAP research group with Prof. Miguel A. Aloy and Dr. Petar Mimica, as a continuation of the previously published work (Mimica & Aloy 2012). The work was published in 2014: J. M. Rueda-Becerril, P. Mimica, & M. A. Aloy. The influence of the magnetic field on the spectral properties of blazars. Monthly Notices of the Royal Astronomical Soci- ety, 438:1856–1869, Feb. 2014b. doi: 10.1093/mnras/stt2335. RMA14. The work consisted in expanding the parameter space for the internal shocks model of blazars previously scanned with the code developed by Dr. Petar Mimica and Prof. Miguel A. Aloy. The aforementioned code was supplemented with the possibility of com- puting the photons spectral index of the synthetic models (described in 4.5.1). The § observational data was obtained from the Fermi LAT Second AGN Catalog (2LAC) database1. We performed all the simulations in this chapter in the supercomputer Tirant. Chapter 5 is based on research performed in the CAMAP research group with Prof. Miguel A. Aloy and Dr. Petar Mimica. The work was published in 2017: J. M. Rueda-Becerril, P. Mimica, & M. A. Aloy. On the influence of a hybrid thermal– non-thermal distribution in the internal shocks model for blazars. Monthly Notices of the Royal Astronomical Society, 468:1169–1182, June 2017. doi: 10.1093/mnras/ stx476. RMA17. The results described correspond to simulations made by using the internal shocks code (Mimica & Aloy 2012) with a hybrid thermal-nonthermal particles distribution injected ( 2.4.2.2), the finite-time particles evolution scheme § ( 2.4.3.2) and the new numerical tool CHAMBA ( 3.2). All the simulations where § § performed using the servers of the Department of Astronomy of Astrophysics of the University of Valencia: Fujiserver1 and ARC1. Astrophysics has meant to me like walking into the wild. I never knew what I was going to find but every step has brought joy and enlightenment. Knowing a bit of the phenomena which take place out there has been like breathing fresh air in the woods, which enriches your lungs and brings you peace, or like a heavy rain, which soaks you with the vital liquid but it is too much that you have to run for shelter. The process of proposing the development of new numerical tools like CHAMBA, has 1https://heasarc.gsfc.nasa.gov/W3Browse/all/fermilac.html iv helped me to get a feeling of what is out there. The process of writing it, on the other hand, has been like climbing a mountain: you never know if you are going to get there or if nature is going to send a storm and make you draw back. We started to climb from high-energy-electrons base camp. We planned the route there, keeping an eye on the weather at all moment for any storm forecast. During the days in base camp we had to deal with fundamental questions like whether it is worth it to go beyond the transrelativistic heights, which so many explorers have gone up and down with great skill over and over for decades, or stay at the foothills of magnetobremsstrah- lung mountain. With a blazarian impulse we decided to leave the tranquility of base camp and hit the crag. We came across unstable (numerical) gravel ravines, climb and rappel steep cliffs and monumental crags. Ergs and ergs of vertical walls. There were moments where no grip was on sight, praying for the rope to hold. Fortunately for our expedition it did, and we made it to the cyclotron peak. JMRB v Contents Abstract i Preface iii Contents vi List of Figures xi List of Tables xiv Acknowledgements xv 1 Introduction 1 1.1 Active Galactic Nuclei . 1 1.1.1 AGNszoo........................... 3 1.2 Blazars ................................ 6 1.2.1 Blazar models . 8 1.2.2 Theblazarzone........................ 9 1.2.3 The blazar sequence .
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