Title: Relativistic jet dynamics from X-ray binaries to Active Galactic Nuclei
Other Titles: Relativistische jet dynamica voor rontgendubbelster-systemen en actieve galactische kernen
Authors: Monceau-Baroux, Rémi; R0261603
Issue Date: 16-Oct-2014
Abstract: In this thesis I study relativistic jets in the context of astrophysics for a variety of conditions, both in the jet and its surroundings. I try in my work to link together three aspects of astrophysics being: the analytic study, simulation and observation. My focus is nevertheless on simulation and I show what role it can play in getting a clearer picture of objects located at huge distances from us and from which many parameters cannot be directly observed.In the course of this thesis, I developed user files for the MPI-AMRVAC code. These files are written in a general way so they can be used to study any kind of relativistic jet from AGN or XRB sources with minimal adjustments. I also developed a series of IDL tools and post-processing scripts to analyse 2D to 3D data sets from relativistic hydro simulations performed with MPI-AMRVAC. These tools allow diverse diagnostics on energy content and the evolving jet morphology of the different simulations. I finally adapted a python script for radio emission which uses the data in post-treatment to produce radiomaps. A description of these tools is available in chapter 2.In chapter 3 I show the implications and consequences of using an opening angle for simulations of relativistic jets. In most simulations to date, this opening angle is discarded although radio observations reveal finite opening angles for many jet systems. By simulating finite opening angle jets I accurately follow the interaction of the jet with its surroundings, which may be of various nature, continuous or following a King atmosphere variation in density for example. I realize a collection of 2D axisymmetrical simulations for different opening angles, for different density ratios with the medium, and for different variations of this medium. For all simulations, the parameters are similar to a canonical FR-II AGN jet. My study shows how this opening angle increases the energy transfer to the medium compared to a conical jet. This is of importance for predicting the role of feedback of AGN jets as commonly parametrized in cosmological models. I assert the dominance of shock heating of the SISM at early stages of propagation of the jet.In chapter 4 I move to full 3D cartesian and relativistic simulations. I use a particular case of XRB jet: SS433. This jet presents a clear precession and my aim is to understand better the effect of such precession on a relativistic jet. With this aim I realize a series of simulations using parameters known from different observations of the SS433 system to compose a global picture. I then vary two of these parameters: the Lorentz factor of the jet and its precession angle. To be able to compare my results with observations, I evolve during simulation time, a passive population of electrons which is used in post processing to realize radio maps of my simulation. The variation of the Lorentz factor allows me to validate the canonical kinematic model of SS433. I nevertheless point out that this model does not take into account interaction with the medium and has tobe corrected in this sense to fit both observations and simulations. The variation of the precession angle helps me to better understand the effect of the precession on energy redistribution. For that, I compare a precessing jet with an equivalent non-precessing version of it. I find that differences are drastic, as the jet interaction with its medium is completely different: from a mainly bullet-like interaction, I now observe a continuous interaction along the helical jet path. The variation of the precession angle also allows me for a first exploration of the discrepancy between medium and large scales of SS433, where the jet is supposed to have a decreased precession angle, as judged from its interaction with the supernova remnant W50.In chapter 5 I study more fully the discrepancy between the medium and large scales of SS433. I explore one of the two scenarios offered to explain how the jet moves from a precession angle of 20° to 10°. One scenario is a time evolution of the jet. But the scenario I explore is more elegant and simple: simply by interacting with the medium I show that the jet recollimates to a smaller precession angle over distance. I also justify the use in many simulations of SS433 of a hollow cone structure instead of a precessing jet. I show that additional to the recollimation, the jet transits from a precessing dynamic helix to a hollow cone at a fixed distance from the source. Both this recollimation and a resulting change of jet dynamics will eventually help the jet to propagate over large distances as I show in the previous chapter: the energy transfer and therefore the interaction with the medium is high for a precessing jet and would result in a fast deceleration.In this thesis I link together the three aspects mentioned before. Using 1D arguments based on a match between inertia and ram pressure, I am able to predict and validate the dynamics of my simulations. I also show that the 1D approximation can be used even for 3D cases in some conditions for an early time of propagation of the jet. Comparing my simulations with observations I am able to validate models used in their interpretation and further develop and correct them like in the case of the SS433 jet, where a dynamical deceleration happens, improving the kinematic canonical model. I clearly justify the use of simulations in the study of astrophysical objects by showing how a simulation can compose a global picture using parameters derived from various sources of observations. I show its ability to fill-in the gap left by observations at various scales and understand the dynamics behind the discrepancy of these observations of a same object from different sources and scales.By studying both AGN and XRB jets I am able to show the similarities between them as shown in chapter 3 and 4 for the same opening angle for a straight jet. By doing so I justify the recent tendency to associate these two classes of objects which are thought to be scaled versions of each other. I also show the different dynamics which can exist in the same object: by studying three different scales of SS433 I am able to have a good global picture of this precessing jet, link these scales together and understand how they differ from a dynamical point of view.
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Plasma-astrophysics Section

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